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Spatial and temporal trends of mercury in the aquatic food web of the lower Penobscot River, Maine, USA, affected by a chlor-alkali plant
Abstract
Mercury (Hg) concentrations in aquatic biota, including fish and shellfish, were measured over the period 2006 – 2012 in the lower Penobscot River and upper estuary (Maine, USA). The Penobscot is a system contaminated with Hg by a chlor-alkali plant that operated from 1967 to 2000, discharging 6 – 12 tons of mercury into the river. Mercury levels in aquatic biota were highest at sites downstream of the chlor-alkali plant and spatial trends were similar to those of sediments. Mean total Hg concentrations in fish muscle (adjusted for size or age) in the most affected areas were 521 (480, 566; 95% CI) ng/g ww in American eels, 321 (261,395) in mummichog, 121 (104, 140) in rainbow smelt, 155 (142,169) in tomcod, 55.2 (42.7,71.4) in winter flounder, and 328 (259,413) in American lobster tail and 522 (488,557) ng/g dw in blue mussel. Levels exceeded the 50 ng/g ww considered protective for piscivorous predators and were of concern for human health, with American eels and American lobster exceeding Maine’s mercury action level of 200 ng/g ww. Calculations of trophic position (using nitrogen isotopes) suggested that the spatial patterns observed in total Hg concentrations were not due to changes in feeding habits of the species. Fish feeding in benthic food webs, as defined by stomach content and stable carbon isotope analyses, showed no change in Hg concentrations over time. In contrast, declining trends in Hg were found in two species dependent on pelagic food webs. The absence of declines in Hg concentrations in the benthically-based food webs, despite the fact that most Hg was discharged into the system more than 40 years ago, is consistent with the long recovery predicted from dated sediment cores and from similar studies elsewhere.
... In this systematic review, we identified three studies investigating the association between distance to a pollutant source and mercury exposure ( Table 6). These studies were conducted in Norway (Tromso and Trondheim), Spain (Murcia) [30], Portugal [31], and the USA [55]. All studies were done in animals: Northern goshawk [27], Bonelli's eagle [28] and fish, lobsters and blue mussels [55]. ...
... These studies were conducted in Norway (Tromso and Trondheim), Spain (Murcia) [30], Portugal [31], and the USA [55]. All studies were done in animals: Northern goshawk [27], Bonelli's eagle [28] and fish, lobsters and blue mussels [55]. Mercury exposure was measured in feathers and blood [30], feathers [31], and soft tissue and stomach content [55]. ...
... All studies were done in animals: Northern goshawk [27], Bonelli's eagle [28] and fish, lobsters and blue mussels [55]. Mercury exposure was measured in feathers and blood [30], feathers [31], and soft tissue and stomach content [55]. All studies compared the results in various regions with different levels of exposure. ...
Purpose of review:
In epidemiologic studies, biomarkers are the best possible choice to assess individual exposure to toxic metals since they integrate all exposure sources. However, measuring biomarkers is not always feasible, given potential budgetary and time constraints or limited availability of samples. Alternatively, approximations to individual metal exposure obtained from geographic information systems (GIS) have become popular to evaluate diverse metal-related health outcomes. Our objective was to conduct a systematic review of epidemiological studies that evaluated the validity of GIS-based geolocation and distance to pollutant sources as an approximation of individual metal exposure based on correlation with biological samples.
Recent findings:
We considered 11 toxic metals: lead (Pb), cadmium (Cd), antimony (Sb), aluminum (Al), arsenic (As), chromium (Cr), nickel (Ni), mercury (Hg), tungsten (W), uranium (U), and vanadium (V). The final review included 12 manuscripts which included seven metals (Pb, Cd, Al, As, Cr, Hg, and Ni). Many studies used geolocation of the individuals to compare exposed (industrial, urban, agricultural, or landfill sources) and unexposed areas and not so many studies used distance to a source. For all metals, except lead, there was more animal than human biosampling to conduct biological validation. We observed a trend towards higher levels of Cd, Cr, Hg, and Pb in biosamples collected closer to exposure sources, supporting that GIS-based proxies for these metals might approximate individual exposure. However, given the low number and heterogeneity of the retrieved studies, the accumulated evidence is, overall, not sufficient. Given the practical benefits and potential of modern GIS technologies, which allow environmental monitoring at a reasonable cost, additional validation studies that include human biosampling are needed to support the use of GIS-based individual exposure measures in epidemiologic studies.
... In 2013 a management plan to remediate the contaminated soils nearby the chlor-alkali site was performed, which could have had an impact on biota downstream the river, due to mobilization of legacy mercury. Sánchez-Fortún et al. (2020) analyzed the temporal trends on THg in feathers from juveniles of the Audouin's gull colony in the Ebro Delta from 2004 to 2019: from 2004 to 2013 a progressive decrease was observed in THg, possibly due to ecosystem recovery (Kopec et al., 2019), followed by a tipping point with increased THg levels in 2014, and a slight increase in THg concentrations from 2014 onwards, although with fluctuations among years. Using compound-specific stable isotopes analyses of amino acids (CSIA-AA), the study concluded that a trophic shift of the individuals in the colony was not responsible for the increased THg levels observed from 2014 onwards (Sánchez-Fortún et al., 2020). ...
... Using compound-specific stable isotopes analyses of amino acids (CSIA-AA), the study concluded that a trophic shift of the individuals in the colony was not responsible for the increased THg levels observed from 2014 onwards (Sánchez-Fortún et al., 2020). Thus, we expected the Audouin's gull colony in the years 2010 and 2014 to be affected by a major extent with Hg transported from the chlor-alkali plant site, while in 2013 and 2017 would be less impacted by anthropogenic pollution due to ecosystem recovery (Kopec et al., 2019). The results of the present study regarding MDF values on these years seem to be consistent with this idea, with individuals presenting higher MDF values in 2010 and 2014, associated to higher influence of chlor-alkali derived Hg (Cransveld et al., 2017;Feng et al., 2019). ...
... Highly contaminated marsh birds and ducks in the estuary that consume insects and benthic organisms have sediment-based food webs (Sullivan and Kopec, 2018). Similarly, using stable carbon isotopes and by analyses of stomach contents Kopec et al. (2018a) concluded that the fish species in the upper estuary (tomcod, American eels, mummichog, and rainbow smelt) have sediment-based food sources. ...
... Since the mobile pool of sediment is the source of depositing material to the long-term sites of sedimentation in the coves of the mainstem of the river and in Mendall Marsh as well as the Orland River (Kelly and Rudd, 2018), it was concluded that a remediation option that lowered the THg concentrations in the mobile pool of the upper estuary would also lower surface sediment THg concentrations, and MeHg and the biota would follow (Table 4, Fig. 3; Kopec et al., 2018a;Kopec et al., 2018b). ...
Fifty years ago, the Penobscot Estuary was contaminated by mercury discharged from the chlor-alkali plant located in Orrington, Maine, USA. Almost all of the mercury was discharged from the plant during the late 1960s and early 1970s. Despite the much lower mercury discharges in recent decades, present-day concentrations in surface sediment remain high (averaging 350–1100 ng/g dw) and are still high in blood of marsh birds (up to 10.5 μg/g), black duck muscle (0.8 μg/g), and lobster muscle (0.4 μg/g). Methyl mercury (MeHg) concentrations in marsh birds exceed levels that impair reproduction. There are health advisories for duck hunters and closures of shellfish fisheries. These continuing high mercury concentrations are caused by the trapping of legacy mercury in a mobile pool of sediment that is retained in the upper estuary above a tidally forced salinity front, which travels up and down the estuary each tidal cycle - slowing the transport of particulate mercury to Penobscot Bay. The trapped legacy mercury continues to be available for methylation 50 years after it first entered the estuary. This is demonstrated by the fact that rates of MeHg production are positively related to the inorganic mercury concentration in parts of the estuary with elevated concentrations of legacy mercury. Thus, remediation measures that would lower the THg concentration in surface sediment would lower the MeHg in birds, fish and shellfish. All of this new information leads us to recommend two remediation options. Addition of mercury binding agents may lower mercury concentrations in birds in some wetland areas. System-wide, we also recommend Enhanced Natural Recovery (ENR), a novel approach that involves the partial removal of the contaminated mobile sediment pool followed by replacement with clean-clay particulates to dilute inorganic mercury concentrations, which would lower methylation rates and mercury concentrations in biota.
... This highlights the long-term attenuation of concentrations in the sediments and food web at this site following the cessation of a point source discharge. Several studies around the world have reported a decline in mercury concentrations following the closure of chlor-alkali plants (Kopec et al., 2019;Reis et al., 2009). ...
Basin land-use interacts with hydrology to deliver chemical contaminants to riverine environments. These chemicals are eventually taken up by aquatic organisms, where they can cause harmful effects. However, knowledge gaps related to the connections between hydrological, chemical, and biological processes currently limit our ability to forecast potential future changes in contaminant concentrations accurately. In this study, concentrations of three pesticide classes (organochlorines, organophosphates, and herbicides) and a standard suite of trace metals were analyzed in the South Saskatchewan River, Canada in 2020 and 2021 in water, sediments, and fishes. Organochlorine pesticides have been banned in Canada since the 1970s, yet there were some detections for methoxychlor and lindane, predominantly in sediment and fish samples, which could be attributed to legacy contamination. Except for malathion and parathion, organophosphate pesticides were scarcely detected in both sampling years in all matrices, and neonicotinoids were below detection in all samples. Conversely, the herbicides 2,4-D and dicamba were detected consistently throughout all locations in water samples for both sampling years. Overall, concentrations were 3 times higher in 2020 when river discharge was ∼2 times higher, suggesting run-off from the surrounding catchment or disturbance of contaminated sediments. Analysis for trace metals revealed that Cu and Zn exceeded sediment quality guidelines in some locations. Mercury concentrations exceeded the guidelines for about 18% of the samples (water and sediment) analyzed. These findings fill gaps in monitoring datasets and highlight key links between hydrology and chemistry that can be further explored in computational models to predict future contaminant trends in freshwater systems.
