The influence of mariculture on mercury distribution in sediments and fish around Hong Kong and adjacent mainland China waters

To study the influence of mariculture on mercury (Hg) speciation and distribution in sediments and cultured fish around Hong Kong and adjacent mainland China waters, sediment samples were collected from six mariculture sites and the corresponding reference sites, 200-300 m away from the mariculture sites. Mariculture activities increased total mercury, organic matter, carbon, nitrogen and sulfur concentrations in the surface sediments underneath mariculture sites, possibly due to the accumulation of unconsumed fish feed and fish excretion. However, methylmercury (MeHg) concentrations and the ratio of MeHg to THg (% MeHg) in sediments underneath mariculture sites were lower than the corresponding reference sites. The % MeHg in sediments was negatively correlated (r = −0.579, p < 0.05) with organic matter (OM) content among all sites, indicating that OM may have inhibited Hg methylation in surface sediments. Three mariculture fish species were collected from each mariculture site, including red snapper (Lutjanus campechanus), orange-spotted grouper (Epinephelus coioides) and snubnose pompano (Trachinotus blochii). The average MeHg concentration in fish muscle was 75 μg kg⁻¹ (wet weight), and the dietary intake of MeHg through fish consumption for Hong Kong residents was 0.37 μg kg⁻¹ week⁻¹, which was lower than the corresponding WHO limits (500 μg kg⁻¹ and 1.6 μg kg⁻¹ week⁻¹).     

Application of a novel open-source program for measuring the effects of toxicants on the swimming behavior of large groups of unmarked fish

The aim of this study was to demonstrate a novel method for measuring the effects of toxicants on the behavior of groups of unmarked fish. Ctrax is an open source Python-based machine vision program that was originally designed to track fruit flies (Drosophila). The effects of the fish anaesthetic quinaldine sulfate on the behavior of groups of 10 unmarked Arabian killifish (Aphanias dispar) in a small arena were measured. Ctrax was able to identify and track the X-Y coordinates of the individual fish over 1 min recording periods. The data was analyzed using specifically written Matlab (The Mathworks™) toolboxes and the effects of quinaldine sulfate on absolute swimming velocity, forward swimming velocity, rate of change in orientation and distance to wall were calculated. Additionally the effects of quinaldine sulfate on path tortuosity were also measured. Ctrax has significant benefits over other available technologies for tracking the 2-dimensional coordinates of fish. In particular the software is open source and thus freely available, it is accurate, requires only simple easily available equipment and able to track potentially large groups of fish (possibly >50) while maintaining their individual identities.     

Use of a food web model to evaluate the factors responsible for high PCB fish concentrations in Lake Ellasjøen, a high Arctic Lake

Background, aim, and scope

Lake Ellasjøen, located in the Norwegian high arctic, contains the highest concentrations of polychlorinated biphenyls (PCBs) ever recorded in fish and sediment from high arctic lakes, and concentrations are more than 10 times greater than in nearby Lake Øyangen. These elevated concentrations in Ellasjøen have been previously attributed, in part, to contaminant loadings from seabirds that use Ellasjøen, but not Øyangen, as a resting area. However, other factors, such as food web structure, organism growth rate, weight, lipid content, lake morphology, and nutrient inputs from the seabird guano, also differ between the two systems. The aim of this study is to evaluate the relative influence of these factors as explanatory variables for the higher PCB fish concentrations in Ellasjøen compared with Øyangen, using both a food web model and empirical data.

Methods

The model is based on previously developed models but parameterized for Lakes Ellasjøen and Øyangen using measured data wherever possible. The model was applied to five representative PCB congeners (PCB 105, 118, 138, 153, and 180) using measured sediment and water concentrations as input data and evaluated with previously collected food web data.

Results

Modeled concentrations are within a factor of two of measured concentrations in 60% and 40% of the cases in Lakes Ellasjøen and Øyangen, respectively, and within a factor of 10 in 100% of the cases in both lakes. In many cases, this is comparable to the variability associated with the data as well as the efficacy of the predictions of other food web model applications.

Discussion

We next used the model to quantify the relative importance of five major differences between Ellasjøen and Øyangen by replacing variables representing each of these factors in the Ellasjøen model with those from Øyangen, in separate simulations. The model predicts that the elevated PCB concentrations in Ellasjøen water and sediment account for 49%–58% of differences in modeled fish PCB concentrations between lakes. These elevated sediment and, to a lesser extent, water concentrations in Ellasjøen are due to PCB loadings from seabird guano. However, sediment–water fugacity ratios of PCBs are consistently greater in Ellasjøen compared with Øyangen, which suggests that internal lake processes also contribute to differences in sediment and water concentrations. We hypothesize that the nutrients associated with guano influence sediment–water fugacity ratios of PCBs by increasing the stock of pelagic algae. As both these algae and the guano settle, their organic carbon content is degraded faster than PCBs, which causes an extra magnification step in Ellasjøen before these detrital particles are consumed by benthic organisms, which are in turn consumed by fish. The model predicts that the remaining ～50% of the differences in PCB concentrations observed between the fish of these lakes are due to other subtle differences in their food web structures.

