Changes in Biological and Physicochemical Parameters of River Water in a Small Hydropower Reservoir Cascade

P. MIHAILOVA¹, I. TRAYKOV², A. TOSHEVA³ and M. NACHEV^4
1 Sofia University St.”Kl.Ohridski”, Dep. of Ecology and EP, Faculty of Biology, BG – 1164 Sofia, Bulgaria
² Sofia University St.”Kl.Ohridski”, Dep. of Ecology and EP, Faculty of Biology, BG – 1164 Sofia, Bulgaria
³ Sofia University St.”Kl.Ohridski”, Dep. of Botany, Faculty of Biology, BG – 1164 Sofia, Bulgaria
⁴ University of Duisburg-Essen, Dep. of Aquatic Ecology, Faculty of Biology, Germany

Abstract

Mihailova, P., I. Traykov, A. Tosheva and M. Nachev, 2013. Changes in biological and physicochemical parameters of river water in a small hydropower reservoir cascade. Bulg. J. Agric. Sci., Supplement 2, 19: 286–289

 

The impact of single small hydropower plants on the environment is thought to be negligible. Their effect progressively increases with the cascade development of the river basins, thus the cumulative environmental effects of small hydropower reservoirs can have a significant impact on the ecological state of the rivers. We have studied the effect of two small hydropower reservoirs on some parameters of river water quality. The Lakatnik Reservoir and the Svrazhen Reservoir are situated in the middle reaches of the Iskar River, directly one after another. The river water is rich in nutrients and organic substances and carries high amounts of suspended sediments. As it flows through the cascade, the river temperature increases, while oxygen concentration, electrical conductivity and suspended sediments decrease, mostly due to the enhanced degradation and transformation of the organic substances in the water. The amount of the phytoplankton depends on the residence time and the amount of the abioseston in the river water. Despite their recent construction, the reservoirs support rich assembly of macrophytes, mostly indicators of eutrophic conditions. The observed changes in biological and physicochemical parameters of the river water are a direct result of increased retention of water in the reservoirs.  The study shows the potential of small hydropower cascades to influence the river water quality.

Key words: chlorophyll-a, SHPP, macrophytes, reservoir cascade, water quality, run-of-the-river reservoirs
Abbreviations: Chl-a – chlorophyll-a; SD – Secchi disc depth; TP – total phosphorus; TSI(Chl) – trophic state index derived according to the Chl-a values; TSI(SD) – trophic state index derived according to the SD values; TSI(TP) – trophic state index derived according to the TP values; AvrgTSI – average value of the individual trophic state indices; Q – river discharge

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