Mercury in the surface water of Swedish forest lakes —concentrations,speciation and controlling factors

Concentrations of total Hg and five operationally defined Hg species were determined in the surface water of 25 Swedish forest lakes of different type. Regional and seasonal variations were studied during the ice-free season of 1986. The concentration of total Hg was usually in the range of 2 to 10 μg m-3. Hg concentrations were highly correlated to the concentration of humic matter measured as water color. Hg concentrations were about twice as high in acidic lakes (pH 5) than in circumneutral lakes, which is attributed basically to the acidity of humic compounds acting as Hg carriers in boreal waters. Significant seasonal variations were caused by hydrological processes. During periods of high water flow, Hg concentrations increased dramatically, especially in humic lakes. Between spring and autumn, chemically reactive Hg compounds were gradually replaced by more inert species. Hg/C ratios were higher than in surface runoff from forest watersheds, indicating a significant impact of direct deposition of Hg on lake surfaces during summer. Regional differences were small despite differences in Hg contamination.     

森林生态系统中土壤有机质组分的固态13C核磁共振波谱表征

Forest management practices such as prescribed burning and thinning in forest ecosystems may alter the properties of soil organic matter (SOM).In this study,surface soils from field plots in the Bankhead National Forest,Alabama,USA,were used to investigate possible SOM transformations induced by thinning and burning.Elemental analysis and solid-state 13C cross polarization magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy were used to characterize SOM fractions in whole soils,humic substances,and density fractions.Our data revealed that the changes in SOM fractions due to the repeated burning carried out in the forest ecosystem studied were involved mainly with alkyl C,O-alkyl C,and carbohydrate functional groups,implying that most prominent reactions that occurred involved dehydrogenation,de-oxygenation,and decarboxylation.In addition,burning and thinning might have also affected the distribution and composition of free and occluded particulate SOM fractions.The limited structural changes in SOM fractions suggested that low-intensity prescribed fire in the forest ecosystem studied will not create major structural changes in SOM fractions.     

Influence of pollution and acidification on metal concentrations in Finnish Lapland lake sediments

Fifteen Finnish Lapland lakes have been investigated to study pollution levels and possible acidification effects on nickel (Ni), copper (Cu), cobalt (Co), zinc (Zn), cadmium (Cd), lead (Pb), manganese (Mn), iron (Fe), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg) and aluminium (Al) concentrations in sediments. Four lakes have average water pH lower than 6.0 and alkalinity lower than 0.050 meq/1. Contamination factor (C_f, ratio of metal concentrations in the uppermost to the deepest layers for a given lake sediment core) of Pb is high, particularly for acidic and acidifying lakes (C_f=5.2–10.4). Ni, Cu, Co, Zn and Cd concentrations increase insignificantly towards sediment surface of some lakes (with a neutral pH) with the rare exception. The influence of passible lake acidification consists of decreasing Cu, Cd, Al, Zn concentrations and organic material contents (loss on ignition) towards the sediment surface. The buffer capacity index (BCI), determined as the ratio of the sum of alkaline and alkaline-earth metals (K, Na, Ca, Mg) to Al, is lower for acidic lakes (from 0.12 to 0.36), whereas for the other lakes the BCI values are higher (from 0.42 to 1.34). Thus, BCI-values, decreased contents of Al, Cd, Zn and Cu, as well as organic matter contents (OMC in the upper lake sediment suggest acidification of freshwater environments.     

Alkalinity destruction by sediment organic matter dissolution during neutralization of acidified lakes

In this study we report on the effect of sediment, from an acidified lake, on the neutralization of the acidified water column. The results of this experimental study show that organic acids (presumably humic or fulvic acids) can dissolve from the sediment and destroy alkalinity as measured by a Gran plot analysis. Alkalinity destruction by organic acid dissolution was shown to be a function of pH. Some Na ion exchange for sediment H⁺ was also observed. This ion exchange was shown to be a function of pH and Na concentration.     

