ANR-1162 THE ALABAMA WATERSHED DEMONSTRATION PROJECT: WATER QUALITY AND GEOGRAPHIC INFORMATION SYSTEMS
ANR-1162, New Oct 1999. Kathryn M. Flynn,
Extension Forester and Coordinator, Associate Professor, Forestry, Auburn University
The Alabama Watershed Demonstration Project:
Water Quality and Geographic Information Systems |
Introduction
This publication provides information about new approaches being used
to link land use patterns and water quality. Areas discussed include the
following:
- Water quality parameters that are commonly used to evaluate stream
water quality
- Geographic Information Systems (GIS) that can be used in the management
of natural resources
- Water quality data incorporation into GIS to evaluate land use impacts
on water quality
- Information about a research project that took place in South Alabama
from 1996 to 1998
This study serves to illustrate how water chemistry data and GIS can
be used to examine the impact of land use on water quality, especially with
respect to nonpoint source (NPS) pollution at the watershed level.
The term watershed refers to the land area that feeds a particular body
of water. An extreme example of a watershed is the Mississippi River. The
watershed or drainage basin of the Mississippi actually encompasses most
of the middle United States and a portion of Canada. Obviously, identifying
and minimizing the causes of NPS pollution within such a large area presents
tremendous logistical problems. For this reason, large watersheds are divided
into smaller areas, called subwatersheds, for management purposes. These
subwatersheds are delineated or identified by determining the drainage area
for a tributary of the larger system. It is possible to identify all of
the subwatersheds of a river. The use of these smaller units to assess water
quality increases the likelihood of identifying most of the sources of NPS
pollution and allows easier determination of the dominant contributors to
water pollution.
Solving the problems associated with NPS pollution presents serious challenges.
NPS pollution does not originate from a single, easily identifiable source
but rather it originates from diverse sources. An understanding of how water
quality is affected by land use and the type of cover present in a given
area is vitally important. Most people manage land in small units such as
a field, a stand of trees, a pasture, or a home site. The activities that
take place in these small areas usually have only minimal impact on local
water quality. However, when the effects of management activities on each
small area within a watershed are added together, the impact can be substantial.
This added-together effect is referred to as cumulative. Addressing cumulative
impacts is generally much more complicated than addressing the problems
of a single water pollution source.
Making management decisions to avoid problems associated with cumulative
impacts is extremely difficult. One of the primary reasons for this is that
the people making the decisions resulting in these small impacts often do
so without knowledge of other land management decisions being made in the
same watershed by other people. Even if a single landowner is making all
of the decisions on several adjacent "chunks" of land within a
single watershed, it is often difficult to predict the effect these activities
will have on overall water quality (or, for that matter, on other characteristics
of the watershed). New technological tools are making it easier to evaluate
these impacts and even to predict how certain activities will impact the
integrity of an area.
Measurements of Stream Water Quality
Our concern about, and knowledge of, water quality has increased dramatically
over the last 30 years. In that time, a number of water quality parameters
(characteristics) have been found to be useful indicators of "good"
or "bad" water quality. The labels "good" or "bad"
are usually assigned relative to a defined use such as drinking water, swimming,
or fishing. The Environmental Protection Agency (EPA) has established limits
for specific water quality parameters that are used to determine how clean
or dirty (degraded) a body of water is.
Some commonly measured water quality parameters include the pH (acidity/alkalinity)
of the water, the amount of total dissolved solids (TDS), and the amount
of total suspended solids (TSS). The total organic carbon (TOC) content
of the water and the concentration of nutrients such as potassium, phosphorus,
and nitrogen are also important variables. Each of these parameters can
be used to evaluate the status of water quality.
Evaluating water quality in a meaningful way is a complex issue. A single
sample from a specific water body can only tell you what the water quality
is at that particular time. This is true because of changes that occur in
water chemistry as water moves downstream, as rainfall and runoff enter
the water body, as evaporation from the soil surface occurs, and as transpiration
(the uptake and loss of water) by plants takes place. In order to develop
an accurate understanding of how clean or dirty a particular body of water
is, especially flowing streams and rivers, it is necessary to collect and
analyze water samples from the same location over time.
Another important factor in evaluating water quality data is the need
for measurement of the flow rate and the dimensions of a stream or river.
This allows you to determine the actual volume of water in the stream, how
rapidly it is moving and the discharge (the amount of water moving through
the stream over time). The actual quantity (load) of nutrients, sediment,
or other materials that is being carried by the stream or river each day
can then be calculated. If you know the size of the watershed, you can express
the load or quantity of a pollutant in the stream each day on a per acre
basis.
The natural characteristics of a watershed will determine the "normal"
condition of each water quality parameter. For example, watersheds with
low nutrient (infertile) soils having a high percentage of sand would be
expected to have stream water that is low in nutrients and low in total
suspended sediments. The sources of nutrients and fine-grained sediments
are limited under these conditions. Therefore, water quality is dependent,
to a large extent, on what takes place within the watershed. These activities
or events are what will alter the natural condition of the water. These
can be natural events such as wildfires, storms, changes in vegetation over
time, or man-induced events such as clearing, planting, and fertilizing.