Conclusions

In conclusion, based on the results of a food web model, we found that the most dominant factors influencing the higher PCB fish concentrations in Lake Ellasjøen compared with Øyangen are the higher sediment and water concentrations in Ellasjøen, caused by seabird guano. Together, sediment and water are predicted to account for 49%–58% of differences in fish concentrations between lakes. Although seabird guano provides a source of nutrients to the lake, in addition to contaminants, empirical data and indirect model results suggest that nutrients are not leading to decreased bioaccumulation, in contrast to what has been observed in temperate, pelagic food webs.

Recommendations and perspectives

The results of this study emphasize the importance of considering even small differences in food web structure when comparing bioaccumulation in two lakes; although the food web structures of Ellasjøen and Øyangen differ only slightly, the model predicts that these differences account for most of the remaining ～50% of the differences in PCB fish concentrations between the two lakes. This study further demonstrates the utility of food web models as we were able to predict and tease apart the influence of various factors responsible for the elevated concentrations in the fish from Lake Ellasjøen, which would have been difficult using the field data alone.     

Threatened and Endangered Species: At What Cost? The Corps of Engineers Looks at Expenditures and Priorities

Current political conditions, primarily budgetary uncertainty, and the related reluctance to make funding commitments for future generations, have raised questions about the costs of conservation and environmental protection that have not previously been asked. As Federal investments are scrutinized and budgets become ever more constrained, the costs associated with environmental requirements could begin to be of greater importance and to influence decisions on Federal projects. In response to concerns about the U.S. Army Corps of Engineers (Corps) spending under the Endangered Species Act (P.L. 93-205) (ESA), a limited investigation was performed to determine the accuracy of reported Corps expenditures. The investigation showed that, for particular groups of species, actual conservation costs for threatened and endangered species may be twice the amounts previously reported in the annual ESA expenditure reporting to the U.S. Fish and Wildlife Service. In light of this finding, the Corps has sought a means to provide more accurate and consistent reporting of expenditures for addressing threatened and endangered species. A Species Costs Template (template) has been developed to identify the types and magnitude of costs related to the ESA and to counteract the impediments (legal, institutional, and practical) to underreporting costs. The template will be used by the Corps for reporting ESA costs beginning with Fiscal Year 2005 (FY05) (reported in January 2006). Five broad categories of expenditures (effects determination costs, ESA protection and conservation costs, equipment costs, opportunity costs, and other species costs) are identified by the template.     

Assessing Biological Integrity Using Freshwater Fish and Decapod Habitat Selection Functions

Comparison between the number of taxa observed and the number expected in the absence of human impact is an easily understood and ecologically meaningful measure of biological integrity. This approach has been successfully applied to the assessment of the biological quality of flowing water sites using macroinvertebrates with the river invertebrate and classification system (RIVPACS) and its derivatives. In this paper, we develop a method similar to the RIVPACS predictive model approach to assess biological integrity at flowing-water sites using freshwater fish and decapod assemblages. We extend the RIVPACS approach by avoiding the biotic classification step and model each of the individual species separately. These assemblages were sampled at 118 least impacted (reference) sites in the Auckland region, New Zealand. Individual discriminant models based on the presence or absence of the 12 most common fish and decapod species were developed. Using the models, predictions were made using environmental measures at new sites to yield the probability of the capture of each of the 12 species, and these were combined to predict the assemblage expected at sites. The expected assemblage was compared to that observed using an observed over expected ratio (O/E). The models were evaluated using a number of internal tests including jackknifing, data partitioning, and the degree to which O/E values differed between reference sites and a set of sites perceived to be impaired by human impacts.     

Integration of long-term fish kill data with ambient water quality monitoring data and application to water quality management

Almost half (354) of all fish kills (805) in South Carolina, USA, between 1978 and 1988 occurred in the coastal zone. These kills were analyzed for causative, spatial, and temporal associations as a distinct data set and as one integrated with ambient water quality monitoring data. Estuarine kills as a result of natural causes accounted for 42.8% followed by man-induced (35.1%) and undetermined causes (22.1%). Although general pesticide usage was responsible for 53.9% of man-induced kills, weed control activities around resorts and municipal areas accounted for slightly more kills (20.9%) than did agricultural (19.8%) or vector control (13.2%) uses. A dramatic decline in agricultural-related kills has been observed since 1986 as the integrated pest management approach was adopted by many farmers. When taken with the few kills (12.0%) resulting from wastewaters, this suggests that these two land-use activities have been successfully managed via existing programs (IPM and NPDES, respectively) to minimize their contributions to estuarine fish kills. Ambient trend monitoring data demonstrated no coastal-wide dispersion of pesticide pollution. These data confirmed the nature of fish kills to be site-specific, near-field events most closely associated with the contiguous land-use practices and intensities. Typically, fish kill data are considered as event-specific data limited to the bounds of that event only. Our analysis has shown, however, that a long-term data set, when integrated with ambient water quality data, can assist in regulatory and resource management decisions for both short- and long-term planning and protection applications.     

