Surface Water Isotope Research Articles

The effect of Indian Summer Monsoon rainfall on surface water δD values in the central Himalaya

AbstractStable isotope proxy records, such as speleothems, plant‐wax biomarker records, and ice cores, are suitable archives for the reconstruction of regional palaeohydrologic conditions. But the interpretation of these records in the tropics, especially in the Indian Summer Monsoon (ISM) domain, is difficult due to differing moisture and water sources: precipitation from the ISM and Winter Westerlies, as well as snow‐ and glacial meltwater. In this study, we use interannual differences in ISM strength (2011–2012) to understand the stable isotopic composition of surface water in the Arun River catchment in eastern Nepal. We sampled main stem and tributary water (n = 204) for stable hydrogen and oxygen isotope analysis in the postmonsoon phase of two subsequent years with significantly distinct ISM intensities. In addition to the 2011/2012 sampling campaigns, we collected a 12‐month time series of main stem waters (2012/2013, n = 105) in order to better quantify seasonal effects on the variability of surface water δ18O/δD. Furthermore, remotely sensed satellite data of rainfall, snow cover, glacial coverage, and evapotranspiration was evaluated. The comparison of datasets from both years revealed that surface waters of the main stem Arun and its tributaries were D‐enriched by ~15‰ when ISM rainfall decreased by 20%. This strong response emphasizes the importance of the ISM for surface water run‐off in the central Himalaya. However, further spatio‐temporal analysis of remote sensing data in combination with stream water d‐excess revealed that most high‐altitude tributaries and the Tibetan part of the Arun receive high portions of glacial melt water and likely Winter Westerly Disturbances precipitation. We make the following two implications: First, palaeohydrologic archives found in high‐altitude tributaries and on the southern Tibetan Plateau record a mixture of past precipitation δD values and variable amounts of additional water sources. Second, surface water isotope ratios of lower elevated tributaries strongly reflect the isotopic composition of ISM rainfall implying a suitable region for the analysis of potential δD value proxy records.

Distribution of H and O stable isotopes in the surface waters of the Sava River, the major tributary of the Danube River

The presented paper describes spatial and temporal variations in extended stable isotope datasets of hydrogen and oxygen (δ2H and δ18O) in the Sava River water that were used to estimate the mean residence time (MRT) of stream water using an exponential flow model. The re-examining MRT was <2 years in the Slovenian part of the Sava River and was in a good agreement with previous estimates and with the MRT estimated in the Sava River at Ostružnica near Belgrade, Serbia. A MRT >2.2 years was observed in the Danube River at Vinča also near Belgrade. The spatial distribution of δ18O in precipitation over the Sava River Basin (SRB) was mapped based on the long-term weighted mean annual δ18O values and established relationship with various geographical controls (latitude, longitude and altitude). The modelled δ18O values in precipitation agree with the measured values in the surface river water at different locations indicating that the spatial variation in the isotopic composition of precipitation is the dominant factor controlling surface water isotope ratios over the SRB.

Characterization of surface water isotope spatial patterns of Scotland

The extended National Waters Inventory of Scotland (NWIS) monitoring network in combination with an extensive, supplementary low flow sampling campaign was used to create isoscapes of surface water for management purposes at high spatial resolution (100 m grid) across Scotland. The δ2H isoscape shows a strong isotopic separation along a north-south and east-west topographic (mountainous to the north and west and lowlands to the east) and climatic (wetter west, drier east) gradients. Isotopes were enriched in the western domain and depleted in the east and central Highland domains. The surface water d-excess isoscape show more complex spatial variability mainly related to contrasting moisture sources (sub-tropical North Atlantic Ocean, the North Sea, Polar Continental, and the Arctic) as well as secondary evaporation processes. The two-year NWIS isotope record exhibited a significant seasonal evaporative effect on surface water isotopes that progresses from winter through to a maximum in autumn as indicated by Local Evaporation Lines (LELs). The surface water isoscapes can be efficiently reproduced with geographically weighted regression (GWR) models using gridded annual precipitation, remotely sensed actual evapotranspiration, land cover, soil wetness, catchment area, and mean elevation. The GWR models showed potential to assess isotopic changes under future climate and land use change.

