Aquatic Fauna in Peril: The Southeastern Perspective Edited By George W. Benz And David E. Collins

Aquatic Fauna in Peril > Status and Restoration of the Etowah River, an Imperiled Southern Appalachian Ecosystem

Status and Restoration of the Etowah River, an Imperiled Southern Appalachian Ecosystem

By Noel M. Burkhead, Stephen J. Walsh, Byron J. Freeman, and James D. Williams

"The last word in ignorance is the man who says of an animal or plant: ‘What good is it?’" — Aldo Leopold, A Sand County Almanac

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Most concern by contemporary scientists and conservation groups about biodiversity loss focuses on regions of rich terrestrial diversity such as tropical rain forests. Much less attention is directed at the decline and loss of aquatic species, communities, and ecosystems, whether they are Amazonian, coral reef, or southern Appalachian (Lydeard and Mayden, 1995; Stiassny, 1996).

ans are emotionally biased towards terrestrial biotas and particularly towards those species that are warm-blooded and endearing — the so-called "charismatic megafauna." It is lamentable that this emotional bias is transferred to the intellectual arena by what science is funded and which resources receive protection (Warren et al., 1997). Relatively few resource managers and science leaders are aware of the rich temperate freshwater biodiversity in rivers of the southeastern United States, or of the alarming levels of imperilment of these systems.

North America north of Mexico harbors the richest temperate freshwater fish fauna in the world (Page and Burr, 1991) and therefore is an important global biodiversity resource. This ichthyofauna consists of about 800 species, of which some 490 species occur in the southeastern United States and about 349 inhabit the southern Appalachians. The Etowah River system harbors 91 native fishes (26 percent of the southern Appalachian fish fauna) and 14 introduced species. The southeastern United States is also rich in other aquatic faunas including freshwater mussels and snails (Neves et al., 1997), aquatic insects (Morse et al., 1997), and crayfishes (Taylor et al., 1996). The levels of extinction and imperilment of fishes and mollusks (mussels and snails) in southern states are truly disturbing: about 20 percent of the fish fauna (Williams et al., 1989; Warren and Burr, 1994; Walsh et al., 1995) and over 70 percent of the mollusk fauna (Neves et al., 1997) are in jeopardy. Although less is known about aquatic arthropods, we suspect that similar levels of decline exist in these animals as well. The fact that the arthropod diversity of the southeastern United States is so poorly known and we do not know the extent that the fauna is imperiled exemplifies a general lack of commitment to study of southeastern aquatic resources.

Causes of habitat destruction and aquatic faunal decline are discussed throughout this volume. The ultimate causes are ignorance and greed in the overall way society perceives and exploits the Earth’s finite natural resources. The consequences of this exploitation are exacerbated by human population size and its continued exponential growth. However, there is basis for hope that society will make commitments and take actions necessary to retain most of the existing biodiversity. Humans have clearly advanced in our moral commitment to the natural world (Nash, 1989). Based on the success of nature television programming, more Americans are concerned now than ever before about the intrinsic values of biodiversity.

Relative to biological conservation, the traditional roles of scientists have been as theoreticians with few real data, prognosticators of doom and gloom, or scribes of decline. Conservation science has matured into a focused, multidisciplinary field that incorporates elements of systematics, ecology, population biology, and genetics to study the causes and patterns of biological simplification, and is beginning to offer scientifically-based solutions to restoring damaged biological systems. Many conservation scientists now recognize that communicating only with other scientists or exclusively relying on government agencies to solve onerous and often politically charged environmental problems is simply not working. Furthermore, at the local level, civic leaders and resource managers are often incapacitated by capricious changes in political will. If meaningful changes are going to occur to correct the most blatant abuses of our aquatic resources, scientists must repackage and effectively communicate their esoteric knowledge directly to the public (Tangley, 1994).

In this paper, we use the Etowah River of north Georgia as a conceptual and practical model for restoration of an imperiled southern Appalachian river system. The terrestrial and aquatic components of the Etowah River watershed together compose the Etowah River ecosystem, and we emphasize that the streams in the watershed cannot be considered independently from the lands they drain. Freshwater fishes are primarily used herein to characterize the aquatic health of the river system because our knowledge of fishes is more comprehensive than any other taxonomic group of the southeastern aquatic fauna. However, because of significant imperilment and extirpation levels of mollusks, we also discuss their status in the Etowah River.

The Etowah River is representative of southern Appalachian river systems: it drains southern Appalachian physiography, it has relatively high aquatic diversity, and high fish endemism. It is beleaguered by a litany of environmental threats that are common to southern Appalachian river systems. As a result of habitat decline, the Etowah River system has lost many species and has others placed on state and federal endangered species lists. This contribution synthesizes original data and information from diverse sources. Via this synthesis, we hope to provide critical background information on the status of the Etowah River that will be useful for protection and recovery of this unique ecosystem.

Methods

Records of fishes are largely based on about 250 collections made by ourselves and colleagues since 1989, but also include a relatively complete survey of national and regional museum holdings and a summary of literature records. Our initial survey work focused on determining the distribution of the threatened Cherokee darter and later expanded into a general survey of Etowah River fishes. Figure 1 depicts Etowah River collection sites (some recent collection sites are not shown).

Collections were made by seining, backpack shocking, boat shocking, and gill netting. All specimens were retained except for those of the most common or protected species. Most of the specimens collected during our surveys are housed at the Florida Museum of Natural History at the University of Florida (UF). Significant holdings of Etowah River fishes are also at the University of Georgia Museum of Natural History (UGAMNH) and the University of Tennessee at Knoxville (UT). Fish nomenclature is based on a combination of Robins et al. (1991), Mayden et al. (1992), and our interpretation of Coburn and Cavender (1992; page 333) regarding recognition of the minnow genera Ericymba and Hybopsis.

Ecological associations of imperilment for Etowah River fishes are derived from our ongoing study of imperilment patterns of southern Appalachian fishes. We summarized a subset of Etowah fish data from the southern Appalachian fauna to generally compare patterns of imperilment for Etowah River and southern Appalachian fishes. The southern Appalachian analysis is based on a matrix of 349 southern Appalachian fishes (contrasting non-imperiled versus imperiled species) and 46 ecological and zoogeographic attributes similar to a study by Angermeier (1995) for the Virginia fish fauna. Attributes were grouped into related categories, and the set of categories for Etowah River fishes included in this review are range size, vertical orientation in the water column, body size, and habitat size. The matrix for each category consists of species (rows) and attributes (columns).

