Deep-water Lake Research Articles

Depth-dependent molecular composition and photo-reactivity of dissolved organic matter in a boreal lake under winter and summer conditions

Abstract. Transformations of dissolved organic matter (DOM) in boreal lakes lead to large greenhouse gas emissions as well as substantial carbon storage in sediments. Using novel molecular characterization approaches and photochemical degradation experiments we studied how seasonal patterns in water column stratification affected the DOM in a Swedish lake under early spring and summer conditions. Dissolved organic carbon (DOC) concentrations were consistently higher above the sediment when compared to surface waters throughout the sampling periods. Photobleaching alone could not explain this difference in DOC because the lake was covered by 40 cm-thick ice during late winter sampling and still showed the same DOC trend. The differences in the molecular diversity between surface DOM in winter and summer were consistent with ongoing photobleaching/decarboxylation and a possible bacterial consumption of photo-products. Additional photo-degradation experiments using simulated sunlight showed a production of highly oxidized organic molecules and low molecular weight compounds in all late winter samples and also in the deep water sample in summer. In the surface summer DOM sample, few such molecules were produced during the photo-degradation experiments, confirming that DOM was already photobleached prior to the experiments. This study suggests that photobleaching, and therefore also the ice cover during winter, plays a central role in surface DOM transformation, with important differences in the molecular composition of DOM between surface and deep boreal lake waters. The release of DOC from boreal lake sediments also contribute to this pattern. Photochemical degradation of DOM may be more extensive following ice-out and water column turnover when non-light exposed and thereby photosensitive DOM is photo-mineralized. Hence, the yearly DOM photo-mineralization may be greater than inferred from studies of recently light-exposed DOM.

A cellular and metabolic assessment of the thermal stress responses in the endemic gastropod Benedictia limnaeoides ongurensis from Lake Baikal

Our objective was to determine if the Lake Baikal endemic gastropod Benedictia limnaeoides ongurensis, which inhabits in stable cold waters expresses a thermal stress response. We hypothesized that the evolution of this species in the stable cold waters of Lake Baikal resulted in a reduction of its thermal stress-response mechanisms at the biochemical and cellular levels. Contrary to our hypothesis, our results show that exposure to a thermal challenge activates the cellular and biochemical mechanisms of thermal resistance, such as heat shock proteins and antioxidative enzymes, and alters energetic metabolism in B. limnaeoides ongurensis. Thermal stress caused the elevation of heat shock protein 70 and the products of anaerobic glycolysis together with the depletion of glucose and phosphagens in the studied species. Thus, a temperature increase activates the complex biochemical system of stress response and alters the energetic metabolism in this endemic Baikal gastropod. It is concluded that the deepwater Lake Baikal endemic gastropod B. limnaeoides ongurensis retains the ability to activate well-developed biochemical stress-response mechanisms when exposed to a thermal challenge.

Supraglacial Streams on the Greenland Ice Sheet Delineated From Combined Spectral–Shape Information in High-Resolution Satellite Imagery

Supraglacial meltwater streams and lakes that form each summer across large expanses of the Greenland Ice Sheet (GrIS) ablation zone have global implications for sea level rise but remain one of the least studied hydrologic systems on Earth. Remote sensing of supraglacial streams is challenging owing to their narrow width (~1-30 m) and proximity to other features having similar visible/near-infrared reflectance (lakes and slush) or shape (dry stream channels, crevasses, and fractures). This letter presents a new automated “spectral-shape” procedure for delineating actively flowing streams in high-resolution satellite imagery, utilizing both spectral and pattern information. First, a modified normalized difference water index adapted for ice ( NDWI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ice</sub> ) enhances the spectral contrast between open water and drier snow/ice surfaces. Next, three NDWI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ice</sub> thresholds are used to mask deep-water lakes and discern open water from slush, in concert with a multipoints fast marching method to rejoin resulting stream fragments. Comparison of this procedure with manual digitization for six WorldView-2 images in southwestern Greenland demonstrates its value for detecting actively flowing supraglacial streams, particularly in slushy areas where classification performance dramatically improves (85.2% success) versus simple threshold methods (52.9% and 59.4% success for low and moderate thresholds, respectively). While a simple threshold approach is satisfactory for areas known to be slush free, the procedure outlined here enables comprehensive stream mapping across the GrIS ablation zone, regardless of slush conditions and/or the presence of similarly shaped glaciological features.

