Assessing mire-river interaction in a pristine Siberian bog-dominated watershed – Case study of a part of the Great Vasyugan Mire, Russia

Abstract

Siberian mires, especially the world’s largest coherent bogs of the Great Vasyugan Mire (Tomsk Region, West Siberian Plain, Russia), play an important role in the regional hydrological cycle, global carbon balance and influence flow formation of the region’s rivers. We revealed the role of natural mires in supplying water to a mire-dominated (80% of the river basin area) Siberian catchment of the Klyuch River that represents typical features of the headwater catchment of the Great Vasyugan Mire, the world’s largest mire in natural and well-preserved conditions. Our research protocol involved an analysis of the electric conductivity of peat water along selected transects of the mire, analysis of groundwater levels and river discharge and electric conductivity of the river water. We used ground-penetrating radar to determine the structure of the peat. We revealed that the examined part of the mire depends solely on the rainwater supply and that minerotrophic groundwater is not present within the area of the research. Average groundwater levels within the mire in the period 2013–2018 reached 0.193 m b.g.l. We also revealed that the natural drainage of mire water does not sustain river discharge throughout the whole year. This means the Klyuch remains an intermittent river dependent on the natural outflow of the mire’s waters, after exceeding the mire’s critical water retention volume. Total retention volume of a mire depends on the peat’s physical features and the mire’s short-term response to excessive thaw and precipitation events. An analysis of river discharge duration curves demonstrated that river discharge can be sustained by the duration reaching from 0.39 up to 0.71 in a year, in dry and wet years, respectively. We concluded that in a specific hydrogeological setup of the mire–river system, natural ombrotrophic mires cannot be considered as systems with a continuous water supply and discharge stabilization. We concluded that the Hortonian vision of infiltration and discharge is not valid in bog dominated basins. In the face of climatic changes in Siberia, we foresee a decrease in the discharge volume from the headwaters of rivers and the increase of river intermittence which may affect total outflow volume, specifically in the upper Ob and Irtysh, by reducing the contribution of surface runoff.