Reversal of the Eutrophication Process: A Case Study

Bayou Texar, Pensacola, Florida, is a bayou estuary which was advancing toward eutrophy, due to nutrient loadings from various sources. The occurrence of characteristic symptoms of eutrophication, coupled with the closing of the bayou for water contact recreation, led to the initiation of an intensive seven-year study. Initial results indicated that Carpenter’s Creek is a prime source of most nitrogen species and that an exchange exists between dissolved phosphates and those adsorbed onto sediments. Carbon fixation rates varied, with the stations closest to Carpenters Creek exhibiting the most productivity. It also appeared that nitrates may be more important in controlling rates of carbon fixation than phosphates. An ensuing study directed at phosphate exchange suggested that reducing conditions in the muds cause substantial release of iron-bound PO4 from the sediment-water interface followed by adsorption onto particles in the aerobic flocculent layer above the interface. This mechanism could allow sufficiently rapid exchange of PO4 between sediment and water resulting in a low, stable concentration in the water as observed. Other investigations involving bacterioplankton, dissolved glucose, and heterotrophic production indicated that algal primary productivity is the major source of dissolved glucose. A final study demonstrated a paucity of benthic macroinvertebrates, probably due to a graded suspension of particles at the sediment-water interface and the absence of a sharply defined bottom. The zooplankton community exhibited low diversity while numbers of individual species were high. The phytoplankton community was composed primarily of dinoflagellates, with diatoms, cryptophytes, chlorophytes and microflagellates occurring in lesser quantities. It was also suggested that the importance from algal blooms to fish kills may be greater than previously indicated. Specific recommendations made after the fourth year of the study were implemented in most part and led to a substantial improvement of water quality and the subsequent opening of the bayou to the public for recreational use.