Mercury Cycling in Lake Gordon and Lake Pedder,Tasmania (Australia). I: In-lake Processes

The processes affecting the concentrations of total mercury (total Hg) and methylmercury (MeHg) in a freshwater system comprising two connected reservoirs in southwest Tasmania were investigated. Surface concentrations of total mercury (total Hg)were temporally and spatially uniform in both Lake Gordon (2.3±0.4 ng L^-1, n = 27) and Lake Pedder (2.3±0.3 ng L^-1, n = 11). The surface concentrations of MeHg in Lake Gordon (0.35±0.39 ng L^-1, n = 25) were more variable than total Hg and MeHg typically comprised 10–20% of total Hg. The relatively high amount of total mercury present as MeHg in Lake Gordon was attributed to the high proportion of wetlandsin the upper catchment (50% of total area) and in-lake contributions (ca. 40% of total MeHg). Despite the close proximity of the two lakes, MeHg concentrations in Lake Pedder were consistently lower than in Lake Gordon. This phenomenon canbe explained in part by the greater contribution of direct rainfall to Lake Pedder leading to the dilution of MeHg. Water column MeHg concentrations were higher in warmer months in bothlakes, reflecting increased net methylation of inorganic mercury.Unlike previous studies of seasonally anoxic lakes, depth profiles of total mercury and MeHg in Lake Gordon were uniform and were not affected by water column stratification occurringin the summer months, and oxygen depletion with depth. This suggests that redox cycling and accumulation of MeHg in the hypolimnion following seasonally-induced anoxia is not a significant part of the mercury cycle in Lake Gordon. The primary location of MeHg production within the lake's water column is not conspicuous. Mercury speciation measurements made above and below the lake system over a period of 19 months indicates that after 20 yr of impoundment, the reservoirs are not significantly affecting MeHg concentrations in the downstreamriverine environment.     

Mercury in Lake Vänern, Sweden Distribution In Surface Sediment And Catchment Budget

Lake Vänern is Sweden's largest lake and freshwater reservoir. Large quantities of mercury were released into the lake during a large part of the 20th century, resulting in serious contamination. The main load originated from one single point source — a chlor-alkali industry. Its releases were drastically reduced in the early 1970's, but nearby sediments displayed alarmingly high concentrations. During summer 2001, fifty-one sediment cores were taken, and analysed for total mercury. It was found that mercury concentrations in surface sediments have decreased significantly between 1974 and 2001, but the influence of the former single point source was still reflected in the concentration patterns. Thirty years ago, sediments around the dominant point source displayed the highest concentrations. Today, the highest concentrations in surface sediments were still found close to it, but also in deep waters in the central part of the lake. Surprisingly, the gradient from the point source is stronger today compared to 1974. A mercury budget, based on the annual sediment accumulation rate, the bulk density, atmospheric load and outflow of mercury, was formed. The surface sediments (0—1 cm, on average corresponding to ～5 yr according to ¹³⁷Cs dating) in accumulation bottoms (water depth >40m) contained approximately 530 kg Hg (corresponding value for year 1974 was 4100 kg Hg). A majority of the present additions of mercury to the lake originates from atmospheric deposition. It was also found that the lake acts as a sink for mercury. In fact, approximately 90—95% of the incoming mercury was retained within the catchment or in the sediments.     

Application of the Regional Mercury Cycling Model (RMCM) to Predict the Fate and Remediation of Mercury in Onondaga Lake,New York

Onondaga Lake exhibits elevated concentrations of total mercury (HgT) and methyl-mercury (MeHg) in the water column, sediments and fish tissue due to industrial inputs, wastewater discharge and urban runoff. The steady-state Regional Mercury Cycling Model (RMCM) was calibrated to Onondaga Lake and applied to evaluate various remediation scenarios. Because of detailed data available for Onondaga Lake, the RMCM was effectively calibrated. Model predictions of water column and fish concentrations of Hg generally agreed with measured values. The model underestimated concentrations of Hg in sediments. Mass balance calculations show that inputs of HgT largely originate from tributary and wastewater inflows to the lake. In contrast, MeHg is largely derived from internal production. Model calculations suggest that elimination of Hg inputs from wastewater effluent and of drainage from a former chlor-alkali facility could greatly decrease Hg concentrations in fish tissue.     

