Enhanced silicate weathering for climate change mitigation – a mesocosm experiment.

Besides rapid decarbonization of all sectors, limiting global warming to well below 2°C will also require active removal of CO2 from the atmosphere. A number of so-called negative emission technologies (NETs) have been proposed for this purpose, including several land-based solutions using natural processes. A promising but yet poorly studied land-based NET is accelerated silicate weathering (EW). When silicates weather, a slow dissolution process occurs, binding CO2 in aqueous form. This CO2 is sequestered for millennia. The idea behind EW is to speed up this natural process, by artificially increasing the weathering rate. This can be achieved by distributing finely ground silicate rock (e.g. basalt) or artificial silicates such as steel slag on soils. While the latter weathers more slowly, using waste streams has the advantage that source material is abundant and that it can be embedded in a circular economy. Thus far, research on EW has mainly been limited to laboratory experiments. Empirical research under more realistic conditions is urgently needed to determine the true climate change mitigation potential as well as the side-effects of EW. An essential step between the lab-based research and applications in the field are mesocosm experiments that allow accurate quantification of the CO2 sequestration and method development for practical C sequestration assessment in the field. In this project, a mesocosm experiment will be set up to accurately quantify CO2 sequestration by EW. Sideeffects on plant growth and plant nutrient concentrations will also be quantified. Specifically, 15 mesocosms will be filled with agricultural soil and planted with maize. Five receive only fertilizer, while the others receive also finely ground basalt (n=5) or steel slag (n=5), i.e., a natural and an artificial silicate. Weathering rates are monitored by analyzing top soil pore water samples as well as leachates for weathering products (DIC, alkalinity, Si, Mg and Ca). Weathering products can also precipitate in the soil and quantification of CO2 sequestration rates thus also requires analysis of carbonates in the soil after the experiment. Plants are harvested at the end of the experiment to quantify plant biomass (above- and belowground) and subsamples are analyzed for important plant nutrients, including N, P, K, Si, Ca, Mg.

Keywords:CARBON SEQUESTRATION

Disciplines:Biogeochemistry, Environmental technologies