Finnish lake survey: the role of organic and anthropogenic acidity

A lake survey consisting of 987 randomly selected lakes was conducted in Finland in autumn 1987. The survey covered the whole country, and the water quality of the lakes can be considered as representative of the approximately 56 000 lakes larger than 0.01 km² in Finland. The median TOC concentration is 12 mg L^-1 and the median pH 6.3. The proportion of lakes with TOC concentrations > 5 mg L^-1 in the whole country is 91 %. Organic anion is the main anion in the full data set (median 89 μeq L^-1). The high organic matter concentrations in Finnish lakes are associated with catchment areas containing large proportions of peatlands and acid organic soils under coniferous forest. The survey demonstrated that organic matter strongly affects the acidity of lakes in Finland. The decreasing effect of organic matter on the pH values was demonstrated by both regression analysis and ion balances. At current deposition levels of ^*SO₄ the pH of humic lakes in Finland is determined to a greater extent by high TOC concentrations than by ^*SO₄ in most areas. In lakes with pH values lower than 5.5 the average organic anion contribution is 56 % and non-marine sulfate contribution 39 %. However, in the southern parts of the country, where the acidic deposition is highest, the minerogenic acidity commonly exceeds the catchment derived organic acidity.     

Evaluation of the Distribution of Mercury in Lakes in Nova Scotia and Newfoundland (Canada)

Distribution and sources of total mercury were evaluated in sixty lakes in Nova Scotia and Newfoundland. The concentration of total mercury in the lake water samples was similar to those observed in other natural water systems. Mercury concentration in the lakes correlated positively with aluminum, total organic carbon, color, iron, and total nitrogens and inversely with pH and sulfate. The lake water quality parameters were placed in three distinct groups using principal component and cluster analyses. The chemical constituents in the groups were identified as being associated with lake watershed geology, atmospheric washouts of long range transported acidic pollutants and dust particles, and a marine source. Stepwise multiple regression applied to the variables in the same principal component and strongly correlating with mercury identified total organic carbon, total nitrogen, pH, aluminum and iron as the best predictors for total mercury concentrations in the study lakes.     

Diatom-inferred pH history of Kejimkujik Lake,Nova Scotia: A reinterpretation

A reanalysis of the diatom-inferred pH profile from a sediment core collected in 1980 from Kejimkujik Lake has been made in the light of improved techniques and ecological information. Using Index B calibrated for lakes in Atlantic Canada, the lake pH was 4.6 to 4.7 before anthropogenic disturbances in the watershed began ca. 1850. These disturbances had little immediate impact on pH, but minima of pH 4.5 were evident in the period 1916 to 1950. A diatom-inferred pH of 4.75 in the surface sediments compares with a measured pH of 4.96 in 1980. Disturbances in the watershed since ca. 1850 resulted in a large increase in a form of Asterionella ralfsii, a diatom associated with colored, humic water. A decline in this diatom since 1950 and an increase in taxa less typical of humic water is consistent with the hypothesis of loss of organic matter accompanying acidification from acidic precipitation.     

长白山不同林型土壤有机碳特征

采用野外采样与室内分析相结合的方法,研究了长白山北坡6种不同林型(阔叶林、针叶林、云冷杉、岳桦林、岳桦-苔原、高山苔原)土壤有机碳及其组分的含量,分析了土壤有机碳分布与铁铝氧化物和黏粒矿物组成之间的关系。结果表明:不同林型之间,阔叶林土壤的有机碳、胡敏素碳、颗粒有机碳、2~0.25 mm大团聚体碳和0.25~0.053 mm微团聚体碳含量最高,云冷杉土壤的易氧化碳含量最高而水溶性有机碳、胡敏酸碳、富里酸碳和颗粒有机碳含量最低;此外,岳桦林土壤的胡敏酸碳和富里酸碳含量显著高于其他林型土壤,岳桦-苔原土壤的水溶性有机碳含量显著高于其他林型土壤,而高山苔原土壤的有机碳和易氧化碳含量显著低于其他林型土壤。相关性分析表明,土壤有机碳含量与非晶质氧化铝含量呈显著的正相关关系(P<0.05),富里酸碳含量与游离氧化铝含量呈显著的正相关关系(P<0.05),而0.25~0.053 mm微团聚体有机碳含量与2种形态氧化铝含量都呈显著的正相关关系(P<0.05)。上述结果指出,不同林型条件下各有机碳及其组分差异显著。     

