Trace Metal Fluxes Research Articles

Significance of groundwater discharge along the coast of Poland as a source of dissolved metals to the southern Baltic Sea

Fluxes of dissolved trace metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) via groundwater discharge along the southern Baltic Sea have been assessed for the first time. Dissolved metal concentrations in groundwater samples were less variable than in seawater and were generally one or two orders of magnitude higher: Cd (2.1–2.8nmolL−1), Co (8.70–8.76nmolL−1), Cr (18.1–18.5nmolL−1), Mn (2.4–2.8μmolL−1), Pb (1.2–1.5nmolL−1), Zn (33.1–34.0nmolL−1). Concentrations of Cu (0.5–0.8nmolL−1) and Ni (4.9–5.8nmolL−1) were, respectively, 32 and 4 times lower, than in seawater. Groundwater-derived trace metal fluxes constitute 93% for Cd, 80% for Co, 91% for Cr, 6% for Cu, 66% for Mn, 4% for Ni, 70% for Pb and 93% for Zn of the total freshwater trace metal flux to the Bay of Puck. Groundwater-seawater mixing, redox conditions and Mn-cycling are the main processes responsible for trace metal distribution in groundwater discharge sites.

Geochronology and historical deposition of trace metals in three tropical estuaries in the Gulf of Guinea

The depositional histories of trace metals (Pb, Cu, and Zn) in sediment cores from three Ghanaian estuaries were reconstructed using radioisotope-derived (210Pb and 137Cs) geochronologies. A core collected from each of the Amisa, Sakumo II and Volta estuaries was analyzed for trace metals and radionuclides. Lead-210 and 137Cs dating via gamma spectroscopy, and trace metal analysis via inductively coupled plasma mass spectrometry (ICP-MS) were used in deriving sedimentation rates, geochronologies and accumulation trends of trace metals. The sedimentation rates in all three estuaries (in the range of 0.54–0.83 cm yr−1) were greater than the predicted sea level rise (∼0.33 cm yr−1) for the Accra Coast of Ghana. The 210Pb depositional rates of 6.83 dpm cm−2 y−1, 2.74 dpm cm−2 y−1 and 1.75 dpm cm−2 y−1 estimated for the Amisa, Sakumo II and Volta estuaries, respectively, are higher than those recorded in other latitudes. Trace metal analysis revealed differences in the concentrations of Cu, Pb and Zn between deeper and surficial layers of each core to be in the range of 10–20%, which is well within the natural variations attributed to geochemical factors. Relative to the Amisa and Volta estuaries, the temporal profiles of Al-normalized metal concentrations and estimated fluxes suggest anthropogenic processes augmented the natural fluxes of trace metals, particularly Zn into the Sakumo II estuary during the last 7 years.

Elevated gas flux and trace metal degassing from the 2014–2015 fissure eruption at the Bárðarbunga volcanic system, Iceland

AbstractThe 2014 Bárðarbunga rifting event in Iceland resulted in a 6‐month long eruption at Holuhraun. This eruption was characterized by high lava discharge rate and significant gas emission. The SO2 flux for the first 3 months was measured with satellite sensors and the petrologic method. High‐resolution time series of the satellite data give 1200 kg/s that concurs with 1050 kg/s obtained from melt inclusion minus degassed lava sulfur contents scaled to the mass of magma produced. A high‐purity gas sample, with elevated S/Cl due to limited chlorine degassing, reveals a similar degassing pattern of trace metals as observed at Kīlauea (Hawai'i) and Erta Ale (Ethiopia). This suggests a common degassing mechanism at mantle plume‐related volcanoes. The trace metal fluxes, calculated from trace element to sulfur ratios in the gas sample and scaled to the sulfur dioxide flux, are 1–2 orders of magnitude stronger at Holuhraun than Kīlauea and Erta Ale. In contrast, volcanoes at convergent margins (Etna and Stromboli, Italy) have 1–2 orders of magnitude higher trace element fluxes, most likely caused by abundant chlorine degassing. This emphasizes the importance of metal degassing as chlorine species. Short‐lived disequilibria between radon daughters, 210Pb‐210Bi‐210Po measured in the gas, suggest degassing of a continuously replenished magma batch beneath the eruption site. Earlier and deep degassing phase of carbon dioxide and polonium is inferred from low (210Po/210Pb) in the gas, consistent with magma transfer rate of 0.75 m/s.