For definitions of basin, drainage, and system, we use those of Page and Burr (1991). The Etowah River is actually a subsystem of the Coosa River system, but throughout this paper we refer to the Etowah River as a system. The usual definition of an endemic freshwater fish is a species that is restricted to a drainage (Jenkins and Burkhead, 1994), but here we restrict it to a species found only in one river system.

The category range size includes four attributes:

1. Wide-ranging — occurring throughout a large geographic area, such as the Southeast, in multiple drainages, and often in more than one basin.
2. Intermediate-ranging — occurring in more than one drainage within a basin, but sometimes occurring in geographically proximate portions of adjacent basins.
3. Localized — restricted to one or more river systems within one drainage, but sometimes occurring in limited portions of several drainages within one basin.
4. Isolated — very restricted distribution, often occurring only at one or several sites within one or a few tributary systems, usually within one drainage.

No attempt was made to distinguish between species which have always been highly localized and others with relictual distributions (i.e., those having experienced range constrictions over geologic time).

The category vertical orientation in the water column is divided into two attributes:

1. Benthic — living on the bottom.
2. Non-benthic — living above the bottom.

Each attribute was averaged across three activities: feeding, spawning, and sheltering.

The category body size is divided into four attributes:

1. Very small — maximum adult length up to 75 mm (2.9 inches) total length (TL).
2. Small — maximum adult length from 76 to 150 mm (3.0 to 5.8 inches) TL.
3. Medium — maximum adult length from 151 to 400 mm (5.9 to 15.7 inches) TL.
4. Large — maximum adult size exceeding 400 mm (15.7 inches) TL.

The category habitat size association is represented by five attributes:

Headwater — tiny headwater or first order tributaries, or small springs that are usually less than 2 m (6.6 feet) wide (stream order is a system that characterizes the degree of branching of a stream system; order number increases when two tributaries of the same order join);

1. Small Creek — usually first or second order streams less than 5 m (16.4 feet) in width.
2. Creek — streams ranging in average width from 5 to 15 m (16.4 to 49.2 feet).
3. Small River — streams ranging in average width from 16 to 99 m (52.5 to 324.8 feet).
4. Large River — streams with an average width of 100 m (328.1 feet) or more.

Our definition of the imperiled fishes and mussels, with few exceptions, includes species federally listed under the U.S. Endangered Species Act of 1973 as threatened or endangered (U.S. Federal Register, 1994a), Category 2 species (U.S. Federal Register, 1994b), and those listed as special concern, threatened, or endangered by Williams et al. (1989) and Williams et al. (1992b). Until intensive status surveys are made for the lined chub, burrhead shiner, frecklebelly madtom, and freckled darter, we regard their most appropriate status to be Category 2 (versus 3C in U.S. Federal Register, 1994b). Also included as a C2 species is an undescribed darter, Percina sp. cf. P. macrocephala. The populations of this species appear to be disjunct and confined to the upper Coosa River system.

We do not support the recent elimination by the U.S. Fish and Wildlife Service of Category 2 candidates from the Animal Candidate Review for Listing as Threatened or Endangered Species that is periodically published in the U.S. Federal Register. Contrary to the argument by Sayers (1996), we believe the C2 status to be a useful category equivalent to Special Concern status employed by the American Fisheries Society and by many states. In effect, this action orphans declining elements of the fauna from direct federal responsibility until they are in imminent jeopardy and merit listing as threatened or endangered.

Assignment of ecological attributes for species was based on published information. Because of incomplete life-history data on the southern upland fish fauna, matrix cells were scored as either present (1) or absent (0), and no cells were left blank. Body and range size categories had a single attribute score of "1" per species. Habitat size and vertical orientation categories frequently had multiple attributes scored as "1" for each species. For example, in the habitat size category, many species occupy creeks, small rivers, and large rivers, and in the vertical orientation category, some species feed at all depths in the water column. Where data for a species were unavailable, we scored cells based on knowledge of closely related taxa or on the morphology of the species in question. Approximately one-third of the fauna required estimating attribute cell scores. However, based on our knowledge of the fish fauna and experience in compiling an encyclopedic reference summarizing life-history data (Jenkins and Burkhead, 1994), on the whole we believe that our attribute assignments for missing data closely approximate reality. Matrices were summed by columns (attributes) for proportional comparisons of the imperiled and non-imperiled subsets of Etowah River and southern Appalachian fishes.

Physical And Biological Setting

"We do not inherit the land from our parents — we borrow it from our children." — Native American adage

Physiography of the Etowah River

The Etowah River is one of four major headwater tributaries of the upper Coosa River system of the Mobile River drainage. The Etowah River joins the Oostanaula River in Rome, Georgia, to form the Coosa River (Figure 2).

Most of the Coosa River in Alabama is impounded; therefore much of the surviving biodiversity of this system is confined to major tributaries in Alabama and Georgia.

The Etowah River occurs entirely within Georgia; its headwaters originate in the southern boundary of the Blue Ridge and the river flows southwesterly through the Upland subsection of the Piedmont, the Talladega subsection of the Blue Ridge, and the Great Valley subsection of the Valley and Ridge provinces (Wharton, 1978; Figure 3).

County and principal tributary names are depicted in Figure 4. In the center of the watershed is Allatoona Reservoir, a large 4,800-ha (11,861-acre) hydroelectric and flood-control impoundment that was completed in 1949 by the U.S. Army Corps of Engineers (Martin and Hanson, 1966). Allatoona Dam is located in a narrow gorge in a zone of faults (Cressler et al., 1979) that, prior to impoundment, probably represented a natural transition area in the character of the river from rolling upland hills and isolated ridges to the valley floor of the Great Valley subsection. Geologically, this fault zone roughly delineates a transition from crystalline metamorphic rocks to sedimentary limestones (Wharton, 1978). Selected physical attributes of the Etowah River system are as follows: drainage area = 4,871 km2 (3,027 square miles); drainage area above Allatoona Reservoir = 1,588 km2 (987 square miles); elevation at mouth = 174 m (571 feet); maximum elevation = 769 m (2,523 feet); greatest stream order = 6; drainage pattern = dendritic; main channel length = 265 km (165 miles); impounded channel length = 51.8 km (32.2 miles); and average gradient = 2.2 m per km (11.6 feet per mile). Historically, the Etowah watershed was inhabited by Native Americans who occupied a major village at a site presently known as the Etowah Indian Mound, located below the Allatoona Dam site (van der Schalie and Parmalee, 1960). Remnants of Native American fish traps still exist in the main channel of the river above and below Allatoona Dam (Figure 5).

