A test of two models of different levels of complexity for predicting changes of phosphorus concentration in a lake's outflow

The objective of this investigation is to compare the ability of a one-box model and a two-box model to predict the temporal variations of total phosphorus in the outflow of several lakes. The one-box model considers only total phosphorus and treats the lake as well-mixed, all year round. The two-box model considers two phosphorus fractions and the epilimnion and hypolimnion. For five shallow Canadian Shield lakes, some of the temporal variability in lake phosphorus concentrations can be explained on the basis of changes in hydraulic inflows and phosphorus loadings. Both models give roughly similar predictions for shallow lakes with high hydraulic loadings (1–200 m/year) and small variations in total phosphorus concentrations. In comparing the settling and hydraulic outflow mechanisms, a sensitivity analysis shows that both models are more sensitive to the settling rate if the lake's hydraulic loadings are less than 1 m/year, and more sensitive to the outflow rate if the lake's hydraulic loadings are greater than 100 m/year. This analysis suggests a priority for concentrating economic and other resources in conducting field measurement programs for testing phosphorus models.     

Impacts of weathered tire debris on the development of Rana sylvatica larvae

Highway runoff has the potential to negatively impact receiving systems including stormwater retention ponds where highway particulate matter can accumulate following runoff events. Tire wear particles, which contain about 1% Zn by mass, make up approximately one-third of the vehicle derived particulates in highway runoff and therefore may serve as a stressor to organisms utilizing retention ponds as habitat. In this study, we focused on the potential contribution of tire debris to Zn accumulation by Rana sylvatica larvae and possible lethal or sublethal impacts resulting from exposure to weathered tire debris during development. Eggs and larvae were exposed to aged sediments (containing either ZnCl2 or tire particulate matter, both providing nominal concentrations of 1000 mg Zn kg(-1)) through metamorphosis. Water column Zn was elevated in both the ZnCl2 and tire treatments relative to the control treatment, indicating that aging allowed Zn leaching from tire debris to occur. Tissue Zn was also elevated for the ZnCl2 and tire treatments indicating that Zn in the treatments was available for uptake by the amphibians. Exposure to both ZnCl2 and tire treatments increased the time for larvae to complete metamorphosis in comparison with controls. We also observed that the longer the organisms took to complete metamorphosis, the smaller their mass at metamorphosis. Our results indicate that Zn leached from aged tire debris is bioavailable to developing R. sylvatica larvae and that exposure to tire debris amended sediments can result in measurable physiological outcomes to wood frogs that may influence population dynamics.     

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.     

Geochemistry and toxicity of sediment porewater in a salt-impacted urban stormwater detention pond

A comprehensive study was carried out to investigate the impacts of road salts on the benthic compartment of a small urban detention facility, Rouge River Pond. Although the pond is an engineered water body, it is representative of many small urban lakes, ponds and wetlands, which receive road runoff and are probable high impact areas. Specific objectives of the study were to document the porewater chemistry of an aquatic system affected by elevated salt concentrations and to carry out a toxicological assessment of sediment porewater to determine what factors may cause porewater toxicity. The results indicate that the sediment porewater may itself attain high salt concentrations. The computations show that increased chloride levels have important implications on the Cd complexation, augmenting its concentration in porewater. The toxicity tests suggest that the toxicity in porewater is caused by metals or other toxic chemicals, rather than high levels of chloride.     

Relationships among Isolated Wetland Size, Hydroperiod, and Amphibian Species Richness: Implications for Wetland Regulations

Abstract: Wetland development within the United States is regulated primarily by size. Decisions concerning wetland destruction or conservation are therefore based in part on three inherent assumptions: (1) small wetlands contain water for short portions of the year; (2) small wetlands support few species; and (3) species found in small wetlands are also found in larger wetlands. We tested these assumptions using data on wetland size, relative hydroperiod (drying scores), and relative species richness of amphibians in depression wetlands of the southeastern United States. We found a significant (p = 0.03) but weak (r² = 0.05) relationship between hydroperiod and wetland size and no relationship (p = 0.48) between amphibian species richness and wetland size. Furthermore, synthetic models of lentic communities predict that short-hydroperiod wetlands support a unique group of species. Empirical investigations support this prediction. Our results indicate that hydroperiod length should be included as a primary criterion in wetland regulations. We advocate a landscape approach to wetlands regulation, focused in part on conserving a diversity of wetlands that represent the entire hydroperiod gradient.     

Microcosm investigations of stormwater pond sediment toxicity to embryonic and larval amphibians: variation in sensitivity among species

Stormwater ponds have become common features of modern development and often represent significant amounts of open space in urbanized areas. Although stormwater ponds may provide habitat for wildlife, factors responsible for producing variation in wildlife use of ponds have received limited attention. To investigate the role of variation in species tolerances of pollutants in structuring pond-breeding amphibian assemblages, we exposed species tolerant (Bufo americanus) and not tolerant (Rana sylvatica) of urbanization to pond sediments in laboratory microcosms. Pond microcosms had elevated sediment metal levels and chloride water concentrations. Among R. sylvatica embryos, exposure to pond sediments resulted in 100% mortality. In contrast, B. americanus embryos and larvae experienced only sublethal effects (i.e., reduced size at metamorphosis) due to pond sediment exposure. Our results suggest variation in pollutant tolerance among early developmental stages of amphibians may act in concert with terrestrial habitat availability to structure amphibian assemblages associated with stormwater ponds.     

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.