Joel W. Snodgrass

INFLUENCE OF BEAVERS ON STREAM FISH ASSEMBLAGES: EFFECTS OF POND AGE AND WATERSHED POSITION

We used a spatial survey of fish assemblage structure in streams and beaver ponds to: (1) determine the effects of beavers on fish assemblage structure at the reach and drainage basin scales, and (2) assess the influences of pond age, watershed position, and pond environment on fish assemblage structure within beaver ponds. Stream impoundment by beavers affected species richness at the reach scale, but this effect was highly dependent on pond age and drainage area above the pond. In headwater streams, species richness per pond increased to a high in ponds 9-17 yr old and then decreased to a low in ponds >17 yr old. Farther downstream, species richness showed little change with pond age. Assem- blage structure varied significantly among unimpounded, impounded, and previously im- pounded stream reaches, and variation in assemblage structure among ponds was related to pond age and physical habitat. In large ponds there was a shift from lotic to lentic species, and as ponds aged, small-bodied minnows were replaced by larger predators. Because there was high species turnover among impounded and previously impounded reaches, beavers affected patterns of species richness at the drainage basin scale; we collected more species in first- and second-order streams (32 and 38, respectively) than in third-order streams (26). Taken together these results indicate: (1) that beavers have a positive effect on fish species richness in low-order, blackwater streams, but maintenance of this effect requires preser- vation of both spatial and temporal dynamics of beaver pond creation and abandonment, and (2) the positive relationship between stream fish species richness and drainage area described for many streams may be a recent phenomenon resulting from the extirpation of beavers from much of their historical range.

Value of artificial habitats for amphibian reproduction in altered landscapes.

Installation and maintenance of stormwater ponds to detain and treat runoff from impervious surfaces is a common method of stormwater control in developed areas. That these ponds capture pollutants, however, is of concern for wildlife species that use the ponds, particularly pond-breeding amphibians. To assess the relative contribution of stormwater ponds to the persistence of amphibian populations in suburban landscapes, we compared amphibian use of stormwater ponds and other available wetlands in suburban and forested watersheds. We surveyed three suburban and three primarily forested first-order watersheds to identify all potential wetlands that might serve as breeding sites for pond-breeding amphibians. We performed call, egg-mass, and larval surveys to measure breeding effort at each wetland in spring and summer 2007 and 2008. In suburban watersheds most (89%) of the wetlands that had breeding activity were either stormwater ponds or otherwise artificial. This pattern was also evident in the forested watersheds, where amphibians were primarily found breeding in wetlands created by past human activity. Late-stage larvae were found only in anthropogenic wetlands in all study areas because the remaining natural wetlands did not hold water long enough for larvae to complete development. Our results suggest that in urban and suburban landscapes with naturally low densities of wetlands, wetlands created by current or historic land uses may be as important to amphibian conservation as natural wetlands or pools and that management strategies directed at urban and suburban landscapes should recognize and incorporate human-created wetlands.

Nondestructive indices of trace element exposure in squamate reptiles

Compared with birds, mammals, fish, and even amphibians, very little is known about the effects of contaminants on reptiles. Recent evidence that many reptile populations may be declining has stimulated demand for toxicological studies of reptiles as well as development of nondestructive sampling techniques useful for assessing and monitoring contaminant exposure. The current study experimentally evaluated the utility of shed skins, tail clips, and blood samples as nondestructive indices of trace element exposure in banded water snakes, Nerodia fasciata. For 13.5 months, snakes were either fed fish from a coal ash-contaminated site or uncontaminated food from a reference site. Snakes fed contaminated prey accumulated As, Cd, Se, Sr, and V in various organs (i.e. liver, kidney, and/or gonads). Moreover, non-parametric discriminant function analysis revealed that snakes could be placed in two groups that reliably reflected their experimental diet based upon Se, Sr, and As concentrations in tail clips, blood, and/or shed skins. We suggest that nondestructive sampling techniques, particularly analyses of blood and tail clips, may be easily applied in evaluations of contaminant exposure in the field and laboratory and may prevent excessive destructive sampling of potentially threatened reptile species.

