Nutrient and Chlorophyll Relations in Selected Streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001
Median concentrations of total nitrogen and total phosphorus exceeded the preliminary recommended criteria set by the USEPA for subecoregion 59 at 11 of the 13 sites. Periphyton chlorophyll a data from the six open-canopy sites were selected to determine the association between total nitrogen and total phosphorus concentrations and chlorophyll a concentrations because these sites represented areas of greatest nutrient and algal concentrations.
Summary statistics for nutrients are listed in table 2. Selected percentile statistics for total nitrogen and total phosphorus are summarized in table 3 . The two reference sites were the only streams with median nutrient concentrations less than the USEPA preliminary recommendations for total nitrogen and total phosphorus (figs. 2 and 3). Median total nitrogen and total phosphorus concentrations were significantly different (p < 0.05) among all three site types (figs. 2 and 3). Among the streams sampled, concentrations of total nitrogen and total phosphorus were highest at the Matfield and Assabet Rivers. It is well documented that point sources are the major impact to the Assabet River especially during the summer low flow (ENSR International, 2000). In addition, a wastewater-treatment plant upstream of the Matfield River site may be the primary source of nutrient loading to this water body. Nutrient concentrations were also high at the Aberjona River, which may be a result of the heavily urbanized drainage basin. Eleven of the sites were nitrogen and phosphorus limited and two sites were only phosphorus limited based on ratios of dissolved nutrient concentrations.
To print out table 2, please use this pdf (243KB).
| Table 2.
Summary of selected nutrient and chlorophyll a concentrations (open-
and closed-canopy sites) for the study site types in the New England Coastal
Basins study area in Massachusetts and New Hampshire
[Sites sampled five times between June 1 and September 30, 2001; mg/L, milligrams per liter; Min, minimum; Max, maximum; µg/L, micrograms per liter; mg/m2, milligrams per square meter; g/m2, grams per square meter; <,less than] |
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| Site type | Total nitrogen (dissolved nitrite + nitrate + total ammonia + organic nitrogen) (mg/L) | Dissolved inorganic nitrogen (dissolved nitrite + nitrate + dissolved ammonia) (mg/L) | Total phosphorus (phosphorus in an unfiltered water sample) (mg/L) | Dissolved phosphorus (mg/L) | Dissolved ammonia (mg/L) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | Median | Max | Min | Median | Max | Min | Median | Max | Min | Median | Max | Min | Median | Max | |
| Reference | 0.32 | 0.44 | 0.54 | 0.07 | 0.13 | 0.22 | 0.006 | 0.019 | 0.043 | ‹0.006 | 0.009 | 0.013 | ‹0.041 | ‹0.041 | ‹0.041 |
| Moderately impaired | .49 | .78 | 2.2 | .12 | .26 | 1.5 | .016 | .039 | .072 | .009 | .017 | .041 | ‹.041 | ‹.041 | .074 |
| Impaired | .64 | 2.2 | 10 | .08 | 1.5 | 9.2 | .024 | .055 | .905 | ‹.006 | .025 | .899 | ‹.041 | ‹.041 | 2.5 |
| Site type | Dissolved nitrite + nitrate (mg/L) | Dissolved nitrite (mg/L) | Orthophosphate (mg/L) | Nitrogen ammonia + organic total (mg/L) | Nitrogen ammonia + organic dissolved (mg/L) |
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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | Median | Max | Min | Median | Max | Min | Median | Max | Min | Median | Max | Min | Median | Max | |
| Reference | ‹0.047 | 0.090 | 0.202 | ‹0.006 | ‹0.006 | ‹0.006 | ‹0.020 | ‹0.020 | ‹0.020 | 0.23 | 0.34 | 0.41 | 0.11 | 0.27 | 0.33 |
| Moderately impaired | .086 | .231 | 1.4 | ‹.006 | ‹.006 | .056 | ‹.020 | ‹.020 | ‹.020 | .28 | .49 | 2.0 | .23 | .36 | 1.1 |
| Impaired | 0.55 | .921 | 6.7 | ‹.006 | .014 | .436 | ‹.020 | ‹.020 | .812 | .35 | .66 | 3.8 | .31 | .58 | 3.7 |
| Site type | Chlorophyll a from phytoplankton (µg/L) |
Chlorophyll a from periphyton (mg/m2) |
Ash-free dry mass (g/m2) |
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|---|---|---|---|---|---|---|---|---|---|
| Min | Median | Max | Min | Median | Max | Min | Median | Max | |
| Reference | 0.40 | 1.3 | 5.5 | 1.4 | 5.4 | 22 | 1.6 | 6.4 | 17 |
| Moderately impaired |
0.30 | 1.2 | 16 | .50 | 5.2 | 59 | 2.7 | 8.4 | 39 |
| Impaired | .30 | 1.4 | 22 | .30 | 17 | 166 | 2.4 | 15 | 70 |
To print out table 3, please use this pdf (257KB).