... input of Hg amounted to 17 g/day in the 1990s and decreased to 0.11 g/day in 2009 due to capture and treatment of site groundwater[78]; slow recovery of river's aquatic food web, need for longer monitoring[79]. ...
Mercury (Hg) emissions from anthropogenic sources pose a global problem. In Central Asia, Kazakhstan's central and northern regions are among the most severely Hg-contaminated territories. This is due to two former acetaldehyde (in Temirtau) and chlor-alkali (in Pavlodar) plants, discharges from which during the second half of the 20th century were estimated over 2000 tons of elemental Hg. However, the exact quantities of Hg released through atmospheric emissions to the environment, controlled discharges to the nearby aquatic systems, leakages in the cell plant, and contaminated sludge are still unknown. The present review is the initiation of a comprehensive field investigation study on the current state of these contaminated sites. It aims to provide a critical review of published literature on Hg in soils, sediments, water, and biota of the impacted ecosystems (Nura and Irtysh rivers, and Lake Balkyldak and their surrounding areas). It furthermore compares these contamination episodes with selected similar international cases as well as reviews and recommends demercuration efforts. The findings indicate that the contamination around the acetaldehyde plant site was significant and mainly localized with the majority of Hg deposited in topsoils and riverbanks within 25 km from the discharge point. In the chlor-alkali plant site, Lake Balkyldak in North Kazakhstan is the most seriously contaminated receptor. The local population of both regions might still be exposed to Hg due to fish consumption illegally caught from local rivers and reservoirs. Since the present field data is limited mainly to investigations conducted before 2010 and given the persisting contamination and nature of Hg, a recent up-to-date environmental assessment for both sites is highly needed, particularly around formerly detected hotspots. Due to incomplete site remediation efforts, recommendations given by several researchers for the territories of the former chlor-alkali and acetaldehyde plant site include ex-situ soil washing, soil pulping with gravitational separation, ultrasound and transgenic algae for sediments, and electrokinetic recovery for the former and removal and/or confinement of contaminated silt deposits and soils for the latter. However, their efficiency first needs to be validated. Findings and lessons from these sites will be useful not only on the local scale but also are valuable resources for the assessment and management of similar contaminated sites around the globe.
... The global annual release of mercury is estimated at approximately 8000 tones [5]. Mercury released into the aquatic environment as a result of natural or anthropogenic processes is present mainly in an inorganic form [6]. Since the presence of Hg(II) ions in water is extremely hazardous to human health, the maximum contaminant level (MCL) in ground and drinking water according to Environmental Protection Agency (EPA) is set to 2 ng mL −1 [7], and the permitted EPA discharge limit for wastewater is 10 ng mL −1 [8][9][10]. ...
In this work, the superior nanoadsorbent (GO-TSC) for highly effective adsorption of mercury ions from water solutions was developed, by grafting the thiosemicarbazide molecules (TSC) to the graphene oxide (GO) nanosheets. GO-TSC combines the extraordinary properties of GO, such as high specific surface area and an excellent dispersibility in aqueous solutions with strong affinity of TSC molecules to Hg(II) ions. The experiments show that the adsorption of Hg(II) on the GO-TSC is significant in a broad pH range, and reaches maximum value (close to 100%) at pH 3-4, with the maximum adsorption capacity of 231 mg g⁻¹ at pH 3.5. Due to the excellent dispersibility of GO-TSC nanosheets, an extremely small GO-TSC dosage of 5 mg L⁻¹ is required to remove Hg(II) ions from aqueous solution in a short contact time (from 10 to 30 min for adsorption of 90-95% Hg(II)). X-ray photoelectron spectroscopy indicate that the adsorption of Hg(II) is based on the chemisorption, and Hg(II) ions can be complexed by a single TSC molecule as bidentate chelating agent (S–Hg–N), or two neighboring TSC molecules (S–Hg–S). Due to the formation of strong S–Hg–N and S–Hg–S interactions, the selectivity of the GO-TSC toward Hg(II) is impressive. Hg(II) ions can be removed from aqueous solutions with very high ionic strength and high concentration of potentially coexisting ions.
... However, mercury trends look markedly different when considering the years before and after management of the chlor-alkali site. First, we found a significant decrease in feather mercury levels from 2004 to 2013, possibly reflecting the reduction of activities associated with the chlor-alkali plant in 2004 (Ercros, 2019) and a consequent decrease in Hg emissions (Pujadas, 2016) with the possibility of ecosystem recovery (Kopec et al., 2019). From 2014 onwards, although the plant operations were decreasing (Pujadas, 2016) until the complete cessation in 2017 (Ercros, 2019), there was a slight increase in feather THg levels over time. ...
As top-predators in marine ecosystems, seabirds are regarded as appropriate bioindicator species for a variety of contaminants. Mercury (Hg) is a global pollutant, which can biomagnify along marine and freshwater food webs. Therefore, mercury body burden in seabirds, such as gulls, will integrate information about pollution in the environment. In the Ebro Delta (NE Spain), legacy mercury pollution from a chlor-alkali industry located ca. 100 km upstream of the Ebro river mouth has been affecting the delta environment. We have analyzed a 15-year temporal series (2004–2019) of Hg in birds from a breeding colony of Audouin’s gull (Ichthyaetus audouinii) in the Ebro Delta to understand how fluctuations in Hg levels are coupled to human activities in the industrial area in the upstream region of the river. Stable isotopic signatures of C and N (δ¹³Cbulk and δ¹⁵Nbulk) are determined to characterize the trophic ecology of the species. Since only δ¹³Cbulk but not δ¹⁵Nbulk was associated with THg levels, we used compound-specific stable nitrogen isotope analysis of amino acids (AA-CSIA) to evaluate the causes of variation in δ¹⁵Nbulk to further investigate the idea of a decoupling of δ¹⁵Nbulk and THg over time. We found Audouin’s gull to be sensitive to Hg variations in the environment due to anthropogenic changes and to be a good indicator species for this contaminant in the Ebro Delta.
... Previous studies have investigated trophic transfers of trace metals such as Hg and MeHg between primary producers and oysters in addition to predatory whelks (Blackmore and Wang 2004), or have indeed compared mussels with barnacles but did not study Hg (Phillips and Rainbow 1988). Various studies have investigated environmental factors that affect Hg uptake in aquatic organisms (Mikac et al. 1996;Diop and Amara 2016;Briant et al. 2017;Calle et al. 2018;Kopec et al. 2019). A future study could investigate how feeding preferences and environmental factors affect bioavailability and uptake of Hg in contaminated sites. ...
The Gippsland Lakes estuary, a Ramsar listed wetland, in Victoria, Australia, is an area of potential concern for metal pollution due to influxes of human population and associated anthropogenic activities. A biomonitoring exercise was undertaken where the concentrations of 9 metals (Cr, Fe, Cu, Zn, As, Se, Ag, Cd and Hg) were analysed in the soft tissue of two common sessile invertebrates: the mussel Mytilus edulis and the barnacle Amphibalanus variegatus from 6 locations on two different occasions throughout the Gippsland Lakes estuary. A salinity gradient exists in the Lakes, from seawater at Lakes Entrance in the east, decreasing down to < 10 PSU in the west at Lake Wellington during times of rainfall, which is a major factor governing the growth and distribution of both species. Dissolved metal levels in general were low; however, Cu at most sites exceeded the 90% trigger values, while all Zn concentrations exceeded the lowest 80% trigger values of the ANZECC marine water quality guidelines for environmental health. Elevated levels of Cu and Zn were found particularly in barnacles at some sites with environmental contamination due to leaching from anti fouling paints and sacrificial zinc anodes. Elevated levels of Ag and Cd were found in mussels at the Hollands Landing site, which is immediately adjacent to a boat ramp, and Cd and Ag at this site are suspected to originate from inland anthropogenic sources. Concentrations of As in M. edulis across all 6 sites in both sampling periods had mean wet weight As concentrations exceeding the maximum level stated in the FSANZ guidelines. A. variegatus contained elevated levels of Hg especially at the North Arm site with a maximum of 13.6 μg Hg/g dry wt., while A. variegatus also showed temporal changes in Hg concentrations across sites. The maximum Hg concentration found in Mytilus edulis was 1.49 μg Hg/g dry wt. at the Hollands Landing site. Previous contaminant studies of biota in the Lakes have targeted sampling of singular predatory or migratory species, such as Black Bream (Acanthopagrus butcheri) and the Burrunan dolphin (Tursiops australis). This is the first biomonitoring study conducted on sessile organisms to assess metal contamination in the system.
... Maitland 1966;Hubert & Rhodes 1989;Duffield & Nelson 1993, 1997Montori et al. 2006;). Even eels [Anguilla rostrata (Le Sueur, 1817)] have been found to incorporate perlids in their diet ( Kopec et al. 2019). Additionally, birds associated with aquatic environments, such as the grey wagtail (Motacilla cinerea Tunstall, 1771), white-throated dipper [Cinclus cinclus (Linnaeus, 1758)] and blue ducks [Hymenolaimus malacorhynchos (Gmelin, 1789)], incorporate stoneflies into their diet (Jost 1975;Veltman et al. 1995;Bougaham et al. 2014). ...
We here review the current knowledge on the trophic ecology of stoneflies, an aquatic insect group of substantial ecological importance in lotic systems. We provide information on the feeding habits of nymphs and adults of the different families and highlight those studies that support particularly interesting findings. Regarding nymphs, we discuss the state of the art on aspects such as foraging strategies and behaviours, food acquisition mechanisms, the existence or absence of electivity for certain trophic resources, and enzymatic activity and its relationship with the assimilation efficiency of food. For adults, we highlight the differential importance of feeding among taxa. For both nymphs and adults, we report what is known about their role in aquatic and terrestrial food webs. Finally, we present some of the gaps on the trophic ecology of these insects and provide some research agendas that could be carried out to fill them.
