A simplified approach to analysing historical and recent tritium data in surface waters          下载免费PDF全文

Robert L. Michel  Pradeep Aggarwal  Luis Araguas‐Araguas  Brent D. Newman  Tomas Vitvar 《水文研究》2015,29(4):572-578

Tritium concentrations in river and stream waters from different locations can be compared by normalizing them using the ratio of tritium concentrations in precipitation and surface water (C_p/C_s) in the study area. This study uses these ratios in a hydrological residence time context to make regional‐ and global‐scale comparisons about river basin dynamics. Prior to the advent of nuclear weapons testing, the C_p/C_s ratio was greater than or equal to 1 everywhere because of the decay of tritium in the watershed after it was deposited by precipitation. After an initial increase in the ratios during the bomb peak, the ratio dropped to less than 1 for most surface waters in the following years. This post‐bomb change in the ratio is due to the retention of the bomb‐pulse water in watersheds on timescales that are long relative to the residence time of tritium in the atmosphere. Ratios were calculated for over 6500 measurements of tritium in river and stream waters compiled by the International Atomic Energy Agency. These measurements span the post‐nuclear era (1940s to present) and include many long‐term datasets, which make it possible to examine residence times of waters in watersheds on a global basis. Plotting C_p/C_s versus time shows that ratios tended to reach a minimum in approximately one to two decades after the bomb peak for most locations. This result suggests that changes affecting quantity and quality of river flows need to be assessed on a multi‐decadal timescale. These long lag times have significant implications for assessing climate or land‐use change impacts on a large number of river systems around the world. The continuing value of tritium in studying surface water systems for both the Southern and Northern Hemisphere is also demonstrated. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

First experiments on the maternal transfer of metals in the cuttlefish Sepia officinalis     

Thomas Lacoue-Labarthe  Michel Warnau  Franois Oberhnsli  Jean-Louis Teyssi  Ross Jeffree  Paco Bustamante 《Marine pollution bulletin》2008,57(6-12):826

The aim of this study was to provide a first insight on the incorporation of eight metals in the eggs of the cuttlefish Sepia officinalis via maternal transfer, using radiotracer techniques (^110mAg, ²⁴¹Am, ¹⁰⁹Cd, ⁶⁰Co, ¹³⁴Cs, ⁵⁴Mn, ⁷⁵Se and ⁶⁵Zn). The cuttlefish was fed daily with radiolabelled crabs for two weeks; it then started to spawn every three days. Among the eight tracers, only ^110mAg, ⁷⁵Se and ⁶⁵Zn were significantly transferred to the eggs. The radiotracer distribution among the egg compartments showed that ⁷⁵Se and ⁶⁵Zn were accumulated mainly in the vitellus whereas ^110mAg was found in similar proportion in the vitellus and the eggshell. During the embryonic development, ⁷⁵Se and ⁶⁵Zn contained in the vitellus were progressively transferred to the embryo, likely to supply its metabolic needs in these essential elements. Although it has no known biological functions, Ag contained in both vitellus and eggshell was also transferred to the embryo. Overall, our results showed that transfer of Ag, Se, and Zn does actually occur from a female cuttlefish to its eggs, at least during the last two weeks before spawning.  相似文献   

Improved understanding of spring and stream water responses in headwaters of the Indian Lesser Himalaya using stable isotopes,conductivity and temperature as tracers     

Soukhin Tarafdar  L. Adrian Bruijnzeel  Bhishm Kumar 《水文科学杂志》2019,64(7):757-770

Stable isotope data are presented for precipitation, spring and stream water in a headwater catchments in the Indian Lesser Himalaya. Isotopic contents of phreatic groundwater followed the local meteoric water line and showed minimal alteration by evaporation, suggesting fast recharge. Mean isotopic values for springs and the stream were close to the weighted annual mean for precipitation, indicating recharge was in synchrony with seasonal rainfall distribution. Precipitation exhibited isotopic declines of ?0.6‰ and ?0.2‰ δ¹⁸O per 100 m rise in elevation in July and August (monsoon), respectively. The time lag of one month between rainfall and spring discharge, combined with the isotopic lapse rate indicated a recharge elevation of 70–165 m above the spring outflow point, implying the water originated within the catchment. Time series of electrical conductivity and temperature of spring, seepage and stream waters confirmed the rapid recharge and limited storage capacity of the shallow aquifers.  相似文献   

