Lake Level Decline Research Articles

Impact of lake water level decline on river evolution in Ebinur Lake Basin (an ungauged terminal lake basin)

Most of the terminal lakes in inland basins, which account for half of the world's lake reserves, have been shrinking at an alarming rate in recent years. In a Terminal Lake Basin, changes in the water level of the lake can lead to variations in the local erosion base level. From the perspective of local erosion base level, we revealed the response of river evolution to change in the water level of lake in Ebinur Lake Basin for the past 5000 years. Our results verified the three geomorphic development stages of natural decline, balance maintenance, and imbalanced decline. In modern times, the decline in the number of rivers entering the lake due to human activities has made the water level of the lake drop 15–30 times that observed from 5 kaBP–0.1 kaBP. The results showed that the average undercut erosion rate of the river entering the lake tends to increase with a rapid decrease in the water level of the lake in the past 5000 years. The instantaneous undercutting rate of the Bortala river section in the basin was 1.6–4.2 times that observed from 5 kaBP–0.1 kaBP. This result showed that a rapid decline in the water level of the lake due to human activities will accelerate the erosion of rivers. Therefore, from the perspective of geomorphology, the river erosion triggered by the rapid decline in the local erosion base level is an important reason for the continuous shrinkage of Ebinur Lake.

A ∼300-year record of environmental changes in Lake Issyk-Kul, Central Asia, inferred from lipid biomarkers in sediments

We measured lipid biomarkers (n-alkanes [n-ALKs] and n-alkanoic acids [n-FAs]) and other components of organic matter (total organic carbon [TOC] and total nitrogen [TN]) in a sediment core from Lake Issyk-Kul, Central Asia, to infer environmental changes in and around the lake during the last ∼300 years. Stratigraphic shifts in lipid biomarkers, TOC and TN, indicate three distinct environmental stages in the lake over the past three centuries: (1) Stage I (1670s–1790s, 51–36 cm sediment depth) corresponds to a period of stable hydrology in the lake, reflected by relatively constant concentrations of n-ALKs and n-FAs and values of related indexes. The interval was a period of relatively low trophic state. Natural factors were the main controls on environmental changes in and around the lake. (2) Stage II (1800s–1970s, 35–15 cm sediment depth) was a period when human activities began to exert influence on the environment in and around the lake. Enhanced agricultural exploitation and greater regional rainfall resulted in delivery to the lake of more land-derived lipids. Logging activity around the lake altered the vegetation, as revealed by shifts in C27/C33 ratios and the average chain length (ACL27−33). A significant decline in lake level caused by excessive water consumption impacted aquatic macrophytes, as revealed by a reduction in macrophyte indicators. Lower nutrient concentrations were inferred for this period. (3) Stage III (1980s–present, 14–0 cm sediment depth) corresponds to a period of accelerating eutrophication. Before year 2000, lake level declined steadily as a result of low rainfall (drought) and high evaporation, which exerted a strong influence on the lake condition. In addition, anthropogenic activities contributed to lake eutrophication. After 2000, the lake experienced a dramatic increase in trophic state, characterized by high algal productivity, as indicated by greater TN, short-chain n-ALKs and short-chain n-FAs. The change was probably caused by flourishing tourism around the lake. In summary, environmental changes in and around Lake Issyk-Kul during the past ∼300 years were originally driven largely by natural factors such as shifts in regional precipitation amount. Human activities (e.g. logging, agriculture, water extraction, and more recently, tourism) took on increasingly important roles during the last two centuries, affecting watershed vegetation, the lake primary producer community and lake trophic status. Changes recorded in the lake sediments over the last ∼300 years are in good agreement with historical records.

