Origin and alteration of suspended and sedimentary organic matter in the contrasting subtropical river systems from South China and Taiwan Island
Abstract
Understanding the integrated basin-wide origin and nature of organic matter (OM) in different river systems draining diverse lithological terrains is important to evaluate the role of river systems on the global carbon cycle. Here, we provide an overview of provenance and composition of OM in suspended particulate matter (SPM) and deposited sediments from the flat, transport-limited Pearl River in South China and the steep, weathering-limited small mountainous rivers from Taiwan Island. We present new data on the organic carbon (OC) and total nitrogen (TN) contents, stable carbon and radiocarbon isotopic compositions of OC (δ13C and Δ14C), as well as grain size distribution and mineral surface area of riverine sediments. These results are combined with published data on SPM and soil profiles in the river watershed in order to determine the provenance and transformation of OM in these two fluvial systems.
In the Pearl River, refractory, aged soil OM account for ~60-90% of the total OM in the SPM and sediments. Most labile OM in the top soil is rapidly degraded, which is indicated by a stronger contribution from soil CO2 into riverine dissolved inorganic carbon during the wet season and flood event compared to the dry season. While the sources from riverine primary productivity and petrogenic OM account for ~0-20% and ~10-20%, respectively, which are increased during the dry season SPM. In contrast, the OM in sediments of Taiwan rivers is mainly derived from the petrogenic OM, accounting for ~50-80%. The remaining materials is dominated by relatively labile, young soil OM. These two contrasting river systems highlight the overarching role that tectonics and bedrock lithology play on modulating the export of terrestrial OM to the ocean and offers a window into understanding the impact of orogenic cycles on the global carbon cycle over geologic timescales.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP33C2345L
- Keywords:
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- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 1030 Geochemical cycles;
- GEOCHEMISTRY;
- 1815 Erosion;
- HYDROLOGY;
- 1862 Sediment transport;
- HYDROLOGY