Sublacustrine Springs Research Articles

Impacts of Different Habitats on the Composition of Bacterial Communities at the Discharging Endpoints of a Hypogene Thermal Karst System

The discharging zones of thermal karst caves provide special environmental conditions for bacteria involved in the biogeochemical processes. The taxonomic composition of bacterial communities inhabiting these still active natural habitats is largely unknown. The aim of this study was to reveal and compare the bacterial diversity of upwelling thermal waters, rock surface biofilms, and cave deposits using high-throughput next-generation sequencing. Two thermal karst caves formed in carbonate rocks and located at the discharging endpoints of the Transdanubian Range (Hungary) were studied: a sublacustrine spring cave and a phreatic hypogene cave. The results of 16S rRNA gene-based Illumina MiSeq amplicon sequencing revealed that almost all samples were dominated by Proteobacteria and/or Epsilonbacteraeota. Other abundant phyla showed habitat-dependent and diverse distributions. Sequences of the thermal waters were mainly associated with different chemolithotrophic sulfur-oxidizing bacteria (genera Thiovirga, Thiofaba, and Arcobacter in the sublacustrine thermal spring cave, whereas genera Sulfurovum, Sulfuricurvum, and Sulfurifustis were characteristic of the phreatic hypogene thermal cave) in accordance with the difference in environmental parameters. Sequences belonging to ammonia-oxidizing (unclassified Nitrosococcaceae) and nitrite-oxidizing bacteria (Nitrospira) were characteristic of the hypogene cave. Sequences related to photoautotrophic bacteria from the lake water and chemoheterotrophic bacteria from the sediment were only found in the sublacustrine spring cave samples.

Lacustrine carbonate towers of Lake Abhe, Djibouti: Interplay of hydrologic and microbial processes

Lake Abhe, located at the triple junction between the Red Sea, Gulf of Aden, and Main Ethiopian rift trends, is a hypersaline and alkaline closed lake that is known for its exposures of massive carbonate chimneys on the flat-lying sediments of the lake's eastern margin. This study describes the morphological, textural, and petrographic characteristics of these chimneys at the basin- to microscopic-scale in order to constrain the carbonate depositional system in the context of basin hydroclimate history. Chimneys occur in three main fields and are assessed according to 1) large-scale (>5 m) morphological variations, 2) meso-scale (cm to <5 m) textures, and 3) micro-scale (<1 cm) fabrics. The dominant chimney fabric is a porous crystalline framework of trigonal prismatic and dendritic calcite crystals that locally contain spherulites, sickle-cell calcite fabrics, and entombed microbial cocci. In addition to the crystalline chimneys, other carbonate sediments include stromatolitic crusts composed of microdigitate laminated columns dominated by crystalline fan microfabrics, as well as carbonate-rich mudstones and relatively rare, localized, carbonate-rich diatomites. Chimneys are interpreted to form primarily as products of mixing between hydrothermal sublacustrine springs and lake waters during lake highstand intervals, while stromatolitic crusts are interpreted to form during lowstand lake levels. Our interpretation of mixing processes is supported by the δ18O composition of chimney calcite, which is representative of lake water and area hot spring endmembers. The observation of stromatolitic crusts with more positive values of δ13C and δ18O than crystalline chimneys indicates that crusts formed during periods of high evaporation and low lake level. Crusts also contain Mg-silicate minerals, which are not present in crystalline chimneys, and further support the interpretation of lowstand depositional conditions. Although the age of chimney formation is not well constrained, evidence from seismic reflection data suggests a pattern of chimney formation during lake level rise and highstand times, followed by lake level fall, subaerial exposure and weathering that occurred at several times throughout the Late Pleistocene and Holocene.

