Nitrogen isotope indicators of seasonal source variability to groundwater

 A nitrogen isotope study of soil water and groundwater in southern Indiana, USA, in 1991–1992 demonstrated considerable variations in nitrate degradation processes compared to an earlier investigation in 1986–1987. Although N-fertilizers were applied in May 1991, the δ¹⁵N values in soil water decreased in February 1992, indicating its delayed release into the system after substantial rainfall. The δ¹⁵N values of groundwater decreased from +12.3‰ in November 1991 to +11.3‰ in February 1992, and to +7.5‰ in March 1992. The increased residence time of nitrate in the soil resulted in increased denitrification, ammonia volatilization and plant uptake, and reduced threat to the groundwater quality. The 1986–1987 study in the area reported that excessive rainfall during the summer rapidly transported the nitrate to deeper horizons and drastically reduced volatilization and microbial reduction of nitrate, thus increasing the immediate threat to the groundwater quality in the area. The present study demonstrated that nitrogen isotopic signatures can be used to determine the effects of local soil type, rainfall, and land-use practices on the fate of nitrate in the subsurface. Received: 18 February 1997 · Accepted: 17 June 1997     

Amelioration of groundwater nitrate contamination following installation of a central sewage system in two Israeli villages

This study traces both the long-term deterioration of the ground water supply in two neighboring villages that had relied upon cesspits/cesspools for waste disposal, as well as the subsequent progressive improvement to original water quality levels. The rapid improvement is attributed to the replacement of the cesspits by a central sewage disposal network. In each of the villages of Kefar Bara and Kefar Kassem, a single, relatively deep, community well supplies drinking water. These wells were drilled into the underlying carbonate Judea Group aquifer that initially provided very high quality potable water. Over time, large increases in the nitrate contamination, reaching to as high as 67 mg/L nitrate, paralleled the population growth. The higher dissolved nitrate concentrations were also marked by enrichments in the δ¹⁵ N (approximately +8 ‰_(air)) values above those of the surrounding and regional uncontaminated background δ¹⁵ N values (in the range of +3 to +6 ‰ _(air)). Within several years after the cesspit disposal was terminated the nitrate values declined to concentrations that were reported (approximately 25 mg/L-NO₃) decades prior, when the water quality monitoring had just commenced. This study demonstrates not only how water quality can degrade but also how it can be restored once the problem is identified and countered. This simple method of ameliorating a water quality problem that was tending towards reaching serious proportions would seem to be quite efficacious for any area lacking economic alternative water resources.     

Groundwater nitrate contamination and risk assessment in an agricultural area,South Korea

The nitrate of groundwater in the Gimpo agricultural area, South Korea, was characterized by means of nitrate concentration, nitrogen-isotope analysis, and the risk assessment of nitrogen. The groundwaters belonging to Ca–(Cl + NO₃) and Na–(Cl + NO₃) types displayed a higher average NO₃ ⁻ concentration (79.4 mg/L), exceeding the Korean drinking water standard (<44.3 mg/L NO₃ ⁻). The relationship between δ¹⁸O–NO₃ ⁻ values and δ¹⁵N–NO₃ ⁻ values revealed that nearly all groundwater samples with δ¹⁵N–NO₃ ⁻ of +7.57 to +13.5‰ were affected by nitrate from manure/sewage as well as microbial nitrification and negligible denitrification. The risk assessment of nitrate for groundwater in the study area was carried out using the risk-based corrective action model since it was recognized that there is a necessity of a quantitative assessment of health hazard, as well as a simple estimation of nitrate concentration. All the groundwaters of higher nitrate concentration than the Korean drinking water standard (<44.3 mg/L NO₃ ⁻) belonged to the domain of the hazard index <1, indicating no health hazard by nitrate in groundwater in the study area. Further, the human exposure to the nitrate-contaminated soil was below the critical limit of non-carcinogenic risk.     