Mount Etna volcano (Italy) as a major “dust” point source in the Mediterranean area

Volcanic emissions represent one of the most relevant natural sources of trace elements to the troposphere. Due to their potential toxicity, they may have important environmental impacts from local to global scale. They can also severely affect the atmospheric and terrestrial environment at timescales ranging from a few to millions of years. Mt. Etna volcano is known as one of the largest global contributors of magmatic gases (CO2, SO2 and halogens) and particulate matter, including some toxic trace elements. The aim of this study is to characterize the chemical composition and the mineralogical features of the volcanogenic aerosol passively emitted from Mt. Etna. Twenty-five samples were collected by filtration technique from different sites between 2008 and 2014. Chemical and mineralogical analyses allowed to discriminate two main constituents: the first is mainly referable to the silicate component in the volcanic plume, like lithic, juvenile fragments or glass shards and crystals (e.g. plagioclases, pyroxenes, oxides); the second constituent consists of soluble compounds like sulphosalts or halide minerals (sulphates, chlorides and fluorides). Fluxes of major and trace metals emitted in the atmosphere have been estimated. By comparing the Etnean trace elements with those from European anthropic emissions, we conclude that Mt. Etna is the main persistent point source of major and trace metals in the Mediterranean region. Results gathered from this investigation is of fundamental importance due to the exposure and potential impact of harmful chemical compounds for hundred thousand tourist visits each year to the summit of Mt. Etna.

An experimental study on the mixing behavior of Ti, Zr, V and Mo in the Elbe, Rhine and Weser estuaries

Estuaries are important interfaces between land and ocean, in which the input of trace metals into the ocean via the rivers is often significantly modified along the mixing gradient between freshwater and seawater. In the present study we have carried out mixing experiments using river water from the Rhine, the Elbe and the Weser and seawater from the North Sea with the aim of gaining more insights into the behavior of titanium (Ti), zirconium (Zr), vanadium (V) and molybdenum (Mo) and their distribution between dissolved and particulate forms during mixing in the estuaries. Little is known about the modification of their concentrations in estuaries and these metals increasingly enter the rivers and the ocean due to their application as so-called high-tech metals in industrial activities. Such laboratory experiments at controlled conditions allow the systematic investigation of chemical changes related to the mixing ratios, independent of further influence factors occurring in natural systems. Adsorptive stripping voltammetry was used for the analytical determination of the four metals. Although our data largely confirmed a strong particle-reactive behavior of Ti and Zr and a mostly conservative behavior of Mo, our mixing experiments revealed partial deviation from this behavior. Vanadium mostly does not follow a strict conservative mixing trend but shows both small ad- and desorption effects along the salinity transect. Also Mo shows some deviations from conservative mixing at mid-salinities. The enrichment of dissolved Ti and Zr at about 50:50 river: seawater mixtures agrees with recently published data of similar field studies and appears to be a systematic effect possibly related to charge transitions on particle surfaces or change of the dissolved metal speciation. The observed effects partly differed in experiments with filtered and non-filtered river water samples, especially for Ti and Zr, highlighting the role of riverine particulate matter for the modification of dissolved trace metal fluxes in estuaries.

Estimation of the Atmospheric Flux of Nutrients and Trace Metals to the Eastern Tropical North Atlantic Ocean*

Abstract Atmospheric deposition contributes potentially significant amounts of the nutrients iron, nitrogen, and phosphorus (via mineral dust and anthropogenic aerosols) to the oligotrophic tropical North Atlantic Ocean. Transport pathways, deposition processes, and source strengths contributing to this atmospheric flux are all highly variable in space and time. Atmospheric sampling was conducted during 28 research cruises through the eastern tropical North Atlantic (ETNA) over a 12-yr period, and a substantial dataset of measured concentrations of nutrients and trace metals in aerosol and rainfall over the region was acquired. This database was used to quantify (on a spatial and seasonal basis) the atmospheric input of ammonium, nitrate, soluble phosphorus, and soluble and total iron, aluminum, and manganese to the ETNA. The magnitude of atmospheric input varies strongly across the region, with high rainfall rates associated with the intertropical convergence zone contributing to high wet deposition fluxes in the south, particularly for soluble species. Dry deposition fluxes of species associated with mineral dust exhibited strong seasonality, with the highest fluxes associated with wintertime low-level transport of Saharan dust. Overall (wet plus dry) atmospheric inputs of soluble and total trace metals were used to estimate their soluble fractions. These also varied with season and were generally lower in the dry north than in the wet south. The ratio of ammonium plus nitrate to soluble iron in deposition to the ETNA was lower than the N:Fe requirement for algal growth in all cases, indicating the importance of the atmosphere as a source of excess iron.

