Effects of Land Use on Water Resources Quality
Michael A. Miller
Wisconsin Department of Natural Resources,
101 S. Webster St.
Madison, WI 53703
MichaelA.miller@wisconsin.gov
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 (municipal or industrial-waste dischargers), poor land
management, water use, and polluted run-off 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 stable 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.
Velocity
High / low-flow
Extremes
Temperature
Turbidity
Toxics
Flow
Regime
Nutrients
Base-flow
Volume
Nutrients
Water
Quality
Seasonal
Cycles
Energy
Relationships
Organic
Material
Dissolved
Oxygen
Organic
Material
Water
Resource
Integrity
Stream
Meander
Riparian
Vegetation
Gradient
Habitat
Structure
Current
Sunlight
Primary
Production
Instream
Substrate
Bank
Stability
Stream
Width / Depth
Land Use Affects on Water Resources
1
Flow 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 effect 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 particulatebound 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 Affects on Water Resources
2
Energy 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 Integrity of Water Resources.
To maintain optimal flow regimes, land management practices that improve the ability of
watersheds to infiltrate and slowly release precipitation will reduce the duration and intensity of
flooding as well as low flow periods. Protection of wetland and ground water recharge areas,
minimization of the amount of impervious surfaces in riparian corridors, and protection or
enhancement of riparian buffer vegetation is extremely important. Cropland soil conservation
practices such as minimum tillage, strip and contour cropping, grassed waterways, filter strips, water
detention basins, and terraces reduce precipitation runoff and increase water infiltration into the soil,
thus promoting ground water recharge. Discouraging stream channelization in favor of land-based
surface runoff management also helps maintain diversity of stream habitat and optimal flow regimes.
To protect water quality, soil conservation practices such as minimum tillage, contour plowing,
strip cropping, grassed waterways, filter strips, and adequate riparian buffers will reduce the delivery
of soil, nutrients, and other pollutants to streams. Improved animal waste management practices
such as barnyard runoff controls, manure storage, and incorporation of manure and pesticides into
the soil also reduce the amount of nutrients and toxics reaching waterways. Reductions in suspended
sediment and increases in riparian buffer vegetation reduce solar heating of water which allows the
water to hold more dissolved oxygen. Proper manure and chemical fertilizer application rates,
diversion of rain water away from barnyards and feedlots, establishment of riparian buffers, and
limiting livestock access to streams also reduce excess nutrient transport to surface waters.
To protect stream and river riparian habitat, stream channelization should be discouraged.
Controlling stream bank and upland erosion will reduce soil delivery to surface waters. Control of
upland runoff dampens high flows which reduces stream bank erosion. With reduced sediment
inputs, streams with extensive sedimentation may scour down to the former stream bed, increasing
stream depth and substrate diversity. Rotational grazing and using fencing to limit livestock access
to streams for watering and stream crossing only, allows streams and rivers to maintain or reestablish
riparian and instream habitat. Stream channels narrow as riparian buffer vegetation is reestablished
resulting in increased stream flow velocity and depth which improves biological integrity by
scouring sediment deposits, decreasing solar heating, increasing aeration, and reestablishing instream
and stream bank cover.
To improve energy relationships, it is important to maintain or enhance riparian buffer vegetation
(which provides food for aquatic invertebrates) by not cropping, mowing, or paving riparian land and
Land Use Affects on Water Resources
3
by limiting livestock access to streams and rivers with fencing or rotational grazing. Reduction of
soil delivery to streams through soil conservation practices and riparian buffers also reduces
sedimentation of stream bottoms and reduces the associated losses of stream bottom plants and
animals.
Summary of the Determinants of the Biological Integrity of Water Resources.
Factors that significantly influence the biological integrity of water resources, land use practices that
reduce biological integrity, and land management practices that lessen land use impacts have been
presented. Traditional soil and water conservation practices developed to maintain agricultural
productivity help protect water resources, but additional land management practices need to be
employed. The various land management practices presented for protecting the biological integrity
of surface waters serve to maintain optimal stream flow, water quality, habitat diversity, and stream
productivity.
Land Use Affects on Water Resources
4