A geochemical survey of spring water from the main Ethiopian rift valley, southern Ethiopia: implications for well-head protection

The report discusses the stable isotope values and major solute compositions of 16 springs and river-water samples along a topographic gradient in the main rift valley of southern Ethiopia. Most of the springs used for drinking water supplies discharge from local flow systems at scales of only tens of meters. The δ¹⁸O and δD values of waters unaffected by shallow evaporation form a local meteoric water line of δD=8.1δ¹⁸O+19.0, almost identical to that for the eastern Mediterranean area. The δ¹⁸O values show an altitude effect of –0.5‰ per 100-m elevation rise. Total dissolved nitrogen concentrations locally exceed 6 mg/L (as N), and phosphate concentrations were elevated above background levels in some springs, exceeding 0.2 mg/L PO₄, probably due to agricultural practices upgradient of the springs. Modest well-head protection should be considered to protect public health from the effects of pollution by agricultural waste, given the very local scale of the flow systems providing spring water to Ethiopian villages. Electronic Publication     

Nitrogen-15 Isotope Enrichment in Benthic Boundary Layer Gases of a Stratified Eutrophic Iron and Manganese Rich Lake

The applicability of the natural abundance of nitrogen gas isotope ratios was used to indicate the spatial distribution of nitrogen transformations in the water column and sediment pore waters of Lake Ngapouri, a small (area 0.19 km²), monomictic, eutrophic lake in the Taupo Volcanic Zone, North Island, New Zealand. Samples were collected from the epilimnion, hypolimnion, benthic boundary layer and at 5-cm intervals from the sediment pore waters at monthly intervals for 1 year. Values of δ¹⁵N [N₂] ranged from −1 to 0.28‰ in the epilimnion, −1.5 to 1.25‰ in the hypolimnion, −1.8 to 12.2‰ in the benthic boundary layer and −0.7 to 3.5‰ in sediment pore waters. Values of δ¹⁵N [N₂] showed a strong seasonal pattern that was related to the loss of dissolved oxygen in the hypolimnion during seasonal stratification. Increases in ¹⁵N-enriched dinitrogen take place in the benthic boundary layer during the periods of anoxia (taken to be dissolved oxygen concentrations <6.3 μM) and may be related to abundant ammonium substrate (up to 275 μM) to support denitrification. Nitrate concentrations increased up to 36 μM with increasing duration of anoxia. We hypothesise that an alternative electron acceptor besides oxygen is required to support the nitrification needed for the production of nitrate. Iron and manganese hydroxides and oxides from material sedimenting out of the water column may have induced chemo-nitrification sufficient to oxidise ammonium in the anoxic benthic boundary layer. The nitrate formed would mostly be rapidly denitrified so that the δ¹⁵N [N₂] would continue to become enriched during the presence of anoxia, as observed in hypolimnion and benthic boundary layer of Lake Ngapouri. The changes in δ¹⁵N [N₂] values indicate the potential use of isotope ratios to identify and quantify potential chemo-nitrification/denitrification in the water column and sediment pore waters of lakes.     

Determining Spatial and Temporal Inputs of Freshwater,Including Submarine Groundwater Discharge,to a Subtropical Estuary Using Geochemical Tracers,Biscayne Bay,South Florida

Geochemical mixing models were used to decipher the dominant source of freshwater (rainfall, canal discharge, or groundwater discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and Sr²⁺/Ca²⁺ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ ¹⁸O = −2.66‰, δD −7.60‰) similar to rainfall (δ ¹⁸O = −2.86‰, δD = −4.78‰). Canal water had a heavy isotopic signature (δ ¹⁸O = −0.46‰, δD = −2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr²⁺/Ca²⁺ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr²⁺/Ca²⁺ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input ratio of canal/precipitation/groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of ±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1–2% of the total fresh and saline water input.     

Using chemical and microbiological indicators to track the impacts from the land application of treated municipal wastewater and other sources on groundwater quality in a karstic springs basin

