Lake Water Balance Research Articles

PRYSM v2.0: A Proxy System Model for Lacustrine Archives

AbstractReconstructions of temperature and hydrology from lake sedimentary archives have made fundamental contributions to our understanding of past, present, and future climate and help evaluate general circulation models (GCMs). However, because paleoclimate observations are an indirect (proxy) constraint on climatic variables, confounding effects of proxy processes complicate interpretations of these archives. To circumvent these uncertainties inherent to paleoclimate data‐model comparison, proxy system models (PSMs) provide transfer functions between climate variables and the proxy. We here present a new PSM for lacustrine sedimentary archives. The model simulates lake energy and water balance, sensors including leaf wax δD and carbonate δ18O, bioturbation, and compaction of sediment to lend insight toward how these processes affect and potentially obfuscate the original climate signal. The final product integrates existing and new models to yield a comprehensive, modular, adaptable, and publicly available PSM for lake systems. Highlighting applications of the PSM, we forward model lake variables with GCM simulations of the last glacial maximum and the modern. The simulations are evaluated with a focus on sensitivity of lake surface temperature and mixing to climate forcing, using Lakes Tanganyika and Malawi as case studies. The PSM highlights the importance of mixing on interpretations of air temperature reconstructions from lake archives and demonstrates how changes in mixing depth alone may induce nonstationarity between in situ lake and air temperatures. By placing GCM output in the same reference frame as lake paleoclimate archives, we aim to improve interpretations of past changes in terrestrial temperatures and water cycling.

Insight into the stable isotopic composition of glacial lakes in a tropical alpine ecosystem: Chirripó, Costa Rica

AbstractTropical high‐elevation lakes are considered sentinels of global climate change. This work characterizes the hydrological conditions of tropical alpine glacial lakes located in the highlands of Chirripó, Costa Rica, using a unique data set of water stable isotopes (δ2H and δ18O) in precipitation, stream water, and lake water between September 2015 and July 2017. A combined dataset of bathymetric, hydrometric, and isotope data collected between July 2016 and July 2017 on Lake Ditkevi was used to calculate the annual water balance of the lake. Evaporation to inflow ratios from three lake systems was estimated using a linear resistance model, the experimentally estimated local evaporation line of Chirripó, and the first glacial lake water evaporation lines in the region. The temporal isotopic variations (δ18O, d‐excess, and lc‐excess) confirm variations in the dry and wet season evaporative conditions for the glacial lakes and consistently average annual low evaporation to inflow (E/I) ratios in the range of 2.0 ± 0.8% and 18.1 ± 12.2%. Lake Ditkevi's water balance indicates annual steady‐state conditions, with an estimated evaporation loss of 650 mm/year (10.0 ± 5.0% of inflow), a high‐water contribution to the catchment (90% of inflow), a residence time of 0.53 ± 0.27 years, and a catchment scale (0.289 km2) water yield or depth equivalent run‐off of 278 mm/yr. These results provide novel information about water balance and evaporation losses in tropical alpine glacial lakes, which can serve as baseline information for future isotope‐based hydro‐climate research in high‐elevation regions in the tropics and elsewhere.

Estimation of water storage changes in small endorheic lakes in Northern Kazakhstan

Both climate change and anthropogenic activities contribute to the deterioration of terrestrial water resources and ecosystems worldwide, with Central Asia and its endorheic lakes being among the most severely affected. We used a digital elevation model, bathymetry maps and Landsat images to estimate the areal water cover extent and volumetric storage changes for eleven small terminal lakes in Burabay National Nature Park (BNNP) in Northern Kazakhstan from 1986 to 2016. Based on the analysis of hydrometeorological observations, lake water balance, lake evaporation and Budyko equations, driven by gridded climate and global atmospheric reanalysis datasets, we evaluate the impact of historical climatic conditions on the water balance of the BNNP lake catchments. The total surface water area of the BNNP lakes decreased by around 7% for that period, mainly due to a reduction in the extent of three main lakes. In contrast, for some smaller lakes, the surface area increased. Overall, we attribute the decline of the BNNP lakes’ areal extent and volume to the prolonged periods of water balance deficit when lake evaporation exceeded precipitation. However, during the most recent years (2013–2016) precipitation increased and the BNNP lake levels stabilized.

