首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The numerous lakes on the Tibetan Plateau play an important role in the regional hydrological cycle and water resources, but systematic observations of the lake water balance are scarce on the Tibetan Plateau. Here, we present a detailed study on the water cycle of Cona Lake, at the headwaters of the Nujiang‐Salween River, based on 3 years (2011–2013) of observations of δ18O and δ2H, including samples from precipitation, lake water, and outlet surface water. Short‐term atmospheric water vapor was also sampled for isotope analyses. The δ2H–δ18O relationship in lake water (δ2H = 6.67δ18O ? 20.37) differed from that of local precipitation (δ2H = 8.29δ18O + 12.50), and the deuterium excess (d‐excess) in the lake water (?7.5‰) was significantly lower than in local precipitation (10.7‰), indicating an evaporative isotope enrichment in lake water. The ratio of evaporation to inflow (E /I ) of the lake water was calculated using both d‐excess and δ18O. The E /I ratios of Cona lake ranged from 0.24 to 0.27 during the 3 years. Observations of atmospheric water vapor isotopic composition (δ A ) improved the accuracy in E /I ratio estimate over a simple precipitation equilibrium model, though a correction factor method provided nearly identical estimates of E /I ratio. The work demonstrates the feasibility of d‐excess in the study of the water cycle for lakes in other regions of the world and provides recommendations on sampling strategies for accurate calculations of E /I ratio.  相似文献   

2.
ABSTRACT

Calibration of hydrological models is challenging in high-latitude regions where hydrometric data are minimal. Process-based models are needed to predict future changes in water supply, yet often with high amounts of uncertainty, in part, from poor calibrations. We demonstrate the utility of stable isotopes (18O, 2H) as data employed for improving the amount and type of information available for model calibration using the isoWATFLOODTM model. We show that additional information added to calibration does not hurt model performance and can improve simulation of water volume. Isotope-enabled calibration improves long-term validation over traditional flow-only calibrated models and offers additional feedback on internal flowpaths and hydrological storages that can be useful for informing internal water distribution and model parameterization. The inclusion of isotope data in model calibration reduces the number of realistic parameter combinations, resulting in more constrained model parameter ranges and improved long-term simulation of large-scale water balance.  相似文献   

3.
Dissolved inorganic carbon isotope (δ13CDIC) is an important tool to reveal the carbon cycle in lake systems. However, there are only few studies focusing on the spatial variation of δ13CDIC of closed lakes. Here we analyze the characteristics of δ13CDIC of 24 sampled lakes (mainly closed lakes) across the Qiangtang Plateau (QTP) and identify the driving factors for its spatial variation. The δ13CDIC value of these observed lakes varies in the range of ? 15·0 to 3·2‰, with an average value of ? 1·2‰. The δ13CDIC value of closed lakes is close to the atmospheric isotopic equilibrium value, much higher than that in rivers and freshwater lakes reported before. The high δ13CDIC value of closed lakes is mainly attributed to the significant contribution of carbonate weathering in the catchment and the evasion of dissolved CO2 induced by the strong evaporation of lake water. The δ13CDIC value of closed lakes has a logarithmic correlation with water chemistry (TDS, DIC and pCO2), also suggesting that the evapo‐concentration of lake water can influence the δ13CDIC value. The δ13CDIC value shows two opposite logarithmic correlations with lake size depending on the δ13CDIC range. This study suggests that the δ13C in carbonates in lacustrine sediments can be taken as an indicator of lake volume variation in closed lakes on QTP. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