The role of hydrothermal fluids in sedimentation in saline alkaline lakes: Evidence from Nasikie Engida, Kenya Rift Valley

AbstractSaline alkaline lakes that precipitate sodium carbonate evaporites are most common in volcanic terrains in semi‐arid environments. Processes that lead to trona precipitation are poorly understood compared to those in sulphate‐dominated and chloride‐dominated lake brines. Nasikie Engida (Little Magadi) in the southern Kenya Rift shows the initial stages of soda evaporite formation. This small shallow (&lt;2 m deep; 7 km long) lake is recharged by alkaline hot springs and seasonal runoff but unlike neighbouring Lake Magadi is perennial. This study aims to understand modern sedimentary and geochemical processes in Nasikie Engida and to assess the importance of geothermal fluids in evaporite formation. Perennial hot‐spring inflow waters along the northern shoreline evaporate and become saturated with respect to nahcolite and trona, which precipitate in the southern part of the lake, up to 6 km from the hot springs. Nahcolite (NaHCO3) forms bladed crystals that nucleate on the lake floor. Trona (Na2CO3·NaHCO3·2H2O) precipitates from more concentrated brines as rafts and as bottom‐nucleated shrubs of acicular crystals that coalesce laterally to form bedded trona. Many processes modify the fluid composition as it evolves. Silica is removed as gels and by early diagenetic reactions and diatoms. Sulphate is depleted by bacterial reduction. Potassium and chloride, of moderate concentration, remain conservative in the brine. Clastic sedimentation is relatively minor because of the predominant hydrothermal inflow. Nahcolite precipitates when and where pCO2 is high, notably near sublacustrine spring discharge. Results from Nasikie Engida show that hot spring discharge has maintained the lake for at least 2 kyr, and that the evaporite formation is strongly influenced by local discharge of carbon dioxide. Brine evolution and evaporite deposition at Nasikie Engida help to explain conditions under which ancient sodium carbonate evaporites formed, including those in other East African rift basins, the Eocene Green River Formation (western USA), and elsewhere.

Environmental determinants of water mite (Acari: Hydrachnidia) distribution in the ancient Lake Skadar system

In comparison to Central Europe, the knowledge about water mites inhabiting the natural lakes of southern Europe is scarce. This is a first study focusing on the water mite species composition and zonation in a large Mediterranean lake, i.e. ancient Lake Skadar basin, and identifying the role of physical and chemical water parameters in their distribution. The Hydrachnidia community of Lake Skadar is composed of 53 species. The most diverse water mite assemblages were found in the littoral zone and in the sublacustrine springs. Our study revealed that water mites were most abundant in the deeper, open part of Lake Skadar. Typically sublacustrine species dominated in all zones and habitats of Lake Skadar. The rheobiontic and rheophilic species also had a substantial share, mainly in sublacustrine springs, but also in the open lake area. The unique feature of the Lake Skadar water mite community was an absence of many species typical for the vernal astatic waters and for the shallow phytolittoral zone, even if such habitats were present. We conclude that the structure of the water mite communities in Lake Skadar are associated with particular zones (sublacustrine springs, littoral, open lake area) of the lake and with local environmental conditions, predominantly temperature.

Quantitative reconstruction of early Holocene and last glacial climate on the Balkan Peninsula using coupled hydrological and isotope mass balance modelling

We investigate the modern hydrology of Lake Ohrid (Macedonia/Albania) using a combined hydrological and isotope-based modelling approach and present a new evaluation of contemporary water balance and palaeoclimate estimates. The combined model is able to estimate hydrological components that cannot be directly measured, and indicates that sublacustrine spring inflow is in the order of 50% higher than previous estimates and groundwater outflow comprises approximately a third of overall water outflow. In combination with sediment core oxygen isotope data, we used the combined model to quantitatively reconstruct past climate, in particular precipitation, during the early Holocene and last glacial period. Calculated precipitation in the early Holocene was higher than the value for present day and was approximately 44% lower than present during the last glacial, assuming the majority of precipitation fell as snow. The estimated amount of precipitation in the last glacial would have been high enough to provide refugial conditions at Lake Ohrid and to support the continuous existence of arboreal vegetation in the catchment. The improved understanding of the modern isotope hydrology of Lake Ohrid is fundamental for explaining the systematics of past isotope variation and providing context for extended sediment records from the lake, which will provide longer-term palaeoclimate reconstructions covering multiple glacial-interglacial cycles.

