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1.
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 Hg. Species determined included total Hg (Hgt), reactive (‘ionic’) Hg (Hgi), monomethylmercury (CH3HgX), elemental Hg (Hg°) and dimethylmercury (CH3)2Hg). Onondaga Lake was found to contain very high levels of Hgt (2 to 25 ng L?1 Hg), Hgj (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 (Hgt), 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.  相似文献   

2.
Experimental results and field data indicated that methyl-Hg was produced within a layer of bacterioplankton near the top of the anoxic hypolimnion of Pallette Lake. In situ incubations at ambient Hg concentrations indicated that the net flux of methyl-Hg from the layer was between 50 and 100 pmol/m2*d. This input was sufficient to account for the summer accumulation of methyl-Hg in the entire hypolimnion and it exceeded atmospheric inputs by 2 orders of magnitude. Maximum rates of net methylation occurred in the same region of the water column where we observed maximum rates of sulfate reduction. The measured rates were: 100 fmol rriethyl-Hg/L*d and 90 nmol SO4/L*d. Sulfate reducing enrichment cultures isolated from the hypolimnion were also able to methylate Hg in the laboratory. Sulfate reduction did not occur in anoxic profundal sediments during summer and we infer from ancillary data that methylation in profundal sediments was also low. Whole-lake rates of sulfate reduction in the hypolimnetic layer and shallow sediments were roughly equivalent, but we cannot yet compare methylation rates at these sites due to large uncertainties in the littoral flux of methyl-Hg. We propose that zones of Hg methylation and SO4 reduction follow the oxic/anoxic boundary in both the watercolumn and sediments. The relative importance of watercolumn and sediment processes will depend on the physical and chemical structure of a given lake.  相似文献   

3.
Research on mercury (Hg) distribution and speciation was carried out in Lake Baikal, a large, strong-oligotrophic freshwater reservoir in Siberia, Russia, during June 1992 and march 1993. In summer, total Hg in the water column ranged from 0.14 to 0.77 ng Hg/L, with the highest concentrations observed in the central basin of the lake in surface water samples. Labile inorganic Hg was found to be 7 to 20 % of the total Hg content. Highest total Hg concentrations were found in river waters: up to 2 ng Hg/L. Labile methylmercury (MeHg) concentrations ranged from 2 to 38 pg Hg/L in the water column, with the higher concentrations in the central part of the lake, and showing a slight increase in near bottom waters. Labile MeHg makes up 1 to 15 % of the total Hg content in the water column, with larger fractions in deep waters. The slight increase of the MeHg gradient with depth corresponds with the O2 minimum region. Highest MeHg concentrations were observed in river waters (up to 145 pg Hg/L) and in some bays of the lake (up to 160 pg Hg/L). In these high temperature- and phytoplankton-rich water masses, the MeHg-fraction increased up to 35 % of total Hg. Labile MeHg concentrations in water samples taken in winter in the southern basin (under the ice cover), showed slightly higher concentrations than in summer, possibly due to an early spring bloom. In rainwater, total Hg ranged from 3 to 20 ng Hg/L and MeHg from 0.1 to 0.25 ng Hg/L. In snow, a large fraction of total Hg is bound to particulate matter; concentrations of total Hg ranged from 8 to 60 ng Hg/L and labile MeHg from 0.1 to 0.25 ng Hg/L. Atmospheric Hg was found to be 0.73 to 2.31 ng/m3 as gaseous Hg and 0.005 to 0.02 ng/m3 in its particulate form. Spatial distribution patterns of atmospheric Hg show slightly higher concentrations over the central part of the lake and the Selenga river delta. In winter, atmospheric Hg values (measured in the southern region), ranged from 1.2 to 6.1 ng/m3 as total gaseous Hg and 0.02 to 0.09 ng/m3 as total particulate Hg, and are higher than in summer, probably influenced by coal burning and traffic by the local population. MeHg contents in fish ranged from 20 ng Hg/g dry weight in small Cottocomephorus to 300 ng Hg/g dry weight in pike and trout species, which were caught in organic-rich waters.  相似文献   