Geothermal heat flux into deep caldera lakes Shikotsu, Kuttara, Tazawa and Towada

Geothermal heat fluxes into the deepest waters of four caldera lakes were measured. Temperature profiles within the stratification period between July and November 2007 allowed a quantification of the acquired heat. Due to their enormous depth, heat input from the lake bed was locally separated from heat fluxes at the surface. In conclusion, a direct measurement of geothermal heat input could be accomplished. Although enhanced geothermal activity could be suspected in all cases, two lakes showed a geothermal heat flux of 0.29 or 0.27 W/m2 (Lake Shikotsu and Lake Tazawa), as found in other regions not affected by volcanism, while both other lakes (Lake Kuttara and Lake Towada) showed a greatly enhanced heat input of 1 or 18.6 W/m2, respectively. In conclusion, within our investigated set, all lakes acquired more heat from the underground than the continental heat flux average. Hence, the heat flux into the lakes from the ground was not dominated by the temperature gradient implied by the inner heat of the earth. Other effects like the general temperature difference of deep lake water and the groundwater or local sources of heat in the underground deliver more important contributions. Obviously the flow of water in the underground can play a decisive role in the heat transport into the deep waters of lakes.

Saws, sonar and submersibles: Expectations of/for underwater logging

Underwater logging is a relatively novel industry focused on extracting wood from standing trees in deep-water lakes and reservoirs. It emerges through a confluence of technological, financial and environmental interests, primarily within small corporations in British Columbia, Canada. Companies now operate in many countries worldwide and may be promoted by dam owners that are moving from a narrow focus on hydroelectric power revenue to exploring ways of extracting profit from these infrastructures. In this paper we use the example of underwater logging to explore the ways in which expectations for new industries create value for these companies. We show how uncertainty, materiality and control of the storyline become three formative factors in explaining why some expectations are realized while others fail. First, uncertainty can be made to be economically productive as long as it is bounded by methodologically reliable accounting. In the case of underwater logging, while unknown timber quantities could be economically damaging, rare, unknown wood is translated into a niche, high-end market that creates additional value. Second, materiality is at the heart of expectations in that companies need to show they have control over the raw materials and ecological consequences of the logging. Third, controlling the storyline becomes a vital part of marketing underwater wood. This produces a somewhat cautious reaction to certification schemes and retailers. The performative nature of expectations thus needs to be considered in explorations of the production of capitalist natures and the consequences of these interventions.

Phytoplankton of Deep-Water Lakes of Southern Ural (Russia) in High-Level Water

The paper deals with the results of original studies of taxonomic diversity and structure of dominant complexes of phytoplankton in the deep-water lakes of Southern Ural in a high-water hydrological cycle. Lake phytoplankton is formed by representatives of Bacillariophyta, Chrysophyta, and Chlorophyta with significant portions of cyanoprokaryotes and Dinophyta.

Comparison of mercury speciation and distribution in the water column and sediments between the algal type zone and the macrophytic type zone in a hypereutrophic lake (Dianchi Lake) in Southwestern China

During a heavy algal bloom in 2009, we collected lake water, surface sediment, sediment cores and porewater samples from Dianchi Lake to investigate the effect of eutrophication and different aquatic habitats (algal and macrophytic) on mercury (Hg) distribution and speciation in hypereutrophic lake. The total Hg (THg) concentration in the sediment and lake water was substantially elevated compared to uncontaminated lakes and reservoirs. The spatial distribution of THg pointed to waste water discharged from Kunming City as the dominant source of Hg in Dianchi Lake. Despite the high concentration of THg, the concentration of methyl mercury (MeHg) was relatively low compared to other deep water lakes and reservoirs, and the ratio of MeHg/THg was generally lower than 1% in lake water and sediments, implying the low potential of Hg methylation. No significant relationship was found between the total organic carbon (TOC) and MeHg in either surface sediment or sediment cores. This result is different from previous conclusions that an increase of organic material load in sediment can enhance the potential of Hg methylation in sediments. A significant relationship between the total S and MeHg in the two cores indicated that sulfur played an important role in Hg methylation. However, because of similar concentrations of MeHg and distinct differences in the S concentration in the two cores, the total S should not be a limiting factor for Hg methylation in sediment. The most important limiting factors controlling Hg methylation were high pH and Eh induced by heavy algal blooms and shallow water depth in Dianchi Lake because Hg methylation will be inhibited and the demethylation of MeHg may be accelerated under alkaline and oxic conditions.

