Hydrology

To understand surface-water hydrology, an understanding of the climate and meteorological patterns is a prerequisite. For this reason, the Pamunkey Indian Tribe have operated and maintained a meteorological station on their reservation since 2018, which measures precipitation accumulation, soil moisture, temperature and salinity, air temperature, wind speed and direction, relative humidity, solar radiation, and leaf wetness (W. Taylor, Pamunkey Indian Tribe member and retired Natural Resources and Environmental Director, oral commun., 2022). This meteorological station could eventually provide an understanding of hydrologic changes over time if this station continues to operate, but the datasets currently generated by the meteorological station as of 2023 are not long enough to provide historical context, or potential extreme or anomalous events. Continued operation of this monitoring station could enhance studies that evaluate meteorological data or model conditions throughout the Chesapeake Bay and support understanding of anomalies and trends at the scale of the Chesapeake Bay watershed. These studies generally predict increases in air temperature and precipitation and diverse changes to the physical riverine landscape and sediment and nutrient transport (Murphy and others, 2022; Ryberg and others, 2018; Rice and others, 2017; Najjar and others, 2009). There is a gap in climate and meteorological knowledge at the watershed scale for the Pamunkey and York river watersheds. However, traditional ecological knowledge suggests that in the Pamunkey River watershed, extreme events, like hurricanes with intense winds and precipitation, have been more frequent over the past 15 to 20 years (J.H. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022; T. Langston, Pamunkey Indian Tribe, Elder, oral commun.; J. Krigsvold, Pamunkey Indian Tribe, Elder, oral commun., 2022).

The U.S. Geological Survey (USGS) has computed the daily mean discharge and annual peak discharge, that is the maximum instantaneous discharge each year, of the Pamunkey River since 1941 and continues to compute these streamflow metrics. Data from USGS station number 01673000, Pamunkey River near Hanover, Virginia, allows for a basic understanding of the hydrology of the Pamunkey River (fig. 3; U.S. Geological Survey, 2022a). The average daily mean discharge from 1941 through 2021 was 986 cubic feet per second (ft³/s), and the minimum and maximum values were 13 and 39,300 ft³/s, respectively. Others have noted interseasonal and interannual discharge and periods of drought and flood vary greatly (Milligan and others, 2019; Hershner and others, 2009). Hershner and others (2009) reported that annual precipitation for the York River watershed was moderately correlated with the average annual discharge in the Pamunkey River (Hershner and others, 2009); however, the authors also found that annual precipitation was not closely correlated with annual streamflow yield in the Pamunkey River. Hershner and others (2009) suggest changes in groundwater storage and alterations to streamflow delivery from infrastructure might contribute to these variables not being correlated (Hershner and others, 2009).

Annual peak discharges for water years (for example, water year 1970 was from October 1, 1969 through September 30, 1970) 1942 through 2021 (fig. 4), do not show a distinguishable pattern. The average annual peak discharge from water years 1942 through 2021 was 10,505 ft³/s, and the minimum and maximum annual peak discharges over the same period were 1,790 and 40,300 ft³/s, respectively. Hershner and others (2009) calculated that peak discharge occurred on average once every 370 days from 1940 through 2006 on the Pamunkey River. Hershner and others (2009) assert that peak discharges were likely quelled after large reservoirs that regulate or divert flow began to be built in 1972. Since publication of Hershner and others (2009), annual peak discharge values from subsequent years are available, and from water years 2010 through 2021, peak discharges do not appear to be quelled, and the most recent water year, 2021, had the third largest peak discharge on record. Peak discharge measurements from future decades and a more thorough analysis of potential changes in peak discharge over time would be needed to evaluate if a statistically significant difference has occurred.

The annual minimum 7-day moving average of daily mean discharge values from 1942 through 2021 were calculated to understand low-flow conditions over time in the Pamunkey River (fig. 5). More lower low-flow magnitudes were observed before 1972 than after, which is when major dam construction occurred in the watershed. Low flows calculated by the same annual minimum 7-day moving average of the daily mean discharge values were used by Hershner and others (2009); however, these authors only considered the period 1970 through 2007 and did not consider much data before the major dam installations in the 1970s. However, Hershner and others (2009) show that periods of the lowest low flows from 1970 through 2007 did not have particularly low amounts of annual precipitation and they hypothesized that low flows from 1970 through 2007 might potentially be caused by periods of seasonal drought (Hershner and others, 2009). The Pamunkey River watershed experienced drought from 1999 to 2002, which could help explain some of the low-flow conditions during that period. A complete understanding of how interannual drought and intra-annual seasonal drought might be affecting the Pamunkey River remains a gap in knowledge.

Flood Risk

Many areas in the Pamunkey River watershed are at risk of flooding, and this flooding poses a major threat to the Pamunkey Indian Reservation. Flood risk locations as of 2021, estimated by the Federal Emergency Management Agency (FEMA) (fig. 6), show many areas throughout the Pamunkey River watershed as low and high risk and some areas as medium and very-high risk. However, most of the Pamunkey Indian Reservation is classified as a special flood hazard area (SFHA) (Federal Emergency Management Agency, 2021). FEMA defines an SFHA as an area having special flood, mudflow, or flood related erosion hazards. These SFHAs require adherence to the National Flood Insurance Program’s floodplain management regulations and need flood insurance.

The Pamunkey Indian Tribe and Reservation are sovereign, but enforcement of floodplain management regulations and access to purchase flood insurance is complicated. The SFHA area on the Pamunkey Indian Reservation (fig. 7) includes all the forested wetland areas adjacent to the Pamunkey River and extends landward to the developed parts of the reservation where there are structures and agricultural plots. Estimates indicate that every year these areas have a 1-percent chance to experience flood, mudflow, or flood related erosion hazards (Federal Emergency Management Agency, 2021). Some of the most vulnerable locations on the reservation are along the shoreline, where homes and the Pamunkey Indian Tribe’s fish hatchery are located. Additionally, Williams Creek at King William County Route 673 – Pocahontas Trail, the only ingress and egress point on the reservation, is included in the SFHA. Pamunkey Tribal members have experienced many occasions where flooding has restricted access to and from the reservation, and flooding has been happening more often in the past 15 to 20 years (K. Moore, Pamunkey Indian Tribe, Elder, oral commun., 2022). When recalling some of the extreme flood events that have occurred in the past 15 to 20 years, and the damage that they caused on the Pamunkey Indian Reservation, one Tribal Elder said, “Events like these show you how vulnerable the reservation is and how much more severe the weather and its impacts are having” (K. Moore, Pamunkey Indian Tribe, Elder, oral commun., 2022).

The most recent FEMA Flood Risk Report published in May 2021 quantified the dollar-loss estimates from multiple size floods in the Pamunkey Indian Reservation at $0 (Federal Emergency Management Agency, 2021). This $0 estimate for the Pamunkey Indian Reservation is inconsistent when comparing it to locations throughout the Pamunkey River watershed that also have a diverse suite of residential and agricultural uses and the potential for disruption. This is due to the methodology of the flood-estimate calculation, which FEMA notes has many shortcomings, including not having reliable elevation measurements for the “first floor” of each building (Federal Emergency Management Agency, 2022).

Dams

According to the U.S. Army Corps of Engineers National Inventory of Dams, 184 dams within the Pamunkey River watershed (fig. 8) meet the following criteria: (1) dams where downstream flooding will likely result in loss of human life; (2) dams where downstream flooding would likely result in disruption of access to critical facilities, damage to those facilities, and would require difficult mitigation efforts; and (3) dams that meet or exceed specific height and size parameters regardless of their potential risk to human life and economics (U.S. Army Corps of Engineers, 2022). Most of the dams within the Pamunkey River watershed are on tributaries of the Pamunkey River: the North Anna River, South Anna River, and Little River. Dams in the Pamunkey River watershed are mostly small low-head dams used for consistency of water supply and irrigation. Dams can cause potentially large changes to a stream’s hydrology, water quality, connectivity, geomorphology, and ecology and may create a barrier to aquatic organism movement (Poff and others, 2007; Santucci and others, 2005). No dams are directly on the Pamunkey River main stem; however, the North Anna River has a dam that creates Lake Anna, and the South Anna River has two dams: the Ashland Mill Dam (fig. 9) and the Ashland Water-Supply Dam.

The North Anna Nuclear Power Plant (NANPP) uses water from Lake Anna for cooling. According to the owner and operator of NANPP, Dominion Energy, at full operation, approximately 2 million gallons of water pass through the facility per minute (Dominion Energy, 2022). After use, the water is discharged into ponds where it has an opportunity to cool after being heated by NANPP. Although the water being used is not necessarily consumed and is eventually returned to the North Anna River, the timing of discharges and temperatures when the water is returned to the North Anna River might be altered and could potentially have ecological effects. Historical water temperature measurements in the northernmost arm of Lake Anna from August 1984 through August 2011 showed an increasing trend, which appeared to become more variable year-to-year from 2000 through 2011 (Via, 2012).

The two dams on the South Anna River, the Ashland Mill Dam and the Ashland Water-Supply Dam, have been recognized by the Virginia Department of Wildlife Resources (DWR) as being barriers to fish passage. The Ashland Mill Dam is a 13-ft dam near the downstream end of the South Anna River. The Virginia DWR have asserted two potential actions to improve fish passage at this location: install a fishway or remove the dam. The Virginia DWR estimates that improvements to fish passage at the Ashland Mill Dam would reopen 9 miles of native spawning habitat for fish, such as Alosa sapidissima (Wilson, 1811) (American shad), Dorosoma cepedianum (Lesueur, 1818) (hickory shad), Alosa aestivalis (Mitchill, 1814) (blueback herring), Alosa pseudoharengus (Wilson, 1811) (alewife), Morone saxatilis (Walbaum, 1792) (striped bass), and Anguilla rostrata (Lesueur, 1817) (American eel) (Virginia Department of Wildlife Resources, 2022). Upstream from the Ashland Mill Dam is Ashland Water-Supply Dam, which is a 3-ft tall low-head dam. The Virginia DWR estimates that creating a simple notch in this dam would reopen 28 miles of stream for fish movement (Virginia Department of Wildlife Resources, 2022).

One Pamunkey Tribal Elder said, “All of the dams [in the Pamunkey River watershed] including the ones for Lake Anna are bound to be impacting the fish. We used to have herrings in this river, and we barely have any at all anymore. The herrings and the shad used to go all the way up [to the top of the watershed] to spawn. So, the dams had to have affected the fish some” (T. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022).

