Stream Degradation: Direct and Indirect Impacts of Amazonian Deforestation

Abstract

The increasing demand for natural resources has accelerated deforestation in the tropics, resulting in impacts on freshwater ecosystems. The extent of deforestation is a critical factor in determining the stream’s physical habitat status condition. We evaluated the direct and indirect impacts of catchment and riparian deforestation on stream physical habitat conditions. To do so, we assessed how deforestation reduces allochthonous inputs, altering channel morphology, and ultimately leading to a decline in physical habitat condition. We used structural equation modeling to evaluate the effects of deforestation on physical habitat variables in 269 stream sites across Eastern Amazonia. We found that sites exhibiting higher physical habitat integrity were associated with greater forest cover in both the catchment and the riparian zone. The loss of riparian vegetation reduced organic matter inputs, decreasing the amounts of organic substrates and dead wood. Those changes resulted in increased sand deposits and lower physical habitat condition scores. However, natural variation in catchment morphology also played an important role, especially in predicting stream morphology features. The effects of deforestation are complex and depend on its extent. Nonetheless, riparian vegetation proved to be an important buffer against the effects of catchment deforestation, and its preservation is essential for maintaining good physical habitat conditions.