中国长江中下游地区浅水湖泊沉积物有机磷研究

Thirteen sediment core samples （0 10 cm） were taken from the seven lakes in the middle and lower reaches of the Yangtze River to determine the contents and distributions of organic phosphorus （P） fractions in the sediments of the shallow lakes in the area. The organic P fractions in the sediments were in the order of moderately labile organic P （MLOP） 〉 moderately resistant organic P （MROP） 〉 highly resistant organic P （HROP） 〉 labile organic P （LOP）, with average proportional ratios of 13.2：2.8：1.3：1.0. LOP, MLOP, and MROP were significantly related to the contents of total organic carbon （TOC）, water-soluble P （WSP）, algal-available P （AAP）, NaHCO3-extractable P （Olsen-P）, total P （TP）, organic P （OP）, and inorganic P （IP）. However, HROP was significantly related to OP and weakly correlated with TOC, WSP, AAP, Olsen-P, TP or IP. This suggested that organic P, especially LOP and MLOP in sediments, deserved even greater attention than IP in regards to lake eutrophication. In terms of organic P, sediments were more hazardous than soils in lake eutrophication. Although OP concentrations were higher in moderately polluted sediment than those in heavily polluted sediment, LOP and MLOP were higher in the heavily polluted sediment, which indicated that heavily polluted sediment was more hazardous than moderately polluted sediment in lake eutrophication.     

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.     

Interpretation of Mercury Concentrations in Eight Headwater Lakes in Kejimkujik National Park, (Nova Scotia, Canada) by Use of a Geographic Information System and Statistical Techniques

The concentration of mercury in eight headwater lakes in Kejimkujik National Park correlated positively with total organic carbon, total nitrogens, aluminum, iron and sodium andnegatively with pH and alkalinity (Gran). Annual average mercuryyield of the lakes correlated positively with basin area to lakesurface area ratio, and watershed areas underlain by granite bedrock and glacial deposits and negatively with greywacke bedrock. Principal component analysis indicated that first threecomponents account for 80% of the total variance in the data.The components were related to physiography and geology of the watershed, hardness of water, and atmospheric washouts of longrange transported acidic pollutants and dust particles. Mercuryin the lake waters was associated with the physiography and geology of the watershed. Total organic carbon, aluminum and iron were good predictors of mercury concentration in the lakewaters as were the basin area to lake surface area ratio, and basin areas underlain by granite bedrock, and Halifax slate forthe lake mercury yield. The results showed that transport of mercury from the watershed is a major source of mercury in thestudy lakes.     

Regional monitoring of lake acidification in Finland

The primary objective of this monitoring is to detect long-term Long-Range Transboundary Air Pollution (LRTAP) induced changes in the water quality of small lakes, throughout Finland, with low conductivity. The monitored lakes (n=171, sampled every autumn since 1990 and in 1987) have a smaller watershed (usually headwater or seepage lakes), a larger lake/catchment ratio, and lower base cation concentrations, alkalinity and pH than Finnish lakes on average. The monitoring network provides background data for air pollution dose/response studies, critical load calculations and for the modelling of acidification scenarios. The declining sulphate deposition seems to be reflected in small headwater lakes all over southern and central Finland as a lowering of the sulphate concentration in the waters. Nitrate concentrations in these lakes have been typically low in the autumn. The base cation concentration is not generally declining, as it is in deposition in many areas. The sulphate concentration in lakes has declined more than base cations. Hydrologically, the recent years have been quite variable because of varying annual precipitation. The variation in alkalinity and pH in typical Finnish lakes is dependent on the content of humic material derived from catchments. The monitoring period is too short to reveal consistent trends in major ion chemistry. However, signs of improvement in recent years can be seen; in comparing 1993 to 1987, years with similar organic acidity and base cations, it seems that the sulphate decline in lakes monitored is compensated by a significant rise in both alkalinity and pH.     

不同经营模式对毛竹土壤活性有机碳的影响

以起始于1984年的长期不同经营模式毛竹林为研究对象,探讨了夏季毛竹林集约经营后土壤有机碳的变化。结果表明:(1)集约经营后0~80 cm土层毛竹林土壤总有机碳平均增加了5.48%,易氧化碳含量平均增加了15.14%,水溶性有机碳含量平均下降了3.98%,三者均未达到显著差异。(2)两种毛竹林土壤总有机碳、易氧化碳、水溶性有机碳的剖面特征均随土层深度的增加而呈现下降趋势,但下降速度不同。集约经营在一定程度上影响毛竹土壤易氧化碳剖面特征。(3)土壤总有机碳、易氧化碳与土壤养分之间相关性均达到极显著水平,而水溶性有机碳与土壤养分之间相关性不显著。(4)集约经营提高了土壤易氧化碳占总有机碳的比例、土壤碳库活度,并在土壤剖面部分土层差异达到显著水平。但其水溶性有机碳占总有机碳的比例3.74%,低于粗放经营毛竹林的4.10%。因此,集约经营的毛竹林,通过配施恰当比例的有机无机肥,结合土壤垦复、除草、合理的竹株留养和采伐等综合竹林经营技术,以达到改善土壤质量和实现毛竹林可持续经营的目的,也可改善土壤生物化学活性。     