Anthropogenic changes in the fluxes to estuaries: Wastewater discharges compared with river loads in small rias

The modification of chemical inputs into estuaries/rias by wastewater discharges is poorly documented. Concentrations and fluxes of nutrient salts, organic matter and trace metals in rivers and wastewaters to the mesotrophic Rias of Ortigueira (38 km2) and Viveiro (27 km2), located on the western Cantabrian coast (Bay of Biscay), were evaluated to assess changes in the land-sea fluxes. Water was sampled monthly during a year in the Mera (6.0 m3 s−1) and Landro (9.4 m3 s−1) rivers flowing into the Rias of Ortigueira and Viveiro, respectively. The urban effluents of Ortigueira (1800 inhabitants; treated sewage) and the Viveiro (7100 inhabitants; municipal treated sewage and untreated industrial wastewaters) were also monitored. Concentrations of chemical compounds and their fluxes were quite similar and close to pristine conditions in both rivers. Nitrate (98% of DIN), the limiting nutrient of ria primary production, was controlled by river flow while phosphate by wastewater discharge. Sewage discharges should not disturb the Ria of Ortigueira. Wastewaters fluxes of phosphate, POC, PON, dissolved Cu and particulate Cd, Cu and Zn into the Ria of Viveiro exceeded those of the Landro River, mainly during summer. Also, untreated wastewater effluents from fish food processing in such small fishing ports can be a source of contamination. The Rias of Ortigueira and Vivieiro are a reference point to evaluate fluvial pristine conditions and wastewater discharges on small estuary-ria receptor systems.

Dynamic Coupling of Iron, Manganese, and Phosphorus Behavior in Water and Sediment of Shallow Ice-Covered Eutrophic Lakes.

Decreasing duration and occurrence of northern hemisphere ice cover due to recent climate warming is well-documented; however, biogeochemical dynamics underneath the ice are poorly understood. We couple time-series analyses of water column and sediment water interface (SWI) geochemistry with hydrodynamic data to develop a holistic model of iron (Fe), manganese (Mn), and phosphorus (P) behavior underneath the ice of a shallow eutrophic freshwater bay. During periods of persistent subfreezing temperatures, a highly reactive pool of dissolved and colloidal Fe, Mn, and P develops over time in surface sediments and bottom waters due to reductive dissolution of Fe/Mn(oxy)hydroxides below the SWI. Redox dynamics are driven by benthic O2 consumption, limited air-water exchange of oxygen due to ice cover, and minimal circulation. During thaw events, the concentration, distribution and size partitioning of all species changes, with the highest concentrations of P and "truly dissolved" Fe near the water column surface, and a relatively well-mixed "truly dissolved" Mn and "colloidal" Fe profile due to the influx of geochemically distinct river water and increased circulation. The partitioning and flux of trace metals and phosphorus beneath the ice is dynamic, and heavily influenced by climate-dependent physical processes that vary in both time and space.

Trace metals in the suspended particulate matter of the Yellow River (Huanghe) Estuary: Concentrations, potential mobility, contamination assessment and the fluxes into the Bohai Sea