Hydrological characterization and prediction of flood levels of acidic pit lakes in the Tharsis mines, Iberian Pyrite Belt

Opencast mining operations frequently lead to the creation of large voids that become anthropogenic lakes when the water table recovers. In the case of sulfide mining the stored water is of an acidic nature with significant concentrations of toxic metals and, therefore, a high pollutant potential. The main goal of the present work is to characterize the hydrological functioning and evolution of four acidic mine pit lakes in the abandoned mines of Tharsis, which is the second most important mine district in the Iberian Pyrite Belt (IPB). We present a simple methodology based on the use of the available orthophotographs and a Digital Terrain Model (DTM) together with the water balance of the pit lakes, which could be applied to other abandoned mining sites, where there is often a lack of hydrogeological information that prevents the application of more complex models. The accumulation of large volumes (5.2 × 106 m3) of acidic and metal-rich waters in these pit lakes poses a serious environmental concern, with dissolved concentrations up to 2000 mg/L of Fe, 223 mg/L of Al, etc. Sierra Bullones and Filón Norte are connected underground and present the same evolution, with water transfers from Sierra Bullones to Filón Norte. The water level in both pit lakes is increasing, with an average rise of 2.8 m/yr since the beginning of flooding. However, the increase in the evaporation rate, as a result of the larger flooded area as the water level rise, would induce a hydrological equilibrium before reaching the overflow level, leading to the formation of a terminal lake. On the other hand, the water level in Filón Centro and Filón Sur pit lakes remain approximately stable. The first behaves as a flow-through or terminal lake, depending on the annual rainfall, while the second acts permanently as a flow-through lake.

Geographic and temporal variations in turbulent heat loss from lakes: A global analysis across 45 lakes

AbstractHeat fluxes at the lake surface play an integral part in determining the energy budget and thermal structure in lakes, including regulating how lakes respond to climate change. We explore patterns in turbulent heat fluxes, which vary across temporal and spatial scales, using in situ high‐frequency monitoring data from 45 globally distributed lakes. Our analysis demonstrates that some of the lakes studied follow a marked seasonal cycle in their turbulent surface fluxes and that turbulent heat loss is highest in larger lakes and those situated at low latitude. The Bowen ratio, which is the ratio of mean sensible to mean latent heat fluxes, is smaller at low latitudes and, in turn, the relative contribution of evaporative to total turbulent heat loss increases toward the tropics. Latent heat transfer ranged from ~ 60% to > 90% of total turbulent heat loss in the examined lakes. The Bowen ratio ranged from 0.04 to 0.69 and correlated significantly with latitude. The relative contributions to total turbulent heat loss therefore differ among lakes, and these contributions are influenced greatly by lake location. Our findings have implications for understanding the role of lakes in the climate system, effects on the lake water balance, and temperature‐dependent processes in lakes.

Estimation of Lake Outflow from the Poorly Gauged Lake Tana (Ethiopia) Using Satellite Remote Sensing Data

Lake Tana is the largest lake in Ethiopia, and its lake outflow is the source of the Blue Nile River that provides vital water resources for many livelihoods and downstream/international stakeholders. Therefore, it is essential to quantify and monitor the water balance of Lake Tana. However, Lake Tana is poorly gauged, with more than 50% of Lake Tana Basin being ungauged from in-situ measurements, making it difficult to quantify the lake inflow from surrounding basins. The lack of in-situ measurements highlights the need for the innovative application of satellite remote sensing. This study explores how freely accessible satellite remote sensing can be used to complement routine weather data to quantify the water balance of Lake Tana and its surrounding catchments. This study particularly investigates whether the outflow from Lake Tana can be estimated with sufficient accuracy as the residual of the lake water balance. Monthly inflow into lake was computed as the total runoff from the surrounding catchments; the runoff was estimated as the residual of the land-based catchment water balance using satellite precipitation improved with an integrated downscaling-calibration procedure, satellite evapotranspiration, and a correction term for changes in land total storage (soil moisture storage and deep percolation). The outflow from Lake Tana was estimated as the residual of lake water balance by combining satellite-based lake precipitation, changes in water storage, and lake inflow with estimated lake evaporation. Evaluation using limited available measurements showed that estimated annual runoff for two gauged subbasins agreed well with measurements, with differences within 4%. The estimated annual outflow from Lake Tana was also close to measured outflow, with a difference of 12%. However, the estimated monthly runoff from catchments and monthly lake outflow were unsatisfactory, with large errors.