Lipid biomarkers in suspended particles from a subtropical estuary: Assessment of seasonal changes in sources and transport of organic matter     

《Marine environmental research》2008,65(5):666-678

Temporal and spatial variations in the composition of particulate organic matter (POM) from Florida Bay, USA were examined. The predominance of short-chain homologues for n-alkanes, n-alcohols and n-fatty acids as well as relatively high abundance of C₂₇ and C₂₈ sterols suggested that an autochthonous/marine source of OM was dominant bay-wide. Several biomarker proxies such as P_aq [(C₂₃ + C₂₅)/(C₂₃ + C₂₅ + C₂₉ + C₃₁) n-alkanes], short/long chain n-alkanes, (C₂₉ + C₃₁) n-alkanes and taraxerol indicated a spatial shift in OM sources, where terrestrial OM rapidly decreased while seagrass and microbial OM markedly increased along a northeastern to southwestern transect. Regarding seasonal variations, POM collected during the dry season was enriched in terrestrial constituents relative to the wet season, likely as a result of reduced primary productivity of planktonic species and seagrasses during the dry season. Principal component analysis (PCA) classified the sample set into sub-groups based on PC1 which seemed to be spatially controlled by OM origin (terrestrial-mangrove vs. marine-planktonic/seagrass). The PC2 seemed to be more seasonally controlled suggesting that hydrological fluctuations and seasonal primary productivity are the drivers controlling the POM composition in Florida Bay.  相似文献   

On the role of mesoscale eddies in the ventilation of Antarctic intermediate water     

Zouhair Lachkar  James C. Orr  Jean-Claude Dutay  Pascale Delecluse 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(6):909-925

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Improved high-resolution global and regionalized isoscapes of δ18O, δ2H and d-excess in precipitation     

Stefan Terzer-Wassmuth  Leonard I. Wassenaar  Jeffrey M. Welker  Luis J. Araguás-Araguás 《水文研究》2021,35(6):e14254

Patterns of δ¹⁸O and δ²H in Earth's precipitation provide essential scientific data for use in hydrological, climatological, ecological and forensic research. Insufficient global spatial data coverage promulgated the use of gridded datasets employing geostatistical techniques (isoscapes) for spatiotemporally coherent isotope predictions. Cluster-based isoscape regionalization combines the advantages of local or regional prediction calibrations into a global framework. Here we present a revision of a Regionalized Cluster-Based Water Isotope Prediction model (RCWIP2) incorporating new isotope data having extensive spatial coverage and a wider array of predictor variables combined with high-resolution gridded climatic data. We introduced coupling of δ¹⁸O and δ²H (e.g., d-excess constrained) in the model predictions to prevent runaway isoscapes when each isotope is modelled separately and cross-checked observed versus modelled d-excess values. We improved model error quantification by adopting full uncertainty propagation in all calculations. RCWIP2 improved the RMSE over previous isoscape models by ca. 0.3 ‰ for δ¹⁸O and 2.5 ‰ for δ²H with an uncertainty <1.0 ‰ for δ¹⁸O and < 8 ‰ for δ²H for most regions of the world. The determination of the relative importance of each predictor variable in each ecoclimatic zone is a new approach to identify previously unrecognized climatic drivers on mean annual precipitation δ¹⁸O and δ²H. The improved RCWIP2 isoscape grids and maps (season, monthly, annual, regional) are available for download at https://isotopehydrologynetwork.iaea.org .  相似文献   

Chemical and strontium isotopic characteristics of shallow groundwater in the Ordos Desert Plateau,North China: Implications for the dissolved Sr source and water–rock interactions     

