Oxygen-isotope record of Late-Glacial climatic change in western Ireland

Oxygen-isotope profiles for the Late-Glacial carbonate sediments from Red Bog and adjacent Lough Gur in County Limerick in western Ireland are readily correlated with the classical hiozones delineated on pollen diagrams for the same cores. The estimated summer temperatures of the Bølling/Allerød were as high as those in the early Holocene and are correlated with increasing Milankovitch summer insolation. This warm phase was abruptly terminated in the Younger Dryas cold episode by a depletion of 4% in δ¹⁸O, suggesting a summer atmospheric temperature decrease of about 12°C, comparable to that inferred from fossil beetle data. The Younger Dryas phase is attributed to a major cooling of the sea-surface temperature by a postulated discharge of icebergs similar to that of the Heinrich events, for the icebergs were much more effective than simple meltwater in cooling the sea surface and thus the climate over Europe. Shorter-term cool phases (Older Dryas. Gerzensee. Preboreal oscillation) are also recognized.     

The water resources of lakes in China

This paper mainly deals with water resources of China's lakes. Lakes in China are mainly scattered over five drainage basins, with a total area of 73,580 km² and a storage capacity of 746,000 million m³, in which the fresh water amounts to 221,000 million m³. The water resources of lakes are not evenly distributed in the regions. Their variations within a year and between years are great. So attention should be paid to the rational utilization of water resources and the problems in mangement need careful and skilful handling.     

Structure and timing of the last deglaciation: Oxygen-isotope evidence

Foraminiferal oxygen-isotope data from 24 tropical Atlantic sediment cores, constrained by 77 ¹⁴C dates, are stacked to form a composite record of isotopic Termination 1.. This record indicates that most of the isotopic transition at the end of the last ice age occurred between 14 ka BP and 6 ka BP. Minor isotopic expression of deglaciation is permitted as early as 16 ka BP, but the most rapid rate of change occurred between 14 ka BP and 12 ka BP. Three ‘steps’ of maximum change are present. Although they are close to the statistical limits of detection in the composite record, the clear presence of the steps in individual records suggests that they are real. We estimate their timing at 14-12 ka BP (Termination 1-a), 10-9 ka BP (Termination 1-b), and 8-6 ka BP (Termination 1-c).Centering of the termination near 11 ka BP is consistent with the ‘Milankovitch’ hypothesis that high summer insolation caused deglaciation. In detail, however, maximum rates of change prior to the 11 ka BP insolation extreme, and the inferred steps require additional mechanisms controlling the tempo of glacial-interglacial climate change. Steps equivalent to those in δ¹⁸O have not been detected in ice-margin retreat data. Steps in the isotopic transition, if real, may record thinning of the ice sheets not accompanied by loss of area. Alternation between near-equilibrium and near-stagnant ice-sheet profiles during deglaciation is hypothesized, perhaps due to calving and unstable ‘down-draw’ of the ice sheets followed by partial re-equilibration. Significant problems remain. The effects of temperature on the isotope record are only partially constrained. Presently available data allow only semi-quantitative intercalibration of ice volume, sea level, and isotopic estimates of glaciation.     

Salt lakes in China:Challenges for reconstructing ecological and climate variations

正1 Introduction Studies on lakes have become an important concern for many scientists since it is well known that lakes can monitor detailed information about ecological,hydrological and sedimentary cycles which can be     

Impacts of climatic variables on water-level variations in two shallow Eastern Mediterranean lakes

Variations in temperature and precipitation have direct impacts on the physical, chemical and biological characteristics of the shallow lakes. This paper examines the possible linkages between climate variables and the water levels of shallow interconnected Lakes Mogan and Eymir, located 20 km south of Ankara in Central Anatolia. The variations in the lakes’ water levels during 1996–2015 are studied and the impacts of climate variables on the lake levels are assessed to address the long-term consequences. The nonparametric Mann–Kendall test was used to quantify trends in the climate variables and the lakes’ level fluctuations between the observation periods 1998–2007 and 2008–2014. Statistical analyses results showed that precipitation and temperature have crucial influence on the variations in the lakes’ levels. The projected increase in temperature and decrease in precipitation over the next century may produce substantial decreases in lake levels, with consequent drying of both lakes.     

Hydrogeological investigations in some selected major lakes: A case study

A detailed hydrogeological investigations comprising well inventory, water level monitoring, lake bathymetry, infiltration and pump tests were carried out in a few selected observation wells in order to estimate transmissivity (T) and storativity (S) in all major lakes which are highly polluted by the discharge of sewage and other chemical effluents in greater Hyderabad. The salient features of results are presented lake wise which would be of immense use in restoration of all lakes. Also, the outcome of this study along with infiltration rates may be used for modeling in future to simulate the surface water-ground water interaction.     

