Figure 1. Location of stream sections surveyed and tributary boundaries in the Metropolitan Atlanta area. (Urban area from Atlanta Regional Commission, 1990.)
As the population of the Chattahoochee River basin continues to grow, an increasing part of land is becoming urbanized. Streams that drain urban areas often have poor water quality resulting from contaminants in storm water and ground water, and have physical habitats degraded by sedimentation and stream bank erosion. Periodic sampling of water chemistry may not detect water-quality problems that occur infrequently, such as during storm runoff. Human induced changes in water quality or habitat can alter the number of individuals and species of fish present in streams. Because fish respond directly to the quality of water they inhabit, they are useful as indicators of the cumulative effects of water-quality problems that may not otherwise be detected. Although the small tributaries of the Chattahoochee River may not be important to people for fishing or recreation, the types of fish living in these streams provide an indication of the quality of water that flows into the Chattahoochee River.
In November 1993, personnel from the U.S. Geological Survey (USGS) surveyed fish in sections of nine tributaries of the Chattahoochee River Basin in Metropolitan Atlanta. The location of survey sites, basin boundaries, and the extent of urban area are shown in figure 1. Eight tributaries, Nickajack Creek, Rottenwood Creek, Sope Creek, Willeo Creek, Nancy Creek, Peachtree Creek, Proctor Creek, and Utoy Creek, receive runoff from urban areas such as subdivisions, office and industrial parks, shopping malls, airports, roads, and golf courses. In addition to these urban basins, Snake Creek was surveyed to provide a comparison of fish populations in a mostly forested basin.
Figure 1. Location of stream sections surveyed and tributary
boundaries in the Metropolitan Atlanta area. (Urban area from Atlanta
Regional Commission, 1990.)
This report summarizes information from historic fish surveys, and describes the results of the November 1993 fish survey. The results indicate the changes in fish populations that may occur as forested and rural basins become urbanized. Colored parts of figure 1 show the extent of urban area in Metropolitan Atlanta in 1990. In contrast to the Snake Creek basin which is 83 percent forested, the other 8 basins range from 70 to more than 90 percent urban area (table 1). Although residences cover a large percentage of area in all urban basins, industrial, commercial, and transportation areas cover approximately one-fourth to one-third of the Rottenwood, Nancy, Peachtree, and Proctor Creek basins. These basins are among the older urban areas of Metropolitan Atlanta.
Table 1. Drainage areas and basin characteristics for tributaries upstream of locations surveyed for fish populations
The group with the largest number of species is the minnow family. Minnows are small fish that can be seen darting around in streams that are only a few feet wide. Other families with large numbers of species are the sunfish and bass family, the catfish family, and the sucker family. Species that have the largest numbers of individuals living in streams typically are minnows and suckers. These species are often not well known because unlike sunfish, bass, and catfish, people do not fish for them, although certain minnows may be used as bait. Minnows have an important role in the aquatic food chain as prey for larger fish, aquatic snakes, turtles, and wading birds such as herons. Suckers can grow to more than one foot long and are named for their down-turned mouth that they use to "vacuum" food from stream bottoms. Although suckers are not popular game fish, they are ecologically important because they often account for the largest fish biomass in streams.
Three species are noteworthy because they are endemic: that is, they live exclusively in the Chattahoochee and Flint River basins. The endemic species are the bluestripe shiner, grayfin redhorse, and greater jumprock. Although many of the basin's native fish also naturally occur in other river basins, these three species are native only to the Chattahoochee and Flint River basins. In addition, the highscale shiner may also have been endemic. However, the highscale shiner has been found in one location in the Savannah River basin. The bluestripe shiner and highscale shiner are listed by the state of Georgia as threatened. In addition, the bluestripe shiner is a candidate for listing under the Federal Endangered Species Act.
In addition to the 42 native species, 8 non-native species have been introduced into the basin by man probably as game fish or released from bait buckets. The introduced, non-native species are the red shiner, white sucker, black bullhead, flat bullhead, spotted bass, smallmouth bass, green sunfish, and yellow perch. Species that survive outside of their native streams often can tolerate a wide range of water-quality and habitat conditions. Consequently, such hardy, non-native fish often thrive in streams where water quality or habitat has been degraded.
