Using Differences Among Carlson's Trophic State Index Values in Regional Water Quality Assessment¹

Abstract

ABSTRACT: Variation among Carlson's three TSI values is unsettling to both the public and the scientific communities. Currently, there is no systematic way to account for differences in the three TSI values. Either (or both) of two mechanisms are proposed to account for differing TSI values on a regional basis. The first mechanism simply transforms the Secchi disk and phosphorus information to conform to their respective regional relationship with chlorophyll. The second mechanism uses the three TSI values to identify modifying processes in a lake and may indicate which TSI value (or combination of values) best reflects a lake's trophic condition. The format that is being proposed using information collected from 60 lakes in the Twin Cities (Minnesota) Metropolitan Area can be applied to other regional situations.