Withdrawals

Surface water is withdrawn from the Pamunkey River watershed for commercial, industrial, agricultural, municipal, and power generation uses. The Virginia Department of Environmental Quality (VDEQ) has reported the withdrawals of surface water in 2021 (Virginia Department of Environmental Quality, 2022b; table 2). The NANPP withdrew the largest amount of surface water in 2021 at 1,855 million gallons per day (Mgal/d). According to Dominion Energy, the operator of the NANPP, all the water withdrawn to cool the plant was returned to Lake Anna, and thus the NANPP had no consumptive use (Dominion Energy, 2023). The three largest surface-water withdrawals for consumptive use in 2021 were from New Kent County at 16.24 Mgal/d, Spotsylvania County at 11.93 Mgal/d, and Hanover County at 5.14 Mgal/d.

The most immediate effect that surface-water withdrawals can have on a stream is that the water being withdrawn is no longer in the stream to support biological communities and ecological function. Surface-water withdrawals can also potentially change the water level of the stream and alter flow regimes and geomorphology. Over time, these alterations can have profound effects on an entire ecosystem. Evaluation of the full suite of potential impacts that withdrawals of surface water might be having on the Pamunkey River remains a gap in knowledge.

Non-Tidal Surface-Water Quality

About 333 miles of non-tidal streams and 18 lake parts in the Pamunkey River watershed have impaired water-quality conditions. Most of these impairments are caused by excessive amounts of bacteria; however, some impairments are caused by concerning levels of dissolved oxygen, pH, toxic contaminants, and metals (Virginia Department of Environmental Quality, 2022c; fig. 11a, fig. 11b). The following sections describe the bacteria, nutrients, and sediment conditions monitored throughout the non-tidal waters of the Pamunkey River watershed. Bacteria conditions are summarized from multiple non-tidal monitoring stations. Nitrogen, phosphorus, and sediment conditions are summarized from a single non-tidal monitoring station: the Pamunkey River near Hanover, Va. (USGS station ID 01673000; fig. 10). This station is part of a 123-station non-tidal stream monitoring network that allows conditions in nearby rivers and throughout the Chesapeake Bay watershed to be compared.

Nitrogen

From 2016 through 2020, the average annual load of total nitrogen carried by the non-tidal Pamunkey River was about 1.5 million pounds (Mason and others, 2021). Atmospheric deposition and agricultural fertilizer are the largest estimated sources of nitrogen in this watershed; each account for about 30 percent of the delivered total nitrogen load (Ator, 2019). After normalizing by watershed area, the 5-year average load (about 2.2 pounds per acre) was lower than 90 percent of non-tidal monitoring stations reporting total nitrogen throughout the Chesapeake Bay watershed. The non-tidal part of the neighboring Mattaponi River had about the same average load over this time (Mason and others, 2021).

Flow-normalized total nitrogen load was about 5 percent higher in 2020 than 1985 (Mason and others, 2021; fig. 12). This change does not represent an increasing trend because of the statistical uncertainty of the results. However, these same loads were about 6 percent higher in 2020 than 2011, representing an increasing trend over this 10-year period. This 6-percent increase of total nitrogen was higher than increases in load at over 70 percent of the 123 non-tidal monitoring network stations that monitor total nitrogen throughout the Chesapeake Bay. The non-tidal Mattaponi River experienced a 10-percent increase in total nitrogen load from 2011 through 2020 (Mason and others, 2021).

The total estimated amount of nitrogen in the non-tidal Pamunkey River watershed decreased by about 3.7 million pounds from 1985 through 2020, representing a reduction of 27 percent (Chesapeake Bay Program, 2020; fig. 13). These changes were primarily caused by reductions in atmospheric deposition and, since the early 2000s, agricultural fertilizer. The Clean Air Act of 1963 (Public Law 88–206, 77 Stat. 392) and its multiple amendments have had transformative effects on the amount of nitrogen released to the atmosphere. Atmospheric nitrogen in the United States peaked in 1980 but has shown marked declines since 1995 when the Clean Air Act Amendment of 1990 (Public Law 101–549) became effective (U.S. Environmental Protection Agency, 2017a). Nitrogen fixation, that is plants converting atmospheric nitrogen into ammonia, was slightly higher in 2020 than 1985, which might reflect increases in crop yields over time. Fertilizer applied to turf grass also increased from 1985 through 2020, likely due to urbanization. Manure, septic systems, and point sources were all small inputs of nitrogen since 1985 (Chesapeake Bay Program, 2020).

The decline in watershed nitrogen inputs since 1985 has not resulted in measured decreases in total nitrogen loads delivered in the Pamunkey River near Hanover, Va. Most nitrogen inputs are not delivered to streams, they are retained in the landscape. From 1985 through 2020, only 11 percent of the total nitrogen inputs within the watershed have been delivered to streams and transported downstream to the tidal Pamunkey River (Mason and others, 2021; Ator, 2019). Delivery of nitrogen from landscape to stream varies by input type. Point sources, like wastewater discharge and combined sewer outlets (CSOs), have direct pathways to streams, while non-point sources, like atmospheric deposition and fertilizer applications, may take complex pathways of varying temporal scales to be delivered to streams. Nitrogen fixation has increased from 1985 through 2020, and nitrogen removal by crops also increased (Chesapeake Bay Program, 2020). The amount of manure applied to agricultural lands has decreased from 1985 through 2020 and represents about 3 percent of the total nitrogen inputs within the watershed (Chesapeake Bay Program, 2020); however, manure is estimated to account for about 10 percent of the delivered load (Ator, 2019). This disparity suggests that manure might have more direct pathways to being delivered to streams than other nitrogen inputs. Across the Chesapeake Bay watershed, groundwater-flow pathways are the primary delivery mechanism of nitrogen as nitrate (Terziotti and others, 2017); however, the ratio of nitrate to total nitrogen that is transported throughout the Chesapeake Bay watershed is lower than in most other watersheds in Virginia (Moyer and Langland, 2020). The Pamunkey River watershed generally did not have high nitrate concentrations in its groundwater (McFarland, 2010); however, some estimates suggest that residence time for nitrate in shallow groundwater within the Pamunkey River watershed, and throughout the Chesapeake Bay watershed, might be one or two decades (Terziotti and Hopple, 2018; Phillips, 2007), underscoring the importance of long-term monitoring to evaluate and better understand this delivery pathway.

Predicted changes in climatic conditions are expected to affect nitrogen fate and transport (Ator and others, 2020). The Pamunkey River watershed is predicted to become warmer and wetter. Warmer temperatures may increase releases of nitrogen from organic matter and facilitate mobilization of nitrogen in soil, potentially promoting delivery to streams (Lintern and others, 2020). Wetter conditions will directly impact changes in total nitrogen load. Studies throughout the Chesapeake Bay watershed have shown a direct relation between streamflow and total nitrogen load (Shenk and others, 2021). Wetter conditions may also lead to more frequent use of CSOs, which might increase the delivery of nitrogen to streams (U.S. Environmental Protection Agency, 2008). However, warmer and wetter conditions may drive the chemical process of denitrification, which reduces nitrate to dinitrogen gas (Chanat and Yang, 2018). Denitrification could plausibly increase in the future thereby decreasing nitrogen loads (Pilegaard, 2013).

Knowledge of the changes in nitrogen sources over time is useful to begin to understand their effects on the trend in total nitrogen load and to evaluate where efforts aimed at reducing nitrogen to streams would be most impactful. From 1985 through 1999, total nitrogen inputs generally increased, but they have decreased from 2000 through 2020 (Chesapeake Bay Program, 2020). The lack of a long-term trend in total nitrogen load (Mason and others, 2021) does not seem to be explained by our understanding of source-specific inputs (Chesapeake Bay Program, 2020) and outputs (Ator, 2019) over time. Groundwater pathways are a key delivery mechanism that provide nitrogen as nitrate to streams throughout the Chesapeake Bay (Ator and Denver, 2012; Lizarraga, 1997), and in the Pamunkey and York river watersheds, groundwater nitrate concentrations are highest above the Fall Zone (Greene and others, 2005; Terziotti and others, 2017). Residence times, that is, the amount of time groundwater takes to be delivered to a stream, are about 10 years throughout the Chesapeake Bay but can vary greatly depending on underlying geology and soils. Gaps in knowledge remain of nitrogen cycling and dynamics throughout the Pamunkey River watershed over time, and the effects land-use changes and best management practices have at reducing nitrogen delivery to meet TMDL benchmarks.

Phosphorus

Phosphorus binds to soil particles, and the highest concentrations of soil phosphorus are above the Fall Zone in the Pamunkey River watershed. This area is especially rich in phosphorus because of the combination of underlying crystalline rock, which is a natural source of phosphorus, and fertilizer and manure applications (Ator and others, 2011). Mineral phosphorus in the non-tidal Pamunkey River watershed is estimated to account for about 35 percent of the delivered total phosphorus load, and fertilizer and manure account for about 30 and 20 percent, respectively (Ator, 2019).

From 2016 through 2020, the average annual load of total phosphorus in the non-tidal Pamunkey River was about 180,000 pounds (Mason and others, 2021). Mineral phosphorus, agricultural fertilizer, and manure were the largest estimated sources of phosphorus in this watershed, constituting 37, 29, and 20 percent of the delivered total phosphorus load, respectively (Ator, 2019). After normalizing by watershed area, the 5-year average load (about 0.26 pounds per acre) in the Pamunkey River was lower than 69 percent of 5-years average loads in the Chesapeake Bay watershed non-tidal monitoring station network. The non-tidal part of the neighboring Mattaponi River had a similar average load over this time of about 0.2 pounds per acre (Mason and others, 2021).

Flow-normalized total phosphorus load at the Pamunkey River near Hanover, Va., was about 54 percent higher in 2020 than 1985 (Mason and others, 2021; fig. 14). This change represents a statistically significant increasing trend over this 35-year period. Flow-normalized total phosphorus load was about 5 percent lower in 2020 than 2011, representing a decreasing trend over this10-year period. This 5-percent decrease was lower than over half of the decreases in load at the 123 station non-tidal network monitoring total phosphorus throughout the Chesapeake Bay. The Mattaponi River experienced a 6-percent increase over 2011–20 (Mason and others, 2021). The decreasing trend in phosphorus in the non-tidal Pamunkey River and the increasing trend in the Mattaponi River over 2011–20 present an interesting difference and a gap in knowledge on changes throughout these non-tidal watersheds and potential downstream responses in the York River.

The total estimated amount of phosphorus in the non-tidal Pamunkey River watershed decreased by about 900,000 pounds from 1985 through 2020, a change of 35 percent (Chesapeake Bay Program, 2020; fig. 15). Rates of atmospheric phosphorus deposition were estimated to be unchanged from 1985 through 2020 (Chesapeake Bay Program, 2020). Like nitrogen, phosphorus coming from fertilizer applied to turf grass increased from 1985 through 2020, likely because of urbanization. Manure, CSOs, and wastewater treatment plant discharge have been small inputs of phosphorus since 1985 (Chesapeake Bay Program, 2020).

