|Home > Draft Report > AQUA-5|
The number of species in each taxonomic group dependent on the five aquatic habitats is shown in Table 3. If appropriate, primary and secondary habitats were evaluated for aquatic animals that are not restricted to one habitat type. For example, some species migrate between different habitats for different parts of their life cycles. In the study area, lakes and ponds contained fewer rare aquatic species than rivers and streams, subterranean waters or springs.
Subterranean aquatic systems are widely dispersed across the South. Caves and springs are widely distributed in the Southeastern United States (Hobbs 1992). Although the distribution of many cave-dwelling animals is not well known (Hobbs 1992, Peck 1998), we do know that aquifers and springs in Texas support rare crayfish, beetles, salamanders, and fish. North Carolina and Virginia caves are home to rare shrimp, aquatic sow bugs, scuds, and crayfish. The springs of Florida and South Carolina provide habitats for unique snails and fish. Tennessee, Alabama, Kentucky, and Arkansas are known for their cave salamanders, as well as cavefish, crayfish, and shrimp (NatureServe 2000a, NatureServe 2000b, Hobbs 1989).
Larger springs may have a unique assemblage of spring-adapted animals. The spring run flowing from it then may have its own unique assemblage (Hubbs 1995) and share some species with the spring habitat.
Many of the species restricted to subterranean aquatic systems are narrow endemics, occurring only in a few isolated localities (NatureServe 2000a, NatureServe 2000b, Hubbs 1995, Hobbs 1989, Burr and Warren 1986). Several characteristics that allow animals restricted to these habitats to be extremely efficient at using the available, often limited, resources could result in declines. These include small body size, late maturity, and infrequent reproduction, which result in low reproductive rates and small population size (Hobbs 1992).
Chemical and physical conditions of waters in caves and springs are relatively stable (Hobbs 1992, Hubbs 1995). The rare animals adapted to subterranean areas are threatened by activities that alter these stable conditions. Subterranean systems are being affected by rapid agricultural and urban growth, which can dewater aquifers and change water chemistry (Hobbs 1992). Groundwater can be contaminated by domestic, municipal, agricultural, and industrial wastes. Changes in the vegetative cover of the drainage basin can alter runoff patterns. Flooding from manmade lakes, pesticides, and sedimentation associated with deforestation and urbanization in the watersheds can also affect groundwater habitats (Petranka 1998, Hobbs 1992).
Recharge areas for springs and caves can be of considerable size (Hubbs 1995). Thus, water quality and quantity can be affected by activities throughout the recharge area, often long distances away from a cave or spring. However, the recharge areas for many important spring or cave systems are not known. Even if the recharge area is known, the potential effects of human activities in these areas are not well documented. Hobbs (1992) suggested that over-extraction of groundwater may slowly concentrate metals or other pollutants to the point that they ultimately become lethal to specialized aquatic cave-dwelling animals.
Because of the value of a reliable clean, clear water supply, springs are often modified so they can be used as water sources. Aquatic vegetation, which can be very important to spring-adapted animals, is often removed. Etnier and Starnes (1991) noted that Tennessee's spring-adapted fish are jeopardized more frequently than would be expected in comparison with fish adapted to other aquatic habitat types. They concluded that the habitats themselves are jeopardized. The same factors that can affect water chemistry in the recharge areas for cave habitats can affect springs. In particular, withdrawal of groundwater can affect the quality and quantity of spring water by concentrating dissolved chemicals and reducing flow (Hobbs 1992). Hubbs (1995) described this condition as an "artificial drought". Hobbs (1992) commented on the need for more States to adopt cave protection laws, and suggested that purchasing important areas for preserves, restricting entry into caves, and public education are necessary means of conserving cave and spring-adapted animals.
Natural lakes are rare in the South. Some of the most important natural lakes include the Carolina bay lakes, cypress ponds, and lakes formed in the floodplains of large rivers (Crisman 1992). Florida and the coastal plain of North Carolina have the most natural lakes. Comparatively fewer rare aquatic animals are dependent on lake habitats than other aquatic habitat types in the South. Construction of dams on the larger rivers in the South has created many reservoirs, which have characteristics similar to natural lakes. However, these artificial habitats do not benefit these rare species.
Lake habitats are threatened by increased sedimentation and eutrophication. These non-point pollution sources are discussed in detail in Aqua 1 Chapter. The most significant threat to natural lake habitats is urban development along the shores, which increases eutrophication (NatureServe 2000a). Guidelines for septic tank drainage need to be implemented and enforced to protect this habitat type.
Permanent and ephemeral ponds are widely dispersed and numerous in the South. Many low-gradient streams have associated oxbows, beaver ponds, and swamps. Rare species from every taxonomic group except mussels depend on ponds. Crustaceans are among the most rare species associated with these habitats. Many amphibian species use only ephemeral ponds for spawning, thus avoiding predation on their eggs and tadpoles by species that require permanent ponds. Some fish (slackwater and trispot darters, for example) use seasonally flooded wetland areas for spawning (McGregor and Shephard 1995, Ryon 1986).
The quality and quantity of these habitats have been reduced by channel straightening, beaver trapping, and drainage systems. Urban development and intensive agricultural and silvicultural activities that drain or fill wetlands are detrimental to permanent and ephemeral ponds (Petranka 1998, Palis 1996, and Vickers and others 1985).