Tidal and seasonal variations of sulfate ion in a New Jersey marsh system

Sulfate variations during a tidal cycle were investigated at three sites in a highly polluted tidal marsh. Sulfate- chlorinity relationships were determined in the light of fluctuations in temperature, dissolved oxygen and pH. The relationships were found to be seasonal in nature, being affected by temperature and rainfall effects on biologic productivity. Both reduction of sulfate ion to a sulfide species and oxidation of sulfide species to the sulfate ion were found to occur. Consideration of the sulfide oxidation process suggests the possibility that metals precipitated as sulfides may be mobilized and redistributed in the marsh system.     

A hydrological simulation of the water regime in two playa lakes located in southern Spain

The subject of this paper is the detailed hydrological simulation of two playa lakes located in southern Spain from January 2011 to March 2012 on a daily basis. These playas are placed over a 400-km ² shallow aquifer, which is exposed to an increasing stress caused by agricultural activities, mainly olive grove plantations. The objective of the paper is to elaborate a detailed numeric model that simulates the water regime of each playa lake on a daily scale. The simulation is compared to measured water level (WL) data of the playas in order to characterize the groundwater–surface interactions. The ultimate objective of this paper is to assess the environmental impact of the increasing anthropogenic water consumption within the area of research. The results of the GW–surface interaction were very consistent with previous works. One of the playa lakes is groundwater-dependent and the other one is presumably a perched playa lake. The GW discharge of the former playa (214 mm) during the research period stands in sharp contrast to no regional GW discharge in the latter. Water level data prove that the hydrological year (2011–2012) had a very negative water budget. The evapotranspiration estimation was almost as high as double the sum of the precipitation, the run-off, and the groundwater discharge. The simulation of an anthropologically altered water regime proves that water retrieval has a harmful impact on the WL of the playa lakes as well as on the aquifer.     

Impact of water overexploitation on highland lakes of eastern Ethiopia

The eastern Ethiopian highland is endowed with large potential of water resources in terms of rainfall, groundwater and surface water. Yet, due to overpumping of lake water and groundwater and environmental degradation, Lakes Haromaya and Adele have completely dried up. The environmental degradation, due to deforestation and clearing of land for farming, has increased the rate of siltation in the lakes that dramatically decreases the lakes’ volume and surface albedo, which increased the rate of evaporation. The impact of these factors is aggravated due to decreasing net recharge to the lake and the alluvial aquifer. Over the last 35 years, pumping of lake water for irrigation, mainly for subsistence farming, domestic and industrial use shows an increasing trend. Hence, the available water for drinking and industrial purposes decreased drastically. In this research, classical Penman aerodynamic combined energy budget, Penman nomogram methods, conventional soil moisture water balance method and Penman–Monteith model were adopted to estimate free evaporation, actual and potential evapotranspirations. The results indicate that evaporation is the dominant factor for the loss of water and water abstraction is 316% higher than the effective precipitation, which is 110 mm/year. Therefore, overexploitation of the available resources has played an aggravating role for the loss of the lakes in the area. The main cause for such resource depletion is the lack of integrated water resources management strategies. The current water shortage in the area has mainly affected urban residents of Harar, Awoday and Alemaya towns and the surrounding villages, which depend heavily on the two lakes. To alleviate the current crises interbasin water transfer and rainwater harvesting would be possible alternatives besides ameliorating environmental situation of the basin.     

A review of some unique aspects of the limnology of shallow Southern African man-made lakes

Large numbers of man-made lakes occur throughout S Africa. Although primarily designed for specific water supply purposes, most of these lakes fulfill a multipurpose role. The need for such large numbers of reservoirs is related to vagaries in rainfall and runoff; these uncertainties have led to the development of a philosophy of conserving water quantity, which has created some unusual limnological conditions. Examination of the hydrography and limnology of 64 S African impoundments reveals that both basin morphometry and water retention times are affected by natural (drought/flood) and artificial (drawdown) factors which, in turn, affect the hydrodynamics of the lakes, whilst the introduction of treated effluents as a water conservation measure gives rise to a large percentage of enriched lakes having extremely high productivity.     

Diffusion of ions in sea water and in deep-sea sediments

The tracer-diffusion coefficient of ions in water, D_j⁰, and in sea water, $\text{D}{}_{\mathrm{j}}{}^1$, differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective $\text{D}{}_{\mathrm{j}}{}^1$ or D_j⁰ values. The tracer diffusion coefficients of ions in deep-sea sediments, D_j,sed., can be related to $\text{D}{}_{\mathrm{j}}{}^1$ by $\text{D}{}_{\mathrm{j,sed.}}\text{= D}{}_{\mathrm{j}}{}^1\text{·}\text{α}\text{θ}{}^2$, where θ is the tortuosity of the bulk sediment and a a constant close to one.     