Hydroclimatic changes of Lake Bosten in Northwest China during the last decades

Bosten Lake, the largest inland freshwater lake in China, has experienced drastic change over the past five decades. Based on the lake water balance model and climate elasticity method, we identify annual changes in the lake’s water components during 1961–2016 and investigate its water balance. We find a complex pattern in the lake’s water: a decrease (1961–1987), a rapid increase (1988–2002), a drastic decrease (2003–2012), and a recent drastic increase (2013–2016). We also estimated the lake’s water balance, finding that the drastic changes are caused by a climate-driven regime shift coupled with human disturbance. The changes in the lake accelerated after 1987, which may have been driven by regional climate wetting. During 2003 to 2012, implementation of the ecological water conveyance project (EWCP) significantly increased the lake’s outflow, while a decreased precipitation led to an increased drought frequency. The glacier retreating trend accelerated by warming, and caused large variations in the observed lake’s changes in recent years. Furthermore, wastewater emissions may give rise to water degradation, human activity is completely changing the natural water cycle system in the Bosten Lake. Indeed, the future of Bosten Lake is largely dependent on mankind.

5. The Effect of Climate Variability on Lake Water Balances and Water Quality in the Apex River Watershed, Baffin Island, Nunavut

Iqaluit, Nunavut is currently facing a water shortage as its population rises, and its drinking water reservoir, Lake Geraldine, is increasingly insufficient. The City of Iqaluit is currently looking into alternative sources of drinking water to supplement this reservoir. This study investigates the effects of inter-annual climate variability on the water chemistry of twenty Arctic lakes in a continuous permafrost region, and the potential implications of these changes on drinking water availability. The twenty lakes are located in the Niaqunguk (Apex) river watershed, Baffin Island, Nunavut (which is adjacent to the Lake Geraldine watershed at Iqaluit) were sampled annually during late July between 2014-2017. Ion concentrations and stable isotopes were measured for each lake annually throughout the study period to compare variability between lakes and between years. Water chemical and physical properties are used to gain insight into the inputs and outputs of each lake, and the changes in estimated water balance between years. This information will be used to determine the impact of different hydrological conditions on water chemistry. Results of water isotope tracers of the twenty lakes indicate that there are important year-to-year changes in the water stable isotopes, indicating inter-annual variations in evaporation rates, suggesting that these lakes are sensitive to changes in summer climatic conditions. Preliminary analyses of the ionic concentrations of the lakes suggest that ion concentrations generally decrease throughout the study period, and largely vary together, signifying the hydrological processes controlling the lake water balances are related to climate variability. This research will provide insights into the hydrologic response of lakes in a continuous permafrost region to long-term climatic change.

Modeling Water and Salt Balance of Bol’shoe Yashaltinskoe Lake

This article is the first to give morphometric and bathymetric relationships for Bol’shoe Yashaltinskoe Lake, derived by processing expedition data. A bathymetric map of the lake is constructed. A method is proposed for modeling lake water balance and water salinity based on geographic analogy and an algorithm for constructing a stochastic vector autoregression process. Realizations of the simulated series of lake water balance components and water salinity variations over 1000 years with a monthly step are constructed.

