Under the Water: Amazon Streams Structural Complexity and Conservation

Aquatic ecosystems are the most threatened in the world and instream disturbances can lead to biodiversity and other environmental services losses. The current understanding of changes in neighboring land-use influences on physical and chemical habitat (PCHab) is limited to temperate zones. However tropical streams are under increased pressure from landscape changes. In our study we assessed landscape and local-scale drivers of change in the PCHab condition of 99 streams of two eastern Amazon regions. Extended forest models explained 1.7 to 35.3% of the variance in PCHab metrics.  There were few congruencies between PCHAb explained by the predictors between the two regions, and most metrics were explained by multiple predictors. Nevertheless, we observed a strong threshold at 70% to 80% catchment forest cover above which water temperature was consistently lower. Sand+fine substrate also responded to catchment forest (6.4%), but woody debris responded to local forest (11.2%), and water column cross sectional area responded to stream-road crossings (10.8%). Our findings highlight the difficulties in generalizing about streams in such structurally diverse and heterogeneous systems that are affected by a variety of disturbances at a variety of scales. Therefore a multidimensional approach is needed when thinking about stream protection and rehabilitation.