Effectiveness of tropical grass species as sediment filters in the riparian zone of Lake Victoria

Abstract

The effectiveness of tropical grass species in strips of different length in trapping sediment from cropland was assessed, and the influence of filter length was determined. The assessment was made under natural rainfall which induced sheet and rill erosion in run‐off plots and then using simulated run‐off which caused concentrated erosion. The evaluated grasses were elephant grass, lemon grass, paspalum and sugarcane. Run‐off plots were on a 10% slope in a randomized complete block design replicated three times. Filter lengths were 2.5, 5 and 10 m against a 10‐m‐long sediment source area planted with maize on a clay loam soil. The results show that sediment trapping effectiveness (TE) increases nonlinearly with increasing filter length for all grasses. Under natural rainfall, more than 70% of sediment was trapped in the first 5 m, and lengthening the strip to 10 m only resulted in a marginal increase in TE. With concentrated run‐off, more than 70% of sediment was trapped in the first 5 m and lengthening the strip to 10 m resulted in a significant increase in TE. Paspalum and lemon grass performed significantly better than other grasses (P < 0.05), owing to their spreading growth pattern over the soil surface. Paspalum also has the highest root density in the upper 0.3‐m layer of the soil followed by lemon grass, hence offering the greatest resistance to erosion from concentrated flow. The results demonstrate that tropical grass filter strips provide a viable means for reducing the sediment flux from cropland.

Sustaining reservoir use through sediment trapping in NW Ethiopia

“…Wanyama et al (2012) evaluated the STE of four tropical grass species, lemon grass (Cymbopogon citratus), elephant grass (Pennisetum purpureum), paspalum (Paspalum notatum) and sugarcane (Saccharum officinarum L.) in croplands in Uganda, under natural and simulated rainfall conditions. Due to their spreading growth pattern and dense network of fine roots, lemon and paspalum grass showed significantly greater STE than elephant grass and sugarcane.…”

“…The use of on-site sediment trapping measures can reduce soil loss by promoting sedimentation within farmers' fields Wanyama et al, 2012;Mekonnen et al, 2014b). Vegetative measures, for example grass barriers, are among the on-site measures that play a significant role in trapping sediments from overland flow (Ritsema, 2003;Blanco-Canqui et al, 2004;McKergow et al, 2004;Stroosnijder, 2009;Wanyama et al, 2012).…”

“…In this study, we split the ST measures into two categories: (i) those that promote sedimentation within farmers' fields 'on-site' measures and (ii) those outside the sphere of influence of individual farmers' fields 'off-site' measures. On-site ST measures reduce overland flow velocity and thereby retard sediment transport, resulting in sediment deposition within fields before sediment can be discharged into streams (Fiener & Auerswald, 2003;Lee et al, 2003;McKergow et al, 2004;Edem et al, 2012;Wanyama et al, 2012). Off-site ST measures reduce concentrated runoff velocity within the (ephemeral) gully and river channel system thereby enhancing infiltration of water and deposition of sediment into ponds and behind check dams (Fiener et al, 2005;Abedini et al, 2012) and into the riparian zone (Newson & Large, 2006;Keesstra et al, 2012).…”

“…The use of on-site sediment trapping measures can reduce soil loss by promoting sedimentation within farmers' fields Wanyama et al, 2012;Mekonnen et al, 2014b). Vegetative measures, for example grass barriers, are among the on-site measures that play a significant role in trapping sediments from overland flow (Ritsema, 2003;Blanco-Canqui et al, 2004;McKergow et al, 2004;Stroosnijder, 2009;Wanyama et al, 2012). This is because of sediment filtration and deposition (Dillaha et al, 1989), upslope ponding (Meyer et al, 1995;Spaan et al, 2005), and decreased flow velocity and increased surface roughness, which decreases sediment transport capacity of surface runoff (Borin et al, 2005).…”

“…For example; Lemon grass (72-92%), Elephant grass (62-84%), Paspalum (65-88%) and Sugarcane (56-82%) in Uganda (Wanyama et al, 2012); Vetiver grass (65%) in Australia (McKergow et al, 2004); Brome grass (70-85%) (Robinson et al, 1996) and Switch grass (92%) (Lee et al, 2000) in the USA; Centipede grass (24-73%) in Japan (Shiono et al, 2007); Black rye (42-69%) in China (Pan et al, 2010) and Vetiver (62%) and Desho (43%) in the lowland part of Ethiopia (Welle et al, 2006). The STE of Desho grass was tested by Welle et al (2006) in the lowland part of Ethiopia but not in the highlands where it performs best (MOARD, 2010).…”