|Lerch, Robert - Bob|
Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2011
Publication Date: 7/1/2012
Citation: Willett, C.D., Lerch, R.N., Schultz, R.C., Berges, S.A., Peacher, R.D., Isenhart, T.M. 2012. Streambank erosion in two watersheds of the central claypan region. Journal of Soil and Water Conservation Society. 67:249-263. Interpretive Summary: Contamination of surface waters by sediment remains a major environmental concern in the United States. Soil washed into streams from agricultural lands represents lost productivity and impaired aquatic habitat. Streambanks are a non-point source of sediment that can contribute substantially to in-stream sediment contamination. This study was undertaken to compare the streambank erosion rates of streams in claypan watersheds with different adjacent land uses and different sized stream channels, referred to as stream order. Study sites were established in the Crooked and Otter Creek watersheds, two claypan watersheds located in northeastern Missouri. The land uses studied included forest, pasture with cattle access to the stream, riparian forest, and row-crop. The effect of season on erosion rates was investigated by obtaining measurements three times a year. Streambank soils were also measured for their amount of nitrogen and carbon. Season was found to be the most important factor affecting streambank erosion. Erosion rates during the winter were much higher than the erosion rates of any other season. Spring and summer erosion rates were low to moderate, and the fall was often marked by low levels of deposition rather than erosion. Overall, there were no statistical differences between the erosion rates of the streams with different adjacent land uses or different stream orders. This indicated that either upstream factors, such as drainage area and land use, or vegetation immediately adjacent to the banks were important factors affecting erosion rates. At the watershed scale, bank sediment contributed more than half of the total in-stream sediment (57%), accounting for 69,000 tons of sediment deposited in these streams annually. In addition, streambanks accounted for an average of one-tenth of the total N exported from the study area on an annual basis. These results indicated that streambanks are a major, if not dominant, source of sediment in these streams and a significant contributor to the total N transported from these watersheds. The benefits of this research were to show that management practices targeting riparian areas could significantly reduce in-stream sediment and improve water quality in streams of claypan watersheds. Growers benefit because stable stream channels prevent loss of productive areas within their fields. The general public benefits from improved water quality which enhances downstream recreation and reduces sedimentation of reservoirs.
Technical Abstract: This study was undertaken to assess the importance of streambank erosion to the total in-stream sediment of two agricultural watersheds within the Central Claypan Areas. The objective of this research was to determine the effect of stream order, adjacent land use, and season on streambank erosion rates. Thirty four study sites were established in 2007 and 2008 within Crooked and Otter Creek watersheds, two claypan watersheds located in northeastern Missouri. At each site, field assessments of eroding bank length were determined along 300-400 m stream reaches. A factorial experimental design was implemented with four land uses (crop, forest, pasture, and riparian forest) and three stream orders (1st, 2nd, 3rd). Each treatment was replicated three times for each stream order, except for the cropped 3rd order treatment as only one suitable treatment site could be found. Streambank erosion was measured using erosion pins, which were installed in randomly assigned plots that included at least 20 percent of the eroded bank length within each site. The effect of different seasons was assessed by measuring the length of the exposed pins three times per year (March, July, and November). The carbon and nitrogen content of bank material was also determined. Sediment loss rates showed that season and the three-way interaction between season, land use, and stream order were highly significant. Erosion rates were consistently higher in the winter months than spring/summer and fall seasons; however, the significant three-way interaction precluded a simple interpretation of the seasonal effect. Soil nutrient concentration data showed that forest sites had significantly lower C and N concentrations than other land uses. At the watershed scale, bank sediment accounted for 47-72 percent of the total in-stream sediment and 9.5-10.2 percent of the total N exported from the study area. These results indicated that streambanks are a major, if not dominant, source of sediment in these streams and a significant contributor to the total N transported from these watersheds. Improved management of riparian areas to decrease streambank erosion would result in significant water quality improvement in streams of the Central Claypan Areas.