Temporal dynamics of dissolved organic matter (DOM) in mountain lakes: the role of catchment characteristics

Climate change is affecting mountain ecosystems by increasing vegetation coverage and altering meteorological conditions. These changes are likely to impact the timing and magnitude of dissolved organic matter (DOM) inputs to lakes from the surrounding catchment. We examined temporal dynamics of DOM using in situ optical sensors that measured DOM fluorescence (fDOM) through the ice-free season in five lakes with differing catchment characteristics. We also measured changes in lake level and compiled daily meteorological data from nearby weather stations. At a seasonal time scale, fDOM dynamics occurred in two phases. fDOM declined in the first phase, which lasted until late July – mid-August, and corresponded to a decline in lake level following spring snowmelt. This decline was more pronounced in lakes with more vegetated catchments. At a shorter time scale, fDOM increased following precipitation events with a 0- to 1-day lag. Rates of fDOM increase per centmetre change in lake level were greater in lakes with vegetated catchments. As climate change increases vegetation coverage, DOM will likely become more dynamic at daily and seasonal time scales and impact water transparency and productivity of mountain lakes.

Reconstructing paleohydrology in the northwest Great Basin since the last deglaciation using Paisley Caves fish remains (Oregon, U.S.A.)

The arid northwest Great Basin underwent substantial hydroclimate changes in the past 15,000 years, greatly affecting its desert ecosystems and prehistoric people. There are conflicting interpretations of the timing of hydrologic changes in this region, requiring more records to resolve the dominant climatic drivers. The Paisley Caves archaeological site, located near former pluvial Lake Chewaucan, contains well-dated, stratified sediments best known for evidence of early human occupation in North America. We present a novel paleohydrologic record for the Chewaucan basin based on the frequency of fish remains (Salmonidae and Cypriniformes, likely tui chub) and their carbon, oxygen, and strontium isotope compositions, from the Paisley Caves. Cypriniformes abundance peaks first at the start of the Bølling/Allerød warm interval (∼14.7 ka) and again during the early Younger Dryas (∼12.8 ka). Isotope compositions indicate tui chub were derived from an expansive Lake Chewaucan throughout the Bølling/Allerød, but mainly from spring- or stream-influenced sources by the late Younger Dryas to the present. Fish abundance dropped sharply through the Younger Dryas and early Holocene, when isotope compositions indicate a mix of habitats. Isotope compositions indicate the driest conditions during the middle Holocene, followed by slightly wetter conditions up to the present. This record agrees with recent pluvial lake reconstructions, supporting the hypothesis that a northward shift in the winter storm track supported deep lakes throughout the Bølling/Allerød in the northwest Great Basin. Lake level decline during the Younger Dryas suggests drying climate, differing from more southerly records. During the Holocene, however, shifts in Chewaucan basin hydrology are consistent with the rest of the western U.S. This highlights the need for region-specific records to inform predictions of the hydrologic impact of climate change on arid regions.

Holocene lake-level fluctuations of Selin Co on the central Tibetan plateau: Regulated by monsoonal precipitation or meltwater?

Over the Tibetan Plateau (TP), lakes as paleoenvironmental archives have been the most extensively investigated for their sensitivities to climate change on different timescales. Well-preserved shoreline and terrace remains surrounding these lakes provide critical geomorphological and sedimentary evidence that can be used to infer past lake levels over geological timescales. These features can offer an analogue for understanding how future lake-levels respond to global warming. In this study, we investigated a series of water level-related depositional profiles around the Selin Co basin from the central TP, by dating 28 samples using K-feldspar luminescence techniques. Combining the obtained chronological data with sedimentological, stratigraphic evidence and differential GPS survey observations, the Holocene history of lake-level fluctuations in Selin Co was inferred. The results show a stable highstand between 10 ka and 7 ka but a striking subsequent lake-level decline. This pattern appears to follow the solar insolation-forced changes in the intensity of the Indian summer monsoon (ISM), particularly during the early Holocene. However, such gradual weakening of ISM intensity after the early Holocene may not interpret the dramatically rapid shrinking of Selin Co, implying other components are largely underrecognized driving factors accounting for the effective moisture of lakes in the early Holocene. Here, we argue that the increased meltwater input from glaciers and permafrost, together with increased precipitation, might have resulted in the high lake level at 10–7 ka, as the high summer temperature during the early Holocene induced massive melting water flow into the lake. By 7 ka, the abrupt lake-level drop is likely related to the decreased meltwater owing to decreasing regional temperatures documented from glacier landforms, ice cores and lacustrine sediments. Therefore, we highlight that meltwater from glaciers and permafrost poured into lakes on the central TP, particularly during warm periods on the millennial timescales, might also dominate the Holocene high lake levels.

