Thirty years after Balbina Dam: Diversity and floristic composition of the downstream floodplain forest, Central Amazon, Brazil

Abstract

The construction of hydroelectric dams causes changes in the diversity and floristic composition of floodplain forests due to the irregularity of the hydrological regime in rivers downstream from the dams. In the Amazon Basin, plans for the construction of dams are threatening the igapós, forests flooded by blackwater rivers. In these floodplains, the distribution of tree species is synchronized with periodic flood events of the topographic gradient. Previous studies on the Balbina Dam show an altered flood pulse downstream. This work discusses the potential long-term impacts on the diversity and floristic composition of an igapó downstream of the dam (Uatumã River) and compares it with an area unaffected by the dam (Abacate River). An evaluation of the vegetation strata-adults, saplings, and seedlings-showed that for all strata, diversity was greater in the high igapó (higher topographies) in the Uatumã area. This may be due to the near-total absence of flooding in the high igapó and to the extent of flooding in the low igapó (low topographies). Thus, in the Uatumã area, seeds of species typical of flooded areas cannot reach the high igapó by water and, thus, tend to be replaced by upland forest species (mainly seedlings). In the low igapó, the typical species have difficulty establishing. Therefore, the Uatumã vegetation forms two different communities, which does not occur in the Abacate area. These effects of the dam led to irreversible changes in the diversity and floristic composition across all strata throughout the entire topography in the downstream region.

Assessing Land Use and Land Cover Changes in the Direct Influence Zone of the Braço Norte Hydropower Complex, Brazilian Amazonia

“…This is in agreement with Fearnside et al (2016) [20], who found that hydroelectric projects can stimulate deforestation around reservoirs in the Amazon. Similar LULCC patterns have been found in other hydroelectric dams constructed in the Brazilian Amazon such as Balbina [41], Belo Monte [42], and Tucuruí [43].…”

River damming affects seedling communities of a floodplain forest in the Central Amazon

“…This occurs because the flood travels through the igapó forest from the low levels to the highest topographies, corroborating the concept of lateral connectivity proposed by Ward (1989). However, in the Uatumã area, lateral connectivity was altered along the entire topography (Rocha et al 2019). The suppression of flooding in the high quotas of the Uatumã area acted as a limiting factor for the establishment, for example, of A. jauari.…”

Mega-dams and extreme rainfall: Disentangling the drivers of extensive impacts of a large flooding event on Amazon Forests

“…A critical need to reformulate EIAs for the licensing of hydroelectric dams was also pointed out in a recent study in which the authors observed the multiple effects after the installation of the Balbina hydroelectric dam in central Amazon. The operation of this hydroelectric plant drastically changed the natural flooding pulses of the Uatumã River downstream of the dam [ 51 ]. Flooded area by Balbina was predicted by Eletronorte to be 1654 km 2 , while posterior analyzes detected 2996 km 2 [ 29 , 52 ].…”