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Scientific Investigations Report 2004-5171

Hydrology and Cycling of Nitrogen and Phosphorus in Little Bean Marsh: A Remnant Riparian Wetland along the Missouri River in Platte County, Missouri, 1996—1997

By: Dale W. Blevins, U.S. Geological Survey, in cooperation with the Missouri Department of Conservation


The lack of concurrent water-quality and hydrologic data on riparian wetlands in the Midwestern United States has resulted in a lack of knowledge about the water-quality functions that these wetlands provide. Therefore, Little Bean Marsh, a remnant riparian wetland along the Missouri River, was investigated in 1996 and 1997 primarily to determine the magnitude and character of selected water-quality benefits that can be produced in such a wetland and to identify critical processes that can be managed in remnant or restored riparian wetlands for amelioration of water quality.

Little Bean Marsh averages 69 hectares in size, has a maximum depth of about 1 meter, and the majority of the marsh is covered by macrophytes. In 1997, 41 percent of the water received by Little Bean Marsh was from direct precipitation, 14 percent was from ground-water seepage, 30 percent from watershed runoff, and 15 percent was backflow from Bean Lake. Although, Little Bean Marsh was both a ground-water recharge and discharge area, discharge to the marsh was three times the recharge to ground water. Ground-water levels closely tracked marsh water levels indicating a strong hydraulic connection between ground water and the marsh. Reduced surface runoff and ground-water availability are stabilizing influences on marsh hydrology and probably contribute to the persistence of emergent vegetation. The rapid hydraulic connection between Little Bean Marsh and ground water indicates that the hydrologic regime of most wetlands along the lower Missouri River is largely a function of the altitude of the marsh bottom relative to the altitude of the water table.

More water was lost from the marsh through evapotranspiration (59 percent) than all other pathways combined. This is partially because the transpiration process of abundant macrophytes can greatly contribute to the evapotranspiration above that lost from open water surfaces. Surface outflow accounted for 36 percent and ground-water seepage accounted for only 5 percent of the losses. Large residence times allows the marsh to greatly affect water quality before water escapes as ground-water recharge or surface outflow.

The shallowness of Little Bean Marsh and ion exclusion during ice formation caused the highest specific conductances of 1,100 to 1,300 microsiemens per centimeter at 25 degrees Celsius to occur during the winter. This concentration of dissolved solutes under ice can make wetlands more vulnerable to toxic contaminants than deeper surface-water bodies.

Dissolved oxygen was less than 5 mg/L (milligrams per liter) for 3 to 4 months and near 0 mg/L for about 1 month in summer. Despite depths of less than 1 meter, temperature stratification persisted more than 3 months during the summers of 1996 and 1997, preventing mixing and contributing to periods of anoxia. Shallow depths and extended periods of anoxia in the marsh limit the ability of some organisms to escape high-temperature stress.

Turbidity in Little Bean Marsh usually was low for several reasons: sediment loadings from the largely flood-plain drainage were low, emergent vegetation shade out algae and shield the water from wind, and high concentrations of bivalent cations increase flocculation rates of inorganic suspended material. The high concentrations of bivalent cations was largely because of a substantial amount of ground-water seepage into the marsh.

Dissolved organic nitrogen was the dominant nitrogen species in Little Bean Marsh. Denitrification and biotic uptake kept more than 62 percent of nitrate (NO3) and 43 percent of ammonium (NH4) concentrations in marsh samples less than a detection limit of 0.005 mg/L. This contrasts with the Missouri River where inorganic NO3 dominates. Consequently, artificial flood-plain drainage that bypasses riparian wetlands likely deliver substantially more biotically available inorganic nitrogen to receiving waters than surface water that has been routed through a remnant wetland. Average total nitrogen concentrations in Little Bean Marsh were substantially less than those at other Missouri River wetlands, roughly one-half the mean concentrations in the Missouri River, but roughly twice the average nitrogen values in reservoirs of the glaciated plains of Missouri.

The largest concentrations of nearly all species of nitrogen and phosphorus and the most intense period of hypereutrophy coincided with a phytoplankton bloom and senescence of River Bulrush (Scirpus fluviatilis) and common cattail (Typha latifolia) in September 1997. The rapid leaching of nitrogen that occurs soon after macrophyte senescence combined with a recent destratification of the marsh probably provided nitrogen to the nitrogen-limited open-water areas and triggered a phytoplankton bloom. Despite the rarity of runoff events, surface runoff from the watershed, combined with atmospheric deposition, contributed more than seven times the 530 kg (kilograms) of nitrogen that escaped Little Bean Marsh in surface outflow during 1997. Atmospheric deposition alone was more than 530 kg. Seepage to ground water contained less than 1.5 percent of the nitrogen leaving the marsh in surface outflow. The slow decay rate of Scirpus fluviatilis and reducing conditions in bottom sediments make burial of organic nitrogen a substantial sink of nitrogen.

