Anthropogenic influences on riverine fluxes of dissolved inorganic carbon to the oceans

Abstract

Bicarbonate (HCO3−), the predominant form of dissolved inorganic carbon in natural waters, originates mostly from watershed mineral weathering. On time scales of decades to centuries, riverine fluxes of HCO3− to the oceans and subsequent reactions affect atmospheric CO2, global climate and ocean pH. This review summarizes controls on the production of HCO3− from chemical weathering and its transport into river systems. The availability of minerals and weathering agents (carbonic, sulfuric, and nitric acids) in the weathering zone interact to control HCO3− production, and water throughput controls HCO3− transport into rivers. Human influences on HCO3− fluxes include climate warming, acid precipitation, mining, concrete use, and agricultural fertilization and liming. We currently cannot evaluate the net result of human influences on a global scale but HCO3− fluxes are clearly increasing in some major rivers as shown here for much of the United States. This increase could be partly a return to pre‐industrial HCO3− fluxes as anthropogenic acidification has been mitigated in the United States, but elsewhere around the world anthropogenic acidification could be leading to decreased concentrations and fluxes.

Alkalinity and dissolved inorganic carbon exports from tropical and subtropical river catchments discharging to the Great Barrier Reef, Australia

“…River inorganic carbon exports can be an important control on the coastal ocean pH and carbonate chemistry (Duarte et al, ; Raymond & Hamilton, ). Compared with other rivers globally, DIC and TAlk concentrations from the Johnstone, Herbert, and Fitzroy rivers were relatively low but typical of the wet tropical climate zone (Cai et al, ; Probst et al, ; Wang et al, ).…”

“…Carbonic acid (H 2 CO 3 ) is the major weathering agent, however, sulphuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ) also contribute to weathering reactions that become increasingly important since the industrial revolution (Berner, Lasaga, & Garrels, ; Li, Calmels, Han, Gaillardet, & Liu, ; Li & Ji, ; Martin, ). Factors that control and influence chemical weathering rates include the availability of weathering minerals, the supply of weathering agents, the hydrology of the watershed, climatic factors such as temperature and precipitation patterns, and anthropogenic disturbance (Raymond & Hamilton, ). A useful natural tracer for helping elucidate the origin of inorganic carbon in rivers is the stable carbon isotopic ratio (δ 13 C) of DIC because of the distinct δ 13 C signature in biogenic, atmospheric, and geologic sources (Li et al, ; Li & Ji, ).…”

“…Factors that control and influence chemical weathering rates include the availability of weathering minerals, the supply of weathering agents, the hydrology of the watershed, climatic factors such as temperature and precipitation patterns, and anthropogenic disturbance (Raymond & Hamilton, 2018). A useful natural tracer for helping elucidate the origin of inorganic carbon in rivers is the stable carbon isotopic ratio (δ 13 C) of DIC because of the distinct δ 13 C signature in biogenic, atmospheric, and geologic sources (Li et al, 2008;Li & Ji, 2016).…”

“…River DIC loads are an important control on the pH and carbonate chemistry of the coastal ocean (Duarte et al, 2013;Raymond & Hamilton, 2018;Semiletov et al, 2016). This is because carbonate alkalinity and free [CO 2 *] have contrasting effects on the water carbonate chemistry.…”

Spatiotemporal Variability and Sources of DIC in Permafrost Catchments of the Yangtze River Source Region: Insights From Stable Carbon Isotope and Water Chemistry

“…Riverine exports of dissolved inorganic carbon (DIC) are a globally important fraction of carbon connecting the land, river, and atmosphere interfaces (Gaillardet et al, ; Marx et al, ; Raymond & Hamilton, ; Raymond et al, ). DIC has been identified as a major dissolved carbon component in permafrost‐affected Arctic rivers (Prokushkin et al, ; Striegl et al, ; Tank, Frey, et al, ; Tank, Raymond, et al, ) and Qinghai‐Tibetan Plateau (QTP) permafrost‐affected streams (Qu et al, ; Song et al, ); however, the DIC sources and cycling across the QTP are poorly understood.…”