The Holocene isotopic record of aquatic cellulose from Lake Äntu Sinijärv, Estonia: Influence of changing climate and organic-matter sources

The well characterized oxygen-isotopic fractionation during cellulose biosynthesis has been utilised by numerous studies of stable isotopes in fine-grained aquatic cellulose. We measured the δ13Ccellulose and δ18Ocellulose values of bulk cellulose and moss fragments from an ∼11.4ka-long core obtained from a shallow, productive, spring-fed, hardwater lake, Äntu Sinijärv, Estonia (59˚3.8′N; 26˚14.5′E; 94.6 m a.s.l.; maximum depth 7.3 m), in order to reconstruct regional Holocene climate and lake-basin evolution. Isotopically, the modern waterbody is a well-behaved, open, hydrological system with negligible evaporative effects. Cellulose-isotope records were compared with down-core measurements of loss-on-ignition (LOI), carbonate and mineral contents, total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ13CTOC, biomarker indices (Palg and Paq), published palaeoecological data and a δ18Ocarbonate record from the same palaeolake. Green microalgae, freshwater macroalgae (Chara) and aquatic bryophytes were important sources of sedimentary cellulose during different phases in the environmental history of the lake. Although a strong palaeoclimatic imprint can be detected in the δ18Ocellulose record from Äntu Sinijärv, notably the Preboreal oscillation, the 8.2ka event and an unnamed cold oscillation ∼3.25ka BP, the isotopic signal of these events may have been amplified by increases in 18O-depleted spring snowmelt. In contrast, δ13Ccellulose was tightly coupled to the Holocene evolution of terrestrial ecosystems and soils by significant inputs of biogenic carbon from the catchment and sublacustrine springs. During the early Holocene, ∼11 – 9ka BP, the δ18Ocellulose and δ18Ocarbonate records diverge markedly, which can be attributed to “no-analogue” seasonal, climatic, hydrological and isotopic conditions resulting from orbital forcing and residual ice-sheet impacts.

A microbial role in the construction of Mono Lake carbonate chimneys?

Lacustrine carbonate chimneys are striking, metre-scale constructions. If these were bioinfluenced constructions, they could be priority targets in the search for early and extraterrestrial microbial life. However, there are questions over whether such chimneys are built on a geobiological framework or are solely abiotic geomorphological features produced by mixing of lake and spring waters. Here, we use correlative microscopy to show that microbes were living around Pleistocene Mono Lake carbonate chimneys during their growth. A plausible interpretation, in line with some recent works by others on other lacustrine carbonates, is that benthic cyanobacteria and their associated extracellular organic material (EOM) formed tubular biofilms around rising sublacustrine spring vent waters, binding calcium ions and trapping and binding detrital silicate sediment. Decay of these biofilms would locally have increased calcium and carbonate ion activity, inducing calcite precipitation on and around the biofilms. Early manganese carbonate mineralisation was directly associated with cell walls, potentially related to microbial activity though the precise mechanism remains to be elucidated. Much of the calcite crystal growth was likely abiotic, and no strong evidence for either authigenic silicate growth or a clay mineral precursor framework was observed. Nevertheless, it seems likely that the biofilms provided initial sites for calcite nucleation and encouraged the primary organised crystal growth. We suggest that the nano-, micro- and macroscale fabrics of these Pleistocene Mono Lake chimneys were affected by the presence of centimetre-thick tubular and vertically stacked calcifying microbial mats. Such carbonate chimneys represent a promising macroscale target in the exploration for ancient or extraterrestrial life.

Prey abundance supporting unusual water mite (Acari: Hydrachnidia) community in a sublacustrine spring and tributary river

Water mites are predators on microcrustations (Copepoda, Cladocera, Ostracoda) and insect larvae (mostly Diptera). Their communities usually have great diversity with high species richness but relatively low abundance. This may have important implications for poorly investigated predator-prey interactions of water mites in natural habitats. A sublacustrine karst spring Torak and the mouth of its tributary river Cikola were examined seasonally from August 2016 to June 2017, with the aim of determining water mite distribution connected to prey availability. Triplicate samples were taken with an Ekman dredge on three distinct depth zones (littoral, sublittoral and profundal zone) at both study sites. Both, the karst spring and the tributary river, had typical lentic water mite communities with no rhithrobiont or crenobiont taxa present. Water mite species richness, abundance and alpha diversity were not governed by depth, but rather by prey availability. Greater copepod, ceratopogonid and chironomid abundances were found to positively correlate with higher abundances of water mites. The population of Limnesia connata, previously reported from lime-poor waters exclusively, was most probably supported by vast prey availability, thus unexpectedly surviving in this karst environment. L. connata, Neumania vernalis and Piona longipalpis were recorded for the first time in Croatia, while L. connata was recorded for the first time in the Dinaric karst.