The Etowah River drains portions of 11 counties. Much of the land use in these counties is agricultural, but there are large cities within and adjacent to the watershed, most notably the sprawling Atlanta metropolitan area south of the system (Figure 6). Other large or moderate-sized cities are Rome, located at the mouth of the Etowah River; Cartersville, situated downstream from Allatoona Reservoir on the north side of the river; and Canton, on the south side of the river upstream from Allatoona Reservoir (Figure 6). In decreasing order, Fulton, Cobb, Floyd, and Cherokee are the most urbanized counties in the watershed.

The main channel and most tributaries of the Etowah River are constantly turbid as a result of soil erosion. During normal water levels, water color is typically brown or greenish, but during high water levels the water is orange-red, characteristic of the clay soils of the region. Little is known about the quality of the river prior to 1900. Jordan (1877) characterized a few tributaries of the lower Etowah River as clear with rocky bottoms as compared to the muddy waters of the Ocmulgee River of Georgia. In his autobiography, Jordan (1922) described the main channel of the Etowah River as muddy during a brief collecting trip in 1876. Given the physiography and surface geology of the drainage, there is little doubt that the Etowah River system was historically as clear as the upper Conasauga River, a sister tributary of the Etowah in the upper Coosa River system. By visiting the Conasauga River in northern Murray County, Georgia, or Polk County, Tennessee, one can see clear water conditions that undoubtedly existed in the Etowah River prior to extensive deforestation and land disturbance.

Status of the Aquatic Fauna

The Coosa River and its major tributaries, including the Etowah River, may hold the dubious distinction of having more recent extirpations and extinctions of aquatic organisms than any other equally-sized river system in the United States. Neves et al. (1997) document the recent mass extinction of 38 species of endemic aquatic snails in the Coosa River. We estimate the Etowah River has more imperiled fishes (17 spp.) and invertebrates (16 spp.) than any other river system of similar length in the southeastern United States (Table 1). The Conasauga River has the second highest number of imperiled species (ten fishes and 15 mollusks). The high levels of imperilment in the Etowah and Conasauga rivers result in large part from the diminution of the high biodiversity of the Coosa River system caused by extensive habitat loss such that only remnants of formerly more widespread assemblages survive in fragmented headwater systems. The high levels of imperilment of the aquatic fauna are not restricted to the relatively intact portions of the upper Coosa River system; many species are jeopardized throughout the entire Mobile River drainage (Lydeard and Mayden, 1995).

We tabulate 17 fishes as imperiled in the Etowah River: two each threatened or endangered, 12 C2 species, and one species on the Georgia state list but not on federal lists. Twelve Etowah River mussels are on federal lists: eight endangered, three threatened, and one C2 species. The mussel list includes five species (upland combshell, southern acornshell, orange-nacre mucket, Coosa moccasinshell, and ovate clubshell) for which there are no museum records, but that are included based on literature or on probable occurrence given their distribution elsewhere in the Coosa River system. Additionally, three gastropods (snails) and one mayfly in the Etowah River are C2 species (Table 1).

Nine of the 17 imperiled fishes are believed to be extirpated. How much of the imperiled mussel species are extirpated is unknown. Combined, this beleaguered fauna overwhelmingly indicates that the Etowah River system has been and continues to be a system under severe stress and in need of immediate remedial attention.

Fish Fauna of the Etowah River

Our earliest knowledge of the fishes of the Etowah River is from collections made by the eminent ichthyologist David Starr Jordan and students in 1876 (Jordan, 1877, 1878; Jordan and Brayton, 1878). The first list of Etowah River fishes was included in a state list compiled by Dahlberg and Scott (1971). Additions to a list of the Etowah fish fauna, as range extensions or descriptions of new species, were made by Suttkus and Raney (1955), Richards and Knapp (1964), Ramsey and Suttkus (1965), Clemmer and Suttkus (1971), Williams and Etnier (1977), Bryant et al. (1979), Burr and Cashner (1983), Suttkus and Etnier (1991), Wood and Mayden (1993), Suttkus et al. (1994), and Bauer et al. (1995). The list of fishes presented herein is the most comprehensive tally to date of the Etowah River ichthyofauna.

The total historic and present fish fauna of the Etowah River numbers approximately 105 species plus one stocked hybrid (striped bass ´ white bass) (Table 2). Uncertainty about the exact number of species inhabiting the Etowah River system relates to the former occurrence of species that may now be extirpated from the system (see Fish Extirpations), and to the taxonomic status of putative new taxa. Of the 105 species, 91 are native. Fifteen of the native species are extirpated from the system, 14 plus one hybrid are nonindigenous, and four are endemic to the Etowah River (Table 2). We consider this list provisional and likely to change in the future. The Conasauga River has long been considered to have the greatest fish and mussel diversity within the upper Coosa River system (Etnier and Starnes, 1994). Only recently has the Etowah River been identified as having an equally diverse, but greatly threatened aquatic fauna (Burkhead et al., 1992; Bauer et al., 1995). We now believe the Etowah River was historically a center of aquatic biodiversity in the eastern Mobile River drainage.

Level of Endemism

The most striking characteristic of the Etowah River ichthyofauna is its high level of fish endemism (four species). To compare the number of endemic fishes in the Etowah River system to that of other systems in the Mobile River drainage, we compared the proportion of endemic fishes to total fish species among the Black Warrior, Cahaba, Conasauga, and Etowah rivers (Table 3). In the tally of total species, we did not include nonindigenous species and marine invaders (except for diadromous forms) that are reported to have penetrated the upper Coosa system in western Alabama or Georgia (Dahlberg and Scott, 1971; Boschung, 1992). Sources of data were as follows: Black Warrior, Mettee et al. (1989); Cahaba, Pierson et al. (1989); and our data for the Conasauga and Etowah rivers. The Black Warrior River has more endemics than the Etowah River (six versus four), but the drainage area of the Black Warrior River is nearly four times as large as that of the Etowah River, and the proportional differences of endemics for the Black Warrior versus Etowah (5.1 versus 4.4 percent) are close. The Etowah River is closest in drainage area to the Cahaba River but has twice the number of endemic fishes.

