Potential impact of nitrate species migration on the subsurface environment of the Saga upland

The potential impact of agricultural nitrates on the subsurface environment and groundwater qualities of the Higashi Matsuura Peninsula [Saga Prefecture uplands, Japan] was evaluated. This geographical site’s phreatic aquifer receives various nitrate species from agriculture recharge and human waste disposal facilities. Most of the wells monitored showed high nitrate concentrations, well above the accepted standard indices. The levels of nitrates in any given area was dependent on the altitude and bedrock composition of the water table and on agricultural practices, particularly on fertilizer usage. At the higher altitudes, nitrate levels were found to be low because of increased water flow induced by the increased hydraulic head pressures. Conversely, nitrate levels in the lower areas were generally higher. In addition, we found that soil nitrate levels correlated with the seasonal use of agricultural fertilizers. The fate of the agricultural nitrates was also examined using a three-dimensional finite element model for simulating the groundwater flow and solute transport processes in fully saturated porous media. The predicted results obtained from the model were in satisfactory agreement with the experimentally obtained site-observed data. We also determined the groundwater concentrations of several soluble cations https://www.w3.org/1998/Math/MathML" display="inline"> [ Ν Η 4 + , Li + , Na + , K + , Ca 2 + and Mg 2 + ] and anions https://www.w3.org/1998/Math/MathML" display="inline"> [ Cl − , NO 3 − , ​ SO 4 2 − and PO 4 3 ] . Piper diagram analysis was used to critically segregate the data with respect to the sources of the dissolved groundwater constituents as well as modifications in the character of water passing through a defined area. In general, it was found that most of the groundwater samples tested were alkaline in composition.