4.
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.  相似文献   

5.
In this study, we evaluated the relative contribution of atmospheric particulate mercury (Hg(p)) and divalent reactive gaseous mercury (RGM) to mercury dry deposition in Japan. The dry deposition fluxes (on a water surface sampler) and atmospheric PM concentrations of Hg, Cd, Cu, Mn, Ni, Pb and V, which were measured concurrently from April 2004 to March 2006 at 10 sites across the nation, were used in this evaluation. We considered that Hg(p) and RGM, but not Hg0, are deposited on the water surface, and that our method of sampling Hg(p) without the use of KCl-coated annular denuders enables the exclusion of a significant amount of RGM artifact. The monthly average dry deposition velocities (= deposition flux/atmospheric PM concentration) of Cd and Pb were found to be similar to each other (Cd/Pb deposition velocities?=?1.06?±?0.58). It was assumed that the deposition velocity of Hg(p) is identical to the mean deposition velocity of Cd and Pb, because the particle size distribution of Hg(p) is likely similar to those of both elements. Using this deposition velocity, the monthly dry deposition flux of Hg(p) was calculated. The average contribution (±1σ) of Hg(p) to the annual deposition flux at ten sites was 26?±?15%. The mercury dry deposition flux increased generally from spring to early summer, which was attributed mostly to the deposition of RGM. This seasonal change correlated to that in photochemical oxidant (primarily O3) concentration in air at most sites. These suggest that mercury dry deposition in Japan is predominantly deposition of RGM, which was formed via oxidation of Hg0 by O3 in the atmosphere.  相似文献   

6.
The spatial and temporal distribution of elemental Hg (Hg°) and reactive Hg (HgR) has been studied on Pallette Lake, Wisconsin during May – August, 1993 and May, 1994. In general, Hg° concentrations near the lake surface greatly exceeded saturation with respect to atmospheric Hg° indicating a flux out (?) of the lake. Evasional losses were estimated using a thin film model and averaged ?101 pmol m?2 d?1 during July and August, 1993. A large portion of atmospherically deposited Hg is re-emitted. Thus, in-lake Hg° production' and evasion to the atmosphere will significantly reduce the amount of Hg which is transported to the sediments, the principal site of methylation. Laboratory experiments were conducted to ascertain the rate of Hg° formation from Hg(II). Reduction was significantly lower in heat sterilized lakewater suggesting Hg° production was biologically mediated. The temporal distribution of epilimnetic Hg°, as measured at the lake center, was influenced by Hg° evasion, Hg° production and advective transport of water parcels of differing Hg content. Spatial gradients in Hg° and HgR were identified and a transport model was employed to estimate the advective flux of Hg°. The importance of atmospheric deposition and sediment-water interaction as sources of HgR to epilimnetic waters were examined. Porewater concentrations of Hg° and HgR were determined on several occasions. During May, 1994, the depletion of lakewater HgR following a input pulse due to rain was observed and the estimated removal rate (16–20% d?1) agrees well with reduction rates obtained in the laboratory (23% d?1).  相似文献   