Excessive input of trace metals contributes much to the degradation of many coastal ecosystems. As one of the most turbid large rivers in the world, the Yellow River, also called Huanghe, transports huge amounts of freshwater and suspended particulate matter (SPM) each year from its catchment as far as thousands of kilometers inland into the Bohai Sea, and has the most profound influence on the ecosystem of the Bohai Sea compared with other rivers that empty into it. In this research, the SPM were collected from the Yellow River Estuary twice in April and August, 2013. Six environmental quality assessment-related trace metals, namely Cd, Cr, Cu, Ni, Pb and Zn, were measured for their total concentrations and fractionations to understand their spatial and seasonal variations, potential mobility, pollution status and fluxes. The total concentrations of Cd, Cu and Pb in the wet season were very similar to their corresponding values in the dry season, while the total concentrations of Cr, Ni and Zn in the wet season were slightly higher than those in the dry season. The distributions of the studied metals in the geochemical fractions showed no notable spatial and seasonal variations. Except for Cd and Ni, the metals in the most labile fraction having the highest potential risk to biota on average accounted for <2% of their respective total concentrations; the percentages of Cd and Ni in this fraction were 54.5% and 10.1%, respectively. Anthropogenic influence on the spatial and seasonal variations of particulate Cr, Cu, Ni and Zn in total concentrations seemed weak and they were dominantly of natural sources. Results indicated that the Yellow River emptied about 0.0081×103, 2.11×103, 0.98×103, 1.10×103, 1.01×103 and 2.64×103ta−1 of particulate Cd, Cr, Cu, Ni, Pb and Zn into the Sea, 86% of which happened in the wet season starting from June through October. These numbers were only 2.5–5.3% of the annual trace metals fluxes in the 1980s. One of the reasons for this was the reduction of SPM load; the fact that previous chemical fluxes data were measured at sites inland far from the mouth of the Yellow River was also responsible for this because a major proportion of SPM recorded at that site were deposited into the river bed during the transport between that site and the mouth of the Yellow River. Such a deposit actually did not reach the Bohai Sea, and probably had no direct influence on the environment and ecosystem of the Bohai Sea beyond the mouth of the Yellow River.

English

Trace metals (Zn, Cu and Pb) fluxes were studied in five intertidal flats at Bodo Creek, Eastern Niger Delta, Nigeria in 2006, and re-evaluated in 2010 following two major oil spills that occurred in the creek. This study is the first to look at trace metal loads in the interstitial sediments of Bodo creek. Standard methods were employed in the sampling campaign and analysis. The concentration of all metals under study were higher than stipulated limit by WHO (2006) during post spill analysis. Concentration of Zn did not vary between stations and months pre-spill but did in post-spill, having values slightly higher than WHO (2006) stipulated limit. During the pre-spill sediment analysis, Pb concentrations ranged from no detection to 0.0012 mg/kg in 2006, increasing to 0.169 mg/kg post spill in 2010. Cu content ranged from 0.1312 - 0.1858 and 0.3374 - 0.4504 mg/kg pre- and post-spill, respectively. In addition to oil-induced metal loadings, the metals concentration dynamics show strong correlation with season. Metals had higher concentrations during the dry season due to reduced water volume in the creek and consequently less dilution. Implication for uptake, bioaccumulation and biotransformation by food species in the creek catchment above biosafety limits for user population is stressed and measures to avert public health consequences are advocated. Key words: Trace metals, inter-tidal sediment, Niger Delta, oil pollution.

Porewater dynamics of silver, lead and copper in coastal sediments and implications for benthic metal fluxes

To determine the conditions that lead to a diffusive release of dissolved metals from coastal sediments, porewater profiles of Ag, Cu, and Pb have been collected over seven years at two contrasting coastal sites in Massachusetts, USA. The Hingham Bay (HB) site is a contaminated location in Boston Harbor, while the Massachusetts Bay (MB) site is 11km offshore and less impacted. At both sites, the biogeochemical cycles include scavenging by Fe-oxyhydroxides and release of dissolved metals when Fe-oxyhydroxides are reduced. Important differences in the metal cycles at the two sites, however, result from different redox conditions. Porewater sulfide and seasonal variation in redox zone depth is observed at HB, but not at MB. In summer, as the conditions become more reducing at HB, trace metals are precipitated as sulfides and are no longer associated with Fe-oxyhydroxides. Sulfide precipitation close to the sediment–water interface limits the trace metal flux in summer and autumn at HB, while in winter, oxidation of the sulfide phases drives high benthic fluxes of Cu and Ag, as oxic conditions return. The annual diffusive flux of Cu at HB is found to be significant and contributes to the higher than expected water column Cu concentrations observed in Boston Harbor. At MB, due to the lower sulfide concentrations, the association of trace metals with Fe-oxyhydroxides occurs throughout the year, leading to more stable fluxes. A surface enrichment of solid phase trace metals was found at MB and is attributed to the persistent scavenging by Fe-oxyhydroxides. This process is important, particularly at sites that are less reducing, because it maintains elevated metal concentrations at the surface despite the effects of bioturbation and sediment accumulation, and because it may increase the persistence of metal contamination in surface sediments.