... Food web is the network of feeding interactions and its structure may affect the entire ecosystem functions (Thompson et al. 2012). Numerous researchers have found that complex spatial heterogeneity existed in food web (Scharroba et al. 2016;Hetherington et al. 2017;Kopec et al. 2019). Theoretical analyses and modeling exercises suggest that there are two main factors shape the spatial heterogeneity of food web structure: resource availability and environmental stress (Anderson and Cabana 2009). ...
The knowledge of food web spatial heterogeneity is important for ecologists and lake managers to understand ecosystem complexity and lake management. Lake Taihu, a large shallow eutrophic lake in China, has two distinct zones: algae- and macrophyte-dominated. In this study, we assessed the spatial heterogeneity of food webs in the two lake zones using stable isotope analysis and isotope mixing model. The basal sources and consumers showed significant differences in δ¹³C and δ¹⁵N ratios between the two lake zones, except for the filter-feeding fishes. Overall, more δ¹³C-depleted and δ¹⁵N-enriched ratios were found in the algae- than the macrophyte-dominated zones for basal sources and consumers. Although the consumers in the algae-dominant zone had higher average δ¹⁵N values, the food web of the macrophyte-dominated zone had longer food chain length and more diverse trophic linkages. These spatial differences may have resulted from resource availability and environmental stress of Lake Taihu ecosystem. Factors associated with spatial trophic heterogeneity should be considered for the management and restoration of this shallow eutrophic lake.
... Bottom sediment, mudflats and marsh soils have accumulated excess Hg from a chloralkali plant (HoltraChem) that operated on the banks of the river from 1967 to 2000 (Bodaly et al., 2008;Geyer and Ralston, 2018;Santschi et al., 2017;Yeager et al., 2018). Production of methylmercury (MeHg) from this contamination has resulted in risk to bird populations and human consumption advisories for fish, shellfish, and birds (Bodaly et al., this volume;Kopec et al., 2018;Sullivan and Kopec, 2017). In this study, the distribution of methylmercury (MeHg) in sediment and marsh soils of the ecosystem were evaluated along with, the biogeochemical controls on production and accumulation. ...
The distribution of mercury and methylmercury (MeHg) in sediment, mudflats, and marsh soils of the Hg-contaminated tidal Penobscot River was investigated, along with biogeochemical controls on production. Average total Hg in surface samples (0-3 cm) ranged from 100 to 1200 ng/g; average MeHg ranged from 5 to 50 ng/g. MeHg was usually highest at or near the surface except in highly mobile mudflats. Although total Hg concentrations in the Penobscot are elevated, it is the accumulation of MeHg that stands out in comparison to other ecosystems. Surface soils in the large Mendall Marsh, about 17 km downstream from the contamination source, contained particularly high %MeHg (averaging 8%). In Mendall marsh soil porewaters, MeHg often accounted for more than half of total Hg. Salt marshes are areas of particular concern in the Penobscot River, for they are depositional environments for a Hg-contaminated mobile pool of river sediment, hot spots for net MeHg production, and sources of risk to marsh animals. We hypothesized that exceptionally low mercury partitioning between the solid and aqueous phases (with log Kd averaging ~4.5) drives high MeHg in Penobscot marshes. The co-occurrence of iron and sulfide in filtered soil porewaters, sometimes both above 100 μM, suggests the presence of nanoparticulate and/or colloidal metal sulfides. These colloids may be stabilized by high concentrations of aromatic and potentially sulfurized dissolved organic matter (DOM) in marsh soils. Thus, Hg in Penobscot marsh soils appears to be in a highly available for microbial methylation through the formation of DOM-associated HgS complexes. Additionally, low partitioning of MeHg to marsh soils suggests high MeHg bioavailability to animals. Overall, drivers of high MeHg in Penobscot marshes include elevated Hg in soils, low partitioning of Hg to solids, high Hg bioavailability for methylation, rapidly shifting redox conditions in surface marsh soils, and high rates of microbial activity.
Metals, many of which are potentially toxic, are present in the aquatic environment originated from both natural and anthropogenic sources. In these ecosystems, these elements are mostly deposited in the sediment, followed by water dissolution, potentially contaminating resident biota. Among several aquatic animals, crustaceans are considered excellent bioindicators, as they live in close contact with contaminated sediment. The accumulation of metal, whether they are classified as essential, when in excessive quantities or nonessential, not only cause damage to the health of these animals, but also to the man who consumes seafood. Among the main toxic elements to animal and human health are aluminum, arsenic, cadmium, chromium, copper, lead, mercury, nickel and silver. In this context, this systematic review aimed to investigate the dynamics of these metals in water, the main bioaccumulative tissues in crustaceans, the effects of these contaminants on animal and human health, and the regulatory limits for these metals worldwide. A total of 91 articles were selected for this review, and an additional 68 articles not found in the three assessed databases were considered essential and included, totaling 159 articles published between 2010 and 2020. Our results indicate that both chemical speciation and abiotic factors such as pH, oxygen and salinity in aquatic environments affect element bioavailability, dynamics, and toxicity. Among crustaceans, crabs are considered the main bioindicator biological system, with the hepatopancreas appearing as the main bioaccumulator organ. Studies indicate that exposure to these elements may result in nervous, respiratory, and reproductive system effects in both animals and humans. Finally, many studies indicate that the concentrations of these elements in crustaceans intended for human consumption exceed limits established by international organizations, both with regard to seafood metal contents and well as daily, weekly, or monthly intake limits set for humans, indicating consumer health risks.
Mercury (Hg) is one of the trace toxic and bioaccumulative global pollutants, and due to its long atmospheric lifetime, it presents a significant global challenge. The present study (1) utilizes total gaseous mercury (TGM) measurements made around a former Hg-cell chlor-alkali plant (CAP) located in Pavlodar, Kazakhstan, and predicts the spatial distribution of Hg over its premises and the nearby city. It then (2) estimates the environmental repartition of Hg deposited by the CAP using three fugacity models of varying complexity: Level I, QWASI, and HERMES. Finally, it (3) predicts long-range Hg transport via forward trajectory-based cluster analysis. The atmospheric Hg levels measured in Pavlodar and around Lake Balkyldak were elevated: in the range of 1–37 ng/m3 with an urban background level at 4.9 ng/m3. Specifically, concentrations up to 37 ng/m3 close to Lake Balkyldak and up to 22 ng/m3 nearby the city’s industrial zone (where the CAP was located) had been observed. Interpolation maps created using kriging also suggest these locations as the primary sources of atmospheric Hg in the city. The Level I fugacity model indicated that almost all of Hg is expected to end up in the atmosphere. The modeling results obtained using more complex QWASI and HERMES models showed that some significant quantity of Hg would still be associated with the sediments of Lake Balkyldak (a large wastewater discharge pond nearby the CAP). The forward trajectory-based cluster analysis method revealed the long-range atmospheric transportation routes and local, regional, and global impact zones. Furthermore, a source-receptor relationship using air transportation pathways to identify “areas of impact” was addressed. During both heating and non-heating seasons, the frequency-based analysis identified the distribution of Hg reaching the territories of Mongolia, northwest China, southwest Kazakhstan. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT-4) model forward trajectory analysis has confirmed similar patterns during heating and non-heating seasons, except with shorter impact distances during the non-heating period. Even though the CAP was closed more than 30 years ago and those past remediation efforts cleaned up the site, the residual Hg pollution seems significant and should be further investigated in different environmental media.
Legacy mercury (Hg) refers to Hg in the environment that originated with antecedent or historical releases and has the potential to continue to impact the environment over time after the source—e.g., atmospheric emissions or industrial releases—has been reduced or eliminated. Depending upon its magnitude and where in the environment it is stored, legacy Hg can affect the cycling of Hg with a turnover time of centuries at the global scale to a few years or decades at watershed or more localized levels. This chapter examines how legacy Hg can impact Hg cycling and recovery in the Everglades. This analysis includes examining the current global cycling of Hg and how disequilibrium related to legacy Hg is expected to continue to influence rates of atmospheric deposition well beyond current and anticipated efforts to reduce anthropogenic emissions. The chapter also considers the question of legacy Hg stored in Everglades soils and sediments and the likelihood that such legacy Hg will militate against restoration efforts over shorter time scales (years).
A new oxadiazole-functionalized polyacrylonitrile fiber (PANAOF) was successfully fabricated by immobilizing the organic molecule 2-chloromethyl-5-phenyl-1,3,4-oxadiazole on aminated fiber (PANAF). The fibers were characterized completely by Fourier-transform infrared spectroscopy, elemental analysis, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. Compared with PANAF, PANAOF showed a higher adsorption capability for Hg²⁺ ions in aqueous solutions. The functionalized fiber PANAOF exhibited a highly selective adsorption for Hg²⁺ when coexisting with other metal ions viz. Pb²⁺, Cd²⁺, Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, Cr³⁺, Ca²⁺, and Mg²⁺. The PANAOF presented the best adsorption capacity for Hg²⁺ at pH 5. Moreover, the adsorption experimental data fit well with the pseudo-second-order kinetic model and Langmuir isotherm. Notably, the PANAOF almost retained its original adsorption capacity (112 mg/g) after five cycles, indicating its excellent reusability in practical applications.
A lobster-trap video (LTV) system was developed to determine how lobster traps
fish for Homarus americanus and how behavioural
interactions in and around traps influence catch. LTV consists of a low-light
camera and time-lapse video cassette recorder (VCR) mounted to a standard trap
with optional red LED arrays for night observations. This self-contained
system is deployed like a standard lobster trap and can collect continuous
video recordings for >24 h. Data are presented for 13 daytime deployments
of LTV (114 h of observation) and 4 day and night deployments (89 h of
observation) in a sandy habitat off the coast of New Hampshire, USA. Analyses
of videotapes revealed that traps caught only 6% of the lobsters that
entered while allowing 94% to escape. Of those that escaped, 72%
left through the entrance and 28% through the escape vent. Lobsters
entered the trap at similar rates during the day and night and in sandy and
rocky habitats. Lobsters generally began to approach the trap very shortly
after deployment, and many appeared to approach several times before entering.