4.
水是人类生存之源,而湖荡被称为地球之“肾”,是河湖水系连接的关键缓冲节点,与人类生存和发展息息相关。长三角平原水系众多,河流纵横,天然湖泊与人工沟渠遍布,平原湖荡湖水与周边地下水的水力联系较为频繁,而地下水对湖泊水均衡贡献尚不明确,对平原湖荡地下水赋存和运移规律的认识不足。本研究以苏州吴江区元荡湖为研究对象,选取氡同位素作为湖水和地下水水力交换过程的示踪剂,建立氡箱模型,揭示元荡湖不同区段与地下水的水力联系过程和补给关系,并通过水位动态验证分析湖水—地下水交互关系。枯水期元荡湖水位和氡浓度空间分布特征指示研究区内地下水向湖水排泄,其中以湖泊西侧较为明显,地下水入流补给的氡为7.137×106 Bq/d,输入量源项占比为90%,地下水流入量为4540.801 m3/d,地下水每日流入量对元荡湖水量的贡献率为2.551%。参数敏感性分析结果表明,风速与地下水222Rn活度为特别敏感参数,取值差异较大时会导致计算误差急剧增大,改善测点布置和提高模型参数精度能有效提高模型计算结果的准确性和可靠程度。借助氡同位素示踪方法,建立湖泊...  相似文献   

5.
The stable oxygen and hydrogen isotopic features of precipitation in Taiwan, an island located at the western Pacific monsoon area, are presented from nearly 3,500 samples collected during the past decade for 20 stations. Results demonstrate that moisture sources from diverse air masses with different isotopic signals are the main parameter in controlling the precipitation's isotope characteristics. The air mass from polar continental (Pc) region contributes the precipitation with high deuterium excess values (up to 23‰) and relatively enriched isotope compositions (e.g., ? 3.2‰ for δ18O) during the winter with prevailing northeasterly monsoon. By contrast, air masses from equatorial maritime (Em) and tropical maritime (Tm) supply the precipitation with low deuterium excess values (as low as about 7‰) and more depleted isotope values (e.g., ? 8.9‰ and ? 6.0‰ for δ18O of Tm and Em, respectively) during the summer with prevailing southwesterly monsoon. Thus seasonal differences in terms of δ18O, δD, and deuterium excess values are primarily influenced by the interactions among various precipitation sources. While these various air masses travel through Taiwan, secondary evaporation effects further modify the isotope characteristics of the inland precipitation, such as raindrop evaporation (reduces the deuterium excess of winter precipitation) and moisture recycling (increases the deuterium excess of summer precipitation). The semi-quantitative estimations in terms of evaluation for changes in the deuterium excess suggest that the raindrop evaporation fractions for winter precipitation range 7% to 15% and the proportions of recycling moisture in summer precipitation are less than 5%. Additionally, the isotopic altitude gradient in terms of δ18O for summer precipitation is ? 0.22‰/100 m, greater than ? 0.17‰/100 m of winter precipitation. The greater isotopic gradient in summer can be attributed to a higher temperature vs. altitude gradient relative to winter. The observed spatial and seasonal stable isotopic characteristics in Taiwan's precipitation not only contribute valuable information for regional monsoon research crossing the continent–ocean interface of East Asia, but also can serve as very useful database for local water resources management.  相似文献   

6.
Shi Qi  Wei Liu  Heping Shu  Fei Liu  Jinzhu Ma 《水文研究》2020,34(20):3941-3954
The sources and storage of soil NO3− in the western Tengger Desert, Northwest China, were explored using water chemistry analysis and stable isotope techniques. In line with the expansion and development of oases, part of the desert has been transformed into cultivated land and artificial forest land. The mean soil NO3− contents found in areas of cultivated land and artificial forest were 123.06 mg kg−1 and 1.26 mg kg−1, far higher and slightly lower than the background desert soil values, respectively. The δ15N-NO3− and δ18O-NO3− values in cultivated soils ranged from 1.00 to 11.81 ‰, and from −1.85 to 8.99 ‰, respectively, and the mean mNO3−/Cl− value in cultivated soils was 2.3. These figures would appear to demonstrate that the rapid increase in the nitrate content in soils is principally due to the use of nitrogen fertilizer. Such increases in soil NO3− storage is likely to promote the leaching of nitrogen into the groundwater where coarsely textured soils exist, the pollution of water sources used for irrigation water, and extreme precipitation events. The δ15N-NO3− and δ18O-NO3− values in groundwater ranged from 3.72 to 6.54 ‰, and from −0.19 to 12.06 ‰, respectively, mainly reflecting the nitrification of soil nitrogen. These values appeared similar to those measured in the soil water in adjacent areas of cultivated land and vegetated desert, indicating that the groundwater has been affected by both natural and artificial NO3−. Artificial afforestation of desert regions would therefore seem to be a useful way of reducing the threat posed by anthropogenic sources to the circulation of NO3−-N within arid regions, as well as promoting wind sheltering and sand fixation. This study explored the NO3− storage and groundwater quality responses to oasis development in arid areas in an attempt to provide effective information for local agricultural organizations and agricultural nitrogen management models.  相似文献   

