Gully hotspot contribution to landscape methane (CH4) and carbon dioxide (CO2) fluxes in a northern peatland

Peatlands are long term carbon catchments that sink atmospheric carbon dioxide (CO(2)) and source methane (CH(4)). In the uplands of the United Kingdom ombrotrophic blanket peatlands commonly exist within Calluna vulgaris (L.) dominated moorland ecosystems. These landscapes contain a range of topographical features that influence local hydrology, climate and plant community composition. In this study we examined the variation in ecosystem CO(2) respiration and net CH(4) fluxes from typical plant-soil systems in dendritic drainage gullies and adjacent blanket peat during the growing season. Typically, Eriophorum spp., Sphagnum spp. and mixed grasses occupied gullies while C. vulgaris dominated in adjacent blanket peat. Gross CO(2) respiration was highest in the areas of Eriophorum spp. (650+/-140 mg CO(2) m(-2) h(-1)) compared to those with Sphagnum spp. (338+/-49 mg CO(2) m(-2) h(-1)), mixed grasses (342+/-91 mg CO(2) m(-2) h(-1)) and C. vulgaris (174+/-63 mg CO(2) m(-2) h(-1)). Measurements of the net CH(4) flux showed higher fluxes from the Eriophorum spp (2.2+/-0.6 mg CH(4) m(-2) h(-1)) locations compared to the Sphagnum spp. (0.6+/-0.4 mg CH(4) m(-2) h(-1)), mixed grasses (0.1+/-0.1 mg CH(4) m(-2) h(-1)) and a negligible flux detected from C. vulgaris (0.0+/-0.0 mg CH(4) m(-2) h(-1)) locations. A GIS approach was applied to calculate the contribution of gullies to landscape scale greenhouse gas fluxes. Findings from the Moor House National Nature Reserve in the UK showed that although gullies occupied only 9.3% of the total land surface, gullies accounted for 95.8% and 21.6% of the peatland net CH(4) and CO(2) respiratory fluxes, respectively. The implication of these findings is that the relative contribution of characteristic gully systems need to be considered in estimates of landscape scale peatland greenhouse gas fluxes.     

Emission of N2O and CH4 from a constructed wetland in southeastern Norway

The Skj?nhaug constructed wetland (CW) is a free surface water (FSW) wetland polishing chemically treated municipal wastewater in southeastern Norway and consists of three ponds as well as trickling, unsaturated filters with light weight aggregates (LWA). Fluxes of nitrous oxide (N(2)O) and methane (CH(4)) have been measured during the autumn, winter and summer from all three ponds as well as from the unsaturated filters. Physicochemical parameters of the water have been measured at the same localities. The large temporal and spatial variation of N(2)O fluxes was found to cover a range of -0.49 to 110 mg N(2)O-N m(-2) day(-1), while the fluxes of CH(4) was found to cover a range of -1.2 to 1900 mg m(-2) day(-1). Thus, both emission and consumption occurred. Regarding fluxes of N(2)O there was a significant difference between the summer, winter and autumn, with the highest emissions occurring during the autumn. The fluxes of CH(4) were, on the other hand, not significantly different with regard to seasons. Both the emissions of N(2)O and CH(4) were positively influenced by the amount of total organic carbon (TOC). The measured fluxes of N(2)O and CH(4) are in the same range as those reported from other CWs treating wastewater. There was an approximately equal contribution to the global warming potential from N(2)O and CH(4).     

Gaseous fluxes in the nitrogen and carbon budgets of subsurface flow constructed wetlands

