Methane in waters and bottom sediments of the North (Severnaya) Dvina mouth area in 2004-2006

The mouth area of the North (Severnaya) Dvina River is characterized by a high concentrations of methane in water (from 1.0 to 165.4 µl/l) and bottom sediments (from 14 to 65000 µl/kg), being quite comparable to productive mouth areas of rivers from the temperate zone. Maximum methane concentrations in water and sediments were registered in the delta in segments of channels and branches with low rates of tidal and runoff currents, where domestic and industrial wastewaters are supplied. In the riverine and marine water mixing zone with its upper boundary, locating far into the delta and moving depending on a phase of the tidal cycle, decrease of methane concentration with salinity increase was observed. The prevailing role in formation of the methane concentration level in water of the mouth area pertains to bottom sediments, which is indicated by close correlation between gas concentrations in these two media. Existence of periodicity in variations of methane concentration in river water downstream caused by tidal effects was found.

北德维纳河（Severnaya Dvina）河口区域的水体与底泥中甲烷浓度处于较高水平：水体甲烷浓度范围为1.0至165.4 µl/l，底泥甲烷浓度范围为14至65000 µl/kg，该浓度水平与温带地区高产能河流河口区域相当。在潮汐与径流流速较低的河道及支流三角洲段，监测到水体与底泥中的甲烷浓度峰值，该区域同时接纳生活与工业废水。在其上限深入三角洲内部、并随潮汐周期相位变化而移动的河海混合带中，观测到甲烷浓度随盐度升高而降低的现象。底泥对河口区域水体甲烷浓度水平的形成起主导作用，这一点可通过两种介质中气体浓度的显著相关性得到印证。研究发现，下游河流水体的甲烷浓度变化存在由潮汐效应引发的周期性特征。