Richard C. Swartz

Assessing potential bioavailability of metals in sediments: A proposed approach

Due to anthropogenic inputs, elevated concentrations of metals frequently occur in aquatic sediments. In order to make defensible estimates of the potential risk of metals in sediments and/or develop sediment quality criteria for metals, it is essential to identify that fraction of the total metal in the sediments that is bioavailable. Studies with a variety of benthic invertebrates indicate that interstitial (pore) water concentrations of metals correspond very well with the bioavailability of metals in test sediments. Many factors may influence pore water concentrations of metals; however, in anaerobic sediments a key phase controlling partitioning of several cationic metals (cadmium, nickel, lead, zinc, copper) into pore water is acid volatile sulfide (AVS). In this paper, we present an overview of the technical basis for predicting bioavailability of cationic metals to benthic organisms based on pore water metal concentrations and metal-AVS relationships. Included are discussions of the advantages and limitations of metal bioavailability predictions based on these parameters, relative both to site-specific assessments and the development of sediment quality criteria.

Effects of natural sediment features on survival of the phoxocephalid amphipod, Rhepoxynius abronius

Effects of sediment particle size and water content on the survival of the amphipod, Rhepoxynius abronius, were examined by manipulating these natural sediment features within static laboratory microcosms. Mean amphipod survival in fine, uncontaminated, field sediments (≥ 80% silt-clay) can be 15% lower than survival in native sediment. Storage of sediments at 4°C over 7–14 days did not change sediment toxicity, but handling (i.e. elutriation and recombination) of muddy sediments increased toxicity. Sediment particle size and organic content had greater impact on the survival of R. abronius than did sediment water content in modifying amphipod survival, but we could not independently separate the effects of these two sediment variables. A new set of criteria is proposed to interpret toxicity results from the amphipod bioassay in the light of the mortality associated with fine sediment particle size. The efficacy of these criteria to separate mortality caused by fine particles and chemical contaminants was tested by analyzing field survey data from 78 Puget Sound (WA) Urban sites. Using our new criteria, the toxicity of these sediments was found to closely reflect the degree of chemical contamination. We propose that an approach similar to this be undertaken for toxicity tests whenever natural environmental factors induce mortality above background levels.

Temporal changes in the benthos along a pollution gradient: Discriminating the effect of natural phenomena from sewage-industrial wastewater effects

Abstract As pollution from the Los Angeles County Sanitation Districts (LACSD) outfalls decreased between 1980 and 1983, the macrobenthic community partially recovered and surficial (0–2 cm deep) sediment contamination and toxicity decreased at 60 m water depth along a pollution gradient from the outfalls. Pollution from the LACSD outfalls continued to decrease but macrobenthic conditions and surficial sediment quality deteriorated 1 km, was unchanged 3 km, and improved 5–15 km from the LACSD outfalls between 1983 and 1986. The net effect of natural phenomena is indicated when ecosystem changes occur in the opposite direction from that expected under prevailing pollution conditions. Our data suggest that the net effect of natural phenomena (e.g. winter storms, El Nino) on the benthos was greater than LACSD wastewater effects 1 km, about equal to LACSD wastewater effects 3 km, and less than the LACSD wastewater effects 5–15 km from the outfalls at the LACSD 1983–1986 mass emission rate. Surficial sediment samples collected beyond the 1 km station from the LACSD outfalls probably represented ⪢ 3 years of natural + effluent particulates accumulation, and they were, therefore, better suited for detecting long-term trends than for testing short-term temporal variability in surficial sediment contamination and toxicity. Nevertheless, some contaminants in the surficial sediments significantly increased between 1983 and 1986, probably primarily reflecting renewed wastewater effects near the outfalls and the effects of natural phenomena (e.g. storm-induced sediment transport or erosion) further from the outfalls. Since natural phenomena may have an effect on the benthos ≥ 3 years of LACSD wastewater effects, short-term benthic changes must be interpreted cautiously at the study site.

