Pigments in Cores of Bottom Sediment as Indicators of the Trophic Status Dynamics in the Benthal of a Large Reservoir

New data on the dynamics of pigment characteristics for different silts of the benthal in the basin-valley Rybinsk Reservoir, the largest source of fresh water of the Upper Volga, are presented. The concept of eutrophication of the reservoir under modern climate warming is supplemented. The content of pigments in cores of bottom sediments (BSs) taken with a period of 10 years (in 2009 and 2019) is compared. According to the latest survey, the mean content of chlorophyll a with pheopigments in cores at the stations is higher, and the carotenoid to chlorophyll ratio (index Е₄₈₀/Е₆₆₅) is lower when compared to the first survey. The relationship between index Е₄₈₀/Е₆₆₅ and the total content of chlorophyll a and pheopigments in cores from most stations is negative similarly to phytoplankton. The contribution of pigment concentrations (chlorophyll a + pheopigments) assigned to the hypertrophic category is increased in the total array of the studied sediment samples. The mean content of sedimentary pigments in lakelike areas is increased in comparison with riverine areas. The dynamics of pigments is clearly pronounced in cores of gray clayey silt and is smoothed in peat-originated silt. Over the period from 2009 to 2019, the mean contribution of autochthonous organic carbon estimated as the sum of chlorophyll and pheopigments increased from 7.7% to 12.3% of total organic carbon in cores. The trends of pigment concentrations in cores indicate an increase in the trophic status of benthal to date. The significance of the pigment characteristics of BSs for monitoring the benthal productivity over the entire period of reservoir operation is discussed.