With sections by Faith A. Fitzpatrick, David W. Hall, Charles A. Peters, Stephen J. Rheaume, Dale M. Robertson, David A. Saad, Barbara C. Scudder, and Daniel J. Sullivan
The morphological and geochemical characteristics of streams as well as ground water movement, storage, and chemistry are controlled by consolidated and unconsolidated rock lithologies and structure in the WMIC. Consolidated rocks in the basin include Precambrian crystalline rock, Cambrian sandstones, and Ordovician dolomite, sandstone, and shale, Silurian dolomite, and Devonian dolomite. These units are overlain by Pleistocene glacial deposits, outwash, and glacio-lacustrine deposits, and Holocene alluvium, colluvium, lacustrine, and eolian deposits. Soils are developed in the glacial deposits and alluvium, or bedrock residuum where the unconsolidated deposits are thin or missing. The depth to the bedrock surface is highly variable and ranges from 0 to greater than 100 ft. below land surface.
Landforms in the WMIC are controlled by underlying bedrock lithology and structure, which have been modified by pleistocene glacial processes. They consist of erosion-resistant bedrock uplands, glacial terminal and recessional moraines, ground moraines, drumlin fields, outwash plains and valleys, dunes, and ancient lake beds. These landforms influence the patterns of drainages and hydraulic characteristics of surface- and ground-water flow.
Four principle aquifers underlying the WMIC study unit: the Sand and Gravel aquifer, Silurian Dolomite aquifer, Sandstone aquifer, and the Basement Complex. These four aquifers have a wide range of water-yields and hydraulic and geologic characteristics.
The WMIC study unit has temperate, continental climate associate with a large annual range in air temperature and little monthly variation in precipitation. The study unit is also located in the mid-latitude belt, marked by large seasonal changes in the solar-zenith angle and day length, which together produce a significant north-south temperature gradient. The north-south gradient and the seasonal range in temperature, however, are modified by the neighboring Laurentian Great Lakes. Mean annual precipitation ranges from approximately 28 to 34 in. per year across the study unit. Evaporation plus evapotranspiration varies from less than 18 in. per year in the north to over 24 in. in the southern regions. Runoff rates vary form approximately 8 in. per year in the southern part of the WMIC to 15 in. per year in the northern part.
The WMIC is composed of four ecoregions: Northern Lakes and Forests, North Central Hardwood Forests, Southeastern Wisconsin Till Plains, and Central Corn Belt Plains. The major plant groups include mixed coniferous-deciduous forest, deciduous forest, upland prairie and brush, boreal forest, and wetland vegetation. Ten federally endangered or threatened species of plants and animals may be found in the WMIC.
Forested land accounts for approximately 40 percent of the WMIC, agricultural land accounts for approximately 37 percent, wetlands account for approximately 15 percent, and about 3 percent of the study unit has the classification of `water'. Several thousand lakes, ranging in size from 0.5 to 138,000 acres, exist within the study unit and account for 3 percent of the areas.
About 96 percent (4,654 out of 4,842 Mgal/d) of the total water used in the study unit, for all withdrawal water-use categories combined, comes from surface-water. The largest single use of surface water (88 percent) is for the generation of thermoelectric power. The next largest use of surface water is public supple, which accounts for about 6.5 percent of total surface water use. About 4 percent (188 Mgal/d) of the water used comes from ground water.
The quality of surface water in the WMIC study unit varies widely, from nearly pristine to highly contaminated. The sparsely populated, heavily forested regions in the northern and northwestern portions of the WMIC generally are characterized by better water quality than those in the southern and southeastern areas. The southern portion of the study unit is more densely populated than the northern areas, with correspondingly higher amounts of industrial and municipal waste discharged to surface waters. In addition, agricultural activities account for much larger percentage of land use in the south, and contribute a concomitantly larger portion of nonpoint-source pollution to surface waters.
During low-flow conditions, most of the surface water in the study unit is of the calcium-magnesium-bicarbonate type. Concentrations of other ions, including sodium, sulfate, and chloride, are generally lowest in the northern and northwestern portions of the study unit. In general, concentrations of major ions are lower in lower-order streams. Concentrations of sodium, sulfate, and chloride are higher in urban areas, and sometimes vary seasonally.
The natural ground-water quality varies greatly in the WMIC study unit. The primary reason for this is the variety of materials that make up the aquifers. The dominant ions in the ground water are usually calcium, magnesium, and bicarbonate. Most of the cities and villages get all or part of their drinking water from ground water sources. Many factors, both natural and man-made, can adversely affect the quality of ground water and result in restrictions on its use. The most common natural constituents that affect ground water quality are hardness, iron, radon gas, dissolved solids, manganese, sulfate, and radium.
The streams in the WMIC are home to wide variety of fish species an communities ranging from cold-water fisheries characterized by species such as brook trout and sculpin to warm-water fisheries dominated by species such as bass and sunfish. Currently 24 families of the fishes that represent 112 species ar known to inhabit the inland streams in Wisconsin. About 51 families of macrophytes may be found in streams and rivers of the WMIC.
Human activities contribute numerous contaminants to surface and ground water in the WMIC through both point and nonpoint source pathways. Anthropogenic contaminants present in the western Lake Michigan drainage systems include polychloinated biphenyls (PCB's), pesticides, other synthetic organic compounds, and trace elements (including metals) in bottom sediments of rivers and harbors. Point sources of pollution in the study unit include mining operations, paper mills and other industrial activities, unlined agricultural manure-storage facilities, barnyards, and large point-source discharges of wastes from sewage plants and industrial operations.
Most major waterways in the WMIC are also adversely affected by nonpoint-source pollutants that enter the waterways in runoff, from the atmosphere, and from contaminated sediments. Nonpoint-source sediment loading to streams in the WMIC is frequently caused by erosion associated with logging operations in the northern part of the study unit and by agricultural activities in the south. Pesticide (herbicide, fungicide, insecticide, and rodenticide) applications to forested lands, farm fields, residential land, urban areas, and golf courses have caused many pesticides and pesticide degradation products to be present in study-unit waters. In addition to atrazine and its metabolites, pesticides frequently detected in water samples collected in agricultural areas include alachlor, metolachlor, and cyanazine.
The WMIC study unit was subdivided into "relatively homogeneous units" (RHUs) to facilitate identification of relations between physiographic features and water quality in the predominant land-use areas of each basin. Land use and cover, surficial deposit, and bedrock type were selected as being the most useful factors to define spatial variations in water-quality of the WMIC area. Therefore, unique combinations of these three factors were used to divide the study unit into 28 RHUs.