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 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   

2.
This study aimed to understand changes in the biogeochemical processing of organic matter (OM) in response to multiple stressors (e.g., littoral area expansion, wastewater input, and hydrological regulation) in East Dongting Lake (Central China) over the past 60 years, using analyses of total organic carbon (TOC), total nitrogen (TN), C/N ratios, δ13C, δ15N, and diatoms from 2 sediment cores collected from the littoral and central parts of the lake. OM mainly originated from phytoplankton and C3 plant‐derived soil OM based on the ranges of C/N ratios (from 7 to 11) and δ13C (between ?27‰ and ?23‰). Littoral area expansion due to siltation caused an increasing influx of terrestrial soil OM in the 1980s and the 1990s, subsequently lowering δ13C values and rising C/N ratios in both sediment cores. Meanwhile, higher δ15N was linked to a high influx of isotopically heavy nitrate from urban and agricultural wastewaters. After 2000, slight decreases in TOC and TN in the littoral area were attributable to reducing inputs of external OM, likely linked to declining sediment influx from the upper reaches resulting from the Three Gorges Dam impoundment. Contrasting increases in TOC, TN, and C/N ratios in the central part indicated a high influx of terrestrial soil OM due to the declining distance from the shoreline with littoral area expansion. Declining δ15N values after 2000 indicated an increase in N2‐fixing cyanobacteria with eutrophication. Changes in diatom assemblages in both the littoral and central zones reflected nutrient enrichment and hydrological alterations. These results indicate that littoral expansion, declining riverine influx, and anthropogenic nutrient inputs are potential driving forces for the biogeochemical processing of OM in floodplain lakes. This study provides sedimentary biogeochemical clues for tracking past limnological conditions of floodplain lakes that are subjected to increasing disturbances from hydrological regulation and eutrophication.  相似文献   

3.
Exchange of groundwater and lake water with typically quite different chemical composition is an important driver for biogeochemical processes at the groundwater‐lake interface, which can affect the water quality of lakes. This is of particular relevance in mine lakes where anoxic and slightly acidic groundwater mixes with oxic and acidic lake water (pH < 3). To identify links between groundwater‐lake exchange rates and acid neutralization processes in the sediments, exchange rates were quantified and related to pore‐water pH, sulfate and iron concentrations as well as sulfate reduction rates within the sediment. Seepage rates measured with seepage meters (?2.5 to 5.8 L m‐2 d‐1) were in reasonable agreement with rates inverted from modeled chloride profiles (?1.8 to 8.1 L m‐2 d‐1). Large‐scale exchange patterns were defined by the (hydro)geologic setting but superimposed by smaller scale variations caused by variability in sediment texture. Sites characterized by groundwater upwelling (flow into the lake) and sites where flow alternated between upwelling and downwelling were identified. Observed chloride profiles at the alternating sites reflected the transient flow regime. Seepage direction, as well as seepage rate, were found to influence pH, sulfate and iron profiles and the associated sulfate reduction rates. Under alternating conditions proton‐consuming processes, for example, sulfate reduction, were slowed. In the uppermost layer of the sediment (max. 5 cm), sulfate reduction rates were significantly higher at upwelling (>330 nmol g‐1 d‐1) compared to alternating sites (<220 nmol g‐1 d‐1). Although differences in sulfate reduction rates could not be explained solely by different flux rates, they were clearly related to the prevailing groundwater‐lake exchange patterns and the associated pH conditions. Our findings strongly suggest that groundwater‐lake exchange has significant effects on the biogeochemical processes that are coupled to sulfate reduction such as acidity retention and precipitation of iron sulfides. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

4.
The vertical sediment profiles (10 cm) of the margins of three shallow subtropical lakes (Rio Grande, Brazil) with different trophic states and surrounding areas were evaluated to identify the effects of the allochthonous input on the methane concentration in the sediment. Sediment cores were collected to quantify the organic matter content (OM) and total carbon (TC), total nitrogen (TN), total phosphorous (TP) and methane (CH4) concentrations.The three lakes were distinguished according to the trophic status and classified as oligotrophic, dystrophic and eutrophic. The natural characteristics of the dystrophic and eutrophic lakes have been changed due to the allochthonous input of leaves and twigs (Eucalyptus sp.) and the excreta of birds, respectively. In the eutrophic lake, the allochthonous input contributed to high autochthonous production. The highest values of OM, TC, TN and TP were found in the superficial sediments of the dystrophic and eutrophic lakes. The accumulation of allochthonous organic matter in the littoral zone promoted changes in the vertical sediment profiles and contributed to increases in the CH4 concentrations in the sediment.  相似文献   

