Pre-industrial atmospheric deposition of mercury: Uncertain rates from lake sediment and peat cores

Lacustrine sediment cores from depositional areas have frequently been used to estimate pre-industrial rates of atmospheric Hg deposition. However, this approach tends to result in overestimates, partly because of Hg inputs from the catchment, partly because of a horizontal redistribution of sediments within lakes. Peat core studies may suffer from a vertical migration of Hg due to water table fluctuations. A natural Hg deposition rate around 2 μg m^?2 y^?1 is suggested to be more realistic than values of 3 to 12 μg m^?2 y^?1 reported from recent studies. The anthropogenic impact on the present Hg deposition may have been underestimated accordingly.     

Sulphate deposition by precipitation into lake Ontario

Measurements of sulphate concentration in precipitation from individual snow storms of several hours duration in the Western Lake Ontario region indicate that approximately 9–66 mg M^?2 of SO is being deposited into the Lake per storm. This amount is up to several times more than daily average values over long periods found by other workers. Using a mean sulphate concentration of 4 mg l^?1 and an annual accumulation of precipitation of 760 mm, the yearly sulphate deposition by precipitation is about 0.1 % of the total mass of sulphate in the Lake; however, more significantly, it is of the same order of magnitude as that discharged directly into the Lake by industry.     

Relations between lake acidification and sulfate deposition in Northern Minnesota,Wisconsin, and Michigan

From a level of 1 kg ha^?1yr^?1 in north central Minnesota, emission-related wet SO₄ deposition increases across northern Wisconsin and northern Michigan to about 18 kg ha^?1yr^?1 in south central Michigan. Samples taken from 82 clearwater (low color) lakes across this region in the summer of 1984 showed a pattern of acidification in proportion to deposition. We found a linear increase in the difference between alkalinity and Ca+Mg and in lake SO₄ concentration with increasing deposition. We developed a simple equation to predict the emission-related SO₄ deposition levels that will cause the alkalinity of sensitive clear-water lakes to go to zero.     

Atmospheric sources,transport and deposition of mercury in Michigan: Two years of event precipitation

To assess the sources, transport and deposition of atmospheric mercury (Hg) in Michigan, a multi-site network was implemented in which Hg concentrations in event precipitation and ambient samples (vapor and participate phases) were determined. Results from the analysis of 2 years of event precipitation samples for Hg are reported here. The volume-weighted average Hg concentration in precipitation was 7.9, 10.8 and 10.2 ng/L for the Pellston, South Haven and Dexter sites, respectively. Yearly wet deposition of Hg for 1992–93 and 1993–94 was 5.8 and 5.5 μg/m² at Pellston, 9.5 and 12.7 μg/m² at South Haven and 8.7 and 9.1 μg/m at Dexter. A spatial gradient in both the Hg concentration and wet deposition was observed. Northern Michigan received almost half the deposition of Hg recorded at the southern Michigan sites. The concentration of Hg in precipitation exhibited a strong seasonal behavior with low values of 1.0 to 2.0 ng/L in winter and maximum values greater than 40 ng/L in summer. The spring, summer and autumn precipitation accounted for 89 to 91% of the total yearly Hg deposition. Mixed-layer back trajectories were calculated for each precipitation event to investigate the meteorological history and transport from potential Hg source regions. Elevated Hg concentrations were observed with air mass transport from the west, southwest, south, and southeast. At each of the sites precipitation events for which the Hg concentration was in the 90th and 10th percentile were-analyzed for trace elements by ICP-MS to investigate source impacts.     

降雨量对洱海流域稻季氮磷湿沉降通量及浓度的影响

为了探究洱海流域稻季氮磷湿沉降规律,于2016及2017年稻季在大理洱海流域收集湿沉降样品,分析样品中总磷(total phosphorus,TP)、总氮(total nitrogen,TN)、NO_3~--N、NH_4~+-N等指标及其变化规律。结果表明,TN、TP湿沉降通量主要受降雨量支配,2016与2017年稻季单次降水TN、TP湿沉降通量与降雨量均呈极显著的线性正相关关系。TN、TP湿沉降浓度总体上随降雨量的增大而减小,同时与是否发生连续降雨及是否大规模施肥有关。以2017稻季氮素湿沉降为例,2017年稻季NH_4~+-N和NO_3~--N湿沉降对TN的占比分别为53.1%和20.6%,湿沉降以NH_4~+-N为主。可溶性无机氮(dissolved inorganic nitrogen,DIN)对TN的占比随着降雨量的增大而减小,随着连续降雨的延续而增大。2016及2017年稻季湿沉降TN质量浓度分别为0.87~4.03和0.90~6.85 mg/L,均远大于湖泊富营养化阀值,对洱海水生生态系统产生不利影响。     