7.
The Chirripó hydrological research site (CHRS) is located within the Chirripó National Park, Costa Rica (between 3100 and 3820 m asl) whereby ~100 km2 are covered by Páramo, a high-elevation tropical grassland ecosystem. A lake district with approximately 30 lakes of glacial origin is also protected in this area. The CHRS has been monitored since April 2015 with the aim of establishing the first water isotope baseline for the Central American Páramo. At a regional scale, the water isotope ratios (δ2H and δ18O) in precipitation and surface water at CHRS are useful for describing the governing moisture transport from the Caribbean Sea and Pacific Ocean and the complex rainfall producing systems across the N–S mountain range of Central America. These data are also providing unique information about the evaporation and water balance conditions of tropical glacial lakes and the formation of orographic and convective precipitation in high-elevation tropical ecosystems. Current data sets from CHRS include continuous lake water temperature and meteorological conditions (i.e., precipitation amount, air temperature and relative humidity), as well as water stable isotopes in precipitation, stream water, and lake water (daily to biweekly sampling frequency). Stream water is collected at several locations across the topographic gradient whereas lake water is sampled in the three main lake systems of CHRS. CHRS serves as a reference site for conducting pilot isotopic research in high-elevation ecosystems to advance the atmospheric, hydrogeological and ecohydrological studies in these understudied biomes. All data from April 2015 to November 2020 are publicly available.  相似文献   

8.
Stable isotope compositions (δD, δ18O and δ34S) of volcanic lake waters, gas condensates and spring waters from Indonesia, Italy, Japan, and Russia were measured. The spring fluids and gas samples plot in a broad array between meteoric waters and local high-temperature volcanic gas compositions. The δD and δ18O data from volcanic lakes in East Indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high-temperature volcanic gases. We investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases. An elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors, providing relatively flat isotope evolution curves in δ18O–δD diagrams. A numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters, lake water temperature and fluxes of meteoric water, volcanic gas input, evaporation, and seepage losses. The same model is used to derive the flux magnitude of the Keli Mutu lakes in Indonesia. The calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters (several 100 m3 volcanic water/day) and indicate a water residence time of 1–2 decades. The δ34S data from the Keli Mutu lakes show a much wider range than those from gases and springs, which is probably related to the precipitation of sulfur in these acid brine lakes. The isotopic mass balance and S/Cl values suggest that about half of the sulfur input in the hottest Keli Mutu lake is converted into native sulfur.  相似文献   

9.
Hydrogen and oxygen isotopes of water are common environmental tracers used to investigate hydrological processes, such as evaporation, vegetation water use, surface water–groundwater interaction, and groundwater recharge. The water isotope signature in surface water and groundwater evolves from the initial rain signature. In mountain terrain, rain water stable isotope composition spatially varies due to complex orographic precipitation processes. Many studies have examined the isotope–elevation relationships, while few have quantitatively investigate the terrain aspect and slope effect on rain isotope distribution. In this paper, we examine the orographic effects more completely, including elevation, terrain slope and aspect, on stable isotope distribution in the Mount Lofty Ranges (MLR) of South Australia, using a multivariate regression model. The regression of precipitation isotope composition suggests that orographic effects are the dominant controls on isotope spatial variability. About 75% of spatial variability in δ18O and deuterium excess is represented by the regression using solely orography-related variables (elevation, terrain aspect and slope), with about 25% of δ18O spatial variability attributed to the terrain aspect and slope effect. The lapse rate is about −0.25‰ for every 100 m at both windward and leeward slopes. However, at the same elevation, δ18O at the leeward slope (eastern MLR) is 0.5‰ larger than that at the windward slope. The difference can be explained by different mechanisms – continuous rain-out processes on the windward side and sub-cloud evaporation on the leeward side. Both δ18O and deuterium excess maps (1 km resolution) are constructed based on the regression results for the MLR. Both maps are consistent with groundwater of local precipitation origin, and useful to examine groundwater recharge.  相似文献   