Cryptic Fish Taxa

All the presumed endemic species noted in Table 2 are recently described or recently discovered taxa. The Etowah darter (Figure 7A) was described in 1993 (Wood and Mayden, 1993), and the Cherokee darter (Figure 7C) in 1995 (Bauer et al., 1995). The remaining undescribed endemic fishes (two darters) were discovered by us in 1993 and 1994. Additionally, two undescribed minnows and one undescribed sucker are known or presumed to have occurred in the Etowah River. All these taxa are morphologically cryptic species similar to the nominal taxa with which they have long been placed. The detection of the undescribed darters was based on discovery of subtle but distinct differences between the two forms in male nuptial coloration. Although the study of these putative darter taxa is presently incomplete, we hypothesize that specific differences exist analogous to those of the greenbreast darter group analyzed by Wood and Mayden (1993). Recognition of these putative species is based on a greater level of systematic scrutiny of the Etowah fish fauna than has previously been applied, and parallels recognition of cryptic darter taxa by other ichthyologists in the Southeast (Boschung et al., 1992; Page et al., 1992).

Fish Extirpations

Fifteen fish species, 16 percent of the nativefauna, are considered to be extirpated from the river system (Table 2). A few of the extirpated forms are globally imperiled: lake sturgeon, blue shiner, and coldwater darter. Their extirpation from the Etowah River is not surprising given widespread habitat deterioration. At least two extirpations (American eel and lake sturgeon) were likely caused by multiple impoundments of the Coosa River system, including Allatoona Reservoir. However, the demise of much of the missing fauna is enigmatic because many of these species are generally regarded as tolerant or persistent species and occur in other degraded rivers. While we have no recent records for these species, we find it difficult to believe that some of them actually are extirpated (e.g., chain pickerel, lined chub, creek chubsucker, and blackspotted topminnow). Perhaps provisional listing here will promote their "rediscovery." Two suckers not included as extirpated are puzzling. The spotted sucker, a relatively tolerant and usually common species, has not been collected by us although it is known from the Etowah River (Beisser, 1989; year of capture not specified). Unknown from the Etowah River is the sometimes elusive river redhorse. We captured the river redhorse in the lower Oostanaula River and suspect that a low-density population persists in the lower Etowah River. Documentation for the extirpated fish fauna, as presently conceived, is as follows:

Lake sturgeon — This species is known from the Coosa and Oostanaula rivers (Boschung, 1992). One of us (BJF) heard an anecdotal report of someone catching a 1.5-m (4.9-feet) specimen with a pitchfork below the spillway dam in Cartersville in the late 1940s. The species is probably extirpated from Georgia and Alabama (Boschung, 1992).

American eel — Jordan and Brayton (1878) listed the American eel as "abundant" in the Alabama River system. A landowner informed one of us (BJF) that eels used to be common in the Etowah River above Allatoona Reservoir.

Alabama shad — Not known from the Etowah River. Boschung (1992) reported it from the Coosa River below Jordan Reservoir. We suspect that prior to multiple impoundments of the Coosa River, the Alabama shad probably occurred in the lower Etowah and Oostanaula rivers. The closely related American shad was known to penetrate the Blue Ridge in the James River in Virginia prior to construction of spillway dams at and above Richmond (Jenkins and Burkhead, 1994).

Blue shiner — One lot of this species at Cornell University (CU 1488) lists the following locality data: Etowah River, Jordan, October 1876. However, Jordan (1877) and Jordan and Brayton (1878) did not report the blue shiner from the Etowah River. Gibbs (1955) erroneously listed records of the blue shiner from the Little River in Cherokee County, Georgia; these were actually from the Little River in Cherokee County, Alabama. The blue shiner was historically distributed in the Oostanaula and Coosa rivers in the Valley and Ridge province (Gilbert et al., 1980). We believe it formerly occurred in the Etowah River system.

Lined chub — Jordan (1877) reported it as "abundant in all tributaries of the Etowah" In their list of material examined, Clemmer and Suttkus (1971) reported two localities for the lined chub above Allatoona Dam, and in their distribution map, the authors plotted another record below Allatoona Dam.

Burrhead shiner — Suttkus and Raney (1955) examined specimens at the United States National Museum collected by Jordan from the Etowah River (USNM 164968 and USNM 164969, one specimen each). These appear to be the last burrhead shiners collected from the Etowah River system.

"Blue sucker" (undescribed Mobile drainage form) — This interesting large-river sucker is not known from the Etowah River system. However, there were no extensive main-channel collections made in the upper Coosa, or lower Etowah and Oostanaula rivers prior to extensive impoundment of the Coosa River. Historically, the blue sucker probably penetrated the upper Coosa River system, including the lower reaches of the Etowah and Oostanaula rivers.

Creek chubsucker — Jordan (1877) reported it from the Etowah River, but later called it the lake chubsucker (Jordan, 1878). Because the mouth of the Etowah River is a significant distance above the Fall Line, we speculate that Jordan’s record was based on creek chubsuckers.

Freckled madtom — In the Etowah River it is known from only one specimen collected in 1962 (UGAMNH 814). The freckled madtom is a widespread species within the Mississippi Embayment (Rhode, 1980). The Etowah River record represents the most upstream collection of the species in the Coosa River system.

Chain pickerel — Jordan (1877) reported it as abundant in tributary ponds of the lower Etowah River system. To our knowledge, no pickerels have since been captured from the Etowah River, thus indicating another enigmatic disappearance.

Blackspotted topminnow — There are no records of this species from the Etowah River. However, it is known from Big Dry Creek (Freeman, 1983), an Oostanaula tributary adjacent to the Etowah River. We consider it likely that the blackspotted topminnow historically resided in the Etowah River.

Coldwater darter — Jordan (1877) misidentified this species as "Boleichthys elegans" (Ramsey and Suttkus, 1965), stating that it was most common in Dykes Pond near Rome. Dykes Creek, presumably where Dykes Pond was located, presently contains a depauperate fish fauna, and no coldwater darters have been recently collected there. Although no other records of coldwater darters are known from the Etowah River, there are several large spring-fed tributaries in the Valley and Ridge portion of the system that may have supported coldwater darter populations.

Trispot darter — There are no records of this species from the Etowah River. It is known from the Valley and Ridge province of the Conasauga and Oostanaula rivers (Freeman, 1983), and we consider it very likely that the trispot darter formerly existed in the lower Etowah River in the same province.

