Abstract

This study was concerned with the insitu effects of the Dedza Pottery’s mining activities on vegetation diversity, and some selected physicochemical parameters. It was undertaken in six mining sites, five in Dedza and one in Ntcheu districts in Malawi. Each mining site was stratified into mined section (experiment) and unmined section (control). The study of vegetation diversity involved the identification and counting of species using the quadrat method. Soil study involved the random collection of soil samples from each section, and analysed for physical characteristics (pH, organic matter, moisture content and texture), and chemical characteristics (Ca, Cd, Cu, Mn, N, P, and Pb). The effect of mining on water quality was determined by collecting water samples at two occasions, before mining season (control) and during mining season (experiment). Water samples were analysed for physical parameters (Total suspended solids (TSS), pH, conductivity and turbidity), and chemical parameters (Cd, Cu, Mn and Pb). The rock samples were analysed for content of Cd, Cu, Mn, and Pb by complete decomposition using acids, while silica by molybdenum-blue calorimetric method. Data analysis involved the use of ANOVA and t-Test to compare characteristics in the mined and unmined sections. Species richness (SR) and species diversity index (SDI) were processed using Ecosim 7.0 ecological software. Relationships between parameters were carried out using Pearson correlation coefficient “r” aided by literature. Mining activities caused a reduction in vegetation species diversity as evidenced by a decrease in vegetation SR in the mined sections (p< 0.1). In the study sites of Mzengeleza, Kuthindi and Mmbale, mining affected the land through the creation of pits and pools, while at Kuthindi and Mzengeleza it encouraged soil erosion. Induction of bank failures was encountered at Kuthindi. The average texture of soils, changed from sandy clay loam (SCL) to clay (C), caused by the dumping of clay subsoils, while soil organic matter (OM) significantly decreased from 7.4 ±2% to 2.94 ± 3% (p<0.05). Available nitrogen in the soil declined significantly (p<0.05), from 0.0091± 0.005 mg/g in unmined sections to 0.0019 ±0.005 mg/g in the mined sections. The drop was attributed to the low OM content in mined sections, since OM and N correlated (r = 0.68; p<0.005). Soil moisture content increased from 2.5 ±2% to 7.5 ± 3% (p <0.05), v due to an increase in clay content in mined sections. The heavy metals (Cd, Cu, Mn and Pb) were generally higher in the topsoils of the unmined sections, as opposed to the mined, but lower than the critical content to cause danger. Low values in mined section could have resulted from the leaching of the metals due to low OM, on which they could have adsorbed or formed complexes and be retained. Cd correlated significantly with OM (r = 0.54; p< 0.05), showing possible formation of complexes with OM. Quartz and kyanite (raw materials) showed significantly high Cd values of 4.3 ±1 µg/g and 5.3 ±1 µg/g respectively. The values are above the critical limit (3 µg/g), raising concerns of danger in the environment. Mining also affected the physical characteristics of water (pH, TSS, and turbidity), as well as the chemical characteristics (Cu, Mn, and Pb). The heavy metals, Cu, Mn and Pb had concentrations of 0.04mg/L, 0.23 mg/L, and 0.13 mg/L respectively, which were within safe limits of the standards. This study therefore, showed that mining significantly affected the following aspects of the environment: species richness, land, and soil properties. There is a possibility of environmental contamination by cadmium through rock mining, when exposed to acidic environments in Dedza. At Kuthindi, mining affected the water quality through increases in the TSS and turbidity, but also caused a decrease in pH, threatening the aquatic life. Regular environmental monitoring visits to the sites by the EAD at district level, land remediation in the mined areas by the pottery, and production of a clear environmental management system, specifying roles of personnel, staff trainings, schedules, and reporting methods, are recommended, to effectively reduce the effects.

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School	: School of Natural and Applied Sciences
Issued Date	: 2008

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