Multiple chemical constituents (nutrients; N, O, H, C stable isotopes; 64 organic wastewater compounds, 16 pharmaceutical compounds) and microbiological indicators were used to assess the impact on groundwater quality from the land application of approximately 9.5 million liters per day of treated municipal sewage effluent to a sprayfield in the 960-km² Ichetucknee Springs basin, northern Florida. Enriched stable isotope signatures (δ¹⁸O and δ²H) were found in water from the effluent reservoir and a sprayfield monitoring well (MW-7) due to evaporation; however, groundwater samples downgradient from the sprayfield have δ¹⁸O and δ²H concentrations that represented recharge of meteoric water. Boron and chloride concentrations also were elevated in water from the sprayfield effluent reservoir and MW-7, but concentrations in groundwater decreased substantially with distance downgradient to background levels in the springs (about 12 km) and indicated at least a tenfold dilution factor. Nitrate-nitrogen isotope (δ¹⁵N–NO₃) values above 10 ‰ in most water samples were indicative of organic nitrogen sources except Blue Hole Spring (δ¹⁵N–NO₃ = 4.6–4.9 ‰), which indicated an inorganic source of nitrogen (fertilizers). The detection of low concentrations the insect repellent N,N-diethyl-metatoluamide (DEET), and other organic compounds associated with domestic wastewater in Devil’s Eye Spring indicated that leakage from a nearby septic tank drainfield likely has occurred. Elevated levels of fecal coliforms and enterococci were found in Blue Hole Spring during higher flow conditions, which likely resulted from hydraulic connections to upgradient sinkholes and are consistent with previoius dye-trace studies. Enteroviruses were not detected in the sprayfield effluent reservoir, but were found in low concentrations in water samples from a downgradient well and Blue Hole Spring during high-flow conditions indicating a human wastewater source. The Upper Floridan aquifer in the Ichetucknee Springs basin is highly vulnerable to contamination from multiple anthropogenic sources throughout the springs basin.     

Distribution and Trophic Importance of Anthropogenic Nitrogen in Narragansett Bay: An Assessment Using Stable Isotopes

Narragansett Bay has been heavily influenced by human activities for more than 200 years. In recent decades, it has been one of the more intensively fertilized estuaries in the USA, with most of the anthropogenic nutrient load originating from sewage treatment plants (STP). This will soon change as tertiary treatment upgrades reduce nitrogen (N) loads by about one third or more during the summer. Before these reductions take place, we sought to characterize the sewage N signature in primary (macroalgae) and secondary (the hard clam, Mercenaria mercenaria) producers in the bay using stable isotopes of N (δ¹⁵N) and carbon (δ¹³C). The δ¹⁵N signatures of the macroalgae show a clear gradient of approximately 4‰ from north to south, i.e., high to low point source loading. There is also evidence of a west to east gradient of heavy to light values of δ¹⁵N in the bay consistent with circulation patterns and residual flows. The Providence River Estuary, just north of Narragansett Bay proper, receives 85% of STP inputs to Narragansett Bay, and lower δ¹⁵N values in macroalgae there reflected preferential uptake of ¹⁴N in this heavily fertilized area. Differences in pH from N stimulated photosynthesis and related shifts in predominance of dissolved C species may control the observed δ¹³C signatures. Unlike the macroalgae, the clams were remarkably uniform in both δ¹⁵N (13.2 ± 0.54‰ SD) and δ¹³C (−16.76 ± 0.61‰ SD) throughout the bay, and the δ¹⁵N values were 2–5‰ heavier than in clams collected outside the bay. We suggest that this remarkable uniformity reflects a food source of anthropogenically heavy phytoplankton formed in the upper bay and supported by sewage derived N. We estimate that approximately half of the N in the clams throughout Narragansett Bay may be from anthropogenic sources.     

Oyster and Macroalgae Bioindicators Detect Elevated δ<Superscript>15</Superscript>N in Maryland’s Coastal Bays

Nitrogen loading from anthropogenic sources, including fertilizer, manure, and sewage effluents, has been linked with declining water quality in coastal lagoons worldwide. Freshwater inputs to mid-Atlantic coastal lagoons of the USA are from terrestrially influenced sources: groundwater and overland flow via streams and agricultural ditches, with occasional precipitation events. Stable nitrogen isotopes ratios (δ¹⁵N) in bioindicator species combined with conventional water quality monitoring were used to assess nitrogen sources and provide insights into their origins. Water quality data revealed that nutrients derived from terrestrial sources increased after precipitation events. Tissues from two bioindicator species, a macroalgae (Gracilaria sp.) and the eastern oyster (Crassostrea virginica) were analyzed for δ¹⁵N to determine spatial and temporal patterns of nitrogen sources. A broad-scale survey assessment of deployed macroalgae (June 2004) detected regions of elevated δ¹⁵N. Macroalgal δ¹⁵N (7.33 ± 1.15‰ in May 2006 and 6.76 ± 1.15‰ in July 2006) responded quickly to sustained June 2006 nutrient pulse, but did not detect spatial patterns at the fine scale. Oyster δ¹⁵N (8.51 ± 0.89‰) responded slowly over longer time periods and exhibited a slight gradient at the finer spatial scale. Overall, elevated δ¹⁵N values in macroalgae and oysters were used to infer that human and animal wastes were important nitrogen sources in some areas of Maryland’s coastal bays. Different nitrogen integration periods across multiple organisms may be used to indicate nitrogen sources at various spatial and temporal scales, which will help focus nutrient management.     