Integrated land and water-borne geophysical surveys shed light on the sudden drying of large karst lakes in southern Mexico

Abstract. Karst water resources play an important role in drinking water supply but are highly vulnerable to even slight changes in climate. Thus, solid and spatially dense geological information is needed to model the response of karst hydrological systems to such changes. Additionally, environmental information archived in lake sediments can be used to understand past climate effects on karst water systems. In the present study, we carry out a multi-methodological geophysical survey to investigate the geological situation and sedimentary infill of two karst lakes (Metzabok and Tzibaná) of the Lacandon Forest in Chiapas, southern Mexico. Both lakes present large seasonal lake-level fluctuations and experienced an unusually sudden and strong lake-level decline in the first half of 2019, leaving Lake Metzabok (maximum depth ∼25 m) completely dry and Lake Tzibaná (depth ∼70 m) with a water level decreased by approx. 15 m. Before this event, during a lake-level high stand in March 2018, we collected water-borne seismic data with a sub-bottom profiler (SBP) and transient electromagnetic (TEM) data with a newly developed floating single-loop configuration. In October 2019, after the sudden drainage event, we took advantage of this unique situation and carried out complementary measurements directly on the exposed lake floor of Lakes Metzabok and Tzibaná. During this second campaign, we collected time-domain induced polarization (TDIP) and seismic refraction tomography (SRT) data. By integrating the multi-methodological data set, we (1) identify 5–6 m thick, likely undisturbed sediment sequences on the bottom of both lakes, which are suitable for future paleoenvironmental drilling campaigns, (2) develop a comprehensive geological model implying a strong interconnectivity between surface water and karst aquifer, and (3) evaluate the potential of the applied geophysical approach for the reconnaissance of the geological situation of karst lakes. This methodological evaluation reveals that under the given circumstances, (i) SBP and TDIP phase images consistently resolve the thickness of the fine-grained lacustrine sediments covering the lake floor, (ii) TEM and TDIP resistivity images consistently detect the upper limit of the limestone bedrock and the geometry of fluvial deposits of a river delta, and (iii) TDIP and SRT images suggest the existence of a layer that separates the lacustrine sediments from the limestone bedrock and consists of collapse debris mixed with lacustrine sediments. Our results show that the combination of seismic methods, which are most widely used for lake-bottom reconnaissance, with resistivity-based methods such as TEM and TDIP can significantly improve the interpretation by resolving geological units or bedrock heterogeneities, which are not visible from seismic data. Only the use of complementary methods provides sufficient information to develop comprehensive geological models of such complex karst environments

Late Quaternary seasonal process variations in lake basins on the NE Tibetan Plateau

The late Quaternary climate history along the north-eastern Tibetan Plateau (NETP) is still a matter of debate with respect to signals in lake deposits and related catchment processes. Here we summarize the current knowledge based on lake development and eolian accumulation in catchments on the NETP. Interlinked processes between selected lakes and their catchments on the NETP show a relatively clear division into summer and late autumn/winter/early spring (October to April) dominated activities based on lake hydrological and eolian variations. Investigated lakes on the NETP experienced seldom water cover or pond/playa status during the Late Glacial with long ice cover periods. Eolian sand deposited in lake beds and/or the eastern parts of the respective catchments as a constant process during the colder season. These processes continued during the early Holocene despite climate warming and increased moisture supply as lake levels still remained relatively low, mainly fed by spring/summer glacier and snow melt. Eolian sand activity dominated in the catchments during the cold periods, while coarse sediments in the lake centers were mainly deposited by fluvial input in spring/summer and/or randomly distributed eolian material in ice cracks after melt in spring. During the mid-Holocene high lake levels occurred due to intensified multiple moisture supply sources. Eolian sand accumulation diminished and was eroded by precipitation thus more fluvial suspension was transported to the lake center. Subsequently, lake level decline until around 3 ka BP signaled a reduction in moisture availability and related surface runoff. Eolian sediment was less preserved due to surface erosion in line with lake level increase during the succeeding period. Fluvial material mixed with eolian sand was transported to the lake center during unfrozen periods. Afterwards fluctuating lake levels and intensive eolian deposits were frequently documented for the last 2 ka demonstrating climate variations similar to present.Fluctuations between the Asian summer monsoon (ASM) and Mid Latitude Westerlies (MLW)/Asian winter monsoon (AWM) influences were recorded with respect to season shifts for the entire Holocene with general dominance of north-westerly surface winds at investigated sites. Inspected periodicities of one lake record and eolian material demonstrate that local effects are of significance for eolian accumulations however, both records react to regional/global climatic changes but with different extend.

