Tackling agricultural pollution
One of the key food security challenges is to make food production more sustainable. Agriculture is an energy intensive activity that produces different pollutants and so reducing agriculture’s environmental footprint is a major focus of research.
Ammonia from the manure of livestock farms and phosphorus from fertilisers are two common agricultural pollutants but scientists funded by the Natural Environment Research Council (NERC) are working to monitor and mitigate their unwanted effects.
Animal manure releases ammonia, a compound rich in nitrogen, into the atmosphere. Prevailing winds can then carry it a few kilometres where the nitrogen is deposited on soils and vegetation. The problem occurs when too much nitrogen lands on a nature reserve or in a river or lake and causes undue fertilization, or eutrophication, which in watercourses causes algal blooms that smothers and chokes other aquatic plants and animals and reduces biodiversity.
Dark algal blooms (left) smother other life forms on Fautec Beach.
Image: S. Haslett
Mark Theobald and colleagues at the Centre for Ecology and Hydrology, which has five sites across the UK, developed the SCAIL model (for Simple Calculation of Ammonia Impact Limits) to simulate the amount of nitrogen deposited downwind from a farm. The models uses an estimate of the ammonia emitted to the atmosphere, which depends on the type of farm and the number and variety of animals kept, along with weather parameters such as average wind speed and wind direction.
The model has been tested on eight pig, poultry and dairy farms of different sizes and types and the SCAIL model is now being used to screen pig and poultry farms located near nature reserves, according to new European Union directives (ref 1). The model can then flag which farms require a more detailed assessment and has been adapted to predict sulphur dioxide and nitrogen oxides emissions from small power plants.
Down by the river
Fertiliser ‘run-off’ from farms is also another source of agricultural pollution. It also causes eutrophication in rivers and water sources when nitrogen- and phosphorus-rich fertilisers are washed into rivers and ponds with detrimental effects.
Scientists funded by NERC have been researching river eutrophication for many years, and pinpoint two major sources: agriculture and household effluent from sewage treatment works and septic tanks. It’s crucial to know which is the main source, or if their contributions differ with the seasons for example, in order to draw up an effective, targeted strategy that best addresses the source of the problem.
Industrial and household effluent are major sources of pollution.
Image: Glen G. Becker
Ecologist Colin Neal and colleagues, also from the Centre for Ecology and Hydrology, have devised such a way to discriminate between agricultural and sewage industry pollution using the chemical element boron, which is used as a whitener in washing powders.
Boron ends up in rivers through the sewage system, and the NERC-funded researchers found that the concentration of phosphorus in English rivers follows the amount of boron (ref 2, ref 3). This tell-tale sign indicates that the two chemicals originate from sewage more than agriculture.
A significant amount of phosphorus from agriculture is trapped in soils and sediments and is washed into rivers by winter rain. At this time, water levels are high which dilutes the effect. On the other hand, phosphorus from domestic sewage is pumped into rivers throughout the year and greatest effects occur in summer when river levels are low. In an unfortunate double-whammy, sewage is less diluted during the summer months where the extra sunlight increases plant and algal growth.
Almost a billion pounds has been spent in the last 15 years in England and Wales removing phosphorus from sewage effluent
Identifying the main contributor to the problem is crucial. Almost a billion pounds has been spent in the last 15 years in England and Wales removing phosphorus from sewage effluent, whilst concurrently there are policy pressures to reduce phosphorus pollution from agriculture, which could affect farming livelihoods but have a less significant effect on reaching environmental goals such as the European Union’s Water Framework Directive that demands cleaner and biologically healthy rivers.
To make agriculture more sustainable without damaging rural economies, researchers advocate an integrated approach involving cost-effective solutions. This requires new multidisciplinary science that includes the complex interactions between the biology, chemistry and environmental impacts of aquatic habitats.
- A simple model for screening the local impacts of atmospheric ammonia (2009)
- The strategic significance of wastewater sources to pollutant phosphorus levels in English rivers and to environmental management for rural, agricultural and urban catchments (2009)
- Decreasing boron concentrations in UK rivers: Insights into reductions in detergent formulations since the 1990s and within-catchment storage issues (2009)