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Dynamic biogeochemical controls on river pCO 2 and recent changes under aggravating river impoundment: An example of the subtropical Yangtze River
Author(s) -
Liu Shaoda,
Lu Xi Xi,
Xia Xinghui,
Zhang Shurong,
Ran Lishan,
Yang Xiankun,
Liu Ting
Publication year - 2016
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/2016gb005388
Subject(s) - biogeochemical cycle , tributary , environmental science , biogeochemistry , total organic carbon , hydrology (agriculture) , organic matter , dissolved organic carbon , benthic zone , environmental chemistry , oceanography , ecology , chemistry , geology , biology , cartography , geotechnical engineering , geography
Abstract 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 main stem (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, seasonally 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.