On the relation of bottom valley-type reservoir hydrocarbon carbon flux and hydrological structure of water body

Abstract

Circulation of carbon in water bodies is a fundamental process of the nutrient cycle in water ecosystems. Carbon flux from bottom sediments is currently the least studied chain of this circulation. The aim of this investigation was the study of HCO3 flux from bottom sediments in the valley-type reservoir and identification of their relationship with the hydrological structure of the water column. Fieldwork and laboratory experiments were conducted at the Mozhaisk reservoir in 2017–2019. These years differed in weather conditions, level regime and stability of water masses. Hydrological surveys were conducted three times during the summer period of each year. They included measuring the vertical distribution of hydrological characteristics and sampling of water and bottom sediments. The Kuznetsov-Romanenko tube method was used to study exchange processes. Hydrocarbonate carbon flux from sediments into the water may range widely (50–900 mgC/m2day). By comparing HCO3 flux with the hydrological structure of the water column, it was revealed that in deep (> 8 m) areas, the release of HCO3 depends on the stratification and thickness of the uniform hypolymnion, where seiches and compensation currents may promote transsedimentation from shallow places to the flooded river bed. In areas with a depth of < 8 m, hydrocarbonate carbon flux from sediments depends much more on the autochthonic organic matter produced by phytoplankton. The relationship between HCO3 flux and the content of organic matter in the soil and its hygroscopic humidity is insignificant.