Coal darter — This recently described darter (Suttkus et al., 1994) is not known from the Etowah River. The coal darter is a large-river species known from the main channel of the Coosa River above the Fall Line, and, like the undescribed "blue sucker," we presume it occurred historically in the lower Oostanaula and Etowah rivers.

River darter — There are no Etowah River records of this large-river species. Stiles and Etnier (1971) reported it from the Conasauga River far upstream from the mouth of the Etowah River; therefore, we conclude it formerly occurred in the lower main channel of the Etowah River.

Ecological Correlates of Fish Imperilment

Understanding shared biological patterns among declining and extinction-prone species is of strong interest to ecologists (Terborgh, 1974; Willis, 1974; Diamond, 1984; Angermeier, 1995; Parent and Schriml, 1995). For rheophilic freshwater fishes, life-history and ecological attributes such as range size, body size, habitat association, and vertical orientation in the water column are attributes for intuitively investigating correlates of imperilment. Herein we generally compare these attributes between the non-imperiled and imperiled fishes in southern Appalachia and the Etowah River. The results of the comparisons are discussed by category below. These comparisons do not establish causal mechanisms but they do allow possible inference for further lines of investigation. The results also contribute to a growing body of evidence that patterns of rarity and extinction are not isolated, random phenomena (Angermeier, 1995; Parent and Schriml, 1995). Lastly, understanding that associations of imperilment span shared suites of ecological adaptations in multiple, evolutionarily diverse families underscores the concept that single-species management is biologically inappropriate and fiscally wasteful.

We consider range size to be the most important correlate of imperilment. It is axiomatic that fishes with small ranges are generally more vulnerable to threats, because even small losses of habitat can be proportionally more serious than similar reductions in species with larger ranges (Moyle and Williams, 1990; Burkhead and Jenkins, 1991; Etnier and Starnes, 1991; Angermeier, 1995). This premise is independent of population density, although it is obvious that, of two species with similar small ranges, the species with the lowest population is potentially more vulnerable. Most non-imperiled species of the southern Appalachians and the Etowah River are wide- and intermediate-ranging, whereas most imperiled species are localized or geographically isolated (Figure 8). Proportional differences of localized and isolated range sizes between the non-imperiled and imperiled faunas are considerable. The species with the most restricted distributions in the Etowah River are the amber and the Etowah darters (federally endangered), and two undescribed darters (Etheostoma spp. cf. E. brevirostrum) that are Category 2 species (Table 1). The latter three species are exclusively endemic to the Etowah River. All of the environmentally degrading factors discussed below (see Threats to the System) can cause reductions in range size.

Benthic specialization is an important correlate of imperilment. Obligate benthic species — those that spawn, feed, and shelter on the stream bottom — compose a substantial fraction of the Etowah’s imperiled fish fauna. Obligate benthic specialization occurs throughout the southern Appalachian and Etowah River fish faunas. The ratio of imperiled benthic fishes to imperiled non-benthic fishes is about 5:1, as opposed to about 2:1 for the same ratio among non-imperiled species in both the Etowah River and southern Appalachian faunas (Figure 9). Of the imperiled fishes in Table 1, 80 percent are obligate benthic species and the remaining ones are associated with the substrate by one or more critical life-history activities (spawning, feeding, or sheltering). The primary form of degradation and destruction of benthic habitats is elevated sedimentation, and the present effects of sedimentation may be heightened by pollutants bound to sediments (see Threats to the System).

Small body size is associated with imperilment in aquatic and terrestrial vertebrates (Diamond, 1984; Angermeier, 1995). For fishes this is partially because most eastern North American species are less than 150 mm (6 inches) in total length. However, a substantially greater proportion of very small- and small-sized species are imperiled versus medium- and large-sized species (Figure 10). Small body size in fishes is correlated with several other ecological attributes associated with imperilment: low intrinsic dispersal capabilities, short longevity, benthic specialization, and generally reduced reproductive potential. Fifteen of 17 imperiled fishes (Table 1) are very small- and small-sized species. The lake sturgeon and the undescribed "blue sucker" are the only imperiled large-sized and medium large-sized species (that formerly occurred) in the Etowah River.

Because the southern upland fish fauna evolved in, and is primarily associated with lotic habitats, we examined flowing-water habitat associations of the imperiled and non-imperiled faunas to determine if differences exist. Prior to our analysis, we speculated that most of the imperiled species would be associated with headwaters, small creeks, and large rivers because of the high degree of degradation of those fluvial water bodies by agriculture and impoundment. Most species in the southern Appalachians and in the Etowah River occur in creeks and small rivers, habitat sizes that probably represent most of the total habitat area available. We found no large differences between frequency distributions of the non-imperiled and imperiled species (Figure 11). While it is impossible to state that there is an equal sampling effort across all habitat sizes, particularly with respect to large rivers, repeated sampling by multiple methods has yielded the best data available. We further realize that as imperiled species become rarer, the probability of detecting them significantly declines (Etnier, 1994). Given these constraints on the best data available, we feel these results imply that habitat degradation and destruction has been relatively ubiquitous across fluvial habitats; all sizes of habitats — small headwater creeks to large rivers — have been despoiled to some degree.

Mussel Fauna of the Etowah River

Like temperate freshwater fishes, freshwater mussels or clams (family Unionidae) are most diverse in the southeastern United States. Of the 297 freshwater mussel taxa recognized (281 species and 16 subspecies) in the United States and Canada (Turgeon et al., 1988), about 90 percent occur in the southeastern United States. About 17 percent (51 species) of this mussel fauna is known from the Etowah River system, where species historically occupied diverse habitats ranging from upland creeks to the main channel of the river.

Adult unionids range in size from 4 cm to more than 25 cm (1.6 inches to greater than 9.8 inches) and the largest may weigh 1 kg (2.2 pounds). Mussels are among the longest lived freshwater invertebrates; many species may live 20 to 40 years and a few species live more than 50 years. Freshwater unionids have a unique relationship with fishes in that about 98 percent of all species require a fish host to complete their life cycles (Fuller, 1974; Hoggarth, 1992).

Mussels were historically common throughout freshwater ecosystems of the southeastern United States. Mussel declines during the past century parallel those of other freshwater organisms, notably snails, and fishes. Williams et al. (1992b) reported 213 species, about 72 percent of the United States mussel fauna, as endangered, threatened or of special concern, and 21 species (7 percent) as possibly extinct. The demise of this widespread and diverse fauna is primarily the result of habitat destruction and deteriorated water quality of southern rivers.

