RAPID ECOLOGICAL CHANGES IN A LARGE SUBTROPICAL LAKE UNDERGOING CULTURAL EUTROPHICATION

This paper describes how human activities have impacted the ecological state of a large subtropical lake, Lake Okeechobee, Florida, USA. Sin ce the early 1900s, the lake has experienced alterations of its hydrol ogy and morphology, and recently there has been an accelerated eutroph ication. Total phosphorus concentrations have doubled, nitrogen: phosp horus ratios have declined by 50%; and lake sediments have accumulated a massive quantity of phosphorus. The biotic community has undergone changes that appear to be due to eutrophication: oilgochaetes have bec ome the dominant macrobenthos; cyanobacteria have replaced diatoms as the dominant phytoplankton; nitrogen limitation has increased in frequ ency, and nitrogen-fixation has become a major route of nitrogen input . There is evidence that the lake has reached a new ecological steady state, buffered against change by nutrient loading from the sediments. Shallow depth and wind-driven sediment resuspension contribute to thi s situation.