Changes in trace metal sedimentation during freshening of a coastal basin

Holocene freshening has turned the Bothnian Bay, northern Baltic Sea into an oligotrophic basin. Sequestering of trace elements has changed significantly during the oligotrophication process. In principle, trace metals have been transferred from permanently buried sulfides to Fe–Mn-oxyhydroxides in the top layers of the sediment. The oxyhydroxide layers restrict the flux of trace metals from the sediment to the oxic bottom water. Hence, Fe–Mn cycling in the suboxic sediment enriches a number of trace metals in the surface sediment. Arsenic, Sn, Ge and Bi show enrichment in the Fe-oxyhydroxide layer, whereas Mo, Cd, Ni, Co, Cu, and Sb are enriched in the uppermost Mn-oxyhydroxide layer. This natural redox cycling in the sediment obscures pollution effects.The oligotrophication process started approximately 3500years ago, reflected in decreasing deposition of Zn, a proxy for phytoplankton production, and formation of Mn oxyhydroxide layers. Similarly, Ba/Al data indicate a decrease in the pelagic input of plankton. Barium data also suggest that dissolved sulfide in the sediment never reached high concentrations. Germanium is closely related to Ba, suggesting that Ge can be used as a proxy for phytoplankton production. Vanadium, U, Re, and Mo all indicate that the bottom water never has been significantly sulfidic during the last 5500years. Rhenium data indicate that the organic carbon oxidation rate has decreased during the last 5500years. Cadmium follows the organic matter distribution, but started to increase 1000YBP (years before present). The reason for this enhanced input of Cd is unclear.

Atmospheric deposition of heavy metals in the mining area of the San Jorge river basin, Colombia

To characterize the atmospheric content of chemical contaminants, samples of atmospheric deposits were collected at several sites in the mining area of the San Jorge river basin, Colombia, during La Nina events (May 2010 and October 2011). Measurements of trace metals (Hg, Cu, Cd, Pb, Ni, and Zn) were performed after rain collection using a bulk deposition sampler in locations near a point source and sampling points located within a range of 30 Km away from the mine. As expected, concentrations were elevated in locations close to the ferronickel mining area with similar levels to other highly polluted areas. Concentrations of bulk precipitation and deposition were measured for Zn (23.07 ± 7.30 ng mL−1 and 227.5 ± 22.3 μg m−2 day−1, respectively) and Ni (2.20 ± 1.35 ng mL−1 and 21.2 ± 4.79 μg m−2 day−1) close to the coal and ferronickel mining. The other metals showed higher concentrations in sites nearby the artisanal and small-scale gold mining communities; and mercury raises special concern because high values of bulk deposition were found (58.3 ± 4.4 μg m−2 day−1), suggesting an intense Hg exposure in local residents. Moreover, no patterns of temporal distribution of heavy metals deposition were found during the sampling period. Overall, these results suggest that trace metal concentrations and fluxes are comparable to other locations in the world that are impacted by regional anthropogenic sources related to mining activities.

Dust and associated geochemical fluxes in a firn core from coastal East Antarctica and its linkages with Southern Hemisphere climate variability over the last 50 years

High-resolution records of dust and trace element fluxes were studied in a firn core from the coastal Dronning Maud Land, representing the past 50 years, to understand the influence of recent climate variability on the transportation and accumulation of these components in East Antarctica. A doubling of dust flux was observed since 1985, coinciding with a shift in the Southern Annular Mode (SAM) index to more positive values. Strong positive correlation (r = 0.68; p < 10−8) observed between dust flux and the SAM suggests that the positive values of the SAM index are likely to be responsible for the recent increase in dust deposition over East Antarctica, through strengthening of westerly winds. NCEP/NCAR reanalysis data reveals that the polar easterlies consistently strengthened since 1985 at the study region, leading to the sinking of dust materials brought by the stronger westerlies. Significant inverse correlation (r = −0.42, p < 0.00004) between the dust flux and δ18O records (proxy for surface air temperature) further suggests that enhancement of the dust flux is taking place during winter periods, possibly due to the reduced moisture content and increased wind intensity. Interestingly, the timing and amplitude of the insoluble dust flux matched remarkably well with the trace metal fluxes of Ba, Cr, Cu, and Zn, confirming that dust was the main carrier of airborne geochemical tracers to East Antarctica in the recent past. The observed doubling of dust and associated trace metal deposition in East Antarctica have wide-ranging implications for understanding the factors driving the inter-continental transportation of impurities and their environmental impact on Antarctica.

