Element Accumulation and Release by Macrophytes in a Wetland Stream

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Abstract
Aquatic macrophyte growth and element accumulation was measured seasonally for 1 yr in Oak Orchard Creek, NY, and compared with stream element loads. The stream flows from drained and cultivated wetland soils upstream into undisturbed wetlands downstream. The stream was calcareous and near saturation with CO2 most of the time. It was enriched with dissolved N, P, and K in both water and sediments, especially just below the cultivated area.Plant biomass was greatest at the lower end of the wetlands in July, ranging up to about 600 g dry wt m−2 and consisting mostly of elodea (Elodea canadensis Michx.) and curlyleaf pondweed (Potamogeton crispus L.). Maximum net biomass accumulation rate was about 0.06 mg C m−2 s−1 for sago pondweed (Potamogeton pectinatis L.).Element concentrations in plant tissues were above limiting levels and showed no definite relationship to season or species, although instream emergent plants showed a fall decrease in major nutrients (N, P, and K). Tissue nutrient concentrations were related to position in the stream, increasing as the nutrient concentrations increased in the water.Maximum nutrient load contained by the plants occurred in July, which corresponded to the maximum standing crop. Potential contributions of major nutrients to the creek from plant senescence that occurred instream ranged from 10 to 100% in summer and fall. However, this contribution is 1 to 2% of total annual stream nutrient load.