Plankton and dissolved inorganic carbon isotopic composition in a river-dominated estuary: Apalachicola Bay, Florida

To characterize the isotopic composition of organisms at the base of the food web and the controls on their variability, the concentration and δ¹³C isotopic composition of dissolved inorganic carbon (DIC) and plankton δ¹³C, δ¹⁵N, and δ³⁴S were measured. The measurements were made during periods of high and low river flow in Apalachicola Bay, Florida, United States, over 3 yr. DIC concentration and δ¹³C values were related to salinity, indicating that conservative mixing of riverine and marine waters was responsible for the overall distributions. The usefulness of DIC δ^13C data for characterizing the trophic processes within the estuary was dependent upon the residence time of water within the season. Plankton δ¹³C values varied from −22‰ to −30‰ and were directly related to estuarine DIC δ¹³C, offset by a factor of roughly −20‰. This offset factor varied with salinity. Values of δ³⁴S in estuarine plankton (station means ranged from 11.4‰ to 13.1‰) were depleted relative to marine plankton (17.7±0.4‰) possibly due to the admixture of³⁴S-depleted sedimentary sulfide with estuarine samples. Values of δ³⁴S in plankton were not related to δ¹³C values of plankton and were only weakly correlated to the salinity of the water from which the plankton were collected, indicating that marine sulfate was the primary source of planktonic sulfur. Values of δ¹⁵N in plankton varied from 5.5‰ to 10.7‰ and appeared related to dominance of the sample by phytoplankton or zooplankton. Estuarine plankton was¹⁵N enriched relative to offshore plankton and estuarine sediment.     

Sulphate Sources in the Sava and Ljubljanica Rivers, Slovenia, Inferred from Sulphur and Oxygen Isotope Compositions

Measurements were made of sulphur and oxygen isotope ratios of sulphate in some Slovenian rivers, lakes and tap waters. δ³⁴S ranged from −0.2 to + 13.3‰, δ¹⁸O ranged from +4.9 to + 13.6‰, and the sulphate content varied from 0.8 to 41.4 mg/L. Rivers flowing from the Julian Alps contain a very low amount of sulphate that is leached from a thin horizon of soil by rain. As confirmed by their low δ¹⁸O values, these sulphates do not enter the rivers directly in rain, but arise from biochemical cycling in the soil. The low δ³⁴S of this sulphate indicates that it originates from the oxidation of sedimentary sulphides. The evolution of sulphates along the river course was investigated for the Sava and Ljubljanica rivers. The variations observed in sulphate from the waters studied result from variations in the contribution of sulphates of different origin. Downstream the Sava River sulphate is depleted in the heavy isotopes of both sulphur and oxygen, with δ-values gradually tending toward the δ-values of groundwater sulphates in the watershed. In contrast, the δ-values of sulphate in the Ljubljanica River are almost constant and similar to those of sulphate in local groundwater. Introduction of water from Italian and Slovenian mines was recorded in the Soča River, where the lowest δ³⁴S value of sulphate sulphur (−0.2‰) was observed. In addition, the influence of sulphate from the oxidation of sedimentary sulphides was recorded in the Sotla River. No evidence was found for introduction of sulphate from factories.     

Water—Rock Interaction in Tarim Basin：Constraints from Oilfield Water Geochemistry

