Nitrate has emerged as one of the most alarming and widespread contaminant of groundwater and surface water resources reported around the globe. Nitrate formation is an integral part of nitrogen cycle and is added either by the natural processes (atmospheric fixation, lightning storms) or through anthropogenic activities (fertilizer applications, septic tanks). Nitrate enters the hydrosphere easily, and its ingestion causes various health risks such as methemoglobinemia, cancer, diabetes, etc. on humans and to some extent on livestock populations as well. Agricultural practices and subsequent fertilizer application along with other anthropogenic activities are assumed to be the primary reason behind elevated levels of nitrate in groundwater.
Phosphorous and Nitrate Loading
Figure 1: Water pollution levels in major river basins related to phosphorus from agricultural, industrial and domestic activities. From: Mekonnen, M.M. and Hoekstra, A.Y., 2018. Global anthropogenic phosphorus loads to freshwater and associated grey water footprints and water pollution levels: A high‐resolution global study. Water resources research, 54(1), pp.345-358.
Figure 2: A satellite image of Lake Erie (Midwest, United States / Ontario, Canada) overlaid on a map of the lake and its tributaries (September 2011). This image shows the algal bloom (green) covering the entire western basin and beginning to expand into the central basin. Scientists are monitoring phosphorus discharge from farms in surface runoff and tile drainage, so they can recommend best management practices to farmers. Original source: Michigan Sea Grant.
Figure 3: Global occurrence of zones with high nitrate concentrations in groundwater. From Zhou, Z., 2015. A global assessment of nitrate contamination in groundwater. International Groundwater Resources Assessment Center. Internship report.
Figure 4: Areas with the highest risk of nitrate contamination of shallow groundwater water, United States. From Nolan et al. ( 1998). A national look at nitrate contamination of ground water. Water Conditioning and Purification, 39(12), pp.76-79.
Figure 5: Nitrate concentration in groundwater and nitrogen input at sampling sites in China, 2000-2012. From Gu et al. (2013). Nitrate in groundwater of China: Sources and driving forces. Global Environmental Change, 23(5), pp.1112-1121.