(Georgia Institute of Technology, 2003-04)
Parker, Amanda K.; Rasmussen, Todd C.; Beck, M. Bruce
The 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).
(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.
(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.