Inter-laboratory comparison of a sediment toxicity test using the marine amphipod Rhepoxynius abronius

Abstract An inter-laboratory comparison of the Swartz et al. (1985) amphipod sediment toxicity test was performed for seven marine sediments of and one a posteriori hypotheses or criteria were tested for three end points (survival, emergence and reburial). The bioassay met the a priori criterion of success, acceptable survival and behavior (emergence and reburial) of controls. It also met two of three a priori hypotheses: acceptable agreement on the rank order of toxicity for all three end points and acceptable agreement on mean values for the end points. The third hypothesis, classification of sediments as toxic or non-toxic, was only met for the emergence end point; however, this was probably due to the narrow range of toxic sediments tested (four of the seven sediments tested were only marginally toxic). Review of these and other amphipod sediment toxicity test data indicates that sediments that are clearly nontoxic (survival is greater than 87%) and those that are clearly toxic (survival is less than 76%) will be accurately classified whereas those of marginal toxicity (survival is between 76% and 87%) can only be classified based on emergence data. An a posteriori comparison indicated that the amphipod sediment toxicity test was more precise in LC50 and EC50 determinations with a reference toxicant (cadmium-amended sediments) than has previously been shown in inter-laboratory comparisons. Based on the results of this study, we recommend the wider use of this toxicity test to determine the toxicity of field-collected marine sediments and for laboratory studies with contaminant-amended sediments.

Acute toxicity of interstitial and particle-bound cadmium to a marine infaunal amphipod☆

Abstract The relative acute toxicity of particle-bound and dissolved interstitial cadmium was investigated using a new bioassay procedure. Interstitial concentration of Cd was controlled by means of peristaltic pumps, allowing separate manipulation of interstitial and particle properties. Addition of small quantities of organic-rich fine particles to sandy sediment resulted in greatly differing particle-bound Cd concentrations in sediment with similar interstitial Cd concentrations. Analysis of variance indicated no significant difference in the survival or ability to rebury in sediment of the phoxocephalid amphipod Rhepoxynius abronius (Barnard), when exposed to sediment with different total Cd concentrations but nearly equal interstitial Cd concentrations; in one case LC 50 data indicated slightly increased mortality in sediment with higher total Cd concentration. At least 70·2–87·9% of mortality could be predicted from past data on mortality based on dissolved Cd concentrations. The acute toxicity of Cd to this infaunal amphipod appears to be due principally to Cd dissolved in interstitial water. Our results indicate that static and flow-through bioassay tests of this organism produce comparable results with regard to mortality and survival, while the flow-through system provides a greater capacity to manipulate experimental conditions.

Life History and Productivity of the Phoxocephalid Amphipod Rhepoxynius Abronius (Barnard)

ABSTRACT Rhepoxyniusabronius (Barnard) (Amphipoda: Phoxocephalidae) is a predominantly subtidal species of the North American Pacific coast. It is also found sub- and intertidally within the polyhaline region of estuaries of Oregon and Washington. Within the Yaquina Bay estuary, Oregon, R. abronius is an annual species producing one or two broods per year. Recruitment occurs over an extended period from mid to late winter through summer. Mortality was 20-25% per month during mid to late spring through fall, and was low in winter through early spring. Mortality may be largely due to predation. Mortality of males appears higher than that of females during the reproductive season. The annual range in biomass was 40– 180 mg ash-free dry weight (AFDW)/0.5 m2, averaging 104 mg AFDW/0.5 m2. Secondary production was 160-216 mg AFDW/0.5 m2/yr and the annual ratio of production to mean biomass was 1.54-2.08. Production and the production: biomass ratio are similar to values reported for other marine amphipods with one or fewer generations per year.

