Adebayo O. Oke

Conservation Strategies for Effective Management of Eroded Landform: Soil Structural Quality, Nutrient Enrichment Ratio, and Runoff Water Quality

Water erosion remains a major threat to soil and water conservation in the humid tropics and, thus, requires effective conservation measures to curb it. To quantify the efficacy of vetiver grass (Chrysopogon zizanioides L.) strips and mulch in soil structural quality buildup and in reducing the eutrophic quality index and enrichments ratios of major nutrients, a study was conducted between 2007 and 2009 on eroded landform (8% slope) of a Typic Kanhapludalf in a subhumid region of southwestern Nigeria. Treatments were vetiver buffer strips (10 m vetiver grass strip [VGS]), vetiver mulch (6 Mg ha−1 vetiver grass mulch [VGM]), combined vetiver strips and mulch (10 m VGS + 4 Mg ha−1VGM), and a control (no buffer strips or mulch). Soil structural quality estimated by water-stable aggregates at 0- to 5-cm depth increased by 36%, 73%, and 64% under 10 m VGS, 6 Mg ha−1 VGM, and 10 m VGS + 4 Mg ha−1 VGM, respectively, more than the control. The corresponding increase in mean weight-diameter under the vetiver systems was 30%, 42%, and 47% higher than the control. The water-stable aggregates and mean weight-diameter at the 5- to 15-cm depth followed a similar trend in the 0- to 5-cm layer. The resistive potentials of the vetiver systems in reducing soil loss, sediment-associated nutrients, total suspended solids, and eutrophic quality index were significantly higher than the control because of an increase in surface hydraulic roughness, which were in the order of 6 Mg ha−1 VGM < 10 m VGS < 10 m VGS + 4 Mg ha−1 VGM. Application of 6 Mg ha−1 VGM appear to be better than 10 m VGS and contributed to the reduction of runoff and enrichment ratios, thus, changing the order to 10 m VGS < 6 Mg ha−1 VGM < 10 m VGS + 4 Mg ha−1 VGM. The results indicate that an integration of vetiver buffer strips and mulch (10 m VGS + 4 Mg ha−1 VGM) had a better control of runoff, soil loss, sediment-associated nutrients, and water quality degradation, as well as improving soil structural quality buildup when compared with vetiver buffer strips or mulch alone.

Classification of river water quality in Ogun and Ona River Basins, Nigeria using CCME framework: Implications for sustainable environmental management

Abstract The limitation posed by the traditional comparison of water quality indicators with guide values or acceptable limits has necessitated the use of water quality indices. Most water quality indices depend on use of weighting factors which have the problem of subjectiveness. These limitations have been overcome by the Canadian Council of Ministers of the Environment (CCME) framework which estimates scope, frequency and amplitude of impairment to water quality status. The framework was used to create 3 Water Quality Indices (WQI) for Agricultural, Health and Environmental evaluation of water quality in the Ogun and Ona Basins which cover 8 rivers, with 27 gauging locations. 32 physical, chemical and microbiological water quality indicators were monitored over a 12-month period. The CCME scores showed that Health WQI ranged between 21 and 42 which rank all the rivers and locations as poor. Environmental WQI was 41–76 which ranks the basins between marginal and fair, while the Agricultural WQI was between 31 and 59; thus making river water quality poor and unfit for aquaculture even though, adequate for irrigation with the acceptable EC (<2.0 dS/m) and low SAR (<1.0). The WQI patterns across the basins were mapped with GIS which reveal specific communities and areas with high pollution levels. The water quality status poses a negative impact on sustainable utilization of river water unless efforts are made to control negative anthropogenic activities in the basins.