210Pb geochronology of sediment accumulation rates in Mexico City Metropolitan Zone as recorded at Espejo de los Lirios lake sediments

A sedimentary sequence from the Espejo de los Lirios lake in the Metropolitan Zone of Mexico City (MZMC) was analyzed in detail for ²¹⁰Pb and ¹³⁷Cs activities, allowing to assess the evolution of the accretion rates in the lake during the last ∼84±4 years. The core revealed the deposition of contemporaneously indigenous lake sediments to the site interspersed with eroded bedrock from the catchment, evidencing episodic increases in sediment accretion which varied from 0.14 to 0.93 cm year⁻¹. Increasing trends in sedimentation rates were found to be closely related to demographic expansion of the Metropolitan Zone of Mexico City and explained on the basis of the erosive processes produced as a result of deforestation created as a consequence of the urban and industrial development of the MZMC.     

汞沉淀对黑麦草中汞含量及其分布的影响

A grass(Italian rye grass)experiment with complete desing of three factos(Hg,grass and exposure)and two levels(with and withou the factor tested)was carried out in Goeteborg,Sweden from May to September,1995,toward understanding the effect of mercury deposition on plant Hg content and its distribution.It has been found that besides the two general pathways of Hg absorption,i.e.root uptake and foliar absorption,mercury deposition can aslo signifcantly incease Hg content and total load in grass.Such effects seem to be confined only within the above-ground parts of grass plant.Estimate has been made to make clear of the contributions of different pathways to Hg Content and total Hg load in the upper part of grass.Results showed that the contribution of Hg deposition accounted for 27%-32%,of Hg content in the above-ground parts of grass plant without adding Hg to the soil.decreasing with the increase of soil and/or air Hg concentrations.The increment of Hg load in the upper part of grass plant caused by Hg deposition during an interval of two weeks varied between 0.01-0.07μg pt^-1,contributing to 17%-48% of the total Hg load in grass plant exposed.     

Time resolution of mercury dose and lake sensitivity related to mercury content in fish

This work treats data from 75 small, mainly oligotrophic Swedish forest lakes. The aim is to study and evaluate the temporal variation of different Hg-dose and lake sensitivity parameters vs. Hg in 1-kg pike and small perch (<10 g). The lakes were treated with different remedies (such as lake liming) during 1987 in order to reduce Hg-levels in fish. Lake water chemistry has a large seasonal variation but the yearly means is clearly affected by the treatments (mean alkalinity is increased from 0.05 to 0.19 mcq^*L⁻¹). There is a marked change of Hg in perch 2 yr after treatment; the median decrease is 33%, a further time delay of about 2 yr is suggested for Hg in pike. Among the dose parameters, Hg in material from sediment traps and in water the fraction RIHg seem to be affected by the remedies with an accentuated decrease during 1988, while a slight increase of total-Hg (THg) in water can be observed. A regression model where the Hg content in perch (Hg-pe) is predicted by Hg-dose, pH and lake water retention time is presented (r²=0.71, n=22) as an example of the importance of using time compatible data with respect to the effect parameter (Hg-pe).     

Acid deposition and lake chemistry in southwest China

A water quality survey has been performed on selected lakes and streams in southwest China. The purpose of the study was to measure the concentrations of acidic deposition and surface water chemistry in a region of severe air pollution, forest decline, and relatively sensitive geology to acidic deposition. We show that, although there are some high elevation lakes of low acid neutralizing capacity (ANC<150μeq L^?1, acidification of lakes has not occurred in southwest China due to production of base cations in soil and dry deposition of dust that serves to neutralize acidic deposition. Water chemistry is buffered by high base cation concentrations (Ca²⁺, Mg²⁺, Na⁺, and K⁺ greater than 300μeq L^?1, and pH values are always greater than 6.5.     