Spatiotemporal distribution of river water stable isotope compositions and variability of lapse rate in the central Rocky Mountains: Controlling factors and implications for paleoelevation reconstruction

Stable isotope-based paleoaltimetry is the most widely used approach for paleoelevation reconstruction. Interpretations of stable isotope data in continental interiors, however, are undermined by surface water isotope compositions that are influenced by multiple factors. Here we present a stable isotope dataset of modern river water samples collected over two summers and one spring from the central Rocky Mountains (Rockies) and the adjacent Great Plains. By examining the spatial and temporal variations of river water δ18O, δD and d-excess values, and their relationships with climatic and geographic parameters, as well as through back trajectory analysis of moisture sources, we elucidate the influences of elevation and climatic parameters on the spatiotemporal variation of river water isotopic values. In the Bighorn River drainage, a typical intermontane drainage in the central Rockies, the isotopic difference between highland and lowland rivers is small, which we attribute to highland precipitation that dominates lowland river discharge. In the North Platte River drainage across the central Rockies and Great Plains, the river water δ18O values show poor correlation with elevation west of 105°W (central Rockies), but increase as elevation decrease east of 105°W (in the western Great Plains). This eastward increase across the western Great Plains leads to an average oxygen isotope lapse rate of −2.3‰/km, which we interpret as being caused primarily by condensation temperature-controlled isotopic fractionation at various elevations, and secondarily by evaporation in the upper reaches of streams that contribute to the North Platte River plus direct contribution of moisture from the Gulf of Mexico in the Great Plains. In this continental interior setting, multiple moisture sources, including recycled continental moisture, contribute to surface water, and evaporation influences river water isotope values to various degrees depending on the relative humidity within an individual river catchment. These results suggest that paleoclimate and atmospheric circulation pattern must be carefully evaluated when applying stable isotope-based paleoaltimetry in continental interiors. Our findings have implications for paleoelevation reconstruction in the study area, including that 1) within the central Rockies, the isotopic difference of river water and unevaporated basinal precipitation can be used to infer paleorelief of the Laramide ranges with respect to the basin floors; 2) along a regional transect crossing the central Rockies and Great Plains, the modern isotope lapse rate of the North Platte River drainage can be used to constrain the paleorelief between the two regions in semi-arid climate.

Characterization of selected conservative and non-conservative isotopes in mine effluent and impacted surface waters: Implications for tracer applications at the mine-site scale

Effluent from Europe's largest active gold mine is discharged to the adjacent River Seurujoki via natural treatment wetlands in Lapland Finland. Site waters, including two sources of mine effluent, treatment wetland surface water and Seurujoki river water were chemically and isotopically characterized. The results of isotopic characterization were evaluated to determine the effectiveness of selected environmental conservative isotopes (δ18O, δD,87Sr/86Sr) as tracers of water/solute source. Non-conservative isotopes (δ7Li, δ26Mg, δ25Mg, δ34SSO4) were evaluated as tracers of fractionation inducing processes that provide insight to contaminant attenuation and mobility mechanisms. The two sources of mine effluent were chemically distinct, and the impacts of mine effluent were persistent in downstream river water to at least 12.8 km. Sr isotope-based estimates of mine effluent discharge to the river were in good agreement with Cl concentration-based estimates, and suggest effluent comprised approximately 4% of river discharge in both June 2013 and June 2015. These instantaneous mixing results were applied in a multi-isotope approach to characterize non-conservative solute and isotopic behavior for Li and SO4. In 2015 7Li was enriched in downstream river water by approximately 3‰ with no discernible concentration change, suggesting ongoing in-stream ion exchange reactions with oxy-hydroxide precipitates. While SO4 was attenuated by over 50% in the downstream direction, the observed 34SSO4 depletion indicates that bacterial sulfate reduction was not a driver of in-stream attenuation. Further, depletion of 18O and deuterium in treatment wetland 4 indicated that fresh meteoric water comprised approximately 25% of the treatment wetland discharge in March 2015. The contemporaneous flushing of numerous contaminants (Na, Ca, Mg, SO4, Mn, and Li) from the wetland supports the conceptual model in which disruption of contaminant concentration gradients will lead to contaminant leaching from the wetlands.

