Application of nitrate fertiliser has helped feed the world’s growing population. However, nitrate leaching from soils can have potentially negative effects on ecosystems and human health.
Nitrate storage and release
The unsaturated (vadose) zone between the base of soils and the water table can be an important store of nitrate. Water moves slowly downward through the unsaturated zone and so a large store of nitrate can accumulate if this water contains nitrate derived from surface sources, such as fertiliser. Release of this store can affect ground- and surface-water quality for decades and it can continue for a long time after changes in farming practice that reduce nitrate leaching.
BGS nitrate transport research
We have been at the forefront of the science of nitrate transport in the unsaturated zone for the past 50 years. We undertook pioneering work in the 1970s to understand how different UK land-use practices affected nitrate leaching to groundwater and how nitrate moves through the unsaturated zone of the major aquifers. Nitrate transport velocities derived in this research have been used model both the amount of nitrate stored in the unsaturated zone and the timescales for peak nitrate concentrations at the water table at the national scale.
It will take decades for the peak to arrive over parts of Great Britain. This delay needs to be taken into account when setting timescales for improvements in water quality associated with land use changes.
Global nitrate storage
Recently, we developed a numerical model to estimate nitrate stored in the unsaturated zone at the global scale. This research revealed substantial increases in nitrate stored in the unsaturated zone globally, up to twice the amount of inorganic nitrogen stored in soils. The models developed in these projects are now being evaluated and compared against approaches used by other European Geological Surveys under the GeoERA groundwater project HOVER.
Our research into nitrate storage and transport in the unsaturated zone has had significant societal impact by supporting policymakers and increasing public awareness through media coverage. Our national-scale modelling supports environmental regulators in the re-assessment of nitrate-vulnerable zones and our hydrogeologists submitted oral and written evidence based on our research to the UK Government’s Environmental Audit Committee Enquiry on Nitrate.
You may also be interested in
We are researching groundwater extremes, the impacts of environmental and climate change on groundwater in the UK and internationally, and what this means for building a more resilient future for our water resources.