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 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 Cycling in Lake Gordon and Lake Pedder,Tasmania (Australia). II: Catchment Processes

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.     

Pollution in a Lowland River System. A Case Study: the Reconquista River (Buenos Aires,Argentina)

The Reconquista river is a lowland watercourse; about three million people and several thousands of industries are settled in its flood plain. It can be considered as one of the most polluted rivers of Argentina. The present work is an attempt to describe the quality of the surface water through 16 physicochemical variables measured monthly in five sites (S₁to S₅) during 1994. Univariate and multivariate analyses of data showed a clear difference of S₁and S₂respect to S₄and S₅for ammonium, ortophosphate, pH, hardness, chloride, phenols, BOD, COD, and DO values. S₃appears to be a transition site. DO content showed a significant negative regression respect to the distance from the mouth. In the multivariate analyses between seasons the concentration of phenols appeared as an important feature. However it can be considered that seasonal variations were difficult to explain because of the river is the receptor of both regular and intermitent pollution pulses. It was concluded that the deterioration of this water body was progressive downriver, the contribution of the Moron creek in S₄determined a sharp adverse change in the physicochemical conditions. In the two downstream sampling stations (S₄and S₅) the values were far from natural conditions.     

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.     

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.     

Impact of Implementation of Large-Scale Drip Irrigation in Arid and Semi-arid Areas: Case Study of Manas River Valley

With the large-scale application of drip irrigation under mulching, drip-irrigated areas have experienced significant changes in the past 10 years in the Manas River valley. Based on long-term monitoring data of soil salt content and groundwater depth and the investigation of shelter forest growth and seedling emergence, this article analyzed the distribution characteristics of soil salt content in different drip-irrigated soil layers and their effect on the environment. The main conclusions are as follows: (1) Two obvious soil layers of salt accumulation are 40–80 cm deep after drip irrigation and 0–5 cm deep before drip irrigation. (2) Salt accumulated in different soil layers after drip irrigation for several years: 0–40 cm and 40–100 cm deep after drip irrigation for 3 and 7 years respectively. (3) Extension of the drip-irrigated area has caused a number of environmental problems in the study area, and countermeasures for agricultural development in arid and semi-arid areas are proposed.     

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.     

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.     

Modern Concepts for the Sustainable Use of Plant Genetic Resources in the Mediterranean Natural Protected Areas: The Case Study of the Alta Murgia Park (Italy)

The high specific richness of the vascular flora of the National Park of ‘Alta Murgia’ (Apulia, Italy) has been originated by a long co-evolutionary process of biophysical and anthropic systems. Natural disturbances on the one hand and the anthropic on the other, as years go by, in their mutual interaction, have created suitable conditions for the coexistence of a high number of taxa. Following an ecological and floristic survey of grasslands of Alta Murgia, many species of great phyto-geographical value or, however, threatened by genetic erosion and/or extinction together with other plants traditionally employed by man as officinal and for food and non-food purposes, were recorded. The ecological conditions that allow the persistence of these plant communities must be searched in the delicate equilibrium established among the natural dynamics and the set of disturbance regime, for great part due to the traditional land use. The actual social and economic transformations of the area, without safeguarding programmes to be carried out according to sustainability criteria, can produce a serious biodiversity decline. Starting from the ‘sustainable use’ definition of the CBD, the present paper deals with some focal points to realize the sustainable management of the biodiversity of the Park of Alta Murgia.     

