EchoBoat and HYPACK: user guide v 1.0

Technical manual for deploying the Seafloor Echo Boat and processing associated data using Hypack

Human‐initiated autocyclic delta failures

River regulations have resulted in changes in the hydrology and particle bud- gets of fluvial systems. Since the 19th century, many rivers have been signifi- cantly modified to control flood hazards, to gain land from swamp areas for agricultural purposes, and to stabilize river-levels and lake-levels to facilitate navigation. These dramatic changes of the river courses have impacted the sediment budgets and grain-size dissemination along them as well as the sedi- ment distribution at the delta mouths in the downstream lakes, which could lead to slope instabilities. Deposits of such catastrophic lacustrine mass move- ments caused by delta collapses have been, for instance, observed in Lake Bri- enz (Switzerland), where relatively thick (0.5 to 1.3 m) and voluminous (>1 million m3) megaturbidites are stacked in the deep basin witnessing these pro- cesses. This study uses sediment cores and seismic data to reconstruct the megaturbidites’ history in Lake Brienz. Data reveal that mass-movement deposits, originating from the Aare Delta, one of the two main inflows, have mean ages of 1853, 1905, 1942 and 1996 CE and that they were unprecedented in, at least, half a millennium. The fact that the numbers of floods and earth- quakes have not changed radically over this time period implies that human impact is the most likely explanation for these failure events. Therefore, the recurrent delta collapses are attributed to the focused sediment accumulation at the front of the channelized inflow in the proximal delta region, caused by the modification of the Aare River through its straightening and channeliza- tion during the late 19th century. These findings indicate that river regulation can affect delta sedimentation, leading to autocyclic delta collapses. Those collapses, in turn, can potentially generate tsunami waves, representing an additional natural hazard for shoreline communities

Human impact on the transport of terrigenous and anthropogenic elements to peri-alpine lakes (Switzerland) over the last decades

Terrigenous (Sc, Fe, K, Mg, Al, Ti) and anthropogenic (Pb and Cu) element fluxes were measured in a new sediment core from Lake Biel (Switzerland) and in previously well-documented cores from two upstream lakes (Lake Brienz and Lake Thun). These three large peri-alpine lakes are connected by the Aare River, which is the main tributary to the High Rhine River. Major and trace element analysis of the sediment cores by inductively coupled plasma mass spectrometry (ICP-MS) shows that the site of Lake Brienz receives three times more terrigenous elements than the two other studied sites, given by the role of Lake Brienz as the first major sediment sink located in the foothills of the Alps. Overall, the terrigenous fluxes reconstructed at the three studied sites suggest that the construction of sediment-trapping reservoirs during the twentieth century noticeably decreased the riverine suspended sediment load at a regional scale. In fact, the extensive river damming that occurred in the upstream watershed catchment (between ca. 1930 and 1950 and up to 2,300m a.s.l.) and that significantly modified seasonal suspended sediment loads and riverine water discharge patterns to downstream lakes noticeably diminished the long-range transport of (fine) terrigenous particles by the Aare River. Concerning the transport of anthropogenic pollutants, the lowest lead enrichment factors (EFs Pb) were measured in the upstream course of the Aare River at the site of Lake Brienz, whereas the metal pollution was highest in downstream Lake Biel, with the maximum values measured between 1940 and 1970 (EF Pb>3). The following recorded regional reduction in aquatic Pb pollution started about 15years before the actual introduction of unleaded gasoline in 1985. Furthermore, the radiometric dating of the sediment core from Lake Biel identifies three events of hydrological transport of artificial radionuclides released by the nuclear reactor of Mühleberg located at more than 15km upstream of Lake Biel for the time period 1970-200

Effects of Alpine hydropower dams on particle transport and lacustrine sedimentation

Abstract.: The effects of high-alpine hydropower damming on lacustrine sedimentation and transport of solid particles were investigated in the glaciated Grimsel area and in downstream Lake Brienz, providing quantitative denudation rates and sediment yield on a source-sink basis. A total of 271 kt/yr of solid particles entered the Grimsel reservoirs on average in the last 71 years, mostly by turbiditic underflows that focused sedimentation in depocenters upstream of obstacles such as bedrock ridges, submerged moraines, or dams. This is equivalent to a sediment yield of 2430 t/(km2yr) in the catchment (111.5 km2) or a denudation rate of 0.94 mm/yr. A total of 39 kt/yr of the fine fraction (<~4 μm) leave the reservoirs and are transported to downstream Lake Brienz, while 232 kt/yr of mostly coarse particles are retained, reducing total sediment input of the River Aare into Lake Brienz by two thirds. Modeling the particle budgets in the Aare with and without dams indicates that the fine fraction budgets are only slightly affected by damming, but that the reservoirs cause a shift in seasonal runoff timing resulting in increasing and decreasing particle transport in winter and summer, respectively. Thus, hydrodamming alters mostly deltaic sedimentation in Lake Brienz, where the coarse fraction is deposited, whereas fine grained distal sedimentation and varve formation on lateral slopes are less affected. All varved records of the reservoirs and Lake Brienz that provide sediment rates and grain size records on an annual basis indicate that climate is the main control on these proxies, while, for instance, the onset of pump storage activity in the reservoirs did not impose any significant change in lacustrine sedimentation patter

