PARENT SESSION
Oral Session #94: Nutrient Cycling.
Presiding: R. Yanai
Thursday, August 8. 1:00 PM to 3:45 PM. Grand Ballroom East, Radisson.
Biogeochemistry of phosphorus in Lake Lanier, GA.
Parker, Amanda*,1, Beck, Bruce1, 1 Warnell School of Forest Resources, Athens, GA
ABSTRACT- Lake Lanier, located to the north of Atlanta and lying between the development corridors of I-75 and I-85, is the single-most important impoundment in Georgia and the subject of intense public and political scrutiny. Sediment transported by runoff introduces abundant iron and phosphorus to Lake Lanier. Suspended solids concentration is highly correlated with total P concentration (R2=0.82). The regression relationship of SSC and TP indicates that 2ug of P are associated with every mg of suspended sediment. This phosphorus load, however, is seldom reflected in the biological response (Lake Lanier TSI [TP] >50; TSI [Chl] <40). Much of the P entering Lake Lanier is thought to be deposited and buried in the sediments. The traditional lake P cycle indicates that P can be released from lake sediments as organic matter is decomposed. The release of P from the sediments predicted by the traditional lake P cycle has never been measured in Lake Lanier. We tested the availability of measurable dissolved phosphate in the presence of iron-rich sediment in a series of experiments in an experimental pond. Results indicate significant reduction of available P in the presence of iron-rich suspended solids. High concentrations of iron in sediment pore waters (>1200 ppm) indicate an abundant supply of iron to bind P. We explored conditions that might lead to release of P from sediments by spiking sediments with labile organic carbon and incubating them anaerobically to force reduction of oxidized iron. Laboratory incubations of labile C enriched sediments indicate that high concentrations of phosphate (3-8 ppm) may be released from iron phosphate compounds when iron is used as an electron acceptor during anaerobic organic matter decomposition. These results indicate that the stoichiometric relationships of Fe, P, and organic C are important to the release of P from the sediments into the overlying water column. Illumination of these relationships will improve our ability to manage water quality of Georgia's most important impoundment.
KEY WORDS: phosphorus cycling, biogeochemistry, iron, lakes