Wet deposition of mercury and ambient mercury concentrations at a site in the Lake Champlain basin

The “Great Waters” program, established in the 1990 Clean Air Act Amendments, mandated that atmospheric deposition of hazardous air pollutants to Lake Champlain (including Hg) be assessed. An assessment of the magnitude and seasonal variation of atmospheric Hg deposition in the Lake Champlain basin was initiated in December 1992 with one year of event precipitation collection, as well as collection of vapor and particle phase Hg in ambient air. Samples were collected at the Vermont Monitoring Cooperative air monitoring site at the Proctor Maple Research Center in Underhill Center, VT. The average volume-weighted concentration for Hg in precipitation was 8.3 ng/L for the sampling year and the average amount of Hg deposited with each precipitation event was 0.069 μg/m². The total amount of Hg deposited through precipitation during 1993 was 9.26 μg/m²/yr. A seasonal pattern for Hg in precipitation was evident, with increased concentrations and deposition during spring and summer months. Meteorological analysis indicated the highest levels of Hg in precipitation were associated with regional transport from the south regardless of season, and with transport from the west, southwest and northwest during spring and summer months. Concentrations of ambient vapor phase Hg were typical of rural locations and consistent across seasons. Ambient particulate Hg concentrations averaged 11 pg/m³ with highest concentrations during the winter months.     

Historical sediment mercury deposition for select South Dakota,USA, lakes: implications for watershed transport and flooding

Purpose

Select South Dakota, USA water bodies, including both natural lakes and man-made impoundments, were sampled and analyzed to assess mercury (Hg) dynamics and historical patterns of total Hg deposition.

Materials and methods

Sediment cores were collected from seven South Dakota lakes. Mercury concentrations and flux profiles were determined using lead (²¹⁰Pb) dating and sedimentation rates.

Results and discussion

Most upper lake sediments contained variable heavy metal concentrations, but became more consistent with depth and age. Five of the seven lakes exhibited Hg accumulation fluxes that peaked between 1920 and 1960, while the remaining two lakes exhibited recent (1995–2009) Hg flux spikes. Historical sediment accumulation rates and Hg flux profiles demonstrate similar peak and stabilized values. Mercury in the sampled South Dakota lakes appears to emanate from watershed transport due to erosion from agricultural land use common to the Northern Great Plains.

Conclusions

For sampled South Dakota lakes, watershed inputs are more significant sources of Hg than atmospheric deposition.

     

Changes in mercury levels in lake whitefish (Coregonus clupeaformis) and northern pike (Esox lucius) in the LG-2 reservoir since flooding

After flooding of the LG-2 reservoir in 1978–1979, it was noticed that Hg levels in fish rose dramatically. In this study the Hg data have been examined on the basis of fish age for lake whitefish (Coregonus clupeaformis) and northern pike (Esox lucius), representing two different trophic levels. Data were fit to Von Bertalanffy functions using non-linear regression analyses. Reductions in error sums of squares indicated that differences among years were the major sources of variation, but that there were differences among stations within years. For age profiles both species showed changes after flooding, whitefish increasing immediately and remaining similar until 8 years after flooding, with decreases afterward, while pike continued to increase until 8 years after flooding, remaining somewhat stable afterwards. For whitefish, cohorts (year classes) from before flooding had similar concentrations, with maxima reached by around 1982, concentrations afterward remaining stable. Subsequent cohorts reached plateaus at around 2–4 years of age, each successive cohort having a lower plateau. For pike, Hg kept increasing in an almost linear fashion, cohorts from before flooding having similar concentrations. Analyses indicated the very gradual return of whitefish to conditions present before flooding, while pike were remaining at much higher levels. Inputs to older pike were therefore not decreasing, but younger pike may have been improving.     

Atmospheric mercury in northern Wisconsin: Sources and species

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 (Hg_p) was found to be approximately 40% in an oxidized form, or operationally defined as “reactive”. However, this was quite variable from year-to-year. Hg_p 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.     