The consequences of changes in forest land cover in the Alpine and Jurassic massifs on the physico-chemical status of deep lake waters

The issue of acidification in lake waters has been the topic of numerous scientific studies in northern Europe and North America. In recent years, interest in the topic has spread to southern Europe and Asia because similar symptoms have been observed (drop in pH and in redox potential, generally accompanied by oxygen depletion). All the scientific work on the issue has concluded that the phenomenon is general and affects, to different degrees, lakes located at low to medium altitudes in mountains (the Vosges mountains and more recently the Jura mountains, in France). The difference in degree is often interpreted as the result of different combinations from three sources, namely acid rain, direct discharges of pollutants and the spread of forests (essentially conifer species). The first two sources have been confirmed, but the third is less perceptible due to slow progression of the phenomenon.Analysis and modelling of changes in land cover in the Hérisson river basin in the Jura mountains (largely carbonated soils) confirmed the direct impact of the forest cover on the physico-chemical quality of lake waters, in particular at the deeper levels (hypolimnion) over the past 30 years. The impact is reinforced by the considerable presence of peat zones around the lakes which, during high-water periods, contribute large quantities of dissolved, particulate organic matter.The goal of this work is to show the direct impact of the increasing forest cover observed on the Jurassic plateaus, caused by a considerable reduction in farming activity over the past 30 years. This work focuses on an analysis of land cover (vegetation), using four satellite images spanning the period from 1975 to 2006, and calls on hydrogeochemical modelling (WARMF) to evaluate changes in the physico-chemical quality, i.e. acidification, of deep lake waters. This first step is followed by a predictive phase prior to measuring the intensity of the physico-chemical changes (pH and redox) over the next 20 years to 2030. The existence of this phenomenon confirms the massive releases of heavy metals recently noted and the biological weakening observed in certain lakes, notably among the benthic fauna.

Time-dependent CO2 variations in Lake Albano associated with seismic activity

Lake Albano (Alban Hills volcanic complex, Central Italy) is located in a densely populated area near Rome. The deep lake waters have significant dissolved CO2 concentrations, probably related to sub-lacustrine fluid discharges fed by a pressurized CO2-rich reservoir. The analytical results of geochemical surveys carried out in 1989–2010 highlight the episodes of CO2 removal from the lake. The total mass of dissolved CO2 decreased from ∼5.8 × 107 kg in 1989 to ∼0.5 × 107 kg in 2010, following an exponential decreasing trend. Calculated values of both dissolved inorganic carbon and CO2 concentrations along the vertical profile of the lake indicate that this decrease is caused by CO2 release from the epilimnion, at depth <9 m, combined with (1) water circulation at depth <95 m and (2) CO2 diffusion from the deeper lake layers. According to this model, Lake Albano was affected by a large CO2 input that coincided with the last important seismic swarm at Alban Hills in 1989, suggesting an intimate relationship between the addition of deep-originated CO2 to the lake and seismic activity. In the case of a CO2 degassing event of an order of magnitude larger than the one that occurred in 1989, the deepest part of Lake Albano would become CO2-saturated, resulting in conditions compatible with the occurrence of a gas outburst. These results reinforce the idea that a sudden CO2 input into the lake may cause the release of a dense gas cloud, presently representing the major volcanic threat for this densely populated area.