Olifeld waters from Cenoxoic and Mesozoic terrestrial and Paleozoic marine environments in the Tarim Basin show no obvious difference in water chemistry except Br and isotopic compositions.The Paleozoic marine strata have higher Br concentrations than the terrestrial sediments,and the lack of obvious relationship between Br and I suggests that Br is not,for the most part,derived from the degradation of organic matter.The oilfield waters are characterized by high TDS(total dissolved solids),ranging from 120000mg/L to 320000mg/L relatively low Mg,high Ca,Sr,and CF relative to Br of evaporating seawater,suggestive of enhanced water-rock interaction,OAA(organic acid anions)concentrations are generally lower than 1500mg/L with high values occurring over the temperature range from 95℃ to 140℃,in the Cambrian to Jurassic systems,and nearby unconformities.Organic acids are considered to be generated mainly from thermal maturation of kerogens during progressive burial of the Jurassic-Triassic and Cambrian-Ordovician systems,biodegradation of crude oils nearby unconformities,and thermochemical sulfate reduction in part of the Cambrian and Ordovician strata.High Al concentrations up to 3mg/L to 5.5mg/L tend to occur in the waters of high OAA or petroleum-bearing intervals,suggesting the presence of organic complexing agents.Calculation by SOLMINEQ.88 with updated database shows that AlAc^2 may account for more than 30% of the total Al.Isotopic measurements(δD,δ18O)provide evidence for the following types of waters:diagenetically-modified connate meteoric water from the Jurassic and Triassic strata;diagenetically-modified connate marine water from the Cambrian and Ordovician strata;subaerially-evaporated water from the Cenozoic and Cretaceous strata;and mixed meteoric-evaporated or/and diagenetically modified connate water from the Carboniferous strata and reservoirs adjacent to the J/C and T/C unconformities.Those waters with very negative δD values from -51.30‰to-53.80‰(SMOW) and positive δ18O values from 2.99‰to 4.99‰(SMOW)in the continuous burial of the Cambrian-Ordovician system are explained to have resulted from hydrocarbon-water and water-rock interactions.     

The application of δ13C and C/N ratios as indicators of organic carbon sources and paleoenvironmental change of the mangrove ecosystem from Ba Lat Estuary, Red River, Vietnam

In this study, two sediment cores (~70 cm) were collected from separate mangrove forests straddling the Ba Lat Estuary, Red River of northern Vietnam, to examine the origins of sedimentary organic carbon (SOC) and reconstruct the paleoenvironment. In addition, mangrove leaves and particulate organic matter were collected and measured for δ¹³C to trace the origins of SOC. The cores were analyzed by high-resolution sections for δ¹³C, TOC, C/N ratios, sediment grain size, water content, and porosity, with values of δ¹³C, TOC, and C/N ratios ranging from −28.19 to −22.5‰, 2.14–30.94 mg/g, and 10.29–18.32, respectively. The δ¹³C and TOC relationship indicated that there were some small residual effects of diagenetic processes on TOC and δ¹³C values in mangrove sediments. However, the shifts of δ¹³C and C/N ratios from the bottom to the surface sediment of the cores explained the change in organic matter sources, with values of C/N > 12 and δ¹³C < −25‰, and C/N < 12 and δ¹³C > −25‰ indicated terrestrial (e.g., mangrove litter) and marine phytoplankton sources, respectively. The covarying δ¹³C, C/N ratios, and sediment grain sizes during the past 100 years in sediment cores showed that the paleoenvironment may be reconstructed into three environments (subtidal, tidal flat, and intertidal mangrove). General trends in δ¹³C and C/N followed a gradual increase in the C/N ratio and a concomitant decrease in δ¹³C from the subtidal, through to tidal flat, and to the intertidal mangrove. δ¹³C and C/N ratios are therefore effective in measuring the continuum of environmental change in mangrove ecosystem.     

Spatio-temporal variations of δ<Superscript>2</Superscript>H and δ<Superscript>18</Superscript>O in precipitation and shallow groundwater in the Hilly Loess Region of the Loess Plateau,China

Groundwater is of utmost significance to socio-economic development and ecological recovery for the Loess Plateau. However, studies regarding the mechanism governing groundwater recharge over this area appear to be inadequate. This study is to examine the spatio-temporal variations of δ²H and δ¹⁸O in precipitation and shallow groundwater. On the basis of this, the mechanisms governing shallow groundwater recharge were explored. Precipitation and groundwater were sampled monthly from May to October during the period 2004–2006 at 13 sites in the Chabagou Catchment (187 km²). In the Caopingxigou Experimental Watershed (0.1 km²), meteorological variables were observed and rainfall larger than 5 mm was sampled immediately after each rain event. Across the area, 90% of the precipitation occurred from May to September primarily in the form of heavy rains or rainstorms with great spatial variability. There were about 30 localized rains in each year. It was indicated that there existed notable seasonality and pronounced spatial variability in precipitation isotopic compositions. Contributing factors and indications of isotopic compositions, as well as their climatic indications such as monsoon intensities and mixing processes of water vapor, were investigated. The δ²H–δ¹⁸O relation of groundwater was found to be δ²H = 3.22 × δ¹⁸O − 38.1, deviating from the local meteoric water line δ²H = 7.57 × δ¹⁸O + 3.9. The range of δ values in groundwater is shrunken to be 15–21% of that in individual precipitations, and groundwater in the middle reaches shows a wider range of δ values. Isotopic results showed that groundwater originates from precipitation with hydrogen and oxygen isotopic compositions being −69 and −9.7‰, respectively, and most groundwater experiences serious evaporation and adequate mixing with old water during infiltration or percolation in the aerated zone. It was also founded that obvious fluctuations of isotopic compositions in groundwater mainly appear in the middle reaches especially at sites that are close to valleys, suggesting varying sources of groundwater from precipitation, precipitation runoff, isotopically enriched surface water and/or lateral recharge of adjacent groundwater.     