Isotopic and geochemical surveys of lakes in coastal B.C.: Insights into regional water balance and water quality controls

Study regionThis study was conducted within a 100,000 km2 area of British Columbia, (B.C.) Canada including Vancouver Island, the Georgia Basin, and the Pacific and Kitimat mountain ranges rising from the Pacific Ocean. Study focusA stable isotope mass balance method is applied to estimate evaporation loss and water yield from a remote network of 560 lakes on Vancouver Island and coastal B.C., based on helicopter sampling surveys conducted between 2008 and 2015. Spatial patterns in derived hydrological parameters are compared to water quality indicators and watershed characteristics to provide insight into water quantity and water quality relationships in the region, to be incorporated within a future critical loads assessment. New hydrological insights for the regionRegional trends in lake water balance, underlying physical drivers, and geochemical processes potentially influencing critical loads of acidity are described. Dominant non-anthropogenic regional drivers of geochemistry include sea spray, lithology, weathering and elevation. Significant contrast is noted in alkalinity between the sedimentary and volcanic substrates on Vancouver Island and igneous intrusive substrates of the Pacific and Kitimat ranges. A positive correlation is found between elevation and water yield to lakes, while the opposite is observed for rivers, which is interpreted to reflect disconnection of low elevation lakes from regional drainage networks. This may invalidate use of river gauge data for critical loads assessment in this or similar regions.

Evaluation of thermokarst lake water balance in the Qinghai–Tibet Plateau via isotope tracers

Thermokarst lakes are a ubiquitous landscape feature, which widely distributed in the pan-arctic and some low latitude regions, and are associated with regional hydrological processes. The studies were taken to obtain a better understanding of the water balance of thermokarst lakes in the Qinghai–Tibet Plateau (QTP) in order to gain insight of the regional hydrological cycle. The characteristics of the stable isotopes δ 18O and δ D were investigated in precipitation, permafrost meltwater, and thermokarst lake water in the continuous permafrost region of the QTP and analyzed the lake water balance using the isotope mass model. The results showed that the δ D–δ 18O relationship in the thermokarst lakes (δ D = 5.45 δ 18O − 18.95) differed from that of the local precipitation (δ D = 8.30 δ 18O + 18.49) and permafrost meltwater (δ D = 5.78 δ 18O − 23.41), and the mean isotope compositions in the thermokarst lakes were −7.2‰ in δ 18O and −58.0‰ in δ D. The more positive isotope signals in thermokarst lakes than in the precipitation and permafrost meltwater revealed that the lakes had experienced stronger isotope enrichment. Additionally, the evaporation-to-inflow ratio (E/I) values were < 1 in most of the thermokarst lakes (84%), which might be explained by the recent expansion of the lake surfaces. However, 16% of the thermokarst lakes had shrunk, owing to thermokarst erosion, lateral expansion as the temperature increases, and lower recharge volume. Moreover, precipitation on the lake surface was only 14–18% of the inflow volume in the thermokarst lakes, and the surface-subsurface inflow and permafrost meltwater are very important for recharging the lakes and maintaining the water balance. The results of this study provide a comprehensive understanding of the influence of climate warming on hydrological processes in the permafrost regions in the QTP.

Impact of irrigation on the water level of Lake Maybar, Northeast Ethiopia

ABSTRACTThe main objective of the research is to investigate the impact of irrigation water use on the water level of Lake Maybar. The collected data were tested for their consistency using outlier test and then analysed to estimate the components of catchment and lake water balances. Water Balance (WTRBLN) software was used to simulate the observed flow (catchment response) at the outlet of river Kori Sheleko. The model performance was tested using a Nash–Sutcliffe correlation, R2, and showed better agreement (R2 = 94.3%) between observed and predicted flows. The lake water balance at two scenarios of development of irrigation within Maybar Lake Basin was analysed. The result at scenario-1 (existing irrigation development) showed a water level reduction of about 0.76 m, and at scenario-2 (exploitation of all potential irrigation areas) it was 1.49 m. Through this impact study using a Water Balance Model, it was shown that the consumptive water use for irrigation development heavily affected the natural water level of Lake Maybar.