7.
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.  相似文献   

8.
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.  相似文献   

9.
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.  相似文献   

10.
An intensive survey of mercury speciation was performed at a site on the Upper St. Lawrence River near Cornwall, Ontario, Canada with a history mercury contamination in sediments. Surface sediments were collected every 1.50 h. Total mercury (Hgtotal), methylmercury (MeHg), organic carbon, inorganic and organic sulphur were determined in the solid fraction. Dissolved Hgtotal, MeHg and dissolved organic carbon (DOC) were measured in pore waters. Concentrations of Hgtotal in the upper layers (first 5 cm) were high, ranging from 1.42 to 25.8 nmol g?1 in solids and from 125 to 449 pM in pore waters. MeHg levels were also high, ranging from 4.34 to 34.1 pmol g?1 in solids and from 40 to 96 pM in pore waters. This amounts to up to 1.4% of Hgtotal present as MeHg in solids and 64% in pore waters. A daily pattern for Hgtotal was observed in the solid fraction. The MeHg distribution in solids and pore waters was not correlated with Hgtotal or DOC, suggesting that the concentrations of MeHg are probably more influenced by the relative rates of methylation/demethylation reactions in the sediment–water interface. Acid volatile sulphide levels and DOC were inversely correlated with organic sulphur (Sorg) levels suggesting that both parameters are involved in the rapid production of Sorg. A positive correlation was also observed between Hgtotal and Sorg in solids (R?=?0.87, p?<?0.01) illustrating the importance of organic sulphur in the retention and distribution of Hg in the solid fraction of the sediments. The results suggest that variations of Hgtotal concentrations in Upper St. Lawrence River surface sediments were strongly influenced by the formation/deposition/retention of organic sulphur compounds in the sediment–water interface.  相似文献   

11.
The suitability of the dialysis technique for the close interval sampling of total dissolved mercury (Hg) in interstitial waters was evaluated through field tests conducted in flooded soils of two hydroelectric reservoirs, as well as in lake sediments and peat bogs. In these shallow water and weakly contaminated environments, we have demonstrated that peepers offer simplicity and yield more consistent results when compared with the squeezed sediment technique; that the presence of O2 in the initial filling solution does not significantly influence total dissolved Hg concentrations, [Hgtot]D, in samples collected from anoxic environments; and that an equilibration period of 8 to 9 days yields slightly less variable results than one of 6.5 days. Using the dialysis technique, we were able to generate close interval vertical profiles of [Hgtot]D, in interstitial waters. A comparison of preliminary results indicates that [Hgtot]D in porewaters collected in both artificial and natural systems are similar and independent of the sampling environment, the depth of the overlying water column, and the history of reservoir impoundment.  相似文献   

12.
The atmospheric chemistry, deposition and transport of mercury (Hg) in the Upper Great Lakes region is being investigated at a near-remote sampling location in northern Wisconsin. Intensive sampling over two years and various seasons has been completed. A multi-phase collection strategy (gas-, particle- and precipitation-phases) was employed to gain insight into the processes controlling concentrations and chemical/physical speciation of atmospheric Hg. Additional chemical and physical atmospheric determinations (e.g. ozone, particulate constituents, meteorology) were also made during these periods to aid in the interpretation of the Hg determinations. For example, correlations of Hg with ozone, sulfur dioxide and synopticscale meteorological features suggest a regionally discernible signal in Hg. Comparison to isosigma backward air parcel trajectories confirms this regionality and implicates the areas south, southeast and northwest of the site to be sources for Hg. Particle-phase Hg (Hgp) was found to be approximately 40% in an oxidized form, or operationally defined as “reactive”. However, this was quite variable from year-to-year. Hgp and other particle constituents (esp. sulfate) show significant correlation and similarity in behavior (concentration ratios in precipitation and in particles). These observations are part of the growing evidence to support the hypothesis that precipitation-phase Hg arises in large part from the scavenging of atmospheric particulates bearing Hg. Observed concentrations of rain and particle-Hg fit broadly the theoretical expectations for nucleation and below-cloud scavenging. Significant increases in the Hg/aerosol mass ratio appear to take place during transport. Enrichment of aerosols is taken as evidence of gas/particle conversion which could represent the step linking gas-phase Hg with rain. The refined budget indicates ca. 24% of total deposition is from summer particle dry deposition, and that this deposition also contributes ca. 24% of all reactive Hg deposition. Additionally, almost all (86%) deposition (wet and dry) occurs during the summer months.  相似文献   

