Abstract
Measurements of pH, total alkalinity, and humic substance were carried out in June 2005 and 2006 in the waters of the Lower Amur between the cities of Komsomolsk-on-Amur and Nikolaevsk-on-Amur; 13 hydrochemical stations were examined at a distance of 489 km. In August 2016, hydrochemical observations were carried out at the mouth of the Amur River, which included measurements of pH, total alkalinity, humic substance, concentrations of the major ions in river water ( \({\text{N}}{{{\text{a}}}^{ + }}\) , K+, Ca2+, Mg2+, Cl–, and \({\text{SO}}_{4}^{{2 - }}\) ) and dissolved organic carbon. The average annual rate of chemical weathering in the Amur River basin was found to be 10.7 t/(km2 year). Weathering of rocks and photosynthesis of organic matter lead to the removal of CO2 from the atmosphere and form an annual export of atmospheric CO2 by the river into the marine environment, equal to \(3.8 \times {{10}^{6}}{\text{ t }}{{\text{C}} \mathord{\left/ {\vphantom {{\text{C}} {{\text{year}}}}} \right. \kern-0em} {{\text{year}}}}\) . It was established that the waters of the Amur River emit CO2 into the atmosphere at a rate of \(4.5 \times {{10}^{6}}\) t C/year. The balance of opposite processes (CO2 export and emission) showed that the Amur River ecosystem is a weak source of CO2 into the atmosphere. The annual flow of alkalinity from the Amur into the marine environment ( \(1.65 \times {{10}^{{11}}}\) mol/year) leads to an increase in the normalized alkalinity in the surface layer off the eastern shores of Sakhalin Island (Sea of Okhotsk) and in the northern part of the Sea of Japan.
