Influence of Three Gorges Dam and drought on particulate organic carbon flux and its source in the lower Yangtze River

• Published in: Biogeochemistry 2022-03, Vol.158 (2), p.269-284
• Main Authors: Panwar, S., Yang, S.
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Biogeochemical cycle; Biogeochemical cycles; Biogeochemistry; Biogeosciences; Biological activity; Calcium carbonate; Canyons; Correlation; Drought; Earth and Environmental Science; Earth Sciences; Ecosystems; Environmental Chemistry; Evapotranspiration; High temperature; Human influences; Hydrology; Life Sciences; Organic carbon; Organic matter; Parameters; Particulate organic carbon; Particulate organic matter; Phytoplankton; Principal components analysis; Radiation; Rain; Rainfall; Relative humidity; River basins; River regulations; Rivers; Solar radiation; Suspended matter; Suspended sediments; Temperature; Weekly; Wind speed
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-022-00889-w

The Yangtze River basin regulated by the gigantic Three Gorges Dam (TGD) is the best location to study the impacts of intense anthropogenic modifications on the global biogeochemical cycles. However, frequent drought periods commencing from 2006 to 2011 may equally act as a strong factor influencing the particulate organic matter (POM) flux. To capture the distinctive role of TGD operations and drought severity on the POM, weekly sampling of total suspended matter (TSM) concentration was conducted at Nantong in the lower Yangtze basin. Biogeochemical parameters (POC% of TSM, PN% of TSM, C/N ratios, and δ 13 C), CaCO 3 %, mean suspended sediment size, and drought parameters (mean temperature, solar radiation, relative humidity, wind speed, evapotranspiration, and rainfall) were evaluated. The inverse power-law correlation between TSM-POC% and TSM-PN% was observed and POC% during 2008–2009 was found to be higher than pre-dam values. The δ 13 C and C/N range from − 25.6 to − 24.1‰ and 4.8 to 9.2, and moderate negative correlation between CaCO 3 -POC% and POC%-δ 13 C were observed. Principal component analysis stipulates that high temperature and solar radiation enhanced evapotranspiration and TGD operations were not found to promote drought in the lower Yangtze basin. The results evince the potential shift of POM source from terrestrial to aquatic biological activity was related to low discharge, low TSM concentration, and dry conditions. The study advances our understanding of the impacts of hydrological connectivity on the POM pool and accentuates the role of phytoplankton as a dominant source of POM in regulated river channels.