Positive mitigation effects of glacial rock flour (GRF) addition on ecosystem CO2, CH4 and N2O fluxes – first results from a gradient experiment

The application of ground silicate minerals to agricultural ecosystems has recently gained popularity as a mechanism for CO2 removal via enhanced mineral weathering that also has the potential to provide valuable co-benefits, including improved crop yields and reduced emissions of other greenhouse gasses. In Greenland, finely grained glacial rock flour (GRF) is naturally generated in vast amounts by glacier movement causing bedrock erosion and deposition. The natural production of GRF means that less energy is needed for grinding the rock material prior to field application. To quantify the influence of GRF on ecosystem carbon balance and greenhouse gas emissions, we applied 10 to 50 t GRF ha-1 yr-1 to an agricultural field in Denmark in a gradient setup with 5 levels plus combinations with fertilizers. Preliminary results of the CO2 fluxes measured by a combination of automated and manual chamber measurements, show that gross primary productivity (GPP, carbon uptake) and ecosystem respiration (Reco, carbon release) both increased gradually with the increased addition of GRF leading to a slightly increased net ecosystem uptake of CO2. In contrast, CH4 and N2O emissions showed a negative response trend with the increasing addition of GRF. The annual quantifications of ecosystem carbon balance and greenhouse gas emissions need further observations including effects during the non-growing season to be finalized. However, our initial results support the hypothesis that silicate mineral amendment overall may enhance CO2 removal in agricultural settings and reduce greenhouse gas emissions, and therefore may be a useful tool for improving the capacity of farmlands to serve as a greenhouse gas sink.