Barely a day has gone by since the COVID-19 pandemic without river pollution being a news headline. Most of the headlines focus on the issues of excess effluent entering rivers. While a serious issue, this is not the only source of river pollution, nor do the press always go into detail about what river pollutants actually are, what their effects are and what safe levels would be.
What is Nitrogen?
Nitrogen is the 7th element (symbol: N) and the most abundant gas in the Earth’s atmosphere, making up around ¾ of air’s volume. It is a vital atom for life, being most commonly used in the ammino acids that are the building blocks of the proteins that control and build bodies.
Animals, including humans, take in nitrogen from the protein in their food and remove excess nitrogen through urination and defecation, including in the form of nitrates (nitrogen compounds bonded to oxygen), urea or, in the case of reptiles and birds, uric acid.
Plants cannot take in atmospheric nitrogen directly like they can with oxygen or carbon dioxide. Instead, they have to take in nitrogen compounds through their roots.
Nitrogen in rivers is most commonly found as nitrates, nitrites or ammonia, all common compounds of nitrogen. Ammonia is notable for it’s distinctive, pungent smell.
Where does it come from?
Nitrogen compounds are naturally produced through organic processes, but human intervention has increased the concentration of these compounds in our waterways.
Numerous sources, including as industrial discharges, wastewater treatment plants, leaky septic systems, fertilizer runoff from pasture and crops paddocks, and runoff from animal manure, can introduce nitrogen into our rivers.
Heavy rains can cause runoff containing nitrogen to enter our rivers and lakes. Vegetation buffers next to farms and rivers can help slow and filter runoff containing possible pollutants like nitrogen, before it reaches the waterway.
Nitrifying bacteria convert urea and ammonia into nitrites and nitrates that plants can use. The largest sources of urea and ammonia are sewage and agricultural fertilisers.
Nitrogen is naturally produced but also comes from fertilizer runoff, wastewater treatment plants and other sources.
Why is it a problem and what are safe levels?
When concentrations of nitrates are high, plants that can use this fertiliser quickly and efficiently grow out of control. This leads to large blooms of plants such as duckweed and algal blooms.
These plants then block light and capture nutrients in the water ways leading to an overall loss of plant life. This leads to a drop in oxygen levels and raising of water temperatures which will kill many aquatic species. High concentrations of nitrogen in our rivers can lead to algal blooms that block light for other plants, reducing biodiversity in a watercourse.
When the algae die, their decomposition uses up further oxygen. This process water enriched with nutrients that increases growth is known as eutrophication.
Under the Water Supply Regulations (2016), at the point where water exits a consumers’ tap water should have no more than:
- 50mg/l* of nitrate
- 0.5mg/l* of nitrite
- 0.5mg/l* of ammonia
*A note that mg/l is almost identical to parts per million (ppm).
Levels higher than this are not only unsafe for humans but also for most invertebrates and fish.
What can you do to help?
The Essex River Watch citizen science project collects water quality data on river health across the Essex Rivers Hub catchment (see our Essex Rivers Hub homepage for a map of the catchment that includes some areas of south Suffolk).
Join fellow citizen scientists in collecting valuable data on river health. By participating in simple observation surveys and water sample testing, you can help safeguard our vital waterways. No experience needed!
Sign up to the Essex River Watch here.
