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Nitrate nitrogen and nitrite nitrogen are the nitrogen in the form of nitrate ions (NO3-) and nitrite ions (NO2-), respectively.
The main causes of groundwater polluted by nitrate nitrogen are the excessive amounts of fertilizer applied to crop fields, improperly treated livestock excrement and/or domestic wastewater.
The nitrogen containing therein, during the infiltration process from the ground surface into the soil, is converted into many different forms such as ammonia nitrogen, nitrate nitrogen, and nitrogen gas through series of microbial reactions and others.
Among these substances, the ammonia nitrogen is usually retained near the surface soil because ammonia ions which are positively charged are attracted by negatively charged soil particles. However, if the ammonia ions are converted into anions (e.g., nitrite ions and/or nitrate ions) by microbial reaction, such anions may easily flow out from the soil, which results in deeper infiltration of the anions into the subterranean strata, usually accompanied by percolating water such as rainwater
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