Patterns and ecological implications of small hydropower development in Brazil

Abstract

The growing demand for renewable energy is fueling a global proliferation of Small Hydropower Plants (SHPs), which represents an emerging threat for freshwater ecosystems and aquatic biodiversity. The general perception that SHPs have low environmental impacts is implied in incentive policies for new contruction, although there is little evidence that “small” necessarily equates to lower impacts – especially if the ecological effects of the sheer number of SHPs are considered cumulatively. Here, I investigate the ecological effects of SHPs on river ecosystems, and potential cumulative changes to river connectivity, habitat loss and water quality. 1) I provide the first global overview of the proliferation of SHPs, summarizing status and trends of science and policy on SHPs. 2) Using Brazil as a case study, I explore the role of current and projected-future SHPs on cumulative river fragmentation, and further identify planned dam portfolios that maximize energy gains while minimizing river connectivity losses. 3) I dive into the case of the Chapecó River Basin (Brazil) to investigate in situ the ecological effects of habitat changes by SHPs on invertebrate and fish communities, and 4) the effects of different SHPs on downstream water thermal regimes. More than 80,000 SHPs are operating in 150 countries and the number of future SHPs are estimated to increase three-fold if all potential is explored. SHPs are the primary source of river fragmentation in Brazilian basins, which does not necessarily translate in significant gains in energy generation capacity. Thus, optimized choices of construction could meet future energy demands with much less river fragmentation. SHPs modify the composition of invertebrate and fish communities of the Chapecó Basin, but the magnitude of changes vary widely among dams and can be in some instances predicted by basic SHP attributes (e.g. dam height). Similarly, the effects of SHPs on water thermal regimes is quite variable among dams, but surface warm-water releases were the most common effect. Overall, these results show that the individual and cumulative ecological effects of SHPs are potentially high, highlighting the need for dissolving the “small” modifier from environmental policies and for strategic planning for future construction.