Mercury Dynamics in the Lahontan Reservoir,Nevada: Application of the QWASI Fugacity/Aquivalence Multispecies Model

The Lahontan Reservoir in western Nevada has among the highest mercury (Hg) concentrations recorded in water, sediments and biota. The QWASI fugacity/aquivalence multispecies model was applied to examine Hg dynamics through a steady-state analysis of high loading conditions. The analysis indicated that the Carson River supplies most Hg in the water and upper sediments, with minimal inputs from the atmosphere and the Truckee Canal. Model estimates suggest that more than 90% of Hg entering the system from the Carson River at high flow is retained in the sediment of the reservoir, with export removing the remainder. Losses due to volatilization are negligible. The amount of methylmercury (MeHg) in the reservoir can be accounted for by inputs from the Carson River with minimal methylation occurring in the reservoir. The lack of species conversion and high retention rate appear to be due to the unreactive mineralogy of particulate Hg. Thus, we suggest that Hg dynamics are similar to that of other highly particle-reactive metals where fate is determined by particle movement. Finally, model results suggest an additional source of Hg to the system, which we hypothesize is from deep contaminated sediment that enters the system through sediment mixing caused by seasonal wet and dry cycles and sediment resuspension.     

Stores from old reservoirs: Sediment Hg and Hg methylation in Ontario hydroelectric developments

We sampled several Ontario Hydro reservoirs to deteimine the changes in mercury (Hg) and organic profiles of sediment cores with reservoir development We also examined Hg methylation among reservoirs of different age and water chemistry. In sediment cores from four Ontario reservoirs, reservoir (watershed) specific differences appeared to supersede general trends, with the differences between headpond and run-of-river reservoirs particularly important In general, the rate of Hg and organic accumulation appeared to increase with reservoir impoundment, but we were unable to discern consistent changes in concentrations of Hg or loss on ignition (LOI) with reservoir impoundment We also observed significant positive correlations of sediment Hg with concentrations of chlorophyll derivatives and bacterial photopigments. Our results are in agreement with earlier studies which indicated that an increase in Hg supply caused by erosion and release from flooded soils is central to the changes in Hg dynamics within reservoirs following impoundment Although Hg methylation activity of sediments, from a series of reservoirs on the Mississagi River was positively correlated with organic content of the sediment, the observed rates were sufficiently variable that the potential effects of reservoir age or preparation methods could not be resolved. Similarly, in our measurements of net methylmercury (MeHg) flux in two older reservoirs, the large range of variation in net MeHg flux observed among replicate samples obscured the potential effects of differences in geology and water chemistry. Future studies should focus on resolving the underlying causes of this variability and in consolidating the ‘microscale’ measurements obtained using sediment core incubation techniques and the ‘macroscale’ values obtained by whole lake mass balance techniques.     

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.     

Modeling the transport and fate of mercury in an urban lake (Onondaga Lake,NY)

A mass balance model was developed to simulate mercury (Hg) cycling in Onondaga Lake, New York. MERC4, a U.S. Environmental Protection Agency model of the physical and biogeochemical transport and transformation of Hg, was modified by the addition of input from two supporting models (Fish Bioenergetics Model 2 and a lake eutrophication model) to model the transport of Hg into and out of plankton and fish. The model calculates the concentrations of total Hg, methylmercury, elemental Hg, and ionic Hg in both dissolved and particulate forms in the water column. The model was calibrated to an extensive data set of temporally and spatially variable Hg concentrations in Onondaga Lake in 1992. In addition to standard transport processes of advection and dispersion included in MERC4, the Onondaga Lake Mercury Model includes remineralization to simulate release of Hg from settling particulates before incorporation into sediment. The model provides an analytical framework for understanding and predicting the behavior of Hg in Onondaga Lake and has potential use in evaluating the relative impact of different source control and remedial alternatives.     

Distribution of mercury in the aquatic food web of Onondaga Lake,New York

Historical discharges of mercury (Hg) to Onondaga Lake, New York, have resulted in elevated Hg concentrations in lake fishes. In 1990, a remedial investigation and feasibility study (RI/FS) was initiated to evaluate problems related to Hg and other hazardous substances in the lake. As part of the RI/FS, the distribution of Hg in the aquatic food web was determined to provide input to a site-specific model of Hg cycling and to evaluate potential ecological risks of Hg in the lake. Mercury concentrations were measured in surficial sediments, sediment interstitial water, lake water, phytoplankton, Zooplankton, benthic macroinvertebrates, and fishes (including planktivores, benthivores, and piscivores). The percentage of total Hg accounted for by methyl-Hg (CH₃Hg) generally increased with higher trophic levels, confirming that CH₃Hg is more efficiently transferred to higher trophic levels than is inorganic Hg. Concentrations of total Hg in amphipods and chironomids were closely related to concentrations of total Hg in sediments, suggesting that sediments are a likely source of Hg for benthic macroinvertebrates. Mercury concentrations in edible muscle tissue (fillets) of lake fishes have declined substantially from values found in the early 1970s, reflecting the large reductions in Hg discharges to the lake that have occurred since that time. The CH₃Hg concentrations in fillets and whole bodies of fishes generally were similar, indicating that concentrations in fillets often can provide estimates of concentrations in whole bodies. Methyl-Hg concentrations and bioaccumulation factors increased with higher trophic levels in both the pelagic and benthic components of the lake food web.     

