Changes in river water quality caused by a diversion hydropower dam bordering the Pantanal floodplain

Abstract

Diversion hydroelectric facilities are proliferating worldwide, yet how they alter water quality has seldom been assessed. This study evaluates effects of a nearly “run-of-river” diversion hydropower dam (210 MW capacity) on water quality in the Correntes River, a tributary to the Pantanal floodplain of Brazil. Water quality was analyzed from eight locations before and after reservoir construction. Relative to an upstream reference site, the reservoir significantly decreased turbidity (mean, 38%) and concentrations of total solids (23%), total phosphorus (28%), and nitrate (14%). Most changes occurred in the upstream segment of the reservoir (except for turbidity). Only turbidity and nitrate were affected by reservoir operator control of the hydraulic retention time, which ranged from 7.3 to 21.2 days. Overall, the most consequential changes in downstream water quality may be sediment and associated phosphorus retention, which over the long term could affect channel geomorphology and reduce floodplain biological productivity.