G03_P01

Source apportionment of fugitive methane emissions using radiocarbon in a Scottish river.

Gulliver P¹, Ascough P¹, Murray  C¹, Taylor C¹, Waldron S²

¹University Of Glasgow, East Kilbride, United Kingdom, ²University of Glasgow , Glasgow, United Kingdom

There is a long history of underground and open cast mining in Scotland. Closure of these mines results in local water table rebound as the mines slowly fill with water. This affects a number of Scottish river catchments and the escape of rebounding mine water provides a simple explanation for the presence of high methane concentrations in spring waters in such a catchment.

However, radiocarbon analysis of the dissolved methane in multiple springs of a Scottish catchment underlain by abandoned mine workings gave results of approximate 70 % modern, clearly showing that the methane is not solely geologically derived.

Radiocarbon analysis of the dissolved inorganic and organic carbon (DIC and DOC respectively) pools at the same sites showed that despite having lower % modern values then the dissolved methane, neither pool had a solely geological signature.

The source organic matter contributing to the majority of the dissolved methane and a significant proportion of the DIC and DOC comes from a much younger source and is biologically produced.

G03_P02

Bulk Organic Carbon Isotopes From the Santa Clara River During Rain Events

Thomas K¹, Hauksson N¹, Druffel E¹

¹UC Irvine, Irvine, United States

Small mountainous rivers leading into the ocean, such as the Santa Clara River in Southern California, export considerable amounts of organic carbon to the ocean, and the magnitude and composition of which reaches the ocean is widely studied. With rainfall events in California mostly during winter, the composition and ¹⁴C age of the organic carbon deposited by rivers is likely dependent on the magnitude of these events. In this study, we measured Δ¹⁴C and δ¹³C values of sedimentary organic carbon (SOC) and particulate organic carbon (POC) after rain events near the Santa Clara River. We present these analyses that show high variability of ¹⁴C age and composition of organic material moved downstream with the amount of precipitation and runoff entering the river. This study contributes to our knowledge of organic carbon cycling from small mountainous rivers.

G03_P03

Anthropogenic perturbations change the quality and quantity of terrestrial carbon flux to the coastal ocean

Wei B^1,2, Mollenhauer G^1,3,4, Kusch S⁴, Hefter J¹, Grotheer H¹, Schefuß E⁴, Geibert W¹, Ransby D¹, Jia G^1,6

¹Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany, ²State Key Laboratory of Marine Geology, Tongji University, Shanghai, China, ³Department of Geosciences, University of Bremen, Bremen, Germany, ⁴MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany, ⁵University of Cologne-Centre for Accelerator Mass Spectrometry, University of Cologne, Cologne, Germany, ⁶Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China

Rivers export organic carbon (OC) sourced from their watersheds, offering an opportunity to assess impacts of climatic change and anthropogenic perturbations on the transfer of terrestrial OC to the ocean. Using ¹³C and ¹⁴C compositions of OC exported by the Pearl River during the Industrial Age, we show that anthropogenic activities primarily control the quantity and quality of terrestrial OC fluxes to the coastal ocean. Damming the river and accelerating coal consumption have led to increasing burial flux of petrogenic OC, a rather stable carbon fraction. Man-made ecosystem changes including deforestation, cropland extension, urbanization, and river management increased fresh terrestrial biospheric OC burial, additionally contributing to the long-term carbon sink. Our data help identifying the drivers of sustained change in terrestrial OC export and reveal that human activities substantially enhance the transfer of petrogenic OC and fresh biospheric OC to the coastal ocean, acting as an important sink for anthropogenic CO₂.