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Understanding the relationship between land use and freshwater quality is necessary for effective water management. This study sought to evaluate the impacts of future land use change on water quality in an agriculture dominated watershed in South Dakota. Taking into account three cases (A1B, A2 and B1) of the FOREcasting SCEnarios (FORE-SCE) of Land use Change modeling framework, possible changes in surface runoff, sediment, nitrate and total phosphorus by the end of the 21st century were assessed relative to the baseline (National Land Cover Database 2011) comprising a multi-year period from the recent past (2006-2014). The Soil and Water Assessment Tool (SWAT) was used for simulating hydrology and water quality, where particular attention was given to land transformation from "high-input" to "low-input" agriculture. The analysis revealed that urban areas and low-input hay/pasture production would expand from conversion of forest, grassland and high-input cultivated cropland. While afforestation might also occur under certain future scenario assumptions such as B1, all the three scenarios are suggestive of complete grassland depletion by the first quarter of this century. Simulation results suggested that water quality would improve with expansion of hay/pasture production (as lowinput agriculture), reducing surface runoff volume, sediment, nitrate and total phosphorus loads by 3-14% across all three future scenarios of land use change. This study provides an example on how physically-based land use projections can be ingested in SWAT modeling to identify possible environmental implications of future land use changes. Similar studies adopted on large scales would be useful to support holistic water resources management strategies and associated policy interventions.

a b s t r a c tThe Missouri River system has a large water storage capacity, where baseflow plays an important role. Understanding historical baseflow characteristics with respect to climate and land use impacts is essential for effective planning and management of water resources in the Missouri River Basin (MORB). This study evaluated statistical trends in baseflow and precipitation for 99 MORB minimally disturbed watersheds during 1950-2014. Elasticity of baseflow to climate variability and agricultural land use change were quantified for the 99 studied watersheds. Baseflow was derived from daily streamflow records with a recursive digital filter method. The results showed that baseflow varied between 38 and 80% (0 and 331 mm/year) of total streamflow with an average of 60%, indicating that more than half of streamflow in the MORB is derived from baseflow. The trend analysis revealed that precipitation increased during the study period in 78 out of 99 watersheds, leading to 1-3.9% noticeable increase in baseflow for 68 of 99 watersheds. Although the changes in baseflow obtained in this study were a result of the combined effects of climate and land use change across the basin, upward trends in baseflow generally coincide with increased precipitation and agricultural land use trends in the basin. Agricultural land use increase mostly led to a 0-5.7% decrease in annual baseflow in the basin, except toward east of the basin where baseflow mostly increased with agricultural land use increase (0.1-2.0%). In general, a 1% increase in precipitation and a 1% increase in agricultural land use resulted in 1.5% increase and 0.2% decrease in baseflow, respectively, during the study period. These results are entirely dependent on the quality of data used; however, they provide useful insight into the relative influence of climate and land use change on baseflow conditions in the Great Plains region of the USA.

Trends in high, moderate, and low streamflow conditions from United States Geological Survey (USGS) gauging stations were evaluated for a period of 1951-2013 for 18 selected watersheds in South Dakota (SD) using a modified Mann-Kendall test. Rainfall trends from 21 rainfall observation stations located within 20-km of the streamflow gauging stations were also evaluated for the same study period. The concept of elasticity was used to examine sensitivity of streamflow to variation in rainfall and land cover (i.e., grassland) in the study watersheds. Results indicated significant increasing trends in seven of the studied streams (of which five are in the east and two are located in the west), nine with slight increasing trends, and two with decreasing trends for annual streamflow. About half of the streams exhibited significant increasing trends in low and moderate flow conditions compared to high flow conditions. Ten rainfall stations showed slight increasing trends and seven showed decreasing trends for annual rainfall. Streamflow elasticity analysis revealed that streamflow was highly influenced by rainfall across the state (five of eastern streams and seven of western streams). Based on this analysis, a 10% increase in annual rainfall would result in 11%-30% increase in annual streamflow in more than 60% of SD streams. While streamflow appears to be more sensitive to rainfall across the state, high sensitivity of streamflow to rapid decrease in grassland area was detected in two western watersheds. This study provides valuable insight into of the relationship between streamflow, climate, and grassland cover in SD and would support further research and stakeholder decision making about water resources.