Abstract-The development of sediment quality criteria for the cationic metals cadmium, copper, lead, nickel, and zinc has focused on the use of acid-volatile sulfide (AVS) as the primary normalization phase for predicting interstitial pore-water concentrations and bioavailability of the metals. To date, most of the research in support of AVS in this context has utilized short-term laboratory exposures, with a relative paucity of information pertaining to long-term exposures. The purpose of this study, therefore, was to investigate the use of AVS as a predictor of metal toxicity to a benthic organism in a long-term laboratory exposure. Clean sediment was spiked with zinc to obtain nominal treatments ranging from Ϫ2.34 to 58.5 g/g dry weight with respect to the molar difference between simultaneously extracted metal (SEM) and AVS. The test was initiated with newly hatched larvae of the midge Chironomus tentans and carried through one complete generation (56 d) during which survival, growth, emergence, and reproduction were monitored. When the molar difference between SEM and AVS (i.e., SEM Ϫ AVS) was Ͻ0, the concentration of zinc in the sediment interstitial water was low and no adverse effects were observed for any of the biological endpoints measured. Conversely, when SEM Ϫ AVS exceeded 0, a dose-dependent increase in the relative concentration of zinc in the pore water was detected. However, the absolute concentration of pore-water zinc at each treatment declined over the course of the study, corresponding to an increase in sediment AVS and to a loss of zinc due to diffusion into the overlying water, which was renewed twice daily. Only when SEM Ϫ AVS exceeded 0 were significant reductions in survival, growth, emergence, and reproduction observed. Together, the chemical and biological data from this study compare favorably with observations made in short-term exposures and thus support the use of AVS as a normalization phase for predicting toxicity in metal-contaminated sediments.

We investigated the influence of sulfide, measured as acid-volatile sulfide (AVS), on the bioavailability of cadmium and nickel in sediments. Seventeen samples from an estuarine system heavily contaminated with cadmium and nickel were analyzed for AVS and simultaneously extracted metals (SEM) and tested in 10-d exposures with the amphipod HyaleNa azteca and the oligochaete Lumbriculus varregatus. Molar SEM (cadmium + nickel)/AVS ratios in the sediments ranged from less than one to greater than 200, with several in the range of 1 to 10. Samples with SEM/AVS ratios greater than one were consistently toxic to Hyalella azteca, whereas sediments with ratios less than one were not. Lumbriculus variegatus was less sensitive to the test sediments than Hyalella azteca, which was consistent with their relative sensitivity to cadmium and nickel in water-only exposures. SEMIAVS ratios in the sediments also appeared to be important in determining bioaccumulation of metals by Lumbrimlus variegatus. These results support other studies with metal-spiked samples in demonstrating the importance of AVS in determining metal bioavailability in sediments and suggest that AVS normalization is a reasonable means for assessing the hazard of some sediment-associated metals to aquatic ecosystems.

Summary In large lakes around the world, depth‐based changes in the abundance and distribution of invertebrate and fish species suggest that there may be concomitant changes in patterns of resource allocation. Using Lake Superior of the Laurentian Great Lakes as an example, we explored this idea through stable isotope analyses of 13 major fish taxa. Patterns in carbon and nitrogen isotope ratios revealed use of both littoral and profundal benthos among populations of most taxa analysed regardless of the depth of their habitat, providing evidence of nearshore–offshore trophic linkages in the largest freshwater lake by area in the world. Isotope‐mixing model results indicated that the overall importance of benthic food‐web pathways to fish was highest in nearshore species, whereas the importance of planktonic pathways increased in offshore species. These characteristics, shared with the Great Lakes of Africa, Russia and Japan, appear to be governed by two key processes: high benthic production in nearshore waters and the prevalence of diel vertical migration (DVM) among offshore invertebrate and fish taxa. DVM facilitates use of pelagic food resources by deep‐water biota and represents an important process of trophic linkage among habitats in large lakes. Support of whole‐lake food webs through trophic linkages among pelagic, profundal and littoral habitats appears to be integral to the functioning of large lakes. These linkages can be disrupted though ecosystem disturbance such as eutrophication or the effects of invasive species and should be considered in native species restoration efforts.

A better understanding of relationships between human activities and water chemistry is needed to identify and manage sources of anthropogenic stress in Great Lakes coastal wetlands. The objective of the study described in this article was to characterize relationships between water chemistry and multiple classes of human activity (agriculture, population and development, point source pollution, and atmospheric deposition). We also evaluated the influence of geomorphology and biogeographic factors on stressor-water quality relationships. We collected water chemistry data from 98 coastal wetlands distributed along the United States shoreline of the Laurentian Great Lakes and GIS-based stressor data from the associated drainage basin to examine stressor-water quality relationships. The sampling captured broad ranges (1.5-2 orders of magnitude) in total phosphorus (TP), total nitrogen (TN), dissolved inorganic nitrogen (DIN), total suspended solids (TSS), chlorophyll a (Chl a), and chloride; concentrations were strongly correlated with stressor metrics. Hierarchical partitioning and all-subsets regression analyses were used to evaluate the independent influence of different stressor classes on water quality and to identify best predictive models. Results showed that all categories of stress influenced water quality and that the relative influence of different classes of disturbance varied among water quality parameters. Chloride exhibited the strongest relationships with stressors followed in order by TN, Chl a, TP, TSS, and DIN. In general, coarse scale classification of wetlands by morphology (three wetland classes: riverine, protected, open coastal) and biogeography (two ecoprovinces: Eastern Broadleaf Forest [EBF] and Laurentian Mixed Forest [LMF]) did not improve predictive models. This study provides strong evidence of the link between water chemistry and human stress in Great Lakes coastal wetlands and can be used to inform management efforts to improve water quality in Great Lakes coastal ecosystems.

The objective of this study was to determine if the acid‐volatile sulfide (AVS) content of freshwater sediments was important in limiting the bioavailability and toxicity of cadmium. Five different concentrations of cadmium were spiked into sediments with three different AVS concentrations, and 10‐d exposures with the oligochaete Lumbriculus variegatus and the snail Helisoma sp. were conducted. Concurrent water‐only cadmium exposures were also conducted. When the cadmium‐to‐AVS ratios were ≤1, toxicity was not observed. At ratios ≤1, mean whole‐body cadmium residue concentrations of organisms were approximately equal to or less than the maximum residues obtained in survivors of the cadmium exposures in water only. These results corroborated the results of a previous experiment conducted with saltwater sediments and indicate that metal/AVS relationships could be used to establish numeric sediment quality criteria for use in the protection of aquatic life.