Experimental and desktop studies were conducted during 2004 to better understand the factors affecting internal phosphorus (P) loading in Spring Lake, Michigan. A prior study in 2003 resulted in estimates that between 55 and 65% of the total phosphorus entering the water column of Spring Lake, on an annual basis, originated via internal loading from the sediments. The results from the current study indicated the following:

Phosphorus release rates were no different at alum concentrations of ≥ 15 mg alum/L compared to 24 mg/L. However, the higher alum concentration is likely to provide greater spatial coverage over the sediments in the lake, more protection from alum redistribution after sediment resuspension, and is still well below concentrations of environmental concern.

Resuspension events, which would cause the sediments to become mixed, substantially increase total phosphorus concentrations in the water column, even at high alum concentrations, although the total soluble phosphorus concentrations remain low in the water column provided alum is present.

Bioturbation has the potential to increase phosphorus release into the water column. However, several lines of evidence in our data suggest that this process does not play a significant role in Spring Lake sediments. Desktop analyses focusing on lake morphometry revealed that Spring Lake is very susceptible to internal loading but not very susceptible to resuspension events. In addition, calculations indicated that given the current concentration of P in the sediment, internal P loading can continue in Spring Lake for another 40 years, even if all new sources of phosphorus are eliminated.

Taken together, these results indicate that an alum application of 25 mg aluminum/L is likely to result in a substantial reduction in the phosphorus concentration in the water column of Spring Lake. The length of treatment effectiveness will depend on the degree to which 1) the alum remains in place on the sediment-water interface and 2) current and future external phosphorus loading to Spring Lake is reduced.


Water Quality -- Measurement, Ecosystem Health, Spring Lake, Michigan


Environmental Monitoring | Natural Resources and Conservation