Study on the stable isotopes in surface waters of the Naqu River basin, Tibetan Plateau

Study on the stable isotopes in surface waters of the Naqu River basin, Tibetan Plateau

Study on the stable isotopes in surface waters of the Naqu River basin, Tibetan Plateau

Study on the stable isotopes in surface waters of the Naqu River basin, Tibetan Plateau

Stable isotopes in surface waters of the Atlantic Ocean: Indicators of ocean‐atmosphere water fluxes and oceanic mixing processes

AbstractThe surface ocean hydrological cycle is explored based on ∼300 new δ18O and δD measurements from surface waters of the Atlantic Ocean and the Mediterranean Sea over the period 2010–2016. Our approach combines these surface observations with salinity (S) and stable isotope measurements of atmospheric water vapor. The distinct regional S‐δ distributions are used to identify different surface water masses and their horizontal advection. Moreover, based on assumptions on the δ‐S characteristics of seawater sources and the isotope composition of the evaporative (δe) and meteoric water (δMW) fluxes, the δ‐S distribution is used to indicate the relative importance of evaporation (E) and meteoric water inputs (MW). Here δe is estimated from the Craig and Gordon's equation using 120 days of measurements of the ambient air above the Atlantic Ocean collected during three cruises. To provide quantitative estimates of the E:MW ratio, we use the box model from Craig and Gordon (1965). This identifies the subtropical gyre as a region where E:MW ∼2 and the tropical ocean as a region were MW:E ∼2. Finally, we show that the δ18O‐δD distribution is better represented by a linear fit than the δ‐S relationship, even in basins governed by different hydrological processes. We interpret the δ18O‐δD distribution considering the kinetic fractionation processes associated with evaporation. In the tropical region where MW exceeds E, the δ18O‐δD distribution identifies the MW inputs from their kinetic signature, whereas in regions where E exceeds MW, the δ18O‐δD distribution traces the humidity at the sea surface.

Evaluating the hydrological and hydrochemical responses of a High Arctic catchment during an exceptionally warm summer

AbstractThe Arctic has experienced substantial warming during the past century with models projecting continued warming accompanied by increases in summer precipitation for most regions. A key impact of increasing air surface temperatures is the deepening of the active layer, which is expected to alter hydrological processes and pathways. The aim of this study was to determine how one of the warmest and wettest summers in the past decade at a High Arctic watershed impacted water infiltration and storage in deeply thawed soil and solute concentrations in stream runoff during the thaw period. In June and July 2012 at the Cape Bounty Watershed Observatory, we combined active layer measurements with major ion concentrations and stable isotopes in surface waters to characterize the movement of different runoff sources: snowmelt, rainfall, and soil water. Results indicate that deep ground thaw enhanced the storage of infiltrated water following rainfall. Soil water from infiltrated rainfall flowed through the thawed transient layer and upper permafrost, which likely solubilized ions previously stored at depth. Subsequent rainfall events acted as a hydrological flushing mechanism, mobilizing solutes from the subsurface to the surface. This solute flushing substantially increased ion concentrations in stream runoff throughout mid to late July. Results further suggest the importance of rainfall and soil water as sources of runoff in a High Arctic catchment during mid to late summer as infiltrated snowmelt is drained from soil following baseflow. Although there was some evaporation of surface water, our study indicates that flushing from solute stores in the transient layer was the primary driver of increased ion concentrations in stream runoff and not evaporative concentration of surface water. With warmer and wetter summers projected for the Arctic, ion concentrations in runoff (especially in the late thaw season), will likely increase due to the deep storage and subsurface flow of infiltrated water and subsequent flushing of previously frozen solutes to the surface.

The influence of lithology on surface water sources.

