Phosphorus sorption by sediments in eutrophic and acidic lakes

Phosphorus (P) binding by aluminum (Al), iron (Fe), and calcium (Ca) in lake sediments was studied in both nutrient-rich (eutrophic) circumneutral lakes and nutrient-poor (oligotrophic) acidic lakes. Aluminum sulfate (alum), used to control internal P loading from the sediment, was applied to several eutrophic lakes in the Minneapolis, MN area. Methods used to determine alum dose were compared and the results of alum treatments applied to the Minneapolis Chain of Lakes were examined. P concentrations improved (decreased) initially in all lakes treated, and three lakes were still experiencing continued benefits at the end of this study. Analysis of the sediment, however, showed that internal P load reductions met the restoration goals in all lakes, which suggests that the importance of external P loading on water quality was underestimated in the lake with short-term treatment benefits.; Binding of P by Al in acidified lakes resulted in the inactivation of a substantial amount of P over nearly five decades in lakes across southern Sweden. In addition, total sulfur (ST) in the lake sediment also increased during the industrial acidification stage (IAS; determined by 210lead dating) in two lakes (Lakes Gardsjon and Gyltigesjon). Based on this evidence and that from other studies, ST levels in sediment cores from 12 lakes were related to elevated levels of Al and Al bound P (Al-P) during the IAS and to increasing sulfate in the deposition over Sweden during the period ∼1930--1970. Of the 12 lakes, four showed increased sediment Al and Al-P during the IAS, three showed increases before the IAS, three showed increases during both periods and two lakes showed increases that could not be related to the IAS. It is hypothesized that forest harvesting, which was at its peak in Sweden in the mid to late 1800s, caused the pre-IAS increases in sediment Al and Al-P, and that liming caused the non-IAS related increases in Al and Al-P through precipitation of Al at time of treatment. In conjunction with Al, Fe and Ca were also generally available for P sorption after treatment with lime, potentially exacerbating P limitation in these lakes.