Our provisional list (Table 4) of mussels thought to have historically existed in the Etowah River is based on records from archeological digs, early collections, and inference from known mussel distributions throughout the remainder of the upper Coosa River system. Mussels were collected in the Etowah River watershed for centuries by Native Americans who used them for a variety of purposes, including food, tools, and jewelry. Mussels excavated from middens at the Etowah Mound Site in Bartow County were analyzed by van der Schalie and Parmalee (1960). Mussel collectors sampled the Etowah River in the early to mid-1800s and most of the shells were shipped to wealthy conchologists who maintained them in their personal collections or donated them to natural history museums.

The present outlook of the mussel fauna of the Etowah River is bleak. Burkhead et al. (1992) estimated that as many as 65 percent of the species may have been extirpated from the system. Mussels are susceptible to many pollutants and most species cannot survive in reservoirs (Fuller, 1974; Williams et al., 1992a). Decline of the Etowah River mussel fauna may have begun around the time of the first gold rush in the United States, in northern Georgia. Gold miners used mercury to coalesce gold fines. Mercury contamination in the Etowah River alluvial floodplain has been dated to 1830 in core sediment samples (Leigh, 1994).

Without a thorough and systematic survey for mussels we cannot know what percentage of the Etowah River mussel fauna survives. In over 200 fish collections that we have made since 1989, we have only observed valves of three dead native mussels. Our efforts to detect mussels — while certainly not a survey — have not been casual either. We have intentionally searched river banks while collecting and canoeing, and have walked islands (particularly where we camped) looking for valves in places where they might normally be observed.

Faunal Fragmentation

One of the most common patterns associated with extirpation is the fragmentation of a species’ range into small, isolated subpopulations within the larger geographic area occupied by the species. Habitat and population fragmentation and the scales on which it can occur are summarized by Harris (1984) and Meffe and Carroll (1994). Fragmentation results from localized environmental degradation and exists at all spatial scales. Widespread losses of aquatic habitats in the southern Appalachians result largely from major impoundments, deforestation, urbanization, and chronic pollution, including sedimentation. Smaller-scale fragmentation occurs from scattered, localized habitat perturbations associated with a variety of anthropogenic activities such as small water supply or farm pond impoundments, isolated residential developments, riparian clearing, landfills, site-specific sedimentation, agricultural runoff, and urban sprawl along transportation routes near streams. While large-scale projects are typically evaluated for potential environmental impacts, many small-scale projects do not receive such attention. In the long run, extensive fragmentation by piecemeal habitat loss may actually harm aquatic species as much or more than large-scale, often controversial projects.

The biological consequences of population fragmentation involve genetic isolation and demographic effects. Genetic isolation can diminish population fitness (Soulé, 1980; Carson, 1983). However, even minimal emigration of a few individuals between insularized populations can maintain at least short-term population heterozygosity (Soulé, 1980). Emigration across relatively permanent barriers such as major dams can be considered "sweepstakes" dispersal, i.e., possible but not likely (Chesser, 1983), while intermittent dispersal across smaller stretches of degraded stream habitat may bolster insular heterozygosity. A pervasive problem in the Etowah River system, and other southern Appalachian rivers, is that ever-increasing habitat loss continually decreases or eliminates temporal opportunities for fishes to disperse across degraded stream reaches. The efficacy of degraded stream habitats contributing to isolation of fish populations has been genetically demonstrated by reduced allele and genotype frequencies in populations of the spotfin shiner (Cyprinella spiloptera) separated by polluted stream reaches (Gillespie and Guttman, 1993), and morphologically demonstrated by the distinctiveness of disjoined populations in the California roach (Hesperoleucas symmetricus) (Brown et al., 1992).

Presently, we know little about the genetic consequences of extensive population fragmentation in southeastern fishes. In the Etowah River system, the distribution pattern of the threatened Cherokee darter suggests severe levels of insularization which warrant further investigation (Figure 12). Bauer et al. (1995) found significant differences in seven out of ten meristic characters between Cherokee darters inhabiting northern and southern tributaries of the Etowah River, suggesting that the degraded main channel of the river was acting as a barrier to dispersal of this tributary species. Barriers creating insularization in the Etowah River have existed for over 100 years as a main-channel spillway dam in Cartersville (Hall and Hall, 1921), and as severe sedimentation and pollution episodes dating to 1830 (Leigh, 1994).

Population responses to habitat fragmentation may contribute to extirpation and extinction more directly than genetic factors (Lande, 1988). Habitat fragmentation directly impacts population dynamics through changes in population size, Allee effects (density-triggered phenomena such as mass emigration or reduction of overall reproductive rates), changes in population structure, decline or extirpation of rare species and habitat specialists, and reduced ability of populations to respond to environmental stochasticity (Shaffer, 1981; Brown, 1984; Lande, 1988; Pimm et al., 1988).

In the Etowah River we have found anomalous distribution gaps of several fish species (e.g., rainbow shiner, Cherokee darter, and rock darter), constricted ranges (e.g., frecklebelly madtom), widespread extirpations (amber and Cherokee darters), and the persistence of a distinct guild of tolerant species in many areas throughout the watershed. A vexing aspect of habitat fragmentation is that rare species may require larger reaches of suitable habitat over time than they actually use at a given time. Freeman and Freeman (1994) discovered that the endangered amber darter, utilized only 40 percent of available suitable habitat during their study. These authors hypothesized that long-term population viability may depend on availability of the additional habitat to support populations during periods of random environmental variation, such as during droughts.

Threats To The System

"Large numbers of feathers, balls of fat approximately one inch in diameter, and chicken parts (wings and feathers) were floating downstream." — Georgia Water Quality Control Board (1970)

All modern biologists studying riverine systems or their faunas in the southeastern United States are working on systems that have a history of episodic degradation that transcends several human generations. Sometimes certain southern streams are described as "pristine," but in most cases the modern application of this word is a misnomer.

The major threats to southern Appalachian rivers are impoundments, sedimentation, harmful agricultural practices, urbanization, and pollution. All of these degrading forces occur to some extent throughout the Etowah River watershed, and these anthropogenic impacts have been repeatedly identified as major causes of aquatic faunal decline and extinction throughout North America (Williams, 1981; Ono et al., 1983; Miller et al., 1989; Williams et al., 1989; Burkhead and Jenkins, 1991; Etnier and Starnes, 1991; Moyle and Leidy, 1992; Warren and Burr, 1994). Below we present data and observations of the effects of impoundment and sedimentation on the Etowah River and a less detailed discussion on the effects of pollution and urbanization.

