Nutrient enrichment can have fast and serious impacts on a receiving body of water. Excess phosphorus in particular, is a common cause of river and lake water quality failures in the UK.
Agricultural activities can have a significant influence on nutrient enrichment of rivers and lakes. Phosphorus and nitrate rich fertilisers spread on land can quickly be mobilised by rainfall – washing directly off the field with surface run-off, draining to under-soil drains into the nearby river, or leaching through the soil where they eventually reach the groundwater aquifer. Livestock can also be a major source of nutrient enrichment, particularly when urine and faeces directly enter the river during drinking (an act known as animal poaching). We are currently working with farmers and land owners to understand what can be done to prevent nutrient loss from fields as part of our Topsoils project. When nutrients are lost, they don’t only have an environmental impact but also an economic impact for the farm as they’re no longer helping the plant to grow as intended.
Nutrient inputs don’t only come from agriculture; we all have a part to play in how much phosphorus ends up in the rivers. For more information on household sources of nutrients visit the river status page.
- Applying fertilisers in the proper amount, at the right time of year and with the right method can significantly reduce how much fertiliser reaches water bodies.
- Keeping animals and their waste out of streams keeps nitrogen and phosphorus out of the water and protects stream banks.
- Planting certain grasses, grains or clovers can help keep nutrients out of the water by recycling excess nitrogen and reducing soil erosion.
- Planting trees, shrubs and grass around fields, especially those that border water bodies, can help by absorbing or filtering out nutrients before they reach a water body.
- Reducing how often fields are tilled (prepared for growing crops) reduces erosion and soil compaction, builds soil organic matter, and reduces runoff.
Nutrient enrichment can have two major effects on the environment:
“Eutrophication is a natural process that occurs in lakes, ponds and slow moving rivers. It is caused by an increase in plant nutrients. Phosphorus is needed by plants for growth, but our dietary choices, as well as an increased use of detergents and chemical fertilisers, is greatly increasing the amount of phosphorus in the environment and causing rapid river plant and algal growth. When this vegetation dies back, there is a spike of microbial activity as the plants are broken down. This leads to the removal of oxygen from the system, stagnation and ultimately fish deaths.”
Drinking water contamination
The time it takes for nitrate to travel through the soil can vary from days to years to decades depending upon the thickness of the soil on top of the chalk, as well as the soil type, with light sandy soils draining more freely than heavy clay soils. Therefore the quality of the water in the aquifer is often dependent upon land practices from many years ago. Across many groundwater sources in the CamEO catchment, nitrate levels are increasing. These concentrations are creeping closer to legal limits for drinking water and some have already exceeded this level (50mg/l), meaning that they need to be blended or treated before going into drinking water supply. Once levels reach a certain threshold (45mg/l) they become included in water company plans for nitrate stripping. This technology is effective but it’s also expensive and needs to be regenerated frequently. Dealing with the problem in this way isn’t a long term solution – with more groundwater aquifers being affected by rising nitrate, the option of blending high nitrate and low nitrate water together won’t be available for long, so more needs to be done to stop nitrogen from travelling into groundwater aquifers in the first place.