The decline in watershed phosphorus inputs since 1985 has not resulted in decreased total phosphorus loads delivered to the Pamunkey River near Hanover, Va. Most phosphorus inputs are not delivered to streams, rather they are retained in the landscape. From 1985 through 2020, only 8 percent of the total phosphorus inputs within the watershed have been delivered to streams and transported downstream to the tidal Pamunkey River (Mason and others, 2021; Ator, 2019). Delivery of phosphorus from landscape to stream varies by input type. Like nitrogen delivery, point sources of phosphorus, like wastewater discharge and CSOs, have direct pathways to streams, but non-point sources, like biosolids and fertilizer applications, may have complex pathways to streams that take varying amounts of time to get there. The amount of manure applied to agricultural lands has decreased from 1985 through 2020 and represents about 6 percent of the total phosphorus inputs within the watershed (Chesapeake Bay Program, 2020); however, manure is estimated to account for about 20 percent of the delivered phosphorus load (Ator, 2019). This disparity suggests that manure might have more direct pathways to being delivered to streams.

Predicted warmer and wetter conditions in the Pamunkey River watershed are expected to affect phosphorus fate and transport (Ator and others, 2020). Warmer temperatures interact with phosphorus like they do with nitrogen; warmer temperatures may increase releases of phosphorus from organic matter and facilitate increases in phosphorus mobilization and delivery to streams (Lintern and others, 2020). Wetter conditions have been linked to increases in phosphorus loads that are attributed to increases in erosion and sediment transport caused by wetter conditions (Lintern and others, 2020; Vidon and others, 2018; Najjar and others, 2010). Wetter conditions might also lead to more frequent use of CSOs, which might increase the delivery of phosphorus to streams (U.S. Environmental Protection Agency, 2008).

From 1985 through 2000, total phosphorus inputs were generally stable at around 2.5 million pounds per year, and then showed a marked decline from 2001 through 2003. From 2003 through 2020, total phosphorus inputs have generally remained stable at about 1.7 million pounds per year (Chesapeake Bay Program, 2020). Although the long-term trend in total phosphorus load is increasing, annual loads have generally remained consistent since 2003 (Mason and others, 2021). From 2011 through 2020 there is a decreasing trend in total phosphorus load; however, the cause remains a gap in knowledge.

Targeted and more measured fertilizer and manure applications could be useful at reducing phosphorus loads because estimates suggest that the current type of applications exceed crop needs in the watershed (Ator and others, 2011). With focused and concerted effort, reducing soil phosphorus is possible but might take 10 years or more (Kleinman and others, 2011). Any management actions to reduce total phosphorus loads might be ineffective unless targeted and more measured fertilizer and manure applications are made (Jarvie and others, 2013; Sharpley and others, 2013). All of the potential responses to changes in management actions remain a gap in knowledge.

Suspended Sediment

Sediment originates in the uplands from a variety of sources, such as agricultural and urban areas and forests, roads, gullies, and mines (Langland and Cronin, 2003). Delivery of sediment to streams throughout the Chesapeake Bay watershed is controlled by natural fluvial processes and bank erosion, and anthropogenic factors, such as agriculture and urbanization. Eroded sediments are stored (for example, in a floodplain) and transported, repeatedly, until ultimately being discharged from a watershed into a receiving downstream waterbody (Noe and others, 2020). Residence times, that is, the amount of time sediment is stored before being remobilized, vary greatly depending on the size of the stream or river. Older sediment stored in the Chesapeake Bay’s tributary watersheds, often termed “legacy sediment,” is thought to be the substantial excess supply of sediment created by landscape disturbances (for example, agriculture and urbanization) and alterations (for example, dam installations) after European settlement in North America (Miller and others, 2019). Anthropogenic landscape disturbances and alterations have continued and have added to the excess sediment stored in these watersheds that are available to be remobilized. These landscape disturbances have caused disruption to the native dynamic equilibrium of streambank erosion and floodplain deposition (storage) unique to each watershed (Wohl, 2015).

From 2016 through 2020, the average annual suspended-sediment load for the non-tidal Pamunkey River was about 99 million pounds (Mason and others, 2021). Erosion of stream channels and agricultural areas were the largest estimated sources of suspended sediment in this watershed, comprising 45 and 35 percent of the total delivered suspended-sediment load, respectively (Ator, 2019). After normalizing by watershed area, this 5-year average load from 2016 through 2020 (about 135 pounds per acre) was lower than 80 percent of non-tidal monitoring stations reporting suspended sediment throughout the Chesapeake Bay watershed. The average load over this time in the non-tidal part of the neighboring Mattaponi River was 50 pounds per acre, which was substantially less than the Pamunkey River (Mason and others, 2021).

Flow-normalized suspended-sediment loads at the Pamunkey River near Hanover, Va., (USGS station 01673000) were about 34 percent higher in 2020 than 1985 (Mason and others, 2021; fig. 16). Flow-normalized suspended-sediment loads were about 16 percent lower in 2020 than 2011, representing a decreasing trend over this 10-year period. This 16 percent decrease in load was higher than the decrease in loads of 88 percent of the non-tidal network monitoring suspended sediment throughout the Chesapeake Bay watershed. The Mattaponi River experienced a 25-percent increase in suspended-sediment load from 2011 through 2020, representing a significant increasing trend (Mason and others, 2021).

The decreasing trend in suspended sediment in the non-tidal Pamunkey River and increasing trend in the Mattaponi River from 2011 through 2020 is identical to the trends in total phosphorus in these rivers over the same period. Phosphorus binds to soil particles, which might help explain these matching trend directions in suspended sediment and total phosphorus; however, a complete understanding of both sediment and phosphorus fate and transport remains a gap in knowledge.

Land use, changes in climate conditions, and management actions further influence sediment dynamics. Models have estimated that average sediment yields from urban areas could potentially be 70 times greater than agricultural areas (Brakebill and others, 2010); however, agricultural areas account for 69 percent of the total sediment delivered to the Chesapeake Bay. This disparity is thought to be because agricultural areas are widespread throughout the watershed, whereas urban areas, although intensive sediment contributors, represent smaller total areas of the watershed (Brakebill and others, 2019). Predicted changes in precipitation accumulation and intensity because of climate change could influence sediment fate and transport; however, more research is needed to evaluate these potential changes. Upstream best management practices (BMPs), implemented throughout the Chesapeake Bay watershed, have been estimated by models to meaningfully reduce sediment loads (Sekellick and others, 2019); however, trends in monitored (observed) sediment loads downstream are not consistent with those predicted reductions (Chesapeake Bay Program Integrated Trends Analysis Team, 2021). One explanation for this unobserved reduction is that active storage in streams and rivers is delaying the effects of the BMPs from being observed at downstream monitoring locations (Noe and others, 2020). The complex phenomena of sediment transport and fate in rivers remains a large gap in knowledge. Measured suspended-sediment load differs from model estimates of this load. Understanding why these differences are present and how to reconcile them remains a gap in knowledge.

Tidal Surface-Water Quality

The tidal reaches of the lower Pamunkey and York rivers have been monitored for decades and continue to be monitored by the Chesapeake Bay Program, the National Estuarine Research Reserve System, the Virginia VDEQ, and others. Understanding the water quality of the tidal Pamunkey and York rivers is complicated because of the influence of the tides that flow upstream in these rivers and other estuarian processes.

Nutrient and sediment conditions, and measures of dissolved oxygen and water clarity, are summarized from multiple tidal monitoring stations on the York and lower Pamunkey and Mattaponi rivers. These stations are part of a 139-station network that represent tidal water-quality conditions throughout the Chesapeake Bay. To determine trends in nutrients and sediment, and other constituents of concern over time in the tidal Pamunkey and York rivers, some analysts have used a generalized additive model approach (Chesapeake Bay Program Integrated Trends Analysis Team, 2021). The generalized additive model was used because of the complex hydrodynamics of estuaries, where sediment and nutrients may move upstream or downstream, make estimating loads extremely difficult; however, estimating concentrations of nutrients and sediment over time has shown to provide a reliable understanding of movement of these constituents in these complex flow environments.

Nitrogen

The average total nitrogen concentration in the tidal Pamunkey River from the most recent 2 years (2020 through 2021) is about 0.7 milligrams per liter (mg/L) (Murphy and others, 2022). This concentration was higher than the concentrations of about half the stations in the 139-station tidal monitoring network (Murphy and others, 2022; fig. 17). From 2012 through 2021, the total nitrogen concentration in the tidal Pamunkey River increased by 0.013 mg/L (Murphy and others, 2022). This increase was higher than the increase at about 75 percent of stations in the tidal monitoring network throughout the Chesapeake Bay reporting total nitrogen from 2012 through 2021. The tidal part of the neighboring Mattaponi River observed a small 0.008 mg/L increase in total nitrogen concentration over the same period (Murphy and others, 2022).

Atmospheric deposition and agricultural fertilizer are the largest estimated sources of nitrogen in the tidal Pamunkey River watershed; each account for about 30 percent of the delivered total nitrogen load. Nitrogen fixing crops also make a large contribution of nitrogen at about 20 percent. (Ator, 2019).

Total nitrogen concentration in the tidal Pamunkey River was about 2 percent higher in 2021 than 1994 (Murphy and others, 2022). This 2-percent change represents a 0.014 mg/L increase in total nitrogen concentration over this 27-year period. This 2-percent long-term increase was higher than the increase at about 90 percent of stations in the tidal monitoring network. Throughout the entire tidal York River watershed, total nitrogen concentration was about 6 percent higher in 2021 than 1994. Throughout the 139-station tidal monitoring network, total nitrogen concentration decreased by about 27 percent (Murphy and others, 2022), making these small increases throughout the tidal York and Pamunkey river watersheds dissimilar to changes observed throughout tidal rivers and streams throughout the Chesapeake Bay.

From 2012 through 2021, no decreasing (improving) trends in total nitrogen were found throughout the tidal York, Pamunkey, and Mattaponi rivers. Mostly no short term (2012 through 2021) trends were found either except for in downstream segments of the York River, which had significant increasing (degrading) trends (Murphy and others, 2022; fig. 18). The long-term period from 1994 through 2021 mostly exhibited no trends except for the persistent degrading trend in the mesohaline segment of the York River and a degrading trend in the tidal freshwater of the Mattaponi River (Murphy and others, 2022). Salinity classifications and extents discussed in the nitrogen and phosphorus sections are explained in the salinity section.

Overall, total nitrogen concentrations throughout the tidal reaches of the York, Pamunkey, and Mattaponi rivers were fairly constant over the short (2012 through 2021) and long (1994 through 2021) term with the exceptions of stations LE4.2 in the mesohaline segment of the York River, which resulted in no trend in the long term and a significant degrading trend likelihood in the short term, and station TF4.4, which changed from a long-term possible degrading trend likelihood to a significant degrading trend likelihood (Murphy and others, 2022).