Ecological patterns of Odonata assemblages in karst springs in central Montenegro

Karstic springs are important habitats for maintaining freshwater biodiversity. However, little is known about Odonata larvae assemblages in karstic springs, and studies about the ecological factors that determine species distribution in these habitats are still lacking. In this study the composition of Odonata larvae communities from 91 springs located in the central part of Montenegro was investigated. The richest fauna was found in sublacustrine springs, followed by limnocrenes, while that of the rheocrenes was less rich. The results obtained confirm the main research hypothesis that Odonata larvae assemblages in the karstic springs in the central part of Montenegro were comparably influenced by the environmental parameters acting on the level of individual springs as well as the factors acting at the landscape level. Odonata larvae assemblages divided springs into four groups. On the other hand, the springs could be divided into three groups based on habitat and landscape characteristics. CCA indicates that disturbance factors such as the permanence and directness of human influence on springs for use as drinking water sources are foremost in determining Odonata assemblages at the level of individual springs. The habitat scale considered several factors that influence Odonate assemblages, including altitude and riparian vegetation. This study proves that further odonatological studies in springs should include both types of factors and their interactions.

Holocene carbonate record of Lake Kivu reflects the history of hydrothermal activity

The sediment record of Lake Kivu reveals a complex volcanogenic and climatic Holocene history. Investigation of the inorganic carbonate record dates the onset of carbonate deposition in the mid-Holocene in Kivu's deep northern and eastern basins and identifies conditions enabling deposition. The magnitude and timing of carbonate-rich sedimentation is not so much controlled by climate but, instead, linked strongly to hydrothermal activity in the basin. Sublacustrine springs supply the vast majority of the calcium and carbonate ions required for supersaturation with respect to aragonite. This major hydrothermal activity that permanently stratifies Lake Kivu today was initiated ∼3,100 y before present (3.1 ka), when carbonate-rich sediments first appeared in the Holocene record. Aragonite is the dominant CaCO3 mineral present in the lake deposits. Both δ13C and δ18O of the aragonite are enriched above the expected kinetic fractionation of meteoric waters, suggesting a volcanogenic influence on the formation waters. Repeated major fluctuations in the carbonate record after 3.1 ka therefore most likely reflect the historical variation in hydrothermal inputs.

Groundwater contributions in water-salt balances of the lakes in the Badain Jaran Desert, China

Groundwater-fed lakes are essential for the ecology in arid and semiarid regions. As a typical arid region, the Badain Jaran Desert (BJD) is famous in the world for the presence of a large number of groundwater-fed saline lakes among the mega dunes. Based on the up to date geological surveys and observations, this study analyzed the groundwater contributions in water-salt balances of the lakes in the desert. We found different types of springs, including the sublacustrine springs that indicate an upward flow of groundwater under the lakebed. A simplified water balance model was developed to analyze the seasonal variations of water level in the SumuBarunJaran Lake, which revealed an approximately steady groundwater discharge in the lake and explained why the amplitude of seasonal changes in lake level is less than 0.5 m. In addition, a salt balance model was developed to evaluate the salt accumulations in the groundwater-fed lakes. The relative salt accumulation time is 800–7,000 years in typical saline lakes, which were estimated from the concentration of Cl−, indicating a long history evolution for the lakes in the BJD. Further researches are recommended to provide comprehensive investigations on the interactions between the lakes and groundwater in the BJD.

