This study aims to assess the impact of climate change on water resources in a large watershed within the Laurentian Great Lakes region, using the fully integrated surface‐subsurface model HydroGeoSphere. The hydrologic model is forced with an ensemble of high‐resolution climate projections from the Weather Research and Forecasting (WRF) model. The latter has been extended with an interactive lake model (FLake) to capture the effect of the Great Lakes on the regional climate. The WRF ensemble encompasses two different moist physics configurations at resolutions of 90, 30, and 10 km, as well as four different initial and boundary conditions, so as to control for natural climate variability. The integrated hydrologic model is run with a representative seasonal cycle, which effectively controls natural climate variability, while remaining computationally tractable with a large integrated model. However, the range of natural variability is also investigated, as are the impacts of climate model resolution and bias correction. The two WRF configurations show opposite climate change responses in summer precipitation, but similar responses otherwise. The hydrologic simulations generally follow the climate forcing; however, due to the memory of the subsurface, the differences in summer propagate throughout the entire seasonal cycle. This results in a set of dry scenarios with reduced streamflow and water availability year‐round and a set of wet scenarios with increased streamflow for all times excluding the spring peak, which does not increase. Most of the analysis focuses on streamflow, but changes in the seasonal cycle of baseflow and groundwater recharge are also analyzed.

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This study investigated the potential for controlled tile drainage (CD) to reduce bacteria and nutrient loading to surface water and groundwater from fall-season liquid manure application (LMA) on four macroporous clay loam plots, of which two had CD and two had free-draining (FD) tiles. Rhodamine WT (RWT) was mixed into the manure and monitored in the tile water and groundwater following LMA. Tile water and groundwater quality were influenced by drainage management. Following LMA on the FD plots, RWT, nutrients, and bacteria moved rapidly via tiles to surface water; at the CD plots, tiles did not flow until the first post-LMA rainfall, so the immediate risk of LMA-induced contamination of surface water was abated. During the 36-d monitoring period, flow-weighted average specific conductance, redox potential, and turbidity, as well as total Kjeldahl N (TKN), total P (TP), NH-N, reactive P, and RWT concentrations, were higher in the CD tile effluent; however, because of lower tile discharge from the CD plots, there was no significant ( ≤ 0.05) difference in surface water nutrient and RWT loading between the CD and FD plots when all tiles were flowing. The TKN, TP, and RWT concentrations in groundwater also tended to be higher at the CD plots. Bacteria behaved differently than nutrients and RWT, with no significant difference in total coliform, , fecal coliform, fecal streptococcus, and concentrations between the CD and FD tile effluent; however, for all but , hourly loading was higher from the FD plots. Results indicate that CD has potential for mitigating bacteria movement to surface water.

When surface water levels decline, exposed streambed sediments can be mobilized and washed into the water course when subjected to erosive rainfall. In this study, rainfall simulations were conducted over exposed sediments along stream banks at four distinct locations in an agriculturally dominated river basin with the objective of quantifying the potential for contaminant loading from these often overlooked runoff source areas. At each location, simulations were performed at three different sites. Nitrogen, phosphorus, sediment, fecal indicator bacteria, pathogenic bacteria, and microbial source tracking (MST) markers were examined in both prerainfall sediments and rainfall-induced runoff water. Runoff generation and sediment mobilization occurred quickly (10-150 s) after rainfall initiation. Temporal trends in runoff concentrations were highly variable within and between locations. Total runoff event loads were considered large for many pollutants considered. For instance, the maximum observed total phosphorus runoff load was on the order of 1.5 kg ha . Results also demonstrate that runoff from exposed sediments can be a source of pathogenic bacteria. Campylobacter spp. and Salmonella spp. were present in runoff from one and three locations, respectively. Ruminant MST markers were also present in runoff from two locations, one of which hosted pasturing cattle with stream access. Overall, this study demonstrated that rainfall-induced runoff from exposed streambed sediments can be an important source of surface water pollution.

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