In 2001 and 2002, fluxes of N(2)O, CH(4), CO(2) and N(2) were measured in two constructed wetlands (CW) for domestic wastewater treatment in Estonia. The difference between the median values of N(2)O, CH(4), and N(2) fluxes in the horizontal subsurface flow (HSSF) CWs was non-significant, being 1.3-1.4 and 1.4-4.1 mg m(-2) d(-1) for N(2)O-N and CH(4)-C, and 0.16-0.17 g N m(-2) d(-1) for N(2)-N respectively. The CO(2)-C flux was significantly lower (0.6 g C m(-2) d(-1)) in one of the HSSF filters of a hybrid CW, whereas the single HSSF and VSSF filters emitted 1.7 and 2.0 g C m(-2) d(-1). The median value of CH(4)-C emission in CWs varied from 1.4 to 42.6 g C m(-2) d(-1), being significantly higher in the VSSF filter beds. We also estimated C and N budgets in one of the HSSF CWs (312.5 m(2)) for 2001 and 2002. The total C input into this system was similar in 2001 and 2002, 772 and 719 kg C year(-1), but was differently distributed between constituent fluxes. In 2001, the main input flux was soil and microbial accumulation (663 kg C year(-1) or 85.8% of total C input), followed by plant net primary production (NPP) (10.2%) and wastewater inflow (3.9%). In 2002, 55.7% of annual C input was bound in plant NPP, whereas the increase in soil C formed 28.5% and wastewater inflow 15.7%. The main C output flux was soil respiration, including microbial respiration from soil and litter, and the respiration of roots and rhizomes. It formed 120 (97.5%) and 230 kg C year(-1) (98.2%) in 2001 and 2002 respectively. The measured CH(4)-C flux remained below 0.1% of total C output. The HSSF CW was generally found to be a strong C sink, and its annual C sequestration was 649 and 484 kg C year(-1) per wetland in 2001 and 2002 respectively. However, negative soil and microbial accumulation values in recent years indicate decreasing C sequestration. The average annual N removal from the system was 38-59 kg N year(-1) (46-48% of the initial total N loading). The most important flux of the N budget was N(2)-N emission (22.7 kg in 2001 and 15.2 kg in 2002), followed by plant belowground assimilation (2.3 and 11.9 kg N year(-1) in 2001 and 2002), and above-ground assimilation (1.9 and 9.2 kg N year(-1), respectively). N(2)O emission was low: 0.37-0.60 kg N year(-1)(.).     

Dynamics of methane emissions from a freshwater marsh of northeast China

In this paper, CH(4) flux was measured from Nov. 2002 to Oct. 2005, to estimate CH(4) emissions in winter and during freeze-thaw period, and interannual variation in CH(4) emissions in freshwater marsh in northeast China. The results showed that there was an obvious CH(4) emission (0.1-2.3 mg m(-2) h(-1)) in the freshwater marsh in winter. Flux of CH(4) in winter (November to March the next year) was about 3.8%, 5.5%, and 2.2% of the whole year in 2003, 2004, and 2005, respectively. Emission of CH(4) significantly increased during the freeze-thaw period (April-June), and was about 30.8%, 20.9%, and 20.6% of the whole year in 2003, 2004, and 2005, respectively. Standing water depth greatly governed interannual variation of CH(4) emissions from marshes during the thaw-freeze period. Interannual variation of CH(4) emissions was significant during the growing season (p<0.05). Standing water depth during April to June was a primary factor, which affected the interannual variation of CH(4) flux during the growing season. Precipitation during the preceding non-growing season affected CH(4) emission indirectly via standing water depth.     

Particulate matter and carbon monoxide multiple regression models using environmental characteristics in a high diesel-use area of Baguio City, Philippines

