Environmental Water
The main concern for nitrates in surface waters are the triggering of Harmful Algal Blooms (HABs). Nitrates can enter surface waters through both point and non-point discharges, most commonly associated with agricultural run-off but also include landfills, wastewater and urban drainage.
While nitrates are an essential nutrient for growth, too much of the nutrient in a water body causes eutrophication which triggers rapid algae (including cyanobacteria) and plant growth. This will create a dense mat of algae over the water surface, blocking off light to the aquatic community and causing temperature change in the water. The increase in photosynthesis taking place for the algae can in turn reduce the amount of inorganic DOC whilst also raising the pH level to far higher than normal during daylight hours, impacting aquatic organisms which rely on electrochemical signals for survival.
The algae bloom cannot endure indefinitely but it’s decomposition only causes further problems as the amount of dissolved oxygen that is required to decompose the bloom causes a severe reduction in the amount available in the water for other organisms. This can lead to hypoxic conditions and eventual anoxia which is fatal to a wide range of aquatic life, creating dead zones where almost no organisms can survive. Depending on the environment, recovery can be complicated. Eutrophication can occur in both lakes, rivers and ocean environments and recovery can be difficult, particularly where a dead zone has been created. It can cause long-term change on aquatic community structure which will have further impacts on nutrient cycling and production in that location.
Algal blooms produce toxins which can be harmful to both aquatic and land-based life alike, presenting risk to anything that comes into contact with the water such as humans and dogs. There is some control in the UK in the form of ‘Nitrate Vulnerable Zones’ (NVZs) in which particularly vulnerable areas are identified and any producers of nitrate leachate in that area have stricter controls to prevent eutrophication. There is also an increasing use of buffer zones which favour plants which have a high nitrate uptake and can therefore remove nitrate from leachate before it reaches the water source.
Drinking Water
Nitrates can also pose a problem for drinking water as high consumption of nitrate affects how the blood is able to carry oxygen, leading to oxygen deprivation and blue baby syndrome. Babies that are bottle fed and under six months old are most at risk of the syndrome (Methemoglobinemia) which can lead to serious illness and death in the worst cases. In adults, high nitrate consumption has been linked with some cancers as well as other health complaints such as nausea, headaches and stomach cramps.
