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    Water Resources

  • UNDERSTAND

    Hydrological Processes

Hydrology

Water is the most precious resource for civilization and every person should expect access to a clean, safe water supply. Delivering this basic right, however, is not trivial where many of the poor live in water-stressed or polluted environments. Understanding the hydrogeological mechanisms of water flow through watersheds and groundwater systems is therefore essential in trying to secure the access to water that populations, agriculture, wildlife and industry need in order to prosper.

Stable oxygen and hydrogen analysis of environmental waters can provide a unique understanding and characterization of many hydrogeological systems. Determination of these isotopes gains understanding of reservoir residence times, groundwater recharge rates and mixing models. Stable isotopes analysis also helps constrain river basin dynamics in catchment hydrology to aid water management and develop strategies for extreme weather events and reducing the impact of droughts.

Analysis of groundwaters

Groundwater contains many components such as organics or salts. Using a headspace equilibration technique allows the oxygen-18 and hydrogen-2 isotopes to be analysed whist avoiding interference from these other components. Our iso FLOW system provides exceptional headspace analysis performance for these samples.

Fresh water samples

The fastest and simplest analysis of fresh water samples is via direct injection of the sample into a furnace system. Our vario PYRO cube Elemental Analyzer equipped with the vario LIQUID sampler allows oxygen-18 and hydrogen-2 isotope analysis separately or sequentially for the fastest throughput. Using our ChromeHD technique uniquely offers the highest precision hydrogen-2 measurement possible.

Dissolved elements

Beyond oxygen and hydrogen isotopes measurements, analysis of the dissolved organic carbon, inorganic carbon and organic nitrogen can provide valuable insight in to primary productivity in freshwater ecosystems as well as polluting anthropogenic inputs. Our new iso TOC cube is the only system able to analyse both carbon and nitrogen isotopes in water samples at low concentrations.

5 results:

Examining nitrogen dynamics in the unsaturated zone under an inactive cesspit using chemical tracers and environmental isotopes
Applied Geochemistry (2017)
Claudia Varnier, Ricardo Hirata, Ramon Aravena

This study evaluates the dynamics of nitrogen compounds generated by infiltration of wastewater from an inactive cesspit in the unconfined and sedimentary Adamantina Aquifer in Urânia, Brazil. A monitoring station, consisting of an 11.2 m well (1.8 m in diameter) with an array of 12 tensiometers and 12 suction lysimeters, was installed to monitor the shallow unsaturated zone from 0.5 to 9 m depth. A monitoring well was also installed below the water level to monitor the shallow aquifer. High amounts of ammonium (up to 96 mg/L NH4+-N) and nitrate (up to 458 mg/L NO3−-N) were observed in the unsaturated zone porewater which is comparable to active septic systems effluents. The distribution of NO3−, Cl− and Na+, typical constituents of sewage effluents, varied seasonally and spatially, which is correlated with changes in infiltration rates between the wet and dry seasons and with hydraulic conductivity variations in interlayered sandy and clayey sediments. A detailed monitoring of porewater geochemistry demonstrated the occurrence of several important reactions affecting nitrogen dynamics in the unsaturated zone: i) oxidation of organic matter, ii) ammonification, iii) nitrification, iv) methanogenesis, v) denitrification and likely, vi) sulfate reduction. The changes in nitrogen compound distribution and δ15NNO3 and δ18ONO3 values in porewater, in association with the N2O concentration and δ15NN2O and δ18ON2O signatures in gas samples, indicate the occurrence of nitrification and denitrification, suggesting the coexistence of reducing and oxidizing microsites in the unsaturated zone. This study indicated that cesspits can generate a significant amount of nitrate even a few years after being inactivated which can represent a potential long-term source of nitrate to groundwater in highly populated areas.

Examining nitrogen dynamics in the unsaturated zone under an inactive cesspit using chemical tracers and environmental isotopes
Applied Geochemistry (2017)
Claudia Varnier, Ricardo Hirata, Ramon Aravena

This study evaluates the dynamics of nitrogen compounds generated by infiltration of wastewater from an inactive cesspit in the unconfined and sedimentary Adamantina Aquifer in Urânia, Brazil. A monitoring station, consisting of an 11.2 m well (1.8 m in diameter) with an array of 12 tensiometers and 12 suction lysimeters, was installed to monitor the shallow unsaturated zone from 0.5 to 9 m depth. A monitoring well was also installed below the water level to monitor the shallow aquifer. High amounts of ammonium (up to 96 mg/L NH4+-N) and nitrate (up to 458 mg/L NO3−-N) were observed in the unsaturated zone porewater which is comparable to active septic systems effluents. The distribution of NO3−, Cl− and Na+, typical constituents of sewage effluents, varied seasonally and spatially, which is correlated with changes in infiltration rates between the wet and dry seasons and with hydraulic conductivity variations in interlayered sandy and clayey sediments. A detailed monitoring of porewater geochemistry demonstrated the occurrence of several important reactions affecting nitrogen dynamics in the unsaturated zone: i) oxidation of organic matter, ii) ammonification, iii) nitrification, iv) methanogenesis, v) denitrification and likely, vi) sulfate reduction. The changes in nitrogen compound distribution and δ15NNO3 and δ18ONO3 values in porewater, in association with the N2O concentration and δ15NN2O and δ18ON2O signatures in gas samples, indicate the occurrence of nitrification and denitrification, suggesting the coexistence of reducing and oxidizing microsites in the unsaturated zone. This study indicated that cesspits can generate a significant amount of nitrate even a few years after being inactivated which can represent a potential long-term source of nitrate to groundwater in highly populated areas.

