[5] Modelling the effect of riparian vegetation restoration on sediment transport in a human-impacted Brazilian catchment

Abstract

Soil erosion threatens both soil and water resources and has 2 increases globally due to changes in land use, mainly the substitution of natural vegetation by agricultural crops and pasture, or the intensification of existing agriculture. Brazil is privileged by a large proportion of natural vegetation and abundant freshwater. Recently, a new Brazilian Forest Act (BFA) has been approved that offers landowners that had committed illegal riparian deforestation in the past amnesty from reforestation, and further reductions of riparian protected areas are currently discussed. Here. We used the Soil andWater Assessment Tool (SWAT) to simulate river discharge and sediment exports in a typical human impacted Brazilian catchment, the Rio das Mortes Basin in the Federal State of Minas Gerais. Our model simulated different scenarios of riparian zone reforestation and their benefits in reducing sediment exports. By restoring the riparian vegetation according to the BFA ignoring amnesties to land owners (i.e. 44.8% of the 200 km2 legal riparian corridor of the river, with a corridor width of 30–50 m), the current annual sediment yield of the catchment of 0.819 t/ha was reduced in 34%. Further, simulated reforestation twice the size demanded by the BFA (60–100 m corridor width) resulted by 34.8% reduction of the current sediment yield. However, reforestation of 5 m homogeneous riparian corridor only, as currently discussed in the Federal Brazilian State of São Paulo, reduced sediment exports by 28%, not considering expected additional erosion due to deforestation outside the simulated reforested 5 m corridor. Our study is the first basin-wide assessment of the role of riparian vegetation in preventing soil erosion in Brazil. Its results support intensive reforestation efforts of the riparian zone and point to substantial negative effects of further reductions of the protected riparian corridor width and amnesties from reforestation to land owners.