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TA6 Applications of Ecotoxicology to Real World Problems
(212) Periphyton response to total nutrient depletion and shifting N:P ratio in a constructed freshwater wetland.
Scott, J1, Doyle, R1, Conry, T2, 1 Baylor University, Waco, Texas, USA2 City of Waco, Waco, Texas, USA
ABSTRACT- Nutrient removal from water flowing through freshwater wetlands often results in longitudinal gradients along the flow path of water. While both N and P concentrations commonly decline, there may also be a shift in N:P ratios along the gradient if specific N and P removal rates are unequal. Decreasing N:P ratio, a result of higher N removal, may subsequently shift periphyton assemblage structure by favoring organisms adapted to better compete for alternate nitrogen sources (i.e. cyanobacterial nitrogen fixers). Since periphyton assemblages play a major role in food web dynamics in freshwater systems, shifting periphyton assemblage structure could adversely impact ecosystem functions. The aims of this ongoing study are to 1) evaluate water column nutrient removal rates in a newly constructed freshwater marsh, 2) determine nutrient limitation status of periphyton along longitudinal nutrient gradients that developed along the flow path of water, and 3) examine changes in periphyton nitrogen fixation rates along the observed gradient. In situ bioassays using nutrient enrichment periphytometers are being employed to test nutrient limitation status. Further, periphyton nitrogen fixation rates are being assessed using the acetylene reduction method on periphyton growing on artificial substrates. Initial results indicate that N removal along the nutrient depletion gradient was substantially greater than P removal, resulting in a decreased N:P ratio. Subsequently, nutrient limitation status revealed a shift from P limitation of periphyton at the wetland inflow, to N limitation at greater distances along the nutrient depletion gradient. Spatial and temporal changes in nutrient removal rates, periphyton nutrient limitation status, and periphyton nitrogen fixation rates will be presented.
Key words: nutrients, wetland, periphyton, nitrogen fixation
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