Shells of freshwater mussels – Hydrological archive of streamflow generation processes

• Applicant: Professor Dr. Bernd R. Schöne
• Subject Area: Palaeontology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574902602

Freshwater ecosystems of boreal, snow-dominated Nordic landscapes are particularly vulnerable to human-induced climate and environmental perturbations. Specifically, ditching, warming and wetting unbalance the travel times and flow paths of rain and snowmelt water through the landscape to recipient streams/rivers. Such changes have significant implications for ecosystem health, water quality, atmospheric CO2 conc., hydroenergy production, forestry, agriculture, drought and flood risk. Stream solute chemistry is an established method in hydrology not only to assess the quality and oxygen content of water, but also to determine the varying proportion of surface, soil and ground water of different ages contributing to streamflow. Numerous reconstructions of streamflow generation processes have been conducted in high-latitude landscapes, but due to the brevity and scarcity of instrumental records which often comprise < 30 years from few catchments, hydrological models can often not be properly validated. With this project we aim to establish shells of the long-lived (< 200 yrs) freshwater pearl mussel, Margaritifera margaritifera as an archive that can provide absolutely dated, seasonally to interannually resolved paleohydrological data. The main purpose of the planned work is to test how the element chemistry of water can be quantitatively reconstructed from shells. Potential effects of temperature and the bivalves’ age and growth rate on the incorporation of elements into the shell will be studied. A specific focus will be placed on properties used in hydrology as flow path tracers: Sr/Ca, Ba/Sr and 87Sr/86Sr ratios. In addition, the use of Mn/Ca will be explored as a proxy for base flow considering that groundwater is typically poor in oxygen. Furthermore, we will study if other elements in streamwater can be quantitatively inferred from the shells which can, e.g., provide information on temporal changes of contamination. We will also test a hypothesis according to which decreasing water pH is reflected in lower concentrations of heavy elements and radiogenic Sr in the shells. If correct, shell growth rate, biomineral size and δ13C values should likewise decline, and Na/Ca should increase. Once the extensive calibration and verification work is completed, we will exemplarily assess the hydroclimatic variability in the study area, northern Sweden (trends and low-frequency oscillations of the storage and release of waters, streamwater quality and pH) since the 19th century. Techniques tested here can serve as a toolset for subsequent studies with other freshwater bivalve species collected elsewhere. This toolset comprises the multiproxy approach (isotopes, elements, growth rate, ultrastructure), analytical techniques (bulk vs compound-specific chemistry) and detrending (mathematical elimination of age/growth rate-related effects on shell chemistry). The planned project bears significant transformative impact in sclerochronology and hydrology.

• DFG Programme: Research Grants