308,409 research outputs found

    Tracing organic matter composition and distribution and its role on arsenic release in shallow Cambodian groundwaters

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    Biogeochemical processes that utilize dissolved organic carbon are widely thought to be responsible for the liberation of arsenic from sediments to shallow groundwater in south and southeast Asia. The accumulation of this known carcinogen to hazardously high concentrations has occurred in the primary source of drinking water in large parts of densely populated countries in this region. Both surface and sedimentary sources of organic matter have been suggested to contribute dissolved organic carbon in these aquifers. However, identification of the source of organic carbon responsible for driving arsenic release remains enigmatic and even controversial. Here, we provide the most extensive interrogation to date of the isotopic signature of ground and surface waters at a known arsenic hotspot in Cambodia. We present tritium and radiocarbon data that demonstrates that recharge through ponds and/or clay windows can transport young, surface derived organic matter in to groundwater to depths of 44 m under natural flow conditions. Young organic matter dominates the dissolved organic carbon pool in groundwater that is in close proximity to these surface water sources and we suggest this is likely a regional relationship. In locations distal to surface water contact, dissolved organic carbon represents a mixture of both young surface and older sedimentary derived organic matter. Ground-surface water interaction therefore strongly influences the average dissolved organic carbon age and how this is distributed spatially across the field site. Arsenic mobilization rates appear to be controlled by the age of dissolved organic matter present in these groundwaters. Arsenic concentrations in shallow groundwaters (< 20 m) increase by 1 μg/l for every year increase in dissolved organic carbon age compared to only 0.25 μg/l for every year increase in dissolved organic carbon age in deeper (> 20 m) groundwaters. We suggest that, while the rate of arsenic release is greatest in shallow aquifer sediments, arsenic release also occurs in deeper aquifer sediments and as such remains an important process in controlling the spatial distribution of arsenic in the groundwaters of SE Asia. Our findings suggest that any anthropogenic activities that alter the source of groundwater recharge or the timescales over which recharge takes place may also drive changes in the natural composition of dissolved organic carbon in these groundwaters. Such changes have the potential to influence both the spatial and temporal evolution of the current groundwater arsenic hazard in this region

    Dissolved organic matter contribution to rain water, throughfall and soil solution chemistry

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    A method is proposed to determine the acidbase properties of natural water samples containing relatively high amounts of dissolved organic matter. The electroneutrality principle as well as titration data are used to estimate the organic anion concentration in open field precipitation, throughfall and soil solutions, and to develop empirical models based on pH and dissolved organic carbon content. The organic acids dissolved in throughfall have a similar acidic site density but are weaker than those dissolved in soil solution, stream and lake waters. This method is usefull to determine the contribution of organic anions to the charge balance and to the buffering capacity of dissolved organic rich waters with low acid neutralizing capacity. It can be used also to determine the respective contribution of natural organics and anthropogenic minerals to the total acidity of throughfall and rain waters

    Determining inorganic and organic carbon

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    Carbon is the element which makes up the major fraction of lipids and carbohydrates, which could be used for making biofuel. It is therefore important to provide enough carbon and also follow the flow into particulate organic and potential loss to dissolved organic forms of carbon. Here we present methods for determining dissolved inorganic carbon, dissolved organic and particulate organic carbon.Peer reviewe

    Bacteriophages as a model for studying carbon regulation in aquatic system

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    The interconversion of carbon in organic, inorganic and refractory carbon is still beyond the grasp of present environmentalists. The bacteria and their phages, being the most abundant constituents of the aquatic environment, represent an ideal model for studing carbon regulation in the aquatic system. The refractory dissolved organic carbon (DOC), a recently coined terminology from the microbe-driven conversion of bioavailable organic carbon into difficult-to-digest refractory DOC by microbial carbon pump (MCP), is suggested to have the potential to revolutionize our view of carbon sequestration. It is estimated that about 95% of organic carbon is in the form of refractory DOC, which is the largest pool of organic matter in the ocean. The refractory DOC is supposed to be the major factor in the global carbon cycle whose source is not yet well understood. A key element of the carbon cycle is the microbial conversion of dissolved organic carbon into inedible forms. The time studies of phage-host interaction under control conditions reveal their impact on the total carbon content of the source and their interconversion among organic, inorganic and other forms of carbon with respect to control source. The TOC- analysis statistics stipulate an increase in inorganic carbon content by 15-25 percent in the sample with phage as compared to the sample without phage. The results signify a 60-70 fold increase in inorganic carbon content in sample with phage, whereas, 50-55 fold in the case of sample without phages as compared with control. This increase in inorganic carbon content may be due to lysis of the host cell releasing its cellular constituents and utilization of carbon constituent for phage assembly and development. It also proves the role of phages in regulating the carbon flow in aquatic systems like oceans, where their concentration outnumbered other species

    Terrestrial and fluvial carbon fluxes in a tropical watershed: Nyong basin, Cameroon