10.
The use of stable isotopes is a practical tool in the study of the lake water budget. This is an one way to study the hydrological cycle in the large numbers of inland lakes on the Tibetan Plateau, in which the isotope record of the sediment is believed to reflect the climatic and environmental changes. The monitoring of stable isotopes of the precipitation, river and lake waters during 2004 in the inland Yamdruk‐tso basin, southern Tibetan Plateau, reveals the lake water δ18O is over 10‰ higher than the local precipitation. This high difference indicates strong isotope enrichment due to lake water evaporation. The simulation results based on the isotope technique show that the present lake water δ18O level corresponds to an average relative humidity of around 54–58% during evaporation, which is very close to the instrumental observation. The simulation results also show that the inland lakes on the Tibetan Plateau have a strong adjustability to the isotope shift of input water δ18O. On average, the isotope component in the inland lake water is to a large extent controlled by the local relative humidity, and can also be impacted by a shift of the local precipitation isotope component. This is probably responsible for the large consistence in the isotope component in the extensive inland lakes on the Tibetan Plateau. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

11.
Characterization of spatial and temporal variability of stable isotopes (δ18O and δ2H) of surface waters is essential to interpret hydrological processes and establish modern isotope–elevation gradients across mountainous terrains. Here, we present stable isotope data for river waters across Kyrgyzstan. River water isotopes exhibit substantial spatial heterogeneity among different watersheds in Kyrgyzstan. Higher river water isotope values were found mainly in the Issyk‐Kul Lake watershed, whereas waters in the Son‐Kul Lake watershed display lower values. Results show a close δ18O–δ2H relation between river water and the local meteoric water line, implying that river water experiences little evaporative enrichment. River water from the high‐elevation regions (e.g., Naryn and Son‐Kul Lake watershed) had the most negative isotope values, implying that river water is dominated by snowmelt. Higher deuterium excess (average d = 13.9‰) in river water probably represents the isotopic signature of combined contributions from direct precipitation and glacier melt in stream discharge across Kyrgyzstan. A significant relationship between river water δ18O and elevation was observed with a vertical lapse rate of 0.13‰/100 m. These findings provide crucial information about hydrological processes across Kyrgyzstan and contribute to a better understanding of the paleoclimate/elevation reconstruction of this region.  相似文献   

12.
Abstract

Water balance studies with stable water isotopes have rarely been conducted in remote and tropical wetland areas. As such, little is known regarding the water balance and groundwater–surface water interaction in the Pantanal, one of the largest and most pristine wetlands in the world. We applied MINA TrêS, a water balance model utilizing stable water isotopes (δ18O, δ2H) and chloride (Cl-) to assess the dry-season hydrological processes controlling groundwater–surface water interactions and the water balance of six floodplain lakes in the northern Pantanal, Brazil. Qualitatively, all lakes exhibited similarity in hydrological controls. Quantitatively, they differed significantly due to morphological differences in controlling groundwater inflow and lake volume. Our approach is readily transferable to other remote and tropical wetland systems with minimal data input requirements, which is useful in regions with sparse hydrometric monitoring.
Editor Z.W. Kundzewicz  相似文献   