Isotopic Characterization of Precipitation, Inflow, and Outflow of Lake Toba as a First Assessment of Lake Water Balance Study

Isotopic characterization of all identified hydrological units in Lake Toba such as precipitation, inflows, outflows, and lake water, as a first assessment of lake water balance study, has been conducted. The isotopic characterization was done through the interpretation of the relationship of d D and d 18 O values of collected samples from various water sources and their variations as a function of time and space. Rain water samples were collected from four rain collectors that were installed in the study area in a monthly sampling for a period of 12 months in 2014. Several samples from various water sources i.e ., inflow streams, outflows, springs, and lake water, were also collected 2-3 times during this sampling period. From monthly sampling of rain water, local meteoric water line ( LMWL ) and the equation of elevations versus d D values have been constructed. Due to the slightly higher temperature in the study area compared with the average temperature on the other parts of the world, the slope of the constructed LMWL is slightly less than the slope of global meteoric water line. Based on the equation of elevations versus d D values, the elevations of four springs around study area have been identified. From the linear relationship of d D and d 18 O values of collected samples from inflow streams, it was found that most of the samples have experienced evaporation process before entering the lake. Due to mixing with other surface water and longer transit time, the d D and d 18 O values of those samples from streams in the Sumatran side are more enriched than those samples from streams in the Samosir side. It was also found that lake water has experienced significant evaporation as indicated by the d D and d 18 O values that were more enriched than any other samples. The d D and d 18 O of Asahan River samples, the only output of Lake Toba, were found to be very close to the d D and d 18 O of the lake. This is because almost all water that flowed in Asahan River originated from the lake. Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";}

Evaporation from a temperate closed-basin lake and its impact on present, past, and future water level

Lakes provide enormous economic, recreational, and aesthetic benefits to citizens. These ecosystem services may be adversely impacted by climate change. In the Twin Cities Metropolitan Area of Minnesota, USA, many lakes have been at historic low levels and water augmentation strategies have been proposed to alleviate the problem. White Bear Lake (WBL) is a notable example. Its water level declined 1.5 m during 2003–2013 for reasons that are not fully understood. This study examined current, past, and future lake evaporation to better understand how climate will impact the water balance of lakes within this region. Evaporation from WBL was measured from July 2014 to February 2017 using two eddy covariance (EC) systems to provide better constraints on the water budget and to investigate the impact of evaporation on lake level. The estimated annual evaporation losses for years 2014 through 2016 were 559 ± 22 mm, 779 ± 81 mm, and 766 ± 11 mm, respectively. The higher evaporation in 2015 and 2016 was caused by the combined effects of larger average daily evaporation and a longer ice-free season. The EC measurements were used to tune the Community Land Model 4 – Lake, Ice, Snow and Sediment Simulator (CLM4-LISSS) to estimate lake evaporation over the period 1979–2016. Retrospective analyses indicate that WBL evaporation increased during this time by about 3.8 mm year−1, which was driven by increased wind speed and lake-surface vapor pressure gradient. Using a business-as-usual greenhouse gas emission scenario (RCP8.5), lake evaporation was modeled forward in time from 2017 to 2100. Annual evaporation is expected to increase by 1.4 mm year−1 over this century, largely driven by lengthening ice-free periods. These changes in ice phenology and evaporation will have important implications for the regional water balance, and water management and water augmentation strategies that are being proposed for these Metropolitan lakes.

Climate stability in central Anatolia during the Messinian Salinity Crisis

Deposition of large amounts of evaporites and erosion of deep canyons within the Mediterranean Basin as a result of reduced basin connectivity with the Atlantic Ocean and the epicontinental Paratethys Sea characterized the Messinian Salinity Crisis (MSC, 5.97–5.33 Ma). The influence of the MSC on Mediterranean environmental conditions within the basin itself has been intensely studied from marine records, but reconstructing the impact of the MSC on circum-Mediterranean continental climate has been hampered by the absence of continuous sedimentary archives that span the duration of the event.Here, we report results of a continental record of carbon (δ13C) and oxygen (δ18O) isotopes from lake carbonates framed by new magnetostratigraphic and 40Ar/39Ar dating, as well as by existing mammal stratigraphy (Kangal Basin, central Anatolia). The sampled section records continuous fluvio-lacustrine sedimentation from ~6.6 Ma to 4.9 Ma, which spans the MSC and the Miocene-Pliocene boundary. This dataset so far represents the only continuous continental paleoenvironmental record of the MSC in the circum-Mediterranean realm.The Kangal Basin isotope record indicates a low degree of evaporation. Furthermore, covariance between δ13C and δ18O suggests a coupling between lake water balance and biologic productivity. Variations in δ13C and δ18O therefore likely reflect changes in the amount of incoming precipitation, rather than changes in δ18O values of incoming precipitation. The most prominent spike in δ13C and δ18O occurs during the acme of the MSC and is therefore interpreted to have resulted from a decrease in the amount of incoming moisture correlative to a period of vigorous erosion and sea level lowering in the Mediterranean Basin. Major sea level lowering of Mediterranean basin waters during the acme of the MSC could have therefore led to slightly dryer conditions over Anatolia, which is also suggested by modeling studies. Overall, changes in δ13C and δ18O values are small. Therefore, we surmise that the MSC had limited effects on the paleoenvironmental and paleoclimatic conditions in the Anatolian interior.

