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A ground‐water flow system in southwestern Minnesota illustrates water movement between geologic units and between the land surface and the subsurface. The flow patterns indicate numerous zones of ground‐water recharge and discharge controlled by topography, varying thicknesses of geologic units, variation in permeabilities, and the configuration of the basement rock surface. Variations in streamflow along a reach of the Yellow Medicine River agree with the subsurface flow system. Increases and decreases in runoff per square mile correspond, apparently, to ground‐water discharge and recharge zones. Ground‐water quality variations between calcium sulfate waters typical of the Quaternary drift and sodium chloride waters typical of the Cretaceous rocks are caused by mixing of the two water types. The zones of mixing are in agreement with ground‐water flow patterns along the hydrologic section.

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Nevin wetland is an area of groundwater discharge. Ground water enters the wetland as springflow and as leakage upward through the organic wetland soils. The average annual water budget was "based on the 3 years 197^ through 1976. Inflow was composed of direct precipitation (7 percent), surface-water inflow (U percent), and groundwater inflow (89 percent). Outflow from the wetland was composed of streamflow (92 percent) and evapotranspiration (8 percent). Some ground water flowed beneath the wetland tut did not discharge within the study area. Groundwater inflow contained 95 percent of the nitrogen that entered the wetland, precipitation contained 2 percent, and surface-water inflow contained 3-percent. Sixty-six percent of the phosphorus input was from ground water, 31 percent from surface water, and 3 percent from precipitation. The wetland retained 21 percent of the nitrogen and 7 percent of the phosphorus entering it. It also retained 80 percent of the sediment that entered it.

No abstract