Publication Date:
2016-06-07
Description:
This paper highlights two aspects of the dynamic biogeochemical controls of riverine pCO 2 in an increasingly impounded large subtropical river (the Yangtze): the terrestrial dominance through internal respiration of land-derived organic carbon and the influence of increased autotrophic activity in impounded areas on river pCO 2 . River pCO 2 and total organic carbon (TOC) increase downstream on the mainstem (pCO 2 : 528–1703 µatm; TOC: 137–263 µmol/L) and vary significantly among tributaries (464–3300 µatm; TOC: 109–340 µmol/L). pCO 2 displays larger spatial variability than temporal variability and is spatially correlated with river organic carbon across the river (p 〈 0.05–0.0001, seasonal independent). pCO 2 is also negatively correlated with dissolved oxygen (r 2 = 0.46, p 〈 0.0001). Respiration of allochthonous organic carbon in water column is concluded as an essential source of CO 2 supersaturation and river heterotrophy. However, significant benthic respiration and/or direct soil CO 2 transport (e.g., via groundwater, ~ 80%) exist at the same time. The temporal and spatial distribution of POC compositional characteristics and chlorophyll a indicate the dominant control of terrestrial processes (e.g., organic matter transport and soil erosion) on the river pCO 2 biogeochemistry, especially in warm seasons. Increased autotrophy and significant pCO 2 decrease (〉60%) do occur in impounded areas (especially in nutrient-rich rivers), but the decrease is mostly temporal and regional (~8% of the data points are significantly influenced, all from the upper reach and/or major tributaries). The paper concludes that terrestrial influence still dominates the pCO 2 biogeochemistry in this increasingly intercepted and regulated river system.
Print ISSN:
0886-6236
Electronic ISSN:
1944-9224
Topics:
Biology
,
Chemistry and Pharmacology
,
Geography
,
Geosciences
,
Physics
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