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Georgia Water Resources Conference
Georgia Water Resources Conference
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ItemIron Reduction and Phosphorus Release from Lake Sediments and Bt Horizon Soil: Incubation Studies to Explore Phosphorus Cycling(Georgia Institute of Technology, 2003-04) Parker, Amanda K. ; Beck, M. BruceSediment from two Georgia Piedmont impoundments and soil from the Georgia Piedmont Bt horizon were incubated with an easily consumable organic carbon substrate in an anaerobic environment to observe iron reduction and phosphorus release. 97% of porewater iron in the Bt horizon soil, 96% of porewater iron in Lake Lanier sediments, and 93% of porewater iron in Lake Oglethorpe sediments was reduced to a soluble form during anaerobic incubation. Phosphorus release followed a similar trend with 83% of total P in Bt horizon porewaters, 77% of total P in Lake Lanier sediment porewater, and 61% of total P in Lake Oglethorpe sediment porewater solubilized. The iron reduction and phosphorus release observed in soil from the Bt horizon collected in the Piedmont region of Georgia indicates that phosphorus transported to Piedmont impoundments may be made biologically available through iron reduction in the sediments. The smaller percentage of P and Fe solubilized in Lake Oglethorpe sediments may indicate that there is less reducible iron in these sediments, and that less P is directly adsorbed or bound to oxidized iron and thus less available for release upon iron reduction. We discuss the implications this work has on lake and watershed management practices in the Georgia Piedmont.
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ItemThe Role of Transported Sediment in the Cycling of Phosphate in Georgia Piedmont Impoundments(Georgia Institute of Technology, 2003-04) Parker, Amanda K. ; Rasmussen, Todd C. ; Beck, M. BruceThe high iron content in the soils and resident parent material of the Georgia Piedmont results in significant transport of iron in runoff to receiving waterbodies. Phosphorus cycling in lakes can be significantly affected by the iron cycle. The work presented here describes experiments to test sorption and desorption of phosphate from Bt horizon soil to help illuminate the role of transported sediment in the cycling of phosphorus in Georgia Piedmont impoundments. We conducted sorption capacity experiments on Bt horizon soil, Lake Lanier sediments, and catalyst grade FeOOH. We also describe experiments to test release of phosphate from Bt horizon soil under elevated pH conditions. Sorption capacity of Bt soil and Lake Lanier sediments is greater than that of FeOOH. Phosphate desorption from Bt horizon soil at pH values of 8-10 fits a linear model with greater desorption at higher pH values. The results presented here further support the alternative phosphorus cycling pathway proposed in Parker and Rasmussen (2001).
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ItemPhosphorus Cycling in Southeastern Piedmont Lakes: An Alternative Pathway(Georgia Institute of Technology, 2001-03) Parker, Amanda K. ; Rasmussen, Todd C.The phosphorus cycling paradigm in lakes is based on data from systems in northern temperate regions. Anoxic respiration in the hypolimnion of north-temperate lakes creates strongly reducing conditions that liberate dissolved inorganic phosphorus (DIP) from settling particulates. Hypolimnetic DIP steadily increases during summer stratification as phosphorus is liberated, and is mixed throughout the water column at fall overturn. This paradigm fails to explain phosphorus cycling in Southeastern Piedmont lakes. No increase in DIP is found in the anoxic hypolimnion during summer stratification; nor is an increase in DIP observed during fall overturn. We hypothesize that the conventional paradigm is not appropriate in iron-rich Southeastern Piedmont lakes because: a) iron-oxide sorption reduces the bioavailability of DIP, and b) the abundance of oxidized iron prevents DIP accumulation in the anoxic hypolimnion. We use iron-oxide chemistry to develop an alternate phosphorus cycling pathway: DIP is released from iron-phosphate particulates when pH increases due to photosynthesis. This mechanism forms a biogeochemical feedback loop that enhances algal blooms.
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ItemPhosphorus Binding by Iron-rich Soil in the Southeastern Piedmont: Implications for Point and Non-point Sources of Phosphorus(Georgia Institute of Technology, 2001-03) Mayhew, Mary C. ; Rasmussen, Todd C. ; Parker, Amanda K.A small impoundment in the Southeastern Piedmont was fertilized on three occasions during the summer of 2000. Liquid fertilizer was directly broadcast over the pond in the first two treatments; in the third treatment the fertilizer was mixed with clay soil and water. The system response to nutrient addition was measured using the Environmental Process and Control Laboratory, which measures a variety of parameters. Only ammonium (NH₄), orthophosphate (PO₄) and turbidity (TUR) are reported here. Response to the first two fertilizations was a similar, immediate elevation in levels of PO₄and NH₄. The third fertilization produced no detectable increase in PO₄and a minimal increase in NH₄. These data support the hypotheses that 1) suspended iron-rich clay from piedmont soils sequesters PO₄and 2) clay soils sequester NH₄in aquatic systems. These mechanisms of nutrient seqestration have important implications for bioavailability in piedmont systems: non-point, sediment-bound nutrients are less available than nutrients from point sources.
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ItemIn Situ Respirometry for the Determination of Autotrophic and Heterotrophic Production in Southeastern Lakes(Georgia Institute of Technology, 1993-04) Porter, Karen G. ; Porter, James W. ; Saunders, Patricia A. ; Parker, Amanda K.Representative and accurate measurements of both autotrophic and heterotrophic production in lakes are essential parts of basic limnological research and lake monitoring, management, and restoration programs. We describe preliminary data that demonstrate the utility of a continuously recording, in situ respirometer for measuring diel oxygen production and consumption in lake water. The data can be used to compute P, R, P vs. I, P vs. T, P/R, P/B and other basic parameters of primary productivity and heterotrophic activity per unit volume of lake water or per unit chlorophyll. In combination with information on morphometry and water residence time, these volumetric production estimates can be used to compute integrated whole lake metabolism and production budgets. In our preliminary studies we found that heterotrophic processes dominated the water column in Lake Oglethorpe, Georgia.