δ18O characteristics of lichens and their effects on evaporative processes of the subjacent soil

The study presents first data on the δ¹⁸O performance of poikilohydrous lichen ground cover, and its potential impact on the isotopic composition of water fluxes arising from subjacent soil layers. As a model organism, the globally distributed lichen Cladina arbuscula was studied under laboratory conditions as well as in the field. During a desiccation experiment, δ¹⁸O of the lichen's thallus water and of its respired CO₂ became enriched by ～7‰ and followed a similar enrichment pattern to that expected from homoiohydrous, vascular plants. However, the observed degree of enrichment was lower in comparison to vascular plants due to (i) the lichen's inherent lower evaporative resistances; and (ii) a stronger effect of the more depleted surrounding water vapour. In lichens growing in their natural habitat, this specific pattern may show substantial variations depending on prevailing microclimatic conditions. Within a field study, thallus water δ¹⁸O of lichens principally proved to become more depleted when close to equilibration with the surroundings. It thereby strongly depended on the absorption of surrounding water vapour. Moreover, the results indicate that lichen mats substantially reduce evaporation rates arising from subjacent soil layers, and may alter the isotopic signal of vapour diffusing away from these layers into more depleted values.     

Tree species of the Central Amazon and soil moisture alter stable isotope composition of nitrogen and oxygen in nitrous oxide evolved from soil

The use of stable isotopes of N and O in N2O has been proposed as a way to better constrain the global budget of atmospheric N2O and to better understand the relative contributions of the main microbial processes (nitrification and denitrification) responsible for N2O formation in soil. This study compared the isotopic composition of N2O emitted from soils under different tree species in the Brazilian Amazon. We also compared the effect of tree species with that of soil moisture, as we expected the latter to be the main factor regulating the proportion of nitrifier- and denitrifier-derived N2O and, consequently, isotopic signatures of N2O. Tree species significantly affected delta15N in nitrous oxide. However, there was no evidence that the observed variation in delta15N in N2O was determined by varying proportions of nitrifier- vs. denitrifier-derived N2O. We submit that the large variation in delta15N-N2O is the result of competition between denitrifying and immobilizing microorganisms for NO3(-). In addition to altering delta15N-N2O, tree species affected net rates of N2O emission from soil in laboratory incubations. These results suggest that tree species contribute to the large isotopic variation in N2O observed in a range tropical forest soils. We found that soil water affects both 15N and 18O in N2O, with wetter soils leading to more depleted N2O in both 15N and 18O. This is likely caused by a shift in biological processes for 15N and possible direct exchange of 18O between H2O and N2O.     

Nitrate degradation without 15N enrichment: a hydrochemical and isotopic study of a fractured rock aquifer including embedded lakes

Water samples from three quarry lakes and the surrounding fractured rock aquifer were investigated for delta18O and delta2H (H2O), delta15N and delta18O (NO3-), as well as anions and cations. Lake water and groundwater can be distinguished by their different chemical and isotopic composition. Because of evaporation processes, 18O and 2H are enriched in the lake water and can be used as natural tracers for the water dynamic of the lakes. The groundwater is characterised by high nitrate concentrations (up to 120 mg/l). Lake internal processes reduce the nitrate concentration in the quarry lakes. However, no enrichment of delta15N and delta18O in nitrate, typical for microbial nitrate degradation, is observed in the lake water. Because of the complex flow paths in the fractured rock aquifer and the intense chemical transformations at the interface between groundwater and lake water, isotopic and hydrochemical data of lake water and groundwater alone do not conclusively explain hydrological and hydrochemical processes of the investigated lake-groundwater system.     