These data confirm the results of previous laboratory-based studies in
demonstrating that behavioural interactions in and around traps strongly
influence the ultimate catch.
Methylmercury (MeHg) is a contaminant of global concern that bioaccumulates and bioamagnifies in marine food webs. Lower trophic level fauna are important conduits of MeHg from sediment and water to estuarine and coastal fish harvested for human consumption. However, the sources and pathways of MeHg to these coastal fisheries are poorly known particularly the potential for transfer of MeHg from the sediment to biotic compartments. Across a broad gradient of human land impacts, we analyzed MeHg concentrations in food webs at ten estuarine sites in the Northeast US (from the Hackensack Meadowlands, NJ to the Gulf of Maine). MeHg concentrations in water column particulate material, but not in sediments, were predictive of MeHg concentrations in fish (killifish and Atlantic silversides). Moreover, MeHg concentrations were higher in pelagic fauna than in benthic-feeding fauna suggesting that MeHg delivery to the water column from methylation sites from within or outside of the estuary may be an important driver of MeHg bioaccumulation in estuarine pelagic food webs. In contrast, bulk sediment MeHg concentrations were only predictive of concentrations of MeHg in the infaunal worms. Our results across a broad gradient of sites demonstrate that the pathways of MeHg to lower trophic level estuarine organisms are distinctly different between benthic deposit feeders and forage fish. Thus, even in systems with contaminated sediments, transfer of MeHg into estuarine food webs maybe driven more by the efficiency of processes that determine MeHg input and bioavailability in the water column.
Seabed mapping, spatially referenced trapping, and mark‐recapture methods have all been useful tools in ecological studies of lobsters and other benthic animals. Here we integrate the three methods to evaluate local population dynamics and movements of American lobsters, Homarus americanus, in coastal fishing grounds in Maine, United States. The study was conducted on five study areas of different size, and used two different sampling protocols. At one site (1 km in area) we used a monthly mark‐recapture sampling interval over a 6‐month period, only tagging a subsample of the catch. At four smaller sites (0.3 km) we used a shorter‐term approach, sampling at 3–4‐day intervals for a 2‐week duration, tagging the entire catch. Tagging data were analysed with a modified Jolly‐Seber model adapted for continuous sampling to estimate population abundance, gains (immigration), and losses (emigration and mortality). Side‐scan sonar surveys of the seabed combined with diver‐based population surveys, stratified by substrate type, provided an independent comparison to mark‐recapture‐based estimates of abundance over the same areas. Spatial referencing of trap catch also allowed us to relate catch rates and lobster movements directly to seabed features. The longer‐term tagging data on the larger study area provided abundance estimates that were more consistent with the diver observations, and estimates of gains and losses statistically more robust, than those derived from the shorter‐term effort on the smaller sites. The flux of lobsters followed the well known seasonal movements on these fishing grounds, with gains and losses from the larger study area ranging over 1000 individuals per day, and an estimated mid‐summer peak density of >65 000 lobsters per km (individuals >50 mm carapace length). This approach may lend itself to broader application with the American lobster.
Lipofuscin content was determined in the brains of 41 American lobsters Homarus americanus (Milne-Edwards) aged 4, 13 and 27 mo reared individually at 19 to 20 degrees C. Lipofuscin was quantified by fluorescence microscopy and image analysis. Lipofuscin granules occurred in each age group and in the oldest group appeared as large aggregations collectively averaging 2.1% of the area of histological sections of the olfactory lobe cell mass. Carapace length-corrected lipofuscin area % gave the highest correlation with age (r = 0.99, p < 0.0001) and a non-linear best fit regression (y = 0.00264 x Age(2.03)). The size and number of lipofuscin granules and carapace length were also significantly related to age. Lipofuscin concentration was not significantly correlated with carapace length within any of the 3 age classes (4 mo: r = -0.078, 13 mo: r = -0.20, 27 mo: r = -0.351). These results suggest the possibility that the lipofuscin technique can differentiate cohorts in natural populations. However, environmental temperature and the possibility of other factors affecting metabolic rate may need to be taken into account when attempting to apply the laboratory model to wild populations.
The English-Wabigoon River system in Northwestern Ontario, Canada, was one of the most heavily mercury-contaminated waterways in the world due to historical discharges in the 1960s from a chlor-alkali plant. This study examines long-term (1970-2010) monitoring data to assess temporal trends in mercury contamination in Walleye, Northern Pike and Lake Whitefish, three species important for sport and subsistence fishing in this region, using dynamic linear modeling and piecewise regression. For all lakes and species, there is a significant decline (36-94%) in mercury concentrations through time; however, there is evidence that this decline is either slowing down or levelling off. Concentrations in the English-Wabigoon fish are elevated, and may still present a potential health risk to humans consuming fish from this system. Various biotic and abiotic factors are examined as possible explanations to slowing rates of decline in mercury concentrations observed in the mid-1980s.
1] In a detailed study of the biogeochemical factors affecting the methylation of mercury in a Chesapeake Bay salt marsh, we examined relationships between mercury methylation and numerous variables, including sulfate reduction rates, organic carbon mineralization rates, iron and sulfur chemistry, and the character of dissolved organic matter (DOM). Our data show that salt marshes are important sites of de novo methylmercury (MeHg) production in coastal ecosystems. Some of the controls on MeHg production that have been well-described in other ecosystems also impacted MeHg production in this salt marsh, specifically the effect of sulfide accumulation on mercury bioavailability. We observed some novel biogeochemical relationships with Hg(II)-methylation and MeHg accumulation, particularly the positive association of Hg(II)-methylation with zones of microbial iron reduction. On the basis of this relationship, we suggest caution in wetland and groundwater remediation approaches involving iron additions. Aqueous phase Hg complexation appeared to be the dominant control on Hg bioavailability across the marsh sites examined, rather than Hg partitioning behavior. A detailed examination of DOM character in the marsh suggested a strong positive association between Hg(II)-methylation rate constants and increasing DOM molecular weight. Overall, our results indicate that net MeHg production is controlled by a balance between microbial activity and geochemical effects on mercury bioavailability, but that a significant zone of MeHg production can persist in near surface salt marsh soils. Production of MeHg in coastal marshes may negatively impact ecosystems via export to adjacent estuaries or through direct bioaccumulation in birds, fish and amphibians that feed in these highly productive ecosystems.
Rainbow smelt (Osmerus mordax) is a recent invader to the lakes of the Hudson Bay drainage in northwestern Ontario, Canada. In some systems, the invasion has been linked to an increase in mercury (Hg) concentration in native predatory fish. This increase may be due to the fact that rainbow smelt are trophically elevated and thus accumulate more Hg than native forage fish species. To test this hypothesis, we compared the trophic positions and Hg concentrations of rainbow smelt and native forage fish in a series of smelt-invaded and reference lakes in northwestern Ontario. A comparison of forage fish δ 15N (an index of trophic position) between the smelt-invaded and reference lakes indicated that rainbow smelt moved into atrophic niche that was unoccupied prior to their arrival. Relationships between δ15N and body size and between Hg concentration and body size differed among the forage species. This indicates that the response of predator Hg concentrations to smelt invasion depends on both the species and size composition of their pre-versus post-invasion diet. At a standardized body mass of 10 g, rainbow smelt were significantly trophically elevated relative to most native forage species, but they did not have significantly higher muscle Hg concentrations. Relationships between Hg concentration and δ15N were weak, both within and among forage fish species. This study shows that trophic elevation on a fine scale (within the forage fish community) may not result in increased contaminant bioaccumulation. It further challenges the general assumptions of food web theory and contaminant bioaccumulation.
Threshold concentrations associated with adverse effects of dietary exposure to methylmercury (MeHg) were derived from published results of laboratory studies on a variety of fish species. Adverse effects related to mortality were uncommon, whereas adverse effects related to growth occurred only at dietary MeHg concentrations exceeding 2.5 µg g(-1) wet weight. Adverse effects on behavior of fish had a wide range of effective dietary concentrations, but generally occurred above 0.5 µg g(-1) wet weight. In contrast, effects on reproduction and other subclinical endpoints occurred at dietary concentrations that were much lower (<0.2 µg g(-1) wet wt). Field studies generally lack information on dietary MeHg exposure, yet available data indicate that comparable adverse effects have been observed in wild fish in environments corresponding to high and low MeHg contamination of food webs and are in agreement with the threshold concentrations derived here from laboratory studies. These thresholds indicate that while differences in species sensitivity to MeHg exposure appear considerable, chronic dietary exposure to low concentrations of MeHg may have significant adverse effects on wild fish populations but remain little studied compared to concentrations in mammals or birds.
The stable isotopes of nitrogen (d15N) and carbon (d13C) provide powerful tools for estimating the trophic positions of and carbon flow to consumers in food webs; however, the isotopic signature of a consumer alone is not generally sufficient to infer trophic position or carbon source without an appropriate isotopic baseline. In this paper, I develop and discuss methods for generating an isotopic baseline and evaluate the assump- tions required to estimate the trophic position of consumers using stable isotopes in multiple ecosystem studies. I test the ability of two primary consumers, surface-grazing snails and filter-feeding mussels, to capture the spatial and temporal variation at the base of aquatic food webs. I find that snails reflect the isotopic signature of the base of the littoral food web, mussels reflect the isotopic signature of the pelagic food web, and together they provide a good isotopic baseline for estimating trophic position of secondary or higher trophic level consumers in lake ecosystems. Then, using data from 25 north temperate lakes, I evaluate how d 15N and d13C of the base of aquatic food webs varies both among lakes and between the littoral and pelagic food webs within lakes. Using data from the literature, I show that the mean trophic fractionation of d15N is 3.4‰ (1 SD 5 1‰) and of d13 Ci s 0.4‰ (1 SD 5 1.3‰), and that both, even though variable, are widely applicable. A sen- sitivity analysis reveals that estimates of trophic position are very sensitive to assumptions about the trophic fractionation of d15N, moderately sensitive to different methods for gen- erating an isotopic baseline, and not sensitive to assumptions about the trophic fractionation of d13C when d13C is used to estimate the proportion of nitrogen in a consumer derived from two sources. Finally, I compare my recommendations for generating an isotopic baseline to an alternative model proposed by M. J. Vander Zanden and J. B. Rasmussen. With an appropriate isotopic baseline and an appreciation of the underlying assumptions and model sensitivity, stable isotopes can help answer some of the most difficult questions
We evaluated the effect of salt and formalin-ethanol sample preservation on carbon and nitrogen isotopic signatures of fish muscle tissue. We found statistically significant effects of the tissue preservation technique on both δ13C and δ15N; however, the magnitude of change was small and directionally uniform. Isotopic shifts were similar to those observed in previous studies in which formalin was used to preserve samples of quail blood and muscle and sheep blood. Because salt preservation caused minimal isotopic shifts (+0.13‰ δ13C, +0.72‰ δ15N), we propose salt as an easy, inexpensive preservation technique for biological samples collected in remote field settings. Specimens preserved with formalin and ethanol were minimally affected by preservation (−1.12‰ δ13C, +0.62‰ δ15N) and therefore may be suitable for ecological applications of stable isotope analysis when carbon and nitrogen sources are differentiated by more than 2‰. Further research is required to evaluate potential long-term storage effects of formalin fixation and alcohol preservation on isotopic signatures of fish tissues.
