75 JAN/FEB 2018—VOL. 73, NO. 1 JOURNAL OF SOIL AND WATER CONSERVATION Beth H. Baker is an assistant Extension pro- fessor in the Department of Wildlife, Fisheries, and Aquaculture, Mississippi State University, Mississippi State, Mississippi. Joby M. Prince Czarnecki is an assistant professor with the Geosystems Resources Institute and Depart- ment of Plant and Soil Sciences, Mississippi State University, Mississippi State, Mississippi. Austin R. Omer is an Extension associate and doctoral candidate in the Department of Wildlife, Fisheries, and Aquaculture, Mississippi State University, Mississippi State, Mississippi. Caleb A. Aldridge is a research associate in the De- partment of Wildlife, Fisheries, and Aquaculture, Mississippi State University, Mississippi State, Mississippi. Robert Kröger is the chief scientific officer with Covington Civil and Environmental, LLC, Gulfport, Mississippi. J. Dan Prevost is a conservationist and project manager with Delta F.A.R.M., Stoneville, Mississippi. Nutrient and sediment runoff from agricultural landscapes with varying suites of conservation practices in the Mississippi Alluvial Valley B.H. Baker, J.M. Prince Czarnecki, A.R. Omer, C.A. Aldridge, R. Kröger, and J.D. Prevost Abstract: Increasing concern regarding environmental degradation in coastal areas that expe- rience annual hypoxic zones has led to the need for mitigation of nutrient laden runoff from inland landscapes. An annual occurrence of a hypoxic zone in the Gulf of Mexico has led to the development and implementation of nutrient reduction strategies throughout the Mississippi River Basin (MRB). With federal, state, and private financial and technical assis- tance, landowners have implemented best management practices (BMPs) to combat nutrient and sediment nonpoint source pollution; however, the effectiveness of these BMPs alone or utilized together has not been quantified. This study uses a field-scale, paired watershed approach in two watersheds in the Mississippi Alluvial Valley to test for differences in sed- iment and nutrient runoff concentrations between four management systems. A total of 774 samples (415 baseflow samples and 359 stormflow samples) were collected from 2011 to 2015. Median baseflow concentrations across all sites within this study were 52 mg L –1 for total suspended solids (TSS), 0.38 mg L –1 for total phosphorus (TP), 0.09 mg L –1 for nitrate-nitrite (NO 3 – -NO 2 – ), and 0.81 mg L –1 for ammonium (NH 4 + ). Median sediment and nutrient concentrations from stormflow samples across all sites within the study were greater than baseflow concentrations. Median stormflow concentrations across all sites were 985 mg L –1 for TSS, 1.21 mg L –1 for TP, 0.32 mg L –1 for NO 3 – -NO 2 – , and 1.04 mg L –1 for NH 4 + . Results showed no strong improvements in water quality from agricultural landscapes where suites of BMPs had been implemented, rather the data showed variability in runoff concentrations indicative of strong influences from environmental and management vari- ables. Study outcomes highlight opportunities to better capture nutrient dynamics at the field scale through adaptive management of BMPs for increased effectiveness of nonpoint source pollution reduction and monitoring. Key words: agriculture—best management practices—nutrient management—water quality With a global need to enhance agricul- ture production while protecting water resources, scientists and policy makers face a prodigious challenge in determin- ing how to manipulate landscapes to fulfill those needs without inflicting environmental harm and within fiscally responsible boundaries. In the United States, North America’s largest river, the Mississippi River, flows over 3,700 km through a high-intensity agricultural sys- tem—specifically in the Corn Belt region of the Midwest, down through the Lower Mississippi Alluvial Valley, and into the Gulf of Mexico. The Mississippi River Basin (MRB) drains roughly 41% of the contig- uous United States (Milliman and Meade 1983) and accounts for 90% of the freshwa- ter loading to the Gulf of Mexico (Mitsch et al. 2001; Rabalais et al. 1996). The MRB serves as a source of water for drinking, food production, industry, and recreation for mil- lions of people, while also providing globally significant ecosystems (e.g., migratory fly- way). However, what the basin is perhaps best known for is as one of the leading agricultural production areas in the world. Agriculture expansion over the last 200 years, due to human population growth and inno- vation, has altered natural landscapes away from grasslands, wetlands, and bottomland hardwood forests, to a mosaic dominated by cropland. From the 1780s to the 1980s, the lower 48 states lost an estimated 23% of their original wetlands; within the 12 pri- mary states that comprise the Mississippi and Ohio River basins, wetland losses between that 200-year period ranged from 42% to 90%, primarily drained for agriculture (Dahl 1990). In addition to land-use alterations, the main channel of the Mississippi River has been shortened, dredged, and stabilized for navigation. While landscape and indus- trial development have benefited human development and economic growth, these changes have also led to environmental deg- radation, including local and downstream water quality issues. Agricultural landscapes contribute non- point source (NPS) pollution to waterways through nutrient- and sediment-laden sur- face runoff and subsurface drainage, posing a threat to watersheds and coastal waters through diminished water quality. In the MRB, NPS pollution is estimated to con- tribute more than 90% of nitrate (NO 3 – ) inputs, 74% of which are agricultural in ori- gin (Rabalais et al. 2002). Increased nutrient loading, primarily nitrogen (N) and phos- phorus (P), can accelerate normal plant growth in a process called eutrophication, which can lead to local effects that include excess algal growth, changes in water clarity, odor, and toxic algal blooms (Chrislock et al. 2013). This process degrades the biologi- cal integrity in streams and receiving waters doi:10.2489/jswc.73.1.75 Copyright © 2018 Soil and Water Conservation Society. All rights reserved. www.swcs.org 73(1):75-85 Journal of Soil and Water Conservation