An idealized model sensitivity study on Dead Sea desertification with a focus on the impact on convection

Abstract. The Dead Sea desertification-threatened region is affected by continual lake level decline and occasional but life-endangering flash floods. Climate change has aggravated such issues in the past decades. In this study, the impact on local conditions leading to heavy precipitation from the changing conditions of the Dead Sea is investigated. Idealized sensitivity simulations with the high-resolution COSMO-CLM (COnsortium for Small-scale MOdelling and Climate Limited-area Modelling) and several numerical weather prediction (NWP) runs on an event timescale are performed on the Dead Sea area. The simulations are idealized in the sense that the Dead Sea model representation does not accurately represent the real conditions but those given by an external dataset. A reference or Dead Sea simulation covering the 2003–2013 period and a twin sensitivity or bare soil simulation in which the Dead Sea is set to bare soil are compared. NWP simulations focus on heavy precipitation events exhibiting relevant differences between the Dead Sea and the bare soil decadal realization to assess the impact on the underlying convection-related processes. The change in the conditions of the Dead Sea is seen to affect the atmospheric conditions leading to convection in two ways. (a) The local decrease in evaporation reduces moisture availability in the lower boundary layer locally and in the neighbouring regions, directly affecting atmospheric stability. Weaker updraughts characterize the drier and more stable atmosphere of the simulations in which the Dead Sea has been dried out. (b) Thermally driven wind system circulations and resulting divergence/convergence fields are altered, preventing in many occasions the initiation of convection because of the omission of convergence lines. On a decadal scale, the difference between the simulations suggests a weak decrease in evaporation, higher air temperatures and less precipitation (less than 0.5 %).

Holocene hydroclimate in the source region of the Yellow River: A new sediment record from Lake Gyaring, NE Tibetan Plateau

Abstract The environmental history of the source region of the Yellow River (SRYR) is vital for understanding its hydrological response to climate processes in the alpine northeastern Tibetan Plateau (TP). In this study, we present the first sediment core record from Lake Gyaring, one of the largest fresh lakes in SRYR, using proxies of total organic carbon, total nitrogen, C/N ratio, δ13Corg, chlorophyll a, and grain size, to discuss the environmental variations over past 10 kyr. The results show that sedimentary organic matter mainly originated from the aquatic macrophytes and phytoplankton, the relative abundance of which can serve as a qualitative indicator of lake level changes of Lake Gyaring. From 10 to 6.2 cal kyr B.P., the notable expansion of macrophytes was favored by the warm conditions and an enlarged littoral zone due to lake-level decline. The abrupt cooling between 8.9 and 8 cal kyr B.P. led to temporal lake-level rises that significantly reduced macrophyte primary production. After 6.2 cal kyr B.P., the lake turned to be phytoplankton-dominated following the cooling trend and stepwise increase in lake level. The inferred climate pattern in the lake catchment with an overall dry early to mid Holocene and moister mid to late Holocene disagrees with the Asian monsoon variations. This phenomenon is well recognized by the lake-level records from most of the northeastern TP lakes, implying that strong evaporation in semi-arid lake catchments could have outweighed the increased regional precipitation during early to mid Holocene and vice versa for mid to late Holocene.