Continuous culture of mixed sediment bacteria in the presence of mercury

Continuous culture methods were used to isolate bacteria from sediment from Lake Ontario. These mixed cultures were grown in chemostats at different dilution rates and the glucose concentration in the culture vessel, the optical density, the biomass of cells, and the number and types of bacteria present were monitored for at least 80 generations. Two bacterial types, bothPseudomonas spp., were present at all dilution rates in significant quantities. The mixed cultures exhibited a reciprocal relationship between dilution rate and biomass (and number of bacteria). When Hg was added to the growth medium at a concentration of 5 mg 1^?1, the bacteria tolerated that concentration at a dilution rate of 0.117 h^?1 substantial changes in the population were noted at a concentration of 10 mg 1^?1 Hg. One of the isolates from the mixed culture would not grow at 5 or 10 mg 1^?1 of Hg in continuous culture at a dilution rate of 0.066 h^?1. In the mixed continuous culture the same isolate showed only minimal response to a Hg concentration of 10 mg 1^?1.     

Measurement of methylmercury and mercury in run-off,lake and rain waters

During one year, samples from eight drainage lakes, seven run-off stations and three deposition sites from various geographical areas in Sweden were collected and analyzed for methyl Hg (MeHg) and total Hg (Hg-tot). The MeHg concentrations ranged from 0.04 to 0.64 ng L^?1, 0.04 to 0.8 ng L^?1, and <0.05 to 0.6 ng L^?1 in run-off, lake water and rain water, respectively. The corresponding Hg-tot concentrations were found in the range 2 to 12 ng L^?1, 1.35 to 15 ng L^?1, and 7 to 90 ng L^?1, respectively. A Hg-tot level of about 60 ng Hg L^?1 was found in throughfall water. The MeHg and Hg-tot concentrations are positively correlated in both run-off and lake water, but not in rain and throughfall water. A strong positive correlation between the MeHg, as well as the Hg-tot concentration, and the water color is observed in both run-off and lake waters, which suggests that the transport of MeHg and other Hg fractions from soil via run-off water to the lake is closely related to the transport of organic substances; and is a consequence of the biogeochemical processes and the water flow pathway. The ratio between the mean values of MeHg and Hg-tot seems to be an important parameter, with an indicated negative coupling to the mean value of pH for run-off water, but a strong positive correlation to Hg-content in fish, the ratio between the area of the catchment and the lake, as well as to the retention time of lake.     

Pollutant wet deposition mechanisms in precipitation and fog water

Wet deposition of acid-related substances takes place by two processes: precipitation scavenging and fog water impaction/sedimentation on natural surfaces. The relative importance of each deposition pathway depends on the frequency of occurrence of precipitation or fog, the magnitude of the event and the efficiency of pollutant removal by each mechanism. The latter, in turn, is governed by the type of cloud or fog, complex precipitation formation mechanisms and cloud-surface interactions. These factors are examined in the light of our current knowledge. Particular emphasis is placed on how cloud micro-physical as well as air and precipitation measurements, made aloft by aircraft and at the ground, have been used to further our knowledge of wet deposition mechanisms. Future research is needed to quantify the importance of the fog-water deposition pathway in eastern North America to better understand the interaction of gaseous pollutants with cloud and fog-water and to improve our knowledge of pollutant scavenging processes in mesoscale and synoptic weather systems.     

Aeolian deposition and soil parent materials in northern Nigeria

The introduction considers the nature of the problem of “drift” soils in northern Nigeria. The physical environment of the survey area is described briefly and the percentages of silt, very fine sand and fine sand occurring in the soils are mapped. Textural belts are identified and the profile distribution frequencies within the belts are tabulated. Parent material origins are discussed and attempts are made to reconcile the apparently aeolian nature of the soil materials, in terms of the particle-size distribution pattern, with the various soil profile morphologies of today.     