In Baguio City, Philippines, a mountainous city of 252,386 people where 61% of motor vehicles use diesel fuel, ambient particulate matter <2.5 microm (PM(2.5)) and <10 microm (PM(10)) in aerodynamic diameter and carbon monoxide (CO) were measured at 30 street-level locations for 15 min apiece during the early morning (4:50-6:30 am), morning rush hour (6:30-9:10 am) and afternoon rush hour (3:40-5:40 pm) in December 2004. Environmental observations (e.g. traffic-related variables, building/roadway designs, wind speed and direction, etc.) at each location were noted during each monitoring event. Multiple regression models were formulated to determine which pollution sources and environmental factors significantly affect ground-level PM(2.5), PM(10) and CO concentrations. The models showed statistically significant relationships between traffic and early morning particulate air pollution [(PM(2.5)p=0.021) and PM(10) (p=0.048)], traffic and morning rush hour CO (p=0.048), traffic and afternoon rush hour CO (p=0.034) and wind and early morning CO (p=0.044). The mean early morning, street-level PM(2.5) (110+/-8 microg/m3; mean+/-1 standard error) was not significantly different (p-value>0.05) from either rush hour PM(2.5) concentration (morning=98+/-7 microg/m3; afternoon=107+/-5 microg/m3) due to nocturnal inversions in spite of a 100% increase in automotive density during rush hours. Early morning street-level CO (3.0+/-1.7 ppm) differed from morning rush hour (4.1+/-2.3 ppm) (p=0.039) and afternoon rush hour (4.5+/-2.2 ppm) (p=0.007). Additionally, PM(2.5), PM(10), CO, nitrogen dioxide (NO2) and select volatile organic compounds were continuously measured at a downtown, third-story monitoring station along a busy roadway for 11 days. Twenty-four-hour average ambient concentrations were: PM(2.5)=72.9+/-21 microg/m3; CO=2.61+/-0.6 ppm; NO2=27.7+/-1.6 ppb; benzene=8.4+/-1.4 microg/m3; ethylbenzene=4.6+/-2.0 microg/m3; p-xylene=4.4+/-1.9 microg/m3; m-xylene=10.2+/-4.4 microg/m3; o-xylene=7.5+/-3.2 microg/m3. The multiple regression models suggest that traffic and wind in Baguio City, Philippines significantly affect street-level pollution concentrations. Ambient PM(2.5) levels measured are above USEPA daily (65 microg/m3) and Filipino/USEPA annual standards (15 microg/m3) with concentrations of a magnitude rarely seen in most countries except in areas where local topography plays a significant role in air pollution entrapment. The elevated pollution concentrations present and the diesel-rich nature of motor vehicle emissions are important pertaining to human exposure and health information and as such warrant public health concern.     

Some local environmental effects on mercury emission and absorption at a soil surface

The purpose of this study was to quantify effects of some local environmental variables on the soil surface exchanges of total gaseous mercury (TGM), under controlled conditions. A dynamic flux chamber with a Tekran mercury analyzer was used to quantify TGM emissions from, and absorption by, a clean, fine sandy loam soil with very low mercury content inside of a building and in a low TGM environment, outside. Simultaneous measurements of mercury flux, air and soil temperatures, ozone concentration, humidity, soil moisture and solar radiation were made. Controlled applications of water were made to change soil H2O content and measure the response of mercury flux. Air-soil exchanges were highly dependent on soil temperature (r2 = 0.78) and the mercury concentration gradient between the TGM in the soil pores and the ambient TGM above the soil surface (r2 = 0.98 for absorption and r2 = 0.408 for emissions). Correlations with air temperature and ozone levels are explained by the relationships of these variables with soil temperature. No detectable correlation was found with solar radiation or humidity. Wet soil maintained higher rates of soil TGM emission and decreased soil absorption. Emissions increased with increasing soil H2O, peaked at approximately field capacity, and then decreased slightly until saturation.     

Mercury speciation and exchanges at the air-water interface of a tropical artificial reservoir, French Guiana

The distribution and speciation of mercury (Hg) in air, rain, and surface waters from the artificial tropical lake of Petit-Saut in French Guiana were investigated during the 2003/04 period. In the air, total gaseous mercury (TGM) at the dam station averaged 12+/-2 pmol m(-3) of which >98% was gaseous elemental mercury (GEM). GEM distribution depicted a day-night cycling with high concentrations (up to 15 pmol m(-3)) at dawn and low concentrations (down to 5 pmol m(-3)) at nightfall. Reactive gaseous mercury (RGM) represented <1% of the GEM with a mean concentration of 4+/-3 fmol m(-3). Diel RGM variations were negatively related to GEM. In the rain, the sum of all Hg species in the unfiltered (HgT(UNF)) averaged 16+/-12 pmol L(-1). Temporal distribution of HgT(UNF) exhibited a pattern of high concentrations during the late dry seasons (up to 57.5 pmol L(-1)) and low concentrations (down to 2.7 pmol L(-1)) in the course of the wet seasons. Unfiltered reactive (HgR(UNF)), dissolved gaseous (DGM) and monomethyl (MMHg(UNF)) Hg constituted 20, 5 and 5% of HgT(UNF), respectively. All measured Hg species were positively related and displayed negative relationships with the pH of the rain. In the reservoir surface waters, dissolved total mercury (HgT(D)) averaged 3.4+/-1.2 pmol L(-1) of which 10% consisted of DGM. DGM showed a trend of high concentrations during the dry seasons (480+/-270 fmol L(-1)) and lower (230+/-130 fmol L(-1)) in the course of the wet seasons. Diel variations included diurnal photo-induced DGM production (of about 60 fmol L(-1) h(-1)) coupled to minute to hour oxidation/reduction cycles (of >100 fmol L(-1) amplitude). Finally, calculated atmospheric Hg inputs to the Petit-Saut reservoir represented 14 mol yr(-1) whereas DGM evasion reached 23 mol yr(-1). Apportionment among forms of Hg deposition indicated that up to 75% of the total Hg invasive flux follows the rainfall pathway.     