Stable isotope study of precipitation and cave drip water in Florida (USA): implications for speleothem-based paleoclimate studies

Stable isotopes of hydrogen and oxygen were used to examine how the isotopic signal of meteoric water is modified as it travels through soil and epikarst into two caves in Florida. Surface and cave water samples were collected every week from February 2006 until March 2007. The isotopic composition of precipitation at the investigated sites is highly variable and shows little seasonal control. The delta18O vs. delta2H plot shows a mixing line having a slope of 5.63, suggesting evaporation effects dominate the isotopic composition of most rainfall events of less than 8 cm/day, as indicated by their low d-excess values. The delta18O values of the drip water show little variability (<0.6 per thousand), which is loosely tied to local variations in the seasonal amount of precipitation. This is only seen during wintertime at the Florida Caverns site. The lag time of over two months and the lack of any relationship between rainfall amount and the increase in drip rate indicate a dominance of matrix flow relative to fracture/conduit flow at each site. The long residence time of the vadose seepage waters allows for an effective isotopic homogenisation of individual and seasonal rainfall events. We find no correlation between rainfall and drip water delta18O at any site. The isotopic composition of drip water in both caves consistently tends to resemble the amount-weighted monthly mean rainfall input. This implies that the delta18O of speleothems from these two caves in Florida cannot record seasonal cycle in rainfall delta18O, but are suitable for paleoclimate reconstructions at inter-annual time scales.dagger.     

Direct equilibration of soil water for delta(18)O analysis and its application to tracer studies

Current methods for stable oxygen isotopic (delta (18)O) analysis of soil water rely on separation of water from the soil matrix before analysis. These separation procedures are not only time consuming and require relatively large samples of soil, but also have been shown to introduce a large potential source of error. Current research at Queen's University Belfast is focused on using direct equilibration of CO(2) with the pore water to eliminate this extraction step using the automated Multiprep system and a Micromass Prism III isotope ratio mass spectrometer (IRMS). The findings of this research indicate the method is less time consuming, more reliable, and reproducible to within accepted limits (+/-0.1% per thousand delta (18)O). In this study the direct equilibration method is used to analyse delta (18)O tracer profiles in the unsaturated zone of field soils, concurrently with chloride tracer profiles, which can be used to assess infiltration rates and mechanisms through the unsaturated zone. Copyright 1999 John Wiley & Sons, Ltd.     

Mbaka lakes isotopic ((18)O and (2)H) and water balances: discussion on the used atmospheric moisture compositions

The water balances of small crater lakes Masoko, Katubwi, Kyambangunguru, Ilamba, Kingiri, located north of lake Malawi (Tanzania), are established with the Craig-Gordon model of evaporation. In this approach, it is difficult to evaluate the isotopic composition of evaporated vapour (deltaE), which is indirectly estimated from the atmospheric moisture signature (deltaA). Given that 'precipitation equilibrium' approach does not lead to realistic solutions in this tropical region, the lake balances are established and discussed from both the sampled deltaA and those derived from the terminal lake Rukwa. The mean local sampled signature (deltaAm : delta(18)O =-13.7per thousand and delta(2)H =-76per thousand) is inferior to that derived from lake Rukwa (deltaAtl : delta(18)O =-10.4per thousand and delta(2)H =-64per thousand), which may be due to altitudinal and latitudinal effects but both are influenced by recycling continental vapour. Water balances enable us to confirm and quantify high inflows and groundwater outflows that account for typologies of Mbaka lakes. The proposed sampling and measurement method allows us then to access reasonable moisture compositions in far-away regions.     

Saisonale Variation von Deuterium und Sauerstoff-18 in Luftfeuchte und Niederschlag über Antarktika

Abstract D and (18)O distributions were investigated in Antarctic precipitation (falling snow) and in water vapour to study their dependance on season and sampling site. Long-term sampling at the former German Georg Forster Station during 1978-93 and at the Japanese Syowa Station during 1994-97 allow conclusions about the present seasonal isotopic variations in the water inflow to Antarctica. The δD and δ(18)O values of precipitation at these East Antarctic coastal stations were compared with corresponding data from the West Antarctic Georg von Neumayer and Halley stations. The monthly means of these long-term data sets show typical hysteresis-like seasonal patterns of isotopic composition. Significant time lags exist regarding station temperatures, while water vapour δD values do not show such hysteresis patterns. Here, half-yearly and even quarter-yearly time components were found by Fourier analysis. Attempts were made to describe the variation in δD and δ(18)O values of water vapour and precipitation as well as in the resulting deuterium excess by the mixed cloud isotopic model (MCIM) of Ciais and Jouzel.     