Analisa Potensi Air Danau Karo Pulau Obi Halmahera

<span><em>The existence of Lake Karo is needed to meet the water needs of nickel mining activities which are located </em><span><em>approximately 5 km to the North with a water storage area of 9.88 km2 and a watershed of 65.84 Km2. The </em><span><em>analysis was carried out based on climate data, topography, watershed, geological maps, geohydrology, lake </em><span><em>maps, river discharge, groundwater potential, land use, environmental documents. The method for estimating </em><span><em>river discharge is developed by Mock (1973), this method requires climate data and soil characteristics, </em><span><em>while in the calculation besides direct surface runoff there is also underground flow. The results of the </em><span><em>simulation monthly discharge during the period 2014-2018, the mainstay discharge simulation of the Karo </em><span><em>Lake watershed area with a probability of 95% is 0.505 m3 / second. The monitoring results show the </em><span><em>symptoms of lake water level decline in recent years due to increased Lake Karo water intake. Therefore it is</em><span><em>necessary to look for other alternative sources to overcome them.</em></span></span></span></span></span></span></span></span></span><br /><br class="Apple-interchange-newline" /></span>

Modeling the volatility changes in Lake Urmia water level time series

The decline in Lake Urmia (LU) water level during the past two decades has been addressed by several studies. However, the conducted studies could not come across a practical solution by considering the sample mean in the lake water level time series. For this, the present study suggests a fresh look to the lake water level decline in LU by addressing the volatility changes instead. The Bayesian change-point detection method was used to define the major and critical change points during the study period from January 1966 to December 2016 on a daily scale. Results indicated that major changes occurred in early 2000, and the time series can be studied under the pre- and post-change point events. Afterward, several methods namely shift-track and mono- and multiple-trend line analyses were used to remove the trends associated with the lake water level time series. The de-trending approaches later were applied separately for the entire study period, before 2000 (i.e., 1966–1999) and afterward (i.e., 2000–2016). Then, the de-trended time series were used, and a generalized autoregressive conditional heteroscedasticity (GARCH) model was fitted to the de-trended time series to predict the volatility changes in the data run. Results indicated to descending and ascending changes, respectively, in short- and long-term persistence after 2000. The GARCH(1,1) model was found to be satisfactory to interpret the pre- and post-turn point events, while the changes in short- and the long-term persistence were calculated as 0.53 to 0.75 and 0.46 to 0.24, respectively. In addition, by considering the lake water level anomaly and coefficient of variation in LU and two neighboring cases of Lake Sevan and Lake Van, it is concluded that the changes are exclusive to LU, and the rate of changes was accelerated after 2006.

Climate History of Southern Mongolia Since 17 ka: The Ostracod, Gastropod and Charophyte Record From Lake Ulaan

Late glacial and Holocene environmental and climate change in the Gobi Desert is poorly understood due to the lack of appropriate geological archives and commonly faced difficulties in establishing reliable chronologies. Here, the relatively well-dated sediment record from the terminal Lake Ulaan is used to reconstruct the lake history and climate in the region. Most abundant calcareous fossils in the lake sediments are ostracod (micro-crustacean) valves. The ostracod assemblage is dominated by Limnocythere inopinata, and generally very shallow conditions and sodium-dominated waters are inferred for Lake Ulaan. A single period of significantly increased silt accumulation in the late glacial was recorded at ca. 16 ka, probably as a result of melting glaciers in the uppermost reaches of the lake’s main tributary, the Ongin River, and the influx of glacially-ground, fine materials. Lake Ulaan had a higher salinity afterwards during the Greenland Interstadial 1, and dry climate prevailed in the region. The lake level started to rise and the salinity decreased since ca. 12.3 ka, leading to the establishment of freshwater conditions in the early Holocene. Highest inflows and highest productivity in and around the lake, and wettest climate conditions in the region were recorded in the early Holocene. Lake conditions, most favourable for the aquatic fauna, culminated ca. 10 ka. Afterwards, Lake Ulaan experienced a step-wise lake-level decline and salinity increase at 9.4 and 6.8 ka. The further shrinkage of the lake and the approaching Ongin River mouth near the central part of the basin is recorded since 3.2 ka.

Can nature-based solutions contribute to water security in Bhopal?