Past atmospheric trace metal deposition in a remote lake (Lake Ngoring) at the headwater areas of Yellow River, Tibetan Plateau

A complete record derived from a core dated both by 210Pb and 137Cs chronologies from Lake Ngoring at the headwater areas of the Yellow River provides new insight into the changing atmospheric deposition of trace metals including Cd, Cr, Cu, Ni, Pb, and Zn. This study showed that there was an inflection in the early 1960s, before which both fluxes and contents of Cd, Ni, Pb, and Zn remained relatively steady or slowly increased, and thereafter continued increases both in fluxes and contents were found. Taking Pb as an example, the flux increased from 0.13 (before 1960) to 0.25 mg m−2 a−1 (averaged 1963–2006). According to atmospheric flux calculations using Al as a reference element, atmospheric fluxes of trace metals generally showed a rapid increase and peaked in recent years, closely following the historical economic development of the neighboring region, mainly for Qinghai and Gansu provinces. The atmospheric inventory for Zn was the highest, reaching 1.068 g m−2, while the lowest was for Cd, at only 0.079 gm−2. The percentage proportions of atmospheric deposition for Cd, Ni, and Zn were 37, 12, and 8.7 %, respectively. Hence, the atmospheric contribution to the trace metal content via long range transport is not negligible when considering input of materials to lake ecosystems.

Trace metal dynamics in the sediments of a constructed and natural urban tidal marsh: The role of iron, sulfide, and organic complexation

Two tidal marshes in the New Jersey Meadowlands, one constructed and one natural were characterized to compare their ability to immobilize trace metals (Cd, Cr, Cu, Mn, Pb, and Zn). Surface and pore waters were sampled four times a year between 2008 and 2010 and sediment cores were collected yearly in the constructed marsh and once in 2010 in the natural marsh. Interactions of trace metals with redox active species such as iron and sulfide as well as with organic matter were investigated. Precipitation with sulfides played a major role in immobilizing certain trace metals, including Cr, Mn, and Pb. At both sites, the presence of sulfide did not preclude the presence of dissolved trace metals in pore-water at concentrations exceeding their metal sulfide solubility product. Thermodynamic equilibrium modeling indicated these dissolved metals remained in solution due to an association with heterogeneous dissolved organic carbon. No net trace metal accumulation in the surficial sediments of the constructed marsh was noted between 2007 and 2010. This implied that a dynamic equilibrium of trace metal flux into and out of the sediments was established, rather than a long-term net accumulation of trace metals. In the constructed marsh, little difference was found between the immobilization potential in the area of intermittent flooding (high marsh) and the area of sustained flooding (low marsh). The newly constructed wetland immobilized significantly more Cr, Mn, and Zn than the natural marsh and similar concentrations of Cd, Cu, and Pb. This may be due to increased redox buffering through a larger FeS buffering pool against tidally induced oxygen delivery.

Chemistry of the heavily urbanized Bagmati River system in Kathmandu Valley, Nepal: export of organic matter, nutrients, major ions, silica, and metals

Water quality in less-developed countries is often subject to substantial degradation, but is rarely studied in a systematic way. The concentration and flux of major ions, carbon, nitrogen, silicon, and trace metals in the heavily urbanized Bagmati River within Kathmandu Valley, Nepal, are reported. The concentrations of all chemical species increased with distance downstream with the exceptions of protons and nitrate, and showed strong relationships with population density adjacent to the river. Total dissolved nitrogen (TDN), dominated by NH4, was found in high concentrations along the Bagmati drainage system. The export of dissolved organic carbon (DOC) and TDN were 23 and 33 tons km−2 year−1, respectively, at the outlet point of the Kathmandu Valley, much higher than in relatively undeveloped watersheds. The cationic and silica fluxes were 106 and 18 tons km−2 year−1 at the outlet of the Bagmati within Kathmandu Valley, and 36 and 32 tons km−2 year−1 from the relatively pristine headwater area. The difference between headwaters and the urban site suggests that the apparent weathering flux is three times higher than the actual weathering rate in the heavily urbanized Bagmati basin. Fluxes of cations and silica are above the world average, as well as fluxes from densely populated North American and European watersheds. End-member composition of anthropogenic sources like sewage or agricultural runoff is needed to understand the drivers of this high rate of apparent weathering.

