Investigating Nitrate with Other Constituents in Groundwater in Two Contrasting Tropical Highland Watersheds

Nitrate is globally the most widespread and widely studied groundwater contaminant. However, few studies have been conducted in sub-Saharan Africa, where leaching potential enhanced during rainy monsoon phase. The monitoring found concentrations over drinking water standards of 10 mg N-NO3− L−1 groundwater, primary supply rural communities. Studies on nitrate movement are limited to volcanic Ethiopian highlands. Therefore, this study aimed evaluate transport fate identify processes that control concentrations. Water table height, nitrate, chloride, ammonium, reduced iron, three other constituents were determined monthly 30 wells two contrasting watersheds years first watershed was Dangishta, with lava intrusion dikes blocked subsurface flow valley bottom. remained within 3 m surface. second without barriers Robit Bata. dropped rapidly months end rain phase disappeared except near faults. average concentration both between 4 5 L−1. Hydrogeology influenced nitrogen. In by dikes, residence time aquifer larger than Consequently, high (in several wells, L−1) decreased slowly due denitrification. Bata, lower, peak only observed month after fertilizer application; otherwise, it an predicted using a multiple linear regression model. Hydrology explained biogeochemistry also significant.