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

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 delta C-13), CaCO3%, 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 delta C-13 and C/N range from - 25.6 to - 24.1 parts per thousand and 4.8 to 9.2, and moderate negative correlation between CaCO3-POC% and POC%-delta C-13 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.

Automated summary

This study investigates the impacts of Three Gorges Dam operations and drought severity on the flux of particulate organic matter (POM) in the lower Yangtze basin. The results indicate that the operations of the dam do not contribute to drought in the region, and the shift in POM source is related to low discharge, low TSM concentration, and dry conditions.