Alum efficacy 11 years following treatment: phosphorus and macroinvertebrates

Abstract

ABSTRACTSteinman AD, Hassett MC, Oudsema M, Rediske R. 2018. Alum efficacy 11 years following treatment: phosphorus and macroinvertebrates. Lake Reserv Manage. 34:167—181.Internal phosphorus loading and benthic macroinvertebrate community structure were analyzed at 4 sites in Spring Lake, Michigan, ˜11 yr following an alum treatment. Phosphorus (P) release rates, benthic macroinvertebrate community structure, sediment chemistry, and water quality variables (total dissolved solids, pH, dissolved oxygen, water clarity) were compared to measurements taken previously (2003/2004: pre-alum application, 2006: 8 mo post-alum application, and 2010: 5 yr post-alum application) at the same sites and using comparable methods. Total phosphorus (TP) concentrations in surface water samples from 2016 (38—45 νg/L) were similar to those measured in 2006 and 2010 (20—80 νg/L) at all sites; however, 2016 TP concentrations in the near-bottom water at the 2 deeper sites were elevated (˜250 and 1,000 νg/L, respectively) compared to TP concentrations of <60 νg/L in 2006 and 2010, suggesting internal loading may be increasing, at least at these 2 sites. In contrast, maximum P release rates from the 2016 sediments were similar to or lower than 2010 rates, and an order of magnitude lower than before alum was applied. Phosphorus content in the sediment was fractionated; loosely sorbed sediment SRP concentrations were very low at all sites. Macroinvertebrate community was similar in density and composition to the 2010 results. These results are suggestive, but not conclusive, that internal P loading is increasing in parts of Spring Lake. Alum application can serve as an effective short-term solution to the longer-term problem of internal P loading, but its effectiveness is critically tied to concurrent reductions in external P loading.