Understanding the temporal and spatial variability of water sources within a basin is vital to our ability to interpret hydrologic controls on biogeochemical processes and to manage water resources. Water stable isotopes can be used as a tool to determine geographic and seasonal sources of water at the basin scale. Previous studies in the Coastal Range of Oregon reported that the variation in the isotopic signatures of surface water did not conform to the commonly observed "elevation effect", which exhibits a trend of increasing isotopic depletion with rising elevation. The primary purpose of this research is to investigate the mechanisms governing seasonal and spatial variations in the isotopic signature of surface waters within the Marys River Basin, located in the leeward side of the Oregon Coastal Range. Surface water and precipitation samples were collected every 2-3 weeks for isotopic analysis for one year. Our results confirmed the lack of elevational variation of surface water isotopes within this leeward basin. While we find elevational variation in precipitation in the eastern portion of the watershed, this elevation effect is counteracted by rainout with distance from the Pacific coast. In addition we found significant variation in surface water isotope values between catchments underlain predominantly by basalt or sandstone. The degree of separation was strongest during the summer when low flows reflect deeper groundwater sources. This indicates that baseflow within streams drained by each lithology is being supplied from two distinctly separate water sources. In addition, the flow of the Marys River is dominated by water originating from the sandstone water source, particularly during the low flow summer months. We interpreted that the difference in water source results from sandstone catchments having highly fractured geology or locally tipping to the east facilitating cross-basin water exchange from the windward to the leeward side of the Coast Range. Our results challenge topographic derived watershed boundaries in permeable sedimentary rocks; highlighting the overwhelming importance of underlying geology.

Controls on the stable isotopes in precipitation and surface waters across the southeastern Tibetan Plateau

Constraining temporal and spatial variability in water stable isotopes (δ18O and δD) is requested for interpreting proxy records of paleoclimate/paleoaltimetry. The southeastern Tibetan Plateau (TP) receives large amounts of precipitation in both summer (JJAS) and spring (MAM) and this makes it different from most other parts of the TP where annual precipitation concentrates only in summer. However, our knowledge of controls on precipitation and surface runoff generation in this region is still far from sufficient. In this study, the δ18O and δD of precipitation and stream waters across the southeastern TP were analyzed to investigate moisture sources and empirical isotope-elevation relationships. Herein, seasonal precipitation patterns, moisture trajectories and precipitation isotopes suggest this region is seasonally dominated by the monsoon in summer and the southerlies (from the Bay of Bengal) or a mix of southerlies and westerlies in spring. Spatially, vertical variations in precipitation seasonality exert profound influences on isotopic variability for stream waters. Larger contributions of spring precipitation (with higher δ18O and d-excess (d-excess=δD-8δ18O) compared to summer precipitation) vs. summer precipitation in the surface runoff generation at lower elevations account for the uncommon altitudinal decrease in streamwater d-excess. Such a cause also contributes to the slightly greater vertical lapse rates of streamwater δ18O (−0.28 to −0.48‰/100m) relative to the Himalayan front. In addition, although a robust δ18O-elevation relationship is demonstrated based upon our measured and other published data on a broad spatial scale (over a 5200m elevation range), this relationship is found to deviate from the empirical/theoretical pattern in the Himalayan front, which is also caused by the substantial spring precipitation in the southeastern TP. It is suggested that long-term changes in δ18O or δD of paleowater in this region actually represent both changes in past regional elevations and contributions of summer vs. spring atmospheric circulations.

Spatial distribution and controlling factors of stable isotopes in meteoric waters on the Tibetan Plateau: Implications for paleoelevation reconstruction

