Lake dwellers occupation gap in Lake Geneva (France-Switzerland) possibly explained by an earthquake-mass movement-tsunami event during Early Bronze Age

High-resolution seismic and sediment core data from the 'Grand Lac' basin of Lake Geneva reveal traces of repeated slope instabilities with one main slide-evolved mass-flow (minimum volume 0.13 km3) that originated from the northern lateral slope of the lake near the city of Lausanne. Radiocarbon dating of organic remains sampled from the top of the main deposit gives an age interval of 1865-1608 BC. This date coincides with the age interval for a mass movement event described in the 'Petit Lac' basin of Lake Geneva (1872-1622 BC). Because multiple mass movements took place at the same time in different parts of the lake, we consider the most likely trigger mechanism to be a strong earthquake (Mw 6) that occurred in the period between 1872 and 1608 BC. Based on numerical simulations, we show the major deposit near Lausanne would have generated a tsunami with local wave heights of up to 6 m. The combined effects of the earthquake and the following tsunami provide a possible explanation for a gap in lake dwellers occupation along the shores of Lake Geneva revealed by dendrochronological dating of two palafitte archaeological sites.

Distribution of major, minor, and trace metals in lake environments of Antarctica

The concentrations of major, minor and trace metals were measured in water samples collected from five shallow Antarctic lakes (Carezza, Edmonson Point (No 14 and 15a), Inexpressible Island and Tarn Flat) found in Terra Nova Bay (northern Victoria Land, Antarctica) during the Italian Expeditions of 1993-2001. The total concentrations of a large suite of elements (Al, As, Ba, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Gd, K, La, Li, Mg, Mn, Mo, Na, Nd, Ni, Pb, Pr, Rb, Sc, Si, Sr, Ta, Ti, U, V, Y, W, Zn and Zr) were determined using spectroscopic techniques (ICP-AES, GF-AAS and ICP-MS). The results are similar to those obtained for the freshwater lakes of the Larsemann Hills, East Antarctica, and for the McMurdo Dry Valleys. Principal Component Analysis (PCA) and Cluster Analysis (CA) were performed to identify groups of samples with similar characteristics and to find correlations between the variables. The variability observed within the water samples is closely connected to the sea spray input; hence, it is primarily a consequence of geographical and meteorological factors, such as distance from the ocean and time of year. The trace element levels, in particular those of heavy metals, are very low, suggesting an origin from natural sources rather than from anthropogenic contamination.

Introduced freshwater blenny influences the diet and body condition of the invasive dice snake in Lake Geneva

Non-indigenous species can have strong impacts on biodiversity by affecting trophic relationships in their new environments. The piscivorous dice snake (Natrix tessellata) has been introduced to Geneva Lake, western Switzerland, where the endangered viperine snake (Natrix maura) is native. Local, dramatic declines in the viperine snake population might be associated with the appearance of the dice snake through dietary overlap between these 2 species, which mainly feed on bullhead (Cottus gobio). In response to this decline, a control program for dice snake was implemented in 2007 to reduce numbers of this introduced snake. In 2010, a new species of fish, the freshwater blenny (Salaria fluviatilis), which shares the same habitat as the bullhead, was introduced into Lake Geneva and has since reached high densities. We determined the impact of freshwater blenny on diet composition and body condition of dice snakes. In addition, we tested for effects of the control program on the body condition of dice snakes and viperine snakes. We collected 294 dice snakes between 2007 and 2013. Based on morphology and a genetic marker (cytochrome b gene), we determined the ®sh species contained in these snakes' stomachs. We found a drastic switch in dice snake diet following the arrival of freshwater blenny, as consumption of bullhead declined by 68% and was replaced by the blenny. In addition, the body condition of dice snakes increased significantly after the arrival of freshwater blenny. The body condition of both snake species was positively correlated with the number of dice snakes removed from the study area. This finding has important implications concerning the conservation of the endangered viperine snake, and suggests that the control program of dice snakes should be continued.

Imaging molasse and quaternary sediments in Lake Geneva, Switzerland, with 3-D high-resolution seismic reflection methods: A case study

A high-resolution three-dimensional (3-D) seismic reflection survey was conducted in Lake Geneva, near the city of Lausanne, Switzerland, as part of a project for developing such seismic techniques. Using a single 48-channel streamer, the 3-D site with an area of 1200 m x 600 m was surveyed in 10 days. A variety of complex geologic structures (e.g. thrusts, folds, channel-fill) up to similar to150 m below the water bottom were obtained with a 15 in.(3) water gun. The 3-D data allowed the construction of an accurate velocity model and the distinction of five major seismic facies within the Lower Freshwater Molasse (Aquitanian) and the Quaternary sedimentary units. Additionally, the Plateau Molasse (PM) and Subalpine Molasse (SM) erosional surface, "La Paudeze" thrust fault (PM-SM boundary) and the thickness of Quaternary sediments were accurately delineated in 3-D.

