AVAILABILITY AND MOBILITY OF ESSENTIAL ELEMENTS ALONG THE SLOPES OF OROBA VALLEY, WINAM GULF CATCHMENT, KENYA

Abstract

The human body depends solely on the soil to obtain essential elements for proper physiological function; therefore, depletions or inadequate uptake of essential elements from soil would negatively affect the health of a human being. Soil erosion is a key driver that may affect soil nutrient supply. The study investigates the availability, mobility, and health implications of essential elements along the gradient of pilot plots of Oroba Valley, Winam Gulf. Soil Erosion is a challenge in the Oroba Valley catchment as the upper part of the valley has steep slopes that rapidly drop from 1,131 m to 929.7 m above sea level over a distance that <1km. This area experiences high rainfall ranging between from 1310 to 2268 mm m-1. The highest recorded soil erosion risk at the Oroba Valley is along the escarpment ranging from 11 > 50 t ha-1 yr -1. An increase of both agricultural land and settlement in the study area between 2013 to 2022 with an increment of 27891 ha and 1958 ha respectively shows the population growth in the study area. Much of the vegetative cover has been converted into agricultural land and wetland with a decrease of 16759 ha between the study periods. Soils collected from pilot plots one and two were analyzed for essential elements and soil characteristics. Soil pH for both the pilot plots one and two ranged from 5.4 to 6.11 which are calcareous while the organic matter (Loss on Ignition - LOI) ranged from 5.42 to 11.12 and 5.99 to 7.82 for plots 1 and plot 2, respectively. Soil Iodine was analyzed in which plot one concentration ranged from 5.33 mg kg-1 to 12.12 mg kg-1 which was higher than in plot two, which ranged from 3.68 mg kg-1 to 4.81 mg kg-1. Thirteen essential elements were analyzed in this study from both soil and plants. Total elements (Acid extract) and plant available (EDTA extract) concentration were deduced. Essential elements Na, Mg, P, S, K, Ca, Cr, Mn, Fe, Cu, Zn, Se, and Mo were analyzed. Iron in soil extracted with EDTA correlated with the concentrations in the plants, with an r2 of 0.4316. The presence of molybdenum in the soil enhances the uptake of calcium in soil by a variance of 2.07, as indicated from soil analyzed by EDTA extraction. Essential elements are majorly obtained through the food chain which is channeled through soil, plants, and animals. Erosion is a main major cause of risk of depletion of essential elements from the soil. The elements' distribution in both plots was mainly affected by their solubility to in water molecules. Each essential element supports the human body's physiological process, which is at risk due to the depletion of the elements in the soil. As soil is the main reservoir that supplies essential elements into the food chain that is soil –plants – animals. Soil erosion and land degradation remediation strategies should be implemented.