Abstract
Soil erosion has become a serious problem in recent decades due to unhalted trends of unsustainable land use practices. Assessment of soil erosion is a prominent tool in planning and conservation of soil and water resource ecosystems. The Universal Soil Loss Equation (USLE) was applied to Nyabarongo River Catchment that drains about 8413.75 km2 (33%) of the total Rwanda coverage and a small part of the Southern Uganda (about 64.50 km2) using Geographic Information Systems (GIS) and Remote Sensing technologies. The estimated total annual actual soil loss was approximately estimated at 409 million tons with a mean erosion rate of 490 t·ha−1·y−1 (i.e., 32.67 mm·y−1). The cropland that occupied 74.85% of the total catchment presented a mean erosion rate of 618 t·ha−1·y−1 (i.e., 41.20 mm·y−1) and was responsible for 95.8% of total annual soil loss. Emergency soil erosion control is required with a priority accorded to cropland area of 173,244 ha, which is extremely exposed to actual soil erosion rate of 2222 t·ha−1·y−1 (i.e., 148.13 mm·y−1) and contributed to 96.2% of the total extreme soil loss in the catchment. According to this study, terracing cultivation method could reduce the current erosion rate in cropland areas by about 78%. Therefore, the present study suggests the catchment management by constructing check dams, terracing, agroforestry and reforestation of highly exposed areas as suitable measures for erosion and water pollution control within the Nyabarongo River Catchment and in other regions facing the same problems.
Highlights
The global freshwater is only 2.5% of total global water of which a little more than 1.2% is surface water [1]
Soil erosion maps are presented with double units where 15 t·ha−1 ·y−1 = 1 mm·y−1 according to Food Agriculture Organization (FAO) recommendation [57,61]
When taking into accounts land cover and land use (C) and support practice (P) factors in 2015, the catchment is associated with an actual soil erosion rate of 490 t·ha−1 ·y−1 or 32.67 mm·y−1 and 22% of the catchment is exposed to extreme soil erosion of 2178 t·ha−1 ·y−1 or 145.2 mm·y−1 that contributed 97.8% of the total annual soil loss (Figure 4b and Table 4)
Summary
The global freshwater is only 2.5% of total global water of which a little more than 1.2% is surface water [1]. Every day, 2 million tons of sewage, industrial and agricultural waste are discharged into the world’s water [2]. Humans have increased the sediment transport by global rivers through soil erosion (by 2.3 ± 0.6 billion metric tons per year) [3]. Pollution can be so severe that the fresh water is no longer usable without incurring unacceptably high cleanup costs [4]. Res. Public Health 2016, 13, 835; doi:10.3390/ijerph13080835 www.mdpi.com/journal/ijerph
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