Station LE4.1 had a significant degrading trend likelihood in total nitrogen in the short (2012 through 2021) and long (1994 through 2021) term. Although the mesohaline segment of the York River has experienced degrading total nitrogen conditions over time, the concentrations were generally low compared to other tidal streams and rivers throughout the Chesapeake Bay (Murphy and others, 2022).

Phosphorus

The average total phosphorus concentration in the tidal Pamunkey River from the most recent 2 years (2020 through 2021) is 0.08 mg/L. This concentration was higher than the total phosphorus concentrations of about 86 percent of the stations in the tidal monitoring network during the same 2020 through 2021 period (Murphy and others, 2022; fig. 19). From 2012 through 2021, total phosphorus concentrations decreased in the tidal Pamunkey River by 0.001 mg/L (Murphy and others, 2022). This decrease from 2012 through 2021 was higher than the total phosphorus concentrations reported by about 56 percent of stations in the tidal monitoring network throughout the Chesapeake Bay. Although this decrease was greater than the decreases of more than half of tidal monitoring stations over this recent 10 year period (2012 through 2021), average total phosphorus concentrations remained relatively high when compared to the other tidal monitoring stations throughout the Chesapeake Bay. The tidal part of the Mattaponi River observed a 0.005 mg/L decrease over the same period (Murphy and others, 2022). Mineral phosphorus, agricultural fertilizer, and urban land were the largest estimated sources of phosphorus in the tidal York River watershed: mineral phosphorus and agricultural fertilizer each accounted for about 35 percent of the delivered load and urban land accounted for about 20 percent of the delivered total phosphorus load (Ator, 2019).

Total phosphorus concentrations in the tidal Pamunkey River were about 5 percent higher in 2021 than in 1985 (Murphy and others, 2022). This 5-percent increase represents about a 0.004 mg/L increase over this 36-year period, which was higher than the total phosphorus values reported by about 85 percent of stations in the tidal monitoring network throughout the Chesapeake Bay. Throughout the entire tidal York River watershed, average total phosphorus concentration was about 14 percent higher in 2021 than 1985. Throughout the 139-station tidal monitoring network, the average total phosphorus concentration decreased by about 24 percent (Murphy and others, 2022), which makes the increases and relatively high average concentrations of total phosphorus throughout the tidal York River watershed dissimilar to changes observed in the tidal rivers and streams throughout the Chesapeake Bay.

From 2012 through 2021, the tidal York, Pamunkey, and Mattaponi rivers had mostly no trends in total phosphorus. However, the mesohaline segment of the York River had a possible degrading likelihood trend in total phosphorus at the same location where total nitrogen conditions were degrading and a possible improving total phosphorus trend in the oligohaline segment of the Mattaponi River (Murphy and others, 2022; fig. 20). No improving long-term (1985 through 2021) trends were estimated throughout the tidal York, Pamunkey, and Mattaponi rivers. Degrading long-term trends were estimated for the oligohaline and mesohaline segments of the York and Mattaponi rivers, and no trends were at any other locations (Murphy and others, 2022; fig. 20).

Overall, total phosphorus concentrations over time throughout the York, Pamunkey, and Mattaponi rivers increased by about 14 percent from 1985 through 2021, which differs from the decrease of about 24 percent for all tidal monitoring stations of streams and rivers in the Chesapeake Bay watershed. Station LE4.1showed a degrading long-term and short-term trend in total phosphorus, just as it did with total nitrogen.

Salinity

The lower parts of the Pamunkey River are tidally influenced, so salty ocean water travels upstream from the Atlantic Ocean and Chesapeake Bay into the York River and eventually into the Pamunkey River. One of the earliest evaluations of the extent of the tidally influenced parts of the Pamunkey River estimated that those parts extend 42 nautical miles upstream from the river mouth (Raney and Massman, 1953). The saline lower Pamunkey River has created a unique riverine environment over time. These environments include a unique ecology of flora and fauna that have adapted over time to these tidally influenced sections of river.

Because of many factors, such as SLR, climate change, and urbanization, salinity concentrations in the Pamunkey River and the extent of the tidal influence might change. When higher-salinity water is rapidly introduced to freshwater rivers, it stresses the local ecology that has come to depend on freshwater over a long period of time. One study modelled changes in salinity concentrations and distributions for the York River under multiple SLR and discharge scenarios and predicted large increases in mean salinity concentrations and greater upstream distributions of saline water (Rice and others, 2011) for all SLR scenarios.

Rising sea levels within the Pamunkey River estuary will be coupled with rising levels of salinity encroaching into freshwater habitats, which is also a concern. Although drought, storm surge, surface-water withdrawal, and dams can all contribute to periodic exposures of tidal freshwater habitats to salinity pulses, up-estuary movement of the salt front associated with increased SLR will be more chronic and pervasive. Tidal freshwater flows around the Pamunkey Indian Reservation, and oligohaline conditions prevail a couple miles downstream from the reservation (fig. 21). Researchers speculate that sufficient saltwater intrusion into tidal freshwater emergent wetland ecosystems might result in changes in biogeochemical cycling and carbon mineralization, which would result in increased sulfate reduction and decreased methanogenesis. Although these conditions might occur with saltwater intrusion, their direction and magnitude of change are exceptionally complex to predict and are dependent on the interactions of dynamic microbial communities and available carbon resources (Dang and others, 2018; Berrier and others, 2022).

In forested wetlands along the Mattaponi and Pamunkey River estuaries, tree species richness tended to decline moving downstream from freshwater forested wetlands to wetlands experiencing oligohaline conditions (Noe and others, 2021). On the Pamunkey River, in tidal forested wetlands experiencing low levels of porewater salinity (rarely over 1.5 parts per thousand [ppt]), trees died at a high level, which resulted in these forested wetlands slowly transitioning to oligohaline marsh (Noe and others, 2021).

Dissolved Oxygen

The amount of dissolved oxygen in aquatic environments is a well-known indicator of water quality and a measure of the oxygen available to living aquatic organisms. Aquatic insects, fishes, mollusks, crustaceans, and so on, have different oxygen demand requirements. Some experts have asserted that a minimum dissolved oxygen concentration of 5 mg/L is needed for suitable habitat for Chesapeake Bay’s flora and fauna (Chesapeake Bay Program, 2022). The U.S. Environmental Protection Agency created multiple criteria for dissolved oxygen conditions in 2003 for the Chesapeake Bay that include magnitude, frequency, and duration (U.S. Environmental Protection Agency, 2003a; U.S. Environmental Protection Agency, 2003b) and has subsequently refined and revised those criteria from 2004 through 2010, which are summarized in Tango and Batiuk (2013) and in 2017 (U.S. Environmental Protection Agency, 2017b). The State of Virginia also has dissolved oxygen criteria based on the specific environment within Virginia (for example, tidal or non-tidal rivers and streams, lakes and reservoirs, and if thermal stratification in a lake or reservoir is present) (Virginia State Water Control Board, 2022a) and criteria for waterbodies that drain to the Chesapeake Bay specifically (Virginia State Water Control Board, 2022b). To simplify these many criteria, Zhang and others (2018) created a metric called dissolved oxygen attainment deficit, which is a percentage that ranges from 0 to −100 percent, where 0 percent deficit means that all criteria were met and that dissolved oxygen conditions for ecological communities were good, and non-zero values represents the extent that dissolved oxygen criteria were not met and ecological conditions need improvement.

The tidal Pamunkey River has generally met these dissolved oxygen criteria from 1985 through 2021, although dissolved oxygen conditions were poor enough to cause some criteria to not be met in both the oligohaline and tidal freshwater segments for a short period around 1995 (Zhang and others, 2018; fig. 22). In the tidal Mattaponi River, the tidal freshwater segment has generally met dissolved oxygen criteria, whereas the oligohaline segment has not met the dissolved oxygen criteria over time except for the period 1992 through 1999 (Zhang and others, 2018).

The mesohaline segment of the York River had the worst dissolved oxygen attainment deficit over time in the York River watershed; deficits ranged from about −8 to −35 percent (Zhang and others, 2018). The poor dissolved oxygen condition in the mesohaline segment of the York River is unsurprising because this segment of river has also been identified as having issues with increased nutrient and sediment loadings over time.

The polyhaline (fig. 21) segment of the York River, near its mouth, is sufficiently deep that it has dissolved oxygen criteria for open water and deep water habitats, defined in (U.S. Environmental Protection Agency, 2003b). The open-water attainment deficit has ranged from 0 to about −18 percent (Zhang and others, 2018). The dissolved oxygen conditions in the deep water of the polyhaline York River have generally been good enough over time to meet all criteria. The attainment deficits in this deep water were around zero from 1985 through 2013; however, from 2014 through 2021, the deep water of the polyhaline York River began to accrue an attainment deficit. The most recent 3-year assessment period (2019 through 2021) had the worst dissolved oxygen attainment deficit throughout the mesohaline and polyhaline York River since 1985 (Zhang and others, 2018).

Dissolved oxygen concentrations are affected by sediment and nutrient loads. Excess sediment and nutrients can lead to eutrophication, which can potentially promote hypoxic or anoxic conditions. Anoxic conditions can release more nutrients from bottom sediments and exacerbate negative ecological impacts. Healthy and diverse aquatic plant and animal communities depend on satisfactory dissolved oxygen levels. This fact underscores the importance of accurately estimating sediment and nutrient loads and characterizing the plant and animal communities throughout the entire York River watershed.

Water Clarity

Secchi disk depth is a measure of water clarity. Secchi disk depth can be determined when a standardized Secchi disk is submerged, and the depth at which the disk is no longer visible is measured. The Secchi disk depth is reduced with increased suspended sediment, algae, and other clarity reducing material, such as organic matter and calcium carbonate. The Secchi disk depth also provides a coarse indicator of general water quality.

Most of the long-term Secchi disk depth trends from 1985 through 2021 were degrading throughout the York, Pamunkey, and Mattaponi rivers. In the long term, the oligohaline and upper mesohaline York and Mattaponi rivers had no trends; while, the oligohaline Pamunkey River had a significantly improving long-term trend (Murphy and others, 2022; figure 23a). From water years 2012 through 2021, the only significant trend for Secchi disk depth was an improvement in clarity in the oligohaline section of the Mattaponi River. No other significant trends were found in the York River watershed in the most recent 10 years; however, possible degrading trends were found in the mesohaline and polyhaline sections of the York River (fig. 23b).