5.
Lacustrine groundwater discharge (LGD) and the related water residence time are crucial parameters for quantifying lake matter budgets and assessing its vulnerability to contaminant input. Our approach utilizes the stable isotopes of water (δ18O, δ2H) and the radioisotope radon (222Rn) for determining long‐term average and short‐term snapshots in LGD. We conducted isotope balances for the 0.5‐km2 Lake Ammelshainer See (Germany) based on measurements of lake isotope inventories and groundwater composition accompanied by good quality and comprehensive long‐term meteorological and isotopic data (precipitation) from nearby monitoring stations. The results from the steady‐state annual isotope balances that rely on only two sampling campaigns are consistent for both δ18O and δ2H and suggested an overall long‐term average LGD rate that was used to infer the water residence time of the lake. These findings were supported by the good agreement of the simulated LGD‐driven annual cycles of δ18O and δ2H lake inventories with the observed lake isotope inventories. However, radon mass balances revealed lower values that might be the result of seasonal LGD variability. For obtaining further insights into possible seasonal variability of groundwater–lake interaction, stable water isotope and radon mass balances could be conducted more frequently (e.g., monthly) in order to use the derived groundwater discharge rates as input for time‐variant isotope balances.  相似文献   

6.
Study of interactions between surface-water and pore-water in lakes is complicated due to spatio-temporal heterogeneities in flow condition across the sediment–water interface. In this study, seasonal hypersaline Maharlu Lake was investigated by collecting surface-water and pore-water samples from four nests of multilevel piezometers installed at different distances from the inflow of rivers to the lake. The hydraulic heads in the piezometers as well as vertical profiles of Mg+2, Na/Cl, and Br/Cl were used to investigate both hydraulic and geochemical interactions between surface-water and pore-water in the lake. Depletion of lake surface water and pore water with respect to B, Br, Li+, K+, Mg2+ and the absence of Mg-K chlorides and sulphates in the lake bed sediments is probably due to leakage of highly evaporated residual brine from the lake. Hydraulic gradients in the multilevel piezometric nests indicate that a general downward flow from surface-water to pore-water occurs across sediment–water interface. Vertical profiles of Br/Cl, Mg2+, and Na/Cl showed that the maximum flow rate was more than 1 m/yr close to the mouth of the inflowing rivers. The downward vertical flow was limited in the area far from the inflowing rivers due to the presence of an impermeable confining halite layer which interrupts the hydraulic connection between shallow pore water (less than 50 cm deep) and deeper zones. The hydraulic and geochemical interactions between surface-water and pore-water across sediment–water interface in the Maharlu Lake are of interest to find out the fate of pollutants and their distribution in the lake.  相似文献   

7.
Porewater profiles often are used to identify and quantify important biogeochemical processes occurring in lake sediments. In this study, multiple porewater profiles were obtained from two eutrophic Swiss lakes using porewater equilibrators (peepers) in order to examine spatial and seasonal trends in biogeochemical processes. Variability in profile shapes and concentrations was small on spatial scales of a few meters, but the uncertainty in calculated diffusive fluxes across the sediment surface was, on average, 35%. Focusing of Fe and Mn oxides toward the lake center resulted in systematic increases in porewater concentrations and diffusive fluxes of Fe2+ and Mn2+ with increasing water depth; these fluxes are postulated to be regulated by the pH-dependent dissolution of reduced-metal phases. Despite higher concentrations of inorganic carbon, NH 4 + , Si and P in pelagic compared to littoral sites, diffusive fluxes of these substances across the sediment surface increased only slightly or not at all with increasing water depth. Porewater profiles did reveal temporal changes in Fe2+, Mn2+, Ca2+ and Mg2+ that were an indirect result of the large, seasonal changes in seston deposition, but no clear seasonal variations were found in diffusive fluxes of nutrients across the sediment surface. The intense mineralization occurring at the sediment surface was not reflected in the porewater profiles nor in the calculated diffusive fluxes. Calculated diffusive fluxes across the sediment surface resulted from decomposition occurring primarily in the top 5–7 cm of sediment. Diffusive fluxes from this subsurface mineralization were equal to the solute release from mineralization occurring at the sediment-water interface. Buried organic matter acts as a memory of previous lake conditons; it will require at least a decade before reductions in nutrient inputs to lakes fully reduce the diffusive fluxes into the lake from the buried reservoir of organic matter.  相似文献   