It is important to note that not all natural waters (waters that are
not affected by human activities) have what would be classified as perfect
water quality. For example, some watersheds have soils that contain high
quantities of salts or minerals or parent material beneath the soil that
generates waters having very acidic or very alkaline pH. These natural characteristics
can make the water undrinkable or unpleasant for bathing or swimming but
the water is still considered normal for that particular area.
Each watershed has, among other things, topographic variation as well
as a variety of soil types and land use categories. The size of watersheds
varies dramatically as do the land use/land cover types occupying the landscape.
The quality of water at the mouth of a stream or river can be viewed as
a reflection of land use impacts within the watershed. The condition of
the water leaving the watershed is determined by the land uses, the types
of land over which runoff moves, the slope, parent material, biological
characteristics, and size of the watershed or drainage basin. Other factors
may also affect water quality.
Even though our knowledge and understanding of water quality has increased
over the last 30 years we still have a lot to learn. It is for this reason
that researchers continue to examine water quality and to look for new tools
with which to acquire a greater understanding of water quality. These efforts
will allow us to deal with existing water quality problems and to grapple
with new problems that continue to emerge. Examples of some of the complicated
water quality issues we face today include the increasing emphasis on intensive
land management, population growth, urban sprawl, potential climate changes,
increasing demand for clean water, and even the failure of septic systems.
Geographic Information Systems
Geographic Information Systems (GIS) is a computer tool now used to address
new and existing water quality problems. GIS uses a computer database to
store large quantities of spatial and temporal data. This allows the integration
of diverse types of information into a form that makes it possible to consider
different approaches to land management and environmental problems before
making management decisions. Spatial data is information that describes
how a specific feature is located or distributed in space. This type of
information can include watershed boundaries, slope, aspect, contour, soil
type, stream location, and land use/land cover. The use of GIS allows people
to process and evaluate these data. Without this type of computer tool,
such large amounts of data would overwhelm us.
Information stored in a GIS will come from a variety of sources. The
greater the quantity and quality of the information, the more complete the
GIS database will be. Sources of information include satellite images, aerial
photographs, Soil Conservation Service (SCS) and Natural Resource Conservation
Service (NRCS) soil maps, United States Geological Survey (USGS) topographic
maps, and survey maps.
Data is entered in the GIS database and the software builds a map of
the area. Actually, the computer builds what are called layers--separate
maps of the same area, each of which contains different sets of information
or themes. These maps are built by providing the computer with geographic
coordinates identifying the location of various features (spatial data).
GIS maps can contain information on ownership boundaries and the location
of man-made features such as roads, houses, and developed areas. They may
also contain information on soil type, slope, land use, land cover, and
the location of streams, rivers, lakes, and other water. Land use information
from different points in time is entered into the database. This temporal
data allows the GIS user to track changes in land use that have occurred
over time (temporal changes). Information on water quality can be entered
into the database, and, if the location of sample sites is known, these
data can be linked to specific locations. This allows the GIS user to make
connections between the type of land use and various physical properties
and the quality of water within the area of interest.
The Global Positioning System (GPS) is another technological advance
making it easier for land managers to develop a GIS database. GPS units
allow people to determine the geographic coordinates of landscape features.
For example, GPS units can be used to locate management units (pastures,
fields, stands) on a map more accurately and easily than before. Today,
farmers with access to a GPS unit can actually mount it on a tractor and
accurately map the location and dimensions of their fields; foresters can
use hand-held units to map the location of stands. GPS coordinates can also
be taken at the site where water quality samples are collected. These coordinates
can then be entered into the GIS database allowing these features to be
positioned on the watershed map.
A GIS database is used to track actual changes taking place over time
within a watershed. Aerial photographs and other spatial data generated
at different points in time (some of it mapped using GPS units) are used
to measure changes in land use, land cover, density of roads, houses, presence
or absence of buffer zones around streams, and other items of interest.
As this information is collected and evaluated, it is possible to make connections
between water quality data (if available) and the changes in land use that
have occurred in an area. Ideally, there will be water quality data available
from several different points in time.
Advances in technology offer land managers the potential to look at the
land and management activities on that land in ways that have never been
readily available. GPS units are now being sold to individuals (although
a good one is still expensive) and GIS software is available that can be
used on personal computers. In time, the availability of these technologies
should improve and the cost decrease. In addition, these technologies are
becoming more user friendly all the time.
The Alabama Watershed Demonstration Project
Following is information on the Alabama Watershed Demonstration Project
that illustrates application of GIS principles and technologies. The research,
funded by a number of forest industry companies and federal agencies, was
conducted by Drs. Graeme Lockaby, Larry Teeter, and Mark MacKenzie. Dr.