Bhojtal, a large man-made lake bordering the city of Bhopal (Madhya Pradesh state, central India), is important for the city's water supply, connoted the lifeline of the city. Despite the dry though not arid and markedly seasonal climate, soil impermeability hampers infiltration into the complex geology underlying the Bhojtal catchment. Rural communities in the catchment are nonetheless high dependent on underlying aquifers. This paper develops baseline understanding of trends in the ecology, water quality and uses of Bhojtal, discussing their implications for the long-term wellbeing of the Bhopal city region. It highlights increasing dependency on water diverted from out-of-catchment sources, and also abstraction across the Bhojtal catchment in excess of replenishment that is depressing groundwater and contributing to reported declining lake level and water quality. Despite some nature-based management initiatives, evidence suggests little progress in haltering on-going groundwater depression and declines in lake water level and quality. Significant declines in ecosystem services produced by Bhojtal are likely without intervention, a major concern given the high dependency of people in the Bhopal region on Bhojtal for their water supply and socio-economic and cultural wellbeing. Over-reliance on appropriation of water from increasingly remote sources is currently compensating for lack of attention to measures protecting or regenerating local resources that may provide greater resilience and regional self-sufficiency. Improved knowledge of catchment hydrogeology on a highly localised scale could improve the targeting and efficiency of water harvesting and other management interventions in the Bhojtal catchment, and their appropriate hybridisation with engineered solutions, protecting the catchment from unintended impacts of water extraction or increasing its carrying capacity, and also providing resilience to rising population and climate change. Ecosystem service assessment provides useful insights into the breadth of benefits of improved management of Bhojtal and its catchment.

Lake Balkhash (Kazakhstan): Recent human impact and natural variability in the last 2900 years

Lake Balkhash is a large and relatively shallow closed-basin lake in the arid part of Central Asia. The lake experienced an ecological crisis in the 1970s and 1980s when the filling of the Kapchagay Reservoir in the middle reaches of its main tributary caused a significant lake-level decline and salinity rise, and resulting biodiversity loss. A sediment core representing 2900 years of lake history was obtained to assess man-made alterations of the lake in the last decades in comparison to the natural status of Lake Balkhash. Analyses of sediments and of ostracod (micro-crustacean) species assemblages and shell chemistry revealed that the lake was probably relatively shallow and more brackish ca. 2900–2200 calibrated years before present (cal a BP) in comparison to the period when the Kapchagay Reservoir was filled. A relatively high lake level and lower salinity prevail since ca. 2200 cal a BP.The uppermost sediments of the obtained core and nearby surface-sediment samples provide evidence for the establishment of hypoxic conditions in Lake Balkhash since the middle of the 1970s. The lake-level decline during the filling of the Kapchagay Reservoir probably caused the redistribution of organic-matter rich littoral sediments to greater depth in the lake where dissolved oxygen became consumed due to the decomposition of organic remains. The spatial and temporal distribution of hypoxia in Lake Balkhash is not known, and systematic studies are required to assess the status of the benthic life and potential impacts of future lake-level, nutrient influx and temperature changes.

Late Holocene hydroclimate variability in Costa Rica: Signature of the terminal classic drought and the Medieval Climate Anomaly in the northern tropical Americas

In the northern tropical Americas (Neotropics), notable hydrological variability has been documented in multi-proxy paleoclimate records between ∼600 and 1200 CE. This interval generally overlaps with the Maya Terminal Classic Drought (TCD: ∼770–1100 CE) and the Medieval Climate Anomaly (MCA: ∼950–1250 CE). There is, however, limited paleoclimate data that provide reliable estimates of terrestrial thermal variability in southern Central America during this time. In this study, we present chironomid-based temperature reconstructions, developed from sediment cores from two lakes: (1) Lago Morrenas 3C, a high-elevation glacial lake located on the crest of the Atlantic slope of the Cordillera Talamanca, Costa Rica, and (2) Laguna Zoncho, a mid-elevation lake located on the Pacific slope in southern Costa Rica. Distinctive shifts in the chironomid assemblages occurred at both sites between ∼610 and 1230 CE. These changes are inferred to reflect an ∼600-year interval characterized by depressed mean annual temperatures at Lago Morrenas 3C and dry conditions and lake level decline at Laguna Zoncho. Taken together, the multi-proxy paleoclimate records from these two lakes, including stable carbon isotope (δ13C) and charcoal data, suggest that middle elevations on the Pacific slope and high elevations on the Atlantic slope of Costa Rica experienced sustained drought, and possible cooling coeval with the TCD-MCA interval. The timing of hydroclimate variability in these records provides support for the hypothesis that cooling and drought in the northern tropical Americas during the TCD and early MCA were linked to thermal changes in the tropical North Atlantic.