Post Minamata incident there has been awareness about mercury toxicity even among the general public. Previous researches contributed a vast amount of data regarding acute mercury exposure, but gradually information about the low dose [Ninomiya, T., Ohmori, H., Hashimoto, K., Tsuruta, K., Ekino, S., 1995. Expansion of methylmercury poisoning outside minamata: an epidemiological study on chronic methylmercury poisoninig outside of Minamata. Environ. Res. 70 (1) 47-50; Lebel, J., Mergler, D., Lucotte, M., Amorim, M., Dolbec, J., Miranda, D., Arantes, G., Rheault, I., Pichet, P., 1996. Evidence of early nervous system dysfunction in Amazonian populations exposed to low-levels of methylmercury. Neurotoxicology 17 (1) 157-167] of mercury toxicity has been trickling in. With mercury contaminating rain-, ground- and sea-water no one is safe. Polluted water leads to mercury laced fish, meat and vegetable. In aquatic environments, inorganic mercury is microbiologically transformed into lipophilic organic compound 'methylmercury'. This transformation makes mercury more prone to biomagnification in food chains. Consequently, populations with traditionally high dietary intake of food originating from fresh or marine environment have highest dietary exposure to mercury. Extensive research done on locals across the globe have already established this, persons who routinely consume fish or a particular species of fish are at an increased risk of methylmercury poisoning. The easy access of the toxicant to man through multiple pathways air, water, food, cosmetic products and even vaccines increase the exposure. Foetus and children are more susceptible towards mercury toxicity. Mothers consuming diet containing mercury pass the toxicant to foetus and to infants through breast milk. Decreased performance in areas of motor function and memory has been reported among children exposed to presumably safe mercury levels. Similarly, disruption of attention, fine motor function and verbal memory was also found in adults on exposure to low mercury levels. It is an occupational hazard for dental staff, chloralkali factory workers and goldminers, etc. Mercury has been found to be a causative agent of various sorts of disorders, including neurological, nephrological, immunological, cardiac, motor, reproductive and even genetic. Recently heavy metal mediated toxicity has been linked to diseases like Alzeihemer's, Parkinson's, Autism, Lupus, Amyotrophic lateral sclerosis, etc. Besides this, it poses danger to wildlife. Therefore, it becomes imperative to spread the information regarding the threat of mercury exposure amongst the scientists and masses.
Fifty years ago, the Penobscot Estuary was contaminated by mercury discharged from the chlor-alkali plant located in Orrington, Maine, USA. Almost all of the mercury was discharged from the plant during the late 1960s and early 1970s. Despite the much lower mercury discharges in recent decades, present-day concentrations in surface sediment remain high (averaging 350–1100 ng/g dw) and are still high in blood of marsh birds (up to 10.5 μg/g), black duck muscle (0.8 μg/g), and lobster muscle (0.4 μg/g). Methyl mercury (MeHg) concentrations in marsh birds exceed levels that impair reproduction. There are health advisories for duck hunters and closures of shellfish fisheries. These continuing high mercury concentrations are caused by the trapping of legacy mercury in a mobile pool of sediment that is retained in the upper estuary above a tidally forced salinity front, which travels up and down the estuary each tidal cycle - slowing the transport of particulate mercury to Penobscot Bay. The trapped legacy mercury continues to be available for methylation 50 years after it first entered the estuary. This is demonstrated by the fact that rates of MeHg production are positively related to the inorganic mercury concentration in parts of the estuary with elevated concentrations of legacy mercury. Thus, remediation measures that would lower the THg concentration in surface sediment would lower the MeHg in birds, fish and shellfish. All of this new information leads us to recommend two remediation options. Addition of mercury binding agents may lower mercury concentrations in birds in some wetland areas. System-wide, we also recommend Enhanced Natural Recovery (ENR), a novel approach that involves the partial removal of the contaminated mobile sediment pool followed by replacement with clean-clay particulates to dilute inorganic mercury concentrations, which would lower methylation rates and mercury concentrations in biota.
The distribution of mercury and methylmercury (MeHg) in sediment, mudflats, and marsh soils of the Hg-contaminated tidal Penobscot River was investigated, along with biogeochemical controls on production. Average total Hg in surface samples (0-3 cm) ranged from 100 to 1200 ng/g; average MeHg ranged from 5 to 50 ng/g. MeHg was usually highest at or near the surface except in highly mobile mudflats. Although total Hg concentrations in the Penobscot are elevated, it is the accumulation of MeHg that stands out in comparison to other ecosystems. Surface soils in the large Mendall Marsh, about 17 km downstream from the contamination source, contained particularly high %MeHg (averaging 8%). In Mendall marsh soil porewaters, MeHg often accounted for more than half of total Hg. Salt marshes are areas of particular concern in the Penobscot River, for they are depositional environments for a Hg-contaminated mobile pool of river sediment, hot spots for net MeHg production, and sources of risk to marsh animals. We hypothesized that exceptionally low mercury partitioning between the solid and aqueous phases (with log Kd averaging ~4.5) drives high MeHg in Penobscot marshes. The co-occurrence of iron and sulfide in filtered soil porewaters, sometimes both above 100 μM, suggests the presence of nanoparticulate and/or colloidal metal sulfides. These colloids may be stabilized by high concentrations of aromatic and potentially sulfurized dissolved organic matter (DOM) in marsh soils. Thus, Hg in Penobscot marsh soils appears to be in a highly available for microbial methylation through the formation of DOM-associated HgS complexes. Additionally, low partitioning of MeHg to marsh soils suggests high MeHg bioavailability to animals. Overall, drivers of high MeHg in Penobscot marshes include elevated Hg in soils, low partitioning of Hg to solids, high Hg bioavailability for methylation, rapidly shifting redox conditions in surface marsh soils, and high rates of microbial activity.
Mercury inputs by surface and ground water sources to Penobscot River from a defunct Hg-cell chlor-alkali plant were measured in 2009–10 and estimated for the entire period of operation of this facility. Over the measured interval (422 days) approximately 2.3 kg (5.4 g day⁻¹) of mercury was discharged to the Penobscot River by the two surface streams that drain the site, with most of the combined loading (1.8 kg Hg, 78%) associated with a single storm with rainfall in excess of 100 mm. Groundwater seepage rates from the site, as estimated from both a radon tracer and seepage meter methods were in the range of 3 to 4 cm day⁻¹ and, when combined with a best estimate of the area of groundwater discharge (11,000 m²) and average seepage/porewater mercury concentration (242 ng L⁻¹, UCL95), yielded a loading of 0.11 g day⁻¹ for site groundwater. None of the municipal or other industrial point sources of mercury to the river between Veazie and Bucksport, Maine exceeded 1 g day⁻¹ individually, nor was the aggregate loading of all such sources >3 g day⁻¹ (based on State of Maine data). Mercury loadings for the three largest tributaries downstream of Veazie Dam were estimated to contribute 4.2, 3.7 and 2.5 g day⁻¹, respectively, to the Penobscot River. Based on sampling (total Hg ~ 2 to 4 ng L⁻¹) and historical mean discharge data (340–460 m³ s⁻¹), the Penobscot River upstream of the plant site contributes as much as 160 g day⁻¹ to the downstream reach depending on river discharge. Estimates of historical (1967–2012) mercury loading using both generic emission factors and measured releases ranged from 2.6 to 27 MT while the mass of mercury found in downstream sediments amounted to 9 MT.
We examined total mercury (Hg) distributions in sediments from the Penobscot River and estuary, Maine, a site of extensive Hg releases from HoltraChem (1967-2000). Our objectives were to quantify: (1) bottom sediment Hg inventories (upper ~1m; 50-100 y); (2) sediment accumulation rates; and (3) contemporary Hg fluxes to bottom sediments; by sampling the Penobscot River (PBR), Mendall Marsh (MM), the Orland River (OR) and the Penobscot estuary (ES). Hg was rapidly distributed here, and the cumulative total (9.28 metric tons) associated with sediments system-wide was within the range released (6-12 metric tons). Evidence of sediment/Hg remobilization was observed in cores primarily from the PBR, and to a lesser extent the ES, whereas cores from MM, most of the OR, the ES, and half from the PBR exhibited sharp peaks in Hg concentrations at depth, followed by gradual decreases towards the surface. Based on background PBR sediment Hg concentrations (100ngg-1), "elevated" (300ngg-1), or "highly elevated" (600ngg-1) Hg concentrations in sediments, and resulting inventories, we assessed impact levels ("elevated"≥270, or "highly elevated"≥540mgm-2). 71% of PBR stations had "elevated", and 29% had "highly elevated" Hg inventories; 45% of MM stations had "elevated", and 27% had "highly elevated" inventories; 80% of OR stations had "elevated" inventories only; and 17% of ES stations had "elevated" inventories only. Most "highly elevated" stations were located within 8km of HoltraChem, in MM, in the PBR, and in the OR. Near-surface sediments in the OR, PBR and MM were all "highly elevated", while those in the ES were "elevated", on average. Mean Hg fluxes to bottom sediments were greatest in the OR (554), followed by the PBR (469), then MM (452), and finally the ES (204ngcm-2y-1).
