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Threats to the Aquatic Fauna

Dams: Among the most damaging habitat alterations to rivers and creeks are dams. In the upper Coosa River basin, major impoundments are located in the Coosa River at the Alabama/Georgia border (Weiss Reservoir), Etowah River (Allatoona Reservoir), and Coosawattee River (Carters Reservoir). The vast majority of stream animals cannot adapt to impounded waters. Their ability to spawn, find food, shelter, and sometimes simply breathe is affected by impounded waters. Additionally, predatory sport fishes are often introduced and become abundant in these new habitats feeding on the non-game species that remain. Major downstream impacts from dams include temperature changes (affecting spawning timing), decreased dissolved oxygen levels (affecting respiratory functions), and wildly fluctuating water levels during electricity generation (scouring the channel, causing bank sloughing, and disrupting spawning). Additionally, migratory pathways for many fishes are blocked by impoundments.

Sedimentation: The most common impact to stream organisms is excess sediments washing into streams, eliminating habitat for many species. Agricultural fields, deforested slopes, construction sites, are common sources of sedimentation in the basin. Sedimentation and the resulting increased turbidity cause bottom habitats to be covered with fine sediments which reduces spawning sites, eliminates shelters and habitat, smothers gill-breathing organisms, and prevents site-feeding organisms (numerous fishes) from finding food. For these reasons and others, sedimentation is considered the number one pollutant of surface waters in the U.S.

Point-Source Releases: Most point-source problems have been corrected since the passage of the Clean Water Act in 1972. A “point-source” release refers to an industrial or other specific discharge that flows from a pipe directly into a stream. Some remaining point-source problems can be associated with wastewater treatment plants that do not properly remove all chlorines or other chemicals from the wastewater discharge. Chlorine can be one of the most lethal chemicals to stream animals when released at even low concentrations.

Non-Point-Source Runoff: In addition to sediment, various chemical compounds such as fertilizers, pesticides, and specific elements (heavy metals) can wash directly into streams and act as a pollutant. Chemicals used for industrial or mining processes (chlorine, and heavy metals), runoff from paved surfaces (nickel, zinc, and petroleum derivatives), and agricultural lands (nitrates, phosphorus, ammonia, and pesticides). Other non- point sources can come from atmospheric deposition (acid rain) and localized chemical spills at highway bridges and railroads. Depending on the chemical, various aspects of an organism’s life cycle can be disrupted. Early life stages of stream organisms (such as mussel glochidia and fish larvae) are particularly susceptible to certain pollutants. Ammonia in fertilizers and animal waste products can pose problems in some areas. Nutrient enrichment of the stream may result in explosive algal growth covering normally rocky bottoms and suffocating animals.

Stormwater Runoff: With increasing developments come problems associated with contaminated and rapid run-off of rainwater into streams. As development in a watershed increases, the conversion of a watershed from pervious surfaces (fields, forests, and gravel roads) to impervious surfaces (asphalt roads, roofs, and drainage tiles), causes rainwater to flow more quickly off of the land. During heavy rains this large rapid “pulse” of water can scour stream channels so severely, that only very large rocks and hard-packed clay surfaces remain. Channel scour eliminates habitat for all types of stream animals and contributes greatly to poor water quality. The process of channel scouring is one of the most severe habitat threats to our rivers and streams in the upper Coosa River basin.

Introduced Species: Exotic species introductions can have devastating impacts on native animals. Although some introduced species may not pose a significant threat to native species, many are a great threat to native wildlife, especially to small isolated populations. Unfortunately, many introduced species may not only become established but actually thrive in their new environment, out competing native species for space and food.  Introduced species typically have no biological controls, so their numbers can skyrocket in the absence of natural predators.

Text Authored by:
Paul D. Johnson - TNARI, Cohutta, GA
Robert S. Butler - USFWS, Asheville, NC

Text Edited by:
Elizabeth Reitz - GA MNH / UGA, Athens, GA

Poster Concept and Design:
Paul D. Johnson - Concept, TNARI, Cohutta, GA
Jeffrey C. Worley - Design, Tennessee Aquarium, Chattanooga, TN