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

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

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

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)

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

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

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

Water Quality and Algal Diversity of Ten Lakes Along the Mountain Loop Highway, Washington

Water quality parameters, watershed characteristics and algal diversity and abundance were compared in ten lakes along the Mountain Loop Highway in Washington State. Water samples were collected in July and August 2014 and analyzed for temperature, dissolved oxygen, alkalinity, conductivity, pH, turbidity, chlorophyll, total phosphorous, total nitrogen, soluble reactive phosphorous, nitrate + nitrite, silica, chloride, sulfate, total organic carbon, dissolved organic carbon and total and dissolved metals (aluminum, antimony, arsenic, barium, beryllium, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, molybdenum, nickel, potassium, selenium, silver, sodium, thallium, thorium, uranium, vanadium and zinc). The watershed characteristics measured were elevation, lake surface area, watershed area, watershed slope, evergreen coverage and primary watershed geology. Live algae were collected and identified to the lowest practical taxonomic level to create a presence/absence species list. Additional algal samples were collected and preserved with Lugol’s iodine and settled for enumeration and biovolume calculations. The lakes in this study had relatively warm temperatures (11-27 °C), high dissolved oxygen concentrations (7-11 mg/L), relatively low alkalinities (\u3c 27 mg/L) and conductivities (\u3c 58 μS/cm) and were at circumneutral pH or basic pH (6.1-7.9). Five lakes were oligotrophic, four lakes were mesotrophic and one lake was eutrophic. Many nutrient and metal concentrations were below detection levels. Dissolved organic carbon concentrations formed two distinct groups of lakes: relatively high dissolved organic carbon (\u3e2.0 mg/L) and relatively low dissolved organic carbon (\u3c 2.0 mg/L). A total of 405 different algal taxa were identified from the ten lakes, of which 256 taxa were unique to an individual lake. Desmids and diatoms represented the majority of the taxa (136 taxa and 101 taxa, respectively). Cyanobacteria dominated the numerical abundance of the ten lakes, representing 86% of the total cell counts. Algal biovolume was dominated by the “other” category, which represented 77% of the total biovolume. Watershed slope was positively correlated with dissolved oxygen and negatively correlated with temperature, total phosphorous, total nitrogen, dissolved organic carbon and desmid counts. These correlations were a result of watershed morphology. Non-parametric cluster analysis created two clusters of lakes that corresponded to the high and low dissolved organic carbon groups. The two clusters of lakes had many differences in water quality, watershed characteristics and algal species richness and taxonomic diversity. The high dissolved organic carbon lakes had gradually sloped watersheds, well-developed shoreline vegetation, relatively high nutrient concentrations and high desmid diversity; the low dissolved organic carbon lakes had steep, rocky watershed slopes, little or no apparent littoral vegetation, relatively low nutrient concentrations and low desmid diversity

EURO-ECOLE: Assessment of the Bioavailability and Potential Ecological Effects of Copper in European Surface Waters ; subproject 4: Evaluation and improvement of the ecological relevance of laboratory generated toxicity data

This report summarizes the acute and chronic toxicity of copper to algae, Daphnia and a few other freshwater species in standard laboratory test water and a wide range of natural surface waters (collected across Europe), with a wide range of pH, dissolved organic carbon (DOC) concentration and hardness. These data can be used for validation of bioavailability models such as the biotic ligand model (BLM)

Carbon Dynamics in Aquatic Ecosystems in Response to Elevated Atmospheric CO2 and Altered Nutrients Availability

Aquatic ecosystems will experience altered inorganic carbon, nitrogen and phosphorous availability in the future due to elevated atmospheric CO2, stronger stratification and anthropogenic activities. Despite its importance in modulating global carbon cycles, how carbon dynamics in aquatic ecosystem response to the future global change remains largely unknown. Here we performed a chemostat experiment to study how equilibrium carbon dynamics response to elevated CO2 and altered N, P availability. Our results show that elevated CO2 led to enhanced photosynthetic carbon uptake and dissolved organic carbon (DOC) production. DOC occupied larger percentage in total organic carbon production in high CO2 environment. N addition stimulated biomass carbon accumulation. Collectively, in the future, high CO2 and low nutrient availability lead to high C: nutrient ratio in both biomass and dissolved organic carbon. It indicates a possible change in nutrient limitation and increase in recalcitrant dissolved organic carbon as long term carbon sequestration. Total carbon consumption remains unclear and will depend on the net effects of depleted nutrients and elevated CO2