13.
Biotic uptake of mercury (Hg) in Davis Creek Reservoir, California increased dramatically in conjunction with the entrainment of anoxic hypolimnetic water into the mixed layer. This indicated a seasonal pulse increase of bioavailable Hg associated with thermal destratification. The effect was more pronounced in juvenile bass (70–200% seasonal increases in muscle Hg concentration), as compared to adults (15–25% increases), and was most distinct in zooplankton, which spiked to concentrations of 3–6 mg/kg, dry weight, immediately following fall destratification (130–270% seasonal increases over pre-fall levels). In addition to the general buildup of methyl Hg in the hypolimnion under anoxic conditions, a dense layer of photosynthetic anaerobic bacteria just beneath the thermocline is implicated as a potentially important seasonal source of methyl Hg to reservoir fish. Hg increases in juvenile and adult fish correspond to late summer and fall entrainment of upper hypolimnetic water, while zooplankton spike increases may be partially related to ingestion or adsorption of Hg-scavenging manganese oxides, which precipitate following full turnover. A simple and effective, syringe-based cold vapor atomic absorption method for total Hg is also described.  相似文献   

14.
A total mercury (total Hg) and methylmercury (CH3Hg) mass balance was developed for Onondaga Lake, NY, based on sampling of tributaries, sediments, water column, and biota in 1992. Thein situ flux of total Hg and CH3Hg from sediments to the overlying water and the rate of net CH3Hg production in the water column were determined experimentally. Fluxes from atmospheric deposition, groundwater, and volatilization were estimated from limited field data and the literature. Ultraclean sampling and analytical techniques developed specifically for Hg were used. Results indicate that tributaries contribute the majority of total Hg entering the lake (13.6 kg in 1992). Other sources of total Hg included groundwater flux (0.02 kg), atmospheric deposition (0.44 kg), and flux from sediments (0.056 kg). Net sedimentation (11.1 kg), outflow (2.8 kg), and volatilization (0.016 kg) were sinks for total Hg. The two major sources of CH3Hg were tributaries (0.26 kg) and net CH3Hg production in the water column (0.60 kg). Flux from sediments accounted for only 0.017 kg CH3Hg. Net sedimentation (0.47 kg), outflow (0.24 kg), and net uptake, by fish (0.20 kg) were sinks for CH3Hg. Gross sedimentation of CH3Hg exceeded net sedimentation by 90%, suggesting that release of CH3Hg from settling particles is a significant process.  相似文献   

15.
The sources and concentrations of total mercury (total Hg) and methylmercury (MeHg) in the upper catchment of the Lake Gordon/Lake Pedder system in Tasmania, Australia were investigated. The catchment area, which contains over 50% wetlands, is located in a temperate region with no obvious point sources of mercury. Surface waters in the region had concentrations of total Hg ranging from 1.2 to 14.4 ng L-1 and MeHg from < 0.04 to 1.4 ng L-1. MeHg concentrations were seasonally dependent, with the highest concentrations occurring in summer. Sediments/soils in the catchment had concentrations of total Hg ranging from 4.0 to 194 ng g-1 and MeHg from <0.02 to 20.1 ng g-1. The low concentrations of total Hg confirmed that this region is pristine as regards mercury and has no geological enrichment of total Hg. The highest total Hg and MeHg concentrations in both sediment/soils and waters were found in bogs whereas the lowest concentrations typically occurred on the wetlandplains. MeHg concentrations, in bog and swamp sediments were correlatedwith the organic matter content (r = 0.942, P < 0.001). Acid volatile sulfide (AVS) measurements indicate that in most sediments AVS was greater than total Hg. Given the high reactivity of inorganic mercury and sulfide, this suggests that most of the particulate mercury in sediments is present as mercuric sulfide. The yield of MeHg from the catchment was estimated to be 3.2 mg ha-1 yr-1 and is higher than published rates measured in non-contaminated temperate catchments in the northern hemisphere. The higher yield was attributed to the generally warmer climatic conditions that favour net methylation and the relatively high rainfall (2–3 m yr-1) of the region, which supplies reactive inorganic mercury to the active zones ofmercury methylation and also flushes MeHg from the catchment.  相似文献   

