David R. Ownby

Watershed-scale analysis of pollutant distributions in stormwater management ponds

Stormwater management ponds have become a common Best Management Practice in urban and suburban landscapes. Stormwater management ponds are designed to hold runoff from impervious surfaces and allow the settling of sediments and associated pollutants. Various semi-aquatic and aquatic wildlife species have been documented using stormwater management ponds as habitat, but these wetland-like systems are not managed to adhere to freshwater habitat pollutant guidelines. To address the potential for pollutant exposure for wildlife, we used a random sample of 68 stormwater ponds and estimated the proportion of ponds in a third-order watershed that exceed toxicity guidelines for trace metals and polycyclic aromatic hydrocarbons in sediments and chloride in surface waters. Ninety-six percent of ponds exceeded consensus-based threshold effect concentrations for at least one trace metal. Concentrations of at least one of the PAHs measured exceeded the threshold effects concentration in 63% of the ponds. Nine percent of ponds exceeded chronic toxicity levels of chloride on all sampling dates, and 21% exceeded acute toxicity concentrations on at least one sampling date. More studies are needed to evaluate toxic effects of pollutants in stormwater management ponds and the potential for interactive effects of pollutants on wildlife.

A qicar approach for quantifying binding constants for metal-ligand complexes

Relative metal-ligand complex stability is predicted by evaluating the relationships between physicochemical properties of metal ions and their experimental biotic and abiotic binding constants, K. Linear regression analysis showed that the softness index (σ(p)) and the covalent index (χ(2)(m) r) were especially useful in model construction for rainbow trout (Oncorhynchus mykiss), fathead minnows (Pimephales promelas) and crustaceansaquatic (Daphnia magna) based on RMSE and F-ratio criterion (F(observed)/F(critical) of ≥4). The absolute value of the log of the first hydrolysis constant |logK(OH)| correlated best with logK values for barley (R(2)=0.74, p=0.02) and earthworm (R(2)=0.82, p=0.01). In contrast, the ionic index Z(2)/r explained most of the variability of logK values for the two clays kaolinite and montmorillonite, while |logK(OH)| was a better predictor of the generic NICA-Donnan parameters for HA and FA (0.67<R(2)<0.80, 0.002<p<0.01). This implies dissimilarity of the nature of the binding sites on biotic and chemical ligands and the different binding mechanisms between metal and ligands.

Ameliorative effects of sodium chloride on acute copper toxicity among Cope's gray tree frog (Hyla chrysoscelis) and green frog (Rana clamitans) embryos

Urban stormwater runoff is composed of a mixture of components, including polycyclic aromatic hydrocarbons, metals, deicing agents, and many others. The fate of these chemicals is often in stormwater detention ponds that are used by amphibians for breeding. Among aquatic organisms, the toxic mechanism for many metals involves interference with active Na(+) and Cl(-) uptake. Addition of cations has been shown to reduce the toxicity of metals among some aquatic organisms through competitive inhibition, but no studies have investigated the interaction between NaCl and Cu among amphibian embryos and larvae. To determine the degree to which NaCl may ameliorate the toxicity of Cu to amphibian embryos and larvae, the authors exposed Hyla chrysoscelis (Copes gray treefrogs) and Rana (Lithobates) clamitans (green frogs) to seven levels of Cu and NaCl in fully factorial experiments. When exposure was in artificial hard water, Cu was highly toxic to both species (96-h median lethal concentration [LC50] of 44.7 µg/L and 162.6 µg/L for H. chrysoscelis and R. clamitans, respectively). However, approximately 500 mg/L of NaCl eliminated Cu toxicity over the range of Cu concentrations used in the experiments (maximum 150 µg Cu/L for H. chrysoscelis and 325 µg Cu/L for R. clamitans). The current results suggest that NaCl is likely responsible for the toxic effects of NaCl and metal mixtures that might be typical of runoff from road surfaces in northern latitudes.