Optimum macrobenthic sampling protocol for detecting pollution impacts in the southern California bight

The optimum macrobenthic sampling protocol [sampling unit, sieve mesh size, and sample size (n)] was determined for detecting ecologically important pollution impacts in the Southern California Bight, U.S.A. Cost, in laboratory processing time, was determined for samples obtained using fourteen sampling units (0.005–0.1 m2 surface area) and two sieve mesh sizes (1.0 and 0.5 mm). Statistical power analyses for t-tests of means were performed to estimate the minimum sample size (nmin) needed to reliably (α=0.05, 1−β≧0.95) reject the null hypothesis of no difference between a reference and both a stimulated and a degraded station on twelve measures of community structure. The optimum sampling protocol for detecting impacts was determined as that with the lowest total cost ×nmin on most measures.Five replicate, 0.02 m2×5 cm deep, 1.0 mm mesh samples per station could reliably distinguish reference from impacted conditions on nine or ten measures of community structure at less than one quarter of the cost of the standard sampling protocol of 5 replicate, 0.1 m2, 1.0 mm mesh samples per station. About 5 replicate, small (<0.1 m2), 1.0 mm mesh samples per station may often be optimal for detecting important structural changes in macrobenthic communities with naturally high species richness and abundance.

Toxicity of sewage sludge toRhepoxynius abronius, a marine benthic amphipod

Relative toxicity of sewage sludges from six treatment plants was determined by the LC50 of sludge-sediment mixtures to the infaunal marine amphipod,Rhepoxynius abronius. LC50s were measured as the increase in the percent total volatile solids (TVS) of the mixture due to the addition of sludge required to kill 50% of the amphipods during a 10-day exposure. LC50s ranged from 2.83% TVS addition for sludge from the small, domestic community of Waldport, Oregon to <0.1% TVS addition for metropolitan, more industrialized sources in Los Angeles, California. The toxicity of the sludge-sediment mixtures is attributed primarily to chemical contamination rather than organic enrichment. Rank correlations between toxicity and specific chemicals were usually not statistically significant, indicating that different combinations of stresses involving multiple or unmeasured factors were probably responsible for observed effects. Integrative measures of contamination (oil/grease concentration; consensus ranking of contamination based on 15 parameters) were significantly correlated withR. abronius survival indicating that the more toxic sludges had a higher overall level of contamination.

Response of the phoxocephalid amphipod,Rhepoxynius abronius, to a small oil spill in Yaquina Bay, Oregon

A spill of approximately 284,000 liters of Bunker C and diesel fuel oils occurred at the entrance of Yaquina Bay, Oregon, following the wreck of the freighterBlue Magpie on 19 November 1983. A portion of this oil entered the lower estuary and was deposited on subtidal benthic habitats occupied by the phoxocephalid amphipodRhepoxynius abronius. This species is particularly sensitive to contaminants in sediment and its life history had previously been studied at the same sites affected by the spill. The oil was initially present as small, sand-coated globules at the study site, and persisted in association with detritus and sediment for months. Bioassays withRhepoxynius abronius showed that the oil globules were not acutely toxic unless mixed into the sediment at concentrations of 1.0 parts per thousand or greater. A series of 10-d bioassays before and after the spill showed that sediment collected from oiled subtidal sites did not become acutely toxic to this species. Although the density of theR. abronius population declined by 75% after the spill, similar declines of the same population were observed at this site in fall 1980. Oil-exposedR. abronius from Yaquina Bay were slightly more sensitive to cadmium in sediment than individuals from Whidbey Island, Puget Sound, Washington. Although mean fecundity was greater in 1984 than in 1981, recruitment following the spill was lower than in the 1980–1981 study. Thus, there is limited evidence for a small impact of the oil spill on this sensitive amphipod.

Agonistic and sexual behavior of the xanthid crab,Neopanope sayi

The social behavior ofNeopanope sayi is more complicated than that usually reported for totally aquatic brachyurans. Ritualized visual displays, especially the Lateral Merus, are important in agonistic encounters. Fights are rare. During sexual interactions stereotyped periodic movements immediately after the male grabs the female may be responsible for species, sexual, and mate discrimination. Behavior prior to the Grab resembles advanced agonistic encounters, which may explain why males almost always copulate with females smaller than themselves. Females mate while in the hard stages of the molt cycle and sometimes when ovigerous.