Water Quality Trends and Changing Agricultural Practices in a Midwest U.S. Watershed, 1994–2006

Abstract

Sediment and nutrient concentrations in surface water in agricultural regions are strongly influenced by agricultural activities. In the Corn Belt, recent changes in farm management practices are likely to affect water quality, yet there are few data on these linkages at the landscape scale. We report on trends in concentrations of N as ammonium (NH(4)) and nitrate (NO(3)), soluble reactive phosphorus (SRP), and suspended sediment (SS) in three Corn Belt streams with drainage areas of 12 to 129 km(2) for 1994 through 2006. During this period, there has been an increase in conservation tillage, a decline in fertilizer use, and consolidation of animal feeding operations in our study watersheds and throughout the Corn Belt. We use an autoregressive moving average model to include the effects of discharge and season on concentrations, LOWESS plots, and analyses of changes in the relation between discharge and concentration. We found significant declines in mean monthly concentrations of NH(4) at all three streams over the 13-yr period, declines in SRP and SS in two of the three streams, and a decline in NO(3) in one stream. When trend coefficients are converted to percent per year and weighted by drainage, area changes in concentration are -8.5% for NH(4), -5.9% for SRP, -6.8% for SS, and -0.8% for NO(3). Trends in total N and P are strongly tied to trends in NO(3), SRP, and SS and indicate that total P is declining, whereas total N is not.

Land Use, Stream Habitat and Benthic Invertebrate Assemblages in a Highly Altered Iowa Watershed

“…2) were indicative of degraded stream conditions throughout the study watershed. Nitrate concentrations at study sites generally exceeded summer values recently reported from streams in other row-crop dominated watersheds of the Midwestern U.S.A., where nitrate concentrations are consistently among the highest in the nation (Bernot et al, 2006;Figueroa-Nieves et al, 2006;Schilling and Spooner, 2006;Heatherly et al, 2007;Renwick et al, 2008;Wagner et al, 2008;Diebel and Vander Zanden, 2009;Warrner et al, 2009). Additionally, nitrate concentration at each of our study sites (range 5 5.6-29.0 mg/L) was higher than 3.2 mg/L, a threshold value that, based on a USEPA Wadeable Streams Assessment, is indicative of poor conditions in Midwestern streams (Van Sickle and Paulsen, 2008).…”

Influence of integrated watershed-scale agricultural conservation practices on lake water quality

“…While necessary to feed and clothe a continually growing human population, these practices can often lead to significant soil erosion (Bennett and Chapline 1928) and surface runoff during rainfall events that produce increased loads of suspended sediment and dissolved solids, and decrease water clarity (Dodds and Whiles 2004;Renwick et al 2008). Despite decades of research and considerable efforts to mitigate suspended sediment loading, suspended sediment continues to be one of the most pernicious pollutants and a significant cause of water quality impairment globally.…”

Quantifying suspended sediment loads delivered to Cheney Reservoir, Kansas: Temporal patterns and management implications

“…For the near term (perhaps one or more decades), given the low sedimentation rate at Cheney Reservoir, voluntary conservation practices in the basin may constitute an acceptable sediment management strategy. Use of conservation practices to minimize sediment runoff has been shown to decrease sediment delivery to streams and reservoirs (McIntyre 1993;Renwick et al 2005;Renwick et al 2008;Richards et al 2008) and prioritized implementation of such practices may further enhance the improvements realized (Legge et al 2013). Between 1994 and 2011, nontargeted best management practices were implemented at more than 1,000 sites in the Cheney Reservoir basin (Cheney Lake Watershed Incorporated, written communication, 2011).…”