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VII. Causes Of Water Pollution
Pollution is an alteration of the physical, chemical, biological, bacteriological, or radiological
properties of water that result in an impairment of designated uses. In assessing the causes of
pollution in streams and lakes, the Division follows the guidance provided by EPA. In order
to help standardize the naming of pollutants, EPA’s Assessment Database (ADB) has a menu
of potential pollutants that can be selected for impaired streams. Additionally, states can
create subcategories. For example, “nutrients” is an EPA category in the ADB. Tennessee
has added “nitrate+nitrite” and “total phosphorus” as sub-categories.
A. Causes of Pollution in Streams and Rivers
Pollutants such as siltation, suspended solids, nutrients, organic enrichment, and low
dissolved oxygen are the leading causes of impairment in Tennessee streams. Silt and
suspended solids impact streams by eliminating habitat, blocking light penetration, and
smothering aquatic life. Organic enrichment caused by excessive nutrients or BOD
stimulates algae growth which causes wide fluctuations in dissolved oxygen levels (Figure
11). These factors alter biological communities to favor species tolerant for these
conditions. The public’s uses of these streams are impacted when biological integrity
goals are not met. Other common pollutants in streams include toxic substances, bacteria,
flow alteration and habitat destruction.
Habitat
Alteration
25.1%
Pathogens
19.6%
Nutrients
9.1%
Siltation
27.9%
Other
3.1%
Organics
2.2%
Flow
Alteration
1.5%
Metals
2.5%
Org. Enr/DO
6.9%
pH
2.2%
Figure 11: Relative Impacts of Pollution in
Assessed Rivers and Streams
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1. Siltation
The most frequently cited pollutant in Tennessee is siltation, impacting over 4,860
miles of streams. Siltation is generally associated with land disturbing activities such
as agriculture and construction. Some of the significant economic impacts caused by
siltation are increased water tre