《Chemie der Erde / Geochemistry》2015,75(3):365-374

In this study, the chemical and Sr isotopic compositions of shallow groundwater and rainwater in the Ordos Desert Plateau, North China, and river water from the nearby Yellow River, are investigated to determine the dissolved Sr source and water–rock interactions, and quantify the relative Sr contribution from each end-member. Three groundwater systems have been identified, namely, GWS-1, GWS-2 and GWS-3 according to the watershed distribution in the Ordos Desert Plateau. Ca²⁺ and Mg²⁺ are the most dominant cations in GWS-1, while Na⁺ is dominant in GWS-3. In addition, there is more SO₄²⁻ and less Cl⁻ in GWS-1 than in GWS-3. The shallow groundwater in GWS-2 seems to be geochemically between that in GWS-1 and GWS-3. The ⁸⁷Sr/⁸⁶Sr ratios of the shallow groundwater are high in GWS-1 and GWS-2 and are low in GWS-3. By geochemically comparing the nearby Yellow River, local precipitation and deep groundwater, the shallow groundwater is recharged only by local precipitation. The ionic and isotopic ratios indicate that carbonate dissolution is an important process controlling the chemistry of the shallow groundwater. The intensity of the water–rock interactions varies among the three groundwater systems and even within each groundwater system. Three end-members controlling the groundwater chemistry are isotopically identified: (1) precipitation infiltration, (2) carbonate dissolution and (3) silicate weathering. The relative Sr contributions of the three end-members show that precipitation infiltration and carbonate dissolution are the primary sources of the shallow groundwater Sr in GWS-3 whereas only carbonate dissolution is responsible for the shallow groundwater Sr in GWS-1 and GWS-2. Silicate weathering seems insignificant towards the shallow groundwater's chemistry in the Ordos Desert Plateau. This study is helpful for understanding groundwater chemistry and managing water resources.  相似文献   

An assessment of metal contamination in coastal sediments of the Caspian Sea   总被引：11，自引：0，他引：11  

de Mora S  Sheikholeslami MR  Wyse E  Azemard S  Cassi R 《Marine pollution bulletin》2004,48(1-2):61-77

An assessment of marine pollution due to metals was made in the Caspian Sea based on coastal sediment collected in Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan. Despite the high carbonate content, the distribution of most metals was largely controlled by terrigenous inputs. Several metals (As, Cr, Ni) exhibited concentrations that exceed sediment quality guidelines. Such metals have a high natural background but anthropogenic activities, notably mining, may further enhance concentrations. This would explain hot spots for Cu and Zn in Azerbaijan and Iran, and Cr at the mouth of the Ural River in Kazakhstan. Contamination by Hg was observed to the south of Baku Bay, Azerbaijan. Some anomalously high concentrations of Ba in the central Caspian are probably from offshore drilling operations, but the elevated U concentrations (up to 11.1 microg g(-1)) may be natural in origin. Several metals (Ag, Cd, Pb) have relatively low levels that pose no environmental concerns.  相似文献   

Isotopic and geochemical evolution of ground and river waters in a karst dominated geological setting: A case study from Lijiang basin,South-Asia monsoon region     

《Applied Geochemistry》2013

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Mixture model based multivariate statistical analysis of multiply censored environmental data     

《Advances in water resources》2013

Environmental data are commonly constrained by a detection limit (DL) because of the restriction of experimental apparatus. In particular due to the changes of experimental units or assay methods, the observed data are often cut off by more than one DL. Measurements below the DLs are typically replaced by an arbitrary value such as zeros, half of DLs, or DLs for convenience of analysis. However, this method is widely considered unreliable and prone to bias. In contrast, maximum likelihood estimation (MLE) method for censored data has been developed for better performance and statistical justification. However, the existing MLE methods seldom address the multivariate context of censored environmental data especially for water quality. This paper proposes using a mixture model to flexibly approximate the underlying distribution of the observed data due to its good approximation capability and generation mechanism. In particular, Gaussian mixture model (GMM) is mainly focused in this study. To cope with the censored data with multiple DLs, an expectation–maximization (EM) algorithm in a multivariate setting is developed. The proposed statistical analysis approach is verified from both the simulated data and real water quality data.  相似文献