Ohio CREP, Water Quality, and Minimum Detectable Change
Water Quality Lab, Heidelberg College
Basin Program Funds:
The Ohio CREP program has a stated goal of reducing sediment loading to the western basin of Lake Erie by 10 percent over 10 years. However, a 10 percent reduction is small and such subtle changes cannot be easily measured statistically given the wide variation of the year-to-year data.
One of the major goals of the Ohio CREP program is to improve water quality in watersheds dominated by agricultural land use by intercepting overland flow from agricultural lands using Best Management Practices (BMP’s) such as in-field grassed waterways, edge-of-field riparian corridor, and constructed wetlands. These structural practices slow the movement of storm runoff, allowing sediment and associated nutrients to settle out and remain on the land rather than entering the stream network. The establishment of water quality goals and a monitoring program to document success in meeting these goals was a requirement of the program.
Data available for evaluation of the success of the Ohio CREP program will be much more detailed than typically available and the historical duration of the baseline data is much longer that typical. Nonetheless, the high levels of temporal variability that are characteristic of water quality data makes subtle but systematic changes difficult to detect with statistical certainty. A statistical technique called “Minimal Detectable Change Analysis” (MDCA) is available that allows the direct calculation of systematic change.
The existing data for the Raisin, Maumee and Sandusky rivers was prepared to put it into the formats needed to use in the MDCA and an analysis conducted. The results were used to see if a 10 percent change in sediment loads is large enough to be detected with statistical certainty and if not, how large a change would be required to achieve statistical significance.
A manuscript describing the outcome of the evaluation of the Lake Erie CREP program was prepared, submitted to the Journal of the American Water Resources Association, extensively revised based on reviewers’ comments, and accepted for publication. The results of this study indicate that more BMP implementation is probably needed, beyond the Lake Erie CREP goals, if water quality improvements are to be proven statistically. Given that the state of Ohio has underfunded the Lake Erie CREP, implementation goals will probably not be met, and the prospects for demonstrating water quality improvements are not promising.
Contact: R. Peter Richards, 419-448-2240