Entrainment‐Based Flux of Phosphorus in Onondaga Lake

Abstract

The upward transport of phosphorus from the upper stratified layers of hypereutrophic Onondaga Lake, mediated by entrainment events, was estimated for the spring-to-fall intervals of 1980 and 1981. The estimates were based on analysis of successive profiles (l-m depth intervals) of dissolved reactive phosphorus, collected on 53 and 36 occasions in 1980 and 1981, respectively. Despite differences in the short-term distributions of the entrainment events between the two years, similar seasonal distributions and magnitudes of transport were observed for the spring-to-late-summer interval of each year. Minimum entrainment occurred during the maximum stability period of late summer. The amount of phosphorus recycled to the upper productive layer of the lake by entrainment in the spring-to-fall interval of 1980 was about 12% of that received from external loadings during the same period. During May and June of 1980 this internal loading component was approximately 30% of the external load. Onondaga Lake is unusually susceptible to this form of internal cycling because of its propensity to develop secondary stratification.