Methane emissions from a constructed wetland treating wastewater--seasonal and spatial distribution and dependence on edaphic factors

Constructed wetlands for wastewater treatment have many advantages. They can be used for several purposes, for example, to reduce levels of organic matter and nutrients, and to retain toxic metals. However, most wetlands are inherently net sources of gaseous compounds like methane and nitrous oxide, which are of environmental concern due to their rapid current accumulation in the atmosphere and their potent global warming capacity. In order to determine the flux of methane from a constructed wetland a study was conducted over two growth seasons on a pilot scale wetland constructed to reduce nutrient levels in secondary treated wastewater. The emissions for the spring to autumn period averaged 141 mg CH(4)m(-2)d(-1) (S.D.=187), ranging from consumption of 375 mg CH(4)m(-2)d(-1) to emissions of 1739 mg CH(4)m(-2)d(-1). The spatial and temporal variations were large, but could be accounted for by measured environmental factors. Among these factors, sediment and water temperatures were significant in all cases and independent of the scale of analysis (r(2) up to 0.88).     

Phosphorus cycling through phosphine in paddy fields

Phosphine emission fluxes from paddy fields, phosphine ambient levels in air, and the vertical profile of matrix-bound phosphine in soil have been measured throughout the growing season of rice in Beijing, China. It was found that both the seasonal and diurnal emission fluxes and ambient levels fluctuate significantly. During the drainage period, phosphine released from the soil with the highest diurnal average flux on the first period of drainage (approx. 17.7 ng m(-2) h(-1)), whereas its highest ambient level (approx. 250 ng m(-3)) occurred at 06.00 h. During the flooded period, phosphine emission was low, and the peaks of phosphine emissions occurred at midnight. The average flux of PH3 emission for the whole season was found to be approximately 1.78 ng m(-2) h(-1). The mass fraction of matrix-bound phosphine is approximately 0.18 approximately 1.42 x 10(-7) (m/m) part of organic phosphorus or 3.4 approximately 9.2 x 10(-9) (m/m) part of total phosphorus in paddy soil. The amount of phosphine emitted to the atmosphere was only a small fraction of the phosphine that remained in the soil in the matrix-bound form. Soil serves both as the source and the sink of PH3.     

Elemental gaseous mercury flux at the water/air interface over the Negro River basin, Amazon, Brazil

The amount of dissolved gaseous mercury (DGM) released annually into the atmosphere by water bodies in each of the 18 major sub-basins of the Negro River tributaries has been estimated for the wet season and adopted for the entire year. Using Remote Sensors (RS) and the Geographic Information System (GIS), an estimate was made for the total flooded area during the period of the wet season (May-July), which corresponds to around 10% of the total basin area. The estimates of DGM evasive flux values were made during four scientific campaigns and ranged from 0.09 to 14 mug m(-2) y(-1). Mercury wet deposition to the same area was estimated using average values of the metal concentration in the rainwater (9.8 ng L(-1)), which varies from 17 to 27 microg m(-2) year(-1). Considering the flooded area of the Negro River Basin as 69,000 km(2), the total amount of mercury emitted by all bodies of water reaches nearly 0.26 ton year(-1), which represents not more than 2% of the total mercury found in wet deposition in this same area.     