The natural recovery of estuaries from contamination is largely determined by the timescale over which contaminated sediment is exported or buried and replaced by cleaner sediment that enters from the watershed or the ocean. That timescale depends on the size of the "pool" of contaminated sediment that resides in the estuary. The larger the pool, the longer the recovery timescale for a given rate of sediment input. A field study was undertaken as part of a study of mercury contamination in the Penobscot estuary to assess the mechanisms affecting the transport and fate of contaminated sediment. Based on measurements of water properties, currents and sediment transport and seabed samples analyzed for sediment properties and contaminant concentrations, a "mobile pool" of contaminated sediment with relatively uniform geochemical characteristics along a 20-km reach of the estuary was identified. This pool of sediment is mobilized seasonally by resuspension and trapping processes associated with salinity fronts that vary in location with discharge conditions. Sediment is transported down-estuary during high discharge and up-estuary during low discharge, with seasonal, bi-directional transport of sediment in the estuary significantly exceeding the annual input of new sediment from the watershed. This continual, bi-directional transport leads to homogenization of the chemical properties of the mobile sediment, including contaminant concentrations. The large mass of mobile sediment relative to the input of sediment from the watershed helps explain the long recovery timescale of contaminants in the Penobscot estuary.
Environmental contaminants are a concern for animal health, but contaminant exposure can also be used as a tracer of foraging ecology. In particular, mercury (Hg) concentrations are highly variable among aquatic and terrestrial food webs as a result of habitat- and site-specific biogeochemical processes that produce the bioaccumulative form, methylmercury (MeHg). We used stable isotopes and total Hg (THg) concentrations of a generalist consumer, the California gull (Larus californicus), to examine foraging ecology and illustrate the utility of using Hg contamination as an ecological tracer under certain conditions. We identified four main foraging clusters of gulls during pre-breeding and breeding, using a traditional approach based on light stable isotopes. The foraging cluster with the highest δ¹⁵N and δ³⁴S values in gulls (cluster 4) had mean blood THg concentrations 614% (pre-breeding) and 250% (breeding) higher than gulls with the lowest isotope values (cluster 1). Using a traditional approach of stable-isotope mixing models, we showed that breeding birds with a higher proportion of garbage in their diet (cluster 2: 63–82% garbage) corresponded to lower THg concentrations and lower δ¹⁵N and δ³⁴S values. In contrast, gull clusters with higher THg concentrations, which were more enriched in ¹⁵N and ³⁴S isotopes, consumed a higher proportion of more natural, estuarine prey. δ³⁴S values, which change markedly across the terrestrial to marine habitat gradient, were positively correlated with blood THg concentrations in gulls. The linkage we observed between stable isotopes and THg concentrations suggests that Hg contamination can be used as an additional tool for understanding animal foraging across coastal habitat gradients.
Understanding the current role of harbor seals in the Gulf of Maine ecosystem requires broad knowledge of harbor seal interactions with the marine community. The research reported here is a contribution to that basic knowledge. First, the study explored the hypothesis that harbor seals forage selectively on preferred prey species without regard to prey species abundance. Second, mercury concentrations in top predators often exceed levels predicted from their consumption of mercury contaminated prey. The study tested the hypothesis that selective foraging on prey fish with elevated mercury concentrations increases mercury exposure in piscivorous harbor seals. This four year study, 2000 through 2003, centered on the large harbor seal haulout site at Mt. Desert Rock, which lies 28 km south of the central Maine coast. Fecal analysis defined the summer diet of harbor seals in the central Gulf of Maine in relation to prey species abundance and age class frequency. Prey fish abundance estimates were based on data from the Maine Department of Marine Resources Inshore Trawl Surveys (2000 - 2003). Mercury concentrations determined for harbor seal prey species were used to predict the dietary exposure of harbor seals to mercury. Foraging harbor seals selected for three primary prey species, silver hake (Merluccius bilinearis), Acadian redfish (Sebastes fasciatus), and Atlantic herring (Clupea harengus), and seals selected for particular age classes within those three primary prey species. There was no relationship between prey selection and total prey species abundance. Instead, foraging seals shifted prey consumption in response to the relative abundance of the preferred prey fish age class(es). Harbor seals in the central Gulf of Maine did not select for fish having elevated mercury concentrations. Mean total mercury concentrations in the species and size of prey fish ingested by harbor seals were at or below 30 ng THg/g w.w. These concentrations were an order of magnitude lower than levels typically associated with mercury-induced behavioral changes in fish. Mercury concentrations in harbor seal fur reflected seal exposure to mercury from ingested prey fish having average mercury concentrations.
Elevated levels of mercury in aquatic environments remote from industrial sources have been broadly attributed to long-range atmospheric transport and deposition of anthropogenic Hg. Evidence in support of this prevailing scientific viewglobal biogeochemical Hg models, sedimentary archives of historic Hg fluxes, and geographic trends in soil Hghave been challenged as being insuf ficiently rigorous to rule out the alternative explanation that natural geologic sources are the principal contributors of Hg in remote locations. In this review, we examine the weaknesses in interpretation and the choice of information that has been used to argue against atmospheric Hg contamination. Analytical advances in measuring trace levels of environmental Hg have greatly narrowed estimates of natural Hg fluxes, providing a clear measure of the relative magnitude of anthropogenic Hg emissions and deposition. Recent experimental results indicate that diagenetic processes cannot explain the mounting number of lake sediment and peat profiles showing substantial increases in Hg flux during the past century. Geologic sources of Hg may be important in specific localities but cannot explain corresponding geographic trends in soil Hg and industrial emission sources. Despite uncertainties in current understanding, there is a broad and geochemically consistent data base indicating that, over large regions of the globe, human-related Hg emissions have increased relative to natural sources since the onset of the industrial period.
Sediment depth profiles of total mercury (THg) and monomethylmercury (MMHg) were collected at 15 sites in an anthropogenically contaminated estuarine system (Lavaca Bay, TX). THg in the solid phase increased with depth to a maximum located at 10−30 cm, which corresponds to historic industrial discharges to the bay. MMHg in the solid phase was highest in the upper 0−3 cm of the cores, decreasing rapidly with depth. The MMHg content of the surface sediment was a narrowly constrained fraction of the total (0.65 ± 0.34%) over a range of sediment types, while making up only 0.01−0.05% of THg at depth. Porewater concentrations exhibited trends similar to but more exaggerated than in the solid phase. The distribution coefficients (log Kd) for inorganic Hg (IHg = THg − MMHg) were similar in most samples, averaging 4.89 ± 0.43. The log Kd for MMHg averaged 2.70 ± 0.78 over all sites and depths but exhibited a subsurface minimum of 2.29 ± 0.67 at the point of maximum dissolved Fe. A time series showed a maximum in both solid phase and porewater MMHg during the early spring, followed by a decrease throughout the remainder of the year.
Mercury concentrations in the atmosphere and oceans are affected not only by anthropogenic emissions but also by climate and ecosystem change.
Stable isotope is a powerful method for characterizing flows of energy through ecosystems. The power of this method, however, may be affected by preservation methods of the samples. We investigated the effects of four common preservatives (salt, formalin, and ethanol and freezing [control] and preservation duration (six and three months) on δ 15N and δ 13C values of two freshwater fish species, Perca fluviatilis (perch) and Blicca bjoerkna (silver bream). Six-month preservation caused little enrichment in δ 15N of both species compared to three month but had almost the same effects on δ 13C values of both species as in three-month preservation. All methods caused significant shifts (enrichment) in δ 15N of both species, and the effects in general were greater in perch (range: 0.28‰-2.19 ‰) than in bream (range: 0.31‰-1.29‰), which suggested that preservative induced shifts in δ 15N was species-specific. The methods caused little enrichment (ethanol-range: 0.03‰-0.26 ‰ bream and 0.30‰-0.48 ‰ perch and salt: 0.18 ‰ perch three month) and depletion (salt-range: 0.03 ‰0.13‰ bream and 0.13‰ perch six month) in δ 13C. Of the preservatives, however formalin had significant but consistent effects on δ 13C in both species (-1.27‰ and -1.25‰) for the entire preservation duration. Preservation-induced shifts in δ 13C were consistent in direction and magnitude for both species. The results suggested that ethanol and salt could be used without correction factor and formalin with correction factor for preservation of samples solely in δ 13C studies.. For the studies requiring use of carbon and nitrogen together, however, ethanol at least six month in preservation may be suitable for storing samples when considering detection of changes less than 2 ‰ is required in ecological applications.
The lower 6 miles of the tidal Passaic River, part of the New York/New Jersey (NY/NJ) Harbor Estuary system, are contaminated with a variety of organic and inorganic chemicals as a result of more than 150 years of heavy industrialization and urbanization. The River's ecology is substantially degraded due to habitat removal/alteration, and the organisms that reside in or utilize the River are exposed to and bioaccumulate chemicals from sediments and food web interactions. We quantify in this study the extent and magnitude of chemical contamination in several fish species (representing a range of trophic levels) and blue crab (Callinectes sapidus). In addition, the concentration of several contaminants of concern are compared to concentrations in similar organisms from other areas of the NY/NJ Harbor Estuary, as well as available tissue-based toxicological effects benchmarks that are reported in the literature. The results suggest that a variety of contaminants are present at elevated levels in each of the species collected from the River. Several contaminants, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), total DDT (2,2-bis[4-chlorophenyl]1,1-dichloroethene), copper, and mercury are present at average concentrations that exceed those from other waterways in the NY/NJ Harbor Estuary. However, the concentrations of contaminants in the River, with few exceptions do not exceed available toxic effects levels as reported in the literature for these or similar fish and crustaceans. This suggests that toxicological risks from bioaccumulative contaminants in the lower Passaic River are limited to select contaminants and species.