Mercury concentrations in northern pike,Esox lucius L., in small lakes of Evo area,southern Finland

We measured Hg concentrations in northern pike (Esox lucius) from 17 small lakes in Evo forest area, Lammi, southern Finland. The mean Hg concentration in muscle tissue of a 1 kg pike ranged from 0.15 to 1.36 μg g⁻¹ (ww) in the lakes. There was a trend towards higher concentrations in acidic and humic lakes than in circumneutral and clear-water lakes. The Hg content of pike from successive lakes of a lake chain was similar, whereas there were clear differences in the Hg concentrations among seepage lakes and the uppermost lakes of other lake chains. The latter was probably due to special characteristics of the lakes: in one lake pike was the only fish species, two of the lakes were regulated by beaver, and one lake was a groundwater or spring lake. Our observations indicate that Hg concentrations in pike can vary considerably from lake to lake in a small geographical area and that the variation among lakes in the accumulation of Hg in fish largely depends on lake characteristics and on the diet of pike.     

Remote mountain lakes as indicators of diffuse acidic and organic pollution in the Iberian peninsula (AL:PE 2 studies)

In the framework of the AL:PE 2 project, studies on acidification and organic pollution in mountain lakes have been conducted in several ranges in the Iberian peninsula: Pyrenees (Northeastern Spain), Sierra de Gredos (Central Spain), Sierra Nevada (Southern Spain) and Serra da Estrela (Central Portugal). These studies focused on water and sediment chemistry and organisms (benthic diatoms, Zooplankton, aquatic macroinvertebrates, and fish) as indicators of acidification. Organic micropollutants (PAH, PCB, DDE, hexachlorobenzene and others) in lake sediments and fish have been studied as tracers of atmospheric pollution. The Iberian peninsula lakes do not show severe anthropogenic acidification. pH values are in the range of sensitive lakes, but the levels of acidic pollutants are low. The status of the organisms surveyed agreed with this diagnosis. Pyrenean lakes showed the highest fluxes of organic pollutants related to fossil fuel combustion., higher pollutioninduced versus natural acidity ratios, and modeled alkalinity and pH declines.     

Origin and Transport of Aeolian Sediment from New Clearcuts into Boreal Lakes,Northwestern Ontario,Canada

Movement of aeolian (wind-blown) inorganic sediment was indexed in and around new riparian and upland clearcuts in northwestern Ontario, Canada with bucket-style terrestrial litterfall traps. Aeolian sediment originated primarily from clearcuts, roads, and skid trails, where soil disturbance was high and forest hitterfall was low. Relatively small amounts of aeolian sediment were recovered from riparian buffer strips and upland forest. Aeolian sediment was observed to reach lakes adjacent to the clearcuts and may be responsible for elevated levels of littoral sedimentation measured in one study lake. However, the amounts of sediment deposition observed are not likely to cause important changes in water quality or benthic habitat for algae, invertebrates, or fish in these lakes.     

A sediment exchange experiment to assess the limiting factors of microbial sulfate reduction in acidic mine pit lakes

Purpose

Microbial sulfate reduction is an alkalinity-producing process and potentially supports the neutralization of acidic mine pit lakes. In many acidic lakes the process does not occur. Sulfate-reducing bacteria are known to be pH sensitive. There are, however, several reports of sulfate reduction occurring in the sediment of acidic lakes. To find out why sulfate reduction occurs in some acidic lakes but not in others, we conducted a field experiment.

Materials and methods

Surface sediment from lake ML111 (pH?2.6, no sulfate reduction), in the Koyne-Plessa lignite mining district of Lusatia in Germany, was incubated in the less-acidic lake ML117 (pH?3.4, sulfate reduction) and vice versa. After 19?weeks of incubation, the sediments were sampled and analyzed for microbial sulfate reduction rates, bacterial numbers, and geochemical composition.