Debates persist about the interpretations of stable isotope based proxies for the surface uplift of the central–northern Tibetan Plateau. These disputes arise from the uncertain relationship between elevation and the δ18O values of meteoric waters, based on modern patterns of isotopes in precipitation and surface waters. We present a large river water data set (1,340 samples) covering most parts of the Tibetan Plateau to characterize the spatial variability and controlling factors of their isotopic compositions. Compared with the amount-weighted mean annual oxygen isotopic values of precipitation, we conclude that river water is a good substitute for isotopic studies of precipitation in the high flat (e.g., elevation >3,300 m) interior of the Tibetan Plateau in the mean annual timescale. We construct, for the first time based on field data, contour maps of isotopic variations of meteoric waters (δ18O, δD and d-excess) on the Tibetan Plateau. In the marginal mountainous regions of the Plateau, especially the southern through eastern margins, the δ18O and δD values of river waters decrease with increasing mean catchment elevation, which can be modeled as a Rayleigh distillation process. However, in the interior of the Plateau, northward increasing trends in δ18O and δD values are pronounced and present robust linear relations; d-excess values are lower than the marginal regions and exhibit distinct contrasts between the eastern (8‰–12‰) and western (<8‰) Plateau. We suggest that these isotopic features of river waters in the interior of the Tibetan Plateau result from the combined effects of: 1) mixing of different moisture sources transported by the South Asian monsoon and Westerly winds; 2) contribution of moisture from recycled surface water; and 3) sub-cloud evaporation. We further provide a sub-cloud evaporation modified Rayleigh distillation and mixing model to simulate the isotopic variations in the western Plateau. Results of this work suggest that stable isotope-based paleoaltimetry studies are reliable in the southern through eastern Plateau margins; towards the central–northern Plateau, this method cannot be applied without additional constraints and/or large uncertainties.

Multi-year impacts of permafrost disturbance and thermal perturbation on High Arctic stream chemistry

Permafrost disturbances (such as active layer detachment (ALD) slides) and thermal perturbation (deep ground thaw from high soil temperatures) alter Arctic surface water chemistry. However, the potential multi-year impacts on water chemistry and the ultimate recovery time are not well understood. This study evaluates the impacts on surface waters and recovery following disturbance of a High Arctic catchment in 2007 from ALDs. We measured ion concentrations and stable isotopes in surface waters collected between 2006 and 2014 from paired catchments — one disturbed and the other not. The years 2007 and 2012 were exceptionally warm and represent unusual thermal perturbation for both catchments. Results indicate that the exposure and mobilization of soluble ions in near surface soil is a key control over dissolved ion concentrations and composition following ALDs. Runoff in the disturbed catchment shows increased total dissolved solute (TDS) concentrations and seasonal TDS fluxes and changes to the relative composition of individual ions in surface water. These impacts persisted for the 7 year study duration after disturbance and are consistent with the thawing of the solute-rich transient layer and upper permafrost. Thermal perturbation increased TDS concentrations and seasonal fluxes in runoff for up to 2 years, as ions released from ground thaw appear to be available for flushing in subsequent summers.

Isotope Evidence of Rainfall and Groundwater for Tracing Recharge Areas in Kaeng Khoi District, Saraburi Province, Thailand

This study was conducted in the districts of Kaeng Khoi and Muang, located in the center of Saraburiprovince, Central Thailand. The purpose was to use a stable isotope technique to iden-tify recharge areas where rainfall infiltrates. Analysis of stable isotopes in groundwater, surface water and rainwater were conducted in September 2014. Isotope compositions of groundwater were found to have δD values that ranged from -37.55‰ to -48.04‰ while δ18O values ranged from -5.30‰ to -7.34‰. The Local Meteoric Water Line (LMWL) in the study area was indis-tinguishablefrom the Bangkok Local Meteoric Water Line (BKK LMWL), and the stable iso-tope values of rainwater in area were more depleted than BKK LMWL. The isotope compo-sitions of surface water revealed that the effect of evaporation could divide the groundwater into two groups, with the first group locally receiving rainfall and the second group interacting directly with surface water. Therefore, care must be taken to prevent groundwater contamination in the latter group due to polluted surface water caused by human activities.