Biogeochemical Cycle of Mercury and Methylmercury in Two Highly Contaminated Areas of Tagus Estuary (Portugal)

Mercury (Hg) dynamics was evaluated in contaminated sediments and overlying waters from Tagus estuary, in two sites with different Hg anthropogenic sources: Cala Norte (CNOR) and Barreiro (BRR). Environmental factors affecting methylmercury (MMHg) production and Hg and MMHg fluxes across sediment/water interface were reported. [THg] and [MMHg] in solids (0.31–125 μg g^?1 and 0.76–201 ng g^?1, respectively) showed high variability with higher values in BRR. Porewater [MMHg] (0.1–63 ng L^?1, 0.5–86% of THg) varied local and seasonally; higher contents were observed in the summer campaign, thus increasing sediment toxicity affecting the sediment/water Hg (and MMHg) fluxes. In CNOR and BRR sediments, Hg availability and organic carbon were the main factors controlling MMHg production. Noteworthy, an upward MMHg diffusive flux was observed in winter that was inverted in summer. Although MMHg production increases in warmer month, the MMHg concentrations in overlying water increase in a higher proportion compared to the levels in porewaters. This opposite trend could be explained by different extension of MMHg demethylation in the water column. The high concentrations of Hg and MMHg and their dynamics in sediments are of major concern since they can cause an exportation of Hg from the contaminated areas up to ca. 14,600 mg year^?1 and an MMHg deposition of up to ca. 6000 mg year^?1. The results suggest that sediments from contaminated areas of Tagus estuary should be considered as a primary source of Hg for the water column and a sink of MMHg to the sedimentary column.     

Simplifying Dynamic River Water Quality Modelling: A Case Study of Inorganic Nitrogen Dynamics in the Crocodile River (South Africa)

The ultimate goal of this study is to develop a simple dynamic river water quality model that can be applicable in a data limited situation and is compatible with typical activated sludge models, so that the model can be used in integrated modelling of wastewater and river water quality in the future. A simplified river water quality model was formulated based on a conceptual hydraulic sub-model and simplification of an existing river water quality model. The simplified water quality was derived from the River Water Quality Model No. 1, which is one of the most comprehensive basic river water quality models available in literature. The applicability of the simplified model in data limited situations was investigated using a case study of inorganic nitrogen (nitrate and ammonia) in the Crocodile River (South Africa). The model was calibrated and validated on the basis of independent data collected for four years (1987–1990). The results show that the model can adequately describe the seasonal dynamics of inorganic nitrogen in the Crocodile River. The sensitivity of the model output to the model inputs was also analysed, and the results indicate that the model is most sensitive to the microbial biomass (nitrifier) followed by hydraulic parameters. The relation of river flow versus concentration of inorganic nitrogen in the downstream section of the river was also examined in order to identify the main source and critical time for nitrate pollution.     

Nitrogen and Phosphorus Levels in Sediments from Tropical Catatumbo River (Venezuela)

Nitrogen (N) and phosphorus (P) concentrations were determined in sediment samples along the bed of Catatumbo river in both Colombian and Venezuelan territories until the river outlet in Maracaibo lake. Total phosphorus was determined by digestion with HCl followed by analysis using the ascorbic acid method and total nitrogen was done using the standard microkjeldahl method plus nitrate-nitrite. Ammonium, orthophosphate and nitrate were determined using standard methods after extraction steps. The mean concentrations along the river bed were found in an interval of 0.035 and 1.492 mg g^-1 dry sed. for nitrogen and 0.027 and 1.039 mg g^-1 dry sed. for phosphorus at 95% confidence level. The mean molar ratio N/P in the river bed was 4.42 and 3.46 for river outlet zones in the lake, which indicates that nitrogen is the limiting nutrient. For comparison with previous results of lake sediments from sites near the river outlet it was concluded that Catatumbo river is a significant source of nutrients to the Maracaibo Lake system because sediment nutrients concentrations from Catatumbo river were higher than the ones in Maracaibo Lake. Statistic studies showed significant differences between countries, zones and similar behaviour in the river bed as related to the affluent rivers.     

