Contemporary Controls on Terrestrial Carbon Characteristics in Temperate and Sub-Tropical Australian Wetlands

A thorough understanding of controls over terrestrial sedimentary organic carbon characteristics in both the present and the past is pivotal to better understand atmospheric CO2 pathways into depositional sinks such as peats, swamps, and lakes. We explored the relationship between wetland sediment organic matter storage, climate (precipitation, temperature) and catchment vegetation data (catchment vegetation cover in percent; leaf carbon content in g/m2) by means of multivariate statistical analyses to investigate patterns of carbon deposition in modern wetlands and to provide a more robust framework for interpreting sediment bulk organic geochemistry as a proxy for past carbon cycling. Carbon and nitrogen elemental concentration and stable isotope composition were analyzed from sub-surface sediments at 18 wetlands in eastern Australia. The statistical analyses indicate that variability in geochemical organic matter data in wetland sediments is best explained by geographic differences in catchment vegetation cover and, by inference, the balance of terrestrial versus aquatic organic matter input to the sediment. TOC/TN of aquatic matter may be additionally driven toward higher (terrestrial) values by nitrogen limitation in the catchment and the lakes. These processes explain up to similar to 40% of the total variance in the sediment geochemistry (redundancy analyses). Up to similar to 10% of the total variance may be attributed to post-depositional processes and organic matter remineralization. The remaining similar to 50% of total variance in the data may be attributed to local conditions across the sites, geochemical processes that were not captured in this study, or to the different timescales covered by the sediments at each site.

Automated summary

By analyzing the elemental concentration and stable isotope composition of sub-surface sediments from 18 wetlands in eastern Australia, the study found that the variability in the geochemical organic matter data is mainly explained by geographic differences in catchment vegetation cover and the balance of terrestrial versus aquatic organic matter input to the sediment. Nitrogen limitation and geographic factors further influenced the TOC/TN of aquatic matter. These processes accounted for approximately 40% of the total variance in sediment geochemistry, while around 50% of the variance could be attributed to local conditions, unaccounted geochemical processes, or different sediment timescales.