Mercury Concentrations in Lake Sediments – Revisiting the Predictive Power of Catchment Morphometry and Organic Matter Composition

Lake sediments are a potential source of mercury (Hg) for aquatic biota. Here, we investigated the predictive power of (a) key parameters for lake catchment morphometry and (b) organic matter composition of sediments in an effort to account for observed variations of total (THg) and methyl (MeHg) mercury concentrations in lake sediments. Using regression models we demonstrate that the morphometric parameters lake depth as well as inclination of catchment soils and lake bottoms can significantly predict variations of THg concentrations, but not MeHg, at profundal lake sediments. Although THg and MeHg concentrations in sediments could not be predicted by specific organic matter sources, as elucidated by atomic C/N ratios, our data suggest that wetland-derived total organic carbon (TOC) contained less THg concentrations than TOC derived from mostly forested watersheds. However, TOC concentrations could significantly predict MeHg concentrations and the proportion of methylated Hg at all sediment stations. Finally, from an ecotoxicological point of view, we propose that concentrations of TOC at surface lake sediments, rather than parameters of catchment morphometry, may predict dietary sources of MeHg for benthic consumers and consequently perhaps for organisms at higher trophic levels.     

Conservation of the short-tailed shearwater Puffinus tenuirostris in Tasmania,Australia

The number of short-tailed shearwater burrows in Tasmania is estimated at 11·4 million of which 80% are annually occupied by breeding birds. Chicks are exploited for food in March and April, and prior to the season usually 50% of burrows contain chicks. The annual commercial harvest is about 400 000 chicks taken from seven colonies containing 5·63 million burrows. This take is well below the maximum sustained yield of 37% of chicks available and represents 14% of the estimated 2·82 million chicks present. The non-commercial harvest is estimated to be 300 000 chicks taken from 104 colonies containing an estimated 1·51 million burrows. Monitoring has shown that on many popular colonies the takes are well in excess of the maximum sustained yield, and management measures to reduce it have been introduced. The short-tailed shearwater is in no danger of decline despite harvesting.     

A Mass Balance Mercury Budget for a Mine-Dominated Lake: Clear Lake, California

The Sulphur Bank Mercury Mine (SBMM), active intermittently from 1873–1957 and now a USEPA Superfund site, was previously estimated to have contributed at least 100 metric tons (10⁵ kg) of mercury (Hg) into the Clear Lake aquatic ecosystem. We have confirmed this minimum estimate. To better quantify the contribution of the mine in relation to other sources of Hg loading into Clear Lake and provide data that might help reduce that loading, we analyzed Inputs and Outputs of Hg to Clear Lake and Storage of Hg in lakebed sediments using a mass balance approach. We evaluated Inputs from (1) wet and dry atmospheric deposition from both global/regional and local sources, (2) watershed tributaries, (3) groundwater inflows, (4) lakebed springs and (5) the mine. Outputs were quantified from (1) efflux (volatilization) of Hg from the lake surface to the atmosphere, (2) municipal and agricultural water diversions, (3) losses from out-flowing drainage of Cache Creek that feeds into the California Central Valley and (4) biotic Hg removal by humans and wildlife. Storage estimates include (1) sediment burial from historic and prehistoric periods (over the past 150–3,000 years) from sediment cores to ca. 2.5m depth dated using dichloro diphenyl dichloroethane (DDD), ²¹⁰Pb and ¹⁴C and (2) recent Hg deposition in surficial sediments. Surficial sediments collected in October 2003 (11 years after mine site remediation) indicate no reduction (but a possible increase) in sediment Hg concentrations over that time and suggest that remediation has not significantly reduced overall Hg loading to the lake. Currently, the mine is believed to contribute ca. 322–331 kg of Hg annually to Clear Lake, which represents ca. 86–99% of the total Hg loading to the lake. We estimate that natural sedimentation would cover the existing contaminated sediments within ca. 150–300 years.     