Hydrogeology of the Skadar Lake basin (Southeast Dinarides) with an assessment of considerable subterranean inflow

The Skadar Lake basin is located in the south-eastern part of the classical Dinaric karst region (northern Mediterranean). This region is well known for its highly developed karst and the presence of all types of karstic features. In addition to the high degree of karstification, the advantage of Skadar Lake’s catchment area in terms of water resources is also reflected in the following factors: a large amount of precipitation, scarcity of soil and vegetation cover, favourable geological and geomorphological conditions for karst aquifer discharge, the isolation of the Skadar basin from the influence of the Adriatic Sea and an availability of water for simple abstraction. For the purposes of a more complete determination of the water balance of Skadar Lake, among other undertakings, it has been necessary to determine the groundwater inflow to the lake through numerous sublacustrine springs (vruljas). By using thermal infrared satellite and terrestrial imaging, the locations of the largest sublacustrine springs have been detected and their yield assessed by means of water balance calculation after the application of the KARSTLOP method. The mean annual groundwater inflow to the lake, from the south-western edge only, is 9.86 m3/s. The total outflow of water from the lake through the Bojana River is around 304 m3/s. The coincidence of several important natural factors leads to the large average specific yield (surface and subsurface) in the Skadar Lake catchment area (54 l/s/km2), which makes this region one of the richest areas of freshwater in the world.

Carbonate build-ups in lacustrine, hydrothermal and fluvial settings: comparing depositional geometry, fabric types and geochemical signature

Abstract Carbonate build-ups in lakes, hydrothermal and fluvial settings are characterized by distinctive geometry, spatial distribution, fabrics and geochemical signature but also by some comparable features. Lake margin bioherms form continuous belts for hundreds of metres to kilometres, subparallel to shorelines. Sublacustrine spring mounds are spaced at hundreds of metres to kilometres and aligned along faults. Hydrothermal travertine mounds and aprons with planar clinoforms or terraced slopes are controlled by faults, thermal water discharge and substrate topography. Fluvial tufa barrages, cascades and terraced slopes are controlled by climate, vegetation and substrate gradient. The wide spectrum of carbonate microfabrics ranges from clotted peloidal micrite and laminated boundstone to crystalline dendrite cementstone. Non-marine carbonate microfabrics cannot be linked to specific depositional environments, and are not deterministic proxies for the interpretation of build-up architecture. Microfabric associations can be indicative, but not exclusive, of specific depositional environments and geometry. Stable isotope geochemistry is a useful tool to distinguish between hydrothermal, karstic freshwater and evaporative lake carbonates. Carbonate precipitation results from a continuum of abiotic and biologically influenced/induced processes in settings where carbonate supersaturation is largely driven by physico-chemical mechanisms and microbial biofilms, even if acting as passive low-energy surface sites for nucleation, are widely present.

Hydrogeochemical processes controlling water and dissolved gas chemistry at the Accesa sinkhole (southern Tuscany, central Italy)

The 38.5 m deep Lake Accesa is a sinkhole located in southern Tuscany (Italy) that shows a peculiar water composition, being characterized by relatively high total dissolved solids (TDS) values (2 g L-1) and a Ca(Mg)-SO4 geochemical facies. The presence of significant amounts of extra-atmospheric gases (CO2 and CH4), which increase their concentrations with depth, is also recognized. These chemical features, mimicking those commonly shown by volcanic lakes fed by hydrothermal-magmatic reservoirs, are consistent with those of mineral springs emerging in the study area whose chemistry is produced by the interaction of meteoric-derived waters with Mesozoic carbonates and Triassic evaporites. Although the lake has a pronounced thermocline, water chemistry does not show significant changes along the vertical profile. Lake water balance calculations demonstrate that Lake Accesa has >90% of its water supply from sublacustrine springs whose subterranean pathways are controlled by the local structural assessment that likely determined the sinking event, the resulting funnel-shape being then filled by the Accesa waters. Such a huge water inflow from the lake bottom (~9·106 m3 yr-1) feeds the lake effluent (Bruna River) and promotes the formation of water currents, which are able to prevent the establishment of a vertical density gradient. Consequently, a continuous mixing along the whole vertical water column is established. Changes of the drainage system by the deep-originated waters in the nearby former mining district have strongly affected the outflow rates of the local mineral springs; thus, future intervention associated with the ongoing remediation activities should carefully be evaluated to preserve the peculiar chemical features of Lake Accesa.

Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central–Southern Italy)

This paper focuses on the chemical and isotopic features of dissolved gases (CH4 and CO2) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH4 and CO2. The δ13C-CH4 and δD-CH4 values of dissolved gas samples from the maximum depths of the investigated lakes (from −66.8 to −55.6 ‰ V-PDB and from −279 to −195 ‰ V-SMOW, respectively) suggest that CH4 is mainly produced by microbial activity. The δ13C-CO2 values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from −5.8 to −0.4 ‰ V-PDB) indicate a significant CO2 contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO2 source feeding the regional thermal and cold CO2-rich fluid emissions. In contrast, the relatively low δ13C-CO2 values (from −13.4 to −8.2 ‰ V-PDB) of Lake Averno indicate a prevalent organic CO2. Chemical and isotopic compositions of dissolved CO2 and CH4 at different depths are mainly depending on (1) CO2 inputs from external sources (hydrothermal and/or anthropogenic); (2) CO2–CH4 isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO2 and CH4 concentrations. In the hypolimnion, where the δ13C-CO2 values progressively increase with depth and the δ13C-CH4 values show an opposite trend, biogenic CO2 production from CH4 using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ13C-CO2 values, and measured δ13CTDIC values are not consistent, indicating that CO2 and the main carbon-bearing ion species (HCO3 −) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO2 and CH4. This study demonstrates that the vertical patterns of the CO2/CH4 ratio and of δ13C-CO2 and δ13C-CH4 are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO2 input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.

Maintaining meromixis in Lake Pavin (Auvergne, France): The key role of a sublacustrine spring

Lake Pavin is a deep meromictic lake. Its water column is divided into two parts: the mixolimnion, which is subjected to mixing during seasonal overturns; and the monimolimnion which remains unmixed. Using high precision and high frequency temperature and conductivity profiles along with continuous temperature measurements, this study reveals the presence of a sublacustrine, intermittent cold spring at the bottom of the mixolimnion at a depth between 50 and 55 m. This cold-water input rises in the water column by saline convection. The use of a simple conceptual model, representing turbulent diapycnal diffusivity and convection correlated with the presence of the spring within the water column indicates its role in maintaining the meromixis characteristic of the lake on the intra-annual time scale. The spring also influences seasonal overturns and thus contributes to establish the depth of the mixolimnion–monimolimnion interface on the inter-annual time scale.

Stratigraphic analysis of lake level fluctuations in Lake Ohrid: an integration of high resolution hydro-acoustic data and sediment cores

Abstract. Ancient Lake Ohrid is a steep-sided, oligotrophic, karst lake that was tectonically formed most likely within the Pliocene and often referred to as a hotspot of endemic biodiversity. This study aims on tracing significant lake level fluctuations at Lake Ohrid using high-resolution acoustic data in combination with lithological, geochemical, and chronological information from two sediment cores recovered from sub-aquatic terrace levels at ca. 32 and 60 m water depth. According to our data, significant lake level fluctuations with prominent lowstands of ca. 60 and 35 m below the present water level occurred during Marine Isotope Stage (MIS) 6 and MIS 5, respectively. The effect of these lowstands on biodiversity in most coastal parts of the lake is negligible, due to only small changes in lake surface area, coastline, and habitat. In contrast, biodiversity in shallower areas was more severely affected due to disconnection of today sub-lacustrine springs from the main water body. Multichannel seismic data from deeper parts of the lake clearly image several clinoform structures stacked on top of each other. These stacked clinoforms indicate significantly lower lake levels prior to MIS 6 and a stepwise rise of water level with intermittent stillstands since its existence as water-filled body, which might have caused enhanced expansion of endemic species within Lake Ohrid.