During 1979 and 1980 finfish and Crustacea were collected seasonally at 11 sites located in and around the Berrys Creek tidal marsh, a tributary creek in the Hackensack Meadowlands region of northern New Jersey. The study was designed to measure the extent of mercury contamination among aquatic macrofauna in conjunction with a documented point-source discharge of the metal into the marsh environment. A total of 689 individual and/or composite samples representing 20 species were collected and subsequently analysed for total mercury concentration using flameless atomic absorption spectroscopy.In potentially-edible species such as white perch, american eel, catfish, carp and blue-claw crab, average mercury concentrations were generally below 0.5 ppm. Only infrequently were mercury concentrations encountered in excess of the US FDA action guideline of 1.0 ppm. Mummichogs, a resident finfish in the marsh, appear to be a more reliable indicator of local mercury contamination. Mummichogs collected in Berrys Creek north of the Route 3 bridge nearer to the point source exhibited statistically-higher concentrations of mercury as compared with fish collected at downstream sites. White muscle and hepatopancreas tissues of blue-claw crab samples appear to be the primary and secondary sites of accumulated mercury, respectively.No immediate health hazard was indicated. However, some concern exists as to the long-term implications of chronic mercury contamination in this heavily-industrialized region.
In the framework of a project aimed at the study of the catchment basin of the Tiber River (Latium Region, Italy), a pilot survey was conducted in order to assess the presence of selected toxic trace elements, namely As, Cd, Hg and Pb, in muscle tissues of fish caught in different tracts of Tiber River (urban area of Rome and different rural areas upstream and downstream). The analysed species were Leuciscus cephalus (Ciprinidae) and Anguilla anguilla (Anguillidae). Determinations were carried out by means of Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICP-MS). Preliminary data (ranges of concentration in μg g−1, freeze-dried mass: As, 0.73–3.62; Cd, 0.0002–0.001; Hg, 0.18–0.31; Pb, 0.02–0.09) revealed no significant differences among the sets of results relevant to the various sampling stations. The total content of each element seems to be related with a general condition of low-level pollution of the area under study.
American lobsters ( Homarus americanus ) have been hatched and reared at the Massachusetts State Lobster Hatchery, Oak Bluffs, Mass., since 1951. Individual lobsters have been held for as long as 10 years. Records have been maintained on seasonal occurrence of hatching, duration of the larval period, occurrence of molting with age and season, and rates of growth.
The peak in hatching intensity occurs in late June or early July when water temperatures approximate 20°C. Time required for larvae to attain the 4th stage appears to be inversely related to temperature above 18°C, with less evidence of temperature‐dependence below this level. Molting frequency declines with age; lobsters molt approximately 9 times during their first growing season but no more than once annually by their sixth growing season. Molting occurs most frequently in early summer and again in early fall. Growth rates indicate that a period of 5 years from date of hatching is required for a lobster to attain legal marketable size—3 3/16 in. carapace length—in Massachusetts. Percentage increase in length per molt declines with age.
The aim of this study was to evaluate mercury and selenium distribution in different portions (exoskeleton, white meat and brown meat) of Norway lobster (Nephrops norvegicus). Some samples were also analysed as whole specimens. The same portions were also examined after boiling, in order to observe if this cooking practice could affect mercury and selenium concentrations. The highest mercury concentrations were detected in white meat, exceeding in all cases the maximum levels established by European legislation. The brown meat reported the highest selenium concentrations. In all boiled samples, mercury levels showed a statistically significant increase compared to raw portions. On the contrary, selenium concentrations detected in boiled samples of white meat, brown meat and whole specimen showed a statistically significant decrease compared to the corresponding raw samples. These results indicate that boiling modifies mercury and selenium concentrations. The high mercury levels detected represent a possible risk for consumers, and the publication and diffusion of specific advisories concerning seafood consumption is recommended.
Species profiles are literature summaries of the taxonomy, life history, and environmental requirements of coastal fishes and aquatic invertebrates. They are designed to assist with environmental impact assessments. The rainbow smelt is an abundant forage fish for commercially and recreationally valuable fishes such as striped bass and bluefish on the East Coast and several species of salmon and trout in the Great Lakes. The rainbow smelt also supports an important sportfishery throughout most of its range. In 1976, the total smelt harvest in the coastal waters of New England was 105,000 lb. Coastal rainbow smelt are anadromous, spawning in freshwater and maturing in saline water. Spawning peaks in spring. Salinities above 12 ppt were fatal to eggs. Reported fecundities are 7,000 to 44,000 eggs per female. Smelt are always found in shallow water (
The blue mussel, Mytilus edulis L. is a widely distributed and locally abundant bivalve mollusc in the North and Mid-Atlantic Regions. It is a valuable commercial species; regional landings in 1986 were worth nearly $4 million. It is a semi-sessile species, anchored by byssus threads to firm surfaces in littoral and sub-littoral environments at salinities ranging from 5 to 35 ppt. It is a suspension feeder, ingesting phytoplankton and detrital particles in the size range of 3--30 /mu/m. The geographical range of the species is limited by lethal water temperatures above 27/degree/C in the south and by temperatures too low for growth and reproduction in the north. Animals from the northern end of the range are stressed by temperatures above 20/degree/C, whereas those near the southern distributional limit are not severely stressed by temperatures as high as 25/degree/C. The blue mussel is diecious and oviparous. The planktotrophic larvae take about 3 weeks to develop and metamorphose. The environmental tolerances of larvae are more restricted than those of adults. The juveniles grow to approximately 1.5 mm while attached to filamentous algae before being carried by water currents to reattach to a firm substrate, often close to adult mussels. Larval and adult blue mussels are important prey items for many animals, including crabs, fishes, and birds. 95 refs., 5 figs., 2 tabs.
Top-level piscivores are highly sought after for consumption in freshwater fisheries, yet these species contain the highest levels of the neurotoxin monomethylmercury (MMHg) and therefore present the greatest concern for MMHg exposure to humans. The slow elimination of MMHg is one factor that contributes to high levels of this contaminant in fish; however, little quantitative information exists on elimination rates by top predators in nature. We determined rates of MMHg elimination in northern pike (Esox lucius) by transferring fish that had naturally accumulated isotope-enriched MMHg (spike MMHg) through a whole-lake Hg loading study to a different lake. Over a period of ~7 years, pike were periodically recaptured and a small amount of muscle tissue was extracted using a non-lethal biopsy. Spike total mercury (THg) persisted in muscle tissue throughout the entire study despite discontinuing exposure upon transfer to the new lake. Spike THg burdens increased for the first ~460 d, followed by a decline to 65% of original burden levels over the next 200 d, and subsequently reached a plateau near original burden levels for the remainder of the study. We estimated the half-life of muscle THg to be 3.3 years (1193 d), roughly 1.2- to 2.7-fold slower than predicted by current elimination models. We advocate for further long-term field studies that examine kinetics of MMHg in fish to better inform predictive models estimating the recovery of MMHg-contaminated fisheries.
Species profiles are literature summaries of the taxonomy, life history, and environmental requirements of coastal fishes and aquatic invertebrates. They are designed to assist with environmental impact assessments. The rainbow smelt is an abundant forage fish for commercially and recreationally valuable fishes such as striped bass and bluefish on the east coast and several species of salmon and trout in the Great Lakes. The rainbow smelt also supports an important sportfishery throughout most of its range. In 1976, the total smelt harvest in the coastal waters of New England was 105,000 lb. Coastal rainbow smelt are anadromous, spawning in freshwater and maturing in saline water peaks in spring. Salinities above 12 ppt were fatal to eggs. Reported fecundities are 7,000 to 44,000 eggs per female. Smelt are always found in shallow water (<6 m deep) and within 2 km of the shore. Larval and juvenile smelt along the coastal feed on planktonic crustaceans. Larger juveniles and adults feed on euphausiids, amphipods, polychaetes, and fish. Smelt move locally to search for optimum water temperatures. Keywords: Osmerus mordax. (AW)
While mercury accumulation in reservoir fish following impoundment is a well known phenomenon, consequences for downstream populations are less understood. In particular, the effects on downstream estuarine populations have only rarely been studied. This study examined data from a Northern Canadian reservoir system to demonstrate that elevated mercury levels can be seen in fish downstream for a distance of over 300 km and into the estuary for some species. The Smallwood Reservoir in Labrador, Canada, created in the mid 1970's, drains into the Churchill River and hence into Lake Melville, a large estuarine fjord. Mercury levels in most species in the Churchill River were elevated immediately following impoundment and have since declined as have the levels in several estuarine species. Return times for downstream fish were similar to those in the reservoir and depended on trophic position and habitat use. Lake whitefish, longnose suckers and northern pike showed evidence of a shift in trophic position below the Churchill Falls tailrace.
Movements of juvenile Homarus americanus (American Lobster; hereafter lobster) on and around a naturally occurring rock reef were monitored over a 3-year period. Lobsters were sampled with baited traps deployed at each often sites. Catch-per-unit-effort (CPUE) and number of lobsters collected per trap haul was calculated for each sampling event. Physical habitat, visually characterized by underwater video and diver observations, differed among sites. Lobster CPUE was significantly greater at rocky sites (>70% density of cobble and/or boulder) containing complex structure, vertical relief from the seafloor, and colonies of macroalgae, sponge, and hydroids. Lobster CPUE was highest from late June to mid-July. Lobsters ranged from 18 to 82 mm carapace length (CL), with 90.7% of tagged lobsters measuring between 30 to 60 mm CL. Relative lobster abundance remained similar over the course of the study. Catch data were kriged to illustrate spatial patterns of distribution. Over the study period, a total of 934 lobsters were tagged and 66 were recaptured, for an overall recapture rate of 7.1%. The majority of recaptured animals (88%) were found at the original tagging site or adjacent sites, with one lobster remaining at liberty for 397 days. Most juvenile lobsters showed fidelity to their initial site of capture on a small, relatively isolated patch of rock-reef habitat in the central basin of Long Island Sound.