Determination of delta2H and delta18O in saline oil-associated waters: the question of simple vacuum distillation of water samples prior to isotopic analyses

The paper deals with analytical and procedural aspects of delta18O and delta2H determination in saline oil-associated waters. The main objective of the study was to show experimentally the qualitative and quantitative applicability of the simple vacuum distillation of saline oil-associated waters while routine procedures of water isotopic analyses are applied. Additionally, two standard off-line techniques of delta2H determination in water - the zinc and the chromium method - have been compared. Each time a typical isotope salt effect has been tracked on the Dead Sea water. The results clearly show that application of the simple vacuum distillation improve the accuracy and reproducibility of delta2H determinations, especially in chromium off-line technique which appeared to be more sensitive to water salinity. The simple vacuum distillation does not improve the quality of delta18O determinations in the range of water salinities studied. Its application to high concentrated brines (for example, Dead Sea water) decreases the time of equilibration but still propagate the isotopic error connected with low water activity (in the case of 18O/16O ratio) and the incomplete water extraction from the remaining salts (in the case of 2H/1H ratio); in consequence, its time-consuming application seems to be baseless.     

Saisonale Variation von Deuterium und Sauerstoff-18 in Luftfeuchte und Niederschlag über Antarktika

Abstract

D and ¹⁸O distributions were investigated in Antarctic precipitation (falling snow) and in water vapour to study their dependance on season and sampling site. Long-term sampling at the former German Georg Forster Station during 1978–93 and at the Japanese Syowa Station during 1994–97 allow conclusions about the present seasonal isotopic variations in the water inflow to Antarctica. The δD and δ¹⁸O values of precipitation at these East Antarctic coastal stations were compared with corresponding data from the West Antarctic Georg von Neumayer and Halley stations. The monthly means of these long-term data sets show typical hysteresis-like seasonal patterns of isotopic composition. Significant time lags exist regarding station temperatures, while water vapour δD values do not show such hysteresis patterns. Here, half-yearly and even quarter-yearly time components were found by Fourier analysis. Attempts were made to describe the variation in δD and δ¹⁸O values of water vapour and precipitation as well as in the resulting deuterium excess by the mixed cloud isotopic model (MCIM) of Ciais and Jouzel.     

Sulphur and oxygen isotopic composition of sulphates in springs feeding the Wieprz river and other springs of Lublin Upland and Roztocze

Springs on Roztocze and Lublin Upland have been studied. Isotopic data are compared with data of chemical analyses. The results of studies allow us to distinguish five types of groundwaters. The differentiation is based upon different lithology; opokas, gaizes, sandy-silty-clay deposits, sands with shell sandstones, marly opokas, marly limestones and 'soft limestones of chalk type. A correlation can be observed between delta34S and the concentration of Ca or Mg ions also a correlation between HCO3- ion concentration and delta18O in sulphates. Probably these correlations are the result of some simultaneous processes, which occur in groundwater. The seasonal variations of the isotopic composition and sulphate concentration were observed in four springs feeding the upper Wieprz. The variations were simultaneous and often similar in these springs. Probably, these variations are caused by the admixture of sulphates coming from shallow water layers (or leached from soil); however the variations of the groundwater level may also change chemical and isotopic composition in groundwater.     

Stable isotope composition of daily and monthly precipitation in Zagreb

Stable isotopic compositions (delta2H and delta18O) of daily precipitation collected in the period from October 2002 to March 2003 and monthly precipitation in the period from 2001 to 2003, as well as the corresponding meteorological data (temperature, amount of precipitation), all collected in Zagreb, Croatia, are presented. delta2H and delta18O values, both daily and monthly, show large variations due to large temperature variations and the different origin of the air masses. Variations are larger for daily samples than for composite monthly samples. Good correlation of delta18O with temperature is obtained for both types of samples. On the basis of the correlation between delta2H and delta18O, the local meteoric water line is close to the global meteoric water line. Deuterium excess of both daily and monthly precipitation indicates that in the Zagreb area, the influence of air masses from the Mediterranean area prevails in the autumn period.     