Karstic sources of water supply for large consumers in Southeastern Europe – sustainability, disputes and advantages

Southeastern Europe is known worldwide as classic karst terrain. In the Alpine orogenic belt the karstified carbonate rocks are either dominant, as in the Dinarides, or widely distributed, as in the Carpathian-Balkans, Hellenides or Pindes. Concerning karstic groundwater resources, this region is by far the richest in all of Europe. Some areas, such as southern Montenegro, are characterized by an intensive and high precipitation affecting the water balance. In several countries in the region, water supply from karstic aquifers prevails. There are very large cities with populations of over a half million that depend on a water supply from karst aquifers. Among them are five capitals. Tapping large springs is the traditional method of water supply in the region but the main concern is their unstable discharge regime. This is why many aquifer control projects have been prepared or proposed in the region, particularly in the Mediterranean coastal area. Unfortunately, few have been executed and completed. Even some springs have been abandoned and water supply reoriented towards surface waters or alluvial aquifers. In contrast, with the tapping of the large sublacustrine spring Bolje sestre in Montenegro, the largest of the projects concerning regional water supply in karst is currently being implemented. Some 1.5 m 3/s of the water from the Skadar basin will supply the coastal zone. It is expected that this project, essential for the national economy, will be completed in 2011. Some other proposed large projects such as overseas karstic spring water transportation from Albania to Italy are still under evaluation. However, large and rich karstic reservoirs in this part of Europe should remain a reliable source for water supply in the future despite some possible negative impacts of climatic variation. There is, in fact, the prospect of and interest in exporting and supplying water to both neighbouring and remote areas.

Mollusc Biodiversity and Endemism in the Potential Ancient Lake Trichonis, Greece

ABSTRACT Ancient lakes are hotspots of biodiversity, often harboring a large number of endemic species that make them prime model systems for evolutionary biologists. Besides such well-recognized ancient or long-lived lakes as Baikal, Biwa, Ohrid, and Tanganyika, there are other potentially old and biodiverse lakes in the world with poorly specified ages and under-studied faunas. We here report on the mollusc fauna of one such lake, Lake Trichonis in continental Greece. This graben lake is situated in a highly tectonized area, characterized by karst features and probably of middle to late Pliocene origin. Lake Trichonis is deep, oligotrophic, and rich in such specific habitat types as macrophyte meadows, rocky shores and sublacustrine spring systems. Moreover, it is a hotspot of freshwater biodiversity in Greece, particularly in molluscs. After reviewing newly collected material and the published mollusc records, we found that at least 33 mollusc species occur in Lake Trichonis, with 24 gastropod and 9 bi...

A 700-year record of climate change based on geochemical and palynological data from varved sediments (Lac Pavin, France)

The Fe-flux budget of the meromictic crater Lac Pavin (French Massif Central) is re-evaluated in the light of new results from detailed sediment investigations (geochemistry, sedimentology, pollen, varve counting). Sedimentation of Lac Pavin during the last 700 years is characterised by high net accumulation of biogenic silica (100–500 g m − 2 yr − 1 SiO 2) and autochthonous Fe-precipitates ( F-Fe exc = 2–200 g m − 2 yr − 1 Fe) at overall high sediment accumulation (e.g. AD 1530–1890: 3.7 mm yr − 1 ). High net accumulation of biogenic silica and Fe exc is sustained by nutrient and Fe-influx via sub-lacustrine springs. The feeding of the groundwater inflow is closely correlated with the seepage of meteoric waters which declines in winter due to freezing of the ground. In the context of the derived local vegetation dynamics, balanced Fe exc-flux is interpreted as a proxy for rainfall during the growing season. Meteorological monitoring data document a significant inverse correlation between monthly temperature and rainfall between May and October which reflects enhanced cloudiness for precipitation above average. Beech, growing under sub-optimal conditions at the high altitude of the study site, represents a major tree component in the catchment of Lac Pavin. Minor temperature decrease in the growing season can explain reduced flowering of beech in the following year. Distinct short term variability of beech characterised by an inverse correlation with the balanced F-Fe exc supports the data interpretation. Two periods with prevailing of overall wetter and cooler conditions in the growing season were derived: ca. AD 1525–1600, and AD 1630–1660. Climate change to drier and warmer conditions is implied around AD 1450 and AD 1620. The Late Maunder Minimum (AD 1675–1715) is characterised by distinct short term variability of the palaeo-hydrological conditions at the study site.