Influence of Modern Stormwater Management Practices on Transport of Road Salt to Surface Waters

Application of road salts in regions with colder climates is leading to ground and surface water contamination. However, we know little about how modern stormwater management practices affect the movement of road salt through urban watersheds. We investigated groundwater contamination and transport of road salts at two stormwater ponds in Baltimore County, Maryland. In association with the ponds, we documented a plume of contaminated groundwater that resulted in Cl- loadings to the adjacent stream of 6574 to 40 008 kg Cl- per winter, depending on winter snowfall. We also monitored Na+ and Cl- ion concentrations and the temporal dynamics of conductivity at a range of stream sites in watersheds with and without stormwater management ponds. Streams draining watersheds with stormwater ponds had consistently higher conductivities and Cl- concentrations during base flow conditions and often exhibited greater peaks in Cl- and conductivity associated with winter storms and subsequent melting events, despite the degree of watershed development. Our results indicate that modern stormwater management practices are not protecting surface waters from road salt contamination and suggest they create contaminated plumes of groundwater that deliver Cl- and Na+ to streams throughout the year.

Relative Toxicity of NaCl and Road Deicing Salt to Developing Amphibians

Recently, increases in both road deicing salt use and impervious cover have caused salinity to increase in urban aquatic environments. Road deicing salts consist of salt, abrasives, metals, and anticaking agents, all of which can be transferred to surrounding aquatic environments through runoff. Few studies have attempted to identify the relative toxicity of road deicing salt ingredients. To investigate the relative toxicity of NaCl and road deicing salt to amphibians, we exposed embryonic Rana ( = Lithobates) clamitans and larval Eurycea bislineata to NaCl and road deicing salt solutions with comparable NaCl concentrations in laboratory microcosms. Chemical analysis indicated the road deicing salt used was similar in chemical make up to other road deicing salt and was predominately (98.2%) NaCl. For both species we found little difference in survival between road deicing salt exposures and NaCl exposures. Our results suggest toxicity of road deicing salt is likely related to loss of osmoregulatory control as a result of NaCl exposure.

SALT TOXICITY TO TREEFROGS (HYLA CHRYSOSCELIS) DEPENDS ON DEPTH

Abstract Salinization of aquatic habitats is an emerging environmental concern, especially in colder climates where salt is used to prevent road icing during winter months. Salt applied to roads is carried into aquatic environments in storm-water runoff, where fluctuating water levels can result in salt stratification and spatially complex exposure scenarios for embryonic and larval pond-breeding amphibians. We conducted an experiment to investigate the potential interaction between oviposition site selection and toxicity of road salt to embryonic Copes Gray Treefrogs (Hyla chrysoscelis). We simulated road-salt stratification in 7-L microcosms containing sediment from a salt-contaminated pond and placed developing eggs at three water depths and directly on the sediment of the microcosms. At the beginning of the experiment, conductivity at the bottom of the microcosms was four to seven (from ∼4.0 to 6.5 mS cm−1) times higher than at the top or middle of the water column (∼1.0 mS cm−1). Subsequently, survival of eggs placed near the bottom and on the bottom of buckets containing salt-contaminated sediment was near 0%, while survival of eggs at the top and middle depths of the contaminated microcosms, and at all depths in control microcosms, was >60%. After hatching, embryos avoided the bottom of contaminated buckets even though much of the vertical salt gradient had dissipated. In contrast, embryos in control buckets clustered at the bottom. Our results suggest that pond-breeding amphibians that place their eggs away from the bottom may avoid some of the toxic effects of salt contamination, and those that place eggs on the bottom may be at particularly high risk.

Attenuation of copper in runoff from copper roofing materials by two stormwater control measures.

