Nitrate contamination of a rural aquifer and accumulation in the unsaturated zone

Groundwater contamination was studied in a rural setting of the Upper Pantanoso Stream Basin (UPSB) in the southeast of Buenos Aires Province, Argentina, where potential contaminant sources include inorganic fertilizer. Nitrate–N concentrations, greater than accepted level for safe drinking-water of 10 mg l⁻¹ were present in 36% of sampled wells and 67% of samples had nitrate concentrations exceeding the background level of 5 mg l⁻¹. Temporal fluctuation of nitrate concentrations in the groundwater was attributed to seasonal fluctuations in recharge and plant growth. Nitrate concentration was measured in deep soil profiles to determine the extent of leaching. Nitrate accumulation in the unsaturated zone of a soil cropped with potatoes was three times higher than the baseline N concentration found in the pasture. The greatest nitrate concentration in the soil profile occurred under irrigated corn where excessive nitrogen was applied. These results show that high fertilization rates and irrigation lead to increased hazards of groundwater pollution.