8.
  相似文献   

9.
Stable isotopes, 2Hwater, 18Owater as well as 18Osulphate and 34Ssulphate, were used to study the flow system of shallow groundwater and soil water at the base area of a former leaching heap at the uranium mining area of Ronneburg, Germany. The flow paths and water‐retention times were estimated by comparison of δ2H and δ18O values in groundwater and soil water to the δ2H and δ18O signature of precipitation, giving distinctive inputs of summer or winter precipitation. The points of measuring the groundwater were divided into three categories with different flow conditions: rapid flow, stagnant conditions and a transition zone by hierarchical cluster analysis of δ2H and δ18O values of groundwater. The transit time of groundwater in the rapid flow area is less than 6 months, whereas water in the stagnant zone is stored for at least 1 year. In soil water, a clear response to different input signals is detectable only in the 30‐cm horizon (retention time is about 6 months), whereas at deeper levels a mixing with older water is taking place. The isotopic composition of the dissolved sulphate was used to identify oxidation of sulphides as the source of sulphate. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

10.
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   

11.
We present the results of a 3‐year monitoring programme of the stable isotope composition of lake water and precipitation at Taozi Lake, in the East Asian monsoon region of China. Our aims were to reveal the spatiotemporal pattern of variation of stable isotopes in a small closed‐basin lake and to quantitatively determine the impacts of precipitation and evaporation on the stable isotope composition of lake water under a humid monsoon climate. In the time domain, the stable oxygen isotopic ratio of the lake water (δ18OL) exhibited substantial seasonal and interannual variations, but the isotope variations between different precipitation events substantially exceeded seasonal and interannual variations. Compared with the stable isotopes in precipitation, δ18OL was substantially positive and dL was negative. In the space domains, the lake water was homogeneously mixed. Indicated by statistic analyses, precipitation plays a dominant role in dynamic of the lake stable isotope during precipitation events of relatively large magnitude, whereas the effect of evaporation is dominant during smaller precipitation events. Results advance our understanding of the stable isotope change rule in the process of lake water evaporation, and it is helpful to identify the climatic significance recorded in stable isotopic compositions of lake bottom sediments.  相似文献   

12.
The isotopic features of Lake Trekhtsvetnoe in the White Sea coast area were studied in 2012–2015 in both winter and summer. Lake Trekhtsvetnoe is a water body, separating from the sea, with constant vertical stratification throughout the observation period. Its isotopic, hydrophysical, and biological characteristics have been studied. By the isotopic profile of lake water body, three zones can be identified in the lake: (1) 0–1 m: mixolimnion zone with δ18O varying from–12 to–11.1‰; (2) 1.0–3.0 m: zone with transitional properties with δ18O varying from–11.1 to–5.5‰; (3) 3.0–7.6 m: monimolimnion zone with highest values of δ18O—from–5.5 to–4.7‰.  相似文献   

13.
The purpose of this study was to examine the historical change in sedimentation rates in lakes that have been impacted by river regulation and agricultural activities in the Ishikari River floodplain. We dated sediment cores using caesium‐137 (137Cs) dating and tephrochronology, and we estimated sediment sources from 137Cs concentrations in the topsoil of representative land covers. We found that, between 1739 and 1963, the distance between the lake and the main river channel and whether or not the lake was connected to the river affected the sedimentation rates. After 1963, agricultural drainage systems were established in the Ishikari River floodplain. The average sedimentation rate before and after the construction of drainage ditches varied between 1–66 and 87–301 mg cm–2 a–1, respectively. The increase in the sedimentation rate after 1963 was caused by the construction of a number of drainage networks, as well as extensive cultivation activity and/or fragmentation of the swamp buffers surrounding the lakes. The 137Cs activities at the surfaces of the lake as well as the catchment‐derived 137Cs contributions and 137Cs inventory in the lake profiles were used to examine the sediment influx from the various drainage areas after the establishment of the drainage system. Our results indicate that the majority of the lake sediments were derived from cultivated areas, and therefore the catchment‐derived 137Cs contribution in the lakes was strongly correlated with the sedimentation rate. The 137Cs inventory across all of the lake profiles was also significantly greater than the atmospheric fallout. We identified a negative correlation between the 137Cs lake profile inventory and the sedimentation rate. This is because the sediment originating from the drainage areas contained low 137Cs concentrations, which diluted the overall concentration of 137Cs in the lake sediment. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

