Carbonate system and CO 2 degassing fluxes in the inner estuary of Changjiang (Yangtze) River, China

Abstract

We examined the carbonate system, mainly the partial pressure of CO 2 ( pCO 2), dissolved inorganic carbon (DIC) and total alkalinity (TAlk) in the Changjiang (Yangtze) River Estuary based on four field surveys conducted in Sep.–Oct. 2005, Dec. 2005, Jan. 2006 and Apr. 2006. Together with our reported pCO 2 data collected in Aug.–Sep. 2003, this study provides, for the first time, a full seasonal coverage with regards to CO 2 outgassing fluxes in this world major river–estuarine system. Surface pCO 2 ranged 650–1440 μatm in the upper reach of the Changjiang River Estuary, 1000–4600 μatm in the Huangpujiang River, an urbanized and major tributary of the Changjiang downstream which was characterized by a very high respiration rate, and 200–1000 μatm in the estuarine mixing zone. Both DIC and TAlk overall behaved conservatively during the estuarine mixing, and the seasonal coverage of these carbonate parameters allowed us to estimate the annual DIC export flux from the Changjiang River as ∼ 1.54 × 10 12 mol. The highly polluted Huangpujiang River appeared to have a significant impact on DIC, TAlk and pCO 2 in the lower reaches of the inner estuary. CO 2 emission flux from the main stream of the Changjiang Estuary was at a low level of 15.5–34.2 mol m − 2 yr − 1 . Including the Huangpujiang River and the adjacent Shanghai inland waters, CO 2 degassing flux from the Changjiang Estuary may have represented only 2.0%–4.6% of the DIC exported from the Changjiang River into the East China Sea.