Isolation as a restoration strategy for nutrient reduction in a small hypereutrophic lake

Abstract

The restoration of a small hypereutrophic urban lake in Baton Rouge, Louisiana was accomplished by isolating the lake from its primary source of nutrient loading: a larger, connecting lake that was heavily contaminated by sewage. Restoration objectives were directed towards reducing phosphorus levels in the system to minimize chronic summer fish kills. Previous studies had identified a critical phosphorus level of 0.4 mg l −1, below which no fish kills had been observed in this system. Above this level the kill frequency was a uniform 3.0%. Water quality data, consisting of 13 parameters, were collected over a four and one-quarter year period, representing conditions before, during and after the isolation. Evaluation of total phosphorus data indicated an approx. 90% reduction in estimated risk of summer fish kills as a result of the isolation. A general reduction in nutrient levels, as well as an increase in system stability, was also observed. Isolation of the lake proved to be a simple and economical means of attaining management objectives.