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Technical Report Number 143

Methods for Classifying Lakes Based on Measures of Development Impacts

Richard A. Osgood, Patrick L. Brezonik, Lorin Hatch

 

Report Covers (pdf, 1,308 KB)

 

Full Report (pdf, 356 KB)

 

Abstract

Numerous classification methods and lake condition indices are available for lakes, but no systematic approach has been used to provide a framework for evaluating cumulative impacts of development on Minnesota’s lakes. In the context of this study, “development” refers to urban, suburban, and near-shore residential development in the vicinity of lakes that may have deleterious effects on lake quality. Such a framework would allow policy-makers and regulators to more effectively regulate land use and lakeshore development to balance the demands for development with the desire to protect natural resources from irreversible or unacceptable impacts.

This report reviews the literature on lake classification, focusing specifically on the goals of classification and identifying the most appropriate classification strategies and indices for describing development and assessing its cumulative impacts on Minnesota lakes. A simple framework then is proposed to classify lakes into subclasses based on mean depth, surface area, and specific conductance. Lakes in the Twin Cities Metro Area (TCMA) and Alexandria Lakes Area (ALA) were grouped into classes based on these subclasses, and the usefulness of the classes was evaluated by examining Secchi Depth (SD) transparency, chlorophyll, and Total Phosphorus (TP) concentrations in a set of TCMA and ALA lakes. Other indicators and classification factors (watersheds, morphometry and mixing condition, chemistry and hydrology, and trophic state and biota) that can be used in conjunction with the lake classification matrix to evaluate cumulative impacts also are described.

Four conclusions were drawn from this evaluation: 1) lakes with mean depths > 16 feet had the best water quality; 2) lakes with conductivity values > 500 µS/cm 2 tended to have the poorest water quality; 3) water quality/clarity was poorer for the TCMA region compared with the ALA region for the classes examined; and 4) ALA and TCMA lakes displayed similar variation with respect to SD transparency-chlorophyll and chlorophyll-TP relationships, suggesting that the lakes function in a similar manner with respect to trophic dynamics.

The second report from this study (WRC Technical Report 144) is entitled, "Cumulative Impacts of Development on Lakes in the North Central Hardwood Forest Ecoregion of Minnesota: An Exploratory Study."