Isotope fractionation of sandy-soil water during evaporation – an experimental study

Soil samples containing water with known stable isotopic compositions were prepared. The soil water was recovered by using vacuum/heat distillation. The experiments were held under different conditions to control rates of water evaporation and water recovery. Recoveries, δ¹⁸O and δ²H values of the soil water were determined. Analyses of the data using a Rayleigh distillation model indicate that under the experimental conditions only loosely bound water is extractable in cases where the recovery is smaller than 100?%. Due to isotopic exchange between vapour and remaining water in the micro channels or capillaries of the soil matrix, isotopic fractionation may take place under near-equilibrium conditions. This causes the observed relationship between δ²H and δ¹⁸O of the extracted water samples to have a slope close to 8. The results of this study may indicate that, in arid zones when soil that initially contains water dries out, the slope of the relationship between δ²H and δ¹⁸O values should be close to 8. Thus, a smaller slope, as observed by some groundwater and soil water samples in arid zones, may be caused by evaporation of water before the water has entered the unsaturated zone.     

Isotopic assessment of sources and processes affecting sulfate and nitrate in surface water and groundwater of Luxembourg

Surface water and deep and shallow groundwater samples were taken from selected parts of the Grand-Duchy of Luxembourg to determine the isotopic composition of nitrate and sulfate, in order to identify sources and/or processes affecting these solutes. Deep groundwater had sulfate concentrations between 20 and 40 mg/L, delta34S(sulfate) values between -3.0 and -20.0 per thousand, and delta18O(sulfate) values between +1.5 and +5.0 per thousand; nitrate was characterized by concentrations varying between < 0.5 and 10 mg/L, delta15N(nitrate) values of approximately -0.5 per thousand, and delta18O(nitrate) values approximately +3.0 per thousand. In the shallow groundwater, sulfate concentrations ranged from 25 to 30 mg/L, delta34S(sulfate) values from -20.0 to +4.5 per thousand, and delta18O(sulfate) values from approximately +0.5 to +4.5 per thousand; nitrate concentrations varied between approximately 10 and 75 mg/L, delta15N(nitrate) values between +2.5 and +10.0 per thousand, and delta18O(nitrate) values between +1.0 and +3.0 per thousand. In surface water, sulfate concentrations ranged from 10 to 210 mg/L, delta34S(sulfate) values varied between -9.3 and +10.9 per thousand, and delta18O(sulfate) values between +3.0 and +10.7 per thousand were observed. Nitrate concentrations ranged from 10 to 40 mg/L, delta15N(nitrate) values from +6.5 to +12.0 per thousand, and delta18O(nitrate) values from -0.4 to +4.0 per thousand. Based on these data, three sulfate sources were identified controlling the riverine sulfate load. These are soil sulfate, dissolution of evaporites, and oxidation of reduced S minerals in the bedrock. Both groundwater types were predominantly influenced by sulfate from the two latter lithogenic S sources. The deep groundwater and a couple shallow groundwater samples had nitrate derived mainly from soil nitrification. All other sampling sites were influenced by nitrate originating from sewage and/or manure. A decrease in nitrate concentration observed along one of the rivers was attributed to denitrification. It appears that sulfate within Luxembourg's aquatic ecosystem is mainly of lithogenic origin, whereas nitrate is often derived from anthropogenic activities.     