Seasonal dynamics of internal waves governed by stratification stability and wind: Analysis of high‐resolution observations from the Dead Sea

AbstractInternal waves in stratified lakes are affected by the seasonally varying stratification and the wind forcing. We studied the seasonal dynamics of internal waves by means of high‐resolution observations and model simulations for the Dead Sea. A two‐layer hydrostatic model provided high correlations between measured thermocline depth and the lake level oscillations. Seasonally, the amplitude of the thermocline fluctuations were anticorrelated with the density difference between the water layers; the largest fluctuations were observed when stratification was weak in spring/fall and moderate to weak fluctuations in mid‐summer when stratification was fully developed. The surface and the internal waves propagated counterclockwise along the coasts at a speed of ~0.5 m s−1. Power spectra of the observed wind as well as the measured and simulated lake level and thermocline depth show a pronounced diurnal period during summer, suggesting forcing by the diurnally varying wind. During spring and fall, when the water column stability diminishes, a hint of longer wind periods appear in addition to the diurnal mode. Accordingly, the lake level and thermocline depth fluctuations respond at lower frequencies. In the fall, the longer wind periods are close to the lake's first vertical normal mode, suggesting that resonant amplification of the internal waves may explain the observed lower frequency response of the level and thermocline oscillations. Reduction of the stratification stability originating from anthropogenic water diversion over the past four decades, associated with lake level decline and salinity increase, have led to increases of internal waves amplitude and periods.

Predictability of Ecological Changes in Lake Kinneret

Several ecological key factors were indicated in the Lake Kinneret ecosystem during 1969-2000: Elevation of the biomass of non-pyrrhophyte-phytoplankton, chlorophyta, cyanobacteria, and diatoms; decline of Peridinium maximal from 215 - 240 to 175 - 200 ranges (g/m2); decline of zooplankton (herbivore and predator) relative to phytoplankton biomass (g/m2); lower loads of Nitrogen and slightly also phosphorus in the river Jordan discharge; decline of precipitations and lake water level; significant decline of epilimnetic nitrogen and minor changes of phosphorus concentrations initiated decline of N/P mass ratio to the establishment of a significant change of the ecosystem to be modified from P to N limitation. What could be other than essential outcome of future prediction that results of 20 years (1969-2000) of routine and comprehensive monitor carried out in Lake Kinneret initiated? The Lake Kinneret ecosystem dynamics after 2000 justified retroactive post-factum earlier conclusion of appropriate predictability.

Net primary productivity dynamics and associated hydrological driving factors in the floodplain wetland of China's largest freshwater lake

Wetlands are thought to be the most unique ecosystem in the world which plays an important role in water and material circulation. However, investigation of ecosystem dynamics in those lake floodplain wetlands that suffering rapid and significant short-term water level fluctuation is quite a challenge. In this study, the short- and long-term characteristics of vegetation NPP (net primary productivity) and their driving mechanism were investigated in the Poyang Lake floodplain wetland, an important international wetland that listed in the Global Eco-region by the World Wildlife Fund (WWF). Attempts were achieved through validating the Carnegie-Ames-Stanford Approach (CASA) model based on observed biomasses of different vegetation types and reconstructed continuous high spatiotemporal resolution (30 m and 16 days) of NDVI data during 2000–2015 according to the fused Landsat and MODIS data. Major result indicates that the intra-annual variation of NPP of most vegetation types shows two peaks in a year due to combined effects of vegetation growth rhythm and seasonal exposure of the lake floodplain. Annual NPP of the lake floodplain ranges in 360.09–735.94 gC/m2 and shows an increasing trend during the study period. The change of NPP in space indicates that the distribution elevation of the major vegetation types decreased and evoluted toward the center lake floodplain. Different from the terrestrial ecosystem, inundation duration is the dominant factor that controls NPP dynamics in the lake floodplain, while the influences of other meteorological factors are much weakened. Recent decline of lake water level was the major reason for the spatio-temporal evolution of annual and seasonal vegetation NPP in the lake floodplain.

