Abstract
Alum dosage requirements to immobilize loosely-bound and iron-bound sediment phosphorus (P) fractions (i.e., redox-sensitive P fractions) in the surface sediments of eutrophic, Squaw Lake, Wisconsin, were determined using alum assay procedures developed by Rydin and Welch (1999). Since the lake exhibits a low buffering capacity (alkalinity = 25 mg Ca L−1), an alkalinity-based calculation could not be used to estimate alum dosage. Redox-sensitive sediment P fractions of surficial sediments, which represented 44% of the inorganic sediment P, were depleted by greater than 90% at an alum (as Al):redox-sensitive P binding ratio of ~ 100:1. Our results suggest that a higher dosage of alum, based on a higher alum:redox-sensitive P binding ratio requirement, is necessary to achieve effective control of sediment P in this lake. However, uncertainties still exist in the calculation of an alum dosage based on redox-sensitive sediment P concentration. More research is needed to validate optimal alum:redox-sensitive P binding ratios for use in sediment P-based alum dosage calculations. Criteria for estimating the layer of profundal sediment (i.e., the volume of redox-sensitive sediment P or the active layer of sediment contributing to diffusive P flux) to treat is also needed in order to estimate a cost-effective alum dosage for reducing internal P loading.
Published Version
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