16.
When balancing the element mercury (Hg) two coal-fired power plant units — one with slag tap boilers (ST, 2 × 220 MW) and one with a dry bottom boiler (DB, 475 MW) were compared. Both systems are provided with electrostatic precipitators (ESP), nitrogen oxides removal (DeNOx) and flue gas desulfurization (FGD) systems. The Hg in the flue gas is predominantly in gas phase. Only 15 % of the Hg introduced by the coal leaves the unit with the bottom or fly ash. Depending on the operating mode, 30 to 40 % of the Hg is separated in the FGD systems. The overall separation rate for the total system ranges between 45 to 55 %, the residue is emitted in the form of gaseous Hg species. At full load, the Hg concentration in the cleaned gas is less than 6 μg/m3. In the flue gas path of another dry bottom boiler (DB1, 480 MW) the concentrations of the gaseous species of bivalent mercury (Hg2+), elemental mercury (Hg0), and total mercury content (Σ Hg) were determined. The sum of the concentrations of Hg2+ and Hg0 is in agreement with the measurement of Σ Hg. Directly downstream of the boiler Hg2+ dominates with 77 %, while Hg0 amounts to 23 %. In the high-dust DeNOx system Hg0 is oxidized almost completely to Hg2+ (96 %). Air heater and electrostatic precipitator do not influence the Hg species concentrations. The FGD system eliminates approximately 80 % of the Hg2+. At the same time the quantity of Hg0 increases by the factor 10. In the cleaned gas Hg0 dominates with 76 % as compared to Hg2+ with 24 %. At full load the concentration of Σ Hg in the cleaned gas is also below 6 μg/m3.  相似文献   

17.
Mercury and organic carbon concentrations vary dynamically in streamwater at the Sleepers River Research Watershed in Vermont, USA. Total mercury (THg) concentrations ranged from 0.53 to 93.8 ng/L during a 3-year period of study. The highest mercury (Hg) concentrations occurred slightly before peak flows and were associated with the highest organic carbon (OC) concentrations. Dissolved Hg (DHg) was the dominant form in the upland catchments; particulate Hg (PHg) dominated in the lowland catchments. The concentration of hydrophobic acid (HPOA), the major component of dissolved organic carbon (DOC), explained 41–98% of the variability of DHg concentration while DOC flux explained 68–85% of the variability in DHg flux, indicating both quality and quantity of the DOC substantially influenced the transport and fate of DHg. Particulate organic carbon (POC) concentrations explained 50% of the PHg variability, indicating that POC is an important transport mechanism for PHg. Despite available sources of DHg and wetlands in the upland catchments, dissolved methylmercury (DmeHg) concentrations in streamwaters were below detection limit (0.04 ng/L). PHg and particulate methylmercury (PmeHg) had a strong positive correlation (r 2?=?0.84, p?<?0.0001), suggesting a common source; likely in-stream or near-stream POC eroded or re-suspended during spring snowmelt and summer storms. Ratios of PmeHg to THg were low and fairly constant despite an apparent higher methylmercury (meHg) production potential in the summer. Methylmercury production in soils and stream sediments was below detection during snowmelt in April and highest in stream sediments (compared to forest and wetland soils) sampled in July. Using the watershed approach, the correlation of the percent of wetland cover to TmeHg concentrations in streamwater indicates that poorly drained wetland soils are a source of meHg and the relatively high concentrations found in stream surface sediments in July indicate these zones are a meHg sink.  相似文献   

