Unexplained gonad alterations in whitefish (Coregonus spp.) from Lake Thun, Switzerland: levels of persistent organic pollutants in different morphs

Since 2000, a surprisingly high number of macroscopical gonad alterations has been reported in whitefish (Coregonus spp.) from Lake Thun, Switzerland. This unique phenomenon is still unexplained and has received much public attention. As one possible trigger for these effects, the presence of persistent, bioaccumulative and toxic compounds acting as endocrine disruptors in the lake has been discussed. In this study, concentrations of selected persistent organic pollutants were examined in two morphs of whitefish from Lake Thun and their link to the observed abnormalities was investigated. Analyzed compound classes included polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated naphthalenes, polybrominated diphenyl ethers and hexabromocyclododecanes. The target substances were identified in all samples and concentrations of the analyzed compounds were highly correlated among each other. These correlations show that the analyzed substances have the same distribution pattern throughout the lake and that uptake, accumulation and elimination processes are similar. Significant differences in contaminant levels within the samples existed between the two analyzed morphs of whitefish, most likely due to different age, food patterns and growth rate. No difference in contaminant levels was observed between fish with abnormal gonads and fish with normal gonads, suggesting no causal link between the investigated lipophilic organohalogen compounds present in fish and the observed gonad abnormalities in whitefish from Lake Thun. A comparison to existing data shows that concentrations in Lake Thun whitefish are at the lower bound of contaminant levels in whitefish from Swiss lakes or from European waters.

Lake sediments as natural seismographs: A compiled record of Late Quaternary earthquakes in Central Switzerland and its implication for Alpine deformation

Central Switzerland lies tectonically in an intraplate area and recurrence rates of strong earthquakes exceed the time span covered by historic chronicles. However, many lakes are present in the area that act as natural seismographs: their continuous, datable and high-resolution sediment succession allows extension of the earthquake catalogue to pre-historic times. This study reviews and compiles available data sets and results from more than 10 years of lacustrine palaeoseismological research in lakes of northern and Central Switzerland. The concept of using lacustrine mass-movement event stratigraphy to identify palaeo-earthquakes is showcased by presenting new data and results from Lake Zurich. The Late Glacial to Holocene mass-movement units in this lake document a complex history of varying tectonic and environmental impacts. Results include sedimentary evidence of three major and three minor, simultaneously triggered basin-wide lateral slope failure events interpreted as the fingerprints of palaeoseismic activity. A refined earthquake catalogue, which includes results from previous lake studies, reveals a non-uniform temporal distribution of earthquakes in northern and Central Switzerland. A higher frequency of earthquakes in the Late Glacial and Late Holocene period documents two different phases of neotectonic activity; they are interpreted to be related to isostatic post-glacial rebound and relatively recent (re-)activation of seismogenic zones, respectively. Magnitudes and epicentre reconstructions for the largest identified earthquakes provide evidence for two possible earthquake sources: (i) a source area in the region of the Alpine or Sub-Alpine Front due to release of accumulated north-west/south-east compressional stress related to an active basal thrust beneath the Aar massif; and (ii) a source area beneath the Alpine foreland due to reactivation of deep-seated strike-slip faults. Such activity has been repeatedly observed instrumentally, for example, during the most recent magnitude 4.2 and 3.5 earthquakes of February 2012, near Zug. The combined lacustrine record from northern and Central Switzerland indicates that at least one of these potential sources has been capable of producing magnitude 6.2 to 6.7 events in the past.

Signatures of slope failures and river-delta collapses in a perialpine lake (Lake Lucerne, Switzerland)

Historical reports from the 17th Century document two destructive tsunamis with runups exceeding 5 m, affecting proximal basins of Lake Lucerne (Switzerland). One event in AD 1601 is coeval with a strong nearby earthquake (MW ca 5.9), which caused extensive slope failures in many parts of the lake. The second event in AD 1687 is associated with an apparently spontaneous partial collapse of the Muota river delta. This study combines high-resolution bathymetry, reflection seismic and lithological data in order to document the sedimentary and morphological signatures of the two subaqueous mass movements that probably generated the observed tsunamis. Such mass movements are significant as a common sedimentation process and as natural hazard in fjord-type lakes and similar environments. The deposits, covering large parts of the basins with thicknesses reaching >10 m, consist of two subunits: A lower ‘massflow deposit’ contains variably deformed sediments from the source areas. Its emplacement affected pre-existing sediments, incorporating thin sediment slices into the deposit and increasing its volume. Deep-reaching deformation near This is an Accepted Article that has been peer-reviewed and approved for publication in the Sedimentology, but has yet to undergo copy-editing and proof correction.

High-resolution late-glacial chronology for the Gerzensee lake record (Switzerland): δ18O correlation between a Gerzensee-stack and NGRIP

Oxygen-isotope variations were analyzed on bulk samples of shallow-water lake marl from Gerzensee, Switzerland, in order to evaluate major and minor climatic oscillations during the late-glacial. To highlight the overall signature of the Gerzensee δ18O record, δ18O records of four parallel sediment cores were first correlated by synchronizing major isotope shifts and pollen abundances. Then the records were stacked with a weighting depending on the differing sampling resolution. To develop a precise chronology, the δ18O-stack was then correlated with the NGRIP δ18O record applying a Monte Carlo simulation, relying on the assumption that the shifts in δ18O were climate-driven and synchronous in both archives. The established chronology on the GICC05 time scale is the basis for (1) comparing the δ18O changes recorded in Gerzensee with observed climatic and environmental fluctuations over the whole North Atlantic region, and (2) comparing sedimentological and biological changes during the rapid warming with smaller climatic variations during the Bølling/Allerød period. The δ18O record of Gerzensee is characterized by two major isotope shifts at the onset and at the termination of the Bølling/Allerød warm period, as well as four intervening negative shifts labeled GI-1e2, d, c2, and b, which show a shift of one third to one fourth of the major δ18O shifts at the beginning and end of the Bølling/Allerød. Despite some inconsistency in terminology, these oscillations can be observed in various climatic proxies over wide regions in the North Atlantic region, especially in reconstructed colder temperatures, and they seem to be caused by hemispheric climatic variations.