Changes in water clarity in the Pamunkey River over time have been observed by Pamunkey Tribal Elders. “The water used to be a whole lot cleaner, it’s been degrading for a long time and the water clarity has been noticeably worse in the past 15 to 20 years” (T. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022). “I used to be able to see the fish in my net 3 to 4 ft deep in the water but now the clarity of the water isn’t good enough to see them like that anymore” (G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022). Data support the Pamunkey Tribal Elders’ observations. For example, in the tidal freshwater Pamunkey River, station TF4.2 is right at the Pamunkey Indian Reservation, and the average Secchi disk depth at this station over the past 2 years is about 0.5 meters whereas observations in 1985 were sometimes over 1 meter (Murphy and others, 2022).

Water Temperature

Water temperature is one of the most fundamental water-quality parameters because it has a major influence on the habitat of aquatic organisms, biological activity and growth, and water chemistry reactions. In the long term (1985 through 2021) and short term (2012 through 2021), water temperature is increasing throughout the tidal York, Pamunkey, and Mattaponi rivers, representing significant degrading trends (Murphy and others, 2022, fig. 24). Climate models predict that air temperatures will become warmer in the future (Najjar and others, 2009), and as air temperatures rise, so do water temperatures. Generally, as more heat is introduced into a system (and temperatures become higher), it increases the rate of chemical reactions. Warmer water holds less dissolved oxygen. This is an important relation to consider as temperatures have been increasing over the past several decades and are expected to continue to increase in the future.

Linking Non-Tidal and Tidal Surface-Water Quality

Hydrogeology

In the part of the Coastal Plain Physiographic Province in Virginia, groundwater flows through regionally extensive aquifers, in between the grains of saturated, permeable sedimentary layers. Less permeable sediments that restrict groundwater flow are designated as confining units, and indistinct transition areas are termed confining zones (McFarland, 2015). Precipitation that infiltrates the land surface and percolates to the water table facilitates groundwater recharge. Most groundwater in unconfined aquifers is discharged to nearby streams, but a small amount will travel downward and recharge deeper aquifers. In confined aquifers, groundwater flows primarily east towards large withdrawal centers and primary discharge areas along large rivers and the Atlantic Coast (McFarland, 2015). Groundwater levels have declined by about −1 to −2 feet per year (ft/yr) as groundwater withdrawals have increased over the past century. Small individual domestic wells are prevalent throughout the Coastal Plain, but withdrawals from these wells probably result in only small and localized groundwater declines (McFarland, 2015).

Aquifers in the Pamunkey River watershed include the unconfined surficial aquifer, and the confined Yorktown-Eastover, Piney-Point, Aquia, and Potomac aquifers, and all are separated by confining units (Masterson and others, 2015). According to McFarland and Bruce (2006), all of the aquifers that are present in the Pamunkey River watershed are also present at the Pamunkey Indian Reservation except for the Yorktown-Eastover aquifer. Before extensive groundwater pumping, groundwater in the Coastal Plain generally flowed from the Fall Zone towards the coast (McFarland and Bruce, 2006). Groundwater withdrawals throughout the part of the Coastal Plain Physiographic Province in Virginia began accelerating in the 1930s and further accelerated from the 1950s through about 1970. Withdrawal rates from about 1970 through 2010 have remained substantially higher than withdrawal rates in the first half of the 20th century (Heywood and Pope, 2009; Eggleston and Pope, 2013). The major pumping centers throughout Virginia alter the pre-development groundwater-flow pathways. In post-development conditions, groundwater flow in most aquifers, especially the Potomac, is generally radially inward and downward, towards large withdrawal centers (McFarland, 2015; Masterson and others, 2016b; fig. 25). Groundwater movement shown in figure 25 is a reasonable approximation of the current conditions throughout the York and Pamunkey river watersheds. The small domestic wells shown at two depths in figure 25 represent the Pamunkey Indian Tribe’s average well depths before 2019 (shallow depth in Piney Point aquifer) and from 2020 to present (deeper depth in Potomac aquifer). All pumping wells shown in figure 25 represent pumping conditions in the general area along cross section A to A’ and do not represent the actual number of wells.

Withdrawals

Groundwater levels in the lower Pamunkey River watershed declined by more than an estimated 1 ft per year on average from 1900 through 2000, which was likely due to anthropogenic withdrawals for industrial and manufacturing uses and municipal drinking-water supply (Masterson and others, 2015). Groundwater has been withdrawn from the Pamunkey River watershed for many anthropogenic uses for at least the last two centuries; however, rates of withdrawal throughout Virginia’s Coastal Plain have increased rapidly throughout most of the 20th century and remained high from about the 1970s through 2010 (Eggleston and Pope, 2013; Heywood and Pope, 2009; fig. 26) These large withdrawals have led to aquifer groundwater-level declines, compaction and subsidence, reversal of groundwater flow from a seaward to landward direction, and increased potential for saltwater intrusion (McFarland, 2010). When groundwater withdrawals in confined aquifers exceed the rate at which groundwater is recharged and water levels decline, the aquifer system can become compacted and may permanently lose storage volume and groundwater-flow pathways may be altered (McFarland, 2010).

In recent years (2010 through 2019), groundwater withdrawals in the Virginia Coastal Plain have been reduced. Total groundwater withdrawals sharply reduced around 2010, and withdrawals from 2010 through 2019 have been sustained at around 2010 levels (Virginia Department of Environmental Quality, written commun., 2022; fig. 27). Groundwater withdrawals are reported only when greater than 10,000 gallons per day during any month or greater than 1 million gallons per month for crop irrigation. Current total groundwater withdrawal rates in the Virginia Coastal Plain remain high overall when compared to rates in the early 1900s; however, the recent reductions starting around 2010, driven primarily by reduced pumping in the industrial and manufacturing sectors (Virginia Department of Environmental Quality, written commun., 2022), could address the declining groundwater levels in the Coastal Plain and potentially contribute to quell aquifer compaction and subsequent subsidence.

Groundwater withdrawals for the localities within the Pamunkey River watershed in the year 2021 ranged from 16.79 to 0.27 Mgal/d (Virginia Department of Environmental Quality, 2022b; table 3). Total withdrawals from King William County were the largest in the Pamunkey River watershed. Most of the groundwater withdrawn in King William County is done by the WestRock Company’s paper mill, approximately 10 miles east of the Pamunkey Indian Reservation. The WestRock Company’s paper mill pumps millions of gallons per day from the Potomac aquifer.

Demand for groundwater resources throughout the York River watershed is estimated to increase by 50 percent from 2010 to 2040 (Virginia Department of Environmental Quality, 2015), which can potentially affect the availability and use of these groundwater resources in the future. The large current groundwater demand in the York River watershed and projected increases, underscores the importance of monitoring these resources so that they might be managed equitably. Mitigating the consequences of large withdrawals could account for the prioritization of health and resource considerations for the future.

Discrete and continuous measurements of water-level depths below the land surface in and around the York River watershed are monitored by the USGS and others groundwater monitoring wells; many of the wells are operated in cooperation with VDEQ. Within the York River watershed, 37 groundwater monitoring wells are currently monitored by the USGS as of 2022 (fig. 28). Water levels at three selected groundwater monitoring wells, in the Potomac aquifer throughout the York River watershed, have declined by an average rate of −1.5 ft/yr for the past 50 to 60 years (fig. 29), with rates ranging throughout the watershed between −1.1 to −2 ft/yr. Observed rates of decline were larger the closer the wells were to the major pumping center in the watershed. The measured rate of groundwater decline at these wells generally agrees with estimates produced by Eggleston and Pope (2013), who estimated an average rate of decline between −0.75 to −1.5 ft/yr, and Masterson and others (2015), who estimated an average rate of decline between −1 to −2 ft/yr.

Two groundwater monitoring wells are near the Pamunkey Indian Reservation. One is approximately 8 miles upstream from the reservation near the Pamunkey River, and one is about 8 miles downstream near the Pamunkey River. The USGS groundwater monitoring well 373737077083201, about 8 miles upstream from the reservation and 35 ft deep in the Piney Point aquifer, has been measuring depth to water level continuously at a 15-minute interval since 2008 with discrete measurements dating back to 1978 (U.S. Geological Survey, 2022a). The data from this well do not appear to have a long-term upward or downward trend, but a cyclical pattern is present, with seemingly large year-to-year variability. This well’s shallow depth might provide insights into seasonal groundwater variation and periods of drought. Further investigation would be needed to understand the groundwater dynamics at and around this location.

The multiple-depth groundwater monitoring well about 8 miles downstream from the Pamunkey Indian Reservation, includes USGS groundwater monitoring wells 373523076523402 through 373523076523405. Measurements are collected at four different depths to evaluate water levels in the Piney Point and Aquia aquifers and two different depths in the Potomac aquifer. These wells have been measuring water-level depth continuously at a 15-minute interval since 2020 and limited discrete measurements before 2020 (U.S. Geological Survey, 2022a). Although only recently installed, these wells will provide insights into groundwater dynamics in the future, especially because they are close to a large pumping center near West Point, Virginia.

The groundwater dynamics underneath the Pamunkey Indian Reservation are complex and influenced by many factors. Large pumping centers throughout the Coastal Plain influence deep, confined, regional aquifers, like the Potomac aquifer (McFarland, 2010). Groundwater availability underneath Pamunkey Indian Reservation lands is largely affected by forces external to the reservation. Continued groundwater monitoring at current groundwater monitoring wells throughout the Chesapeake Bay and in and around the York and Pamunkey river watersheds is necessary to provide the data for the Tribe, scientists, and regulators to evaluate the availability of groundwater resources over time, recognize patterns in groundwater levels, observe periods of potential drought, and provide information about how groundwater withdrawals throughout the region are affecting the Pamunkey Indian Tribe at the local scale.

A few well-established groundwater models have been created to provide insights into the groundwater dynamics of the Coastal Plain physiographic province of Virginia (Robinson and Reay, 2005; Heywood and Pope, 2009; Masterson and others, 2016b). Notably, the model created by Heywood and Pope (2009) uses spatial and numerical methods to predict changes in regional groundwater levels in the Coastal Plain physiographic province of Virginia and has the capability to evaluate different scenarios for future proposed pumping and the responses to each individual aquifer. This model is used by VDEQ to predict future groundwater levels in response to changes in pumping and provides an essential and foundational tool to begin evaluating groundwater in this region. More recently, Masterson and others (2016b) created a numerical model to simulate groundwater conditions throughout each hydrogeologic section and aquifer. Their model estimates hydrologic budgets at all depths, water levels, and storage and predicts future hydrologic conditions under different climatic scenarios. Overall, these groundwater models are extremely useful tools to estimate hydrogeologic conditions and have demonstrated a degree of accuracy when comparing model outputs to monitored data from groundwater monitoring wells. As future climatic and anthropogenic changes complicate our ability to accurately model groundwater systems, efforts aimed at improving the accuracy and reliability of groundwater models and additional efforts in model verification and validation could provide vital information to the Pamunkey Indian Tribe and residents throughout this region about the future availability and use of the groundwater resources.

