SNY MAGILL NONPOINT SOURCE POLLUTION MONITORING PROJECT, CLAYTON COUNTY, IOWA: WATER YEARS 1992 AND 1993


L.S. Seigley, M.D. Schueller, M.W. Birmingham, G. Wunder, L. Stahl, T.F. Wilton, G.R. Hallberg, R.D. Libra, and J.O. Kennedy


Iowa Department of Natural Resources, Geological Survey Bureau,
Technical Information Series 31, 1994, 103 p.

ABSTRACT


Since 1992, a consortium of state and federal agencies has been monitoring the water quality of Sny Magill and Bloody Run creeks as part of the Sny Magill Watershed Nonpoint Source Pollution Monitoring Project. The objective of this project is to monitor and assess improvements in water quality resulting from the implementation of special water-quality projects designed to improve farm management practices in the Sny Magill watershed. Two years of water-quality data have been collected. Unusually wet conditions during Water Year 1993 make it difficult to assess whether any improvements in water quality that did occur are attributable to improvements in farm management practices.

Precipitation during Water Year 1992 was 124% of normal and 169% of normal for Water Year 1993. The above normal rainfall for Water Year 1993 directly impacted water quality measurements made on both Sny Magill and Bloody Run creeks. Annual mean discharge for Sny Magill increased from 17.1 cubic feet per second in 1992 to 36.6 cubic feet per second in 1993; Bloody Run discharge increased from 26.3 cubic feet per second to 42.1 cubic feet per second. Total suspended sediment discharge for Sny Magill increased from 1,940 tons in 1992 to 13,086 tons in 1993, and increased from 2,720 tons to 22,174 tons on Bloody Run. The average nitrate and triazine pesticide concentrations also increased in response to the increased precipitation and water flux.

The number of benthic macroinvertebrate taxa increased from 60 taxa in Water Year 1992 to 73 taxa in Water Year 1993. Based on the benthic macroinvertebrate data, the water quality in Sny Magill and Bloody Run watersheds was rated "good" to "very good" for both years. Sites located on the tributaries to Sny Magill tended to have better water quality than the main stem sites on Sny Magill. Benthic data from 1993 suggests the water quality may have improved from 1992, however, this improvement is speculative because of the short period of record and the unusual climatic conditions of 1993.

As part of the annual fish assessment, a total of 1,570 fish were sampled in Water Year 1992 and 1,338 in Water Year 1993. The fluctuations in the annual fish populations are a normal response to variation in precipitation, runoff, water clarity, and water stage during the period of sampling. The fish sampled in both Sny Magill and Bloody Run creeks are fish typically found in coldwater streams. For both years, the fish population was dominated by a single species, the fantail darter.

The habitat assessment for Water Year 1993 also recorded the effects of above normal rainfall. Data collected in 1993 show that stream flow during the habitat assessment was two to three times higher in 1993 than Water Year 1992. Also in 1993, stream width and depth were greater at most locations, and noticeable silt deposition and scouring had occurred along many of the stream reaches.