Reduction of sediment yield by riparian vegetation recovery at distinct levels of soil erosion in a tropical watershed

Abstract

Riparian vegetation plays an important role in sediment retention, thus reduces sediment yield in watersheds. The Brazilian Forest Law (Law 12,651/2012) requires maintenance of fixed-width buffers of riparian vegetation but allows the continuity of agriculture, livestock, and forestry farming activities in some parts of the Areas of Permanent Preservation (APP). This paper aimed to evaluate sediment reduction by recovering the APPs with vegetation strips of permitted widths (5, 8, 15, and 30 m), as per the Forest Law. We considered three land use scenarios that present distinct erosion rates - predominance of areas with forest cover, pasture, and agriculture. The Soil and Water Assessment Tool (SWAT) model was used to simulate sediment yield in these scenarios at the Jundiaí-Mirim Watershed in São Paulo, Brazil. The SWAT was calibrated and validated for monthly streamflow. We obtained statistical indices for the processes of calibration and validation, respectively, as: NS = 0.77 and 0.70, PBIAS = -10.2 and -12.5, and RSR = 0.48 and 0.55. The highest reduction in sediment yield (30%) was observed with the total recovery of the APPs (vegetation strips of 30 m) in the current land use scenario. The recovery of the APPs with vegetation strips of 5, 8, and 15 m yielded sediment reduction below 10% in the alternative land use scenarios. The APP strips with reduced recovery maintained high rates of sediment yield. Additionally, even with a total recovery of the APP it is necessary to adopt soil conservation practices throughout the basin’s agricultural area to minimize the impacts on water resources.

Benthic Macroinvertebrates Associated with Riparian Habitat Structural Diversity in an Eastern Amazon Stream Urbanization Gradient

“…Catchment modification, land use and local or stream reach habitat conditions and river flow runoff influence hydrodynamics and the particle size of sediments and their transport or deposition (Silva et al, 2007;Zerega et al, 2021). The highest percentages of gravel were found in altered and impacted areas, where accelerated erosive processes occur, associated with the removal of riparian vegetation (Martins et al, 2021b), lower RHDI scores and as a likely result of rapid washout, fine sand and very fine sand were consistently lower and highly variable in Altered and Impacted areas, respectively.…”

Strategies and Public Policies for Soil and Water Conservation and Food Production in Brazil

“…Increase soil organic matter [39,55,100,101] Avoid soil compaction [40,[102][103][104]] Avoid the use of pesticides [37,105] Consider the capacity of use and agricultural aptitude of land [106] Maintain the areas of permanent preservation and riparian vegetation [107] Under no-tillage conditions (Figure 6), due to a lack of soil mobilization, a more stable and porous structure can be formed, and newly formed pores and the rearrangement of soil particles can be preserved if operations are carried out with machines with low ground pressure [108]. Furthermore, the highest soil runoff rate was observed in a farm under conventional tillage conditions, while farms using no-tillage systems in the long term had the lowest rates [59].…”