Tracing hotspots of soil erosion in high mountain environments: how forensic science based on plant eDNA can lead the way. An opinion

Abstract

High mountain environments are among the most fragile on Earth. Due to anthropogenic disturbances and the exposure to extreme weather events, the rates of soil erosion have recently been accelerating, resulting in ecological degradation and geological hazards. Ecological restoration of mountains and an improved understanding of nature-based solutions to mitigate land degradation is therefore of utmost urgency. Identifying hotspots of soil erosion is a first step towards improving mitigation strategies. A promising methodology to identify erosion hotspots is sediment source fingerprinting, that differentiates the properties of soil from different sources, using signatures such as elemental geochemistry or radionuclides. However, in areas with complex lithologies or shallow and poorly developed soils, geochemical fingerprints allow only a rough distinction between erosion hotspots. In this opinion paper, we explore the relevance of environmental DNA (eDNA) that originates from plant litter and fixes onto fine soil particles, as a targeted sediment fingerprinting method sensitive to vegetation that could potentially allow the identification of erosion hotspots and their relative importance from sedimentary deposits. Pioneering studies indicate that eDNA allows not only the detection of specific vegetation communities, but also the identification of individual plant species. Supported by the increasing availability and quality of vegetation maps and eDNA reference libraries, we argue that sediment source fingerprinting using eDNA from plant litter, will evolve into a valuable method to identify hotspots of soil erosion and allow stakeholders to prioritize areas where ecological restoration is necessary in high mountain environments.

Improving the design and implementation of sediment fingerprinting studies: summary and outcomes of the TRACING 2021 Scientific School

“…The sediment fingerprint approach may be considered to have reached a certain level of maturity (see the analogy with Burns ( 2002 ) on the stormflow-hydrograph separation based on isotopes). We argue that applying the sediment fingerprinting method yet in another catchment will most probably have a limited impact on the advancement of science (although sediment tracing studies might be of great value in unexplored environments or to decipher emerging environmental problems, as it has recently been shown for mountainous catchments) (Frankl 2022 ). On the contrary, by better organising and compiling all our available datasets, we might, for instance, be able to use mixing models to formulate hypotheses about sediment sources in different regions or anthropogenic contexts and contribute in a more unified and visible way to improve our understanding of sediment transfer processes.…”

“…This is because models will always produce an output, even when the input data is highly flawed. A similar case can be made regarding the use of mineralogical properties (Hein et al 2013 ) and environmental DNA (Evrard et al 2019 ; Frankl 2022 ) as sediment tracers, as these fingerprints cannot be used – at this stage – for quantitative source attribution.…”

Environmental DNA as an emerging tool in botanical research

“…These groundbreaking studies have paved the way for studies documenting plant community biodiversity (Fahner et al, 2016; Edwards et al, 2018; Carvalho‐Silva et al, 2021; Osathanunkul et al, 2021; Barnes et al, 2022; Ariza et al, 2022), rare plant conservation (Hartvig et al, 2021), sampling sand for meiofaunal communities (Castro et al, 2021), assessing community structure, including root associations (Blaalid et al, 2012; Martínez‐García et al, 2014; Ruppert et al, 2019), eDNA ecology in the soil (Foscari et al, 2022), and tracking human land use (Foucher et al, 2020). Lastly, contemporary soil eDNA is beginning to be utilized for forensic ecology, by connecting soil ecological habitats and eDNA to the origin of soil and sediments (Flojgaard et al, 2019; Frankl et al, 2022).…”

Validating the accuracy of multiple sediment fingerprinting methods

“…D. Wang et al, 2018). Some new tracers have emerged in recent studies, such as n-alkanes (Galoski et al, 2019), compound-specific stable isotopes (Hirave et al, 2021;Mabit et al, 2018;Upadhayay et al, 2018), and eDNA (Frankl et al, 2022). The optimization of the mixing model may improve the accuracy of the sediment source tracing results to some extent, such as via the choice of data corrections Koiter et al, 2018) or through the use of Bayesian mixing models based on prior information and conditional probability (Stock et al, 2018;Torres-Martínez et al, 2021).…”

“…The potential of fingerprint tracers has been explored like color properties (Martínez‐Carreras et al, 2010; Nosrati, Akbari‐Mahdiabad, et al, 2021), fallout radionuclides (Gourdin et al, 2014; Ni et al, 2017), magnetic parameters or geochemistry (Franz et al, 2013; Ramon et al, 2020; W. D. Wang et al, 2018). Some new tracers have emerged in recent studies, such as n‐alkanes (Galoski et al, 2019), compound‐specific stable isotopes (Hirave et al, 2021; Mabit et al, 2018; Upadhayay et al, 2018), and eDNA (Frankl et al, 2022). The optimization of the mixing model may improve the accuracy of the sediment source tracing results to some extent, such as via the choice of data corrections (Collins, Walling, et al, 2010; Koiter et al, 2018) or through the use of Bayesian mixing models based on prior information and conditional probability (Stock et al, 2018; Torres‐Martínez et al, 2021).…”