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The Changjiang River supplies huge amounts of fresh water and dissolved and particulate substances to the East China Sea, thereby exerting a great influence on the coastal ecosystem. Meanwhile, the construction of the Three Gorges Reservoir (TGR) has reallocated the annual discharge, likely affecting the transportation of carbon in its various forms. The transport and transformation of carbon in Changjiang River and the effect of the TGR were discussed based on three field campaigns, a 1 year time series investigation, and historical data. Our results indicated the following: (1) Dissolved inorganic carbon (DIC) was derived from the upper stream and was significantly diluted downstream by the low-DIC waters from two large lakes. Dissolved organic carbon (DOC) was a product of anthropogenic input and showed no clear relationship with discharge. particulate organic carbon (POC) within total suspended matter (POC%) was below the global average. (2) The TGR has not measurably affected the transport of DOC downstream of the reservoir dam. However, downstream grain size has decreased and autochthonous processes have increased, resulting in a sharp increase in POC% since reservoir construction. (3) For the period 1997-2010, estimated annual DIC flux was 16.9 Tg yr À1. The regulation of river flow by the TGR has decreased the river DIC flux to the East China Sea in the autumn and increased it in the spring. Furthermore, the South-North Water Diversion will reduce the high-DIC water from the upper reach, thus affecting the biogeochemistry of the Changjiang estuary and the ecosystem of the nearby coastal ocean.

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Human-induced changes in carbon fluxes across the land-ocean interface can influence the global carbon cycle, yet the impacts of rapid urbanization and establishment of wastewater treatment plants (WWTPs) on coastal ocean carbon cycles are poorly known. This is unacceptable as at present ∼64% of global municipal wastewater is treated before discharge. Here, we report surface water dissolved inorganic carbon (DIC) and sedimentary organic carbon concentrations and their isotopic compositions in the rapidly urbanized Jiaozhou Bay in northeast China as well as carbonate parameters in effluents of three large WWTPs around the bay. Using DIC, δC and total alkalinity (TA) data and a tracer model, we determine the contributions to DIC from wastewater DIC input, net ecosystem production, calcium carbonate precipitation, and CO outgassing. Our study shows that high-DIC and low-pH wastewater effluent represents an important source of DIC and acidification in coastal waters. In contrast to the traditional view of anthropogenic organic carbon export and degradation, we suggest that with the increase of wastewater discharge and treatment rates, wastewater DIC input may play an increasingly more important role in the coastal ocean carbon cycle.

The Yellow River of China runs mainly through an arid and semiarid midlatitude region that has experienced substantial anthropogenic and climatic change. This area includes the carbonate-rich Loess Plateau and carries water of exceptionally high carbonate content. To investigate the processes by which dissolved inorganic carbon (DIC) is biogeochemically modified as the river approaches the sea, a multipronged field investigation was conducted in the Yellow River estuary, [2005][2006][2007][2008][2009]. The project included four research cruises (spring and fall), a year of monthly sampling at a lower-river hydrological station (Lijin), and in situ bottle incubations. Our study revealed that 4-11% of the Yellow River DIC was removed from the water column in the estuarine mixing zone and thus was not transported to the sea. DIC removal was greater in the spring and occurred at a higher salinity range than in the fall. As a unique feature of the Yellow River estuary, calcium carbonate (CaCO 3 ) precipitation was nearly as important as net biological production in the DIC removal. Longer freshwater-seawater mixing distances (and times) and higher DIC concentrations in the freshwater end member also promoted net biological production and CaCO 3 precipitation, thus encouraging DIC removal.

The high HCO 3 concentrations in the Yellow River (China) are generally believed to originate primarily from the carbonate-rich Loess Plateau as a result of carbonate weathering reactions that consume atmospheric CO 2. We studied chemical weathering across the entire Yellow River basin in 2007 and 2009 and found that the amounts of CO 2 consumption by carbonate and silicate weathering were 87.61×10 9 mol/a and 10.70×10 9 mol/a, respectively. As the source of water for the Yellow River, although the Qinghai-Tibet Plateau accounts for only 30% of the area of the basin, it has a strong leaching effect and contributes a majority (61%) of the atmospheric CO 2 consumption of the entire basin and a majority of the riverine DIC flux (66%) to the ocean. As a result, the dissolved inorganic carbon (DIC) concentrations in this river are among the highest of the world's major rivers. In contrast, despite the abundant carbonate mineral content in the Loess Plateau, the high ratio of evaporation to precipitation (4.2) limits the weathering processes, and the low amount of runoff restricts the transport of weathering products, which results in a relatively low contribution (38%) to the basin-wide atmospheric CO 2 consumption, which is much lower than was previously thought. The Qinghai-Tibet Plateau is the origin of the high levels of HCO 3 in and acts as the main DIC contributor to the Yellow River.