Geochemical trends through time and lateral variability of diatom floras in the Pleistocene Olorgesailie Formation, southern Kenya Rift Valley

The Olorgesailie Formation (1.2–0.49 Ma) consists of fluvial and lacustrine rift sediments that have yielded abundant Acheulean artifacts and a fossil hominin ( Homo cf. erectus). In testing prior understandings of the paleoenvironmental context, we define nine new geochemical zones. A Chemical Index of Alteration suggests increased catchment weathering during deposition of Members 1, 2, 7, 11, and 13. Biophile elements (Br, S) peak in M8–9 and lower M13 possibly reflecting increased input from soil erosion. REE data show that the Magadi Trachytes supplied most siliciclastic grains. Sixteen diatom stages indicate conductivities of 200–16,000 μS cm − 1 and pH of 7.5–9.5 for five deep-water lakes, ten shallow lakes and sixteen wetlands. These results are compared with diatom data from other sections in the basin and show aquatic spatial variability over km-scale distances. Similar floras are traceable over several kilometers for M2, M3 and M9, indicating broadly homogeneous lacustrine conditions during these times, but diatoms in other members imply variable conditions, some related to local tectonic controls. This lateral and temporal variability emphasizes the importance of carrying out stratigraphic sampling at multiple sites within a basin in efforts to define the environmental context relevant to human evolution.

Liquefaction Probability Curves for Surficial Geologic Deposits

Liquefaction probability curves that predict the probability of surface manifestations of earthquake-induced liquefaction are developed for 14 different types of surficial geologic units. The units consist of alluvial fan, beach ridge, river delta topset and foreset beds, eolian dune, point bar, flood basin, natural river and alluvial fan levees, abandoned river channel, deep-water lake, lagoonal, sandy artificial fill, and valley train deposits. Probability is conditioned on earthquake magnitude and peak ground acceleration. Curves are developed for water table depths of 1.5 and 5.0 m. Probabilities are derived from complementary cumulative frequency distributions of the liquefaction potential index (LPI) that were computed from 927 cone penetration tests. For natural deposits with a water table at 1.5 m and subjected to a M7.5 earthquake with peak ground acceleration (PGA) = 0.25 g , probabilities range from 0.5 for beach ridge, point bar, and deltaic deposits. The curves also were used to assign ranges of liquefaction probabilities to the susceptibility categories proposed previously for different geologic deposits. For the earthquake described here, probabilities for susceptibility categories have ranges of 0–0.08 for low, 0.09–0.30 for moderate, 0.31–0.62 for high, and 0.63–1.00 for very high. Retrospective predictions of liquefaction during historical earthquakes based on the curves compare favorably to observations.

Disappearance of a crater lake: implications for potential explosivity at Soufrière volcano, St Vincent, Lesser Antilles

Soufriere volcano in St Vincent, West Indies, is one of the most active volcanoes in the Eastern Caribbean with at least six eruptions since 1718 AD, the latest of which occurred in 1979. Prior to the 1979 eruption, the active crater hosted deep-water lakes during periods of repose, which were always replenished within a few years after the eruptions. In 1979, the crater was filled with 108 m3 of fragmental material and, despite constant precipitation, has remained virtually dry ever since, with the exception of a small shallow pond. A resistivity survey was conducted in July 2006 to investigate groundwater occurrence in the crater. Results from the resistivity data inversion on several 2-D profiles show a shallow horizontal conductor across the crater floor, consistent with a water-saturated aquifer. They also show that the post-1979 pond, currently present in the crater lake is in fact an outcropping part of the groundwater water reservoir. The reservoir water table is ∼28 m above the pre-1979 lake level and reflects mass equilibrium in the system where constant seepage underground balances the meteoric recharge. We suggest that the groundwater body extends at depth to the bottom of the pre-1979 crater lake, either due to a significant structural discontinuity or because of a reduction of permeability at depth. The estimated maximum volume of water stored underground is 10–30 × 106 m3 and energy considerations indicate that 2.4–7.3 × 1010 kg of magma would potentially be sufficient to vaporise the whole groundwater body. This amount of magma represents only 13–41% of the mass erupted during the last eruption in 1979 which was the smallest of the past 3 eruptions (1902, 1971–72, 1979). Since explosive phreatic or phreatomagmatic eruptions at Soufriere seem to be linked to magma-water interaction within confined space, the results from this survey suggests that phreatic or phreatomagmatic activity is a distinct possibility during future magma intrusion in the summit area, despite the apparent disappearance of water in the summit crater.