Effects of dredging on benthic diatom assemblages in a lowland stream

The objective of this study was to assess the effects of dredging on the structure and composition of diatom assemblages from a lowland stream and to investigate whether the response of diatom assemblages to the dredging is also influenced by different water quality. Three sampling sites were established in Rodríguez Stream (Argentina); physico-chemical variables and benthic diatom assemblages were sampled weekly in spring 2001. Species composition, cell density, diversity and evenness were estimated. Diatom tolerance to organic pollution and eutrophication were also analyzed. Differences in physico-chemical variables and changes in benthic diatom assemblages were compared between the pre- and post-dredging periods using a t-test. Data were analyzed using Principal Components Analysis (PCA), non-metric multidimensional scaling (MDS) ordination and cluster analysis. The effects of dredging in the stream involve two types of disturbances: (i) in the stream bed, by the removal and destabilization of the substrate and (ii) in the water column, by generating chemical changes and an alteration of the light environment of the stream. Suspended solids, soluble reactive phosphorus and dissolved inorganic nitrogen were significantly higher in post-dredging periods. Physical and chemical modifications in the habitat of benthic diatoms produced changes in the assemblage; diversity and species numbers showed an immediate increase after dredging, decreasing at the end of the study period. Changes in the tolerance of the diatom assemblage to organic pollution and eutrophication were also observed as a consequence of dredging; in the post-dredging period sensitive species were replaced by either tolerant or most tolerant species. These changes were particularly noticeable in site 1 (characterized by its lower amount of nutrients and organic matter previous to dredging), which showed an increase in the amount of nutrients and oxygen demand as a consequence of sediment removal. However, these changes were not so conspicuous in sites 2 and 3, which already presented a marked water quality deterioration before the execution of the dredging works.     

Impacts of Urbanization on Stream Habitat and Fish Across Multiple Spatial Scales

We analyzed the relation of the amount and spatial pattern of land cover with stream fish communities, in-stream habitat, and baseflow in 47 small southeastern Wisconsin, USA, watersheds encompassing a gradient of predominantly agricultural to predominantly urban land uses. The amount of connected impervious surface in the watershed was the best measure of urbanization for predicting fish density, species richness, diversity, and index of biotic integrity (IBI) score; bank erosion; and base flow. However, connected imperviousness was not significantly correlated with overall habitat quality for fish. Nonlinear models were developed using quantile regression to predict the maximum possible number of fish species, IBI score, and base flow for a given level of imperviousness. At watershed connected imperviousness levels less than about 8%, all three variables could have high values, whereas at connected imperviousness levels greater than 12% their values were inevitably low. Connected imperviousness levels between 8 and 12% represented a threshold region where minor changes in urbanization could result in major changes in stream condition. In a spatial analysis, connected imperviousness within a 50-m buffer along the stream or within a 1.6-km radius upstream of the sampling site had more influence on stream fish and base flow than did comparable amounts of imperviousness further away. Our results suggest that urban development that minimizes amount of connected impervious surface and establishes undeveloped buffer areas along streams should have less impact than conventional types of development.     

Ecological effects of coastal marsh impoundments: A review

Many coastal resource managers believe estuarine marshes are critically important to estuarine fish and shellfish, not only because of the habitat present for juvenile stages, but also because of the export of detritus and plant nutrients that are consumed in the estuary. Concern has been widely expressed that diking and flooding marshes (impounding) for mosquito control and waterfowl management interferes with these values of marshes. Major changes caused by impoundment include an increase in water level, a decrease in salinity, and a decrease in the exchange of marsh water with estuarine water. Alteration of species composition is dramatic after impoundment. Changes in overall production and transport phenomena, however—and the consequences of these changes— may not be as great in some cases as the concern about these has implied. Although few data are available, a more important concern may be the reduction of access by estuarine fish and shellfish to the abundant foods and cover available in many natural, as well as impounded, marshes. Perhaps even more important is the occasional removal of free access to open water when conditions become unfavorable in impounded marsh that is periodically opened and closed. Collection of comparative data on the estuarine animal use of various configurations of natural and impounded marshes by estuarine animals should lead to improved management of both impounded and unimpounded marshes.