青藏高原水源涵养能力时空变化规律

利用水均衡原理和地表能量平衡原理定量评估青藏高原地区水源涵养量,利用多年降雨和蒸发数据研究青藏高原水源涵养能力在空间上的分布状况及其随时间的变化过程,探讨近几十年来青藏高原水源涵养能力时空变化规律。结果表明,近几十年来青藏高原主要形成了3个水源涵养量持续减少的中心区域和2个水源涵养量增强的区域,其中水源涵养能力减弱的区域主要分布于雅鲁藏布江源头、青藏高原南部边缘地带和青海省东部与甘肃交界地带;水源涵养能力增强的区域主要分布于雅鲁藏布江中游河谷地带、澜沧江和金沙江中游河谷地带。     

土壤-水混合实验同位素变化研究

土壤是一个复杂的系统,研究土壤对输入水分中氢氧稳定同位素组成的影响对了解水分在土壤中的运移机理及流域径流分割等具有重要作用。通过两种不同土壤与同一种输入水之间和同一种土壤与两种不同输入水之间的两组混合实验,研究土壤水与输入水达到同位素平衡的时间和引起二者同位素变化的原因。实验结果表明,土壤水与输入水之间同位素变化主要由混合作用引起;土壤对输入水氢氧同位素的吸附现象较难观测到,易被氢氧同位素测样误差掩盖,有待进一步研究;土壤水和输入水在混合搅拌条件下最快能在0.5～1h达到同位素平衡。     

拉萨河谷大气水汽日变化特征

基于近10年(1999~2008年)地基GPS遥感的大气可降水量(GPS-PW)资料和地面气象资料,分析了拉萨河谷各季GPS-PW日变化特征及其对夏季降水日变化特征的影响。结果表明,在拉萨河谷各季GPS-PW都具有明显的日变化特征。春、夏、秋和冬季GPS-PW平均日变化幅度分别为1.0mm、1.7mm、1.0mm和0.8mm。GPS-PW日最小值和最大值出现的时间随季节变化不大,分别出现在08:00~10:00UTC和15:00~18:00UTC。各季GPS-PW日变化序列的谐波分析结果表明,日循环(24h)与半日循环(12h)是GPS-PW日变化的主要信号。日循环信号夏季最强,冬季最弱;半日循环信号夏季最强,春季最弱。在夏季GPS-PW达到日最大值的时间比平均逐时降水频次和降水量达到日最大值的时间约早2h。GPS-PW日变化对夏季降水日变化特征具有重要影响。     

Effect of groundwater on the ecological water environment of typical inland lakes in the Inner Mongolian Plateau

To explore the causes of the ecological environment deterioration of lakes in the Inner Mongolia Plateau, this study took a typical inland lake Daihai as an example, and investigated the groundwater recharge in the process of lake shrinkage and eutrophication. Using the radon isotope (²²²Rn) as the main means of investigation, the ²²²Rn mass balance equation was established to evaluate the groundwater recharge in Daihai. The spatial variability of ²²²Rn activity in lake water and groundwater, the contribution of groundwater recharge to lake water balance and its effect on nitrogen and phosphorus pollution in lake water were discussed. The analysis showed that, mainly controlled by the fault structure, the activity of ²²²Rn in groundwater north and south of Daihai is higher than that in the east and west, and the difference in lithology and hydraulic gradient may also be the influencing factors of this phenomenon. The ²²²Rn activity of the middle and southeast of the underlying lake is greater, indicating that the ²²²Rn flux of groundwater inflow is higher, and the runoff intensity is greater, which is the main groundwater recharge area for the lake. The estimated groundwater recharge in 2021 was 3 017×10⁴ m³, which was 57% of the total recharge to the lake, or 1.6 times and 8.1 times that of precipitation and surface runoff. The TN and TP contents in Daihai have been rising continuously, and the average TN and TP concentrations in the lake water in 2021 were 4.21 mg·L^?1 and 0.12 mg·L^?1, respectively. The TN and TP contents entering the lake with groundwater recharge were 6.8 times and 8.7 times above those of runoff, accounting for 87% and 90% of the total input, respectively. The calculation results showed that groundwater is not only the main source of recharge for Daihai, but also the main source of exogenous nutrients. In recent years, the pressurized exploitation of groundwater in the basin is beneficial in increasing the groundwater recharge to the lake, reducing the water balance difference of the lake, and slowing down the shrinking degree of the lake surface. However, under the action of high evaporation, nitrogen and phosphorus brought by groundwater recharge would become more concentrated in the lake, leading to a continuous increase in the content of nutrients and degree of eutrophication. Therefore, the impact of changes in regional groundwater quantity and quality on Daihai is an important issue that needs further assessment.     