There is no temperature dependence of net biochemical fractionation of hydrogen and oxygen isotopes in tree-ring cellulose

The isotopic composition of tree-ring cellulose was obtained over a two-year period from small diameter, riparian zone trees along an elevational transect in Big Cottonwood Canyon, Utah, USA to test for a possible temperature dependence of net biological fractionation during cellulose synthesis. The isotope ratios of stream water varied by only 3.6% and 0.2% in deltaD and delta18O, respectively, over an elevation change of 810m. The similarity in stream water and macroenvironment over the short (13km) transect produced nearly constant stem and leaf water deltaD and delta18O values. In addition, what few seasonal variations observed in the isotopic composition of source water and atmospheric water vapor or in leaf water evaporative enrichment were experienced equally by all sites along the elevational transect. The temperature at each site along the transect spanned a range of > or = 5 degrees C as calculated using the adiabatic lapse rate. Since the deltaD and delta18O values of stem and leaf water varied little for these trees over this elevation/temperature transect, any differences in tree-ring cellulose deltaD and delta18O values should have been associated with temperature effects on net biological fractionation. However, the slopes of the regressions of elevation versus the deltaD and delta18O values of tree-ring cellulose were not significantly different from zero indicating little or no temperature dependence of net biological fractionation. Therefore, cross-site climatic reconstruction studies using the isotope ratios of cellulose need not be concerned that temperatures during the growing season have influenced results.     

Experimental calibration and field investigation of the oxygen isotopic fractionation between biogenic aragonite and water

Marine molluscs have long been recognised as potential records of palaeoclimate change using the patterns and differences in the stable isotopic composition of the carbonate shells. The aim of this study is to improve the robustness of this approach for aragonitic molluscs by completing the first experimental calibration of the fractionation between water and biogenic aragonite. Fractionation factors were calibrated by growing specimens of the freshwater mollusc Lymnaea peregra under controlled conditions of water temperature and isotopic composition. Fifteen populations of L. peregra were maintained at constant temperature and isotopic conditions for five months (at five different temperatures and using three different water compositions). Water samples and temperature measurements were taken regularly throughout the experiment. The temperature dependence of the fractionation factor, between 8 and 24 degrees C, is given by: 1000 ln alpha=16.74x(1000T(-1))-26.39 (T in Kelvin) and the relationship between temperature (T), delta(18)O(carb) and delta(18)O(wat) is given by: T=21.36-4.83xdelta(+ degrees )O(carb)-delta(+ degrees )O(wat) (T is in degrees C, delta(18)O(carb) is with respect to Vienna Pee Dee Belemnite (PDB), the International Atomic Energy Agency (IAEA) replacement standard for PDB, and delta(18)O(wat) is with respect to Vienna standard mean ocean water (VSMOW)) The outcome of the controlled experiment is compared with previous studies on synthetic, and biogenic, calcite and aragonite from field and laboratory investigations. These comparisons suggest that although a vital offset exists between the fractionation of isotopes in synthetic and biogenic aragonite for molluscs in general, there is no vital effect that is specific either to freshwater, or to individual, genera. Therefore, the calibrated relationship may be used for any freshwater or marine mollusc to derive palaeotemperatures providing the isotopic composition of the environmental water can be reliably constrained. Copyright 1999 John Wiley & Sons, Ltd.     

Isotopic characteristics of meteoric waters in the Belgrade region

The stable isotope composition of hydrogen (delta(2)H) and oxygen (delta(18)O) in monthly precipitation and river water (Sava River and Danube) samples in the Belgrade area gathered between 1992 and 2005 are determined. The local meteoric water line delta(2)H=7.8 (+/-0.2) delta(18)O+7.3(+/-1.6) (r(2)=0.98, n=60, sigma=0.52) for the whole period of observation is close to the global meteoric water line. The amount-weighted mean delta(2)H and delta(18)O values of precipitation were-65+/-27 per thousand and-9.4+/-3.4 per thousand, respectively. Good correlation between delta(18)O values (r approximately >0.67) and ambient temperature and relative humidity was obtained. Stream-water data ranged from-94 to-60 per thousand for delta(2)H and from-11.0 to approximately 5.7 per thousand for delta(18)O with highly statistically significant difference (p>0.01) between the Sava River and the Danube. In addition, the isotopic compositions of local precipitation and adjacent river water at monitoring sites were compared. Obtained data will give an opportunity to improve the knowledge of mixing stream water and local groundwater, and assessment of potential groundwater risks and pressures in the Belgrade basin.     

