Phosphorus in Lake Okeechobee has increased from less than 40 ppb in 1968 to over 100 ppb today. 30, 000 tons of phosphorus settled at the bottom of Lake Okeechobee, turning the sandy bottom of the lake into mud and muck. In the 1980s, phosphorus caused algal blooms which covered more than 40% of Lake Okeechobee. In the 1980s, algal blooms occurred 8 months out of the year; in the 1990s, algal blooms occurred 12 months out of the year. Algal blooms occur with high phosphorus and high light penetration. Algal blooms cause macroinvertebrates to die due to anoxia (lack of dissolved oxygen) and toxic ammonia. 
Algal bloom in Lake Okeechobee (picture from sfwmd.gov) Phosphorus makes cattail and some exotic plants to grow. Over 20, 000 acres of native plants in Lake O's littoral zone have been lost to exotic species which like the increased nutrient levels. Phosphorus prevents submerged plants from getting enough light, often killing the submerged plants. Phosphorus loading rates to Lake Okeechobee have averaged approximately 570 metric tons/year with an average outflow of 150 metric tons/year and an accumulation of 420 metric tons/year into lake sediments. The current goal for phosphorus in Lake Okeechobee is 40 ppb. To achieve this, load into lake must be less than 400 metric tons/year. The major source of phosphorus to the watershed is feed, fertilizer, and detergents to support agriculture (98% in 1992). 8% of this phosphorus reaches Lake Okeechobee. Changing the water level of the lake affects the phosphorus levels because when the lake is too high and flooding occurs, littoral vegetation does not receive enough light and dies. This allows phosphorus to remain in the water column or accumulate in lake sediments. |