The number of individual fish and species captured in the 9 streams are shown in table 3 (html) (gif). The streams are presented, from left to right, in descending order of the number of native species captured. The largest number of native species and individuals (with the exception of Peachtree Creek) was found in Snake Creek, the basin mostly covered by forest. One of the 3 endemic species, the grayfin redhorse, was found in Snake Creek. Although the 8 urban streams vary from 2 to 15 in the number of native species found, they share several characteristics in their fish populations. Generally, less than 50 percent of the number of fish found in Snake Creek were found in the urban streams, and up to 91 percent of the fish in urban streams were from non-native species. Native minnow and sucker species were almost completely absent in Nancy, Peachtree, Rottenwood, Proctor, and Utoy Creeks. These 5 creeks differ from Sope, Nickajack, and Willeo Creeks in the amount or proximity of industrial, commercial, and transportation areas (table 1). Although Utoy Creek has a lower percentage of area in this category, an industrial park is located immediately upstream of the sampling location.
The large number of mosquitofish found in Peachtree Creek may indicate poor water quality. Similar to the non-native red shiner, white sucker and green sunfish species, mosquitofish are tolerant of a wide range of water-quality conditions. After mishaps, such as chemical or sewerage spills which decrease fish populations, mosquitofish can repopulate a stream rapidly. They have short life cycles, and unlike other fish species listed in table 2, they bear their young live rather than lay eggs.
Stream habitats can be compared by estimating the amount of stream bottom that is covered by different materials (Meador and others, 1993b). The percentage of each stream section covered by the major types of bottom materials is shown in figure 2. These materials differ in their importance to fish as habitat. Most fish live near larger bottom materials such as gravel, cobble, and boulders. These larger materials provide spaces where food organisms such as aquatic insects live. Many fish spawn their eggs in nests constructed from gravel, or in holes and cracks in boulders and bedrock. Other important habitats that provide food and hiding places are aquatic plants, fallen logs, and accumulations of sticks and leaves.
Figure 2. The percentage of stream bottom covered by different
materials in each stream section. The percentage of materials such as
logs, roots, mud, silt, or old tires are included in the "other"
category. (See fig. 1 for stream-section location.)
Sand is a natural part of the stream bottom; however, in basins without effective erosion control, sand often covers a large part of the stream bottom burying or filling the spaces between gravel and cobble. As a consequence, the abundance of food organisms and spawning areas required by fish are decreased. The bluestripe and highscale shiner are threatened because their spawning sites among clean boulders and bedrock are increasingly buried by sand and silt.
Differences in fish populations among streams may be caused by factors other than habitat. For example, Rottenwood and Utoy Creeks, which have poor fish populations, both have a large percentage of their stream bottoms covered by gravel, cobbles, and boulders that provide good habitat (fig. 2). In comparison, although poor sand habitat covers greater than 50 percent of the stream bottoms in Sope and Willeo Creeks, they support a larger number of species than Rottenwood or Utoy Creeks. All urban streams, regardless of the quality of their physical habitat, were determined to have fish populations with fewer native species, and generally less than one-half the number of fish found in the forested stream.
The USGS National Water-Quality Assessment Program is measuring water chemistry and contaminants in stream water, bottom material, and organisms to better understand water quality in these urban basins. Such information will help us to understand factors that contribute to the differences in fish populations among these streams, and ultimately to protect the water quality of the Chattahoochee River.
References
Atlanta Regional Commission, 1990, Land Use/Cover Digital Data.
Meador, M.R., Cuffney, T.F, and Gurtz, M.E. 1993a, Methods for sampling fish communities as part of the National Water-Quality Assessment Program, U.S. Geological Survey Open-File Report 93-104, 40 p.
Meador, M.R., Hupp, C.R., Cuffney, T.F., and Gurtz, M.E. 1993b, Methods for characterizing stream habitat as part of the National Water-Quality Assessment Program, U.S. Geological Survey Open-File Report 93-408, 48 p.