Optimizing a remotely sensed proxy for plankton biomass in Lake Kivu

Many regions of the world, including inland lakes, present with suboptimal conditions for the remotely sensed retrieval of optical signals, thus challenging the limits of available satellite data-processing tools, such as atmospheric correction models (ACM) and water constituent-retrieval (WCR) algorithms. Working in such regions, however, can improve our understanding of remote-sensing tools and their applicabil- ity in new contexts, in addition to potentially offering useful information about aquatic ecology. Here, we assess and compare 32 combinations of two ACMs, two WCRs, and three binary categories of data quality standards to optimize a remotely sensed proxy of plankton biomass in Lake Kivu. Each parameter set is compared against the available ground-truth match-ups using Spearman's right-tailed ρ. Focusing on the best sets from each ACM-WCR combination, their performances are discussed with regard to data distribution, sample size, spatial completeness, and seasonality. The results of this study may be of interest both for ecological studies on Lake Kivu and for epidemio- logical studies of disease, such as cholera, the dynamics of which has been associated with plankton biomass in other regions of the world.

Bacteria Source Tracking in Lake Darling Watershed, 2005

Monitoring of Iowa's surface waters during the past five years has demonstrated the regular occurrence of fecel bacteria in surface water resources.

Fish ecology in Lake Banyoles (NE Spain): a tribute to Ramon Margalef

Lake Banyoles is the second largest lake in the Iberian Peninsula and due to this relative uniqueness, its peculiar geological origin, and its considerable age attracted the early attention of the late Professor Ramon Margalef. One of the first papers by Margalef was on the biota of Lake Banyoles and two of the first four Ph.D. theses that he supervised were about the limnology of this lake. Unfortunately, the uniqueness of this lake also implied that it was the first place of introduction into the Iberian Peninsula of several exotic fish species, early in the XXth Century and nowadays the lake fish assemblage is dominated by invasive species, and some native ones have been extirpated. Although the limnological studies in Lake Banyoles were pioneering within the Iberian Peninsula, studies on fish ecology of the lake did not start until 1989. Thereafter, four Ph.D. theses have been completed on different aspects of the fish assemblages of Lake Banyoles. The aim of this paper is to provide a short overview of this research, largely brought about by the considerable limnological information previously available for this lake, thanks to the insightful, pioneering work of Professor Margalef

A High-Resolution 2D/3D Seismic Study of a Thrust Fault Zone in Lake Geneva, Switzerland

P130 A HIGH-RESOLUTION 2D/3D SEISMIC STUDY OF A THRUST FAULT ZONE IN LAKE GENEVA SWITZERLAND M. SCHEIDHAUER M. BERES D. DUPUY and F. MARILLIER Institute of Geophysics University of Lausanne 1015 Lausanne, Switzerland Summary A high-resolution three-dimensional (3D) seismic reflection survey has been conducted in Lake Geneva near the city of Lausanne Switzerland where the faulted molasse basement (Tertiary sandstones) is overlain by complex Quaternary sedimentary structures. Using a single 48-channel streamer an area of 1200 m x 600 m was surveyed in 10 days. With a 5-m shot spacing and a receiver spacing of 2.5 m in the inline direction and 7.5 m in the crossline direction, a 12-fold data coverage was achieved. A maximum penetration depth of ~150 m was achieved with a 15 cu. in. water gun operated at 140 bars. The multi-channel data allow the determination of an accurate velocity field for 3D processing, and they show particularly clean images of the fault zone and the overlying sediments in horizontal and vertical sections. In order to compare different sources, inline 55 was repeated with a 30/30 and a 15/15 cu. in. double-chamber air gun (Mini GI) operated at 100 and 80 bars, respectively. A maximum penetration depth of ~450 m was achieved with this source.

Stable isotopes in lake Geneva carbonate sediments and molluscs: Review and new data

New isotopic results on bulk carbonate and mollusc (gastropods and bivalves) samples from Lake Geneva (Switzerland), spanning the period from the Oldest Dryas to the present day, are compared with pre-existing stable isotope data. According to preliminary calibration of modern samples, Lake Geneva endogenic calcite precipitates at or near oxygen isotopic equilibrium with ambient water, confirming the potential of this large lake to record paleoenvironmental and paleoclimatic changes. The onset of endogenic calcite precipitation at the beginning of the Allerod biozone is clearly indicated by the oxygen isotopic signature of bulk carbonate. A large change in delta(13)C values occurs during the Preboreal. This carbon shift is likely to be due to a change in bioproductivity and/or to a `'catchment effect'', the contribution of biogenic CO2 from the catchment area to the dissolved inorganic carbon reservoir of the lake water becoming significant only during the Preboreal. Gastropods are confirmed as valuable for studies of changes in paleotemperature and in paleowater isotopic composition, despite the presence of a vital effect. Mineralogical evidence indicates an increased detrital influence upon sedimentation since the Subboreal time period. On the other hand, stable isotope measurements of Subatlantic carbonate sediments show values comparable to those of pure endogenic calcite and of gastropods (taking into account the vital effect). This apparent disagreement still remains difficult to explain.