13.
The study reports and discusses the differences in δ13C and δ18O values of shells between several species of freshwater snails. Shells were derived from sediment samples collected from depths of 0.5, 1, 2 and 3 m along transects in two shallow eutrophic lakes located in mid-western Poland. Mean δ13C values of the shells ranged between −7.5 and −3.8‰ in Lake Jarosławieckie and between −8.1 and −5.2‰ in Lake Rosnowskie Duże, whereas mean δ18O values ranged between −2.2 and −0.2‰ and between −2.2 and 0.4‰ respectively in the studied lakes. A similar order of species in terms of shell isotope values, from least to most 13C and 18O-depleted was observed in both lakes and seems to indicate constancy of the factors controlling the stable isotope compositions of snail shells. We postulate that the nearly 4‰ difference in the mean carbon stable isotope values between the species was primarily controlled by the amount of metabolic carbon incorporated into the shells and the δ13C values of the snail food. Different growth cessation temperatures and microhabitats of the species studied result in temporally and spatially varied DIC δ13C values, water δ18O values and water temperature of shell precipitation, and may thus differentiate the δ13C and δ18O values of shells. The range of δ13C and δ18O values of individual shells from a sediment sample (mean 2.35 and 2.15‰, respectively) is interpreted as reflecting an intraspecific variability of isotope compositions in shells from a population and changes of the ambient conditions during the accumulation of the sediment layer. The species-specificity and intraspecific variability in C and O isotopic compositions of shells allow concluding that in palaeolimnological studies, stable isotope analyses should be performed on a set of mono-specific shells representing mean isotope compositions of the species for the interval studied rather than single shells or multispecific bulk shell material.  相似文献   

14.
In the present study, the stable isotopes δ18O and δ2H were used for assessment of the water balance in a heterogeneously structured catchment area in the Lusatian Lignite Mining District, in particular, for estimation of the annual groundwater inflow and outflow (IGW and OGW) of Mining Lake Plessa 117. The application of stable isotopes was possible since the water exchange in the catchment area had reached steady‐state conditions after the abandonment of mining activities in 1968 and the filling of the voids and aquifers by re‐rising groundwater in the years thereafter. Diverging slopes of the Evaporation Line and the Global Meteoric Water Line manifested as evaporation from the lake catchment area. The calculated isotope water balance was compared with the commonly used surface water balance, which is unable to differentiate between IGW and OGW, and with a local groundwater model. The groundwater model calculated an IGW of about 811 000 m3 yr?1 and an OGW close to zero, whereas the isotope water balance showed fluxes of about 914 000 and 140 000 m3 yr?1, respectively. Considering the contribution of the groundwater inflow to the total annual input into the lake (ΔIT) and the mean residence time (τ), where the groundwater model and the isotope water balance calculated 42 and 47% for ΔIT and 4·3 and 3·9 years for τ, respectively, it was shown that both water balance calculation methods led to comparable results despite the differences in IGW and OGW. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

15.
As a result of water regulation, dykes (i.e., embankments against floods) were constructed along the Tisza River and meanders were cut to control the floods in the region. These cut‐off meanders resulted in oxbow lakes that are important locations for nature conservation. We collected water samples over 5 years in 7 campaigns to measure the δ18O (‰) and δ2H (‰) ratios in 45 oxbow lakes from the Upper Tisza Region (NE‐Hungary). We applied Random Forest Regression involving climatic data to reveal the connection with the stable isotopes. We determined that isotope ratios changed as a function of time, due to evaporation and a varying water supply (precipitation and groundwater). The average difference in the isotopic ratios for the river and oxbows increased from spring to winter, but decreased between the oxbows on both sides of the dyke. We found that isotope ratios were determined by the maximum monthly temperature in the case of oxbows in the active floodplain, whereas in case of oxbows on the reclaimed side, this was also influenced by the maximum monthly temperature, and the cumulative evaporation. As direct measurement of evaporation is difficult to evaluate, stable isotope measurements provided an effective quantitative alternative to estimate evaporation. Measuring the seasonality of the δ18O and δ2H is important to interpret the results and these data are useful to water management experts to identify the lakes at risk of running dry.  相似文献   