新疆库米什盆地硝酸盐型盐湖中锶离子迁移富集规律研究

新疆库米什盆地是典型的硝酸盐型盐湖分布区,盆内盐湖中Sr2+的含量明显比新疆其他盐湖要高,但对该地区盐湖中Sr2+的迁移富集规律尚未开展深入研究.本文以库米什盆地硝酸盐型盐湖为研究对象,探讨了研究区硝酸盐型盐湖中Sr2+的迁移富集规律.研究结果表明:①库米什盆地水体和沉积物中的Sr2+均具有自北西至南东向逐渐迁移富集的...     

Environmental and diagenetic variations in carbonate associated sulfate: An investigation of CAS in the Lower Triassic of the western USA

An integrated stable isotope, elemental and petrographic analysis of Early Triassic (Spathian) carbonates and evaporites along a proximal to deep environmental transect reveals significant variations in δ³⁴S composition of carbonate associated sulfate (CAS). The variations in the δ³⁴S of CAS are strongly correlated with the Ca/Mg composition of carbonates, suggesting that the variations are driven by the degree of dolomitization. The δ³⁴S of dolostones and evaporites are similar to one another and exhibit lower δ³⁴S values than limestones from all localities.Three hypotheses may explain the differences in δ³⁴S between proximal dolostones/evaporites and inner/middle shelf limestones: (1) limestones experienced anaerobic sulfate reduction and subsequent incorporation of ³⁴S-enriched sulfate into CAS during diagenesis, while dolostones did not—this is unlikely because of the lack of correlation between δ³⁴S_CAS and TOC, as well as other indicators of diagenesis, (2) dolomitization controlled the δ³⁴S_CAS in proximal paleoenvironments, where the source of the ³⁴S depleted fluids was either continentally-derived or the result of Rayleigh distillation during evaporite formation, and (3) a δ³⁴S depth gradient existed during the Early Triassic such that limestones formed in distal waters are more enriched in ³⁴S versus evaporites and dolostones formed in proximal settings—we do not favor this hypothesis because the strong correlation between Ca/Mg and δ³⁴S_CAS implies that dolomitization controls the δ³⁴S_CAS in these samples. Results from subtidal, well-preserved (non-dolomitized) limestones suggest that the δ³⁴S of Spathian seawater sulfate may have been heavier than previously suggested from analyses of evaporite deposits alone.     

Oxygen isotope biogeochemistry of pore water sulfate in the deep biosphere: Dominance of isotope exchange reactions with ambient water during microbial sulfate reduction (ODP Site 1130)

Microbially mediated sulfate reduction affects the isotopic composition of dissolved and solid sulfur species in marine sediments. Experiments and field data show that the composition is also modified in the presence of sulfate-reducing microorganisms. This has been attributed either to a kinetic isotope effect during the reduction of sulfate to sulfite, cell-internal exchange reactions between enzymatically-activated sulfate (APS), and/or sulfite with cytoplasmic water. The isotopic fingerprint of these processes may be further modified by the cell-external reoxidation of sulfide to elemental sulfur, and the subsequent disproportionation to sulfide and sulfate or by the oxidation of sulfite to sulfate. Here we report values from interstitial water samples of ODP Leg 182 (Site 1130) and provide the mathematical framework to describe the oxygen isotope fractionation of sulfate during microbial sulfate reduction. We show that a purely kinetic model is unable to explain our data, and that the data are well explained by a model using oxygen isotope exchange reactions. We propose that the oxygen isotope exchange occurs between APS and cytoplasmic water, and/or between sulfite and adenosine monophosphate (AMP) during APS formation. Model calculations show that cell external reoxidation of reduced sulfur species would require up to 3000 mol/m³ of an oxidant at ODP Site 1130, which is incompatible with the sediment geochemical data. In addition, we show that the volumetric fluxes required to explain the observed data are on average 14 times higher than the volumetric sulfate reduction rates (SRR) obtained from inverse modeling of the porewater data. The ratio between the gross sulfate flux into the microbes and the net sulfate flux through the microbes is depth invariant, and independent of sulfide concentrations. This suggests that both fluxes are controlled by cell density and that cell-specific sulfate reduction rates remain constant with depth.