Prakash Basnyat and Ms. Ashley Hamilton also participated in the study.
This research examined sources of NPS pollution in small watersheds of the
Alabama Coastal Plain region and related multiple land uses to nonpoint
sources of pollution at the watershed level. Two other Extension publications
describe additional information acquired during this study. They are ANR-1150,
"The Alabama Watershed Demonstration Project: Water Quality, Nonpoint
Source Pollution, and BMPs--What Landowners Know," and ANR-1167, "The
Alabama Watershed Demonstration Project: Biotic Indicators of Water Quality."
A GIS database was developed as part of this project. Land use/land cover
information was generated using satellite imagery and aerial photography
and verified with spot visits to sites within the watershed. The land use/land
cover information was incorporated as part of the GIS database. The watershed
was found to be fairly homogenous in terms of land use. Although forest
was the dominant land cover type (85 percent), the watershed also contained
agricultural and urban areas. Agricultural uses included pastureland for
beef and dairy cattle, row crops (cotton, corn, tobacco, wheat, and soybeans)
and livestock production (poultry and pork). A variety of silvicultural
practices were found to occur within the area, including extensive loblolly
pine plantations, thinning and clearcutting harvesting regimes, forest regeneration
practices (natural and artificial), and fertilization (agriculture and forestry
related). Most of the forested area is devoted to industrial silviculture
although privately owned forest land and natural stands of unmanaged Coastal
Plain forests are also present.
The land use/land cover types identified in this study included pine
(28.3 percent), mixed pine/hardwood (46 percent), forest regeneration (8.6
percent), clearcut, (2 percent), row crop (5 percent), pasture (9 percent),
urban (0.2 percent), and water (0.4 percent). The GIS database was used
to calculate the total area for each subwatershed and to determine the percentage
of area within each subwatershed devoted to each of the eight land use types.
In addition, the number of poultry houses, residential dwellings, and stream-road
crossings was determined. The subwatersheds included in the study were found
to range from 546 to 4,216 hectares in total size.
Fifteen watersheds were selec ted for intensive water sampling. Sites
were chosen to provide a variety of land uses for evaluation. An example
of the sampling design appears in Figure 1. Samples were collected upstream
from where a smaller stream flowed into a larger stream. This allowed the
researchers to determine the water quality associated with management of
small areas and made it easier to link the land use/land cover information
to water quality data. Samples were collected at the same site within each
of the 15 watersheds every two weeks during the winter and early spring
of 1997 and 1998. All of the streams had moving water and contained water
all year (perennial streams). The majority fell within the Sepulga River
Basin.
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Figure 1. Watershed sampling sites |
The GIS database was used to delineate the area within each subwatershed
that would directly contribute water to a stream. The land use/land cover
information was then placed over this contributing zone that consists of
only a portion of each subwatershed. This allowed any differences in water
quality between the subwatersheds to be related to actual land use/land
cover differences. Basically, if you collect samples from the mouth of each
stream (Figure 1) and you find that nitrate concentrations are highest at
Point B, intermediate at Point A, and lowest at Point C, the next logical
step is to determine what is different about the areas feeding these three
streams.
This research suggests that forests act as sinks for nitrate--that is,
they take up nitrate. In fact, as forested area within a contributing zone
increased, downstream nitrate levels decreased. The forest regeneration
and agricultural lands were identified as sources of nitrate. This is probably
due to fertilization practices. The data indicate that intact streamside
management zones (SMZs) are very important for maintaining water quality.
The study also found that none of the water chemistry variables measured
exceeded Environmental Protection Agency (EPA) allowable limits. This indicates
that water quality within the study area was good during the period in which
samples were collected.
According to the researchers, maintaining water quality within the Sepulga
River Basin will be dependent upon maintenance of adequate SMZs and the
use of best management practices (BMPs). This is particularly true for the
smaller streams within the watershed because these are the primary sources
of downstream pollution. The methods of evaluating water quality and relating
it to land use/land cover that were developed during this study make it
possible to calculate the buffer size required to maintain target levels
of water quality.
Obviously, our ability to evaluate water quality and to manage land in
such a way that water quality is maintained has improved dramatically in
the last three decades. As technological advances continue and the tools
become easier to use, the activities described in this publication will
become commonplace. Continued efforts by researchers will ensure that we
have the potential to maintain a safe, reliable, and plentiful supply of
water for drinking, recreation, and wildlife. Ensuring that this potential
is realized will require the efforts of all land managers.
For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information.
Issued in furtherance of Cooperative Extension work in agriculture and
home economics, Acts of May 8 and June 30, 1914, and other related
acts, in cooperation with the U.S. Department of Agriculture. The Alabama
Cooperative Extension System (Alabama A&M University and Auburn
University) offers educational programs, materials, and equal
opportunity employment to all people without regard to race, color,
national origin, religion, sex, age, veteran status, or disability.
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