Further discussion about the features of Lake Puma Yum Co, South Tibet, China

Further discussion about the limnological features of Lake Puma Yum Co, South Tibet, China, is provided based on the results of several investigations. By using depth data from all over the lake, the whole submarine topography has been compiled. Horizontal analysis of the water's physicochemical features indicates that compared with the relatively uniform water features at other lake areas, apparent spatial heterogeneity exists in the water of the subaquatic alluvial fan induced by the Jiaqu River, the biggest inflow. Vertical analysis of water characteristics using two-factor analysis of variance with no re-experiment indicates that temperature, dissolved oxygen, and pH of the water vary with water depth rhythmically, whereas other parameters demonstrate no evident vertical variation, which shows that chemical stratification is not obvious. But this does not exclude slightly higher concentrations of Ca2+ induced by lower pH at the bottom of deep lake water. The hydrochemistry difference between inflow water and lake water reveals the loss of Ca2+ in lake water, which indicates calcite deposition may be an important characteristic of lake sediment.

Jurassic sedimentary features and tectonic settings of southeastern China

Two types of the Jurassic basins are distinguished in SE China based on their geodynamic features: the Late Triassic-Early Jurassic post-orogenic basins and the Middle Jurassic intra-continental extensional basins. The Lower Jurassic sequence shows a change from coarse- to fine-grained accumulation, suggesting a gradually deepening depositional environment from river to shore-lake and to deep-water lake. In contrast, the Middle Jurassic accumulation was changed from claystone to conglomerate along the coastal provinces in SE China, indicative of an initial crustal uplift. The Wuyi Mountains have been a paleogeograghic separating zone since the Middle Jurassic. The Late Jurassic strata are absent in most areas of SE China. A large-scale bimodal intra-continental rift-type volcanism occurred during the Middle Jurassic along a 40–60 km wide and 200 km long area in western Fujian and southern Jiangxi provinces, which is most likely the strongest volcanism in SE China since the Cambrian. The SHRIMP zircon U-Pb analyses on the rhyolite from the Dongkeng basin in the southern Jiangxi area yield a concord U-Pb age of 160±0.5 Ma, providing an upper age limit for the bimodal volcanic eruption. The analyses of the basin features indicate a change of the depositional environment during the interval from Middle Triassic to Late Triassic from a shallow-sea to an intra-continent in SE China in response to the strong collision between the Yangtze and North China Blocks. Sedimentary structures record a southward direction of Early Jurassic paleo-currents, reflecting that their source areas were to the north side. We propose that the Wuyi region was uplifted as early as Middle Jurassic, followed by a wide E-W-trending extended depression and bimodal volcanism in the western foot of the Wuyi Mountains. Presumably the uplift of the Wuyi domain changed the Middle Jurassic paleogeographic outline and formed the transformational tectonic regime from compression to extension as a tectonic response to the Pacific plate subduction.

A comprehensive study across methods and time scales to estimate surface fluxes from Lake Kinneret, Israel

Summary Estimation of surface fluxes in general, and evaporation rates over lake surfaces in particular, is a difficult task. While previous studies of Lake Kinneret, Israel, have looked at evaporation rate using a single timescale or single measurement method, this is the first comprehensive study to reconcile and explain the differences between a variety of measurement and calculation methods (pan evaporation, water and heat balance, aerodynamic methods and Penman simplified methods) across a multitude of temporal scales (10 min, 1 h, daily, monthly). The cross validation of the methods suggests that the hourly calculation with the aerodynamic methods may result in a better estimation of the monthly Bowen Ratio for the energy balance methods, and therefore may increase its reliability. We also show that comprehensive measurements and calculations of monthly heat storage change in the lake can be used to verify the hourly results of the hydrodynamic method, and the daily calculations of the Penman’s equation method. Moreover, using the Penman’s equation it is suggested that daily Pan A evaporation measurements are nearly similar to the evaporation from the deep water lake when the heat storage change is not taken into account. It is suggested that subject to data availability, the cross validation of multiple methods increases the reliability and confidence of the measured and calculated surface fluxes.