Concerns have been raised over diffuse and non-point sources of metals including releases from copper (Cu) roofs during storm events. A picnic shelter with a partitioned Cu roof was constructed with two types of stormwater control measures (SCMs), bioretention planter boxes and biofiltration swales, to evaluate the ability of the SCMs to attenuate Cu in stormwater runoff from the roof. Cu was measured as it entered the SCMs from the roof as influent as well as after it left the SCMs as effluent. Samples from twenty-six storms were collected with flow-weighted composite sampling. Samples from seven storms were collected with discrete sampling. Total Cu in composite samples of the influent waters ranged from 306 to 2863 μg L(-1) and had a median concentration of 1087 μg L(-1). Total Cu in the effluent from the planter boxes ranged from 28 to 141 μg L(-1), with a median of 66 μg L(-1). Total Cu in effluent from the swales ranged from 7 to 51 μg L(-1) with a median of 28 μg L(-1). Attenuation in the planter boxes ranged from 85 to 99% with a median of 94% by concentration and in the swales ranged from 93 to 99% with a median of 99%. As the roof aged, discrete storm events showed a pronounced first-flush effect of Cu in SCM influent but this was less pronounced in the planter outlets. Stormwater retention time in the media varied with antecedent conditions, stormwater intensity and volume with median values from 6.6 to 73.5 min. Based on local conditions, a previously-published Cu weathering model gave a predicted Cu runoff rate of 2.02 g m(-2) yr(-1). The measured rate based on stormwater sampling was 2.16 g m(-2) yr(-1). Overall, both SCMs were highly successful at retaining and preventing offsite transport of Cu from Cu roof runoff.

An enriched stable isotope technique to estimate the availability of soil zinc to Lumbricus terrestris (L.) across a salinization gradient

An enriched stable isotope approach was developed to evaluate Zn bioavailability to Lumbricus terrestris. The decrease in (68)Zn/(66) Zn in organ tissues was used to assess the relative magnitude of the bioavailable soil Zn pool. This tool was then used to specifically evaluate bioavailability as a function of soil cation distribution. Storm-water pond soils were modified using two treatment regimens whereby H(2)O-extractable Zn was varied either by different ZnCl(2) amendments or by constant ZnCl(2) amendment followed by varying the soil cation distribution through salt amendments (NaCl or CaCl(2)). Earthworms previously equilibrated in (68) Zn-spiked soil were introduced to experimental soils, and after 2 d, removed for analysis of isotopic ratios in specific tissues. Despite a wide range of H(2)O-extractable Zn values produced by the salt treatments (0.007-24.3 mg/kg), a significant relationship between Zn turnover rate in earthworm tissues and H(2)O-extractable Zn in the salt-treated soils was not observed. Rather, considering both treatment regimens, turnover rate better correlated with Zn present in broader pools, such as that extracted by 6M HNO(3). The bioavailability of trace metals to earthworms may be poorly characterized by loosely bound fractions such as the pore water. Additionally, the turnover rate of (68)Zn in anterior organ tissues may be an effective tool to evaluate the relative magnitude of the bioavailable soil Zn pool.

Predation on Green Frog Eggs (Rana clamitans) by Ostracoda

Abstract Predation has long been known as a structuring force of larval amphibian assemblages with aquatic vertebrates and insect larvae being noted as important predators. However, no studies report predation by micro-predators (i.e., organisms less than one half the size of amphibian eggs) on eggs or larvae. Here we report the consumption of Green Frog (Rana clamitans) eggs by at least four species of the crustacean class Ostracoda (Dolerocypris sinensis, Cypridopsis vidua, Eucypris fuscatus, Physocypria sp.). We initially observed Green Frog egg consumption in microcosms containing sediment from stormwater management ponds. We subsequently conducted feeding studies in which we manipulated densities of three of the species and recorded time to complete consumption of a single egg. Ostracods often consumed eggs in three days (before eggs hatched), but did not appear to attack tadpoles in the microcosms. Overall density of ostracods was correlated with egg mortality in the microcosms and Eucypris fuscatus consumed eggs most efficiently during feeding trials. Because one of the ostracods we observed feeding on amphibian eggs (C. vidua) is common among temporary wetlands, and one (D. sinensis) represents the first reported occurrence of the species in North America, there is a need for further investigations of ostracod predation on amphibian eggs under field conditions.