Mercury (Hg) Transport in a High Arctic River in Northeast Greenland

In a warming climate, mercury (Hg) pathways in the Arctic can be expected to be affected. The Hg transport from the high arctic Zackenberg River Basin was assessed in 2009 in order to describe and estimate the mercury transported from land to the marine environment. A total of 95 water samples were acquired and filtered (0.4 ??m pore size), and Hg concentrations were determined in both the filtered water and in the sediment. A range of other elements were also measured in the water samples. Hg concentrations in the filtered water were in general highest in the beginning of the season when the water came mainly from melted snow. THg concentrations in the sediment were in general relatively constant or slightly decreasing until mid-August, where after the concentrations increased. A principal component analysis separated the samples into spring, summer and autumn samples indicating seasonal characteristics of the patterns of element concentrations. The total amount of Hg in the sediment transported was estimated to 2.6 kg. Approximately 60% of the sediment-transported Hg occurred during a 24-h flood in the beginning of August caused by a glacial lake outburst flood. The total amount of transported dissolved Hg was estimated to 46 g, and 13% of this transport occurred during the 24-h flood. If it is assumed that the Hg transport by Zackenberg River is representative for the general glacial rivers in East Greenland, the total Hg transport into the North Atlantic from Greenland alone is approximately 4.6 tons year^?1 with an estimated annual freshwater discharge of ??440 km³.     

Mercury speciation in open ocean waters

Vital to our understanding of the biogeochemical cycling of Hg and the origin of the enhanced monomethylmercury (MMHg) concentrations in biota is knowledge of the sources, behavior and fate of methylated Hg species in natural waters. Methylated Hg species, dissolved gaseous and reactive mercury were measured in the equatorial Pacific Ocean in early 1990. Both dimethylmercury (DMHg) and MMHg were found in the subthermocline waters of the equatorial Pacific Ocean. Maxima in alkylmercury species in the O₂ minimum region coincided with a decrease in reactive mercury. A significant inverse correlation between DMHg, and MMHg, concentration and O₂ content was observed. A maximum in reactive mercury was observed in the region of the thermocline, with similar concentrations in the surface and deeper waters. Atmospheric deposition is not a significant source of MMHg to this region. The data suggest formation of alkylmercury species in the low oxygen zone, with Hg(II) being the most likely substrate. A model for the cycling of Hg species in the equatorial Pacific Ocean is presented. These results are the first direct evidence of a significant open ocean source of methylated Hg species and suggest a pathway for mercury accumulation in pelagic fish.     

Influence of Physical and Chemical Characteristics on Mercury in Aquatic Sediments

Given the variation observed in mercury in fish from natural lakes, it is difficult to determine what represents a background mercury level. Mercury in aquatic sediments is a potential source of this trace metal to biota, notably fish. Site specific factors, such as acidity and dissolved organic carbon have been shown to affect the mobilization of mercury and methylation of mercury. Methyl mercury is the most toxic form of this metal and the form most readily accumulated by biota. Thirty-four headwater lakes, selected for a range in pH, were sampled for sediment mercury levels as part of an investigation of the impacts of acid rain on insular Newfoundland lakes. Selected physical and chemical data were also collected on all of the study sites. Acidity was not found to be significantly related to sediment mercury concentrations despite the wide range in pH. Pearson correlation analysis indicated that sediment mercury level was positively correlated with WA:LA (watershed to lake area ratio). WA:LA was also correlated with Secchi depth and colour. Linear regression was used to estimate the parameters of a model relating sediment mercury to WA:LA. Watershed area to lake area ratio was more important than site specific factors in governing the concentration of sediment mercury in lakes without industrial input.     

