Seasonal sediment and nutrients transport patterns

Authors: Moriasi, Daniel; Guzman Jaimes, Jorge; Steiner, Jean; Starks, Patrick; Garbrecht, Jurgen

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2014
Publication Date: 7/14/2014
Publication URL: http://handle.nal.usda.gov/10113/60562
Citation: Moriasi, D.N., Guzman Jaimes, J.A., Steiner, J.L., Starks, P.J., Garbrecht, J.D. 2014. Seasonal sediment and nutrients transport patterns. Journal of Environmental Quality. 43:1334-1344.

Interpretive Summary: Excess sediment, nitrogen, and phosphorus loads are common causes of water quality degradation in agricultural watersheds. Nevertheless, continuous long-term and high resolution datasets to determine sediment and nutrient loadings and their sources in order to design mitigation strategies are sparse and expensive to collect. In this study water quality data measured across a range of flow at Cobb Creek (CC), Lake Creek (LC), and Willow Creek (WC) USGS stream gauge sites within the Fort Cobb Reservoir Experimental watershed (FCREW) were used to develop water quality-streamflow discharge (Q) relationships for the three gauge sites. The developed water quality-Q equations were used to generate continuous long-term daily, monthly, and seasonal concentrations and loads data. The generated data were used to determine seasonal patterns (December 2004 and September 2013) for suspended sediments (SS), total nitrogen (TN), and total phosphorus (TP) for each gauge site relative to their respective state thresholds. Decreasing and increasing monotonic trends were observed for the seasonal time series loads for all three sites but they were insignificant. Differences in time series patterns from one year to another and from one season to another were hypothesized to be due to variable climate and cropped area landuse and the corresponding management. The largest loads were estimated during the wet springs and summers of 2007, 2008, and 2009. In general, the spring and summer loads were driven by climate metrics and specifically by precipitation. Based on the average daily, monthly, seasonal and long-term concentrations, at least the SS, TN, and TP target concentrations were exceeded to some extent in all seasons. This was in agreement with previous findings that Fort Cobb Lake and four streams were degraded for nutrients and suspended solids. Also the study results showed that the priority locations to implement the TN and TP conservation practices (CPs) are the LC and WC during winter and spring. Common CPs to mitigate nutrients and suspended sediments include nutrient management, no-till, conversion of cultivated land to pasture, riparian buffers or animal exclusion. Although based on hydrology only, water duality-discharge relationships are potential cost-effective alternatives to generate continuous long-term and high temporal resolution data needed to determine sediment and nutrient concentrations and loadings to water bodies.

Technical Abstract: It is essential to understand sediment and nutrient sources and their spatial and temporal patterns in order to design effective mitigation strategies. However, long-term data sets to determine sediment and nutrient loadings are scarce and expensive to collect. The goal of this study was to determine seasonal patterns of suspended sediment (SS), total nitrogen (TN), and total phosphorus (TP) concentrations and loadings for three USGS gauge sites located at the Fort Cobb Reservoir Experimental watershed (FCREW) located in southwestern Oklahoma. Measured instantaneous discharge, SS, TN, and TP concentration data were used to develop log-normal water quality-discharge relationships. The water quality-discharge relationships were used to generate estimated seasonal concentrations and loads based on hourly or 30-minute interval discharge. The estimated concentrations and loads were used to determine seasonal patterns for SS, TN, and TP relative to the respective state water quality criteria. Decreasing and increasing monotonic trends were observed for the seasonal time series loads for all three sites but they were insignificant based on the Spearman test (a = 0.05). The largest loads were estimated during the wet springs and summers. The study SS, TN, and TP target concentrations were exceeded in one season or another. The study results showed that the priority locations to implement the TN and TP conservation practices were the Lake Creek and Willow Creek during the winter and spring seasons. Common practices to mitigate nutrients and suspended sediments include nutrient management, no-till, conversion of cultivated land to pasture, riparian buffers or animal exclusion.