On the sampling day, the samples were vacuum filtered through a 0.45-micron filter (Durapore). The filtered samples was analysed for its carbon content in DOM with a thermocatalytic oxidation method using IR registration (TOC-VCPN analyser, Shimadzu) in the geochemistry laboratory of the PGI FEB RAS. The variation coefficient of the analysis of the samples and standards did not exceed 3%. Samples of brackish water from Blagodati Lake were diluted with bidistilled water to salinity no greater than 3%.
To determine the content of carbon in the POM water samples were filtered through Whatman GF/F filters that were previously calcined at 450 °C for 2 h. The carbon concentration in the POM was determined by a TOC-analyser using the SSM-5000A module.