Abstract
Sediments are an essential part of the aquatic environment that define its transformation and development. The construction of dams results in severe changes in sediment fluxes. This study aims to assess how the sediment load of the upper Moskva River is affected by the Mozhaysk Dam flow regulation and to estimate its dynamics over the years of the reservoir’s existence. Our analysis of the 1968, 2012 and 2016 detailed field data shows a 20-40% decrease in the proportion of the spring flood in the annual sediment load into the reservoir, which is caused by changes in the streamflow regime of the inflowing rivers. The peak suspended sediment concentrations have decreased 5- to 10-fold, likely due to a significant decline in the watershed’s cultivated land area, which caused a decrease in the erosion rate. In the Moskva River below the dam, the seasonal dynamics of the suspended sediment concentration no longer corresponds to the natural regime. The annual suspended load of the Moskva River below the Mozhaysk Reservoir decreased up to 9-fold. The sediment retention in the reservoir has dropped from 90% to 70-85% and is to some extent restored by an outflow of the particulate organic matter produced in the reservoir. We also described the relationships between water turbidity and suspended sediment concentration of the reservoir’s tributaries, which allow for the first time to estimate the sediment load with higher accuracy than was previously possible.
Highlights
Sediment is an essential part of a river ecosystem that defines its transformation and development (Vanmaercke et al 2011; Wang et al 2016)
We have assessed the effect of the Mozhaysk Dam on the suspended sediment transport in the Moskva River and addressed the dynamics of its sediment load over the past 50 years
The major part of the annual suspended load into the Mozhaysk Reservoir is received during the spring flood, but its share decreased from 90% to 50-75% over the past half-century, likely due to the transformation of the river flow regime confirmed by various authors
Summary
Sediment is an essential part of a river ecosystem that defines its transformation and development (Vanmaercke et al 2011; Wang et al 2016). Soil erosion determines the chemical composition of the river water and its nutrient supply. Erosion, sediment transport, and deposition in the river system control the patterns of the spatial distribution of the riparian biomes. The macrophyte growth increases the self-purification capacity of a river and its resilience to human pressure; floodplain sediments act as a spawning and nursery zone for freshwater fish. Many aquatic organisms are sensitive to water turbidity and bedload properties (Shields 2009). This dictates the need to study the sediment flow in rivers as a necessary step towards understanding and predicting the dynamics of freshwater ecosystems, and preserving the habitat for indigenous species
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