太湖五里湖水域背角无齿蚌中汞的残留

作为建立淡水环境下持久性污染物“背角无齿蚌观察”体系的又一尝试,利用NIC汞分析仪（MA-2000型）对采自太湖污染最严重水域——五里湖代表样点的背角无齿蚌（Anodontawoodiana）及用于对照的底泥中重金属汞的残留进行了测定。结果显示,汞在背角无齿蚌和底泥样本中的浓度平均值分别为0．005mg·kg-1干重和0．135mg·kg-1干重;浓度范围分别为0．000-0．011mg·kg-1干重和0．063．0．227mg·kg-1干重。蚌样和底泥样本中汞的残留浓度均明显低于国家相关的食品卫生（GB2762--1994）、限量标准（NY5073--2001）,或农用淤泥（GB4284-1984）、土壤环境质量（GB15618--1995）标准。另外,底泥样本中汞的地积累指数（Igeo）仅为-1．96。两类样本中汞的残留状况一致反映出目前太湖五里湖水域汞的污染程度很低。近年来五里湖全湖水域的清淤工程应该是导致这种现象的原因。不同样点汞浓度的地理差异仅在底泥样本中达到显著水平。     

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 in vegetation and lake sediments from the U. S. arctic

Global atmospheric concentrations of mercury (Hg) appear to be increasing and with it the potential for ecosystem exposure and ecological effects. From 1990 to 1993 we examined U. S. arctic ecosystems over a broad spatial scale to develop baseline information on current concentrations of trace elements, heavy metals (including Hg), persistent organic compounds, and radionuclides in various components of the terrestrial and freshwater biosphere. Matrices reported here include, vegetation (lichens and mosses) and lake sediments. Total Hg in two lichen and two moss species from Alaska were generally low (0.02–0.112 μg/g dw), compared to reported values from other arctic locations and showed a statistically significant negative relationship between total Hg content and distance from the marine coastline.²¹⁰Pb dated sediment cores indicated that average preindustrial total Hg accumulation rates were over four times greater in arctic Schrader lake than in subarctic Wonder Lake. Both lakes indicated a small increase (5–8%) in total Hg flux to the sediments during the last 145 years, much smaller than similar increases in total mercury for lakes in the north central U. S. The likely source of recent increases in Hg in these Alaskan ecosystems is long range atmospheric transport. While we can detect increases in mercury in lake sediments likely due to anthropogenic activities, values are low and there appears to be no immediate threat to terrestrial environments and inland freshwaters of arctic Alaska from long range atmospheric transport and deposition of Hg.     

Comparison of mercury concentrations in modern lake sediments and glacial drift in the Canadian Shield in the region of Ottawa/Kingston to Georgian Bay,Ontario, Canada

An ongoing problem in evaluating the significance of mercury (Hg) in surficial materials is distinguishing sources of natural (spatial) variation of the geological/geochemical environment from sources (airborne, waterborne, etc.) of anthropogenic (temporal) variation. The Geological Survey of Canada (GSC) has carried out a series of sampling programs, including one in the southeastern part of the geologically complex Canadian Shield, in order to link the easily observable lithological variations of bedrock with the chemical composition of overlying glacial deposits and lake sediments. This research aims to provide a base against which observed variations in life systems can be judged as natural or anthropogenic. In the study area, high concentrations of Hg and other trace elements in lake sediment and glacial sediments can be related to glacial dispersal from mineralized bedrock and/or bedrock with high natural background concentrations of these elements.     

Method development and sample processing of water,soil, and tissue for the analysis of total and organic mercury by cold vapor atomic fluorescence spectrometry

Atomic Fluorescence-based methods have been developed for measuring ultratrace levels of mercury (Hg) in environmental (water, soil) and biological (fish tissue) samples. In addition, methods for preparation of water, soil, and tissue samples have been developed. For the analysis of total Hg in soil, sediment and fish the samples are digested with concentrated nitric acid in sealed glass ampules, and subsequently autoclaved. Water samples are digested using standard brominating procedures. A Merlin Plus, PS Analytical atomic fluorescence spectrometer (AFS) system equipped with an autosampler, vapor generator, fluorescence detector and a PC based integrator package is used in the determination of total Hg. The determination of Hg mercury species in water, without pre-derivatization, involves adsorbent pre-concentration of the organomercurials onto sulfydryl-cotton fibers. The organic Hg compounds are eluted with a small volume of acidic KBr and CuSO₄ and extracted into dichloromethane. Sediment, soil and tissue samples are homogenized and the organomercurials first released from the sample by the combined action of acidic KBr and CuSO₄ and extracted into dichloromethane. The initial extracts are subjected to thiosulfate clean-up and the organomercury species are isolated as their chloride derivatives by cupric chloride addition and subsequent extraction into a small volume of dichloromethane. Analysis of organic Hg compounds is accomplished by capillary column chromatography coupled with atomic fluorescence detection.     