Bacteriophages as a new trophic link in the ecosystem of the deep-water Lake Baikal

Bacteriophages as a new trophic link in the ecosystem of the deep-water Lake Baikal

Water and gas chemistry at Lake Kivu (DRC): Geochemical evidence of vertical and horizontal heterogeneities in a multibasin structure

Waters and dissolved gases collected along vertical profiles in the five basins (Main, Kabuno Bay, Kalehe, Ishungu, and Bukavu) forming the 485 m deep Lake Kivu (Democratic Republic of the Congo) were analyzed to provide a geochemical conceptual model of the several processes controlling lake chemistry. The measured horizontal and vertical variations of water and gas compositions suggest that each basin has distinct chemical features produced by (1) different contribution from long circulating fluid system containing magmatic CO2, responsible of the huge CO2(CH4)‐rich reservoir hosted within the deep lake water; (2) spatial variations of the biomass distribution and/or speciation; and (3) solutes from water‐rock interactions. The Kabuno Bay basin is characterized by the highest rate of magmatic fluid input. Accordingly, this basin must be considered the most hazardous site for possible gas outburst that could be triggered by the activity of the Nyiragongo and Nyamulagira volcanoes, located a few kilometers north of the lake.

Numerical modeling of magnetization of a precipitating rock suspension

The influence of collisions between the clusters of a precipitating material on its magnetization at the precipitation stage in an aqueous medium is analyzed. In laboratory experiments, when the sedimentation rate exceeds the value of this rate under natural conditions by several orders of magnitude, collisions are an important factor which sharply decreases the value of magnetization. Only the case of precipitation in distilled water, when the probability of aggregation of particles with their collision approach is small, can be an exception to this rule. Under natural conditions, the concentration of the precipitating solid phase plays the decisive role. For the conditions of deep-water lakes and coastal sea basins with the relatively high sedimentation rate its concentration is sufficient for intensification of the flocculation process, beginning from a certain depth. However, the quantity of material precipitating on the surface for areas distant from continents is too small and in these regions the role of collisions is of negligible importance. The magnetization of the precipitating suspension under conditions of intense flocculation has a linear dependence on the field and is defined by at least seven parameters, which characterize both magnetic and nonmagnetic particles. Such a multiparametric dependence of the magnetization value on the precipitation conditions is responsible for the practical impossibility of estimating the magnitude of the ancient geomagnetic field by the method of reprecipitation in view of the impossibility of adequately reproducing in the laboratory the precipitation conditions in the natural basins.

137Cs in deep-water lakes: Analysis of the peculiarities of water contamination and purification

The assessment of 137Cs concentration in water based on the model of radionuclide absorption by the bottom sediment of a closed water body is applicable to deep-water lakes with slower water circulation (the time of water exchange exceeding 10 years). The low river runoff from such lakes does not determine their water purification from 137Cs because of the predominance of the process of 137Cs sorption by suspension and bottom sediment. The contamination of a deep-water arctic lake with global 137Cs is reconstructed.

Parallel life history evolution in mouthbrooding cichlids from the African Great Lakes

The existence of ancient deep-water lakes provides an opportunity to study the independent adaptation of aquatic organisms to pelagic, benthic, and rocky shore habitats. With improving resolution of their phylogenetic relationships, the many cichlid fish species endemic to the African Great Lakes Malawi, Tanganyika, and Victoria provide a significant resource for the comparative study of such evolutionary processes. Here, we show that cichlid lineages colonizing rocky shores and pelagic habitats in the different lakes have independently evolved larger eggs and lower fecundities than benthic lineages, suggesting parallel adaptive life-history evolution. By contrast, other pelagic teleost fishes in both marine and freshwater habitats, including African lakes, typically produce large numbers of very small eggs. Our results also suggest that decreased fecundity and increased egg size not only occurred independently in each lake but occurred independently in the colonization of rocky and pelagic habitats.