| Table 3. Percentile
statistics of total nitrogen, total phosphorus, and periphyton chlorophyll
a concentrations for the study sites in the New England Coastal
Basins study area in Massachusetts and New Hampshire [n, number of samples; mg/L, milligrams per liter; mg/m2, milligrams per square meter] |
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| Minimum | 25th percentile | 50th percentile | 75th percentile | Maximum | a | |
|---|---|---|---|---|---|---|
| Total nitrogen (mg/L) | 0.32 | 0.64 | 0.90 | 2.1 | 10 | 65 |
| Total phosphorus (mg/L) | .006 | .030 | .044 | .065 | .905 | 65 |
| Periphyton chlorophyll a1 (mg/m2) | 2.2 | 5.2 | 17 | 41 | 166 | 30 |
| Periphyton chlorophyll a2 (mg/m2) | .30 | 3.3 | 6.0 | 15 | 52 | 65 |
| 1 Open-canopy sites. 2 Closed-canopy sites. |
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| Figure 2. Total nitrogen concentrations among site types in New England Coastal Basins study area. [Result of Tukey's multiple-comparison test [Helsel and Hirsch, 1992] among groups are presented as letters, and concentrations with at least one letter in comon do not differ significantly; for example, concentrations among all three groups differ significantly. |
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| Figure 3. Graph showing Total phosphorus concentrations among site types in the New England Coastal Basins study area. (Results of Tukey's multiple-comparison test [Helsel and Hirsch, 1992] among groups are presented as letters, and concentrations with at least one letter in common do not differ significantly; for example, concentrations among all three groups differ significantly.) |
Summary statistics for chlorophyll a from phytoplankton and periphyton samples and ash-free-dry mass are listed in table 2 . Selected percentile statistics for periphyton chlorophyll a are summarized in table 3. Chlorophyll a concentrations were higher at the open-canopy sites than the closed-canopy sites (table 3). There were no significant relations between chlorophyll a in phytoplankton and total nitrogen and total phosphorus. However, chlorophyll a concentrations from periphyton samples increased significantly with total nitrogen and total phosphorus concentrations at the open- and closed-canopy sites. Correlation coefficients were higher at the open-canopy sites (rho = 0.64 to 0.71) than at the closed-canopy sites (rho = 0.36 to 0.40). This indicates that light affected the algal biomass and the relation between nutrient and chlorophyll a concentrations. There was no significant temporal variation in phytoplankton or periphyton samples collected throughout the sampling period.
Median concentrations of periphyton chlorophyll a were highest at nutrient-impaired sites (table 2). There were significant differences (p < 0.05) in median periphyton chlorophyll a concentrations among all three site types for open-canopy sampling sites (fig. 4). There were significant differences between reference and impaired sites and between moderately impaired and impaired sites at the closed-canopy sampling locations, but not between reference and moderately impaired sites (fig. 5). Concentrations of chlorophyll a from periphyton were significantly higher (p < 0.05) at open-canopy sites than at closed-canopy sites. Chlorophyll a concentrations from phytoplankton were not significantly different among site designations. This suggests that periphyton may be a better indicator of eutrophication than phytoplankton in wadeable NECB streams, regardless of canopy conditions.
Comparison of periphyton chlorophyll a concentrations from the six sampling sites that had open- and closed-canopies indicated that open-canopy sites had higher concentrations of chlorophyll a among all three site types (fig. 6). Periphyton chlorophyll a concentrations from samples collected at closed-canopy reference and moderately impaired sites were less than the median literature value for moderately enriched streams (21 mg/m2) (Biggs, 1996). Chlorophyll a concentrations from most samples collected at closed-canopy impaired sites had concentrations greater than the median literature value for moderately enriched streams. Chlorophyll a concentrations from samples collected at open-canopy sites had higher ranges of chlorophyll a concentrations than those at closed-canopy sites for all three site types. Generally, most of the chlorophyll a concentrations from open-canopy reference and moderately impaired sites had concentrations less than the median literature value for moderately enriched streams (fig. 6). Chlorophyll a concentrations from open-canopy impaired sites, however, were generally between the median literature value for moderately enriched and enriched streams (fig. 6). Nutrient concentrations, types of substrate, and stream velocities were similar between the closed- and open-canopy sampling locations at the same site, indicating that light is affecting algal biomass as measured by chlorophyll a.
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| Figure 4. Graph showing Chlorophyll a from periphyton samples among site types at the open-canopy locations in the New England Coastal Basins study area. (Results of Tukey's multiple-comparison test [Helsel and Hirsch, 1992] among sites are presented as letters, and concentrations with at least one letter in common do not differ significantly; for example, concentrations among all three groups differ significantly.) |
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| Figure 5. Graph showing Chlorophyll a from periphyton samples among site types at the closed-canopy locations in the New England Coastal Basins study area. (Results of Tukey's multiple-comparison test [Helsel and Hirsch, 1992] among sites are presented as letters, and concentrations with at least one letter in common do not differ significantly; for example, concentrations between the reference and moderately impaired sites do not differ significantly.) |
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| Figure 6. Graph showing Chlorophyll a from periphyton samples among site types at the six sites with open- and closed-canopy sampling locations in the New England Coastal Basins study area. |
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