Subcatchment output of mercury and methylmercury at Svartberget in northern Sweden

The subcatchments of two tributaries and the headwater mire of the 50 ha Swartberget catchment were studied. Monthly sampling was conducted during 1993 on the two tributaries and at the outlet of a mire. This was complemented by more intensive sampling during spring flood and a rain-driven episode at the end of July. Samples were analyzed for total methylmercury (MeHg), total mercury (Hg-tot) and TOC. The MeHg and TOC content of water were also fractionated into humic and non-humic components. Outputs budgets based on continuous flow monitoring and monthly volume weighted average concentrations of MeHg/ Hg were calculated for the subcatchments of the two tributaries and the mire. There was a pronounced decline in MeHg concentrations at all sampling locations during the spring flood. A clear pattern of the seasonal variation in the MeHg outputs was evident at all three sampling locations. Minimum MeHg concentrations occurred during spring flood and increased during the summer to peak levels in the autumn before tapering off during the winter (except for at the mire). The mire had larger increases in MeHg concentrations during the summer and did not decline during the winter. The warmth and increased soil humidity may promote the biogeochemical processes, including methylation, demethylation which make MeHg available for export by runoff from the soil. Variations in Hg-tot concentrations were differed from MeHg in streams that there were increases in Hg-tot concentrations with flow during both spring flood and the July rain event in runoff from the forested tributaries. The highest outputs of both humic and non-humic MeHg occurred during summer from all subcatchments. Those high outputs extended into the autumn at the mire. The largest monthly output of Hg-tot was during the spring flood period and the next largest was during the period of summer rainfall. Despite the similarity in mineralogy and atmospheric deposition on the two tributary subcatchments, there was ca 30% larger ouput of MeHg per unit area from the tributary which had deeper riparian peats. The output of Hg-tot, however, was higher on the catchment with the shallower riparian peats. The difference in the geometry of the riparian zone may contribute to these differences in output. The annual output concentrations at the mire outlet of MeHg was 0.65 ng /L and of Hg-tot was 4.04 ng/L. In the main tributary MeHg was 0.42 ng/L and Hg-tot was 3.64 ng/L. In the Västrabäcken tributary, the mean MeHg concerntration was 0.25 ng/L and the Hg-tot concerntration was 4.02 ng/L. Among the three subcatchments the largest annual output fluxes of MeHg were from the mire, 0.16 g/km2^*yr, the next from Kallkällbäcken below the mire, 0.12 g/km2^*yr, and the lowest from Västrabäcken, 0.08 g/km2^*yr.     

Long-term changes in concentration and deposition of atmospheric mercury over Scandinavia

Samples for measurements of total gaseous mercury (Hg) in air have been collected since 1980 in south-western part of Scandinavia. A collection program for precipitation samples used to determine changes in depositional fluxes of total Hg has been in operation since 1987. A comparison of today's total gaseous Hg levels in air and the total Hg concentrations in precipitation with the ones found earlier, shows a clear decrease with time. At the Swedish west-coast, yearly average air concentrations and median levels of 3.3 and 3.1 (1980–1984), 3.2 and 2.8 (1985–1989), and 2.7 and 2.6 ng Hg/m³ (1990–1992), respectively, were found. Increased average and median winter concentrations were always found, with levels at 3.7 and 3.4, 3.7 and 3.3, and 3.0 and 2.7 ng Hg/m³ for the respective time period. Higher winter values were expected due to increased anthropogenic emissions and changes in the mixing height of the atmosphere. The corresponding total wet deposition rates decreased from 27 (1987–1989) to 10 μg Hg/m² yr. (1990–1992). A finding of special interest was the decreased number of episodic events of high total gaseous Hg levels in air, from 1990 and further on. In addition, the frequency distribution of the concentrations of Hg in air seems to be different for these years compared to the other two time periods. A frequency distribution of air concentrations of Hg more resembling a normal distribution was found for the years 1990 to 1992. The decrease of the atmospheric burden of total gaseous Hg and deposition of total Hg are most probably connected to lower emissions in source areas on the European continent. It seems logical to state that the problem of high Hg depositional fluxes to Scandinavia, is best solved by abatement strategies on the regional scale.     

Recent changes in the deposition of heavy metals in northern Europe

Carpet-forming bryophytes (mosses) have been used extensively since the late 1960's in assessing regional and temporal variability of atmospheric heavy-metal deposition. A large-scale decrease in heavy-metal deposition occurred during the 1970's in Sweden, probably also in other parts of northern Europe. The decrease was closely related to known changes in atmospheric emissions.