Abstract
The most advanced stage of water erosion, the gully, represents severe problems in different contexts, both in rural and urban environments. In the search for a stabilization of the process in a viable manner it is of utmost importance to assess the efficiency of evaluation methodologies. For this purpose, the efficiency of low-cost conservation practices were tested for the reduction of soil and nutrient losses caused by erosion from gullies in Pinheiral, state of Rio de Janeiro. The following areas were studied: gully recovered by means of physical and biological strategies; gullies in recovering stage, by means of physical strategies only, and gullies under no restoration treatment. During the summer of 2005/2006, the following data sets were collected for this study: soil classification of each of the eroded gully areas; planimetric and altimetric survey; determination of rain erosivity indexes; determination of amount of soil sediment; sediment grain size characteristics; natural amounts of nutrients Ca, Mg, K and P, as well as total C and N concentrations. The results for the three first measurements were 52.5, 20.5, and 29.0 Mg in the sediments from the gully without intervention, and of 1.0, 1.7 and 1.8 Mg from the gully with physical interventions, indicating an average reduction of 95 %. The fully recovered gully produced no sediment during the period. The data of total nutrient loss from the three gullies under investigation showed reductions of 98 % for the recovering gully, and 99 % for the fully recovered one. As for the loss of nutrients, the data indicate a nutrient loss of 1,811 kg from for the non-treated gully. The use of physical and biological interventions made it possible to reduce overall nutrient loss by more than 96 %, over the entire rainy season, as compared to the non-treated gully. Results show that the methods used were effective in reducing soil and nutrient losses from gullies.
Highlights
In the last decades, the primary research focus in water erosion was mainly erosion from interrills, as well as along rills, for which experimental lots were used (Valentin et al, 2005) for the determination of soil loss rates linked to surface runoff under different climate conditions as well as soil practices, using empiric models (Poesen et al, 2003).The study of gully erosion has to date been neglected due to the difficulties of investigation and of prediction (Valentim et al, 2005)
There is a longstanding concern about the importance of this kind of erosion as sediment source, ignored so far in traditional assessments of water erosion
Three classical gully areas were studied using different practices of erosion control: (a) gully recovered by means of physical practices, and biological barriers; (b) gully under recovery by means of physical practices; (c) gully under no kind of intervention
Summary
The primary research focus in water erosion was mainly erosion from interrills (either laminar or superficial), as well as along rills, for which experimental lots were used (Valentin et al, 2005) for the determination of soil loss rates linked to surface runoff under different climate conditions as well as soil practices, using empiric models (Poesen et al, 2003).The study of gully erosion has to date been neglected due to the difficulties of investigation and of prediction (Valentim et al, 2005). The primary research focus in water erosion was mainly erosion from interrills (either laminar or superficial), as well as along rills, for which experimental lots were used (Valentin et al, 2005) for the determination of soil loss rates linked to surface runoff under different climate conditions as well as soil practices, using empiric models (Poesen et al, 2003). Santos et al (2002) stated that gully formation begins with interrill erosion (laminar or superficial), followed by concentrated runoff, initiating rill formation, which further evolves into gullies as a result of the increase in dimensions of the channel. Foster (1986), cited by Poesen et al (2003), stated that in 1980 the term ephemeral gully erosion was introduced aiming to include erosion in concentrated runoff at a greater scale than from gullies in rills, but less than from classical gullies. Bank gullies are channels formed as a consequence of the height of the water fall, resulting from the different level of the drainage area and the terrace or water stream, in places of erodible banks (Vandekerckhove et al, 2000)
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