Deforestation facilitates widespread stream habitat and flow alteration in the Brazilian Amazon

Stream flows and connectivity have been impacted by road crossings and other changes in land use worldwide, with potential negative impacts for aquatic biodiversity. We investigated how pervasive stream flow, habitat, and connectivity alteration is predicted to be in tributaries of the Brazilian Amazon, represented through stream impoundments. We mapped impoundments associated with roads or agricultural land use across the Amazon's Curuá-Una basin and identified landscape factors correlated with each type of impoundment. Impoundments were widespread, and deforestation and the land use changes it facilitated was the driving factor underlying their creation. We found, on average, one impoundment per 7.5 stream kilometers, or 3 km2, of deforested land, a concentration significantly higher than in areas of native forest, which had an average of one impoundment per 117 stream kilometers or 100 km2. Continuing to slow deforestation and agricultural conversion would reduce new agricultural impoundments and conditions facilitating soil erosion and subsequent impoundments at road-stream crossings. If Brazil's Forest Code can be effectively enforced, it could contribute substantially to slowing down deforestation and restoring areas already affected. There is an additional need for incentives for sustainable agricultural practices that directly reduce impacts to streams and remove in-stream cattle water impoundments. These possible solutions to address stream alterations would be strengthened by regulatory oversight for watershed management in the Amazon basin through implementation of existing Brazilian water laws, which could provide the groundwork for better valuing aquatic resources in the world's largest freshwater ecosystem.