When to conduct an isotopic survey for lake water balance evaluation in highly seasonal climates

AbstractOne‐time or short‐term lake water isotopic surveys are often employed to evaluate regional lake water balance. However, it can be difficult to determine the optimal time‐window for sampling to obtain a representative long‐term perspective of lake water balance in settings influenced by seasonal variations in precipitation, evaporative loss, glacial/snow meltwater, and larger seasonal shifts in isotopic composition of precipitation. This is especially true for areas of the Tibetan Plateau that are influenced by the summer Indian monsoon. Although high‐frequency sampling is always preferred as the most rigorous approach to characterize the water budget of lakes or watersheds, this may be impractical in remote regions and over large spatial scales. To assess the potential sensitivity of isotope balance characterization to seasonal variability, we used a weekly lake water isotope data set acquired over a period of 3 years on the Tibetan Plateau to evaluate the potential inaccuracies that might have arisen from using isotopic data collected during narrower time‐windows. For this assessment, we use weekly isotopic data collected during the study and assume that these sampling events were stand‐alone one‐time surveys. We then demonstrate the sensitivity of the isotope balance method in this setting, particularly for the rainy season that significantly underestimated the evaporation/inflow. In contrast, isotopic composition of the lake water was found to be more representative of long‐term conditions when sampled in October on the Tibetan Plateau. To broaden our evaluation of seasonality effects over a range of climatic zones, published high‐frequency isotopic data were also compiled, and a similar assessment was carried out for selected regions of the world. The synthesized data and model outputs, which confirm pronounced variations in lake water isotopic composition and evaporation/inflow across a range of seasonal climates, were used to determine optimal sampling windows for these specific regions.

How does the groundwater influence the water balance of a lowland lake? A field study from Lake Stechlin, north-eastern Germany

The subsurface catchment of Lake Stechlin is quite complex. Water level measurements in groundwater wells with different screen depths show that groundwater in the lake’s catchment may partly discharge to the lake and partly leak to deeper aquifers. Simple steady-state 2D vertical modelling of eight different scenarios (different leakage areas, different hydraulic conductivities) was conducted in order to explore the local and regional groundwater flow system around Lake Stechlin and the origin and possible magnitude of lacustrine groundwater discharge. A comparison of the different scenarios with in situ measurements of lacustrine groundwater discharge by temperature sticks and seepage meters revealed that only a part of the groundwater recharge in the catchment discharges to the lake while the rest leaks into deeper aquifers. This implies a differentiation of the subsurface catchment into a local and a regional flow system and impacts on travel times and chemical reaction time scales.

