Efeitos da cobertura vegetal ripária sobre o metabolismo e biodiversidade de córregos de mata atlântica na bacia do Rio Guapiaçú, RJ

Abstract

Land cover changes cause physical alterations in lotic ecosystems, as reductions in shading and input of allochthonous organic matter, eutrophication and pollutants inputs. These modifications simultaneously influence both; community composition and ecosystem process, compromising ecosystems function and its capacity of to provide ecosystem services (e.g. nutrient cycling, supply of water and products derived from biodiversity). Ecosystem metabolic process (Gross Primary Production (GPP); and Ecosystem Respiration (ER)), are very important aspects to study when assessing the influence of riparian vegetation on stream ecosystems, since these rates are strongly influenced by shading, nutrient concentration, and input of allochthonous organic matter and also affects biodiversity. Tropical areas face high deforestation rates, while the regeneration capacity of tropical forests is smaller compared to temperate ones. This thesis presents descriptive studies evaluating influences of riparian deforestation and related changes in abiotic template in stream metabolism, macroinvertebrates diversity and distribution and abundance of freshwater decapods in Guapiaçu River catchment, RJ, as well as a literature review of studies about the impacts of land use in stream metabolism. The review of literature shows that urban and agricultural land use increases metabolic rates in streams, what was usually attributed to shading reduction and specially to the increase in nutrients concentrations, which can stimulate both GGP and ER. It was also verified that there is a large scarcity of studies about this theme in tropical forest ecosystems and just one study was found to streams in this biome. The studies conducted in Guapiaçú River catchment show that both GPP and ER of streams in Atlantic Rainforest are positively related to riparian deforestation increase. A path analysis model developed to describe the cascade effects linking riparian deforestation to metabolic alterations and biodiversity changes indicated that reduction in shading and increases in ammonium concentration led to a reduction in oxygen daily minimum saturation. This was in part caused by increase of oxygen consumption, as consequence of increased in PPB and R rates, this last one strongly influenced by ammonium concentrations. This reduction on oxygen saturation was the mainly variable related to macroinvertebrates biodiversity reduction, which was also negatively affected by shading reduction. Freshwater decapods were few abundant in the studied catchment and occurred primarily in highly shaded small streams with abundance of leaf litter substrates. We registered the occurrence of amphidromous species, what indicates the maintenance of relative ecosystem connectivity along streams and rivers in the studied catchment, since these organisms uses all stretches during their life cycles. This species can be locally extinct due the construction of a dam in lower Guapiaçú River (in progress), thus we recommended that mitigation actions (e.g. constructions of artificial passages) should be applied