A synthesis of thermokarst lake water balance in high-latitude regions of North America from isotope tracers

Numerous studies utilizing remote sensing imagery and other methods have documented that thermokarst lakes are undergoing varied hydrological transitions in response to recent climate changes, from surface area expansion to drainage and evaporative desiccation. Here, we provide a synthesis of hydrological conditions for 376 lakes of mainly thermokarst origin across high-latitude North America. We assemble surface water isotope compositions measured during the past decade at five lake-rich landscapes including Arctic Coastal Plain (Alaska), Yukon Flats (Alaska), Old Crow Flats (Yukon), northwestern Hudson Bay Lowlands (Manitoba), and Nunavik (Quebec). These landscapes represent the broad range of thermokarst environments by spanning gradients in meteorological, permafrost, and vegetation conditions. An isotope framework was established based on flux-weighted long-term averages of meteorological conditions for each lake to quantify water balance metrics. The isotope composition of source water and evaporation-to-inflow ratio for each lake were determined, and the results demonstrated a substantial array of regional and subregional diversity of lake hydrological conditions. Controls on lake water balance and how these vary among the five landscapes and with differing environmental drivers are assessed. Findings reveal that lakes in the Hudson Bay Lowlands are most vulnerable to evaporative desiccation, whereas those in Nunavik are most resilient. However, we also identify the complexity in predicting hydrological responses of these thermokarst landscapes to future climate change.

Constraining paleohydrologic change during the Paleocene-Eocene Thermal Maximum in the continental interior of North America

Quantifying the relationship between carbon cycle perturbations and the hydrologic cycle in the geologic past is crucial to accurately modeling how future anthropogenic carbon emissions and resulting radiative forcing might affect the hydrologic cycle. Interpreting changes in proxy records for insight into paleohydrologic change is complex, and documented records of paleohydrologic response to past global warming are rare. We use the relationship between two independent proxy records, the stable isotope ratios of hydrogen in n-alkanes and oxygen in tooth enamel of Coryphodon, to examine paleohydrologic change in the continental interior of North America during the Paleocene-Eocene Thermal Maximum (PETM) hyperthermal ~56Ma. The Coryphodon δ18O record allows us to infer shifts in surface water isotope values through time by applying an empirical relationship between tooth enamel and precipitation δ18O values. Precipitation δ18O values increase by ~4‰ during the PETM, but n-alkane hydrogen isotope ratios show no directional change during the PETM. We explore multiple hypotheses that could explain the differences between the isotope records, including a change in apparent fractionation as a result of plant community change, a shift in the slope of the local meteoric water line, a change in the season of rainfall, or a shift in the season of lipid production. We model the changes that would be required to reconcile the isotope records for each hypothesis and evaluate the likelihood of each of the scenarios. We posit that the most likely hypothesis for the observed differences between the isotope records is a change in either the season of rainfall or the season of lipid production during the PETM.

Groundwater recharge mechanisms inferred from isoscapes in a complex tropical mountainous region

AbstractStable isotope variations and groundwater recharge mechanisms remain poorly understood across the tropics, particularly in Central America. Here stable isotopes (δ18O and δ2H) in groundwater, surface water, and rainfall are used to produce high‐resolution (100 m2 grid) isoscapes for Costa Rica, from which an isotope ratio of precipitation to groundwater (P/GW) is estimated to elucidate the dominant groundwater recharge processes. Spatially, groundwater and surface water isotope ratios depict the strong orographic separation into the Caribbean and Pacific slopes induced by moisture transport directly from the Caribbean Sea and the eastern tropical Pacific Ocean. P/GW isotope ratios reveal that groundwater recharge is biased toward intensive and more depleted monthly rainfall across the Pacific slope with clear evidence of secondary evaporation indicating slower soil matrix recharge processes. On the other hand, P/GW isotope ratios indicate a weak influence of secondary evaporation across the Caribbean slope suggesting rapid recharge via preferential flow paths.

