Principal Investigator: Mary C. Mayhew (Gainesville College)
Principal Investigator: Edmond A. Mayhew (Gainesville College)
Sponsor: GWRI
Start Date: 1991-04-01; Completion Date: 1992-03-01;
Keywords: water quality, phosphorus, chlorophyll, transparency, sedimentation, clay, trophic state
Description:
There is evidence that southeastern reservoirs have lower than expected concentrations of phosphorus and algae due to coprecipitation with clays. This appears to be true for Lake Lanier, a major reservoir in N.E. Georgia. The purpose or this study was to investigate the effects of clay on phosphorus and algae and to determine the impact of these effects on Carlson’s Trophic State Index. Clays from the watershed were collected and measured for their phosphorus content and adsorption of phosphorus, which was similar to that for kaolin. Suspensions of clay were added to cultures of the blue-green alga Chroococcus limneticus grown in Bold’s medium and in Rhodes’ medium. Little coprecipitation of algae and phosphorus occurred in the more concentrated Bold’s medium; the more dilute Rhodes’ medium showed precipitation of algae and phosphorus with clay additions. Sediment traps in a tributary of Lake Lanier had high rates of sedimentation of organics and phosphorus, although there did not appear to be a direct coupling between clay and algal sedimentation, as some previous studies indicated. Field sampling of the lake showed deposition of algae, phosphorus, inorganics (clay), and organic matter from upstream to open lake stations. The result indicates that clays do have a profound effect upon Lake Lanier and that the Trophic State Indices for chlorophyll and phosphorus are low due to clay coprecipitation. The TSI for transparency is influenced by inorganic turbidity but is nonetheless the best indicator of the trophic status of the lake eutrophy. An important finding of this study is that siltation is reducing the phosphorus and algae in the water column, and thus slowing the effects of eutrophication. If silt loading is controlled without controlling phosphorus loading, the lake will show algal blooms and other characteristics of eutrophy.