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R.A. Rebich

Publications and source records attributed to R.A. Rebich.

7 recordsLinked to original sources
USGS2005

Phosphorus component in AnnAGNPS

The USDA Annualized Agricultural Non-Point Source Pollution model (AnnAGNPS) has been developed to aid in evaluation of watershed response to agricultural management practices. Previous studies have demonstrated the capability of the model to simulate runoff and sediment, but not phosphorus (P). The main purpose of this article is to evaluate the performance of AnnAGNPS on P simulation using comparisons with measurements from the Deep Hollow watershed of the Mississippi Delta Management Systems Evaluation Area (MDMSEA) project. A sensitivity analysis was performed to identify input parameters whose impact is the greatest on P yields. Sensitivity analysis results indicate that the most sensitive variables of those selected are initial soil P contents, P application rate, and plant P uptake. AnnAGNPS simulations of dissolved P yield do not agree well with observed dissolved P yield (Nash-Sutcliffe coefficient of efficiency of 0.34, R2 of 0.51, and slope of 0.24); however, AnnAGNPS simulations of total P yield agree well with observed total P yield (Nash-Sutcliffe coefficient of efficiency of 0.85, R2 of 0.88, and slope of 0.83). The difference in dissolved P yield may be attributed to limitations in model simulation of P processes. Uncertainties in input parameter selections also affect the model's performance.

Transactions of the American Society of Agricultur↗
USGS2004

Herbicide concentrations in the Mississippi River basin: The importance of chloroacetanilide herbicide degradates

The proportion of chloroacetanilide herbicide degradates, specifically the ethane sulfonic (ESA) and oxanilic (OA) acids, averaged 70% of the total herbicide concentration in samples from the Upper Mississippi River. In samples from the Missouri River and the Ohio River, the proportion of chloroacetanilide degradates in the total herbicide concentration was much less, 24% and 41%, respectively. The amount of tile drainage throughout the Mississippi River Basin appeared to be related to the occurrence and distribution of chloroacetanilide degradates in water samples. Pesticide concentrations in streams of the Mississippi River Basin have been well characterized. However, recent research demonstrates that in order to more fully understand the fate and transport of pesticides, the major pesticide degradates need to be included in the analysis. From March 1999 through May 2001, water samples from four major junctures of the Mississippi River Basin were collected and analyzed for a suite of herbicides and their degradate compounds. Each sampling site was selected to represent a major part of the Mississippi River: upper and lower Mississippi, Missouri and Ohio Rivers. Each basin has unique landscape variables, geology, hydrology, precipitation, and land use, which is reflected in the pesticide content at the most downstream sample site near the mouth of the Mississippi River. Atrazine was the most frequently detected herbicide (detected in 97% of the samples), followed by metolachlor (60%), and acetochlor (31%). The most frequently detected degradates were metolachlor ESA (69%), followed by deethylatrazine (62%), metolachlor OA (37%), and alachlor ESA (37%). Metolachlor ESA was detected more frequently than its parent compound (69 vs. 60%), as was alachlor ESA (37 vs. 9%). After an improvement was made in the analytical method, metolachlor ESA was detected in every sample, metolachlor OA in 89% of the samples, alachlor ESA in 84%, acetochlor ESA in 71%, and acetochlor OA in 66%.

Mississippi River Basin↗
USGS2001

Dynamics of diffuse pollution from US southern watersheds

To understand the effects of diffuse pollution information on the source of pollutants, quantities in transport, mode of transport, transient nature of the pollution event, and most importantly, a consideration of remediation efforts need to be known. For example, water quality research in the Yazoo Basin uplands in Mississippi has shown sediment loads from a conventional-till upland soybean watershed to be about 19,000kg/ha/yr, and responsible for 77-96% of P and N in transport. In contrast, sediment loads from a comparable no-till soybean watershed were only 500kg/ha/yr, transporting about 31% of P and N in transport. Sediment loads from a nearby forested area were low, about 200kg/ha/yr, but responsible for about 47-76% of P and N in transport. Transient pollution events are responsible for the transport of large quantities of sediment, nutrients, and pesticides; in some storm events nearly the annual load. Best management practices (BMPs) must be designed to remediate diffuse pollution and the transient nature of pollution events which can have a profound effect on the ecological health of steams and reservoirs. Copyright ?? 2001 .

Water Research↗
USGS1998

Cotton herbicides in the surface waters of the Mississippi Alluvial Plain (the Delta)

The U.S. Geological Survey is conducting two studies to assess the environmental fate of herbicides used in cotton producing areas of the southeastern United States. The first study is evaluating surface-water quality on a regional basis and relating water quality to land use. The second study is examining the use of Best Management Practices to reduce off-site movement of agricultural chemicals in surface-water runoff. Maximum concentrations of the herbicides fluometuron and norflurazon in samples from surface water in edge-of-field studies were 23 and 7 micrograms per liter, respectively. Also, they were detected in the runoff of nearly every sampled storm for the 1997 water year at concentrations higher than 1.0 microgram per liter. Fluometuron and norflurazon were measured frequently in samples from rivers and streams in cotton producing areas, but the frequency of occurrence and the maximum concentrations were less than those in the edge-of-field studies.

Conference Paper↗
USGS1995

Estimation of sediment-discharge reduction for two sites of the Yazoo River basin demonstration erosion control project, north-central Mississippi, 1985-94

Sediment-discharge reduction was estimated at two Demonstration Erosion Control sites in north-central Mississippi for the period 1985 through 1994. Decreasing trends were detected in flow-adjusted sediment discharge at Hotopha Creek near Batesville for the study period. The annual reduction in sediment discharge at this site was about 7 percent (0.68 ton per day per year). Decreasing trends were also detected in flow- adjusted sediment discharge at Otoucalofa Creek Canal near Water Valley for the study period. The annual reduction in sediment discharge at this site was about 11 percent (5.33 tons per day per year). The computations used to estimate sediment-discharge reduction were based on time series of instantaneous sediment discharges for the study period. Non-parametric procedures were used to compute trends in sediment discharge and to quantify reductions over time at the two sites. Parametric procedures were then used to verify the non-parametric results.

Water-Resources Investigations Report↗