Mercury Concentrations in Stream and River Water: An Analytical Framework Applied to Minnesota and Wisconsin (USA)

The total concentration of all mercuryspecies in water, [THg]_w, is a key water qualitymeasure. This paper proposes an analytical framework forthe analysis, interpretation and eventual projection ofstream (and river) [THg]_w. Mercury (Hg) isconceptualized as being distributed among four carriergroups in water: suspended mineral particles, particulateorganic carbon, dissolved organic carbon, and inorganiccomplexes and ions. The conceptual understanding is used asa statistical analytical framework and turned into aquantitative model for Minnesota and Wisconsin based on some1000 data cases from 18 streams (watershed area: 9 ha–115500km²). The resultant model yields a coefficient ofdetermination of 92% for [THg]_w of the fitting datasubset, or 94% for the evaluation subset. Its coefficientshave well defined physical meanings, and are generallyconsistent with independent field measurements from the sameregion or elsewhere. The model provides a comprehensive andquantitative view of the Hg contents of the carriers: thecontents increase with the proportion of watershed area aswetlands or as forests, rise drastically and then fallprecipitously during spring snowmelt, and otherwise peak inthe growing season and reach a minimum in the presence ofsnowpack. The model further reveals that dissolved Hg tendsto increase with emission-related wet sulfate depositionacross the data region.     

Geochemistry of Coalbed Natural Gas (CBNG) Produced Water in Powder River Basin, Wyoming: Salinity and Sodicity

Extraction of natural gas from a confined coal aquifer requires the pumping of large amounts of groundwater, commonly referred to as produced water. Produced water from the extraction of coalbed natural gas is typically disposed into nearby constructed discharge ponds. The objective of this study was to collect produced water samples at outfalls and corresponding discharge ponds and monitor pH, electrical conductivity (EC), calcium (Ca), magnesium (Mg), sodium (Na), and alkalinity. Outfalls and corresponding discharge ponds were sampled from five different watersheds including Cheyenne River (CHR), Belle Fourche River (BFR), Little Powder River (LPR), Powder River (PR), and Tongue River (TR) within the Powder River Basin (PRB), Wyoming from 2003 to 2005. From Na, Ca, and Mg measurements, sodium adsorption ratios (SAR) were calculated, and used in a regression model. Results suggest that outfalls are chemically different from corresponding discharge ponds. Sodium, alkalinity, and pH all tend to increase, possibly due to environmental factors such as evaporation, while Ca decreased from outfalls to associated discharge ponds due to calcite precipitation. Watersheds examined in this study were chemically different form each other and most discharge ponds with in individual watersheds tended to increase in Na and SAR from 2003 to 2005. Since discharge pond water was chemically changing as a function of watershed chemistry, we predicted SAR of discharge pond water using a regression model. The predicted discharge pond water results suggested a high correlation (R ²?=?0.83) to discharge well SAR. Overall, results of this study will be useful for landowners, water quality managers, and industry in properly managing produced water from the natural gas extraction.     

Reconstruction of Climate and Landscapes of the Medieval Period on the Basis of Palynological Study of Paleosols Buried under Kurgans and Dendrochronological Data from Altai (South of Western Siberia)

Eurasian Soil Science - Light loamy ordinary chernozems buried under two kurgans of a large Early Medieval necropolis Srostki-1 constructed in 890 ± 105…975 ± 85 AD (calibration by...     

Mercury Levels of Soils,Sediments and Fish in French Guiana,South America

This study examines the level of mercury contamination for different components of the biosphere in French Guiana. The spatial variability of the contamination of the waters, soils and sediments in the catchment area of the Sinnamary River is studied. The contamination of the trophic chain isdiscussed by analysis of the flesh of fish for the principal species represented in nine Guianese rivers, especially species consumed by human populations. The mercury contamination of sediments and soils, is extremely heterogeneous and that of fish is generalised. For carnivorous fish, the average mercury content is 0.48 μg g^-1 (±0.28) (fresh weight) and for non-carnivorous species, 0.05 μg g^-1 (±0.07). The concentrationsmeasured are greater than the European standards forconsumption for 4.7% of the carnivorous individuals.     

