The role of zooplankton in the intrabiocoenotic phosphorus cycle and factors affecting phosphorus excretion in a lake

The temporal and spatial excretion rates of specific size groups of limnetic zooplankton were studied by measuring changes in soluble reactive phosphorus following incubation. Animals were collected in the epilimnion and hypolimnion of Stonehouse Pond, New Hampshire from August, 1972 to July, 1973 and separated into > 0.308 and < 0.308 (mm) size groups. Temporal excretion rates varied considerably within groups, however, similar patterns were observed in both strata. Peak excretion rates were observed in the spring and fall with a low in winter months. In addition, smaller animals excreted at higher rates and excretion rates of both size groups in the epilimnion exceeded those in the hypolimnion.The phosphorus uptake of natural seston relative to the amount released by zooplankton is considered using mass balance equations and kinetic analyses. During the spring of 1973 excretion rates increased, however, this increase was offset by an even greater rise in the rate of phosphorus uptake by the seston. This suggests that during this period the phosphorus excretions of zooplankton were not sufficient to meet the amount of phosphorus being removed by the seston.The experimental work was based on a thesis submitted to the Graduate School of the University of New Hampshire in partial fulfillment of the requirements for the degree of Doctor of Philosophy.