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MAPPING OF NITRATE AND PHOSPHORUS IN A NORTHEAST IOWA WETLAND
The Beaver Valley Wetland is located in Northwest Cedar
Falls. The wetland is a small,
shallow water system that is primarily fed by the surrounding watershed.
Our objective was to collect data from the wetland and West Lake in order
to observe any trends, if present. The
parameters observed consisted of: Cl-, NO3-, SO42- (concentrations measured by
Dionex Dx-100 Ion Chromatograph and Dionex 4270 Integrator), Total P
concentrations (persulfate digestion method followed by ascorbic colorometric
method from Standard Methods) for shallow and deep water samples, pH, Dissolved
Oxygen, Conductivity, and Total Dissolved Solids (measured by field
instruments). The wetland was
observed buffering: pH, Conductivity (Microsiemens/cm), Total Dissolved Solids
(mg/L), Nitrate (mg/L), Chloride (mg/L), and Sulfate (mg/L) in shallow and deep
water. Each of these parameter
fluctuations were less than 0.5. Total P concentrations differ both spatially and temporally
in June and July. This could be due in part to the wetland’s buffering
capacity, the phosphorus cycle in relation to increased pH (as pH increases
PO43- is released from the sediment), and the dilution of P in rainwater.
Stratification was not expected to occur due to the shallow water depth
of the wetland; however, total P concentrations differed for shallow and deep
water samples in both June and July. In
June, there is a 70.6 µg/L difference for shallow and deep Total P averages.
Shallow water P analysis have a range of 645-939 µg/L in comparison to
deep water P analysis range of 735-1200 µg/L . Spatially, Total P at depth in
June, shows a decreasing concentration trend from the inflow to the outflow.
Temporally, shallow water P samples increased 368 µg/L from June to
July. Similarly, deep water P
samples increased 265 µg/L. Shallow
water P sample in July ranged from 931 to 1380 µg/L.
Deep water P samples ranged from 853 to 1347 µg/L .
Spatially, both shallow and deep water samples showed an increasing trend
in Total P concentration. This is
primarily due to July’s higher amount of rainfall to wash Phosphorus into the
lake from surface runoff and the increased pH and its relationship to the
phosphorus cycle. Concentrations of
P in sediment show a increasing trend from inflow to outflow as well.
The mass calculation resulted in 32,300 kg of P present in the lake
sediment. The water volume was
calculated to be 7.2 x 104 m3 .
The Total P in the water is 61.21 kg for June, and 85.38 kg for July.
Nitrate in water for June was calculated to be 303.51 kg, and in July the
Nitrate was too dilute to be measured by the Ion Chromatograph. This
research was supported by the Roy J. Carver Charitable Trust and the Iowa Space
Grant Consortium. |