Continuous measurements of stable isotopes of carbon dioxide and water vapour in an urban atmosphere: isotopic variations associated with meteorological conditions

Isotope ratios of carbon dioxide and water vapour in the near-surface air were continuously measured for one month in an urban area of the city of Nagoya in central Japan in September 2010 using laser spectroscopic techniques. During the passages of a typhoon and a stationary front in the observation period, remarkable changes in the isotope ratios of CO₂ and water vapour were observed. The isotope ratios of both CO₂ and water vapour decreased during the typhoon passage. The decreases can be attributed to the air coming from an industrial area and the rainout effects of the typhoon, respectively. During the passage of the stationary front, δ¹³C–CO₂ and δ¹⁸O–CO₂ increased, while δ²H–H₂Ov and δ¹⁸O–H₂Ov decreased. These changes can be attributed to the air coming from rural areas and the air surrounding the observational site changing from a subtropical air mass to a subpolar air mass during the passage of the stationary front. A clear relationship was observed between the isotopic CO₂ and water vapour and the meteorological phenomena. Therefore, isotopic information of CO₂ and H₂Ov could be used as a tracer of meteorological information.     

Diurnal variations in the photosynthesis-respiration activity of a cyanobacterial bloom in a freshwater dam reservoir: an isotopic study

The stable isotopic analyses of molecular oxygen dissolved in water (delta18O(DO)) and dissolved inorganic carbon (delta13C(DIC)), supplemented with basic chemical measurements, have been carried out on a diurnal basis to better understand the dynamics of photosynthesis and respiration in freshwater systems. Our observations have been carried out in a lowland dam reservoir, the Sulejow Lake (central Poland), during the summer cyanobacterial bloom. All data obtained, isotopic, hydrochemical, and biological, show a high mutual consistency. Namely, the lowest delta18O(DO) values, obtained at 10:00 and 14:00 (16.0 and 15.5 per thousand, respectively), correspond to the highest amount of cyanobacterial cells observed (66 and 63 mg dm(-3), respectively), whereas the minimum delta13C(DIC) (-10.6 per thousand) obtained at 22:00 corresponds to the maximum content of organic matter (110 mg dm(-3)). This evidence suggests that isotopic assays of delta18O(DO) and delta13C(DIC) are a reliable tool for the quantitative study of biochemical processes in freshwater systems.     

Using environmental isotopes 2H and 18O for identification of infiltration processes in floodplain ecosystems of the River Elbe

We examined a floodplain area in the middle section of the river Elbe Valley with regard to hydrogeological and hydrological processes using isotopic methods. Over two years, river water and groundwater have been analysed for temporal and spatial chemical and isotopic (delta2H and delta18O) changes. By these methods we assessed the flow dynamics of the river-groundwater infiltration system. At low and mean river stages there is a general hydraulic gradient from the higher areas at the margin of the valley towards the floodplain. During floods river water infiltrates into the adjacent aquifer not primarily through the river banks but first through surface water inflow from north to south, via depressions and gullies from the back of the floodplain. The early stage of river water infiltration is characterized by a sharp decrease in conductivity and in concentrations of SO4(2-) and Cl- in the hydraulically connected shallow aquifer. delta2H and delta18O values show a similar tendency. We observed a significant minimum in stable isotope ratios during the flood in March 1999. Using a simple mixing equation it was calculated that the groundwater in the upper, shallow aquifer consists of around 70% river water in the transition zone (well 13) during flooding.     

IR spectroscopic study of the chemical composition of epiphytic lichens

Changes in the chemical composition of lichens exposed to pollutants are investigated by means of FTIR spectroscopy. According to model experiments, alkyl nitrates, ammonium salts, amines, and sulfones develop in the lichen thallus through the action of ammonia and nitric and sulfuric acids. Spectroscopic data of modeling experiments enabled nitrogen- and sulfur-containing substances to be identified as the main air pollutants in the vicinity of a pig-breeding complex and information to be obtained on the content of the pollutants and their impact on the lichens.