D/H fractionation during the sublimation of water ice
Icarus (2016)
Christophe Lécuyer, Aurélien Royer, François Fourel, Magali Seris, Laurent Simon, François Robert

Experiments of sublimation of pure water ice have been performed in the temperature range -105°C to -30°C and atmospheric partial pressures ranging from 10−6 to 10−1 mb. Sampling of both vapour and residual ice fractions has been performed with the use of a vacuum line designed for the extraction and purification of gases before the measurement of their D/H ratios. Sublimation was responsible for sizable isotopic fractionation factors in the range 0.969 to 1.123 for temperatures lying between -105°C and -30°C. The fractionation factor exhibits a cross-over at temperatures around -50°C with the water vapour fraction being D-depleted relative to the residual ice fraction at T<-50°C (αice-vapour=0.969 to 0.995). This cross-over has implications for the understanding of the atmospheric water cycle of some terrestrial planets such as the Earth or Mars. The magnitude of deuterium enrichment or depletion between ice and water vapour cannot explain the differences in the D/H ratios amongst Jupiter comets and long–period comets families nor those that have been documented between Earth's and cometary water.

D/H fractionation during the sublimation of water ice
Icarus (2016)
Christophe Lécuyer, Aurélien Royer, François Fourel, Magali Seris, Laurent Simon, François Robert

Experiments of sublimation of pure water ice have been performed in the temperature range -105°C to -30°C and atmospheric partial pressures ranging from 10−6 to 10−1 mb. Sampling of both vapour and residual ice fractions has been performed with the use of a vacuum line designed for the extraction and purification of gases before the measurement of their D/H ratios. Sublimation was responsible for sizable isotopic fractionation factors in the range 0.969 to 1.123 for temperatures lying between -105°C and -30°C. The fractionation factor exhibits a cross-over at temperatures around -50°C with the water vapour fraction being D-depleted relative to the residual ice fraction at T<-50°C (αice-vapour=0.969 to 0.995). This cross-over has implications for the understanding of the atmospheric water cycle of some terrestrial planets such as the Earth or Mars. The magnitude of deuterium enrichment or depletion between ice and water vapour cannot explain the differences in the D/H ratios amongst Jupiter comets and long–period comets families nor those that have been documented between Earth's and cometary water.

The distribution of nitrogen speciation and sources of nitrate in the north of Taihu Lake
Environmental Earth Sciences (2016)
Da Li, Xia Jiang, Kun Wang, Binghui Zheng

Meiliang Bay and Gonghu Bay, in the north of Taihu Lake, are important water sources for the city of Wuxi, and increased eutrophication now threatens the safety of drinking water. The distribution of nitrogen (N) speciation and source of N in the surface waters in the north of Taihu Lake is studied, which was an important first step in controlling N pollution. The result shows that the average concentration of ammonia (NH4+) and nitrate (NO3−) of surface water in Meiliang Bay was 0.32 and 0.35 mg/L, while 0.21 and 0.74 mg/L of Gonghu Bay, in which both bays had serious nitrate pollution. The concentrations of NH4+ and NO3− in the surface water of the two bays had a trend of gradual decrease from north to south. The maximum concentrations of NH4+ and NO3− of two bays were observed near the inflowing rivers, and the maximum concentrations of NH4+ in surface water of two bays were 0.49 and 0.61, and 0.77 and 1.38 mg/L of NO3−. The concentration of NH4+ in the interstitial water of the two bays had a trend of gradual decrease from west to east, but NO3− had the opposite tendency. The maximum concentrations of NH4+ in the interstitial water of the two bays were 5.88 and 4.64, and 3.58 and 7.18 mg/L of NO3−. The exchangeable NH4+ content in the sediment of Meiliang Bay had a trend of gradual decrease from north to south, but Gonghu Bay showed the reverse. The exchangeable NO3− content in the sediment of Meiliang Bay had a trend of gradual decrease from east to west, but a decreasing trend from north to south was observed in Gonghu Bay. The maximum concentrations of exchangeable NH4+ were determined, and the values were 96.25 and 74.90 mg/kg, as well as NO3− with the values of 12.06 and 7.08 mg/kg. Chemical fertilizer and domestic sewage were the major sources of nitrate in surface water of Gonghu Bay, contributing 39.16 and 47.79%, respectively. Domestic sewage was the major source of nitrate in Meiliang Bay, contributing 84.79%. The denitrification process in Gonghu Bay was more apparent than in Meiliang Bay. Mixing and dilution processes had important effects on changing the concentration of nitrate transportation in the two bays.