The removal of beaver during the past 400 years has reduced the number of wetlands in the South (White and Wilds 1997). Beaver have recovered in many areas but populations in the Southern Appalachian Mountains have been slow in returning. Absence of this "keystone" species contributes to the isolation of many amphibian populations (Herrig and Bass 1998).
In some areas, fire suppression has allowed shading to develop resulting in colder temperatures in the ponds and extention of the maturation time for tadpoles (NatureServe 2000a
Pesticides and accidental chemical spills may threaten species dependent on pond habitats because of the small volume and isolated nature of these waters.
Rare mussels, snails, and fish have the greatest dependency on riverine habitats (Table 3). While the numbers of rare insects and reptiles that rely on this habitat type are small, riverine habitats support about half the rare species in each of these groups. None of the rare crustaceans or amphibians included in this Assessment is known to depend exclusively on river habitats
At least one-sixth of all river miles in the United States are now impounded (Abell and others 2000, Benke 1990). Dams have created barriers to dispersal that have genetically isolated populations of many aquatic animals, inhibited movement, or created unsuitable habitats for the fish that are hosts to the mussel's larvae. Dams have blocked migration routes for herrings, suckers and sturgeons.
Flow releases from dams rarely emulate natural, daily, or seasonal discharges; the results are marginal to unsuitable habitats for the native aquatic species living in these tailwaters. In extreme cases, unsuitable conditions may extend for up to 125 miles downstream (Abell and others 2000).
Dams can convert shallow, flowing, oxygenated streams into deep, still, stagnant pools. In North America, at least 36 species of snails from the Mobile River system have become extinct since the beginning of European settlement (USDI Fish and Wildlife Service 2000). A series of dams on the Coosa River is believed to have caused the immediate extinction of 20 snail species (Lydeard and Mayden 1995, USDI Fish and Wildlife Service 2000). Reservoirs have flooded much of the flowing water habitats needed for stream-dwelling or spring animals (NatureServe 2000a). For example, the Amistad gambusia went extinct when Amistad Reservoir flooded its only known location (NatureServe 2000b). Dams collect sediment, degrading the habitat for mussels and their fish hosts (Parmalee and Bogan 1998).
Channelization and commercial sand and gravel dredging operations decrease river habitat diversity, directly remove mussels from their beds, and create "motionless pools alternating with unbroken stretches where silt and sand constantly scud along the bottom" (Hart and Fuller 1974).
Petroleum spills, urban and agricultural pesticides, chemical, manufacturing, and wood product wastes are among the most insidious pollutants (Hart and Fuller 1974, Abell and others 2000). The impacts from these pollutants are often both immediate and persistent.
Sediment contributes to river degradation (NatureServe 2000b). Sediment sources are discussed in detail in Aqua 1 Chapter. The turbidity associated with sediment runoff can interfere with feeding for both sight and filter feeders and can shade out aquatic vegetation or erode away attached algae. Once the sediment settles into the river, it may bury slow-moving benthic organisms and eggs, clog interstitial spaces, and armor the stream bottom.
Conant and Collins (1998) reported that egg-laying reptiles whose nests are on sandbars or banks of rivers could be affected by various human activities. The habitats required for nesting could be covered by impoundments or affected by channel maintenance dredging (Dodd, 1997). Eggs, which often remain buried for several months, may also be destroyed by off-road vehicles; agricultural, silvicultural, and mining activities; road construction; and residential or industrial construction.
Both perennial and intermittent streams are important to aquatic species. Individuals from all of the rare aquatic groups considered in this Assessment depend on stream habitats. Stream habitats and the composition and diversity of aquatic animals change in a predictable way as stream order (size) increases (Sheldon 1988). More rare crustacean species are associated with intermittent streams than any other aquatic species group. Further studies of aquatic insects, however, may reveal an even stronger dependency by this group on intermittent streams. Wallace and others (1992) suggest that headwater streams of the Southern Appalachians probably contain a greater diversity of aquatic insects than any other region of North America, and that fish and salamander diversity is also relatively high there.
Removal of riparian vegetation along streams (Petranka 1998) and intensive ground disturbance within riparian ares may adversely alter stream habitats, especially for crustaceans and amphibians (Petranka and others 1994, Petranka 1998).
Because they have less volume of water, small streams may be exposed to higher concentrations of pollutants, including sediments, than rivers. Petroleum spills; urban and agricultural pesticides; and industrial wastes are particularly damaging to streams (Hart and Fuller 1974, Abell and others 2000) and can affect individuals from all taxonomic groups. Water withdrawals for rural and urban uses may excessively reduce base flow of small streams, further shrinking available habitat (Abell and others 2000).
Indirect impacts of pollutants or habitat alterations may occur through a reduction in food organisms for the animals discussed (NatureServe 2000b). Other examples of more direct effects of human activities include disturbances to the nests of egg-laying reptiles (Conant and Collins 1998). Etnier and Starnes (1991) reported a disproportionately high number of Tennessee's rare fish are in medium-sized rivers. They hypothesize that impoundments on medium rivers produce habitat changes that are not as well tolerated by animals adapted to streams of this size, relative to those adapted to larger river habitats. They concluded that the habitats themselves are threatened.
|Glossary | Sci.Names | Process | Comments | Final Report|