Influence of organic carbon decomposition on calcite dissolution in surficial sediments of a freshwater lake

A multi-sensor approach was used to determine high-resolution porewater gradients of Ca(2+), CO(3)(2-), H(+) and O(2) in sediment cores along a depth transect from eutrophic Lake Sempach (Switzerland). We quantified the reproducibility of measurements and analyzed concentration profiles with a one-dimensional diffusion-reaction model to quantify benthic fluxes. Calculation of oxic respiration in the sediment showed that almost all settled organic carbon was degraded with O(2) at shallow depths while only 28% was decomposed aerobically at the deepest location. Fluxes were highest at 8 m depth (24.4 mM m(-2) d(-1)) and lowest at the deepest site of 85 m (7.1 mM m(-2) d(-1)). Dissolution of calcite from the sediment was also depth dependent. A total of 1.1 mM m(-2) d(-1) was found for the shallowest site, and values decreased with depth to 0.6 mM m(-2) d(-1) at the deepest site.     

Mercury budget of a small forested boreal catchment in southeast Norway

We present input and output fluxes of total mercury (Hg(tot)) and methyl mercury (MeHg) based on throughfall, litterfall and stream water samples from 2004/2005 from a small forested catchment (Langtjern) in Norway. Hg(tot) input via throughfall and litterfall was estimated to 6.7 and 2.7 microg m(-2) yr(-1), respectively, which is considerably lower than previously reported from other boreal catchments in Scandinavia. A likely cause for the low input flux is the sparseness and low productivity of the forest in the Langtjern catchment, with less atmospheric scavenging and lower litterfall fluxes than previously studied sites. In addition there has been a general decrease in mercury (Hg) in the atmosphere on the northern hemisphere in the last decade. The estimated output flux of Hg(tot) with surface water was 2.5 microg m(-2) yr(-1), which is comparable to what has been reported elsewhere. The ratio of Hg(tot) output flux to input flux was 26%, which is considerably higher than reported from other sites. This illustrates that catchment properties have greater importance for surface water export of Hg than the current atmospheric input. The estimated total soil pool of Hg(tot) in the catchment was 17.4 mg m(-2). This corresponds to roughly 8000 years of the current surface water output flux and 2000 years of the current input flux.     

Influence of anthropogenic sources on total gaseous mercury variability in Grenoble suburban air (France)

Total gaseous mercury (TGM) has been monitored at Champ sur Drac, a suburban site of Grenoble in southern east France. TGM measurements have been made over 4 periods of approximately 10 days throughout 1999-2000 using cold vapour atomic fluorescence absorption technique. The first monitoring campaign was initiated on November 4, 1999, followed by three other campaigns respectively on January 12, 2000, April 10, 2000 and July 17, 2000. Concurrent monitoring of O3, NO, NO2, SO2 and of meteorological parameters have also been performed. The mean TGM concentration was 3.4 ng m(-3) with maximum hourly mean concentration of 37.1 ng m(-3). Although mean TGM concentration was not greatly different from those previously measured in the troposphere, the greater TGM variability as well as the occurrence of high TGM concentration linked to particular wind conditions suggested the strong influence of anthropogenic sources. The chlor-alkali plant located nearby, the others chemical industries using fuel combustion and the municipal waste incinerator were thought to contribute to mercury pollution events.     

Effect of specific gas loading rate on thermophilic (55 degrees C) acidifying (pH 6) and sulfate reducing granular sludge reactors

The effect of the specific gas loading rate on the acidifying, sulfate reducing and sulfur removal capacity of thermophilic (55 degrees C; pH 6.0) granular sludge bed reactors treating partly acidified wastewater was investigated. A comparison was made between a regular UASB reactor and a UASB reactor continuously sparged with N(2) at a specific gas loading rate of 30 m(3)m(-2)d(-1). Both UASB reactors (upflow velocity 1.0 mh(-1), hydraulic retention time about 5h) were fed a synthetic wastewater containing starch, sucrose, lactate, propionate and acetate and a low sulfate concentration (COD/SO(4)(2-) ratio of 10) at volumetric organic loading rates (OLR) ranging from 4.0 to 49.8 gCODl(-1) reactord(-1). Immediately after imposing an OLR of 25 gCODl(-1) reactord(-1), the acidification and sulfate reduction efficiency dropped to 80% and 30%, respectively, in the UASB reactor. Both efficiencies recovered slowly to 100% during the course of the experiment. In the N(2) sparged reactor, both the acidification and sulfate reduction efficiency remained 100% following the OLR increase to 25 gCODl(-1) reactord(-1). However, the sulfate reduction efficiency gradually decreased to about 20% at the end of the experiment. The biogas (CO(2) and CH(4)) production rate in the UASB was very low, i.e. <3l biogasl(-1) reactorday(-1), resulting in negligible amounts (<20%) of H(2)S stripped from the reactor liquid. The total H(2)S concentration of the N(2) sparged UASB reactor effluent was always below 25 mgl(-1), but incomplete sulfate reduction kept the maximal H(2)S stripping efficiency below 70%.     

