Investigating the storage of organic carbon, nitrogen and phosphorus in pond sediment

The present study evaluates the sediment mass and storage of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in a managed agricultural pond, representative for ponds situated in Central Europe. The study is designed to enhance understanding of the functioning of such ponds as nutrient sinks and the capacity to retain TOC, TN and TP within the pond's sediment layer. In order to assess the distribution of sediments and the storage of nutrients, orthomosaics and digital elevation models (DEMs) were generated from imagery recorded by unmanned aerial vehicles (UAVs) in 2021 and 2022. The thickness of the sediment was measured at 174 points over nine diving campaigns, with the volume estimated comparing three interpolation methods. Sediment core samples were analysed to determine their physical and chemical composition. In addition, water samples were collected from the inlets and outlets to trace potential pathways of nutrients. The pond was found to store 330.9 t ha−1 TOC, 16 t ha−1 TN and 0.8 t ha−1 TP with an sediment mass of 1,460 t ha−1. The DEM comparison indicates areas of sediment loss and accumulation, with the overall sediment mass remaining stable. The vertical distribution of nutrients indicated the presence of layered sediment deposition, which suggests a complex history of sediment and nutrient retention. The pond acts as a nutrient sink, but sediment and nutrients can be temporarily resuspended and lost to receiving waters during fish harvest. Further research should explore sediment connectivity and nutrient pathways into ponds in agricultural landscapes.