Effects of Land Use on Water Resource Quality Michael A. Miller Wisconsin Department of Natural Resources, 101 S. Webster St. Madison, WI 53703 There is an intimate relationship between the land and water resources. Protecting ground water, lakes, rivers, streams, and wetlands requires wise land use. Human population growth and changes in land use increasingly impact aquatic environments. This paper provides a brief overview of some of the affects that land uses have on water resource quality, and reports on ways land management practices can protect our water resources. With greater control of point source pollution (e.g. smoke stacks or discharge pipes), poor land management, water use, and nonpoint source pollution remain the most significant threats to our water resources. Control of cropland and construction site erosion, urban runoff, and management of livestock manure, agrochemicals, and industrial waste are needed to maintain water resource quality. Protection of riparian areas and wetlands also benefit water resources and help conserve ecologically important habitats. Water conservation and promoting the infiltration of rainfall and snowmelt helps maintain adequate stream flows. Major determinants of the biological integrity (health) of water resources are illustrated in the figure below, and each is described in the following text. Fl owRegi meHabi t atStructureWat erQualityEner gyRelationshipsWat erResourceIntegrityVe l o ci tyBase-f l owVo l u meHigh / l ow-f l owExt r emesTemperat ur eTurbidityNut r i ent sDissolvedOxygenOrgani cMat erialToxicsInstreamSubst r at eCurrentBankStabilityRi par ianVegetationGradi entNut r i ent sOrgani cMat erialSunl i ghtSeasonalCy cl e sSt r eamMeanderPr i ma ryProduct ionSt r eamWidth / Depth Land Use Effects on Water Resources 1Flow regime (the quantity of water in a stream and how it changes over time) is a major determinant of the biological integrity of stream and river resources. Land cover has a significant affect on the water cycle, which in turn affects stream and river flow regimes. The formation of streams and rivers in post-glacial Wisconsin was strongly influenced by the presence of watersheds dominated by prairies and forests. As watershed landscapes are increasingly modified for agricultural and urban uses the dynamics of the water cycle are altered. Decreasing the amount of plant cover (particularly perennial vegetation) in watersheds reduces the quantity of precipitation stored in vegetation and the amount of rainfall returned to the atmosphere via evapotranspiration, which increases surface runoff and reduces water infiltration. Increasing proportions of impervious surfaces (e.g. parking lots, roads, and rooftops) within watersheds also increases surface runoff and reduces rainfall and snowmelt infiltration to the watertable. Decreased infiltration lowers the watertable thereby reducing groundwater discharge via springs and seeps, causing some surface waters to flow intermittently. Changes in flow regime alter the physical and biological characteristics of aquatic communities, as stream morphology (shape) and some plant and animal communities that evolved under post-glacial conditions cannot withstand changes in the historic watercycle. Water quality is another major determinant of the integrity of water resources that is strongly influenced by land use. Nonpoint source pollution from rural and urban land use activities reduces water quality by adding sediment, nutrients, toxics, organic materials, and pathogens to surface and ground waters. Inputs of phosphorus from manure and commercial fertilizers may cause an excess of nutrients (eutrophication) in streams, rivers, or lakes, which often results in excessive aquatic plant growth and algal blooms. High nitrate levels resulting from excessive or improperly applied manure and chemical fertilizers may leach into the ground water reducing drinking water quality. By volume, soil is the greatest pollutant entering Wisconsin's waterways. Sediment covers important stream and river-bottom habitat, scours aquatic life, increases turbidity, and delivers particulate-bound nutrients, toxics, and pathogens to water resources. Increased surface runoff, water turbidity, and reductions in riparian vegetation all act to warm surface waters. Warming and eutrophication of surface waters reduces the amount of dissolved oxygen (DO) in water. DO is an important regulator of aquatic life and a good indicator of stream health. Riparian and instream habitat quality are major determinants of water resource quality that are influenced by land use. Reductions in riparian vegetation by cropping, grazing, and urban development affects aquatic and terrestrial habitat and the animal communities that occur there. Increased surface runoff erodes stream banks reducing riparian habitat quality and changes stream channel shape (morphology). Straightening of meandering stream channels of rural and urban streams to reduce flooding or to accelerate crop field drying, changes stream flow velocity and greatly reduces the quantity of instream and riparian habitat. Sedimentation reduces the quality and quantity of instream habitat for insects and fish by covering a diverse stream bottom with a uniform layer of sediment. The unstable substrate resulting from shifting bottom sediment inhibits the establishment of rooted aquatic plants and smothers stream bottom animals. Land Use Effects on Water Resources 2Energy relationships are also major determinants of water resource quality that are influenced by land use. Streams and rivers receive energy inputs from solar radiation (primary production) and from allocthonous inputs (leaves, grasses, twigs that wash into streams). Headwater streams generally have a more intimate relationship with the land than higher order (larger) streams, and their productivity is more significantly influenced by reductions in organic inputs, loss of riparian vegetation, or increases in stream siltation. Reductions in organic inputs resulting from riparian habitat loss or sedimentation can significantly reduce stream productivity as aquatic insects and other stream bottom invertebrates depend on plant material as a primary food source. When the productivity of these organisms are reduced, animals higher in the food chain such as fish and fish predators are also affected. Land Management Practices that Protect the Biological