Mixing of Rhône River water in Lake Geneva (Switzerland-France) inferred from stable hydrogen and oxygen isotope profiles

Depth profiles were sampled at different locations throughout Lake Geneva on a monthly and seasonal basis over the course of 2 years and analysed for their stable hydrogen and oxygen isotope compositions. The isotopic compositions indicate an isotopic stratification in the metalimnion during summer and fall. This is related to mixing of Rhône River water, which in summer is dominated by snow and glacier melt waters, and lake water, with the latter having a homogenous isotopic composition. The observed interflow layer is 7-15 m thick and can be traced by the distinct stable isotope composition of the water for about 55 km throughout the lake as well as into shallow bay regions. Depth of the interflow layer close to the Rhône River mouth is similar to those previously described based on echo-soundings and turbidity profiles of sediment dispersion. In contrast to previous descriptions of the interflow within Lake Geneva, the stable isotope compositions allow for direct, natural tracing of the Rhône River water even in cases where the turbidity and conductivity measurements do not indicate such an interflow. In addition, the method allows for a quantification of the Rhône River and lake water in the interflow with the fraction of Rhône River water within the interflow estimated to be up to 37% in summer. The isotopic composition further indicates different vertical mixing processes within the two lake basins of Lake Geneva, related to the density gradients and local stability within the water column. The method may be applicable to other lakes in catchments with large differences in the topography as water that originates from high altitudes or glaciers has a distinct oxygen and hydrogen isotope composition compared to other sources of water originating at lower altitudes and/or from direct precipitation over the lake. Stable isotope measurements thus improve the understanding of the circulation of water within the lake, which is fundamental for an evaluation of the water residence times, dissolved pollutant and nutrient transport as well as oxygenation.

Climatic and anthropogenic influence on the stable isotope record from bulk carbonates and ostracodes in Lake Neuchatel, Switzerland, during the last two millennia

Lake Neuchatel is a medium sized, hard-water lake, lacking varved sediments, situated in the western Swiss Lowlands at the foot of the Jura Mountains. Stable isotope data (delta(18)O and delta(13)C) from both bulk carbonate and ostracode calcite in an 81 cm long, radiocarbon-dated sediment core represent the last 1500 years of Lake Neuchatel's environmental history. Comparison between this isotopic and other palaeolimnologic data (mineralogical, geochemical, palynological, etc.) helps to differentiate between anthropogenic and natural factors most recently affecting the lake. An increase in lacustrine productivity (450-650AD ca), inferred from the positive trend in delta(13)C values of bulk carbonate, is related to medieval forest clearances and the associated nutrient budget changes. A negative trend in both the bulk carbonate and ostracode calcite delta(18)O values between approximately 1300 and 1500AD, is tentatively interpreted as due to a cooling in mean air temperature at the transition from the Medieval Warm Period to the Little Ice Age. Negative trends in bulk carbonate delta(18)O and delta(13)C values through the uppermost sediments, which have no equivalent in ostracode calcite isotopic values, are concomitant with the recent onset of eutrophication in the lake. Isotopic disequilibrium during calcite precipitation, probably due to kinetic factors in periods of high productivity is postulated as the mechanism to explain the associated negative isotopic trends, although the effect of a shift of the calcite precipitation towards the warmer months cannot be excluded.

Species-specific population structure in rock-specialized sympatric cichlid species in Lake Tanganyika, East Africa.

Species richness and geographical phenotypic variation in East African lacustrine cichlids are often correlated with ecological specializations and limited dispersal. This study compares mitochondrial and microsatellite genetic diversity and structure among three sympatric rock-dwelling cichlids of Lake Tanganyika, Eretmodus cyanostictus, Tropheus moorii, and Ophthalmotilapia ventralis. The species represent three endemic, phylogenetically distinct tribes (Eretmodini, Tropheini, and Ectodini), and display divergent ecomorphological and behavioral specialization. Sample locations span both continuous, rocky shoreline and a potential dispersal barrier in the form of a muddy bay. High genetic diversity and population differentiation were detected in T. moorii and E. cyanostictus, whereas much lower variation and structure were found in O. ventralis. In particular, while a 7-km-wide muddy bay curtails dispersal in all three species to a similar extent, gene flow along mostly continuous habitat appeared to be controlled by distance in E. cyanostictus, further restricted by site philopatry and/or minor habitat discontinuities in T. moorii, and unrestrained in O. ventralis. In contrast to the general pattern of high gene flow along continuous shorelines in rock-dwelling cichlids of Lake Malawi, our study identifies differences in population structure among stenotopic Lake Tanganyika species. The amount of genetic differentiation among populations was not related to the degree of geographical variation of body color, especially since more phenotypic variation is observed in O. ventralis than in the genetically highly structured E. cyanostictus.