ESTIMATION OF PHOSPHORUS EXCHANGE BETWEEN LITTORAL AND PELAGIC ZONES DURING NIGHTTIME CONVECTIVE CIRCULATION

A fluorescent dye was used in Eau Galle Reservoir, Wisconsin, to examine nighttime convective circulation patterns and exchanges of P between the littoral and pelagic zones during 25-26 July and 12-13 September 1988. Cooler littoral bottom water moved into the pelagic zone at night as an interflow at 2.5 m in July and at 4.0 m in September. Warmer pelagic water moved into the littoral zone as a surface flow during both periods. The littoral zone exhibited high total P concentrations above the sediment in July, but much lower concentrations in September. Estimated net areal total P flux to the pelagic zone was 1.8 mg m-2 d-1 in July but only 0.2 mg m-2 d-1 in September. Net areal total P flux in July accounted for approximately 22% of the summer average, lakewide internal total P load to the reservoir.