Results and discussion

Incubation of ML117 sediment in ML111 resulted in a partial inhibition of sulfate reduction while incubation of ML111 sediment in ML117 did not initiate sulfate reduction. We observed a linear relationship between sediment pH and sulfate reduction, while there was no relation with sedimentary iron content. Sulfate reduction was not only affected by the water quality but also by the experimental treatment. Homogenization of the sediment prior to incubation stimulated microbial sulfate and iron reduction. Due to the low pH, incubation in ML111 resulted in the dissolution of reduced inorganic sulfur.

Conclusions

We conclude that the water pH is the major regulator of sulfate reduction in the surface sediment of acidic lakes. The rate of sulfate reduction in the sediment of acidic lakes depends on a fragile equilibrium between proton flux between water and sediment, and buffering reactions in the sediment.     

Siltation and radiocesium pollution of small lakes in different catchment types far from the Fukushima Daiichi nuclear power plant accident site

The Fukushima Daiichi nuclear power plant accident caused radioactive pollution in northeastern Honshu Island, Japan. This study examined the influence of snowmelt and rainfall on soil erosion processes and siltation of small lakes in Miyagi Prefecture (150 km northwest of the power plant). Two sets of slopes and lakes, respectively in pasture and forest catchments, were examined. Snowpack thickness, soil infiltration, surface runoff volume, soil and sediment physicochemical properties, Cs concentration of precipitation, meltwater, and rainwater, and lake siltation rates were determined. The total radioactive Cs content in precipitation was 0.7–7.4 BqˑL⁻¹ and was below the Japanese standard (10 BqˑL⁻¹). Total radioactive Cs was at the allowable level in water flowing down the pasture catchment slope (0.1–9.2 BqˑL⁻¹) during snowmelt and rainfall, as well as in pasture (0.9–8.8 BqˑL⁻¹) and forest (0.7–5.2 BqˑL⁻¹) catchment lake water. There was no soil erosion (surface runoff) in the forest catchment. Soil losses in the pasture catchment were 23 due to rainfall and 9 kg ha⁻¹ yr⁻¹ following spring snowmelt. After snowmelt, a 0.5 and 0.2 mm thick layer of silt was deposited in pasture and forest catchment lakes, respectively, and 1.4 and 0.6 mm were deposited during the rainfall period. Average siltation rates were 1.9 and 0.8 mmˑyr⁻¹ for pasture and forest catchment lakes, respectively. The upper layer of lake bottom sediments is represented mainly by silt fractions (2–50 μm), with high organic matter (4.0–5.7%) and radiocesium (1100–1600 kgˑha⁻¹) contents.     

红壤侵蚀退化地土壤对不同来源可溶性有机碳的吸附特征

选取南方典型红壤侵蚀退化地恢复后的马尾松林为研究对象,通过在室内模拟芒萁(Dicranopteris dichotoma)和马尾松(Pinus massoniana)的鲜叶与凋落叶的浸提液在侵蚀退化地原状土柱的淋溶过程,分析了植被恢复过程中马尾松林土壤对不同来源可溶性有机碳(DOC)吸附特征及影响因素。结果表明:(1)红壤侵蚀退化地对不同来源DOC的吸附作用具有明显差异,来自马尾松鲜叶的DOC平均截留量最大为2.39mg/kg,来自芒萁鲜叶的DOC平均截留量最小为1.67mg/kg,说明马尾松鲜叶的DOC更易被表层土壤吸附,芒萁鲜叶的DOC更易进入深层土壤,不同来源DOC组成和性质的差异是其主要原因。(2)随着退化地的植被恢复,土壤渗滤液的DOC浓度增加,土壤截留DOC能力下降。土壤DOC截留量与粉粒和土壤pH呈正相关,与土壤DOC含量、土壤有机碳含量和砂粒呈负相关,其中土壤有机碳含量可以解释DOC截留量变化的51.4%,是影响土壤DOC截留能力的关键因素。(3)光谱特征表明芳香类化合物、腐殖类物质易被土壤吸附,吸附能力更强的物质可以解吸土壤中亲水性腐殖类物质。淋溶后DOC光谱特征的变化由不同来源DOC的化学组成和土壤有机碳的性质共同决定。红壤侵蚀退化地对不同植物来源的DOC吸附作用特征主要受DOC和土壤SOC性质的共同调控,对进一步认识退化红壤的固碳机制具有重要参考价值。