The Northeast States and Eastern Canadian Provinces mercury study: a framework for action: summary of the Canadian chapter

The objective of this paper is to give an overview of the findings of the Canadian chapter of the Northeast States and Eastern Canadian Provinces Mercury Study, which was conducted between 1995 and 1998. The Canadian chapter provided information on mercury emissions, sources and levels in air, water, biota and humans. Industry, governments and universities provided information for the Canadian chapter. The study showed that the Northeast States and Eastern Canadian Provinces (NES/ECP) is a region impacted by airborne mercury. Annual mercury emissions for the NES/ECP region are estimated to be approximately 19 t (12%) of the combined Canadian and US national anthropogenic mercury emissions of 155 t/year. 210Pb-dated lake sediment cores from Atlantic Canada showed a mercury enrichment factor of 2.5 for coastal sites with mercury increases starting in 1860. Regional mercury wet deposition for the NES/ECP region was 7-11 microg/m2/year. Provincial and federal fish health advisories have been updated in the ECP for children and women of child-bearing age limiting the consumption of freshwater fish, as well as fresh or frozen shark, tuna or swordfish.     

Scaling of atmospheric mercury emissions from three naturally enriched areas: Flowery Peak,Nevada; Peavine Peak,Nevada; and Long Valley Caldera,California

With the development of analytical capabilities that allow for almost real time measurement of mercury concentrations in air, the fluxes of mercury between environment compartments is being more carefully scrutinized. Recent advances have demonstrated that the mercury cycle is much more complicated than previously realized. This study quantified the mercury emissions from three areas with low levels of mercury enrichment associated with precious and base metal mineralization and recent volcanic/geothermal activity. Area emissions were calculated using Geographic Information System technology, and in situ derived mercury fluxes and those parameters found to statistically be dominant in controlling emissions. The most important controls on emission strengths were found to be geologic while environmental parameters such as light and temperature were found to drive the diel pattern typically observed for mercury emissions. Calculated area averaged emissions were 18.5, 10.0, and 13.6 ng/m2 h for the Flowery Peak, NV, Peavine Peak, NV, and Long Valley Caldera, CA areas, respectively. These emissions are an order of magnitude higher than values applied in global models for natural sources. This study, along with other recent work, demonstrates that natural sources may contribute more mercury than previously recognized to the atmospheric mercury pool.     

Foliar exchange of mercury as a function of soil and air mercury concentrations

Previous research has indicated that foliar mercury (Hg) flux is bi-directional, with influence from both atmospheric and soil Hg. This work investigated the role of soil and air Hg concentrations on foliar Hg exchange using a single-plant gas-exchange system. The exchange of Hg vapor with aspen seedlings grown in soil Hg concentrations of 0.03+/-0.01, 5.8+/-0.5, and 12.3+/-1.3 microg g(-1) and exposed to atmospheric Hg concentrations of 2.4+/-0.5, 11.0+/-0.9, and 30.4+/-2.2 ng m(-3) was measured. At background atmospheric Hg concentrations of 2.4 ng m(-3), foliage released Hg at all three soil Hg concentrations and fluxes ranged from 1.6 to 5.5 ng/m(2)/h. At higher atmospheric Hg concentrations (>11 ng m(-3)), net deposition to foliage ranged from -9 to -47 ng/m(2)/h, exhibiting increase uptake with higher air Hg concentrations. Fluxes associated with aspen showed an immediate response to changes in atmospheric Hg concentrations. Compensation points, the air concentration where no net flux of Hg vapor occurred, were 3-4 ng m(-3) in the light and 2-3 ng m(-3) in the dark for trees grown in soils of 0.03 and 6 microg g(-1) Hg content, and 5-6 ng m(-3) in the light and 2.5-3.5 ng m(-3) in the dark for trees grown in 12 microg g(-1) Hg soils.     