Isotopic Approach to Determining the Fate of Ammonium Regenerated from Sediments in a Eutrophic Sub-estuary of Waquoit Bay,MA

We measured fluxes of NH₄⁺ and NO₃⁻ and δ¹⁵N of NH₄⁺, sediment, and porewater NH₄⁺ from incubated sediment cores along a nitrate gradient and in different seasons from Childs River, MA. NH₄⁺ flux was low at the downstream site with the lowest concentration of organic matter (high salinity) but otherwise did not differ along the estuary. The δ¹⁵N of regenerated NH₄⁺ ranged from +6.1‰ to +15.3‰ but did not vary significantly with season or salinity; the mean for the entire estuary was +10.4 ± 0.5‰. Based on differences between the δ¹⁵N of regenerated NH₄⁺ and sediment, and expected isotopic fractionation due to remineralization, we concluded that nitrification occurred after remineralization of NH₄⁺. Differences between the δ¹⁵N of regenerated NH₄⁺ and the δ¹⁵N of porewater NH₄⁺ provided further evidence of nitrification. We estimated that 11% to 48% of remineralized NH₄⁺ underwent coupled nitrification–denitrification before release into the water column. In spite of losses to denitrification, NH₄⁺ flux released 1.4 mol N m⁻² year⁻¹ to the water column and could provide 42% of phytoplankton nitrogen requirements.     

Isotopic composition of dissolved boron and its geochemical behavior in a freshwater-seawater mixture at the estuary of the Changjiang （Yangtze） River

The isotopic composition of dissolved boron, in combination with the elemental concentrations of B, Cl and salinities in freshwater-seawater mixed samples taken from the estuary of the Changjiang River, the largest one in China, was investigated in detail in this study. Brackish water and seawater samples from the estuary of the Changjiang River were collected during low water season in November, 1998. Boron isotopic compositions were determined by the Cs2BO^＋2-graphite technique with a analytical uncertainty of 0.2‰ for NIST SRM 951 and an average analytical uncertainty of 0.8‰ for the samples. The isotopic compositions of boron, expressed in δ^11B, and boron concentrations in the Changjiang River at Nanjing and seawater from the open marine East Sea, China, are characterized by δ^11B values of -5.4‰ and 40.0‰, as well as 0.0272 and 4.43 mg B/L, respectively. Well-defined correlations between δ^11B values, B concentrations and Cl concentrations are interpreted in terms of binary mixing between fiver input water and East Sea seawater by a process of straightforward dilution. The offsets of δ^11B values are not related to the contents of clastic sediment and to the addition of boron. These relationships favor a conservative behavior of boron at the estuarine of the Changjiang River.     

Hydrogeochemistry,environmental isotopes and the origin of the Hamamayagi-Ladik thermal spring (Samsun,Turkey)

Hamamayagi thermal spring (HTS) is located along the North Anatolian Fault Zone. The thermal spring has a temperature of 36°C, with total dissolved solids ranging from 485.6 to 508.5 mg/L. Hard, brittle, and gray limestones Permian aged are the reservoir rocks of the HTS. δ¹⁸O–δ²H isotope ratios clearly indicate a meteoric origin for the waters. The δ³⁴S value of sulfate in the thermal water is nearly 4.1‰ and implies a diagenetic environment characterized by reduced sulfur compounds. The δ¹³C ratio for dissolved inorganic carbonate in the HTS lies between −1.78 and −1.62‰, showing that it originates from the dissolution of fresh-water carbonates. Quartz geothermometry suggests a reservoir temperature of 52–85°C for the Hamamayagi geothermal field, but chalcedony geothermometers suggest reservoir temperatures between 30 and 53°C.     

