(Georgia Institute of Technology, 2003-04)
Parker, Amanda K.; Beck, M. Bruce
Sediment 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.
(Georgia Institute of Technology, 2003-04)
Lin, Z.; Beck, M. Bruce
A modified Recursive Prediction Error (RPE) algorithm is used to discover structural change in modeling dynamics of dissolved oxygen (DO) in an aquaculture pond. The small aquaculture pond with a surface area of 1.75 acres, located at Whitehall Forest near the University of Georgia campus, was fertilized on three occasions during the summer of 2000. System responses to nutrient addition have been observed using the University of Georgia’s Environmental Process Control Laboratory (EPCL) for a continuous fivemonth period with 15-minute sampling intervals. A subset of these data – for a period of 36 days from July 1st through August 5th, 2000 – is examined in detail to observe and understand the dynamics of photosynthesis and DO in situ. A mechanistic model performs quite well for describing the concentrations of algae and DO during an algal bloom condition but poorly after the bloom ends. The results of recursive estimation indicate that another process, probably photosynthesis and respiration of macrophytes, may dominate the diurnal variation of DO when the algal biomass in the water column becomes negligible.
(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).