On‐ and Off‐site Erosion Impacts of Restoration Measures in a Tropical Karst Watershed

Karst areas are vulnerable landscapes which, if unprotected, could be permanently degraded. To bridge the gap existing in the reduction of on- and off-site impact of restored tropical karst areas, this study was carried out in a 3.5 ha karst watershed of the Brazilian savanna (Cerrado). Precipitation, surface runoff, and soil loss were measured in representative runoff plots (22.1 x 1.84 m), used to assess the watershed erosion and sediment yield to a downstream sinkhole. The study was carried out during three hydrologic years, between September 2018 and May 2020. The predominant soils in the watershed were Lithic entisol and Quartzsamment, and the original land covers were natural savanna, seasonal forest, and degraded pastureland (Andropogon gayanus). The latter was restored with native savanna species, in the lower part of the watershed, and with a reformed pastureland, in the upper part. The USLE rainfall erosivity (R), soil erodibility (K), and soil cover (C) factors, runoff, soil loss, and the original soil and sediment textures were obtained from the runoff plots. The watershed soil loss and sediment yield were obtained by the USLE and GIS. Precipitation and rainfall erosivity ranged from 936 to 1223 mm, and from 6694 to 7746 MJ mm ha(-1) h(-1), in the period, respectively. Although the ecological watershed restoration reduced mean soil loss from 11.6 to 5.8 Mg ha(-1) year(-1), and sediment yield from 29.2 to 14.6 Mg year(-1), on- and off-site soil loss tolerances were still exceeded in 29 and 61% of the basin area, respectively. Ecological restoration also reduced the sand and clay content of the sediment entering the underground caves and river downstream, contributing to their hydrologic sustainability.