Northern Dvina River: Long Periods of Increased and Decreased Water and Ionic Runoff in the 19th–21st Centuries

Abstract This paper analyzes long-term time series of annual and seasonal water and ionic runoff of the Northern Dvina River measured near the village of Ust’-Pinega, where hydrological and hydrometric observations commenced in 1882 and 1947, respectively. Long increased and decreased-runoff phases have been distinguished and their main parameters determined. It is established that the difference between the increased and decreased-runoff phases in long-run annual average water runoff values is 17% for the annual runoff, 16% for the snow-melt flood runoff, 32% for the winter runoff, and 38% for the summer–autumn runoff. It is concluded that changes in the chemical runoff during the transition from a increased water runoff phase to a decreased water runoff phase are pronounced to a lesser extent. The greatest differences between the contrasting water runoff phases in ionic runoff are typical for the summer–autumn hydrological season and for the winter low-water season: during increased-runoff phases, the ionic runoff is 14–17 and 10–11% higher, respectively, compared to decreased-runoff phases. During snow-melt flood periods and on average for the year as a whole, the ionic runoff during increased water runoff phases is only 5–8% higher compared to decreased water runoff phases. The relative dynamic constancy of the hydrochemical load exerted by the Northern Dvina River on the White Sea, regardless of its water content fluctuations, is determined by an inverse relationship between the water flow and the concentration of chemicals. In addition, the anthropogenic impact on the ionic composition in the river catchment basin is insignificant, which makes it possible to maintain the established relationships despite ongoing climate change.