Earthshape 2 Estimation of the direct and indirect sediment transport along a climate gradient in Chile [funded by DFG]

Project staff:

Paulina Grigusova
Robin Fischer


Ground-dwelling animals act as ecosystem engineers that affect the structure and composition of the vegetation and thereby also ecosystem processes like soil formation, soil erosion, decomposition and carbon storage. Bioturbation has also links to the vertical and horizontal redistribution of solid and soluble particles in landscapes and increases the patchiness of water and nutrient availability with consequences for plant assemblages and for soil organisms. However, most published studies on bioturbation have a local perspective and comprehensive, spatially explicit analyses of the influence of ground-dwelling organisms on rates of sediment and nutrient redistribution in the weathering zone and on hill slopes covering a broad climatic gradient are lacking. We thus aim to i) estimate the spatial distribution, abundance and functional type of the bioturbators in the EarthShape primary focus areas and along its climate gradient, ii) quantify the vegetation along this gradient and determine its relation to distribution and abundance of burrowing animals, iii) quantify effects of bioturbators on soil, nutrients and sediment redistribution, and iv) derive catchment-wide redistribution and erosion rates of the effects of bioturbators by using remote sensing and modelling techniques based on plot-derived transfer functions between climate, vegetation and abundance of species.


Working Packages

We will quantify the current direct (gravitational) and indirect (sediment flux derived from the erosion of animal mounds by water) sediment transport caused by bioturbators, and then link this to the long-term (Holocene) sediment flux. We will use a multi-method approach in order to bridge multiple temporal (daily – millennial) and spatial (plot-catchment) scales. We build roughly upon the approach by Black and Montgomery (1991), in combination with methods used by Seitz et al. (2015), Mosbrucker (2017) and Larsen et al. (in review) in order to measure surface change created by bioturbation. We will use 4 plots (5 m x 5 m) (subsequently referred to as erosionsubplots) per catchment (two south, two north facing, located on upper and lower hillslope positions (adapted to the local conditions).


To monitor surface change on an hourly basis, the plots will be equipped with mounted customtaylored time-of-flight-cameras (ToFC; principal of terrestrial laser scanning) which will create highresolution DSMs in the cm/mm range (e.g. Eltner et al. 2017, Mosbrucker et al. 2017). For this, we will develop small and energy-efficient TFC devices using the new Texas Instruments OPT8241- CDK-EVM circuit. Besides the quantification of surface change, this approach is necessary to get better information on the shorter term burrowing activity of animals (information that is crucial for WP1). Another benefit is that the method is not invasive once the scaffolding is established.


In order to understand how much sediments exit the plots, two plots per catchment will be complemented with a small portable V-shaped runoff weir installed downstream of the monitoring plot, equipped with turbidity and pressure sensors to quantify water and sediment discharge from the sites (measurement period of 12 months/primary area). The calibration of the turbidity sensors will be done by creating artificial flows with variable sediment loads during field work periods. These instruments will be installed as minimally invasive as possible, e.g. using natural confinements and where necessary, the plot will be confined with a small metal lining. These measurements are necessary to validate the soil erosion model (described below).


We will also investigate the relative importance of hillslope gradient and vegetation cover within the highly different settings by performing ~20 experiments (the number of experiments will be adjusted with regards to the derived data) within the four primary areas (5 experiments /day, in total 80 experiments, 16 work days) using a portable Tübingen rainfall simulator (Iserloh et al. 2013) withan adjustable table already on site (in close cooperation with EarthShape I (P13) and Wagner et al. II). We will carefully sample soil columns (ca. 30 cm x 50 cm x 10 cm) including a range of fresh animal mound types, and those without signs of animal activity in similar areas, and test the quantity of erosion in a set of gradients and rainfall intensities related to the environmental conditions of the sampled area (using rainfall data derived from EarthShape weather stations and high-resolution surface data from the existing EarthShape platform, EarthShape project Hofmann et al. I and Hofmann et al. II, with the rainfall simulator and a simple colour tracer). Eroded sediment from the rainfall experiments will be quantified and analysed for grain size and soil chemistry (~80 samples). Statistical relationships between the tested variables (vegetation cover, mound size, gradient and rainfall intensity) will be established using linear mixed effect models.


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