Responses of the fish community to the flood pulse and siltation in a floodplain lake of the Trombetas River, Brazil

Abstract

The distributions of the fish species were examined in relation to environmental variables, to evaluate the effects of environmental degradation on the fish community of Batata Lake, a typical Amazonian clearwater lake. From 1979 to 1989, tailings composed of water and clay, extracted from bauxite by water jets, were discharged into Batata Lake. The tailings spread into about 30% of the lake's area, where the level of the lake bottom rose and turbidity increased. In the present study, multivariate analyses were performed on data for environmental parameters and fish density and biomass. Fish were collected with gillnets during the annual hydrological cycle (filling, flood, drawdown and dry periods), in the silted area, the partly silted area (intermediate) and the natural area. Values of the Shannon index, density and biomass were compared among areas and periods to evaluate the effects of the tailings on community structure. Sediment resuspension, which reduces transparency, is accentuated in shallow water, and was the main factor regulating differences in the community structure between the natural and silted areas. The decrease in transparency occurs mainly during the filling period in the silted area and during the low-water period in the silted and intermediate areas, when sediment resuspension increases concentrations of nutrients and chlorophyll-a. The strong influence of migratory and piscivore species in low-transparency waters is likely associated with the greater bacterioplankton productivity and turnover rate observed by other authors in the silted area, increasing the importance of the heterotrophic food chain in Batata Lake. Reduction of transparency in the silted area was a selective factor for fish species. The death of part of the flooded forest vegetation was decisive in lowering densities of the igapo´-associated species in the silted area. The unconsolidated substrate, the death of part of the igapo´forest and the negative effects of low transparency -inhibiting resident visually oriented species in the affected areas -are the main factors causing the low diversity in the silted area as a whole. The correlations between CPUEs, conductivity and nutrients and chlorophyll-a concentrations do not appear to reflect cause-effect relationships, indicating that these environmental parameters are poor predictors of fish density in Batata Lake. Hydrobiologia (2005) 545:75-91 Ó Springer 2005

The role of Campsurus notatus (Ephemeroptera: Polymitarcytidae) bioturbation and sediment quality on potential gas fluxes in a tropical lake

“…Because of the colloidal and unconsolidated features of the clay, there are still bauxite tailings Hydrobiologia (2007) 586: 143-154 149 suspended in the water column, with huge consequences for plankton (Bozelli, 1994;Ané sio et al, 1997;Huszar & Reynolds, 1997) and fish communities (Lin & Caramaschi, 2005). However, the sediment was the most affected compartment since the disturbance destroyed some ecological niches and created others.…”

Feeding ecology of Auchenipterichthys longimanus (Siluriformes: Auchenipteridae) in a riparian flooded forest of Eastern Amazonia, Brazil

“…In eastern Amazonia, this species is very abundant in flooded environments, called várzea or igapó (Merona et al, 2001;Lin & Caramaschi, 2005;Montag, 2006). These environments are formed during the rainy season which the high water level inundates the riparian forest (Barthem & Goulding, 2007).…”

Influence of environmental parameters on fish assemblage of a neotropical river with a flood pulse regime, Central Brazil

“…It makes interactions between the aquatic and terrestrial environment possible (Junk et al, 1989), regulates the model of the aquatic communities (Quirós & Baigún, 1985;Townsend, 1996;Rodrigues et al, 2002), propitiates the high diversity of the lotic environment associated to the floodplain because of the elevated heterogeneity of the habitat (Luiz et al, 2004;Thomaz et al, 2007), including in clear water rivers (sensu Sioli, 1984), such as the Mortes River, characterized by a low concentration of nutrients, but that support a rich aquatic flora and fauna (Goulding, 1993). It also modifies the limnological characteristics of rivers because of the quantities of organic matter received from the floodplain (Townsend, 1996), and influences the fish-environmental parameter relationship (Lin & Caramaschi, 2005). However, Junk & Wantzen (2003) state that systematized and detailed studies about the influence of the hydrology and hydrochemical parameters on flora and fauna of Neotropical rivers with a floodplain are scarce.…”