The spatiotemporal distribution of dissolved inorganic and organic carbon in the main stem of the Changjiang (Yangtze) River and the effect of the Three Gorges Reservoir

Abstract

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.

Sources, Transport, and Transformation of Dissolved Organic Matter in a Large River System: Illustrated by the Changjiang River, China

“…The Changjiang River, which is also known as Yangtze River, originates in the Tibetan Plateau and flows 6,300 km through various geomorphologies to the East China Sea. It has a catchment area of 1.8 × 10 6 km 2 and annual average discharge of 960 km 3 (Zhang et al, ). The river basin is located in the temperate zone (24.5–35.5°N), and the average annual precipitation is 1,100 mm (70–90% of which occurs during the wet season of May to October; Zhang et al, ).…”

“…It has a catchment area of 1.8 × 10 6 km 2 and annual average discharge of 960 km 3 (Zhang et al, ). The river basin is located in the temperate zone (24.5–35.5°N), and the average annual precipitation is 1,100 mm (70–90% of which occurs during the wet season of May to October; Zhang et al, ). Approximately half of the precipitation is lost due to evaporation (Yang et al, ).…”

Controls on the sources and cycling of dissolved inorganic carbon in the Changjiang and Huanghe River estuaries, China: 14C and 13C studies

“…Human activities including river damming, wastewater input, urbanization, and runoff could also affect riverine DIC concentrations (Raymond et al 2004;Chen et al 2008;Zeng et al 2011;Zhang et al 2013). These activities have changed the fluxes of both particulate and dissolved constituents in many large rivers, such as the Changjiang and Huanghe Rivers in China, in the last two decades (Yang et al 2006;Wang et al 2008;Zhang et al 2014).…”

Spatial and seasonal dynamics of organic carbon in physically fractioned sediments associated with dam construction in the middle Lancang-Mekong River

“…As suggested by previous studies (e.g. Nilsson et al 2005;Zhang et al 2014), the high level of water needed for maintaining electricity production during the dry season may enhance the dissolved organic carbon inputs coming from the bank.…”