Dynamics of surface runoff and soil loss from a toposequence under varied land use practices in Rwizi catchment, Lake Victoria Basin
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Date
2017
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of Soil and Water Conservation
Abstract
In this study, we quantified surface runoff and soil loss along a toposequence considering
four land use systems and three topographic segment positions in Rwizi catchment,
Lake Victoria Basin (LVB). The land use systems were grassland dominated by a local species
known as “Omugugu” (Cyperus spp.), tree plantation of pine (Pinus sabiniana) and eucalyptus
(Eucalyptus globus), mulched banana (Musa Paradisiaca), and unmulched banana, topographically
located on the foot slope, midslope, and summit. Runoff and soil loss magnitude and
trends under varied rainfall regimes were measured using closed runoff plots measuring 2 ×
20 m (40 m2). A split plot experimental design was adopted for the study. In total, 36 runoff
plots were installed considering the land use and topographic factors with three replications.
Observed monthly rainfall values varied from 9.3 to 167 mm (75 ± 54 mm). Annually, the
registered rainfall depth was 680 mm. The annual rainfall depth was below the long-term
annual mean for the area. Nearly all rainfall events with a depth greater than 10 mm contributed
relatively heavy runoff, while rainfall events less than 10 mm in general caused minor
surface runoff at the sites. Annual runoff within the catchment at the studied sites varied from
42 to 411 m3 ha–1 y–1. The average observed cross-site annual runoff was 151 ± 95 m3 ha–1 y–1.
Results show that annual runoff was in the order of tree plantation > unmulched banana sites
> grassland = mulched banana. Soil losses were greatest (1.5 t ha–1 y–1) and lowest (0.8 t ha–1
y–1) on unmulched banana and mulched banana sites, respectively. Annual soil loss showed
an increase with topographic slope segment position. Average annual soil loss on the upper
slope position facets (1.7 t ha–1 y–1) were 2.4 folds higher than those observed on the footslope
position facets (0.7 t ha–1 y–1), giving a percentage difference of 83%. We did not detect a statistical
difference in runoff (p > 0.05) due to either land use system or toposequence position.
However, statistical differences were observed in soil loss (p < 0.05) for land use system and
toposequence position. While the observed annual soil loss magnitude is within the tolerable
thresholds, a sustained maintenance of best land use practices is still critical in maintaining the
delicate balance on the fragile hillslopes in the study area.
Description
Keywords
Lake Victoria Basin, Land use system, Runoff, Soil loss, Toposequence
Citation
Bamutaze, Y., Wanyama, J., Diekrugger, B., Meadows, M., & Opedes, H. (2017). Dynamics of surface runoff and soil loss from a toposequence under varied land use practices in Rwizi catchment, Lake Victoria Basin. Journal of Soil and Water Conservation, 72(5), 480-492. doi: 10.2489/jswc.72.5.480