16.
Isotopic exchange with atmospheric vapour can strongly influence the isotopic values of evaporating surface water bodies (e.g., lakes), influencing our understanding of hydrological processes across aquatic and terrestrial environments. Rather than measure the isotopic values of the atmosphere directly, it is much more common to estimate values by assuming equilibrium with local precipitation. This assumption may introduce large errors, thereby biasing hydrological inferences and understanding. The pattern and magnitude of this error has been quantified only in a few circumstances. We compared observations of vapour and precipitation isotope values over a four-year record collected in a montane environment in the central Rocky Mountains of North America. We further investigated factors and conditions promoting disequilibrium. Scenario comparisons assessed the impact of theoretical and methodological elements on the accuracy of the equilibrium assumption. We found that the equilibrium assumption was not well supported by direct and continuous observations of vapour isotopes using tower-based laser isotope spectroscopy, particularly during the summer months. Across all scenarios, errors associated with the equilibrium assumption were high, credibly ranging from 14 to 154 ‰ for δ2H and 1.5 to 16.3 ‰ for δ18O. Environmental covariates (e.g., vapour pressure deficit, air pressure) helped explain some of the apparent disequilibrium. Although the equilibrium assumption for estimating atmospheric vapour isotope values may not be applicable in a continental montane environment, our findings highlight opportunities for using direct vapour isotope measurements to better understand vapour sources, air mass mixing, and phase changes over complex mountainous terrain, which in turn may better constrain regional- to global-scale hydrological process estimates, such as evapotranspiration rates and the water budgets of mountain lakes.  相似文献   

17.
Riparian cottonwood forests in dry regions of western North America do not typically receive sufficient growing season precipitation to completely support their relatively high transpiration requirements. Water used in transpiration by riparian ecosystems must include alluvial groundwater or water stored in the potentially large reservoir of the unsaturated soil zone. We used the stable oxygen and hydrogen isotope composition of stem xylem water to evaluate water sources used by the dominant riparian cottonwood (Populus spp.) trees and shrubs (Shepherdia argentea and Symphoricarpos occidentalis) in Lethbridge, Alberta, during 3 years of contrasting environmental conditions. Cottonwoods did not exclusively take up alluvial groundwater but made extensive use of water sourced from the unsaturated soil zone. The oxygen and hydrogen isotope compositions of cottonwood stem water did not strongly overlap with those of alluvial groundwater, which were closely associated with the local meteoric water line. Instead, cottonwood stem water δ18O and δ2H values were located below the local meteoric water line, forming a line with a low slope that was indicative of water exposed to evaporative enrichment of heavy isotopes. In addition, cottonwood xylem water isotope compositions had negative values of deuterium excess (d‐excess) and line‐conditioned (deuterium) excess (lc‐excess), both of which provided evidence that water taken up by the cottonwoods had been exposed to fractionation during evaporation. The shrub species had lower values of d‐excess and lc‐excess than had the cottonwood trees due to shallower rooting depths, and the d‐excess values declined during the growing season, as shallow soil water that was taken up by the plants was exposed to increasing, cumulative evaporative enrichment. The apparent differences in functional rooting pattern between cottonwoods and the shrub species, strongly influenced the ratio of net photosynthesis to stomatal conductance (intrinsic water‐use efficiency), as shown by variation among species in the δ13C values of leaf tissue.  相似文献   