Natural acidification of lakes and rivers in Japan: The ecosystem of Lake Usoriko (ph 3.4–3.8)

Most of the acid lakes and rivers in Japan have been influenced by acid waters of volcanic origin. Acidophilic and acidotolerant organisms are observed in these natural acid lakes and rivers, each of which has its own ecosystem and history. Lake Usoriko (pH 3.4–3.8) is a lake which.has been acidified by strongly acid water containing sulfuric acid and hydrochloric acid. The ecosystem of Lake Usoriko consists of aquatic vascular plants, aquatic bryophytes (Drepanocladus fluitans, etc.), algae, fish (Tribolodon hakonensis), insects, Zooplankton, fungi and bacteria. The paleosediment distributed along Lake Usoriko's northern shore is partly silicified and it contains fossils of a moss (Drepanocladus fluitans) and diatoms such as Pinnularia braunii var. amphicephala which are also distributed in the present lake. ¹⁴C dating of the specimens in the paleosediment, shoots of D. fluitans and the wood and cones of Picea glehnii gave values in the range 11500–34000y B.P. This record shows how long Lake Usoriko has been an acid lake.     

Regional and Seasonal Inputs of Mercury into Lake St. Pierre (St. Lawrence River), a Major Commercial and Sports Fisheries in Canada

Lake St. Pierre (LSP), constituted of a 120 km² stretching of the St. Lawrence River (Southern Québec), hosts the largest freshwater fishery industry in Canada. The lake drains, through its main tributaries, an important area of agrarian land and was subjected to intense industrial activities in the past century. In this paper, we present (1) an estimation of the seasonal aquatic mercury (Hg) inputs to LSP from the St-Lawrence River and two major tributaries; (2) a reconstruction, by the analysis of sediment cores, of the historic inputs of Hg into LSP and in a large riparian wetland, Bay St. François. Our results indicate that the aquatic Hg inputs to LSP (290 kg Hg between April 2003 and April 2004) are moderately elevated with most of the inputs occurring from the St. Lawrence River, either in spring or early winter, during high flow episodes. The sediment profiles suggest a recent decrease in Hg inputs, likely attributable to improvements of industrial practices. The observed perturbation of the surface sediments give evidence of an active hydrodynamic regime, suggesting that LSP could only act as a transitory system for suspended sediment and Hg, with seasonal accumulation and recurrent re-suspension resulting from changes in the hydrodynamic regime. Finally, we observed positive MeHg fluxes from the sediment to the water at different seasons in Bay St. François. However, Hg levels in fish like walleyes of LSP are reported to be low, which could be explained by faster fish growth rates following in part intense fishing pressure in LSP.     

Grain Size Partitioning of Mercury in Sediments of the Middle Odra River (Germany/Poland)

The Odra River is the second largest river in Poland, running from Czech Republic through a large part of Poland before entering the Baltic Sea. For the last century its catchment area has been heavily polluted by anthropogenic emissions. The aim of this study is to determine the distribution of mercury in different grain size fractions of surface sediments from the middle course of the Odra River. Mercury concentrations were determined in bulk sediments of different grain size fractions using the cold vapor atomic fluorescence spectrometry method. The total mercury concentration in bulk sediments varied from 0.051 to 1.31 mg/kg dry weight. The concentration of total mercury was determined in the grain size fractions <0.2, 0.2–0.5, 0.5–1.0, 1.0–2.0 and >2.0 mm to be (in mg/kg d.w.): 0.118–2.99, 0.033–0.99, 0.034–1.17, 0.035–1.97 and 0.017–3.65, respectively. Gradual decrease in the mercury concentration with increasing grain size from fine to coarse fraction has been observed only for sediments taken from the river bed. Although, no similar gradual decrease in the mercury concentrations has been observed for sediments from the river banks, finer sediments (<0.2 mm) still tend to show higher concentrations of mercury.