Effects of Impoundments

The present assemblage of drainages, environments, and associated faunas of southern Appalachia began to assume their pre-European colonization configuration after the last glacial retreat at the beginning of the Holocene (10,000 years before present; Hackney and Adams, 1992). Major anthropogenic modifications to riverine habitats began with the arrival of European immigrants. The earliest alterations of North American rivers by European descendants were primarily canals and low-head spillway dams (Palmer, 1986). However, in the years spanning the 1930s to the late 1970s, approximately 144 large dams were constructed in the southeastern United States. Today, 98 percent of all southeastern rivers are blocked by at least one major dam, and some major rivers are nearly or completely impounded (Hackney and Adams, 1992; Soballe et al., 1992). Most large impoundments in the southern Appalachians are hydroelectric-flood control facilities, or are associated with hydrogeneration as pump-storage impoundments. Hydrogenerated electricity only produces about two to three percent of the energy used during peaking power consumption. These colossal edifices are clearly major landscape-scale causes of aquatic faunal decline, fragmentation, and extirpation in southern Appalachia, including the Etowah River. In addition to large impoundments, there are over a million farm pond impoundments on first- and second-order tributaries in the Southeast (Menzel and Cooper, 1992). Negative ecological effects vary between large and small impoundments as discussed below.

Large Impoundments

Large impoundments are not benign replacements of river sections with lakes. Rather, they are hybrid environments (Soballe et al., 1992) that lack the productive littoral zone of natural lakes and the mosaic of riffle-run-pool habitats characteristic of upland streams. Impoundments dramatically alter habitat and reduce biodiversity in the inundated river portion. Hydrogeneration creates episodic fluctuations in downstream flow levels, resulting in dramatic physicochemical changes of the river environment. These negative effects may extend for many kilometers below a large dam. The main deleterious effects of large impoundments include the following: 1) loss of system connectivity; 2) alteration or elimination of natural flood cycles or natural low-water periods; 3) concentration of pollutants and sediments deposited in impounded reaches; 4) providing focal points for introductions of nonindigenous fishes; 5) alteration of nutrient cycling and natural trophic webs; 6) thermal alteration of the river below the dam by hypolimnotic water release; 7) bank destabilization and scouring or armoring (compacting and hardening to a crust-like layer) of downstream substrates; 8) truncation and isolation of tributaries entering the reservoir; and 9) changes in physicochemical parameters below the dam such as daily or seasonal reductions in dissolved oxygen (DO) (U.S. National Research Council, 1992; pages 200-201; Stanford and Ward, 1992, Table 5.1; Yeager, 1994).

Allatoona Reservoir has multiple negative effects on many species of native fishes and aquatic invertebrates. Besides permanently eliminating significant segments of the free-flowing Etowah River (ca. 52 river km; about 32.3 river miles) and lower portions of impounded tributaries, the reservoir has been an introduction point for several nonindigenous fishes (Beisser, 1989).

Water release from the dam apparently does not dramatically alter the natural temperature regimes of the river (Stokes et al., 1986). Water quality immediately below the dam was characterized as moderately polluted in 1969, based on low DO concentrations and reduced macroinvertebrate abundance and diversity (Georgia Water Quality Control Board, 1970). While sampling fish in early September 1993 we recorded a low DO of 2.7 parts per million (ppm) and detected the distinct odor of hydrogen sulfide. A persistent benthic boundary layer, high in hydrogen sulfide, occurs in deeper sections of Allatoona Reservoir (G. S. Beisser, Georgia Department of Natural Resources, pers. comm.). Water-level fluctuations in the Etowah River below the dam vary seasonally, weekly, and daily based on hydrogeneration demands. Figure 13 illustrates daily and weekly variations in discharge at a site just below the dam and at a site in the lowermost river during August and September 1994. Weekend reduction of discharges to base flows are evident. Daily fluctuations during these months were approximately 1.5 m (4.9 feet) at the upstream gauge and 1 m (3.3 feet) at the downstream gauge. These daily discharge variations create a highly unstable environment. The fluctuating water levels and associated velocities have scoured and armored the substrate throughout the upper one-third of the river below the dam. Large gravel, rubble, and small boulders of riffles are generally embedded in a matrix of sand and clay, eliminating most interstitial habitat available for macroinvertebrates.

Allatoona Reservoir seriously impacts the main-channel fish fauna below the dam (Figure 14). Only five species, all uncommon, were sampled immediately below the dam: one nonindigenous species (common carp) and four centrarchids. The numbers of fishes collected at sites downstream from the dam were strongly negatively correlated with proximity to the dam. Diversity of the ichthyofauna does not reach a downstream maximum until 64 river km (40 miles) below the dam.

The present downstream fauna probably differs substantially from the fauna that occurred historically in the vicinity of the dam site, and it is clearly unlike the main-channel fauna above the dam. The fish community below the dam is dominated by suckers (Catostomidae), large catfishes (Ictaluridae, excluding madtoms), and sunfishes (Centrarchidae), and there are notably fewer species of minnows (Cyprinidae) and darters (Percidae) than in the Etowah River upstream of Allatoona Reservoir. Nonindigenous species occurring only below the dam are red shiner and grass carp. Prior to construction of the dam and associated changes, the total fauna of the lower Etowah River probably exceeded our estimated number of cumulative species by as much as 30 percent. The extirpated fauna probably included lake sturgeon, American eel, Alabama shad, undescribed Mobile "blue sucker," coal darter, river darter, and species surviving elsewhere in the system such as largescale stoneroller, Alabama shiner, silver chub, bluehead chub, riffle minnow, speckled madtom, frecklebelly madtom, greenbreast darter, rock darter, amber darter, and freckled darter.