DEVELOPMENT OF EXPECTATIONS OF LARVAL AMPHIBIAN ASSEMBLAGE STRUCTURE IN SOUTHEASTERN DEPRESSION WETLANDS

We surveyed larval amphibians and fish in 25 relatively pristine depression wetlands on the upper Atlantic coastal plain of South Carolina to examine relationships among hydroperiod length, fish presence/absence and larval amphibian assemblage structure. Our goals were to test the application of general models of lentic community structure to Southeastern depression wetlands and to develop expectations of larval amphibian assemblage structure at reference sites. Amphibian species richness showed a unimodal pattern along a hydroperiod gradient, with wetlands that contained water for 8–10 mo/yr having the highest species richness. Wetlands that contained water for longer periods (i.e., dried only during severe drought) often contained fish and had relatively low amphibian species richness. Most species occurred along a restricted portion of the hydroperiod gradient, and some species were found almost exclusively in wetlands with fish. Associations among the occurrence of species led to relatively discrete breaks in assemblage structure along the hydroperiod gradient. Canonical correspondence analysis of catch-per-unit-effort data identified four groups of wetlands with similar assemblage structure: (1) short (drying in spring), (2) medium (drying in summer), and (3) long (drying in fall or semi-annually) hydroperiod wetlands without fish; and (4) long hydroperiod wetlands with fish. Our results suggest that general models of community structure in lentic systems are applicable to southeastern isolated wetlands and should form the basis for developing expectations of larval amphibian assemblage structure in these systems.

Influence of Hydroperiod, Isolation, and Heterospecifics on the Distribution of Aquatic Salamanders (Siren and Amphiuma) among Depression Wetlands

We used occurrence data gathered over a four-year period to assess relationships among hydroperiod length (amount of time a wetland holds water during a year), wetland isolation from other aquatic habitats, and the occurrence of sirens (Siren intermedia and S. lacertina) and amphiumas (Amphiuma means) among depression wetlands of the upper Atlantic Coastal Plain. The combined occurrence of sirens and amphiumas was positively correlated with hydroperiod length and negatively correlated with distance to the nearest intermittent aquatic habitat. Occurrences of individual species were negatively correlated with either distance to the nearest intermittent aquatic habitat or elevation difference between wetlands and the nearest permanent aquatic habitat. Siren lacertina showed higher than expected allopatric distribution in relation to other species, suggesting biological interactions may further limit the distribution of sirens and amphiumas among depression wetlands.

Effects of food ration on survival and sublethal responses of lake chubsuckers (Erimyzon sucetta) exposed to coal combustion wastes

Study organisms in chronic toxicological bioassays are often provided with excessive resources to remove food limitations as a confounding experimental variable. Under more ecologically realistic situations, resources are often less abundant and such restrictions may alter the responses of organisms to environmental contaminants. Here, we investigated the interaction between resource level and sediment toxicity in the lake chubsucker, Erimyzon sucetta. For 78 days we fed fish one of three ration levels (1X, 2X, 4X; uncontaminated food) that was grazed directly from either clean sand or coal ash-contaminated sediments. Despite provision of uncontaminated food, fish exposed to the contaminated sediments accumulated significant whole body concentrations of As, Se, Sr, and V. Food ration affected the pattern of Se accumulation, with lowest concentrations accumulated by fish supplied with the lowest rations (1X). Paradoxically, fish in the 1X-ash treatment were most adversely effected by ash-exposure, despite having Se burdens much lower than fish in the 2X- and 4X-ash treatments. Fish in the 1X-ash treatment exhibited higher mortality, lower proportional growth, and increased incidence of fin erosion compared to fish provided with higher rations. Such results may, in part, be explained by the apparent inability of fish with reduced rations to maintain positive energy balance, as evidenced by their higher standard metabolic rates compared to control fish fed similar rations. Our results underscore the importance of considering resource quantity and nutritional factors in chronic bioassays in order to draw more ecologically realistic conclusions about contaminant effects.

Chemical fractionation of Cu and Zn in stormwater, roadway dust and stormwater pond sediments

This study evaluated the chemical fractionation of Cu and Zn from source to deposition in a stormwater system. Cu and Zn concentrations and chemical fractionation were determined for roadway dust, roadway runoff and pond sediments. Stormwater Cu and Zn concentrations were used to generate cumulative frequency distributions to characterize potential exposure to pond-dwelling organisms. Dissolved stormwater Zn exceeded USEPA acute and chronic water quality criteria in approximately 20% of storm samples and 20% of the storm duration sampled. Dissolved Cu exceeded the previously published chronic criterion in 75% of storm samples and duration and exceeded the acute criterion in 45% of samples and duration. The majority of sediment Cu (92-98%) occurred in the most recalcitrant phase, suggesting low bioavailability; Zn was substantially more available (39-62% recalcitrant). Most sediment concentrations for Cu and Zn exceeded published threshold effect concentrations and Zn often exceeded probable effect concentrations in surface sediments.

