New publication: Climate‐driven change in the water sourced by trees in a deglaciating proglacial forefield, Torres del Paine, Chile

The colonization of proglacial margins by vegetation following glacier recession is a slow process, not least because glacially produced sediments are commonly well drained. Following from human‐induced climate change, warming could increase both growth rates and water availability because of glacier melting, so compensating for situations where climate change reduces precipitation. Compensation is likely a function of location, which will control access to meltwater and groundwater, themselves spatially variable. For the Olguin glacier (Torres del Paine, Chile), we test the hypothesis that as climate has warmed and precipitation has fallen, tree growth rate response is dependent upon the access of trees to glacial meltwater. Cores were taken from trees in three revegetating zones: (Z1) proglacial stream proximal, (Z3) proglacial stream distal, and (Z2) intermediate between Z1 and Z3. For trees within each zone, we measured annual tree‐ring widths and δ2H values. Z1 growth rates were strongly correlated with temperature and Z3 with precipitation, and Z2 showed a shift from precipitation correlation (i.e., following Z3) to temperature correlation (i.e., following Z1) through time. δ2H values were lowest at Z1, reflecting water of glacial origin, were highest at Z3, reflecting meteoric water supply, and shifted through time at Z2 from meteoric to glacial. Increased water supply associated with temperature‐driven glacier recession may compensate for decreasing water supply from precipitation to influence tree growth. This compensation is likely related to the spatial organization of the subsurface flux of glacial melt and leads to different revegetation processes to those envisaged in the classical chronosequence model of vegetation following glacier recession.

The paper has been published in Ecohydrology and a copy is available here.

New Paper Published: Making stratigraphy in the Anthropocene: climate change impacts and economic conditions controlling the supply of sediment to Lake Geneva

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.

The paper can be obtained here. The paper was picked up by a number of local media sites, (1), (2), (3) and (4).

New Paper Published : A framework for using small Unmanned Aircraft Systems (sUASs) and SfM photogrammetry to detect salmonid redds

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.

Dr. Nico Bätz awarded Dick Chorley Medal and Prize

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

New Paper Published : Morphological response of an Alpine braided reach to sediment-laden flow events

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.