The Anthropocene has been proposed as a profound, globally synchronous rupture in the history of the Earth System with its current state fundamentally different to that of the Holocene and driven by the geological force of human activity. Here, we show how stratigraphy is being made in a lake that is heavily impacted upon by climate change and human activities. For one of the largest inner-Alpine catchments in the European Alps, we draw attention to how sedimentation rates are a product of non-stationary, reflexive, human actions. In Lake Geneva, we identify both a human-induced climate change (HCC) signature and the effects of a recent economic shock on sediment extraction upon sediment loading to and sedimentation rates in the lake. The HCC signature thus reflects the nature of climate change impacts in this basin, where sediment accumulation rates evolve with climate, but where economic conditions contribute to shifts in the supply of sediment to the lake. Following social theory, we call this glocalization because of the combined importance and inseparability of human impacts across different spatial scales. The nature of human impacts on sediment delivery to the lake mean that the influence of humans is unlikely to be captured in the long-term depositional record.
Salmonid populations are widely distributed globally and are of economic, cultural and ecological importance. Evidence suggests that they are in decline in many parts of the world and one of a number of hypotheses for their decline is the degradation of spawning habitat. Knowledge of spawning sites and their evolution through time is a means of estimating regional population dynamics and sizes. Traditionally, spawning sites have been identified visually. However, this may not allow a precise quantification of the real extent of salmonid reproduction and of its evolution through time (i.e. within the spawning season). This paper develops a framework for using small Unmanned Aircraft Systems (sUASs) and Structure from Motion (SfM) photogrammetry to detect salmonid redds, the nests that are the distinctive footprint of spawning, through analysis of inter-epoch Digital Elevation Models (i.e. DEMs of Difference). SfM-derived DEMs of Difference are an effective tool to investigate spawning because of the distinctive ellipsoidal erosion-deposition pattern of salmonid redds, which discriminates them from other stream-bed elevation changes. The method detects more redds (e.g. those covered by algae or biofilm) compared with classical visual observation, allowing for a better and more rigorous detection of spawning grounds. SfM photogrammetry also provides additional information relevant to understanding salmonid spawning, including redd-density and probable female lengths, without disturbance of the spawning sites.
This paper has been published in Ecological Indicators and can be accessed here.
Nico Bätz has been awarded the 2019 Dick Chorley Medal and Prize by the British Society for Geomorphology. The award is for an outstanding research paper first authored by an early career researcher. Nico received the award for the paper:
Bätz, N., Cherubini, P., Colombini, P. and Lane, S.N., 2016. Groundwater controls on biogeomorphic succession and river channel morphodynamics. Journal of Geophysical Research – Earth Surface, 121, 1763–1785
Bakker, M., Antoniazza, G., Odermatt, M. and Lane, S.N., 2019. Morphological response of an Alpine braided reach to sediment-laden flow events. Journal of Geophysical Research – Earth Surface, 124, 1310-28.
Braided gravel?bed rivers show characteristic temporal and spatial variability in morphological change and bedload transport under steady flow and sediment supply rates. Their morphodynamic behavior and long?term evolution in response to nonstationary external forcing is less well known. We studied daily morphological changes in a well?constrained reach of an Alpine braided river that is subject to regulated sediment?laden flows, associated with hydroelectric power exploitation, as well as occasional floods. We found that net reach erosion and deposition were forced by upstream sediment supply, albeit in a nonlinear fashion. The spatial distribution of morphological change and inferred spatially?distributed sediment transport rates varied strongly along the braided reach and between successive sequences of flushing. Local morphological change was driven by two factors: (1) local relief, leading to the preferential filling of topographic lows and erosion of highs, particularly during longer duration floods, which allow braided dynamics to be maintained; and (2) system memory, leading to a negative autocorrelation in bed level changes where erosion was followed by deposition of similar magnitude and vice versa. This effect was associated with the temporary storage of high sediment loads from flushing due to the abrupt on?off nature of these flows and reveals the relatively efficient transport of sediment in a river that is heavily impacted upon by flow abstraction. In general, the internal morphodynamics of the braided river condition their own response to external forcing events and thus sediment transfer.
A copy of the paper can be accessed here.
AGU has published a « Research Spotlight » highlighting a paper by Stuart Lane and Pete Nienow « Decadal?Scale Climate Forcing of Alpine Glacial Hydrological Systems » in Eos. It can be read here.