Soil carbon sequestration and the role of earthworms in an enhanced weathering mesocosm experiment

Korte inhoud:Virtually all scenarios that limit global warming to 1.5°C require large scale carbon dioxide removal (CDR). Enhanced Weathering (EW) is considered an attractive CDR technology because of the permanence of sequestered inorganic carbon and because of its scalability. Yet, a great challenge in EW research is quantification of weathering and C sequestration rates. In addition, soil (macro)biota such as earthworms were postulated to stimulate silicate dissolution both physically and chemically. However, quantitative data on how earthworms influence (in)organic C sequestration in enhanced weathering systems are lacking. To evaluate the effect of earthworms on EW, we set up a mesocosm experiment with the following treatments: control soil, soil with basalt, soil with earthworms and soil with basalt and earthworms.In this experiment, basalt increased dissolved inorganic carbon (DIC) export by only 40 kg CO2 ha-1. No significant differences in soil organic or inorganic carbon stocks were detected in this short-term experiment. Nonetheless, using a novel Ge/Si and δ30Si EW monitoring we found qualitative proof of mineral weathering. Moreover, we calculated a substantial minimal basalt weathering rate (mWr) (>10-12 mol total alkalinity m-2 s-1) from the large increase in exchanged base cations. Also the soil CO2 efflux showed conisderable CDR; addition of 100 ton basalt ha-1 decreased SCE in non-worm soils by approximately 2 ton CO2 ha-1 after 4.5 months. This decrease may reflect both inorganic and organic carbon sequestration, as organic matter stabilization may have increased due to the increase in soil exchangeable cations.Earthworms did not increase but decrease DIC export and we did not observe an earthworm-induced increase in soil inorganic C sequestration. Instead, earthworms were found to enlarge clay precipitation and base cation exchange, withholding dissolved cations in the soil system, increasing calculated basalt weathering rate and presumably organic matter stabilization. Within this short-term experiment however, SCE increased more through earthworm activity in basalt relative to control mesocosms, possibly indicating stimulation of earthworm gut microbiota. In conclusions, earthworms did not cause net CDR within this short experimental timeframe, yet basalt dissolution was stimulated with expected benefits for organic matter stability in the long run.

Jaar van publicatie:2023

Trefwoorden:Preprint

Toegankelijkheid:Open