Oxygen and hydrogen isotope signatures of Northeast Atlantic water masses

Only a few studies have examined the variation of oxygen and hydrogen isotopes of seawater in NE Atlantic water masses, and data are especially sparse for intermediate and deep-water masses. The current study greatly expands this record with 527 δ18O values from 47 stations located throughout the mid- to low-latitude NE Atlantic. In addition, δD was analyzed in the 192 samples collected along the GEOTRACES North Atlantic Transect GA03 (GA03_e=KN199-4) and the 115 Iberia-Forams cruise samples from the western and southern Iberian margin. An intercomparison study between the two stable isotope measurement techniques (cavity ring-down laser spectroscopy and magnetic-sector isotope ratio mass spectrometry) used to analyze GA03_e samples reveals relatively good agreement for both hydrogen and oxygen isotope ratios. The surface (0–100m) and central (100–500m) water isotope data show the typical, evaporation related trend of increasing values equatorward with the exception for the zonal transect off Cape Blanc, NW Africa. Off Cape Blanc, surface water isotope signatures are modified by the upwelling of fresher Antarctic Intermediate Water (AAIW) that generally has isotopic values of 0.0 to 0.5‰ for δ18O and 0 to 2‰ for δD. Along the Iberian margin the Mediterranean Outflow Water (MOW) is clearly distinguished by its high δ18O (0.5–1.1‰) and δD (3–6‰) values that can be traced into the open Atlantic. Isotopic values in the NE Atlantic Deep Water (NEADW) are relatively low (δ18O: −0.1 to 0.5‰; δD: −1 to 4‰) and show a broader range than observed previously in the northern and southern convection areas. The NEADW is best observed at GA03_e Stations 5 and 7 in the central NE Atlantic basin. Antarctic Bottom Water isotope values are relatively high indicating modification of the original Antarctic source water along the flow path. The reconstructed δ18O–salinity relationship for the complete data set has a slope of 0.51, i.e., slightly steeper than the 0.46 described previously by Pierre et al. (1994, J. Mar. Syst. 5 (2), 159–170.) for the tropical to subtropical Northeast Atlantic. This slope decreases to 0.46 for the subtropical North Atlantic Central Water (NACW) and the MOW and to 0.32 for the surface waters of the upper 50m. The δD–salinity mixing lines have estimated slopes of 3.01 for the complete data, 1.26 for the MOW, 3.47 for the NACW, and 2.63 for the surface waters. The slopes of the δ18O–δD relationship are significantly lower than the one for the Global Meteoric Water Line with 5.6 for the complete data set, 2.30 for the MOW, 4.79 for the NACW, and 3.99 for the surface waters. The lower slopes in all the relationships clearly reflect the impact of the evaporation surplus in the subtropics.

Factors affecting dispersion of radionuclides in north western coast of Mediterranean Sea, Egypt

This study aims to analyze the principal factors affecting the interaction of 137Cs, 60Co and 89Sr with coastal sediments and their importance for migration of these ions in surface water. The second goal is to assess the acceptability of radiological consequences of proposed routine discharges of nuclear installations for radioactive materials into surface water as well as to confirm the suitability of the site to select and to establish limits for radioactive discharge into water. Uptake of the investigated ions by Mediterranean Sea bottom sediment samples have been studied as a function of liquid to solid ratio (V/m) and contact time using batch technique. The suspended sediment concentration, different discharge rates of radionuclides and the distance between the source point in the sea and the beach were investigated. The obtained results show that Kd of Cs+, Co2+ and Sr2+is 20, 32 and 10 l/g, respectively. The lowest effective dose is for 89Sr, while the highest effective dose is for 137Cs, at the same distances. A mathematical model for the migration of the investigated isotopes in surface water was constructed to predict the concentration of these ions for both different distances and time periods.

Determining Seasonal Natural Effects over Isotopic Baselines for CO2 Storage Monitoring

Dissolved carbon stable isotopes in surface waters can be utilized as a monitoring tool of CO2 geological storage and as a good indicator of potential CO2 leakages, since each source of carbon has a specific isotopic signature. The isotopic carbon baseline value and its range will determine whether the situation responds to a leak or a natural modification as part of the system's annual cycle and its seasonal effects. We measured water temperature, pH, dissolved inorganic carbon (DIC) concentration and other geochemical variables, during the different annual stages, in order to characterize the contribution of different sources of carbon to the natural isotopic evolution of DIC in the area of Hontomin. This area is the selected site for the Spanish research facility for CO2 geological storage operated by CIUDEN. The average value for δ13C-DIC at the study site is -10.7 ‰ (V-PDB), which is very different of the CO2 generated during the oxycombustion process (about -28 ‰ vs V-PDB). After statistical analysis of the sampling efforts, we observed light differences on their average isotopic values which imply certain seasonal effects, although we could not find effects over the DIC concentration.