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<br /> <br />K <br /> <br />Field Studies of Glacial and Dune Terrain <br /> <br /> <br />Glacial terrain and dune terrain are characterized by <br />land-surface depressions, many of which contain lakes and <br />wetlands. Although much of the glacial terrain covering the <br />north-central United States (see index map) has low topo- <br />graphic relief, neighboring lakes and wetlands are present at a <br />sufficiently wide range of altitudes to result in many variations <br />in how they interact with ground water, as evidenced by the <br />following examples. <br />The Cottonwood Lake area, near Jamestown. North <br />Dakota. is within the prairie-pothole region of North America. <br />The hydrologic functions of these small depressional wetlands <br />are highly variable in space and time. With respect to spatial <br /> <br />Cottonwood Lake, Nevins Lake, <br />North Dakota Michigan <br /> <br /> <br />\ <br /> <br />Island lake, Nebraska <br /> <br />EXPLANATION <br /> <br />~ SEMIPERMANENT WETLAND <br /> <br />~ SEASONAL WETLAND <br /> <br />-195- WATER TABLE CONTOUR-Number <br />is in feet greater than 1,640 feet <br />above sea level. Contour interval <br />5 feet <br /> <br /> <br />+ <br /> <br />TRANSIENT GROUND-WATER <br />DIVIDE <br /> <br />--+- DIRECTION OF SEEPAGE <br /> <br />variation, some wetlands recharge ground water, some <br />receive ground~water inflow and have outflow to ground water, <br />and some receive ground-water discharge. Wetland Pl <br />provides an example of how their functions can vary in time. <br />The wetland receives ground-water discharge most of the <br />time; however, transpiration of ground water by plants <br />around the perimeter of the wetland can cause water to <br />seep from the wetland. Seepage from wetlands commonly <br />is assumed to be ground-water recharge, but in cases like <br />Wetland Pl. the water is actually lost to transpiration. This <br />process results in depressions in the water table around <br />the perimeter of the wetland at certain times, as shown in <br /> <br />u, <br /> <br /> <br />Cottonwood Lake area, North Dakota. (Photograph by <br />Thomas Winter.) <br /> <br />99006' <br /> <br />\0 <br /> <br />P2 <br /> <br />.- <br /> <br />Base from U.S. Geological Survey <br /> <br />o <br />, <br /> <br />300 600 FEET <br />I I <br /> <br />Ffgure K-1. Transpiration directly from ground water causes cones of depression to form by late summer around the <br />perimeter of prairie pothole Wetland P1 in the Cottonwood Lake area in North Dakota. (Modified from Winter. T. C., and <br />Rosenberry, D.o., 1995, The interaction of ground water with prairie pothole wetlands in the Cottonwood Lake area, east- <br />central North Dakota. 1979-1990: Wetlands. v. 15, no. 3, p. 193-211.) (Used with permission.) <br /> <br />, <br /> <br />48 <br />