Land use impact on soil erosion at different scales in the Brazilian semi-arid

Julio Cesar Neves Dos Santos,Maria João Simas Guerreiro,Eunice Maia De Andrade,Helba Araújo De Queiroz Palácio,Pedro Henrique Augusto Medeiros

doi:10.5935/1806-6690.20170029

Abstract

Erosion and sediment transport processes are strongly dependent on the spatial scale and land use. The objective of this study is to analyse the effects of slash and burn of vegetation followed by grass cultivation for grazing, on the hydrological and sedimentological behaviour at different spatial scales in a semiarid region in Brazil. Rainfall, runoff and soil loss were measured during three years (total of 116 rainfall-runoff events) at three spatial scales: 1 m² and 20 m² plots and 2.8 ha watershed. During the first year (2009) the native dry tropical forest/Caatinga vegetation was maintained, whereas on the following years (2010 and 2011) the original vegetation was cleared using slash and burn techniques to grow pasture (Andropogon gayanus Kunt). Annual runoff coefficient is highest at the 20 m² plot among the investigated scales. Runoff presented the same trend in all years. Sediment yield was strongly influenced by the land cover. Slash, burn and pasture cultivation strongly impacted sediment yield: the first two events after the land cover change yielded roughly ten times more sediment than similar events in the years with native cover and after grass development. The change was most noticeable at the catchment scale due to erosion along the stream, redefining the drainage network.

Highlights

Soil erosion is a process of detachment and transportation of soil materials by rainfall and runoff, wind, gravity and other natural or anthropogenic agents that disaggregate and remove soil materials at one point on the Earth’s surface and deposit it elsewhere (VERHEIJEN et al, 2009)
Burn and pasture (Andropogon gayanus Kunt) cultivation produced an intense change in sediment yield on the studied semiarid area, especially in the first runoff generated events when the catchment was still adapting to the land use change
In the first two events after the land cover change, sediment yield was increased by at least ten times of that observed for similar rainfall evens in the years with native dry tropical forest cover (2009) and after grass full development (2011); 2

Summary

Introduction

Soil erosion is a process of detachment and transportation of soil materials by rainfall and runoff, wind, gravity and other natural or anthropogenic agents that disaggregate and remove soil materials at one point on the Earth’s surface and deposit it elsewhere (VERHEIJEN et al, 2009). Water erosion includes rill and sheet erosion, with the detachment of sediment from the soil surface profile only (MERRITT et al, 2003). For simplification purposes the two processes are often considered together in erosion modelling: sheet erosion, through raindrop action and runoff, removes an uniform thin layer (or sheet) of the fertile upper soil horizon (DLAMINI et al, 2011); and rill erosion that scours and transports sediments through a concentrated flow of water in narrow, erodible channels (YAN et al, 2008). Changes in land use and land management may increase soil erosion. Chaplot et al (2005) concluded that land use change from forest to crops (9% to 100%) may increase rill erosion up to 600 %, and Gafur et al (2003) found that human intervention has influenced sediment yield in Bangladesh. The scientists of the aforementioned studies intentionally altered land use by slash and burn practices, changing hydrological behaviour and sediment yields in the studied plots

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