13 Water Quality
Jeny C. Ritchie l and Frank R. Schiebe 2
I USDA-ARS Hydrology Laboratory, BARC-West, Bldg-007, Beltsville, MD 20705 USA
2 SST Development Group Inc., 824 North Country Club Road, Stillwater, OK 74075 USA
13.1 Introduction
Water quality is a general tenn used to describe the physical, chemical, thennal,
and/or biological properties of water. We often define it in tenus of human usage for
consumption, recreation, and aesthetics. In broader tenus the quality of water affects
all components of the aquatic ecosystem. The quality of water suitable and desirable
for use by one organism may be completely unsuitable for another. Thus, water
quality is a parameter that cannot be defined easily nor can standards be set that meet
all uses and user needs. For example, physical, chemical, and biological parameters
of water that are suitable for human consumption are quite different from those
parameters suitable for a farmer irrigating a crop.
We usually defme substances affecting water quality as coming from either point
or nonpoint sources. Point sources are associated with substances that can be traced
to a single source, such as a pipe or a ditch. Once a point source has been identified,
managing the efiluent from the point source requires a commitment of time and
resources. Nonpoint substances are more diffuse and associated with the landscape
and its response to water movement and land use. All human and natural activities
contribute nonpoint substances to runoff water thus affecting its quality. For example,
organic substances contained in runoff from forested lands can be considered detrimental to the hydrolimitic waters of receiving lakes if an oxygen demand is created
that depletes oxygen from the water body that make it unsuitable for fish and other
organisms. Agriculture, industrial, and urban areas are all major anthropogenic
sources of nonpoint substances. These substances are considered pollutants when they
are detrimental to the existing water quality. Detennining source areas for nonpoint
pollutant is a major concern and management problem. Once identified and defined,
controlling nonpoint sources is a major management concern because the diffuse
nature of the source makes them difficult to control. Polluting substances that may
lead to deterioration of water quality (eutrophication) affects most freshwater and
estuarine ecosystems in the world (Dekker et al. 1995). In the United States, off-site
downstream deterioration of water quality has been estimated to cost billions of
dollars per year. Timing, amount, and sources of pollutant transfer to water bodies are
generally not fully understood by water resource managers responsible for developing
strategies to control these pollutants. Standards have been established in many
G. A. Schultz et al. (eds.), Remote Sensing in Hydrology and Water Management
© Springer-Verlag Berlin Heidelberg 2000
Jeny C. Ritchie l and Frank R. Schiebe 2
I USDA-ARS Hydrology Laboratory, BARC-West, Bldg-007, Beltsville, MD 20705 USA
2 SST Development Group Inc., 824 North Country Club Road, Stillwater, OK 74075 USA
13.1 Introduction
Water quality is a general tenn used to describe the physical, chemical, thennal,
and/or biological properties of water. We often define it in tenus of human usage for
consumption, recreation, and aesthetics. In broader tenus the quality of water affects
all components of the aquatic ecosystem. The quality of water suitable and desirable
for use by one organism may be completely unsuitable for another. Thus, water
quality is a parameter that cannot be defined easily nor can standards be set that meet
all uses and user needs. For example, physical, chemical, and biological parameters
of water that are suitable for human consumption are quite different from those
parameters suitable for a farmer irrigating a crop.
We usually defme substances affecting water quality as coming from either point
or nonpoint sources. Point sources are associated with substances that can be traced
to a single source, such as a pipe or a ditch. Once a point source has been identified,
managing the efiluent from the point source requires a commitment of time and
resources. Nonpoint substances are more diffuse and associated with the landscape
and its response to water movement and land use. All human and natural activities
contribute nonpoint substances to runoff water thus affecting its quality. For example,
organic substances contained in runoff from forested lands can be considered detrimental to the hydrolimitic waters of receiving lakes if an oxygen demand is created
that depletes oxygen from the water body that make it unsuitable for fish and other
organisms. Agriculture, industrial, and urban areas are all major anthropogenic
sources of nonpoint substances. These substances are considered pollutants when they
are detrimental to the existing water quality. Detennining source areas for nonpoint
pollutant is a major concern and management problem. Once identified and defined,
controlling nonpoint sources is a major management concern because the diffuse
nature of the source makes them difficult to control. Polluting substances that may
lead to deterioration of water quality (eutrophication) affects most freshwater and
estuarine ecosystems in the world (Dekker et al. 1995). In the United States, off-site
downstream deterioration of water quality has been estimated to cost billions of
dollars per year. Timing, amount, and sources of pollutant transfer to water bodies are
generally not fully understood by water resource managers responsible for developing
strategies to control these pollutants. Standards have been established in many
G. A. Schultz et al. (eds.), Remote Sensing in Hydrology and Water Management
© Springer-Verlag Berlin Heidelberg 2000