Description
Diatom reconstructions of historical phosphorus and chloride concentrations and sediment accumulation rate, based on sediment cores from 55 lakes in Minnesota, provide a unique opportunity for examining temporal and spatial trends in eutrophication, validating eutrophication models, and providing historical perspective for developing nutrient criteria. Sediment cores, obtained by a piston corer between 1995 and 1998, were sectioned and dated. Sections corresponding to 1750, 1800, 1970, and 1993 time-periods were used in this analysis. Distinct regional patterns in historic (mean of 1750 and 1800) phosphorus concentrations were evident: Northern Lakes and Forests lakes averaged 15 μg/L (± 1), North Central Hardwoods Forests lakes averaged 24 μg/L (± 2), and Western Corn Belt Plains lakes averaged 47 μg/L (± 6). Comparing these values to the recent 1990s values suggests no change in the NLF lakes (15 μg/L ± 1), but significant increases in the CHF (38 μg/L ± 5) and WCP lakes (67μg/L ±16). Comparisons were made between the historic values and two empirical models routinely used to help set in-lake phosphorus goals in Minnesota. The first model (Vighi and Chiaudani 1985), based on the morphoedaphic index, is used to predict the background phosphorus concentration of a lake. The second (MINLEAP) is an ecoregion-based model that predicts in-lake phosphorus based on morphometry, watershed area, and ecoregion characteristics (Wilson and Walker 1989). Comparisons between historic phosphorus concentrations and model predictions indicate good correspondence at model-predicted values less than about 30 μg/L. Lastly, the use of diatom-inferred values is explored as a part of Minnesota's efforts to develop water quality standards for nutrients.
Date Issued
2002-09
Number of Pages
111
Decade
Associated Organization
Publisher
Minnesota Pollution Control Agency (St. Paul, Minnesota)
Keywords
Publication Series
Status
Format
Rights Holder
Minnesota Pollution Control Agency
Rights Management
Public Domain