A study on the impact of heavy metals on the diversity and adaptability of plants around north mara gold mine, Tanzania

Naturally, plants respond differently to elevated levels of heavy metals. Both the impact of gold mining wastes on the diversity of plant species at the study area and their responses to elevated levels of heavy metals had not been documented prior to the work reported in this thesis. Three parallel line transects of 3500m long, 100m apart were established perpendicular to the gold mine wastes. Cover abundance and composition of plant species were systematically recorded using nested quadrats along each transect. At each site where vegetations had been collected, soil samples were collected from depths of 0-15cm and 15-30cm. Samples from each depth were mixed to form a composite sample. Samples of plants and soils were analyzed for heavy metal (Cu, Pb, Cr, Zn, Cd and Ni) levels using AAS. Soils were also analyzed for pH. To assess plant species response to heavy metals, shoot and root portions of 30 plant species randomly sampled from 24 plots were used. Results indicated that there was a decrease of plant diversity and composition with distance from the mine wastes source. However, t-test showed that the decrease was not significant (p > 0.05). In addition, Monte Carlo Permutation test showed that the measured heavy metals were not significantly influencing the distribution patterns of plants. The decrease was probably caused by bioavailable Pb, Cr, Cd and Ni which were above the recommended ranges but not Cu and Zn. Of the species sampled for adaptability analysis; 20, 13 and 9 were found to be heavy metal hyperaccumulators, excluders and indicators/sensitive respectively. A plant species can be an accumulator of one element and/or excluder of or sensitive to another. Although the diversity and composition loss observed is not statistically significant this does not rule out the urgency of conservation measures to protect the flora and fauna of the studied area.