18.
The direct H2Oliquid–H2Ovapour equilibration method utilizing laser spectroscopy (DVE-LS) is a way to measure soil pore water stable isotopes. Various equilibration times and calibration methods have been used in DVE-LS. Yet little is known about their effects on the accuracy of the obtained isotope values. The objective of this study was to evaluate how equilibration time and calibration methods affect the accuracy of DVE-LS. We did both spiking and field soil experiments. For the spiking experiment, we applied DVE-LS to four soils of different textures, each of which was subjected to five water contents and six equilibration times. For the field soil experiment, we applied three calibration methods for DVE-LS to two field soil profiles, and the results were compared with cryogenic vacuum distillation (CVD)-LS. Results showed that DVE-LS demonstrated higher δ2H and δ18O as equilibration time increased, but 12 to 24 hr could be used as optimal equilibration time. For field soil samples, DVE-LS with liquid waters as standards led to significantly higher δ2H and δ18O than CVD-LS, with root mean square error (RMSE) of 8.06‰ for δ2H and 0.98‰ for δ18O. Calibration with soil texture reduced RMSE to 3.53‰ and 0.72‰ for δ2H and δ18O, respectively. Further, calibration with both soil texture and water content decreased RMSE to 3.10‰ for δ2H and 0.73‰ for δ18O. Our findings conclude that the calibration method applied may affect the measured soil water isotope values from DVE-LS.  相似文献   

19.
Large differences in δ 2H of primary producers between aquatic and terrestrial ecosystems are used to identify subsidies, discriminate organic matter sources, and reduce uncertainty in food web studies. Previous investigations of hydrogen isotope ratios suggest there may be predictable differences between the δ 2H of water and organic matter for different types of primary producers. We define the difference in the net isotopic discrimination between water and bulk organic matter (om) as: ΔH = (δ 2Hom ? δ 2Hwater) ÷ (1 + δ 2Hwater ÷ 1,000). We summarized ΔH values from published literature and we measured the δ 2H of water and primary producers in order to compare ΔH among aquatic and terrestrial primary producers. Measurements were made from three water body types (lake, river, coastal lagoon) and their associated watersheds. Although we predicted a large and equivalent net isotopic discrimination for aquatic primary producers, we found considerable variability among groups of aquatic producers. Macroalgae, benthic microalgae, and phytoplankton had more negative ΔH values (i.e. greater isotopic discrimination) than both aquatic macrophytes and terrestrial vegetation. The more positive δ 2Hom and hence lower ΔH of terrestrial vegetation was expected due to relative increases in the heavier isotope, deuterium, during transpiration. However, the more positive values of δ 2Hom and relatively low ΔH in aquatic macrophytes, even submerged species, was unexpected. Marine macroalgae had high variability in δ 2Hom as a group, but low variability within distinct species. Variability among types of primary producers in δ 2Hom and in ΔH should be assessed when hydrogen is used in isotopic studies of food webs.  相似文献   

20.
In situ pH profiles are reported for the first time for Lakes Nyos and Monoun. The pH profiles were converted to CO2 profiles using HCO3− profiles calculated from conductivity data. Recent observations (1993–1996) at Lake Nyos indicates that CO2 still accumulates below 180 m depth at a rate of 125 Mmol year−1. At Lake Monoun, the majority of CO2 is present below a depth of 60 m, only 25 m below the saturation depth. Consequently, a potential danger of gas explosion is high at both lakes, and artificial degassing of the lakes should be performed as soon as possible. A system for industrial degassing of the lakes is proposed. The system, based on the self-sustained gas lift principle, consists of multiple pipes (14 cm in diameter) with different intake depths; 12 pipes for Lake Nyos (four each at 185, 195 and 205 m) and three pipes for Lake Monoun (at 70, 80 and 90 m). The stepped degassing at different depths is intended to keep the maximum stability of the lakes. The proposed degassing operation was simulated using the code for both lakes. In 5 years, approximately 50% of currently dissolved CO2 in Lake Nyos and 90% in Lake Monoun will be removed. The expected changes in the thermal and chemical structures of the lakes as degassing proceeds will be most easily monitored with a carefully calibrated CTD equipped with a pH sensor. The simulation indicates that the discharged degassed water will sink to a level of neutral buoyancy, i.e. to a maximum of 70 m at Lake Nyos and 35 m at Lake Monoun. There would be no possibility of triggering a gas explosion by this plunge of discharged water because the water present there would have already been replaced by water at lower CO2 concentration, during the degassing from shallower pipes.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号