Mass Movement-Induced Tsunami Hazard on Perialpine Lake Lucerne (Switzerland): Scenarios and Numerical Experiments

Previous studies of the sediments of Lake Lucerne have shown that massive subaqueous mass movements affecting unconsolidated sediments on lateral slopes are a common process in this lake, and, in view of historical reports describing damaging waves on the lake, it was suggested that tsunamis generated by mass movements represent a considerable natural hazard on the lakeshores. Newly performed numerical simulations combining two-dimensional, depth-averaged models for mass-movement propagation and for tsunami generation, propagation and inunda- tion reproduce a number of reported tsunami effects. Four analysed mass-movement scenarios—three based on documented slope failures involving volumes of 5.5 to 20.8 9 106 m3—show peak wave heights of several metres and maximum runup of 6 to [10 m in the directly affected basins, while effects in neighbouring basins are less drastic. The tsunamis cause large-scale inundation over distances of several hundred metres on flat alluvial plains close to the mass-movement source areas. Basins at the ends of the lake experience regular water-level oscillations with characteristic periods of several minutes. The vulnerability of potentially affected areas has increased dramatically since the times of the damaging historical events, recommending a thorough evaluation of the hazard.

Palynostratigraphy of the last centuries in Switzerland based on 23 lake and mire deposits: chronostratigraphic pollen markers, regional patterns, and local histories

A total of 23 pollen diagrams [stored in the Alpine Palynological Data-Base (ALPADABA), Geobotanical Institute, Bern] cover the last 100 to over 1000 years. The sites include 15 lakes, seven mires, and one soil profile distributed in the Jura Mts (three sites), Swiss Plateau (two sites), northern Pre-Alps and Alps (six sites), central Alps (five sites), southern Alps (three sites), and southern Pre-Alps (four sites) in the western and southern part of Switzerland or just outside the national borders. The pollen diagrams have both a high taxonomic resolution and a high temporal resolution, with sampling distances of 0.5–3 cm, equivalent to 1 to 11 years for the last 100 years and 8 to 130 years for earlier periods. The chronology is based on absolute dating (14 sites: 210Pb 11 sites; 14C six sites; varve counting two sites) or on biostratigraphic correlation among pollen diagrams. The latter relies mainly on trends in Cannabis sativa, Ambrosia, Mercurialis annua, and Ostrya-type pollen. Individual pollen stratigraphies are discussed and sites are compared within each region. The principle of designating local, extra-local, and regional pollen signals and vegetation is exemplified by two pairs of sites lying close together. Trends in biostratigraphies shared by a major part of the pollen diagrams allow the following generalisations. Forest declined in phases since medieval times up to the late 19th century. Abies and Fagus declined consistently, whereas the behaviour of short-lived trees and trees of moist habitats differed among sites (Alnus glutinosa-type, Alnus viridis, Betula, Corylus avellana). In the present century, however, Picea and Pinus increased, followed by Fraxinus excelsior in the second half of this century. Grassland (traced by Gramineae and Plantago lanceolata-type pollen) increased, replacing much of the forest, and declined again in the second half of this century. Nitrate enrichment of the vegetation (traced by Urtica) took place in the first half of this century. These trends reflect the intensification of forest use and the expansion of grassland from medieval times up to the end of the last century, whereas subsequently parts of the grassland became used more intensively and the marginal parts were abandoned for forest regrowth. In most pollen diagrams human impact is the dominant factor in explaining inferred changes in vegetation, but climatic change plays a role at three sites.

Pollen and charcoal in lake sediments compared with historically documented forest fires in southern Switzerland since AD 1920

Charcoal in unlaminated sediments dated by 210Pb was analysed by the pollen-slide and thin-section methods. The results were compared with the number and area of forest fires on different spatial scales in the area around Lago di Origlio as listed in the wildfire database of southern Switzerland since AD 1920. The influx of the number of charcoal particles > 75 µm2 in pollen slides correlates well with the number of annual forest fires recorded within a distance of 20-50 km from the coring site. Hence a size-class distinction or an area measurement by image analysis may not be absolutely necessary for the reconstruction of regional fire history. A regression equation was computed and tested against an independent data set. Its use makes it possible to estimate the charcoal area influx (or concentration) from the particle number influx (or concentration). Local fires within a radius of 2 km around the coring site correlate well with the area influx of charcoal particles estimated by the thin-section method measuring the area of charcoal particles larger than 20 000 µm2 or longer than 50 µm. Pollen percentages and influx values suggest that intensive agriculture and Castanea sativa cultivation were reduced 30-40 years ago, followed by an increase of forest area and a development to more natural woodlands. The traditional Castanea sativa cultivation was characterized by a complete use of the biomass produced, so abandonment of chestnut led to an increasing accumulation of dead biomass, thereby raising the fire risk. On the other hand, the pollen record of the regional vegetation does not show any clear response to the increase of fire frequency during the last three decades in this area.