Streamwater Particulate Mercury and Suspended Sediment Dynamics in a Forested Headwater Catchment

Due to the inherent differences in bioavailability and transport properties of particulate and dissolved mercury (Hg_P and Hg_D), it is important to understand the processes by which each is mobilized from soil to stream. Currently, there is a paucity of Hg_P data in the literature despite the fact that it can be the dominant fraction in some systems. We analyzed Hg_P in conjunction with volatile solids (VS, an estimate of organic content) and total suspended solids (TSS) and investigated the viability of using turbidity as a surrogate measure of Hg_P. Samples were collected for flow conditions ranging from 72 to 8,223 L?s^?1 during October 2009 through March 2010 in a 10.5-km² forested headwater catchment. Total Hg concentrations ranged from 0.28 to 49.60 ng L^?1, with the relative amount of Hg_P increasing with discharge from approximately 40% to 97%. Storm dynamics of Hg_P and Hg_D were not consistent, indicating unique controls on the export of each fraction. During high-flow events, Hg_P was consistently higher on the rising limb of the hydrograph compared with the receding limb for a range of discharge events, with this hysteresis contributing to a degraded relationship between Hg_P and streamflow. Overall, Hg_P was strongly positively correlated with VS (r ²?=?0.97), confirming the known association with organic carbon. Due to a consistent organic fraction of the suspended solids (34?±?6%), Hg_P was also well correlated with TSS (r ²?=?0.95), with an average of 0.10 ng of Hg_P per milligram of TSS in this system. Stream turbidity measured with an in situ sonde also had a strong correlation with TSS (r ²?=?0.91), enabling commutative association with VS (r ²?=?0.86) and Hg_P (r ²?=?0.76). Turbidity can explain more than twice the temporal variance in Hg_P concentrations (n?=?50) compared with discharge (r ²?=?0.76 versus 0.36), which leads to improved monitoring of Hg_P dynamics and quantification of mass fluxes.     

Mercury in Small Freshwater Lakes: A Case Study: Lake Velenje, Slovenia

Lake Velenje is located in one of the most polluted regions ofSlovenia, the ?alek Valley. The major source of pollution is the coal-fired thermal power plant in ?o?tanj (?TPP). In the past, dumping of coal ash directly into Lake Velenje and drainage water from the ash disposal site resulted in unique chemical characteristics of the lake water, such as very high pH (10–12) and high concentrations of heavy metals. The introduction of a closed cycle ash transport system in 1995resulted in a very fast recovery of the lake water quality. The aim of our study was to establish the sources, fate and distribution of mercury in Lake Velenje. In order to establishrecent sources of mercury, total mercury and methylmercury concentrations were measured in various environmental samples(lake inflows, outflow, rainwater, sediments, etc.). Total mercury and methylmercury concentrations were measured at thesurface and at different depths to establish mercury cycling, its transport and chemical transformations in the lake. Generalwater quality parameters (such as pH, Eh, O₂, temperature,TDS, conductivity) were also determined. The results show that the major sources of mercury in Lake Velenje are lake inflows and wet deposition. Total mercury andmethylmercury concentrations in the water column are very low (total mercury: 0.2–2.7 ng L^-1; methylmercury: 20–86 pg L^-1) and can be compared to other non-contaminated freshwater lakes. These results suggest that the major form of mercury emitted from thermal power plant stacks is volatile Hg⁰, whichhas no or very little influence on the nearby surroundings, but rather is subject to long-range atmospheric transport.     

Mercury Sources to Lake Ozette and Lake Dickey: Highly Contaminated Remote Coastal Lakes, Washington State, USA

Recent studies have shown that the lower basin of the Salado River is highly polluted with copper and chromium. In order to evaluate the effect of those metals on Notodiaptomus conifer, a representative calanoid copepod, we carried out two (acute and chronic) experimental assays. In the first one, the 24- and 48-h EC₅₀ values were determined in nauplii and adults. Chronic assays were conducted to evaluate the time of development for nauplii, time of development for each copepodite stage, total development time, growth, number of ovigerous females, fecundity, and time required to produce the first egg sac. Additionally, the effect of those metals on the equiproportional model proposed for copepods was evaluated. Acute experiments reveled that juveniles were more sensible than adults. Although growth was not seriously affected by metal exposition, development time was delayed and reproductive variables were altered with the increase of metal concentrations. The deviation from the equiproportional model proposed for copepods proved to be a useful parameter to provide relevant information on toxicity of both metals along development time. In comparison with other zooplanktonic species, the highest sensitivity of N. conifer to copper and chromium makes it a suitable bioindicator in ecotoxicological tests.     

