Evaluating the suitability of sedimentological, geochemical, and biological proxies for reconstructing floodplain palaeohydrology

Abstract

Fundamental insight into the long-term ‘geoecohydrological’ dynamics of rivers and floodplains is required for their sustainable management. To study these dynamics, a multi-proxy approach is essential. While suitable proxies are available for reconstructing floodplain geomorphology and past vegetation, the suitability of the available proxies for past hydrology to reconstruct floodplain wetness has not yet been evaluated. In this study, we apply a multi-proxy analysis combining testate amoebae and several geochemical proxies for decomposition (humification, carbon and nitrogen stable isotopes), in comparison to sedimentological (stratigraphy, loss on ignition) and palaeobotanical records, to obtain independent hydrological reconstructions of alluvial floodplains in contrasting environmental settings to explore the suitability of the available proxies for past hydrology to reconstruct floodplain wetness.

This study concludes that testate amoebae cannot provide a continuous and reliable hydrological reconstruction, as they are insufficiently preserved in alluvial peat deposits. In addition, mineral particles within the tests size range hamper the analysis in mineral-dominated sediment units. As organic matter decomposition is low when water tables are high and vice versa, we expected the decomposition proxies to reflect the hydrological conditions. While the amount of humic acids appears to depend mainly on the substrate rather than the decomposition of the organic matter in it, the analyses of carbon and nitrogen stable isotopes provide promising results, for both peat and non-peat deposits.