Content of Pigments in the Bottom Sediments in a Small Valley–Channel Reservoir

Abstract

This paper presents the first data on the content of plant pigments in the bottom sediments of the Uvod Re-servoir (Volga basin, Russia), unique in its hydrological regime, which support the hypothesis of more intensive carbon accumulation in small water bodies. It is established that the average concentration of chlorophyll a and its transformation products at the stations is 62.6 ± 10.0 μg/g dry sediment, 35.2 ± 4.5 mg/(m2 mm) of wet sediment, and 0.73 ± 0.09 mg/g organic matter of sediments. The ratio of organic carbon to the pigment concentration varies within 400–6000 depending on the type of bottom sediments, which significantly exceeds the values known for macrophytes and phytoplankton. Despite the features of hydrodynamics and geomorphology of the reservoir, the spatial distribution of sedimentary pigments is consistent with the structure of the bottom sediment complex, which is typical for water bodies of different types. A decrease in differences between the pigment concentrations in the sandy and silty biotopes of the Uvod Reservoir compared to the Upper Volga was noted. Average concentration of chlorophyll a with pheopigments (58.5 ± 6.7 μg/g of dry sediment), calculated considering the areas of bottom sediments of different types, in the Uvod Reservoir is 2.3 times higher than in the Gorky Reservoir (25.3 ± 1.5 μg/g), from which water inflows through the Volga–Uvod Canal. According to the content of sedimentary pigments, the trophic state of the reservoir is mesotrophic. Features of eutrophication in the Uvod Reservoir are more distinctly expressed than in the Gorky Re-servoir.