The Nature and Distribution of Metals in Soils of the Sydney Estuary Catchment, Australia

Total topsoil 50th percentile Cu, Pb and Zn concentrations (n?=?491) in the Sydney estuary catchment were 23 ??g?g^?1, 60 ??g?g^?1 and 108 ??g?g^?1, respectively. Nine percent, 6% and 25% of samples were above soil quality guidelines, respectively and mean enrichment was 14, 35 and 29 times above background, respectively. Soils in the south-eastern region of the catchment exhibited highest metal concentrations. The close relationship between soil metal and road network distributions and outcomes of vehicular emissions modelling, strongly suggested vehicular traffic was the primary source of metals to catchment soils. Catchment soil and road dust probably make an important contribution to contamination of the adjacent estuary. The concentration of soil metals followed the land use trend: industrial?>?urban?>?undeveloped areas. A high proportion (mean 45%, 62% and 42%, for Cu, Pb and Zn, respectively) of metals in the soils may be bioavailable.     

Mercury Cycling in an Urbanized Watershed: The Influence of Wind Distribution and Regional Subwatershed Geometry in Central Indiana,USA

The global cycle of mercury (Hg) is reasonably well-understood, as are some of the natural and anthropogenic sources of Hg to the atmosphere. Less well understood are the regional and local characteristics of Hg deposition and subsequent watershed-scale transport, important parameters for assessing human risk to various avenues of Hg exposure. This study employed a two-part strategy for understanding coupled deposition and transport processes in central Indiana (USA), including Indianapolis, a typical large city with multiple coal-fired electric utilities and other Hg emission sources. A spatial analysis of Hg concentrations in surface soils revealed elevated Hg proximal to many of the large emission sources, with a distribution aligned along a southwest-northeast axis corresponding to the mean wind direction in this region. This soil distribution suggests some local depositional impact from local utilities, with wind modification affecting the regional pattern. Post-depositional transport of Hg was assessed using a series of streambank sampling arrays as the White River and various tributaries travelled through the urban core of Indianapolis. Streambank sediments had peak Hg concentrations in the urban core, where several local sources are present and where a number of subwatersheds join the main trunk of the White River, suggesting local emission and/or rapid Hg transport from urban subwatersheds due to their relatively high proportion of impervious surfaces. High Hg values persist in White River sediments into rural areas tens of kilometers south of Indianapolis, raising concerns for anglers collecting fish in this apparently “pristine” environment.     

Conservation of plant species,alliances and associations of the treeless high country of Tasmania,Australia

The treeless high country of Tasmania has considerable conservation and catchment value. Much of its area lies within National Parks and other reserves of similar tenure, but many species and communities are confined to land of less secure status. Much high mountain land is subject to stockgrazing and burning, both of which activities have led to deterioration in vegetation and soils. The reservation status of species and communities can be made near perfect with relatively small additions to the State Reserve system. However, the impacts of trampling and deliberate fires do not respect reserve boundaries, and their mitigation or elimination requires some intensive management.     

The Source of Anthropogenic Heavy Metals in Fluvial Sediments of a Rural Catchment: Coxs River,Australia

A serious health scare involving thesupply of drinking water to Sydney, Australia hasrecently focussed attention on the environmentalstatus of river catchments of the main reservoir, LakeBurragorang. Although the Coxs River – a majorcatchment of Lake Burragorang – comprises mainlyforests and grazing land, it supports a moderate sizedtown, power stations and coal mines. The heavy metal content of stream-bed sedimentscharacterises environmental impact in this ruralcatchment and sources of contamination. Sediment in acreek flowing through a country town (population 12 000) is markedly enriched in Cr, Pb and Zn (3×, 18×and 52×, respectively) over background, probably dueto a long history of metal-based industry. The highestCu, Pb and Zn concentrations (204, 332 and2460 μg g^-1, respectively) in fluvialsediment in the town are, however associated withdischarges from a sewage treatment plant. Twocoal-based power stations in the catchment contributeconsiderable Cu and Ni (maximum concentrations 562 and157 μg g^-1, respectively) to ambient fluvialsediments, possibly from cooling towers and coalstorage areas. The highest Co and Cr concentrations(113 and 490 μg g^-1) in fluvial sediments ofthis catchment are associated with coal-miningactivities. Selective extraction indicates that about50% of the anthropogenic fraction may bebioavailable, whereas sequential extraction proceduressuggest that <25% is associated with the easilyexchangeable/adsorbed phase.Two dams restrict the migration of heavy metals downthe Coxs River and sediment discharging into LakeBurragorang is low in metals.     

