Molly A. Rideout with Katherine McMahon and Ryan J. Newton

UW-Madison Department of Civil and Environmental Engineering

Studies have shown that specialized activated sludge bacteria take up large quantities of volatile fatty acids such as acetate during enhanced biological phosphorus removal (EBPR), while releasing massive amounts of phosphate into the system. Preliminary research was conducted to determine whether bacterial communities in freshwater lake sediments reacted in the same manner to the addition of acetate. Several sediment samples were taken from Lake Mendota (Madison, Wisconsin) from varying depths and stored in anaerobic bottles. After addition of acetate, a subset of samples were placed on a mixer to simulate the agitation that occurs during EPBR, while the rest were incubated under the conditions normally found at the sediment-hypolimnion interface (without mixing). Sub-samples were taken and assayed for soluble reactive phosphorus content over a period of two weeks. Significant phosphorus release (0.5-2.5 mg/L) was observed in the samples, peaking around the eighth to tenth day, although the time and maximum amount exhibited significant variation across replicates. Unexpectedly, agitation of sediment did not seem to affect release as dramatically as has been shown in EBPR. However, several technical difficulties may have influenced the results. Therefore, no definite conclusions could be made regarding the conditions under which acetate caused maximum phosphorus release, but these preliminary studies suggest that further work should be done to investigate this potentially important part of the freshwater phosphorus cycle.