Trends in Onondaga Lake Nearshore Monitoring Data Onondaga Lake Ambient Monitoring Program – 2011 Report

Jul 6, 2011

Prepared for Ecologic, LLC & Onondaga County Department of Water Environment Protection by William W. Walker, Jr., Ph.D. & Jeffrey D. Walker, M.Eng.

Summary: This report describes an analysis of long-term trends in Secchi depth, turbidity and bacteria levels at nearshore sites on Lake Onondaga between 1999 and 2010. Trend analyses were performed separately for dry weather, wet weather, and all samples. To account for differences in the frequencies of wet vs. dry samples in each year, the data were also adjusted to reduce the effects of antecedent rainfall in each sampling event. The trend analyses were performed and compared across three different methods (linear regression, Mann-Kendall, and Seasonal Kendall) using the R statistical programming language and wq package.

Results indicate increases in water clarity under both dry and wet weather throughout the lake from 1999 to 2010. Decreases in fecal coliform and E. coli bacteria are evident at several sites during wet weather. Increases in fecal coliform at southern sites during dry weather can be attributed to an intentional change in disinfection practices at the Metro plant in 2004.

Citation: Walker, W.W. and J.D. Walker. 2011. Trends in Onondaga Lake Nearshore Monitoring Data Onondaga Lake Ambient Monitoring Program – 2011 Report. Prepared for Ecologic, LLC and Onondaga County Department of Water Environment Protection by William W. Walker, Jr., Ph.D. and Jeffrey D. Walker, M.Eng. July 2011.

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