Interactions Between Benthic Phosphorus Release and Sulfur Cycling in Lake Scharmützelsee (Germany)

Sulfur (S) conversions were determined during summer stratification in 1995/96 to assess the extent to which benthic release of phosphorus (P) is influenced by the S cycling in eutrophic, dimictic, sulfate-rich (61.33 ± 10.41 mg SO42- l-1) freshwater Lake Schamützelsee. Hypolimnetic SO42- reduction (4.56 ± 0.73 g (S) m-2 d-1) forming ΣH2S (44.71 ± 17.57 mg ΣH2S m-2 d-1), leading to iron sulfide precipitation (5.62 ± 1.72 mg FeS m-2 d-1) and dissolved iron depletion in the hypolimnion has a major influence on benthic P mobilization and release. The most important inorganic S pool is the CRS (FeS2 + S° + H2S; 15.1 % total S), being 1.3 to 6.6 times higher than the AVS (FeS + H2S) in the uppermost 0 - 8 cm sediment. This diminishes the ability of the sediment to bind P (indicated by 14.6 % loosely bound P (NH4Cl-P) and an exhaustion of the redox-sensitive P (BD-P)), leading to interstitial water P concentrations up to 10.8 mg l-1 and P release rates of 2.64 ± 0.56 mg P m-2 d-1. As a consequence the P content of the lake increased fourfold within 58 days.     

Seasonal variability in the Mercury speciation of Onondaga Lake (New York)

Dissolved and particulate Hg speciation was determined on four occasions in the Spring to Fall interval of 1989, at three depths of the water column of Onondaga Lake, New York; an urban system in which the sediments and fish flesh are contaminated with H_g. Species determined included total Hg (Hg_t), reactive (‘ionic’) Hg (Hg_i), monomethylmercury (CH₃HgX), elemental Hg (Hg°) and dimethylmercury (CH₃)₂Hg). Onondaga Lake was found to contain very high levels of Hg_t (2 to 25 ng L^?1 Hg), Hg_j (0.5 to 10 ng L^?1 Hg), and CH₃HgX (0.3 to 7 ng L^?1 Hg), which generally increased with depth in the lake. These concentrations represent a significant level of contamination, based upon comparisons with other polluted and pristine sites. Elemental Hg levels were typically about 0.05 ng L^?1 and (CH₃)₂Hg was near the limits of detection (?0.001 ng) L^?1 in most samples. The greatest CH₃HgX concentrations in the hypolimnion, as well as the largest gradients of both CH₃HgX and (Hg_t), were observed upon the first onset of stratification, in early summer. These concentrations did not become more pronounced, however, as stratification and H₂S levels in the hypolimnion increased throughout the summer. The very low concentrations of (CH₃)₂Hg in these MeHg and sulfide-rich waters calls into question the belief that CH₃HgX and H₂S will react to yield volatile dimethyl-mercury, which can then escape to the atmosphere by diffusion. Mercury speciation was highly dynamic, indicating active cycling within the lake, and an apparent sensitivity to changes in attendant Iimnological conditions that track the stratification cycle.     

Mercury Extraction from Contaminated Soils by l-Cysteine: Species Dependency and Transformation Processes

A new approach in soil remediation washing techniques is the use of l-cysteine based on the formation of organic complexes. In this study, the applicability of l-cysteine for the mobilisation of different mercury species from contaminated soils was evaluated. Soils were treated with l-cysteine solutions with S?CHg molar ratios of 1, 2, 10, 20, 100 and 200. In 24?h batch experiments, leachates with water could mobilise 1% of Hg. The addition of l-cysteine led to an increase of Hg mobilisation of 42% for soils with inorganically bound Hg. In column experiments, the maximum Hg removal rate was 75%. For soils with organically bound Hg or HgS, only 1?C5% of Hg was mobilised. Thus, the extraction of Hg from soils with l-cysteine is highly dependent on the Hg-binding form. Hg speciation analyses of leachates indicate that Hg?Cl-cysteine complexes are labile complexes which can be easily transformed. Soil samples speciation analysis revealed that reduction to elemental mercury takes place at low S?CHg ratios (1 to 10), assumingly by microbial activity. At higher S?CHg ratios of 10 and 100, precipitation of stable Hg?CS complexes could be observed. These species transformation processes are limitations for considering l-cysteine leaching as a remediation strategy.     