Influence of larval period on responses of overwintering green frog (Rana clamitans) larvae exposed to contaminated sediments

Pond-breeding amphibians exhibit large intra- and interspecific differences in the duration of the aquatic larval phase. In contaminated aquatic environments, a prolonged larval phase means prolonged exposure to pollutants and, potentially, more severe toxic effects. In the laboratory, we tested this hypothesis by exposing green frog larvae (Rana clamitans) to commercial clean sand (control), sediment from an abandoned surface mine (mine), or sediment contaminated with coal combustion waste (CCW). By collecting eggs late in the breeding season, we obligated larvae to overwinter and spend a protracted amount of time exposed to contaminated sediments. The experiment was continued until all larvae either successfully completed metamorphosis or died (301 d). Larvae exposed to mine sediments accumulated significant levels of Pb and Zn, whereas larvae exposed to CCW-contaminated sediment accumulated significant levels of As, Se, Sr, and V. Larvae exposed to mine sediments suffered sublethal effects in the form of reduced growth and size at metamorphosis, but the proportion of larvae successfully completing metamorphosis (93%) was the same for both control and mine treatments. In contrast, larvae exposed to CCW-contaminated sediment suffered greatly reduced survival (13%) compared to both control and mine treatments. Moreover, among larvae in the CCW treatment, the majority of mortality occurred during the latter part the overwintering period (after day 205), corresponding to the onset of metamorphosis in the controls. Our results suggest that the length of the larval period may be one of many life-history or ecological characteristics that influence the sensitivity of aquatic breeding amphibians to environmental pollutants.

Mercury Concentrations in Tissues of Osprey From the Carolinas, USA

Abstract Mercury (Hg) contamination is believed to be one of the most significant pollution hazards to wildlife in the southeastern United States, yet comprehensive studies of Hg contamination of piscivorous raptors are rare in this region. We analyzed total Hg (THg) concentration in tissues of 39 osprey (Pandion haliaetus) primarily from coastal counties of South Carolina, USA, to describe tissue distribution of Hg and to determine whether age or sex influenced Hg accumulation. To determine whether Hg poses health risks to osprey breeding in this region, we also measured selenium in all tissues and the percentage of THg that was methylated in a subset of individuals. Osprey with adult plumage tended to have higher and more variable Hg concentrations in their tissues than younger birds. Whereas highest concentrations of Hg were found in liver and kidney of older birds, chicks had highest concentrations in keratinized tissues. Mercury concentrations were correlated between feathers and soft tissues, but talon concentrations of Hg were better correlated with organs than to feathers in most cases. Contrary to previous studies on birds, we found no relationship between Hg concentration in primary feathers and the sequence in which the feather was molted. We attribute this observation to the irregular and protracted molting pattern of osprey. Also contrary to other studies, feather concentrations of Hg were considerably lower than concentrations in liver and kidney. Osprey with high concentrations of Hg in their livers and kidneys accumulated as much as 99% of it as Hg(II), suggesting that demethylation and sequestration of Hg(II) may be even more critical to mitigating adverse effects than it is for other birds that eliminate most of their Hg burden in feathers. In addition, selenium was co-sequestered with Hg in the liver and kidneys and may further mitigate any adverse effects. Based on these findings, we suggest that most osprey in this region are not currently at risk of Hg toxicosis, but recommend that additional ecotoxicological studies be performed to monitor risk to osprey in this coastal region facing heavy development. We also suggest that concentrations of Hg in talon and claw may serve as important indicators of previous exposure and provide useful information for natural resource managers seeking to assess health risks to birds.

Radiocesium in fish from the Savannah River and Steel Creek: potential food chain exposure to the public.

This study examined radiocesium (137Cs) levels in fish from the vicinity of the Department of Energys Savannah River Site (SRS), a former nuclear weapons production facility in South Carolina. Fish from the Savannah River were sampled above (upstream), along, and below (downstream) the SRS, and from Steel Creek, a tributary that runs through the SRS. There was some off-site contamination of 137Cs in the Savannah River watershed due to low-level releases from past nuclear production on the SRS. The null hypotheses tested were that there would be no differences in 137Cs levels as a function of location along the river, and between species collected from the river and from Steel Creek on the SRS. For six of eight species of fish collected from the Savannah River, there were no differences in 137Cs levels in muscle from fish collected above, along, or below the SRS; exceptions were bowfin and shellcracker. Fish collected from Steel Creek had significantly higher levels (by about an order of magnitude) of 137Cs in muscle tissue than fish collected in the Savannah River. However, no fish from either Steel Creek or the Savannah River had 137Cs levels above the European Economic Community limit for fresh meat of 0.6 Bq/g. Lifetime cancer risk was calculated using the cancer slope factor of 3.2 x 10(-11)/pCi, and various fish consumption scenarios reflecting actual data from Savannah River fishermen. Using mean 137Cs concentrations and median fish consumption for 70 years for Black males-the group with the highest consumption-the excess lifetime risk associated with the eight species of fish in the Savannah River ranged from 9.0 x 10(-7) to 1.0 x 10(-5). The same calculation for fish from Steel Creek gave risk estimates from 1.4 to 8.0 x 10(-5). The 95% level for consumption by Blacks, however, was about 70 kg/year. Black fishermen consuming that amount of bass from Steel Creek would sustain a lifetime risk of 3.1 x 10(-4), whereas the same consumption of Savannah River bass would yield a risk estimate of 1.5 x 10(-5).