The drag coefficient (CDN), Stanton number (CHN) and Dalton number (CEN) are of particular importance for the bulk estimation of the surface turbulent fluxes of momentum, heat and water vapor at water surfaces. Although these bulk transfer coefficients have been extensively studied over the past several decades mainly in marine and large-lake environments, there are no studies focusing on their synthesis for many lakes. Here, we evaluated these coefficients through directly measured surface fluxes using the eddy-covariance technique over more than 30 lakes and reservoirs of different sizes and depths. Our analysis showed that generally CDN, CHN, CEN (adjusted to neutral atmospheric stability) were within the range reported in previous studies for large lakes and oceans. CHN was found to be on average a factor of 1.4 higher than CEN for all wind speeds, therefore, likely affecting the Bowen ratio method used for lake evaporation measurements. All bulk transfer coefficients exhibit substantial increase at low wind speeds (< 3 m s-1), which could not be explained by any of the existing physical approaches. However, the wind gustiness could partially explain this increase. At high wind speeds CDN, CHN, CEN remained relatively constant at values of 2 10-3, 1.5 10-3, 1.1 10 -3, respectively. We found that the variability of the transfer coefficients among the lakes could be associated with lake surface area or wind fetch. The empirical formula C=b1[1+b2exp(b3 U10)] described the dependence of CDN, CHN, CEN on wind speed well and it could be beneficial for modeling when coupling atmosphere and lakes.

Increase in concentration in the atmosphere of greenhouse gases (GHG) is considered as one of the possible reasons of climatic changes. Recently all their possible anthropogenic sources including artificial reservoirs are considered. The actual task is the inventory of GHG emissions various sources for possible reduction and parameterization of emission from the underlying surface to define the conditions of interaction with the atmosphere in climate models. The work concerned questions of time-spatial changes of contents and emission of methane from a surface of polytypic reservoirs. On the basis of comparison of the field observations on the Mozhaisk and Gorky reservoirs the distinctions of contents and specific fluxes of methane for reservoirs with various water residence time and hydrological regime are shown. Comparison with literary data has shown that emission rate from reservoirs of a boreal zone with slow water exchange can be underestimated.

Authors present their investigation of spatial and temporal changes of methane emission from the surface of the Mozhaisk reservoir, situated 120 km to the west from Moscow, Russia. Seasonal changes in the content and specific flow of methane were revealed for different morphological areas of the reservoir based on the data of field observations in 2015-2018. In the low-flow Mozhaisk reservoir, the methane content in the surface and bottom layers of the deep-water areas at the end of the summer stratification period may differ by three orders of magnitude. According to the results of flux measuring by «floating chambers» in the entral area of the reservoir from the beginning of June to the end of the period of direct stratification (August-September) methane flux increased from less than 1 to 16 mg 4-C/(m**2 hour). The simultaneous measurements with “floating chambers” of 2 types (simple – for taking samples of the integral flux, and with a shield, rejecting bubbles – for samples of diffusion flux) revealed typical values of these flux components and their change during the sampling period. In the beginning of stratification diffusive flux predominates with mean values 0,2 mg4-/(m2 hour) and forms 100% of the total flux while methane concentration near bottom is low.The increase of the total methane flux is associated with an increase of the bubble component: its ratio grows from 75% to 98.7%. Integral methane flux rapid increase is observed when the upper edge of bottom anoxic zone reaches the lower edge of epilimnion. Supported by RGS 17-05-41095.