Groundwater Quality

In the Pamunkey River watershed, the Potomac aquifer is the deepest aquifer and generally possesses better water quality, based on direct measurements, than surface and shallow aquifers (McFarland, 2010). Surficial and shallow aquifers close to the land surface are more susceptible to contamination from non-point source pollutants, such as agricultural runoff, leaking septic systems and other underground storage tanks, stormwater, and so on. Multiple confining layers may help compartmentalize potential influxes of pollutants, thereby providing some protection to deeper aquifers. Groundwater in deep aquifers, like the Potomac aquifer, can move extremely slowly (Pope and others, 2020), meaning pollutants that reach these deep aquifers could potentially persist for long periods. Groundwater pumping, especially large or intense pumping, has changed groundwater-flow directions towards major pumping centers (McFarland, 2010; Masterson and others, 2016b). Another major and well-known threat, caused by groundwater pumping near a coast, is saltwater intrusion into aquifers (McFarland, 2017). Although landward saltwater intrusion in Virginia is much less compared to saltwater intrusion in other States along the Atlantic Coastal Plain, such as North Carolina, Delaware, and New Jersey, there could potentially be a delayed response in intrusion to the vast amount of groundwater withdrawals in Virginia over the past century (Masterson and others, 2016b). For the Pamunkey Indian Tribe, “Everyone here on the reservation is on well and septic systems. So, the quality of our water is an issue [especially because] we’re all drinking groundwater” (R. Gray, Pamunkey Indian Tribe, Chief, oral commun., 2022).

All residents of the Pamunkey Indian Tribe have a well and are using groundwater for drinking water and all other residential and commercial uses (R. Gray, Pamunkey Indian Tribe, Chief, oral commun., 2022). New wells were constructed in 2020 because the quality of water pumped from them before 2020 was determined to not be sufficient for human consumption. The old wells were approximately 40 to 100 ft below the land surface and were pumping water from the Piney Point aquifer, whereas the new wells were drilled to approximately 280 ft below (fig. 25) the land surface to reach the Potomac aquifer, where water-quality was determined to be sufficient for human consumption. Tribal Elders noted that water from the prior shallow wells had a bad odor and taste, which forced many to purchase expensive filtration systems and others to stop using the water from their wells altogether (T. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022). The new wells in the Potomac aquifer are expected to provide water safe for human consumption to the Pamunkey Indian Tribe because the Potomac aquifer is known to have minimal contamination and known to have protection from multiple confining units (McFarland, 2010). Anthropogenic contamination has not been detected yet in the Potomac aquifer in this part of the Coastal Plain. However, two potential contamination sources to the aquifer include anthropogenic sources and saltwater intrusion combined with downward flow gradients caused by major pumping centers (Masterson and others, 2016b). Long-term monitoring of groundwater quality can inform users about water-quality concerns, inform users about health concerns related to groundwater quality, and provide insights on the movement of pollutants.

Land Subsidence

Land subsidence is the vertical sinking of the land mass at often large spatial scales. The primary driver of subsidence in the southern Chesapeake Bay region is groundwater withdrawal from aquifers, which when combined with gravitational compaction, leads to a loss of volume in aquifers and the subsequent loss of volume and net elevation in aquifers (Poland, 1984; Galloway and Burbey, 2011). More than half of the RSLR observed in the southern Chesapeake Bay region is caused by subsidence, and more than half of the subsidence in this area is caused by aquifer compaction from groundwater withdrawals (Eggleston and Pope, 2013; Karegar and others, 2017). Subsidence rates in the southern Chesapeake Bay region are the highest on the eastern seaboard, ranging from −1.1 to −4.8 millimeter per year (mm/yr), and local rates of subsidence in the York River estuary range from −2.8 to −3.8 mm/yr (Eggleston and Pope, 2013; Mitchell and others, 2017; fig. 30).

The Pamunkey Indian Reservation lies approximately 10 mi west of West Point, Virginia; West Point is a focal point of subsidence within the southern Chesapeake Bay region. In the 1970s, subsidence was measured at West Point by leveling; the measured rate, −3.76 mm/yr, was among the highest measured rates in the Chesapeake Bay at that time (Holdahl and Morrison, 1974). Because the Pamunkey Indian Reservation is close to the subsidence epicenter at West Point, it has relatively high rates of subsidence—most recently estimated to be approximately−3.2 mm/yr (Eggleston and Pope, 2013; Milligan and others, 2019; fig. 30).

Groundwater withdrawal is often used for private wells on individual residences, municipalities, and industry within municipalities, with a high degree of spatial variability, as is much of the southern Chesapeake Bay region. Compared to other causes of subsidence, groundwater withdrawal is an easier cause to study and address. When subsidence is caused by groundwater withdrawal, reducing or managing withdrawal rates and recharging aquifers have been successful methods of quelling subsidence (Galloway and Burbey, 2011). Because of spatial variability of groundwater withdrawals in Virginia and variability in municipality management efforts, resultant rates of RSLR also vary considerably throughout the region. Subsidence from aquifer compaction, because of groundwater withdrawal, is affecting the Pamunkey Indian Reservation at a regional scale, that is, major groundwater withdrawal focal points throughout the Coastal Plain of Virginia and Maryland have the largest effects on the groundwater levels and subsidence observed directly on the Pamunkey Indian Reservation. In the future, cooperation between large groundwater users; tribal, State, and local governments; and other stake holders will be crucial to continue quelling subsidence.

Other drivers of subsidence, like the glacial isostatic adjustment, contribute to some degree to local subsidence in the southern Chesapeake Bay region. Other potential drivers of subsidence include bedrock dissolution, drainage and degradation of organic soils, settling of disturbed soils, volcanic disturbances, tectonic motions, and settling of the impact crater in the Chesapeake Bay; however, there is no evidence that these potential drivers are contributing to local subsidence significantly (Eggleston and Pope, 2013).

In addition to land subsidence’s contribution to RSLR, land subsidence can also lead to greater nuisance flooding and extreme flooding associated with storm surges (Karegar and others, 2017). In the southern Chesapeake Bay, the relatively shallow topographic relief of coastal areas, such as those of the Pamunkey Indian Reservation, mean frequent or permanent inundation will eventually cause large monetary damages and displace hundreds of thousands of people from their homes (Eggleston and Pope, 2013). Rising water levels, coupled with subsidence, will push groundwater levels upwards, damaging private and municipality infrastructure and exacerbating precipitation-driven flooding (Eggleston and Pope, 2013).

The Pamunkey Tribal Elders are very aware of these threats and have been experiencing them firsthand. Pamunkey Tribal Elder, Grover Miles, said “I have witnessed it. The reservation is sinking, and I can prove it to you. Forty-five years ago, I dug a well for my parents. It was 38-ft deep. If you go anywhere on the reservation today, you will hit water at 10 ft. And for the past 15 years, as soon as the tide rises, I’ve got water in my back field, which didn’t happen prior to 15 years ago” (G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022).

High-resolution monitoring of groundwater levels and subsidence signals at the local scale in and around the Pamunkey River watershed will be important in making informed decisions regarding aquifer management. As rates of SLR will increase because of elevation loss caused by subsidence, it is important that subsidence rates be incorporated when calculating local rates of RSLR and determining vulnerability of the Pamunkey Indian Tribe, Reservation, and its water resources to SLR and climate disruption. The USGS and partner agencies are currently measuring vertical land motion and subsidence in many ways, including with global positioning system benchmarks and extensometers throughout Virginia and a new extensometer installed at West Point, Virginia, in 2023 (U.S. Geological Survey, 2022b). In concert with these land-motion monitoring activities, continued monitoring of the groundwater monitoring well network throughout the York River watershed and throughout Virginia and neighboring States can provide the data necessary for scientists to analyze and interpret future changes in RSLR.

Sea-Level Rise

Although the rates of SLR have been highly variable over the last 18,000 years, sea level has been steadily rising along the Atlantic Coast of the United States since that time (Riggs and others, 2011). Some of the highest rates of SLR in the contiguous United States are in the Chesapeake Bay region, where they are twice the average global rate per year (Eggleston and Pope, 2013). On a global scale, SLR is driven by thermal expansion of water in the oceans, coupled with melting landlocked ice sheets, which add volume to ocean waters (Pilkey and Pilkey, 2019). On a regional scale, many complex and interacting factors contribute to SLR. Subsidence from aquifer-system compaction because of groundwater extraction, isostatic adjustment of the Laurentide Ice Sheet’s glacial forebulge, changes in surface- and deep-water current circulation such as the Gulf Stream (Atlantic Meridional Overturning Current), and gravitational redistribution of land-based glacial meltwater are all factors that contribute to regional and local SLR along the Atlantic Coast (Strain, 2014; Pilkey and Pilkey, 2019).

Sea level has been rising along the coasts of the contiguous United States, including coastal Virginia, for the past century (Sweet and others, 2022; Ezer and Atkinson, 2015; fig. 31). Higher sea levels amplify the impacts of flooding, storm surges, high tides, wetland loss, and coastal erosion (Sweet and others, 2022; Eggleston and Pope, 2013). Climate change contributes to the SLR experienced today and the SLR that will come in the decades and centuries in the future (Reidmiller and others, 2018; Hall and others, 2019). However, even if drastic mitigations were taken to limit the rise in average global air temperatures, the oceans will continue to respond to historical and current atmospheric conditions, and sea levels will continue to rise in the future (Fox-Kemper and others, 2021). This reality stresses the importance of gaining a better understanding of the extent these impacts will have in the Pamunkey River watershed now and in the future.

A 3-ft rise in sea level by 2100 is plausible in coastal Virginia (Riggs and others, 2011; Pilkey and Pilkey, 2019; Sweet and others, 2022). The maximum expected rise by 2100 is 6 ft, and some researchers suggest as much as 10 ft (Pilkey and Pilkey, 2019; Sweet and others, 2022); these estimates do not include the effects from land subsidence, erosion, or future construction. Any of these estimates (fig. 32) will have substantial repercussions for the Pamunkey Indian Tribe and Reservation, such as submergence of parts of the Pamunkey Indian Reservation; displacement of people; alteration of ecosystems; disruption of normal business; and loss of or damages to homes, buildings, infrastructure, agricultural lands, and culturally important lands.

The Pamunkey Tribal Elders are very concerned about their land being completely submerged under water in the future. They made estimates of how soon they think the reservation will be completely under water that ranged from 30 to 100 years (W. Cook, Pamunkey Indian Tribe, Elder, oral commun., 2022; J. Krigsvold, Pamunkey Indian Tribe, Elder, oral commun., 2022; T. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022; G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022). Tribal Elders have noted that “There are a lot of places both on the reservation and throughout the surrounding counties that used to be dry all the time and now they are wet all the time. Especially in the last 15 years, it’s been happening really fast” (J.H. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022; T. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022; G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022).

