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 22% of the summer average, lakewide internal total P load to the reservoir.