Riparian Deforestation Affects the Structural Dynamics of Headwater Streams in Southern Brazilian Amazonia

Abstract

Comparative studies of streams with altered versus conserved riparian zones are important to evaluate the degree of alterations caused by inappropriate use of these streams' vital buffer zones. The aim of this study was to determine the impact of riparian deforestation on the habitat structure of southern Brazilian Amazonian headwater streams, as well as to provide elements for impact assessment and the monitoring of these water bodies. We selected ten sites and two headwater streams at each site; one stream was located in an area with preserved riparian vegetation (pristine streams) and the other stream in a deforested riparian zone (altered streams). Stretches of these streams were analyzed across hydrological periods (dry period, beginning of the rainy period, and end of the rainy period) for hydromorphological aspects, water physical-chemical variables, and habitat integrity (proportion of forestation in buffer zones and habitat integrity index). Compared to pristine streams in all the hydrological periods analyzed, altered streams presented lower oxygen concentration (~1.0 mg/L), an increase of 1 o C in water temperature, and less organic material availability. We found that riparian deforestation affects habitat structure variability among hydrological periods, making them more homogeneous. Therefore, beyond the necessary broadening of the spatial scale of studies in this region, monitoring these understudied headwater stream environments is also crucial for determining the magnitude of deforestation effects on these vulnerable aquatic ecosystems.Key-words: riparian zone; environmental impact; lotic ecosystems; temporal variation; water physical-chemical conditions ResumoEstudos comparativos entre riachos com zona ripária alterada e conservada são importantes para avaliar o grau de alteração provocado pelo uso indevido desta zona tampão vital aos corpos de água. Logo, o objetivo deste estudo foi determinar o impacto do desmatamento da florestal ripária sobre a estrutura do habitat de riachos de cabeceira no sul da Amazônia, e fornecer elementos para avaliação de impacto e monitoramento desses corpos de água. Nós selecionamos 10 locais e em cada local 2 riachos, sendo um riacho localizado em área com floresta ripária preservada (riachos pristinos) e outro riacho com a floresta ripária desmatada (riachos alterados). Trechos destes riachos foram analisados durante 3 períodos hidrológicos (período de seca, enchente e vazante) para a caracterização de aspectos hidromorfologicos, variáveis físico-químicas e de controle para a integridade do habitat (proporção de floresta em área ripária e índice de integridade do habitat). Em relação aos riachos íntegros, em todos os períodos hidrológicos avaliados, os riachos alterados apresentaram menor concentração de oxigênio (~ 1,0 mg/L), aumento de 1 o C na temperatura da água e menor disponibilidade de material orgânico alóctone. Nós detectamos que o desmatamento da floresta ripária afeta a variabilidade na estrutura do habitat entre os períodos hidrológicos, torn...

Measurement of the Ecological Integrity of Cerrado Streams Using Biological Metrics and the Index of Habitat Integrity

“…HII may be recommended as part of those protocols, since it partly reveals effects of disturbance to the aquatic communities. HII remains an inexpensive measure of riparian zone structural variables such as canopy openness, litter bank volume, number of retention devices, proportion of benthic substrate components, and water temperature [54], and should be considered for monitoring riparian deforestation in Northern Brazil’s Cerrado river ecosystems. The HII is directly related to the degree of environmental conservation and has been successfully used in other studies to evaluate the integrity in aquatic systems [55,56,57,58,59].…”

“…Northern Cerrado rivers are similar to Amazonia rivers in that they vary throughout the rainfall and dry period cycle [60]. Bleich et al [54] found severe alterations in habitat structure (especially water temperature, oxygen, suspended materials, and nitrite concentrations) and availability of substrates (litter, trunks, and retention devices) in altered streams (measured by HII) in comparison to pristine ones. According to Pearson [61], current velocity is one of the main environmental correlates with species abundances and multivariate scores in tropical Australia.…”

Autochthonous primary production in southern Amazon headwater streams: Novel indicators of altered environmental integrity

“…In southern Amazonian, deforestation of the riparian forest also led to the loss of variability in headwater stream habitat structure across hydrological periods (Bleich et al, 2014). -Delgado et al, 2006).…”

“…The increased autochthonous primary production in altered streams, that are poor in nutrients in the southern Amazon (Bleich et al, 2014), reflects the greater insolation in these environments, which were previously shaded by riparian forest (Fletcher et al, 2000). However, the lower amount of algae during flooding in the southern Amazon reflects the possibility that rains scour these organisms.…”

“…The hypothesis is that autochthonous primary production increases in altered streams and varies among hydrological periods. Altered and pristine streams classifications were based in the habitat integrity index, where altered streams presented median value of 0.52 and pristine streams, 0.98 (Bleich et al, 2014). To test this hypothesis, we quantified the autochthonous primary production (presence of macroscopic periphytic algae, free algal biomass in the water column, and the richness and cover of aquatic herbaceous plants) of a set of headwater streams with and without riparian deforestation, and its variation among hydrological periods.…”