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

Abstract

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 perialpine 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 2,300 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 1970-2000.

Physical effects of thermal pollution in lakes

“…It was redirected into LB during the Jura Correction in 1878 effectively reducing the average hydraulic residence Figure 1. Area of investigation: (a) Lake Biel (LB) with watershed and monitoring stations (black diamonds), arrows indicate river flow direction (map modified from Thevenon et al [2013]), (b) LB Multibeam/LIDAR bathymetry [Hilbe, 2015] with locations for field sampling points (M1, M2, M3, and CB).…”

Spatial heterogeneity of benthic methane dynamics in the subaquatic canyons of the Rhone River Delta (Lake Geneva)

“…Thus, together with minerogenic particles, particulate organic carbon has been trapped in upstream reservoirs (Cole et al 2007) and does not contribute as significantly to the sedimentation regime of the Rhone River delta and its canyons. In addition to their particle retaining role (Anselmetti et al 2007;Thevenon et al 2013), alpine reservoirs have dramatically changed the seasonality of the annual discharge (Loizeau and Dominik 2000) with lower discharge during summer, higher discharge during winter, and a reduction of peak flood events (Finger et al 2007). The active canyon is likely heavily impacted by such sediment and hydrodynamic regime changes.…”

Radioactivity in Food: Experiences of the Food Control Authority of Basel-City since the Chernobyl Accident

“…After 1965, the fallout clearly decreased. One can clearly see this in sediment profiles of lakes (e.g., lake sediment investigations in Switzerland) [12].…”