14.
Among the perennially frozen lakes of the Dry Valleys of South Victoria Land (Antarctica), some are dry‐based, i.e. frozen to the bottom. One of these is studied here by a multiparametric investigation (isotopic composition in δD and δ18O, ions, gas and ice texture analyses). A sediment layer about 10 cm thick appearing at a depth of 3·5 m is also studied by grain size, X‐ray diffraction and scanning electron microscope analyses. The information retrieved indicates that this ice‐block lake results from a build‐up in two steps and explains how aeolian sediments were included as a layer into the ice. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

15.
Stable water isotopes (δ18O and δ2H) are an important source signature for understanding the hydrological cycle and altered climate regimes. However, the mechanisms underlying atmospheric water vapour isotopes in the northeast Qinghai‐Tibetan Plateau of central Asia remain poorly understood. This study initially investigated water vapour isotopic composition and its controls during the premonsoon and monsoon seasons. Isotopic compositions of water vapour and precipitation exhibited high variability across seasons, with the most negative average δ18O values of precipitation and the most positive δ18O values of water vapour found during the premonsoon periods. Temperature effect was significant during the premonsoon period but not the monsoon period. Both a higher slope and intercept of the local meteoric water line were found during the monsoon period as compared with in the premonsoon period, suggesting that raindrops have been experienced a greater kinetic fractionation process such as reevaporation below the cloud during the premonsoon periods. The δ2H and δ18O signatures in atmospheric water vapour tended to be depleted with the occurrence of precipitation events especially during the monsoon period and probably as a result of rainout processes. The monthly average contribution of evaporation from the lake to local precipitation was 35.2%. High d‐excess values of water vapour were influenced by the high proportion of local moisture mixing, as indicated by the gradually increasing relative humidity along westerly and Asian monsoon trajectories. The daily observation (observed ε) showed deviations from the equilibrium fractionation factors (calculated ε), implying that raindrops experienced substantial evaporative enrichment during their descent. The average fraction of raindrops reevaporation was estimated to be 16.4± 12.9%. These findings provide useful insights for understanding the interaction between water vapour and precipitation, moisture sources, and help in reconstructing the paleoclimate in the alpine regions.  相似文献   

16.
Limited information exists on one of the mechanisms governing sediment input to streams: streambank erosion by ground water seepage. The objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow/erosion with precipitation, stream stage and soil pore water pressure. The streambank site was located in Northern Mississippi in the Goodwin Creek watershed. Soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity (Ks) with depth, but differences between lateral Ks of a concretion layer and the vertical Ks of the underlying layers contributed to the propensity for lateral flow. Goodwin Creek seeps were not similar to other seeps reported in the literature, in that eroded sediment originated from layers underneath the primary seepage layer. Subsurface flow and sediment load, quantified using 50 cm wide collection pans, were dependent on the type of seep: intermittent low‐flow (LF) seeps (flow rates typically less than 0·05 L min?1), persistent high‐flow (HF) seeps (average flow rate of 0·39 L min?1) and buried seeps, which eroded unconsolidated bank material from previous bank failures. The timing of LF seeps correlated to river stage and precipitation. The HF seeps at Goodwin Creek began after rainfall events resulted in the adjacent streambank reaching near saturation (i.e. soil pore water pressures greater than ?5 kPa). Seep discharge from HF seeps reached a maximum of 1·0 L min?1 and sediment concentrations commonly approached 100 g L?1. Buried seeps were intermittent but exhibited the most significant erosion rates (738 g min?1) and sediment concentrations (989 g L?1). In cases where perched water table conditions exist and persistent HF seeps occur, seepage erosion and bank collapse of streambank sediment may be significant. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