Denitrification experiments indicate that denitrification rates were limited by NO3 in the water column. Consequently, decomposition and nitrification of NH4 and organic nitrogen are the rate limiting steps of nitrogen removal in Little Bean Marsh. The NO3-limited rates of denitrification also indicate that Little Bean Marsh has a large unused capacity for nitrogen removal. These data indicate that the vast extent of riparian marshes along the Missouri and Mississippi Rivers may have had a substantial role in limiting NO3 loads to the Gulf of Mexico before agricultural development of flood plains. Drainage and removal of riparian marshes may be a major cause of the increased NO3 loads to the Gulf of Mexico.

Periods of anoxia had much larger effects on phosphorus release than the other variables. The largest concentrations of phosphorus occurred in late summer and corresponded with senescing macrophytes, periods of anoxia, and a large algal bloom in Little Bean Marsh. Low water levels prevented the escape of phosphorus in surface outflow during these periods of highest phosphorus concentrations. Dry weather in late summer is typical and probably makes the correspondence of low water levels, anoxia, and consequent low phosphorus release a common occurrence in marshes along the Missouri River. Little Bean Marsh retained more than 95 percent of the phosphorus it received. The amount of phosphorus in surface inflows to the marsh were more than one order of magnitude greater than that escaping in surface outflows. The long hydraulic residence time of the marsh and large contributions of iron from ground water (that provide many sorption sites for phosphorus) make the marsh an effective sediment and phosphorus trap.



Background and Problem

Purpose and Scope

Study Area Description

Methods and Materials


Hydrologic Inputs

Ground-Water Interactions

Hydrologic Outputs

Water Chemistry

Specific Conductance

Dissolved Oxygen





Turbidity and Total Suspended Solids

Dissolved Organic Carbon

Trophic Indicators

Nitrogen Cycling and Denitrification

Sinks and Sources of Nitrogen

Atmospheric Contributions

Contributions from Storm Runoff

Ground-Water Contributions


Phosphorus Cycling


Sinks and Sources of Phosphorus

Comparisons with the Missouri River, nearby Wetlands, and Missouri Reservoirs

Summary and Conclusions



  1. Map showing location of Little Bean Marsh and monitoring sites
  2. Graph showing mean monthly air temperatures in 1997 compared to 30-year means recorded at the Kansas City International Airport
  3. Graph showing monthly precipitation measured at Little Bean Marsh in 1997 compared to 30-year means recorded at the Kansas City International Airport
  4. Maps showing historical evolution of Little Bean Marsh
  5. Map showing bathymetry of Little Bean Marsh
  6. Photograph showing denitrification chambers in Little Bean Marsh
  7. Charts showing inflow and outflow water budgets for Little Bean Marsh during 1997
  8. Graph showing specific conductance, marsh water level, mean ground-water level, precipitation, and days with mean air temperatures below 0 degrees Celsius at Little Bean Marsh
  9. Maps showing altitude of potentiometric surface near Little Bean Marsh during (A) low water-table conditions on February 17, 1997, and (B) high water-table conditions on October 24, 1996
  10. Graph showing Missouri River stage, marsh water level, mean ground-water level, and precipitation at Little Bean Marsh
  11. Boxplots of constituent concentrations in samples collected from Little Bean Marsh in 1997
  12. Graph showing daily maximum and minimum dissolved-oxygen concentrations at site M3 in Little Bean Marsh
  13. Graph showing dissolved-oxygen concentrations at site M3 in Little Bean Marsh during March 1997
  14. Graph showing water temperatures near the top and bottom of Little Bean Marsh at site M3 and average daily wind speed at the Kansas City International Airport
  15. Graph showing daily mean air and water temperatures at site M3 in Little Bean Marsh
  16. Graphs showing hourly water temperatures 0.5 meter below water surface at site M3 in Little Bean Marsh during 1996 and 1997
  17. Graph showing median daily fluctuations of pH at site M3 in Little Bean Marsh, 1996–1997
  18. Graph showing hourly fluctuations of pH at site M3 in Little Bean Marsh during May 1997
  19. Graphs showing total nitrogen and dissolved ammonium nitrogen concentrations with time at Little Bean Marsh
  20. Graphs showing chlorophyll a and nitrite plus nitrate concentrations with time in Little Bean Marsh
  21. Graphs showing total phosphorus and soluble reactive phosphorus concentrations with time at Little Bean Marsh
  22. Graph showing ratios of particulate nitrogen to particulate phosphorus with time at Little Bean Marsh
  23. Graphs showing logarithmic plots of geometric means of chlorophyll a concentrations with (A) total phosphorus concentrations and with (B) total nitrogen concentrations for scour and oxbow lakes along the Missouri River and Little Bean Marsh
  24. Diagram showing conceptual compartments and dominant processes involving nitrogen in Little Bean Marsh
  25. Graphs showing Eh in bottom sediment in relation to depth at six sites in Little Bean Marsh, 1997 and 1998
  26. Graph showing concentrations of nitrous oxide in denitrification chambers after 48 hours showing differences between chambers with ambient concentrations of nitrate and those spiked with nitrate
  27. Graph showing denitrification rates in relation to temperature in denitrification chambers spiked with nitrate in Little Bean Marsh
  28. Graph showing denitrification rate in relation to dissolved-oxygen concentration in denitrification chambers spiked with nitrate in Little Bean Marsh on July 28, 1997
  29. Diagram showing conceptual compartments and dominant processes involving phosphorus in Little Bean Marsh