Le paysage pour aborder les interactions entre environnement alpin et sociétés

Depuis l’automne 2015, un module « Enjeux paysagers » a été introduit au premier semestre du master universitaire en sciences de l’environnement (MUSE), formation interdisciplinaire et interfacultaire de l’université de Genève (Suisse). Ce nouveau module intervient au cours d’une première étape d’initiation à l’interdisciplinarité et d’immersion aux thématiques de l’environnement. Ce texte revient sur cette expérience pédagogique, dans un esprit réflexif partagé par les auteurs, tous intervenants dans le MUSE, et issus de différentes disciplines. Le paysage est placé ici comme « notion-laboratoire » pour favoriser les ponts entre les disciplines enseignées et améliorer la mise en avant d’une interdisciplinarité, voire d’une transdisciplinarité, entre sciences de la société et sciences naturelles et exactes.In the autumn of 2015, a module entitled “Landscape Issues” (in French, “Enjeux paysagers”) was introduced in the first semester of the University Master of Environmental Sciences (in French, Master Universitaire en Sciences de l’Environnement, MUSE), an interdisciplinary and interfaculty training course at Geneva University (Switzerland). This new module is part of a first stage in the initiation to the interdisciplinary study of environmental themes. The article describes this teaching experiment in a reflective mode shared by the authors, all of whom are teachers of different disciplines and work in the MUSE programme. The landscape is positioned here as a “laboratory-concept” for fostering links between the disciplines taught and promoting interdisciplinarity, or transdisciplinarity, between social, natural and exact sciences

Endospore-forming bacteria as new proxies to assess impact of eutrophication in Lake Geneva (Switzerland-France)

Measurements of chemical composition and biological parameters of sediment cores are used as proxies for changes in past environmental conditions and more recently the human impact on ecosystem health. In this study, endospore-forming bacteria are proposed as a new biological proxy for such paleoecological reconstructions. A sediment core providing a record for the past 90years (137Cs and magnetic susceptibility dating) was retrieved from the Rhone Delta of Lake Geneva. X-ray fluorescence was analyzed at a 0.2-cm resolution, while DNA extracts, elemental geochemistry and grain size were obtained at 4-cm intervals. The total number of bacteria and endospore-forming bacteria were quantified by qPCR using the 16S rRNA gene and the endosporulation-specific spo0A gene. Furthermore, a spo0A fragment was subjected to amplicon sequencing to define OTUs (operational taxonomic units) and the phylogenetic affiliation of the endospore formers. The results showed that despite the fact that the quantity of extracted DNA decreased with the age of the sediment, the abundance of endospore-forming bacteria remained constant. However, the diversity of this group of bacteria changed significantly, reflecting the eutrophication of the lake from 1960 to 1990. The shift in community composition was linked to the dominance of anaerobic clostridia-like endospore formers. This trend has reversed in the last 10years of the record, suggesting a recovery after perturbation. This study shows that the abundance and diversity of endospore-forming bacteria can be used as proxies to reconstruct lake history. We hereby successfully introduce a new strategy for paleoecology that could also be applied to ocean sediments and long sediment cores

Human impact on the transport of terrigenous and anthropogenic elements to peri-alpine lakes (Switzerland) over the last decades

Terrigenous (Sc, Fe, K, Mg, Al, Ti) and anthropogenic (Pb and Cu) element fluxes were measured in a new sediment core from Lake Biel (Switzerland) and in previously well-documented cores from two upstream lakes (Lake Brienz and Lake Thun). These three large peri-alpine lakes are connected by the Aare River, which is the main tributary to the High Rhine River. Major and trace element analysis of the sediment cores by inductively coupled plasma mass spectrometry (ICP-MS) shows that the site of Lake Brienz receives three times more terrigenous elements than the two other studied sites, given by the role of Lake Brienz as the first major sediment sink located in the foothills of the Alps. Overall, the terrigenous fluxes reconstructed at the three studied sites suggest that the construction of sediment-trapping reservoirs during the twentieth century noticeably decreased the riverine suspended sediment load at a regional scale. In fact, the extensive river damming that occurred in the upstream watershed catchment (between ca. 1930 and 1950 and up to 2300 m a.s.l.) and that significantly modified seasonal suspended sediment loads and riverine water discharge patterns to downstream lakes noticeably diminished the long-range transport of (fine) terrigenous particles by the Aare River. Concerning the transport of anthropogenic pollutants, the lowest lead enrichment factors (EFs Pb) were measured in the upstream course of the Aare River at the site of Lake Brienz, whereas the metal pollution was highest in downstream Lake Biel, with the maximum values measured between 1940 and 1970 (EF Pb >3). The following recorded regional reduction in aquatic Pb pollution started about 15 years before the actual introduction of unleaded gasoline in 1985. Furthermore, the radiometric dating of the sediment core from Lake Biel identifies three events of hydrological transport of artificial radionuclides released by the nuclear reactor of Mühleberg located at more than 15 km upstream of Lake Biel for the time period 1970 to 200

Enregistrement des événements de haute énergie et formation d'ooïdes dans des sediments littoraux du Léman (Petit-Lac)

Notre étude des sédiments superficiels du littoral lémanique (Petit-lac) se divise en deux parties : l'enregistrement des tempêtes et les ooïdes. etc