Preliminary results on the role of rivers in total Hg concentrations in marine sediments and benthic organisms of a coastal area of Italy

The paper reports the results of mercury (Hg) concentrations in the <20 μm grain-size fraction of shallow sediments of the northern Tyrrhenian sea, collected near the mouths of rivers flowing down from the Monte Amiata area (central Italy), which is characterized by cinnabar mineralization which was developped as mercury mine in the past. A few species of benthic marine organisms collected in the sediment sampling area were also analyzed. From the results, it emerged that the rivers contribute to the Hg concentration in the marine sediments which already contain high natural Hg background levels. The benthic organisms, which reflect sediment contamination, showed high Hg concentrations as well.     

Complexing properties of nitrilotriacetic acid in the lake environment

At concentrations above 1 ppm NTA can react with sparingly soluble compounds to release the metal and associated anions through complexation. It also interacts with sediment to release certain metals depending on the abundance of the metals in the sediment. In situ and laboratory experiments have been carried out to study such interactions and also to follow the fate of these released metals after NTA has degraded. Degradation of certain NTA-metal complexes in lake water medium has also been studied. It was found that certain NTA complexes (Cu, Ni, Cd, Hg) are very resistent to degradation.     

Bioenergetic calculation of mercury accumulation in fish

A numerical model was developed for the bioaccumulation of mercury (Hg) in fish. The model is based on the bioenergetic calculation of fish growth, food consumption, respiration, specific dynamic action and waste losses (egestion/excretion) using the program of Hewett and Johnson (1992). Based on the predation and food results obtained, the accumulation of Hg in fish is calculated taking into account the concentrations of methyl mercury (MeHg) in food and water, its intake and accumulation from food and from water, and the removal of Hg from the body. Some species at various levels of food web are considered in the multistep model applications. The model is used to compute the changes of Hg contents in perch (as prey) and pike (as predator) caused by the release of Hg from the bottom sediments when the Kokemäki River in Western Finland was dredged. The model results were not far from the observed results even though the forcing conditions had been described only roughly.     

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.     

Development of methodology for predicting reacidification of calcium carbonate treated lakes

As part of the EPRI funded Lake Acidification Mitigation Project(LAMP), an ongoing study to evaluate the feasibility of acid lake liming, two models (WAM and ALaRM) have been tested for two calibrated Adirondack Mountain study lakes(Woods and Cranberry). A priori predictions of reacidification rates based on Ca carbonate application and historical hydrological data are presented. WAM (Watershed Acidification Model) is a deterministic model that is capable of simulating the movement of water and chemical constituents through a watershed. WAM generates indata in the form of hydrologic and alkalinity to ALaRM (Acid Lake Reacidification Model), a general mass balance model developed for the temporal prediction of the principal chemical species in both the water column and sediment pore water of small lakes and ponds. A matrix of runs to determine model sensitivity to input loadings, kinetic coefficients, and sediment dosage levels indicate that reacidification of the water column is most sensitive to variation in hydrologic loading followed by variation in sediment dosage levels. Baseline estimates (initial water column alkalinity between 400 to 500 μeqL^?1) indicate that reacidification to near zero alkalinity occurs after a time period equivalent to approximately two to three average hydraulic retention times.     

Mercury and Methylmercury Dynamics in the Hyporheic Zone of an Oregon Stream

The role of the hyporheic zone in mercury (Hg) cycling has received limited attention despite the biogeochemically active nature of this zone and, thus, its potential to influence Hg behavior in streams. An assessment of Hg geochemistry in the hyporheic zone of a coarse-grained island in the Coast Fork Willamette River in Oregon, USA, illustrates the spatially dynamic nature of this region of the stream channel for Hg mobilization and attenuation. Hyporheic flow through the island was evident from the water-table geometry and supported by hyporheic-zone chemistry distinct from that of the bounding groundwater system. Redox-indicator species changed abruptly along a transect through the hyporheic zone, indicating a biogeochemically reactive stream/hyporheic-zone continuum. Dissolved organic carbon (DOC), total Hg, and methylmercury (MeHg) concentrations increased in the upgradient portion of the hyporheic zone and decreased in the downgradient region. Total Hg (collected in 2002 and 2003) and MeHg (collected in 2003) were correlated with DOC in hyporheic-zone samples: r ²?=?0.63 (total Hg-DOC, 2002), 0.73 (total Hg-DOC, 2003), and 0.94 (MeHg-DOC, 2003). Weaker Hg/DOC association in late summer 2002 than in early summer 2003 may reflect seasonal differences in DOC reactivity. Observed correlations between DOC and both total Hg and MeHg reflect the importance of DOC for Hg mobilization, transport, and fate in this hyporheic zone. Correlations with DOC provide a framework for conceptualizing and quantifying Hg and MeHg dynamics in this region of the stream channel, and provide a refined conceptual model of the role hyporheic zones may play in aquatic ecosystems.