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.