Yellow-phase American eels, Anguilla rostrata, were displaced 10–17 km between tidal fresh water and salinity-stratified water and followed to determine the degree of home site fidelity, swiftness of homing and whether environmental factors affect orientation or homing behaviour. Twenty-one eels were tracked continuously (eight eels displaced up the estuary, eight down the estuary and five controls) in the Penobscot Estuary, Maine, USA for 4–80 h each, while recording position every 20 min. Nine of the 16 displaced eels (56%) returned to their capture site either during the track or shortly afterwards. Three of the remaining seven eels made substantial progress towards their capture site within the time observed. Eels homed with equal frequency whether displaced up or down the estuary in an average of 220 h ±87 (SE). After release, no eel moved farther away from its capture site. The eels were active mostly at night but used only the appropriate tidal currents rather than directed swimming to move about their home range and to home. Control tracks provided a home-range estimate in this habitat of 6.7 ±1.6 km of estuary or 325 ±64 ha. Lunar phase or position of the moon did not appear to influence either homing behaviour or activity patterns. This study shows that orientation and homing to a specific site in eels occurs relatively quickly and with no initial errors in orientation.
Eye size was correlated with body length and gonad development in 112 untreated and 33 hormone injected female Anguilla anguilla. A length-related measure of eye size was developed as an index of sexual maturity. Eels of eye index of 6.5 or less were classed as sexually immature adults, those of < 6.5 as sexually Maturing adults. Structural changes in the eye during maturation were examined. Total numbers of rods increased markedly while density of photoreceptors remained approximately constant. Cone density decreased with degenerative changes occurring. Changes in the eye were found to be essentially complete early in the maturation process.
Wildlife may be exposed to mercury (Hg) and methylmercury (MeHg) from a variety of environmental sources, including mine tailings, industrial effluent, agricultural drainwater, impoundments, and atmospheric deposition from electric power generation. Terrestrial and aquatic wildlife may be at risk from exposure to waterborne Hg and MeHg. The transformation of inorganic Hg by anaerobic sediment microorganisms in the water column produces MeHg, which bioaccumulates at successive trophic levels in the food chain. If high trophic level feeders, such as piscivorous birds and mammals, ingest sufficient MeHg in prey and drinking water, Hg toxicoses, including damage to nervous, excretory and reproductive systems, result. Currently accepted no observed adverse effect levels (NOAELs) for waterborne Hg in wildlife have been developed from the piscivorous model in which most dietary Hg is in the methyl form. Such model are not applicable to omnivores, insectivores, and other potentially affected groups, and have not incorpotated data from other important matrices, such as eggs and muscle. The purpose of this paper is to present a comprehensive review of the Hg literature as it relates to effects on wildlife, including previously understudied groups. We present a critique of the current state of knowledge about effects of Hg on wildlife as an aid to identifying missing information and to planning research needed for conducting a complete assessment of Hg risks to wildlife. This review summarizes the toxicity of Hg to birds and mammals, the mechanisms of Hg toxicity, the measurement of Hg in biota, and interpretation of residue data.
It is well established that Anguillid eels undergo a complex suite of morphological and physiological changes during their transformation from resident, yellow-phase juveniles to actively migrating silver-phase eels. While it has been shown that some morphological measures can be used successfully to identify sexually maturing European eels, Anguilla anguilla, as well as Australian short fin, Anguilla australis, and long fin, Anguilla dieffenbachii eels, this relationship has never been quantitatively assessed for American eels, Anguilla rostrata. American eels of varying sexual development were collected from three locations on the St. Lawrence River: Lake St. Lawrence, Quebec City and Kamouraska. Sexual development of each eel was assessed with gonadosomatic index (GSI), oocyte diameter and degree of oocyte development. Morphological measures of total length, weight, head width, pectoral fin length and vertical and horizontal eye diameters were obtained from each fish. We used this data to test two hypotheses: (i) resident yellow phase eels, suspected migrants and known migrants are morphologically indistinguishable; and (ii) if differences exist, they cannot be used to reliably predict gonadal development or migratory status. Univariate analysis (ANOVA and ANCOVA) indicated that there were highly significant differences in all of the measured parameters and thus we were able to reject the first hypothesis. However, we failed to reject the second hypothesis as the high degree of overlap between groups eliminated the ability of any single measure to differentiate between resident and migratory eels. A multivariate discriminant model was developed that could classify only 72–80% of the eels correctly based on their morphological characters. While morphological measures may have some potential as a rapid, cost-effective method of pre-screening individual eels, morphological measures should not be considered a definitive indicator of sexual maturity or migratory status for female American eels in the Upper St. Lawrence River.
Home ranges, dispersal patterns, and habitat associations of juvenile winter flounder (Pseudopleuronectes americanus) were studied using acoustic tags and three tracking systems in the Hampton-Seabrook Estuary in New Hampshire, USA. This is the first study that we know of to use electronic tags on juvenile winter flounder, and on flatfish ≤ 19 cm.
For the first two tracking periods, both wild and cultured age 1 fish were followed by a combination of handheld hydrophones and a VRAP system. Although both cultured and wild fish maintained similar home ranges, the cultured fish immediately emigrated approximately 1000 m out of the release area while the wild fish maintained high release site fidelity. Cultured fish acclimated to the release site using in-situ cages displayed higher site fidelity after release. Cultured flounder habitat use was very similar to wild flounder habitat use in terms of bottom water temperature, dissolved oxygen, salinity, depth, and sediment composition.
For the third tracking period only wild juvenile flounder were followed to discern when and at what size fish leave the estuary. Fish (n = 10) were tracked passively by an array of six submersible receivers stationed throughout the estuary. A total of 244,985 fixes were recorded by the receivers during the lifespan of the tags. The majority of these fixes were recorded by the receivers at the release site (72%) and immediately down-estuary (25%). Eighty percent of the fish remained in the immediate release area for the first two weeks, but as time at large increased, several fish dispersed down-estuary, and two individuals left the estuary for the sea. Estuary exits occurred in the winter by the largest individuals. Final positions of the tagged fish indicated that 20% had left the estuary all together, 30% of the tagged fish were still at the release site, 20% were approximately 500 m down-estuary from the release site, and 30% were unaccounted for.
Understanding these movement patterns and habitat associations of both cultured and wild juvenile winter flounder is significant for developing techniques for enhancement programs and for defining essential fish habitats within this important nursery area.
Seasonal variability of mercury content of Mytilus edulis (L.) was studied at monthly intervals for 18 mo (June 1978–December 1979) in a natural population from a typical estuarine environment (St. Lawrence Estuary). Body-size-induced variability was observed in the same population in spring 1980. The regression coefficients of log-log relationships between mercury content and body size of the mussels varied with time. However, the regression coefficients were never higher than 1; this indicates, therefore, no net accumulation of mercury with age of the bivalve. A normalization method, taking into account shell length and soft-tissue dry weight, is proposed to minimize the metal variations due to size differences of the mussels. The normalized mercury contents vary seasonally by a factor of two. Minimum values were observed during summer. This factor (2) is taken as the minimal difference which can be accepted as indicating a significant geographical trend in a mussel watch-type study in estuarine environments. In the St. Lawrence Estuary and Gulf, size-normalized concentrations range from 69 to 378 ng Hg g-1 (dry weight); highest levels were observed in areas where freshwater influence is maximum, while lower contents were encountered in regions of highest Atlantic influence. In the Gulf, mercury in mussel soft tissue is 3x104 times that of the seawater. There is some indication of a decrease in the previous measured levels near the mouth of the Saguenay fjord in the Lower St. Lawrence estuary.
The measurement of concentrations of persistent bioaccumulating chemicals in ecological samples is an important tool in ecotoxicological science. It is important to consider the need for both chemical and biological precision when designing research programmes for studying environmental pollution. The balance between chemical and biological precision is discussed on the basis of a database from the Swedish Contaminant Programme covering the period 1969–1989. The negative consequences of the analysis of pooled samples instead of individual specimens are demonstrated. The importance of various biological parameters such as sampling sites, content of fat and age of the specimens analyzed is shown. The prerequisite of a sufficiently long lime-span and frequency of sampling in monitoring studies is shown.
Some of the ways that the application of stable isotopic tracers have contributed to the extremely hard task of understanding the energy and food web relations in benthic communities are illustrated in this review. Several methods are presented and their relative advantages are discussed, namely the use of endmembers, nitrogen isotopes, carbon isotopes, and sulfur isotopes. Special attention is given to the application of multiple tracers and transects sampling, natural and man-made perturbation experiments, and 15N additions as N cycle tracers.
Even at low concentrations in the environment, mercury has the potential to biomagnify in food chains and reaches levels of concern in apex predators. The aim of this study was to relate the transfer of total mercury (THg) and methylmercury (MeHg) in a Gulf of St. Lawrence food web to the trophic structure, from primary consumers to seabirds, using stable nitrogen (δ15N) and carbon (δ13C) isotope analysis and physical environmental parameters. The energy reaching upper trophic level species was principally derived from pelagic primary production, with particulate organic matter (POM) at the base of the food chain. We developed a biomagnification factor (BMF) taking into account the various prey items consumed by a given predator using stable isotope mixing models. This BMF provides a more realistic estimation than when using a single prey. Lipid content, body weight, trophic level and benthic connection explained 77.4 and 80.7% of the variation in THg and MeHg concentrations, respectively in this food web. When other values were held constant, relationships with lipid and benthic connection were negative whereas relationships with trophic level and body weight were positive. Total Hg and MeHg biomagnified in this food web with biomagnification power values (slope of the relationship with δ15N) of 0.170 and 0.235, respectively on wet weight and 0.134 and 0.201, respectively on dry weight. Values of biomagnification power were greater for pelagic and benthopelagic species compared to benthic species whereas the opposite trend was observed for levels at the base of the food chain. This suggests that Hg would be readily bioavailable to organisms at the base of the benthic food chain, but trophic transfer would be more efficient in each trophic level of pelagic and benthopelagic food chains.