Calculation of water balance China Lake (between 2008-2014)

Introduction. The main characteristic of hydrometeorological mode of China Lake, is the water balance of inland waters, defined process flow and water flow. Based on the water balance is determined by water exchange, physical and chemical processes in reservoirs and estimated effects of measures aimed at possible economic use of water resources.&#x0D; Purpose. The aim is analyze of physical - geographic, morphometric, hydrological, hydraulic characteristics of China Lake and the rivers that feed them; calculation of the components of the water balance of the lake China (in 2008-2014) and determine the water balance of residuals.&#x0D; Methods. In the analysis of available materials observations known statistical methods used; in determining the unknown components of water balance - similar hydrological methods and operating regulations.&#x0D; Results. Receipt of lake water balance China (2008-2014) in the largest extent determine precipitation on the water surface of the lake (from 17 to 77%), while expenditure is the highest percentage of evaporation from 38,7 to 86,1%. The greatest value of residuals observed in the summer months, received their size residuals are found within the acceptable.&#x0D; Conclusion. The authenticity of the definition of the components of the water balance of the lake. China will also be checked accuracy of the values of salinity of water in the reservoir as a result of payments salt balance.

HYDROLOGICAL AND HYDROCHEMICAL FEATURES OF THE LARGEST LAKES OF THE YAMAL PENINSULA

The results of hydrological survey of the largest lakes of the Yamal Peninsula – Neyto 1st, Neyto-Erto, Neyto-Malto, Yambuto and Yarato 2 nd , undertaken in September 2007 are presented. The morphometric characteristics of these lakes as well as the hydrological properties of their water at the end of the autumn low water stage were determined. Many of the largest lakes of Yamal have a complex bottom topography due to the presence of cryptodepressions cutting deeply into the bottom. They are both shallow lakes with an average depth less than3 m and lakes with average depths exceeding 10–20 m. There is thorough vertical mixing of the water masses (even in deep-water hollows) due to the impact of wind and convection. Extremely low mineralization and very low content of hydrocarbonates in the water result from the dominance of atmospheric precipitation in the input part of the lake water balance. Greenish coloring of water in some of the surveyed lakes and moderate supersaturation with oxygen in all the lakes evidence a considerable development of cold-loving phytoplankton species (during the growing season it is promoted by a longer daylight duration).

Identifying, characterizing and predicting spatial patterns of lacustrine groundwater discharge

Abstract. Lacustrine groundwater discharge (LGD) can significantly affect lake water balances and lake water quality. However, quantifying LGD and its spatial patterns is challenging because of the large spatial extent of the aquifer–lake interface and pronounced spatial variability. This is the first experimental study to specifically study these larger-scale patterns with sufficient spatial resolution to systematically investigate how landscape and local characteristics affect the spatial variability in LGD. We measured vertical temperature profiles around a 0.49 km2 lake in northeastern Germany with a needle thermistor, which has the advantage of allowing for rapid (manual) measurements and thus, when used in a survey, high spatial coverage and resolution. Groundwater inflow rates were then estimated using the heat transport equation. These near-shore temperature profiles were complemented with sediment temperature measurements with a fibre-optic cable along six transects from shoreline to shoreline and radon measurements of lake water samples to qualitatively identify LGD patterns in the offshore part of the lake. As the hydrogeology of the catchment is sufficiently homogeneous (sandy sediments of a glacial outwash plain; no bedrock control) to avoid patterns being dominated by geological discontinuities, we were able to test the common assumptions that spatial patterns of LGD are mainly controlled by sediment characteristics and the groundwater flow field. We also tested the assumption that topographic gradients can be used as a proxy for gradients of the groundwater flow field. Thanks to the extensive data set, these tests could be carried out in a nested design, considering both small- and large-scale variability in LGD. We found that LGD was concentrated in the near-shore area, but alongshore variability was high, with specific regions of higher rates and higher spatial variability. Median inflow rates were 44 L m−2 d−1 with maximum rates in certain locations going up to 169 L m−2 d−1. Offshore LGD was negligible except for two local hotspots on steep steps in the lake bed topography. Large-scale groundwater inflow patterns were correlated with topography and the groundwater flow field, whereas small-scale patterns correlated with grain size distributions of the lake sediment. These findings confirm results and assumptions of theoretical and modelling studies more systematically than was previously possible with coarser sampling designs. However, we also found that a significant fraction of the variance in LGD could not be explained by these controls alone and that additional processes need to be considered. While regression models using these controls as explanatory variables had limited power to predict LGD rates, the results nevertheless encourage the use of topographic indices and sediment heterogeneity as an aid for targeted campaigns in future studies of groundwater discharge to lakes.