A 14 ka high-resolution δ18O lake record reveals a paradigm shift for the process-based reconstruction of hydroclimate on the northern Tibetan Plateau

The influence of the mid-latitude westerlies (MLW) competing with the Asian summer monsoons (ASM) over the Tibetan Plateau (TP) remains a matter of discussion on how and to which extent both atmospheric systems have been controlling hydro-climate during the Holocene. Depleted oxygen isotopes in lake deposits were commonly interpreted in terms of enhanced summer monsoon moisture supply, implying a migration of the ASM deep into the interior of the plateau during Holocene periods. In order to test this relationship we used a high resolution oxygen isotope record (mean 20 yr resolution) in combination with carbonates and mineral phases, titanium flux, grain size and ostracod abundances derived from a 6.84 m long sediment core in the endorheic Kuhai Lake basin, north-eastern TP. The results confirm 1) continuous positive co-variance between enriched δ18Ocarb and total carbonates during the last 14 ka, indicative of dominant seasonal influence on multi-decadal to centennial scale isotopic signatures in lake water and respective carbonate precipitation, 2) negative co-variance between allochthonous sediment flux and δ18Ocarb (and carbonates) attributed to relative increase of flux rates during non-summer seasons, 3) correspondence of lake level variations with carbonate mineral phases and the occurrence/disappearance of ostracod assemblages, and 4) inverse relationships between isotopic signatures in ASM-dominated and MLW-controlled lake records across the TP. Enriched δ18Ocarb in Kuhai Lake sediments was primarily a result of high evaporation during the summer seasons, while ASM-related rainfall amount did not play an important role, likely counterbalanced by isotopic signatures from different water sources. Conversely, depleted δ18Ocarb was mainly attributed to water supply during non-summer seasons of colder temperatures and generally light isotopic signatures from MLW-derived sources. This finding may lead to a paradigm shift in such way that depleted δ18O in carbonates is primarily not the result from ASM-related rainfall as previously assumed. The reconstructed hydro-climatic history of Kuhai Lake indicates the dominance of westerly-derived climate during the Younger Dryas interval (12.8–11.5 ka) under very shallow pond-like conditions. Despite climate amelioration during the early Holocene (11.5–7.5 ka) hydrological conditions remained unstable with frequent alternations between dominance of summer and winter seasons. During the middle Holocene (7.5–5.5 ka) the lake experienced highest lake levels dominated by summer monsoon-related water supply, assigned to the Holocene hydro-climatic optimum. Frequent high-amplitude fluctuations afterwards (5.1–2.9 ka) refer to cooling/drying events under enhanced MLW influence accompanied by a strong lake level decline. The late Holocene (2.9 ka- Present) period experienced moderate isotopic variations and fluctuating lake levels in response to variable influence of summer- or winter-related hydro-climatic conditions.This seesaw-like pattern with amplitudes of >10‰ in δ18Ocarb resembles fluctuations in cave records and variations between air and seawater (Dole effect). High correspondence with cooling events derived from North Atlantic drift ice and meltwater discharge indicate close ties to northern hemispheric climate transmitted by the MLW across the TP.

The cost of addressing saline lake level decline and the potential for water conservation markets

The world's saline lakes are shrinking and human water diversions are a significant contributor. While there is increased interest in protecting the ecosystem services provided by these lakes, the cost of protecting water levels has not been estimated. To explore this question we consider the case of Great Salt Lake (Utah, USA) where human diversions from three rivers have caused the lake level to decline during the last century. Recent work has suggested the restoration of inflows is necessary to maintain a target elevation consistent with well-functioning ecosystems. We construct cost estimates of increasing water inflows using conservation cost curves for each river basin. We then compare the cost of uniform cutbacks to cap-and-trade systems which allow intra- and inter-basin trading. The cost of water to permanently implement uniform water right cutbacks to increase inflows by 20% above current levels is $37.4 million. Costs and cost-savings are sensitive to alternative allocation, inflow, and cost assumptions, and we estimate significant cost reductions from intra-basin water conservation markets (5–54% cost decrease) and inter-basin water conservation markets (22–57% cost decrease).