The predicted impacts to the Pamunkey Indian Tribe and Reservation from RSLR are many and could have profound effects on the Tribe’s ability to continue to inhabit the current reservation lands. Observations made by the Pamunkey Tribal Elders indicate impacts from RSLR have already started with notable increases in the amount of land that has become submerged or permanently inundated, shoreline erosion, and increases in flood frequency and magnitude. Monitoring RSLR could support health, safety, and preservation of the Pamunkey Indian Tribe and Reservation.

Riparian

The Pamunkey River watershed supports vast riparian areas, which are water-dependent lands adjacent to streams and a transition zone between streams and uplands. They maintain important physical, biological, and ecological functions by facilitating interactions between land, air, water, and vegetation (Klapproth and Johnson, 2009). Riparian areas provide for a disproportionally large amount of biodiversity. Additionally, these ecosystems are critical for maintaining geomorphological integrity of stream banks and channels and protecting streams from upland pollutant runoff, thus buffering adjacent aquatic habitat from erosion, disturbance, and nutrient loading from upland sources (Newson and Sear, 2001; Klapproth and Johnson, 2009).

Development of urban and agricultural land threatens riparian ecosystems and those ecosystems for which they provide a buffer. Riparian zone restoration targeting for the York River watershed revealed that across the 7,780 miles of shoreline in the watershed, 248 miles would benefit water quality and habitat based on adjacent upland land uses (Newson and Sear, 2001).

Wetlands

National Wetland Inventory 2016 surveys in the Pamunkey River watershed tally over 46,000 acres of wetlands (fig. 33). The Pamunkey River watershed also contains tidal freshwater marsh and forest, brackish marsh communities, and salt-marsh communities (U.S. Fish and Wildlife Service, 2016). In addition to providing many ecosystem services critical for human populations, tidal wetlands provide important habitat for a wide array of biota. High rates of primary productivity give tidal wetlands on the Pamunkey River an important foundational role in trophic webs, providing food for lower-level organisms, such as mollusks, crabs, and fish. Tidal wetlands also provide critical nursery habitat for many ecologically and economically important anadromous fish and blue crabs, and habitat for many bird species, including migratory waterfowl (Perry and Atkinson, 2009; Mitchell and others, 2017). Additionally, wetlands provide ecosystem functions that are critical to the human populations living in the York River watershed, including water filtration, floodwater abatement, wave attenuation, and shoreline protection.

In addition to human disturbance and development, tidal wetlands throughout the York River estuary are threatened by climate disruption and SLR. The National Oceanic and Atmospheric Administration tide gage on the York River estimates local SLR to be 4.93±0.34 mm/yr (National Oceanic and Atmospheric Administration, 2021). Compounded with relatively high rates of local subsidence, some estimates ranging from 2.8 to 3.8 mm/yr, local rates of relative sea-level rise (RSLR) will be even higher (Eggleston and Pope, 2013; Mitchell and others, 2017).

Many factors contribute to rates of marsh elevation change, which makes predicting elevation change rates for individual marshes challenging. If wetlands in the York River estuary cannot stay above local RSLR, stress from increased salinity and inundation might cause succession between marsh types, and sometimes, loss of wetland acreage entirely (Neubauer, 2011; Ensign and others, 2014). Mitchell and others (2017) quantified marsh acreage change between the 1970s and 2009, and found that wetland acreage decreased by 2.7 percent in the York River estuary during their study period with 20 centimeters of SLR. Spatial patterns of loss varied based on multiple interacting factors, and marshes in some areas expanded with SLR (Kirwan and others, 2016a; Mitchell and others, 2017).

Wetlands, along with the biota that inhabit them, vary along a salinity gradient of the Pamunkey River estuary (Perry and Atkinson, 2009). Salinity levels in the Pamunkey River estuary range from tidal freshwater in the upriver stretches to polyhaline in the downstream reaches (Perry and Atkinson, 2009; Raey, 2009). Four Chesapeake Bay National Estuarine Research Reserve (CBNERR) monitoring locations on the York and Pamunkey river estuaries are positioned along the salinity gradient to capture water quality conditions over varying salinity levels throughout the estuary (fig. 10) and provide useful data on salinity levels, marsh types, vegetation communities, and where changes have occurred over time (Chesapeake Bay National Estuarine Research Reserve, 2022). Site PMK012.18 is in tidal freshwater, TSK000.23 in oligohaline, YRK015 in mesohaline, and CHE019.38 in polyhaline.

In their natural state, coastal ecosystems are resilient and can keep pace with SLR by vertical accretion of sediments and lateral migration (Riggs and others, 2011; Buchanan and others, 2022). However, when sediment inputs are reduced or migration pathways are not available, tidal wetlands are imperiled and potentially converted to open water (Buchanan and others, 2022). Wetland habitats currently compose about 55 percent of the total land in the Pamunkey Indian Reservation (fig. 34). The wetland habitats on the reservation are dominated by tidal freshwater forested wetlands and tidal freshwater herbaceous emergent wetlands. Downstream from the Pamunkey Indian Reservation, tidal freshwater forested wetlands might be transitioning to tidal oligohaline emergent marshes under current SLR conditions (Noe and others, 2021). Tidal freshwater emergent marshes might also be transitioning to tidal oligohaline emergent marshes in the York River estuary (Perry and Atkinson 2009). Even if a sufficient sediment supply and migratory pathways allowing lateral movement were available (Buchanan and others, 2022), Tribal wetlands would still suffer a net loss of territory. Wetlands will also be lost on the reservation in areas where current infrastructure precludes lateral migration.

Increased RSLR will not only have deleterious impacts to Tribal wetlands but will also cause the intertidal zone to elevate into upland habitats, which could cause increased erosion in areas not typically exposed to wave energy and currents. In addition, increased RSLR has the potential to convert areas that are currently low-lying upland habitat into non-tidal wetland habitat by elevating the current water table closer to the soil surface (Pilkey and Pilkey, 2019). Elevated groundwater levels caused by RSLR might also cause drinking water to become contaminated with saline water (Pilkey and Pilkey, 2019).

Wetland ecosystems rely on complex sediment accumulation dynamics to maintain elevation and keep pace with SLR (Goodwin and others, 2001; Ensign and others, 2014). Coastal wetlands around the Chesapeake Bay vary in their ability to maintain equilibrium with rising water levels (Kirwan and others, 2016b). Many marsh complexes around the Chesapeake Bay are monitored for surface-elevation change, but relatively few have been monitored for geodetic signatures of subsidence. Although some marshes may have positive surface-elevation trends suggesting a positive response to SLR, undetected subsidence could negate those positive trends. If coastal wetlands experience inundation and salinity beyond the tolerances of their vegetation communities, those communities will either die out entirely and become mud flats or be succeeded by alternate marsh types (Goodwin and others, 2001; Ensign and others, 2014).

Submerged Aquatic Vegetation

SAV is a critical component of the ecology of the Chesapeake Bay and its tributaries. Different species of SAV grow throughout the York River estuary, and their distribution is based on salinity tolerances (fig. 35) (Moore and others, 2009). One of the most important ecosystem functions of SAV and adjacent mud and sand flats is to provide nursery habitat for several ecologically and economically important species, such as blue crabs and anadromous fish (Stockhausen and Lipcius, 2003; Lipcius and Ralph, 2011; Moore and others, 2009). However, turbidity, sedimentation, nutrient loading, and competition with invasive species all threaten SAV in the York River estuary (Moore and others, 2009).

Zostera marina L. (eelgrass) is a polyhaline seagrass that grows only near the mouth of the York River in high-salinity waters and is the only seagrass species found in the Chesapeake Bay (Moore and others, 2009). Ruppia maritima L. (widgeon-grass) grows throughout the salinity gradient, from tidal freshwater to polyhaline conditions (Moore and others, 2009). Stuckenia pectinata (L.) Börner (sago pondweed) and Potamogton perfoliatus L. (redhead grass) are found in brackish waters of lower salinities (Moore and others, 2009). Freshwater SAV in the York River watershed grows in areas with little-to-no salinity, and communities are dominated by Vallisneria americana Michx. (watercelery), the invasive Hydrilla verticillata (L.f.) Royle (waterthymes), and Myriophyllum spicatum L. (Eurasian watermilfoil) (Moore and others, 2009). Macroalgae (seaweeds) are not dominant in the York River estuary, but in areas of excess nutrient loading, macroalgae may outcompete eelgrass (Moore and others, 2009). Waterthymes spread rapidly, can outcompete native SAV, and is abundant in freshwater and oligohaline segments of the York and Pamunkey rivers (Orth and others, 2006; Moore and others, 2009).

SAV is important because it provides habitat for a multitude of aquatic fauna, but need a certain level of water quality to thrive. Sediment and nutrients from anthropogenic stressors played a major role in a large-scale loss of SAV in the York River estuary that reached its minimum in the 1980s (Stockhausen and Lipcius, 2003). Although high-resolution empirical data on current stocks of SAV in the upriver segments of the Pamunkey River is lacking, Tribal members have pointed out a major decline in water clarity, which studies have suggested correlates with lower abundance of SAV (Henderson, 2021).

Fishes

There is no record of the names given to different types of fish by indigenous peoples of this region, nor were any systematic biological surveys of the York River watershed conducted by early European colonists. Early European writings (circa 1624); however, describe some coastal Virginia fishes, like Alosa pseudoharengus (alewife) and Alosa aestivalis (blueback herring), collectively called river herring, and Acipenseridae (sturgeon), which were very familiar to colonists recently arrived from England. Other fish species had no old-world equivalents and were generally ignored (Jenkins and Burkhead, 1994). Even less is known about the relationship between indigenous people and the fish they likely harvested, but several types, including sturgeon, river herring, and Alosinae spp. (shad), were—and still are—culturally significant to the Pamunkey Indian Tribe and other Tribes that live along Virginia’s coastal rivers (G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022).

Before the start of the 19th century, the fish assemblage of the tidal Pamunkey River could be separated into two categories of native (that is, original) species. The first of these groups was dominated by perhaps 30 resident species of Cyprinidae (minnows), Catostomidae (suckers), Centrarchidae (sunfishes) and other less common taxa. All fishes in this category completed their entire life cycle within the tidal Pamunkey River. They were common but probably never abundant. Most were small, measuring less than 15 centimeters in length and lived for only a few years. A few native species like Lepisosteus osseus (Linnaeus, 1758) (longnose gar) and Amia calva (Linnaeus, 1766) (bowfin) lived longer and grew larger, but neither make an appetizing food source (Jenkins and Burkhead, 1994).