Changes in the fish community structure in flow-regulated sections of the Tallapoosa River were reported by Kinsolving and Bain (1993) and Travnichek and Maceina (1994). Both studies presented evidence of faunal recovery and did not detect the extirpation level or degree of community replacement that we have observed in the Etowah River. The community shifts in the lower Etowah river may be partially due to increased large-river habitat and associated riverine species, e.g., mooneye, smallmouth buffalo, and blue catfish. We suspect that the increase in faunal composition in the lower Etowah River is explained by persistence or recolonization by a guild of relatively tolerant species — the macrohabitat generalists of Kinsolving and Bain (1993). Because our data are qualitative (presence or absence of species), we cannot document any shifts in biomass, but we have observed low abundance of most species in the main channel 30 to 40 km (18.6 to 25 miles) below the dam. Other factors that may also contribute to an increase in the total number of species in lower river segments are improved water quality by dilution from tributaries and progressive amelioration of fluctuating water levels. The fact that the Tallapoosa fish fauna shows greater recovery at similar distances below large hydropower dams than is evident in the lower Etowah, despite similar faunas in the two rivers (Table 2; Williams, 1965), suggests that additional factors may be causing faunal depression in the lower Etowah River. Diminution of the Etowah River fauna below Allatoona Dam may be the collective result of hydrogeneration, pollution, and sedimentation.

Small Impoundments

Small impoundments primarily include farm ponds and small, off-river water supply impoundments. Most farm ponds in the southeastern United States were constructed in the last 50 years and represent nearly 0.5 percent of the land surface (Menzel and Cooper, 1992). About half of the surface area of small inland water bodies (those less than 16 ha or 39.5 acres) in Georgia is farm ponds (Menzel and Cooper, 1992). The damaging effects of farm ponds on native fishes are similar to those summarized for large impoundments except for negative impacts associated with hydrogeneration (U.S. National Research Council, 1992; Stanford and Ward, 1992). In most southern river systems the sheer number of farm ponds and their role in tributary fragmentation has not been sufficiently evaluated. In Settingdown Creek, an upper Piedmont tributary of the Etowah River, there are at least 13 farm ponds on order 1 and 2 tributaries (Figure 15). Although we have not estimated the total number of farm ponds in the Etowah River watershed, we surmise the density of farm ponds elsewhere in the system, except perhaps in the Blue Ridge province, is similar to Settingdown Creek.

Small off-river water supply impoundments are becoming an attractive source of municipal water to growing communities and major metropolitan areas. Tentative plans proposed to construct a series of reservoirs around the greater Atlanta metropolitan area for future water supply. In the Etowah River watershed, plans exist to impound Yellow Creek in eastern Cherokee and western Dawson counties for water supply, and plans have been drafted for a similar impoundment on Sharp Mountain Creek (Figure 16). The Yellow Creek impoundment will eliminate a healthy population of the threatened Cherokee darter and further contribute to fragmentation of the system. Water supply reservoirs on tributaries may also affect water quality and flow in the main channel of the Etowah River, especially if water is released to augment flow and availability at downstream municipal water intakes during natural low-flow periods. Sharp Mountain Creek also harbors Cherokee darters and the endangered amber darter, and it is one of the few remaining large tributaries of the Etowah River system that is relatively undisturbed.

Sedimentation

Sedimentation in eastern North America is often characterized as a form of nonpoint- source pollution (Karr and Schlosser, 1977). Herein we focus heavily on sedimentation because it is a widespread and serious problem in many fluvial systems. Unnatural sedimentation rates began with European colonization of North America. Sedimentation rates of Atlantic slope rivers are estimated to be four to five times greater than rates prior to European colonization (Meade, 1969). Intensive early sedimentation of the southeastern Piedmont was particularly associated with cotton farming and slavery and the fact that land was cheaper than labor; nutrient-exhausted fields were cheaper to abandon than to reclaim and exposed fields were simply left to erode (Trimble, 1974). Abandoned cultivated fields that were stripped of top soils typically became deeply gullied and in some cases it took as long as 75 to 100 years for erosion to be stabilized by natural revegetation (Trimble, 1974). Although overall current levels of sedimentation may be less than those in the first half of this century (Georgia Erosion and Sedimentation Control Panel, 1995; Pimentel et al., 1995), vastly accelerated sedimentation remains a ubiquitous threat in all southern upland river systems. The economic costs of soil erosion are staggering. Throughout the United States the annual costs of water-caused soil erosion is estimated to be about 7.4 billion dollars and annual costs for all causes of soil erosion are estimated to be 44 billion dollars (Pimentel et al., 1995). These estimates, however, do not consider the biological impacts of sedimentation and their intangible costs on humans. Herein we define sedimentation, examine the historical and present-day causes in the Etowah River watershed, and briefly review its effects on aquatic organisms.

Types of Sedimentation

Some biologists have synonymously referred to sedimentation and siltation (e.g., Burkhead and Jenkins, 1991; Bogan, 1993). Siltation is a form of sedimentation that refers to the deposition of silts (finely particulate soils) on stream or lake bottoms. Sedimentation encompasses a size range of solid particles including silt, sand, gravel, cobble, etc. Sediment transport along the bottom and suspended in the water column is a natural fluvial process of  all rivers. The amount of sediment transported through a stream system is dependent on the quantity of sediment eroded into a stream and on the ability of a stream to carry washed-in sediments to a downstream outlet (Gordon et al., 1992). Increased sedimentation usually results from land-use practices that increase the amount of soil available to erosion. The total sediment load may be defined as the sum of bedload plus suspended bed-material load plus washload (Gordon et al., 1992). In southern upland streams bedload material consists of coarse substrates such as small rubble, gravel, and coarse sands that are moved along the bottom by rolling, sliding, or bouncing. Suspended bed-material load represents the smaller fractions of bedload that will remain in suspension for an appreciable time but that settle out when water velocity decreases. Washloads are the smallest sediments in particle size, such as fine sands, silts, and clays, and are readily suspended in low water velocity.

Washloads are considered supply-limited, i.e., dependent on bank or terrestrial sources of material, but are not limited by a stream’s capacity to carry them in suspension. Bed-material load is capacity-limited, i.e., dependent on channel morphology, discharge, gradient, and substrate composition and configuration (Gordon et al., 1992). Habitat-destructive portions of the total sediment load are the suspended bed-material loads that fall out of suspension during periods of stable or diminished flows. These sediments, when excessive at a level above a stream’s ability to flush them, can blanket the stream bottom and diminish the overall habitat complexity by filling interstitial spaces of the substrate. Fine silts, sands, and clays of the washload directly harm organisms by fouling mucous membranes of gills and egg surfaces. Species that are especially sensitive to high levels of sedimentation are those that evolved in upland streams where historic levels of sedimentation were usually low and water transparency was normally high.

Causes of Sedimentation

While geologists may consider sedimentation rates on temporal scales as large as one million to 100 million years (Meade et al., 19