Soil organic carbon (SOC) is the largest terrestrial stock of organic carbon. Understanding the SOC balance requires consideration of lateral fluxes of carbon in water, e.g. dissolved organic carbon (DOC), and vertical fluxes of carbon gases. However, the interactions between SOC and DOC and the response to climate change at catchment or larger scales remain unresolved. This work investigates how temperature and hydrology control the production and export of DOC in the Susquehanna Shale Hills Critical Zone Observatory in Pennsylvania, USA. We developed the catchment-scale hydro-biogeochemical reactive transport model BioRT-Flux-PIHM to simulate the DOC dynamics. We estimated the daily DOC production rate (Rp; the sum of local DOC production rates in individual modeling grid cell) and the daily DOC export rate (Re; the product of concentration and discharge at the stream outlet) to downstream ecosystems. Simulations showed that Rp varied by less than an order of magnitude and primarily hinged on seasonal temperature change. In contrast, Re varied by more than three orders of magnitude with a strong dependence on discharge and hydrological connectivity. During summer, high temperatures led to high atmospheric water demand (and evapotranspiration) that dried and disconnected hillslope to stream. Rp reached its maximum but Re was at its minimum. The stream only exported DOC from the organic-poor groundwater and from soil water in the narrow organic-rich swales with enriched DOC such that DOC accumulated in the catchment. During the wet period (winter and spring), Rp reached its minimum but Re peaked because the stream was re-connected to a greater uphill area, flushing out the stored DOC. This study illustrates the temporal asynchrony of DOC production, mostly controlled by temperature, and DOC export, primarily governed by hydrological flow paths at the catchment scale. This work provides new insights into how DOC production and export interact at multiple scales, and emphasizes the importance of considering different constraints when projecting the response of lateral and vertical carbon fluxes to climate changes.

Dynamics of dissolved organic carbon at the catchment scale: Is it temperature or hydrology controlled?

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.