  1. Specific conductance and concentrations of selected nutrients in ground-water samples collected from monitoring wells near Little Bean Marsh
  2. Sample analyses and storm loads of surface inflow to Little Bean Marsh
  3. Analyses of surface-water samples collected from Little Bean Marsh
  4. Means and ranges of selected constituent concentrations and properties of water samples collected from the Missouri River, Little Bean Marsh, and other wetlands along large rivers of the Midwestern United States
  5. Concentrations of selected ions in water samples collected from Little Bean Marsh
  6. Correlation coefficients (r), coefficients of determination (r2), and levels of significance (p) for the relation between chlorophyll concentrations and concentrations of total nitrogen, total phosphorus, and total suspended solids in Little Bean Marsh
  7. Classification of the trophic state of Missouri reservoirs used by Jones and Knowlton (1993); May–September means of total phosphorus, total nitrogen, chlorophyll a, and total suspended solids for Missouri reservoirs by physiographic region (Jones and Knowlton, 1993); means of monthly samples of four oxbows along the Missouri River (Knowlton and Jones, 1997) from 1994–1996; and 1997 annual means for Little Bean Marsh
  8. Loads of selected constituents in surface outflows from Little Bean Marsh
  9. Concentrations of selected nutrients with depth in bottom sediment cores collected from Little Bean Marsh in 1997
  10. Amounts of denitrified nitrogen generated in in-situ experiments
  11. Spearman’s rho values and levels of significance (p) for correlation of phosphorus with mean daily dissolved oxygen at five sites in Little Bean Marsh
  12. Spearman’s rho values and levels of significance (p) for correlation of phosphorus with chlorophyll concentrations at five sites in Little Bean Marsh


Conversion Factors and Datum
Multiply    By    To obtain
centimeter (cm)   0.3937   inch (in.)
meter (m)   3.281   foot (ft)
kilometer (km)   0.6214   mile (mi)
hectare (ha)   2.471   acre
hectare (ha)   0.003861   square mile (mi2)
cubic meter (m3)   264.2   gallon (gal)
Flow rate cubic meter per day (m3/d)   35.31   cubic foot per day (ft3/d)
cubic meter per day (m3/d)   264.2   gallon per day (gal/d)
kilometer per hour (km/h)   0.6214   mile per hour (mi/hr)
gram (g)   0.03527   ounce, avoirdupois (oz)
kilogram (kg)   2.205   pound avoirdupois (lb)
gram per cubic centimeter (g/cm3)   62.4220   pound per cubic foot (lb/ft3)
    Hydraulic conductivity    
meter per day (m/d)   3.281   foot per day (ft/d)
    Hydraulic gradient    
meter per kilometer (m/km)   5.27983   foot per mile (ft/mi)
    Application rate    
kilograms per hectare per year [(kg/ha)/yr]   0.8921   pounds per acre per year [(lb/acre)/yr]

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F = (1.8 x °C) + 32

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Altitude, as used in this report, refers to distance above the National Geodetic Vertical Datum of 1929 (NGVD 29).

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or micrograms per liter (µg/L).

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For more information about USGS activities in Missouri contact:


U.S. Geological Survey

Missouri Water Science Center

1400 Independence Road

Rolla, Missouri 65401

Telephone: (573) 308-3667

Fax: (573) 308-3645

or access the USGS Missouri Water Science Center home page at:

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Last modified: Thursday, January 10 2013, 06:39:45 PM
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