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Title: Effects of convective hydraulic circulation on phosphorus transport in aquatic macrophyte beds
Authors: Aquatic Plant Control Research Program (U.S.)
James, William F.
Barko, John W.
Keywords: Convection
Littoral zone
Biogeochemical cycles
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: Phosphorus (P) dynamics in aquatic macrophyte beds and P exchanges between littoral and pelagic zones, driven by nighttime convective circulation, were examined in Eau Galle Reservoir, Wisconsin, during summer 1989. Rates of P release from littoral sediments, measured in laboratory incubation systems, increased in a linear fashion with pH under both aerobic and anaerobic conditions. Estimated rates of P release from littoral zone sediments, based on field measurements of pH and oxygen, averaged 3.6 mg m⁻² day⁻¹ under aerobic conditions, and were in close agreement with independently determined diffusional fluxes across the littoral sediment interface. Marked vertical gradients in P developed during the summer in bottom waters of the littoral zone. The littoral zone, dominated by submersed macrophytes, cooled more rapidly at night than the pelagic zone on 72 percent of midsummer days (June-August), promoting nighttime convective circulation. Based on patterns of dye dispersion during these periods of circulation, cooler littoral bottom water originating within macrophyte beds moved into the pelagic zone as an interflow confined to the base of the epilimnion, while warmer pelagic water moved into the littoral zone as a surface flow. Hourly volumetric flow rates were linearly related to mean negative horizontal temperature gradients that developed during the night. Net TP flux from the littoral to the pelagic zone ranged from 0.12 to 0.43 mg m⁻² hr⁻¹ and averaged 0.22 mg m⁻² hr⁻¹ for the summer. Nighttime convective circulation appears to be an important mechanism for movement of littoral P from macrophyte beds to the pelagic zone in this reservoir.
Appears in Collections:Technical Report

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