Mercury and metals in South African precipitation

Even though mercury (Hg) is a global pollutant there are few studies of its concentration in the Southern Hemisphere, either in the atmosphere or in atmospheric deposition, and this is particularly true for Africa and developing nations such as South Africa. Emission inventories suggest that there is the potential for anthropogenic impact through elevated deposition in South Africa to sensitive ecosystems. To begin examining such impact, measurements of Hg and other trace metals (Al, Fe, Mn, Co, Ni, Cu, Zn, Cd and Pb) were made of rain collected using a bulk deposition collector at Cape Point, at the tip of Africa, and in Pretoria, a city within the industrial and mining heartland of South Africa. As expected, concentrations and fluxes were elevated in Pretoria, the more urban location. However, there is also evidence that Cape Point site can be impacted by regional pollution during the winter. The volume weighted mean Hg concentration at Cape Point was 10.6 ng L−1 compared to 15.8 ng L−1 in Pretoria. Comparison of rain concentrations for Hg and other metals, and relative fluxes (normalized to Al), indicate the importance of regional sources of contamination to both sites. The importance of impacted air masses at Cape Point was further investigated using ancillary data (CO and Rn) and back trajectory analysis. Overall, these results suggest that Hg and trace metal concentrations and fluxes are comparable to other locations in the world that are impacted by regional anthropogenic sources.

Significance of submarine groundwater discharge in the coastal fluxes of mercury in Hampyeong Bay, Yellow Sea

Submarine groundwater discharge (SGD) and various solutes released with SGD have received particular attention recently; however, understanding of the impact of SGD on trace metal fluxes in the coastal ocean is limited. To understand the contribution of SGD to the coastal Hg input, the Hg mass fluxes associated with SGD were estimated from Hampyeong Bay, a coastal embayment in the Yellow Sea. Hg concentrations in filtered groundwater and seawater ranged from 1.3 to 4.4pM and from 0.83 to 2.0pM, respectively, and Hg concentrations in unfiltered seawater ranged from 1.7 to 4.6pM. The Hg flux estimation showed that SGD was the prime input source of Hg in the bay (18±12molyr−1), contributing 65% of the total input. Atmospheric deposition was the second dominant source of Hg (8.5±2.7molyr−1), contributing 31% to the total input. The results of the current study suggest that SGD can be a significant source of Hg in estuarine/coastal systems; therefore, estimating the coastal mass budgets of Hg must include SGD as a prime source of Hg.

Mobilization of trace metals in a tropical turbid estuary influenced by a monsoon season

The selective removal of trace metals by suspended matter in high turbidity zones plays a major role in the fluvial transport of terrigenous metals to the marine environment. The seasonal longitudinal variability of trace elements (Cu, Zn, Cd, Ni, Pb, Fe, and Mn) in Cochin estuary, a tropical positive estuary, was studied and the results were compared with the prevailing situation in other subtropical waterways. The hydrodynamical features showed increasing turbidity downstream with increasing salinities during both the seasons. In contrast with the temperate estuaries where the development of turbidity maxima causes the removal of metals, the estuaries of tropics modify the fluvial transport of metals by the way of redistribution between the dissolved and particulate fractions in the intermediate salinities. In Cochin estuary, the distributional features of trace metals are primarily influenced by the variations in salinities and river discharges. Consequently, this gives rise to two different types of distributional patterns: (1) during premonsoon, the estuarine reactivity is more pronounced and hence, mid-estuarine solubilization of the particulate metal appears to play a prominent role in controlling the fluxes of trace metals studied and (2) but during monsoon, the hydrological conditions influence the downstream transport of the metals more by physical dilution than chemical reactivity.