INVESTIGATING THE IMPACT OF MINING ACTIVITIES ON AGRICULTURAL AND HYDROLOGICAL PROCESSES: A CASE STUDY IN ST. JOHN WATERSHED KOKOYAH DISTRICT, BONG COUNTY, LIBERIA.

Abstract

For the past 12 years, gold mining has resulted in changes in land cover in the Kokoyah District, St. John's Basin, Bong County, Liberia. Changes in land cover have altered the basin flow, causing variation within the stream runoff and groundwater movement volume. This research centered on investigating the impacts of mining on agriculture and hydrological processes. The main focus was on assessing land cover changes due to mining that affects farmland, and stream flow. SURQ and GWQ determined the changes in the current flow with a place on the rainiest months from July to October and the most sunshine months of December to March with the help of remote sensing data and the Soil and Water Assessment Tool (SWAT) model. The satellite imageries of Landsat7 and Landsat8 from USGS earth explorer were obtained and processed in ArcGIS, and two land use land cover maps of 2008 and 2020 were created. The unsupervised classification was performed, and the accuracy of the classified maps was assessed by ground-truthing using GIS and Google Earth. The LULC analysis results show that mining sites and bare land increased by 16.75% and 26.83 % in 2020, while agricultural land decreased by 25.47 % in 2020. The two LULC maps used to run SWAT assessed the effects land cover changes had on agriculture and the streamflow. Therefore, 16 sensitive flow parameters were identified for the basin flow simulation. The model performance was evaluated with the help of coefficient of determination (R2), a Nash-Sutcliffe simulation efficiency (ENS), and a percent deviation (PBIAS). The R2, NSE, and PBIAS values during calibration were 0.89, 0.86, and -12.16 % and validation were 0.82, 0.82, -7.0 % respectively. The analysis from SWAT indicated that the average monthly streamflow for wet months (rainy season) and dry month (dry season) increased by 4.5 % for 2008 and 106 % for 2020, respectively. The streamflow evaluation was used to analyze the surface runoff (SURQ) and groundwater flow (GWQ). The SURQ increased by 32.4 % in 2008, while GWQ decreased by -15.7 % in 2020 due to the increased mining activity. These results indicate the impact of mining on land and water resources. Therefore, this result can be used to assess natural resources and agriculture activity within the ecosystem where mining activity is being carried out.