Peat enrichment with clay minerals to reduce CO2 emissions: a proof of principle study

Over 80 % of the Dutch peatland is permanent grassland for agricultural use. To maintain these peat meadows the land is drained, resulting in carbon decomposition and greenhouse gas emissions. Currently most measures to reduce emissions from drained peatland are hydrological, limiting the exposure of peat to oxygen. In our research we aim to study whether a non-hydrological measure -the enrichment of peat with clay minerals- can reduce CO2 emissions.

Previous research in peat meadows indicate that clay content might be linked to peat degradation. Several studies show correlations between higher clay contents and lower organic matter decomposition rates, subsidence rates or higher SOC densities. Clay minerals can be highly reactive, due to their size, shape and charge. and it is known that clay minerals are important determinants in organic matter dynamics. From studies in mineral soils it is known that clay minerals affect the carbon accessibility for the microbial community. Mechanisms by which accessibility is affected are physical protection, adsorption, aggregate inclusion, organo-mineral complexation. Clay can directly affect the heterotrophic activity, by adsorption and immobilization of exoenzymes or by a shift in microbial community composition. Mineral amendments can also have an indirect effect on microbial activity by changing the environment: clay can induce changes in aeration, water retention, pH and nutrient availability.

We hypothesized that the introduction of clay minerals in a peat matrix can result in interaction with organic components in several ways resulting in reduced peat oxidation. As a first step to test whether clay enrichment can reduce the CO2 emissions from peat we set up long term incubation study in the lab. We mixed peat with 7 different naturally occurring clay types and incubated these together with control samples without clay for >1000 days in which we periodically measured CO2 respiration.

The results from this experiment show that peat enrichment with clay can slow down CO2 emissions-rates.  The emission reduction varied widely between clay types. A number of clays induced a clear reduction in CO2 emissions which started after approximately 100 days of incubation. For these samples the cumulative emission reduction of up to a 33% was observed over the 3-year incubation period, compared to the control samples without clay. Also, the inhibitory effect of clay varied over time, being strongest after ca 100 days. Remarkably some of the tested clay types did not show any effect, whereas other types of clay reduced the emission rate.

Currently we are in the process of verifying the results. The next steps in this research include zooming in on different clay types, their effect on microbial community composition and activity and testing clay amendments in the field.