The origin of high δ<Superscript>18</Superscript>O zircons: marbles,megacrysts, and metamorphism

The oxygen isotope ratios (δ¹⁸O) of most igneous zircons range from 5 to 8‰, with 99% of published values from 1345 rocks below 10‰. Metamorphic zircons from quartzite, metapelite, metabasite, and eclogite record δ¹⁸O values from 5 to 17‰, with 99% below 15‰. However, zircons with anomalously high δ¹⁸O, up to 23‰, have been reported in detrital suites; source rocks for these unusual zircons have not been identified. We report data for zircons from Sri Lanka and Myanmar that constrain a metamorphic petrogenesis for anomalously high δ¹⁸O in zircon. A suite of 28 large detrital zircon megacrysts from Mogok (Myanmar) analyzed by laser fluorination yields δ¹⁸O from 9.4 to 25.5‰. The U–Pb standard, CZ3, a large detrital zircon megacryst from Sri Lanka, yields δ¹⁸O = 15.4 ± 0.1‰ (2 SE) by ion microprobe. A euhedral unzoned zircon in a thin section of Sri Lanka granulite facies calcite marble yields δ¹⁸O = 19.4‰ by ion microprobe and confirms a metamorphic petrogenesis of zircon in marble. Small oxygen isotope fractionations between zircon and most minerals require a high δ¹⁸O source for the high δ¹⁸O zircons. Predicted equilibrium values of Δ¹⁸O(calcite-zircon) = 2–3‰ from 800 to 600°C show that metamorphic zircon crystallizing in a high δ¹⁸O marble will have high δ¹⁸O. The high δ¹⁸O zircons (>15‰) from both Sri Lanka and Mogok overlap the values of primary marine carbonates, and marbles are known detrital gemstone sources in both localities. The high δ¹⁸O zircons are thus metamorphic; the 15–25‰ zircon values are consistent with a marble origin in a rock-dominated system (i.e., low fluid_(external)/rock); the lower δ¹⁸O zircon values (9–15‰) are consistent with an origin in an external fluid-dominated system, such as skarn derived from marble, although many non-metasomatized marbles also fall in this range of δ¹⁸O. High δ¹⁸O (>15‰) and the absence of zoning can thus be used as a tracer to identify a marble source for high δ¹⁸O detrital zircons; this recognition can aid provenance studies in complex metamorphic terranes where age determinations alone may not allow discrimination of coeval source rocks. Metamorphic zircon megacrysts have not been reported previously and appear to be associated with high-grade marble. Identification of high δ¹⁸O zircons can also aid geochronology studies that seek to date high-grade metamorphic events due to the ability to distinguish metamorphic from detrital zircons in marble.     

Tracing infiltration and recharge using stable isotope in Taihang Mt., North China

The groundwater in headwater region is an important recharge source for the adjacent mountain-front plain. In order to reveal the relationship among precipitation, soil water and groundwater, from June to September in 2004, stable isotopes (deuterium and oxygen-18) in precipitation and soil waters at the depths of 10, 20, 30, 50, 70, 90, and 110 cm were analyzed at two sites covered by black locust (Robinia Pseudoacia L.) (Site A) and grass predominated by Themeda triandra (T. japonica (Willd.) Tanaka) and Bothriochloa ischaemum (B. ischaemum (L.) Keng) (Site B) in an experimental catchment at Taihang Mt., North China, respectively. The δ¹⁸O of precipitation in daily rain events shows large variations (−13.3 to −4.3‰) with a mean of 8.1‰. The δ¹⁸O and δ D of soil waters along profiles in two sites suggest that the influence of canopy cover was just up to 10 cm in top soil water. The soil water moved over the zero flux plane at 70 cm in-depth is expected to escape the evaporative effect at the end of September in both sites. The results show that the stable isotope, instead of tritium as tradition, can be used to trace the soil water behaviors based on the movement of isotopic peak along the vertical profiles in this semi-arid and semi-humid mountainous region. The infiltration depths of soil water in Taihang Mt. are 12 and 10 mm/day from June to September in 2004 in Site A and Site B, respectively. Tracing by stable isotope, recharge fluxes of soil water to local groundwater are of 3.8 and 3.2 mm/day in Site A and Site B, respectively. The results provide desirable information for assessment of local groundwater resources. An erratum to this article can be found at