Erosion processes and connectivity shape biological communities recorded by environmental DNA in sedimentary archive: implication for paleo-environmental reconstruction

Recent studies highlight the critical role of changes in connectivity, erosion processes and sediment sources in shaping biological communities in palaeo-environmental reconstructions (e.g., Giguet-Covex et al., 2023; Morlock et al., 2023). Such processes can lead to misinterpretations attributing shifts in biodiversity around lakes to environmental changes, when in fact they may be due to the introduction of previously unconnected sediment sources driven by human activities (e.g. land management) or extreme climate events.

To assess the impact of changes in connectivity and accelerated erosion on biological communities, we analysed sediment archives from the Dzoumogné reservoir (Mayotte Island, France). This reservoir drains a small catchment (1038 ha) that underwent significant land-use changes (e.g. deforestation, agricultural intensification) during a well-documented period (2011-2021). We reconstructed land-use changes, erosion rates and sediment sources, as well as biological communities using sediment DNA (sedDNA) based on seven genetic markers targeting plants (trnL, rbcL), fungi (ITS), metazoa (16S, 18S) and vertebrates (12S).

Our results show a 450% increase in operational taxonomic units (OTUs) and shifts in OTUs detected in 23 taxonomic groups following the first deforestation phase (2012-2013) and subsequent agricultural intensification resulting in landscape fragmentation. During this period, sedDNA identified an increase in forest-derived species (e.g. Streptophyta and terrestrial fungi) and agricultural species (e.g. banana, cassava, cattle). These changes coincide with accelerated sediment delivery and erosion rates (+310% between 2011 and 2015). Between 2015 and 2021, declining water levels (driven by climate and human activities) combined with high sediment and nutrient inputs continued to drive major shifts in aquatic communities. These included increases in OTUs belonging to the taxonomic groups Chlorophyta and Ciliophora - key indicators of eutrophication and water quality degradation. The high primary production associated with algae and microorganisms likely explains the observed increase in invertebrate and fish communities higher up the trophic chain within just two years of changes in sediment connectivity and sources.

This study highlights how rapid shifts in biodiversity in both terrestrial and aquatic systems are driven by increased erosion and connectivity of previously isolated land use areas (e.g. forests, croplands). Understanding these connectivity dynamics is crucial to avoid misinterpretation of biodiversity change in lake sediment records.

 

References:

Giguet-Covex, C., Jelavić, S., Foucher, A., Morlock, M. A., Wood, S. A., Augustijns, F., Domaizon, I., Gielly, L., & Capo, E. (2023). The Sources and Fates of Lake Sedimentary DNA (pp. 9–52).

Morlock, M. A., Rodriguez‐Martinez, S., Huang, D. Y., & Klaminder, J. (2023). Erosion regime controls sediment environmental‐based community reconstruction. Environmental DNA, 5(6), 1393–1404.