Mercury cycling in the water column of a seasonally anoxic urban lake (Onondaga Lake,NY)

Onondaga Lake, New York, is a hypereutrophic, urban lake that was subjected to industrial discharges of mercury (Hg) between 1947 and 1988. Water samples were collected from April through November 1992 and analyzed for filtered and unfiltered total Hg, methylmercury (CH₃Hg), dimethylmercury, ionic Hg, and elemental Hg to characterize the biogeochemical cycling of Hg during water column stratification and hypolimnetic anoxia. In the spring and late fall when the water column was isothermal, total Hg and CH₃Hg concentrations were relatively constant throughout the water column, at approximately 3–7 ng/L and 0.3–1 ng/L, respectively. Through the summer and early fall, CH₃Hg concentrations systematically increased in the deeper waters, reaching peak concentration in August and September. In September 1992, CH₃Hg concentrations increased from 0.3 ng/L in the epilimnion to 10.6 ng/L in the hypolimnion, an increase of nearly 2 orders of magnitude. At the same time, total Hg increased from 6.6 ng/L in surface water to 21.7 ng/L at depth, a 3-fold increase. The spatial and temporal patterns observed for CH₃Hg agree well with manganese, suggesting that CH₃Hg and manganese are controlled by processes of the same or parallel cycles.     

Natural Mercury Levels in Geological Enriched and Geological Active Areas: Case Study of Katun River and Lake Teletskoye,Altai (Siberia)

Natural geological Hg deposits control the Hg levels inthe upper Katun river. Very high levels of total Hg areobserved in the watercolumn (up to 20 ng L^-1) and thesediments (up to 244 μg g^-1) close to the depositarea, but almost normal levels (1.8 ng L^-1 in the watercolumn and 0.14 μg g^-1 in the sediments) are reached60 km downstream of that zone. In general, low dissolvedmethylmercury (MMHg) concentrations were found (0.04–0.05 ngL^-1) due to unfavourable methylation conditions. The MMHgconcentrations in the sediments vary from 23.3 ng g^-1, inthe vicinity of the geological Hg deposits, to 0.17 ng g^-1 60 km downstream.Total Hg levels in Lake Teletskoye (a geological activearea) are slightly increased (1.1–1.8 ng L^-1) compared toLake Baikal and fairly constant alover the Lake, suggestingmultiple sources. High mercury concentrations in springs andsoils coincide with high radon concentrations in the samecompartments as well as high soil exhalation fluxes. Theseresults in combination with the fact that Lake Teletskoye islocated in an active fault zone suggest that the Rn and Hgsources may be fault aligned spring waters and deep seatedgases escaping through open cracks. Methylmercuryconcentrations in the Lake (0.03–0.1 ng L^-1) werecomparable to the concentrations found in Katun river butrelative to the total Hg burden this means a higher percentage.     

Half a Century of Mercury Contamination in Lake Vänern (Sweden)

Lake Vänern is Sweden's largest freshwater reservoir. It has been significantly affected by mercury contamination during the latter half of the 20th century. The aim of this study was to analyse the spatial and vertical mercury distribution, whereas 46 sediment cores were sampled in 2001 and analysed for total mercury. Several of these cores were dated presenting sediment accumulation rates varying from 6–8 mm yr^?1 outside major rivers to ～2 mm yr^?1 in the deeper areas. This was made using ¹³⁷ Cs, which was verified by ²¹⁰ Pb dating. Cluster analysis was used to identify five areas with similar accumulation and mercury concentration regimes. In areas far from shore, surface concentrations ranged from 0.1 to 0.5 ppm Hg, while the deeper layers in contaminated areas held concentrations up to 11 ppm Hg. In total, ～50 tonnes of mercury accumulated in the lake's sediment between ～1940–2001; almost 80% (or 37 tonnes) originate from before the mid 70's when the recovery period began, and at least 30 tonnes can be attributed to the former point source – a chlor-alkali industry.