17.
A three‐dimensional, numerical free‐surface‐flow simulation model is developed to investigate hydrodynamics of a lake and the predictive capabilities of the numerical model are validated by comparing them with field results obtained from Lake Naini, Uttar Pradesh, using environmental isotope (δ18O, δD and 3H) techniques. This has been carried out in order to understand the hydrodynamics of a lake (i.e. circulations, mixing and transport of water within the lake). Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

18.
Understanding plant water use patterns is crucial for comprehending the dynamics of the soil–plant-atmosphere continuum and evaluating the adaptability of plants across diverse ecosystems. However, there remains a gap in our comprehension of non-halophyte plants' water uptake patterns and driving factors in temperate coastal regions. For this reason, we used locust trees (a widely planted non-halophyte tree species in northern China) as a study subject. We collected water isotope data (δ2H and δ18O) for locust trees xylem and soil over two consecutive growing seasons. The MixSIAR model was used along with five distinct sets of input data (single isotopes, uncorrected dual isotopes, and corrected dual isotopes incorporating δ2H data obtained by soil water line or cryogenic vacuum distillation methods) to infer water utilization patterns. The results indicated that locust trees primarily absorb shallow soil water (0–20 cm, 29.4% ± 16.9%) and deep soil water (120–180 cm, 24.7% ± 5.8%). Pearson's correlation analysis revealed the key driving factors behind water uptake patterns were vegetation transpiration and soil salinity. Remarkably, the build up of salts in the lower soil layer (60–120 cm) hinders the absorption of water by plants. To prevent high salt concentrations from affecting water uptake in non-halophyte plants, we recommend implementing sufficient irrigation from March to April each year to meet the water needs of plant growth and regulate the accumulation of salts in various soil layers. This study reveals the dynamic water utilization strategy of non-halophyte plants in temperate coastal regions, offering valuable information for water resources management.  相似文献   

19.
The medium shallow lake Grimnitzsee (maximum depth: 9.9 m; mean depth: 4.6 m; area: 7.7 · 106 m2) which is situated in the biosphere reserve “Schorfheide-Chorin” in northern Brandenburg (Germany) was studied in 1994 and 1995. A bathymetric map of Grimnitzsee is given for the first time. The lake is usually polymictic although in 1994 and 1995 relatively long summer stratification was observed due to very high global radiation input. Nutrient concentration, light climate, oxygen status, phytoplankton biomass and the species composition of littoral diatoms characterize the lake as eutrophic. Special features deducible from the lake's polymictic character were the multiple development of aerobic or anaerobic strata above the sediment, the fast recovery of silicon concentration in the water column after diatom sedimentation, the importance of resuspension for the success of planktonic diatom populations, and an only moderate correlation between chlorophyll a concentration and light attenuation as well as seston dry weight probably due to the influence of suspended particles.  相似文献   

20.
Here, we studied the isotope characteristics and source contributions of soil water in the permafrost active layer by collecting soil samples in July 2018 in Yangtze River basin. Soil moisture and temperature showed decreasing trends from 0–80 cm, and an increasing trend from 80–100 cm. The value of δ18O and δD first increased and then decreased in the soil profile of 0–100 cm; however, d-excess increased from 0–100 cm. δ18O values became gradually positive from the southwest to northeast of the study area, while d-excess gradually increased from southeast to northwest. The evaporation water line (EL) was δD = 7.56 δ18O + 1.50 (R2 = 0.90, p < 0.01, n = 96). Due to intense solar radiation and evaporation on the Tibetan Plateau, the elevation did not impact the surface soil. The altitude effect of the soil depths of 0–20 cm was not obvious, but the other soil layers had a significant altitude effect. Soil moisture and temperature were closely related to the stable isotopic composition of soil water. The contribution of precipitation to soil water on the sunny slope was 86%, while the contribution of the shady slope was 84%. However, the contribution of ground ice to soil water on sunny slope was 14% and the shady slope was 16%. The contribution of ground ice to soil water increased with increasing altitude on the sunny slope, but the contribution of ground ice to soil water had no obvious trend on the shady slope.  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