The other category of indigenous fish species was migratory (diadromous) and included: Alosinae (shads), river herrings, striped bass, American eel, and Acipenser oxyrinchus (Mitchill, 1815) (Atlantic sturgeon). They moved annually and predictably between the Atlantic Ocean and coastal rivers like the Pamunkey River to spawn (anadromous) or to live as adults (catadromous) in riverine freshwater habitats. Some, like Morone americana (Gmelin, 1789) (white perch) and Perca flavescens (Mitchill, 1814) (yellow perch), are considered semi-migratory and move seasonally within the Pamunkey River. Historically, adult river herrings, that is, alewife and blueback herring, left the ocean early each spring to enter the Pamunkey River in large schools that numbered in the hundreds of thousands each year. Because these river herring spawning runs were seasonally predictable and involved huge numbers of fish, densely packed in relatively shallow water, they were depended upon by indigenous peoples and early European fishers as an abundant source of high-quality protein. A significant proportion of adult river herring die after spawning, and their carcasses contribute marine-derived nutrients that accelerate primary production in coastal freshwater rivers and marshes during spring months (Jenkins and Burkhead, 1994).

During the 19th century, the advent of highly efficient fishing methods increased harvesting and increased pollution. Furthermore, the construction of hundreds of low-head dams caused dramatic declines in populations of native migratory fishes, including Atlantic sturgeon, American shad, blueback herring, and alewife (Klauda and others, 1991; Atlantic States Marine Fisheries Commission, 1999). Despite substantial recovery efforts in Virginia and elsewhere, including harvest moratoria on river herrings, that is, alewife and blueback herring; hatchery propagation for American shad; and listing of Atlantic sturgeon under the Endangered Species Act (16 U.S.C. 1531-1544), there is little evidence of restoration success. Consequently, the culturally significant and economically valuable fisheries once supported by these species are no longer an important feature of Tribal life (Jenkins and Burkhead, 1994).

In response to a growing interest in recreational angling throughout the 20th century, natural resource agencies stocked a variety of non-native fishes in some Virginia rivers (Hewitt and others, 2009). Compared to native fishes, most of the introduced species were large, long lived, predatory, and broadly tolerant of environmental conditions. For example, some natives of the Mississippi River, like the Pylodictis olivaris (Rafinesque, 1818) (flathead catfish) and Ictalurus furcatus (Valenciennes in Cuvier and Valenciennes, 1840) (blue catfish), have become widely established and numerically dominant in their new freshwater rivers, including the Pamunkey River (Hilling and others, 2021). The ecological effects that abundant, non-indigenous predator fishes have on native (resident and migratory) Pamunkey River fishes are difficult to quantify. However, the potential for impacts is substantial, especially when combined with aquatic habitat loss from pollution, dams, and other migration impediments; SLR; and salinity intrusion within the upper York River watershed.

Pamunkey Tribal Elders have witnessed a dramatic shift in the fish assemblages within the Pamunkey River watershed in a relatively short amount of time. Two Pamunkey Tribal Elders recall that when they were younger, they fished mainly for river herring, that is, alewife, blueback herring, American shad, striped bass, and Ictalurus punctatus (Rafinesque, 1818) (channel catfish) (T. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022; G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022). Grover has been commercially fishing the Pamunkey River every year for the past 66 years and said, “We’ve lost herrings. There are very few herrings now. We also used to fish for White Perch but now there’s not enough to fish for them” (G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022; K. Moore, Pamunkey Indian Tribe, Elder, oral commun., 2022). Multiple Tribal Elders also noted that when they were younger, they would easily be able to catch over 100 hundred American shad, but in recent years, they would be lucky to catch 10 (T. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022; G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022). They also noted that in recent years, the fish that they catch are overwhelmingly blue catfish. “The Blue Catfish are eating everything, they’re changing the environment” (K. Moore, Pamunkey Indian Tribe, Elder, oral commun., 2022). Pamunkey Tribal Elders attribute these losses in native fish populations to several factors including overfishing, the introduction of non-native species, rivers and their tributaries being fragmented from dams and other infrastructure, and poor water quality (G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022; T. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022).

The fish communities supported by the Pamunkey River have changed substantially over time, and this change has hindered the ability of the Pamunkey Indian Tribe to fish as a primary means of income. Most of the Tribal Elders noted that the fishery is currently not in a state where they are able to fish as a sole source of income but would like to see it recover to a point where that would be possible for future generations (G. Miles, Pamunkey Indian Tribe, Elder, oral commun., 2022; T. Langston, Pamunkey Indian Tribe, Elder, oral commun., 2022; K. Moore, Pamunkey Indian Tribe, Elder, oral commun., 2022).

Freshwater Mussels

Freshwater mussels (Unionidae [Rafinesque, 1820]) are important contributors to biological diversity in Virginia’s streams and rivers, though they live a mostly hidden existence within riverine sediments. Limited surveys of the tidal Pamunkey River have documented at least 10 unionidae species, like Elliptio congaraea (Lea, 1831) (Carolina slabshell) and Lasmigona subviridis (Conrad, 1835) (green floater) (Brian Watson, Virginia Department of Wildlife Resources, oral commun., 2022). Some taxa, like the ubiquitous Elliptio complanata (Lightfoot, 1786) (eastern elliptio), are common, but most (80 percent) known freshwater mussel species in the Pamunkey River are threatened by habitat loss, pollution, salinity intrusion, and introduced predators (Brian Watson, Virginia Department of Wildlife Resources, oral commun., 2022).

Freshwater mussels tell an important story about the interconnectedness of the Pamunkey River ecosystem. Most unionidae mussels produce parasitic larvae called glochidia that must latch onto the gills of a host fish to survive (Jones, 2015). Some glochidia, like those of the Pyganodon implicata (Say, 1829) (alewife floater), will attach only to migratory fish, such as blueback herring and alewife (New York Natural Heritage Program, 2021), which are also in severe decline in many coastal rivers for many of the same reasons (Limburg and Waldman, 2009). For this reason, conservation efforts for rare freshwater mussels may also depend on successful management of native fish populations (Brian Watson, Virginia Department of Wildlife Resources, oral commun., 2022). Mussels are efficient filter feeders that can increase light penetration into otherwise turbid waters, like oysters do in saline parts of the York River watershed. Increased filtration of water allows better light penetration, which might result in the production of more SAV, which in turn provides critical habitat for juvenile fish, including host fish species, in tidal freshwater reaches of the Pamunkey River.

Land-use throughout the York and Pamunkey rivers estuary has changed considerably, impacting riparian and fluvial geomorphology, riparian and benthic habitat, and the flora and fauna that depend upon those habitats. Freshwater mussel (unionidae) survivability is at great risk because of their environmental sensitivity and the degrading habitat. Unionidae have been shown to be reliable indicators of habitat health (Simmions and Reed, 1973; Lees, 2005) because of their sensitivity to environmental impacts. Simmons and Reed’s 1973 study of macrobenthic communities, in particular, demonstrated the suitability of unionidae as environmental indicators in the North Anna and Pamunkey rivers.

The North Anna River watershed was the site of extensive pyrite mining from 1885 to 1920 (Simmions and Reed, 1973). The acidified tailings from the extensive mining operations were found to have caused considerable negative impacts on water quality, including erosion, increased sedimentation, and loss of aquatic life and vegetation. As of 1973, fin fish populations were reduced by 65 percent and macrobenthic organisms were reduced by 40 to 60 percent: freshwater mussels composed 30 percent of this macrobenthic reduction (Simmions and Reed, 1973). Subsequent efforts to repopulate mussels in the North Anna River downstream from the confluence with Contrary Creek have been unsuccessful (Simmions and Reed, 1973).

Although impoundments are generally considered harmful to biodiversity, the dam creating Lake Anna was shown to create a downstream recovery zone for macrobenthic fauna, including unionidae, that were unable to reestablish on the North Anna downstream from its confluence with Contrary Creek before the impoundment’s construction (Simmions and Reed, 1973; Lees, 2005). The complete absence of unionidae in the North Anna River downstream from its confluence with Contrary Creek before impoundment construction, despite the presence of insect and fin fish species, suggested that freshwater mussels are more sensitive indicators of environmental conditions and habitat suitability (Simmions and Reed, 1973; Lees, 2005).

Freshwater mussels are easily impacted by several anthropogenic land-use changes, including: (1) water acidification and habitat destruction from mining, (2) erosion and sedimentation, (3) impoundments cutting off fish species critical for mussel-larval life stages and distribution, and (4) impervious surface and agricultural runoff increasing to sedimentation and nutrient loading (Lees, 2005). Lees’ 2005 study of unionidae richness in the Pamunkey River watershed incorporated geographic information system data to assess land-use impacts on mussel distribution, and sampling the same locations, compared his results with the number of species found in a study by Riddick (1973). Compared with the 10 mussel species identified by Riddick in 1973 at Pamunkey River survey sites, only 4 species remained at the Pamunkey River survey sites in 2005 (Lees, 2005). Low abundance and species richness of unionidae in the Pamunkey River seem associated with agriculture and cropland, high abundance of silt, and lack of pebble/cobble substrate (Lees, 2005). Freshwater mussels seem to be recolonizing the area downstream from the Lake Anna impoundment, apparently confirming predictions by previous studies that the reservoir acts as a buffer of sediments and pollutants and helps improve downstream habitat quality (Simmions and Reed, 1973; Lees, 2005). The lower Pamunkey River was reported to be devoid of unionidae, possibly because of salinity fluctuations (Lees, 2005). Although mussels are repopulating some areas of the Pamunkey and York rivers, there exists an overall loss of diversity. Increased levels of sedimentation in the Pamunkey River, largely attributed to agricultural land use and associated nutrient loading, will continue to create conditions challenging for mussel recovery (Langland and others, 2006; Raey, 2009). Tribal members interviewed recalled seeing mussel shells on the eastern bank of the Pamunkey Indian Reservation and better water quality around the reservation during their youths, but not anymore. This anecdotal evidence supports recent studies that describe the loss of unionidae in the York River watershed because of increased sedimentation and decreased water quality (J. Krigsvold, Pamunkey Indian Tribe, Elder, oral commun., 2022; K. Moore, Pamunkey Indian Tribe, Elder, oral commun., 2022).

Land-use changes throughout the Pamunkey River watershed that are sources of erosion, runoff, and sedimentation, such as agriculture and other development, are likely contributing to the negative effects observed in its watershed ecology and habitat. These effects could be further compounded with the loss of freshwater mussel diversity, not only because of the importance unionidae play in Tribal culture and food sovereignty, but also because of the role unionidae have in maintaining water quality and ecological integrity and the lower habitat quality that their absence will bring.

Surface Water

Surface-Water Quality

Groundwater

Land Subsidence and Sea-Level Rise

River Ecology