Total mercury and methylmercury levels in fish from hydroelectric reservoirs in Tanzania

Total mercury (THg) and methylmercury (MeHg) levels have been determined in fish species representing various tropic levels in four major hydroelectric reservoirs (Mtera, Kidatu, Hale-Pangani, Nyumba ya Mungu) located in two distinct geographical areas in Tanzania. The Mtera and Kidatu reservoirs are located along the Great Ruaha River drainage basin in the southern central part of the country while the other reservoirs are located within the Pangani River basin in the north eastern part of Tanzania. Fish mercury levels ranged from 5 to 143 microg/kg (mean 40 microg/kg wet weight) in the Mtera Reservoir, and from 7 to 119 microg/kg (mean 21 microg/kg) in the Kidatu Reservoir downstream of the Great Ruaha River. The lowest THg levels, in the range 1-10 microg/kg (mean 5 microg/kg), were found in fish from the Nyumba ya Mungu (NyM) Reservoir, which is one of the oldest reservoirs in the country. Fish mercury levels in the Pangani and Hale mini-reservoirs, downstream of the NyM Reservoir, were in the order of 3-263 microg/kg, with an average level of 21 microg/kg. These THg levels are among the lowest to be reported in freshwater fish from hydroelectric reservoirs. Approximately 56-100% of the total mercury in the fish was methylmercury. Herbivorous fish species contained lower THg levels than the piscivorous species; this was consistent with similar findings in other fish studies. In general the fish from the Tanzanian reservoirs contained very low mercury concentrations, and differed markedly from fish in hydroelectric reservoirs of similar age in temperate and other regions, which are reported to contain elevated mercury concentrations. The low levels of mercury in the fish correlated with low background concentrations of THg in sediment and flooded soil (mean 2-8 microg/kg dry weight) in the reservoir surroundings. This suggested a relatively clean reservoir environment that has not been significantly impacted by mercury contamination from natural or anthropogenic sources.     

Atmospheric mercury deposition in Guizhou, China

The atmospheric deposition of mercury including total gas phase mercury (TGM), gas phase divalent mercury (Hg2+), and gas phase monomethyl mercury (MMHg) was investigated. Samples were collected from central cities and nature reserve areas across the province. Techniques and equipment including moss bags, KCl-coated denuder and GARDIS-1A portable mercury vapor analyzer were employed for sample collection and analysis. The reliability of techniques and analytical methods used for the project was evaluated. The deposition of atmospheric mercury was reported in species in this important mercury polluted province for the first time. The spatial and temporal variability of mercury emissions were investigated and reported. Contribution of coal mercury emissions to the atmosphere mercury deposition of the province was also investigated.     

Urinary mercury in people living near point sources of mercury emissions

As part of the European Mercury Emissions from Chlor Alkali Plants (EMECAP) project, we tested the hypothesis that contamination of ambient air with mercury around chlor alkali plants using mercury cells would increase the internal dose of mercury in people living close to the plants. Mercury in urine (U-Hg) was determined in 225 individuals living near a Swedish or an Italian chlor alkali plant, and in 256 age- and sex-matched individuals from two reference areas. Other factors possibly affecting mercury exposure were examined. Emissions and concentrations of total gaseous mercury (TGM) around the plants were measured and modeled. No increase in U-Hg could be demonstrated in the populations living close to the plants. This was the case also when the comparison was restricted to subjects with no dental amalgam and low fish consumption. The emissions of mercury to air doubled the background level, but contributed only about 2 ng/m(3) to long-term averages in the residential areas. The median U-Hg levels in subjects with dental amalgam were 1.2 microg/g creatinine (micro/gC) in Italy and 0.6 microg/gC in Sweden. In individuals without dental amalgam, the medians were 0.9 microg/gC and 0.2 microg/gC, respectively. The number of amalgam fillings, as well as chewing, fish consumption, and female sex were associated with higher U-Hg. The difference between the countries is probably due to higher fish consumption in Italy, demethylated methyl mercury (MeHg) being partly excreted in urine. Post hoc power calculations showed that if the background mercury exposure is low it may be possible to demonstrate an increase in U-Hg of as little as about 10 ng/m(3) as a contribution to ambient mercury from a point source.