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    The Nyong watershed, with an area of 27 800 km2 and a mean annual discharge of 390 m3 s−1, is the second largest river in Cameroon. The Nyong watershed serves as an outstanding study area for the examination of carbon fluxes in humid tropical environments because of its limited anthropogenic impact and homogeneous silicate bedrock. Between April 2005 and April 2007, we sampled water at seven stations, from the small watershed of the Mengong (0.6 km2) to the Nyong at Edea (24 500 km2), and monitored temperature, pH, dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) contents, as well as the isotopic composition of DIC (δ13CDIC)andDOC(δ13CDOC).We estimated terrestrial net ecosystemproductivity in theNyong River watershed and measured fluvial fluxes of carbon to the ocean and the atmosphere. The Nyong River basin sequesters significant amounts of carbon on an annual basis: ~7 920 000t C year−1 (300 g C m−2 year−1). The combined dissolved organic, dissolved inorganic and atmospheric fluxes of carbon from the Nyong River only export 3% of this flux fromthe basin on an annual basis. This includes a minimumCO2 outgassing of 1487 g Cm−2 year−1, comparable to 115% of the annual flux of DOC and four times greater than the flux of DIC

    Spatial and temporal variation in degradation of dissolved organic carbon on the main stem of the Lamprey River

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    Degradation of dissolved organic carbon by microbial and photolytic processes was examined along the main stem of the Lamprey River Watershed located in southeastern New Hampshire. Eight sites were chosen and sampled biweekly throughout the seasonal hydrograph. Lab incubations were employed to assess microbial degradation of dissolved organic carbon (DOC) where one set of samples was exposed to natural sunlight for a day to assess photolytic degradation. Mean biodegradable dissolved organic carbon (BDOC) throughout the study period was 5.8% with no significant variation observed between sites. Temporal variation was found to be a much stronger driver of DOC composition with summer showing the highest degradation of 8.6% and winter the lowest. Initial DOC concentration was found to be the only significant positive predictor of BDOC on both an annual and seasonal scale. Photolysis had no significant effect on DOC degradation or availability of DOC to the microbial pool. Findings suggest that temporal variation is a significant driver of DOC composition via DOC sources that change throughout the season

    Short term effects of exposition to artificial ultraviolet radiation on Parabroteas sarsi (Copepoda, Calanoida)

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    The increase in the penetration of ultraviolet radiation that has been reported lately for freshwater ecosystems in southern South America would allegedly generate alterations in ecological processes. In this respect the mortality of Parabroteas sarsi, a calanoid copepod distributed in South American lakes and ponds, was studied. Specimens were reared at two different concentrations of dissolved organic carbon and subjected to 72 h exposure to artificial ultraviolet radiation. At high dissolved organic carbon concentration the mortality of P. sarsi increased at 24 h and stabilized at 48 and 72 h, whereas at low dissolved organic carbon concentration mortality increased linearly during the studied period. The results support both the description of a screen effect of dissolved organic carbon against ultraviolet radiation, and the potential photorepairing role of visible radiation that explains the increase of mortality in conditions of low dissolved organic carbon concentration

    Atmospheric CO2 consumption by continental erosion : present-day controls and implications for the last glacial maximum

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    The export of carbon from land to sea by rivers represents a major link in the global carbon cycle. For all principal carbon forms, the main factors that control the present-day fluxes at the global scale have been determined in order to establish global budgets and to predict regional fluxes. Dissolved organic carbon fluxes are mainly related to drainage intensity, basin slope, and the amount of carbon stored in soils. Particulate organic carbon fluxes are calculated as a function of sediment yields and of drainage intensity. The consumption of atmospheric/soil CO2 by chemical rock weathering depends mainly on the rock type and on the drainage intensity. Our empirical models yield a total of 0.721 Gt of carbon (Gt C) that is exported from the continents to the oceans each year. From this figure, 0.096 Gt C come from carbonate mineral dissolution and the remaining 0.625 Gt C stem from the atmosphere (FCO2). Of this atmospheric carbon, 33% is discharged as dissolved organic carbon, 30% as particulate organic carbon, and 37% as bicarbonate ions. Predicted inorganic carbon fluxes were further compared with observed fluxes for a set of 35 major world rivers, and possible additional climatic effects on the consumption of atmospheric CO2 by rock weathering were investigated in these river basins. Finally, we discuss the implications of our results for the river carbon fluxes and the role of continental erosion in the global carbon cycle during the last glacial maximum

    Assessment of leachable and persistent dissolved organic carbon in sludges and biosolids from municipal wastewater treatment plants

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    Environmental regulation of organic pollutants has not kept pace with the growth in the number and diversity of legacy and emerging organic substances now in use. Simpler and cheaper tools and methodologies are needed to quickly assess the organic pollutant risks in waste materials applied to land such as municipal wastewater treatment sludges and biosolids. This study attempts to provide these, using an approach that consists of chemical leaching and analysis of dissolved organic carbon and determination of its biodegradability by measuring persistent dissolved organic carbon. Primary and secondary sludges, dewatered sludge cake, and anaerobically and thermally treated biosolids obtained from various types of municipal wastewater treatment plants were used in the study. The study found little variability in the levels of dissolved organic carbon leached from primary sludges obtained from different municipal wastewater treatment plants but found significant differences for secondary sludges based on levels of nitrification at the municipal wastewater treatment plants. As predicted treated biosolids leached less dissolved organic carbon than untreated dry sludges but had relatively higher proportions of persistent or poorly biodegradable dissolved organic carbon. Across all tested sludges and biosolids persistent dissolved organic carbon ranged from 14 to 39%, with biosolids that have undergone anaerobic digestion and thermal treatment more likely to contain greater relative proportion of persistent dissolved organic carbon than untreated sludges. The approach presented in this study will be useful in assessing the effectiveness of current and widely employed sludge treatment methods in reducing persistent organic pollutants in biosolids disposed on land
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