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 in the basin-valley Rybinsk Reservoir, the largest source of fresh water on the Upper Volga, are presented. The concept of eutrophication of the reservoir under modern climate warming is supplemented. The content of pigments in bottom sediment cores taken after 10 years (in 2009 and 2019) was compared. According to the latest survey, the average content of chlorophyll a with pheopigments in cores at the stations is characterized by higher values, and the carotenoid/chlorophyll ratio (index Е 480 /Е 665 ) is lower than according to the first survey. The relationship between the index Е 480 /Е 665 and the total content of chlorophyll a and pheopigments in cores from most stations is negative, as in phytoplankton. In the total array of studied sediment samples, the contribution of pigment concentrations (chlorophyll a + pheopigments) belonging to the hypertrophic category is increased. The average content of sedimentary pigments in lake-like areas increased compared to riverine areas. The dynamics of pigments is clearly expressed in cores of gray clayey silt and smoothed in peat–originated silt. Over the period from 2009 to 2019, the average contribution of autochthonous organic carbon, estimated from the sum of chlorophyll and pheopigments, increased from 7.7% to 12.3% of total organic carbon in cores. The trends of the pigment concentrations in cores indicate an increase in the trophic state of benthal to date. The significance of the pigment characteristics of bottom sediments for monitoring the benthal productivity over the entire period of reservoir operation is discussed.