Terrestrial dissolved organic carbon consumption by heterotrophic bacterioplankton in the Huanghe River estuary during water and sediment regulation

Abstract

Nearly 20%–50% of the annual terrestrial dissolved organic carbon (DOC) from the Huanghe (Yellow) River was transported to the estuary during the 5–14 d of water and sediment regulation. The concentration of DOC increased sharply during the period of water and sediment regulation, which may promote the terrestrial DOC consumption by heterotrophic bacterioplankton. Water and sediment regulation provides an ideal condition for the study of terrestrial DOC consumption by heterotrophic bacterioplankton when terrestrial DOC increases sharply in rainy season, which may help to seek the fates of terrestrial DOC in the estuaries and coasts. In this study, the concentration and stable isotope of DOC, the biomass, growth, and respiration of heterotrophic bacterioplankton were determined. By the study, we found both average percent contribution of terrestrial DOC to the DOC pool and Contribution of terrestrial DOC to the carbon composition of heterotrophic bacterioplankton decreased as distance from the river mouth increased offshore, which was deceased from (39.2±4.0)%, (37.5±4.3)% to (30.3±3.9)%, (28.2±3.9)% respectively. 255–184 μg C/(L d) terrestrial DOC was consumed by heterotrophic bacterioplankton. And 29%–45% terrestrial DOC consumed by heterotrophic bacterioplankton releasing as CO2 by respiration. Comparing with tropical estuary, terrestrial DOC consumed by heterotrophic bacterioplankton was lower in temperate estuary (this study). Temperature may limit the consumption of terrestrial DOC by heterotrophic bacterioplankton.