18.
The cycling of dissolved gaseous Hg (DGM) has been examined in our studies of the troposphericHg cycle, air-water exchange and their importance to the biogeochemical behavior and fate of Hg in temperate lakes. Five seepage lakes in northcentral Wisconsin, ranging in pH from 4.7 to 7.2, have been studied under a variety of limnological conditions which included the following seasonal periods: summer (peak stratification), fall (following turnover) and late winter (under ice). Analytically, DGM was determined after purging lake water with argon and collecting the volatile Hg fraction on gold coated sand. The Hg collections were analysed by pyrolysis in a two-stage Au amalgamation gas train with detection by atomic fluorescence spectroscopy (AFS). In addition, chemical speciation of the volatile fraction has been achieved by trapping on a nondestructive substrate followed by gas chromatographic separation and AFS detection. The DGM consists principally of elemental Hg (Hgo) under all sampling conditions, with no significant contribution from volatile organic Hg species (detection limit of 3 femtomolar). Atmospheric gaseous Hg, which also consists principally of Hgo, was measured and the air-water partitioning determined. In general, the lake waters have been supersaturated with Hgo relative to the atmosphere. Supersaturation was greater in the summer, ranging from ca. 1.4 to 12 times (x) the saturation concentration. During the other sampling periods, Hgo ranged from saturation to ca. 7x the equilibrium concentration. The flux of Hg from the lakes due to gas evasion is significant and is estimated at approximately 10% of the annual atmospheric input of Hg to the lakes. An apparent relationship between Hgo and pH has been observed with lakes of lower pH having smaller Hgo concentrations.  相似文献   

19.
The depletion of hypolimnetic DO and the upper depth boundary of anoxia for four different years (1978, 1979, 1980 and 1981), and the accumulation of sulfide for a single year (1981), are documented for ionically enriched hypereutrophic Onondaga Lake, NY, USA. The depletion rate, represented as the areal hypolimnetic oxygen deficit (AHOD, g m?2 day?1), was extremely high (1.2–2.7 g m?2 day?1), The large differences in the rate within individual years and from year to year were largely a result of differences in attendant vertical mixing (parameterized as the hypolimnetic heating rate). The entire hypolimnion (depth interval from 11 to 20 m) was without O2 by late June of all 4 yr; anoxia was observed above the hypolimnion on some occasions when secondary stratification occurred. Sulfide accumulated progressively in the hypolimnion in 1981 following the onset of anoxia to a volume weighted concentration of I1 mg L?1. The ionic discharge from an adjoining alkali manufacturer exacerbated the problem of limited O2 resources of the hypolimnion by: (1) decreasing vertical mixing, (2) prolonging the duration of stratification, (3) causing abbreviated turnovers, and (4) encouraging increased rates of phytoplankton settling.  相似文献   

20.
The aim if this study was to assess the distribution of mercury in water, suspended particulate matter, surface sediments and biota from the Sado estuary, which, for the most part, is classified as a natural reserve, so as to evaluate its environmental quality status in terms of mercury contamination. Besides the diffuse sources of mercury coming into the Sado estuary, there are also additional contributions from the northern industrial zone and from the urban areas within the system. Applying national and international guidelines to different environmental matrices, the results obtained show that the system does not seem to be under environmental risk as far as mercury contamination is concerned. These quality guidelines can be used to rank and prioritise sites of concern. Hence, the area at the northern industrialised area deserves particular attention. The concentration of mercury in sediments of this area (0.54?mg kg?1) simultaneously succeeded the European Union Water Framework Directive (EU-WFD) reference value, the OSPAR Convention Ecotoxicological Assessment Criteria (EACs) and is classified as class 2 in degree of contamination by the National legislation, which implies some legal restrictive rules. Considering the stations close to urbanised areas, one exceeded the OSPAR EACs for dissolved mercury, whilst the other exceeded the EU-WFD reference value for mercury concentrations in sediments. No statistical significant relations were found between mercury concentrations in biota (Ulva sp, Hediste diversicolor, Scrobicularia plana, Cerstoderma edule and Carcinus maenas) and in the abiotic matrices (sediment and water column, including mercury in its dissolved form and associated to suspended particulate matter). This paper provides an overview of the guidelines for Hg proposed for a considerable number of coastal systems of the northern hemisphere and highlights the complex interactions of Hg in the different environmental compartments in low contaminated systems.  相似文献   

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