Climate change is a primary factor influencing alterations in watershed hydrology. Associated changes in temperature and precipitation can influence the fate and transport of non-point source pollution within a watershed, which complicates the application of best management practices (BMPs) for pollution mitigation. Understanding the sensitivity of BMP implementation as climate change is critical for proper management of water resources. The objective of this study is to understand the effects of BMPs on sediment and nutrient yields in the Meramec River watershed in eastern Missouri, U.S.A due to changes in climate. The Soil and Water Assessment Tool (SWAT) was used to model the flow, sediment and nutrient yields across the watershed. Multi-site calibration (1996-2012) and validation (1981-1995; 2012-2014) gave varied results, ranging from very good to acceptable, for the monthly flow, sediment load, total nitrogen (TN) and total phosphorus (TP). Various BMPs were implemented into the calibrated model in conjunction with climate data from four Coupled Model Intercomparison Project Phase 5(CMIP5) projections to estimate the effects of climate change on watershed yields. Implemented BMPs include riparian buffers, vegetated filter strips, terrace, grassed waterway, and tillage. BMPs were implemented in subwatersheds with high sediment and nutrient outputs as well as relatively high ecological value. Results indicate that BMPs could achieve reductions in a range from 2 to 76% for sediment loss, 1 to 64% for TN loss, and 5 to 54% for TP loss. Among the individual BMPs assessed, vegetated filter strips were most effective when considering the reduction in sediment and nutrient loads. This study highlights the effectiveness of a range of BMPs in reducing the sediment and nutrient loads and provides quantitative measures for determining the most effective individual BMP and the optimal combination of BMPs based on current and future climate scenarios.

The natural flow regime within a watershed can be considered as the expected temporal patterns of streamflow variation in the absence of human impacts. While ecosystems have evolved to function under these conditions, the natural flow regime of most rivers has been significantly altered by human activities. Land use change, including the development of agriculture and urbanization, is a primary cause of the loss of natural flow regimes. These changes have altered discharge volume, timing, and variability, and consequently affected the structure and functioning of river ecosystems. The Meramec River watershed is located in east central Missouri and changes in land use have been the primary factor impacting flow regimes across the watershed. In this study, a watershed model, the Soil and Water Assessment Tool (SWAT), was developed to simulate a long-term time series of streamflow (1978-2014) within the watershed. Model performance was evaluated using statistical metrics and graphical technique including R-squared, Nash-Sutcliffe efficiency, cumulative error, and 1:1-ratio comparison between observed and simulated variables. The calibrated and validated SWAT model was then used to quantify the responses of the watershed when it was a forested natural landscape. An Indicator of Hydrologic Alteration (IHA) approach was applied to characterize the flow regime under the current landcover conditions as well as the simulated natural flow regime under the no land use change scenario. Differences in intra- and inter-annual ecologically relevant flow metrics were then compared using SWAT model outputs in conjunction with the IHA approach based on model outputs from current and no land use change conditions. This study provides a watershed-scale understanding of effects of land use change on a river’s flow variability and provides a framework for the development of restoration plans for heavily altered watersheds.