Climate change and eutrophication risk in English rivers: summary
Published 23 March 2016
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1. Chief Scientist’s Group research summary
This project investigated how climate change might affect eutrophication risk in rivers across England. Eutrophication is the term used to describe too much nutrient in water, causing algae and plants to grow excessively. This biological response can in turn result in dramatic reductions in available oxygen and damaging effects on fish and other freshwater life.
Reductions in river flow because of climate change could directly affect the concentration of nutrients and the risk of eutrophication. Phosphorus is considered the primary driver of eutrophication. This study looked specifically at how future changes in river flow may alter the dilution of phosphorus as a first step to understanding wider eutrophication risk
1.1 Overall approach
This work examined the relationship between current (2009 to 2014) phosphorus concentrations and river flows. The relationships been phosphorus and flow reflected whether sites were dominated by point sources of phosphorus (treated sewage discharges) or diffuse sources of phosphorus (catchment run-off). We then used these relationships to project future phosphorus concentrations by applying them to modelled river flow changes between a 1961 to 1990 climate baseline and the 2050s (2040 to 2069). We used time series of future river flows from 115 sites across the UK developed for the Future Flows and Groundwater Levels project. For each site we also showed how different future climate might affect the results. This helps us to understand some of the uncertainty in eutrophication risk as a result of uncertainty in climate projections. There is medium confidence that summer flows will decrease and Future Flows probably covers the range.
We plotted the concentrations of phosphorus for 3 different scenarios: the present day; a future plausible management scenario; and achieving good ecological status as currently defined by the EU Water Framework Directive (WFD) requirements.
1.2 Results
Changes in river flow as a result of climate change are likely to cause small increases in annual average phosphorus concentrations in rivers compared to the baseline.
However, this varies across the country and between climate change scenarios. Changes in phosphorus concentrations during the summer and low flow periods are of more relevance to eutrophication risk and show greater rates of increase than annual averages.
Improvements in wastewater treatment (a reduction to 0.5 mg l-1 phosphorus at each point source) have the potential to reduce future phosphorus concentrations and improve WFD status for phosphorus. However, these improvements alone are not sufficient to produce good phosphorus status at all the investigated sites, suggesting that further intervention would be necessary, for example by reducing inputs of phosphorus from diffuse sources.
The work has resulted in a national scale picture of flow related changes in phosphorus concentrations and indicates where we might need to target intervention to meet phosphorus standards in the future. More work would be needed to provide a more sophisticated assessment of eutrophication risk. Further work should take account of some of the other drivers of eutrophication such as warmer temperatures and the duration and timing of low flow periods. For example, periods of calm, stable weather and low rainfall can encourage the development of blue green algae. Conversely, more stormy weather could increase nutrient run off from agricultural land. It would be useful to compare, in different catchments, the contribution of changes in land use and management practice with those from managing sewage sources in controlling phosphorus concentrations in rivers.
1.3 Publishing details
This summary relates to information from project SC140013, reported in detail in the following output:
Report:
SC140013/R
Title:
Climate change and eutrophication risk in English rivers
March 2016
Project manager:
Matt Charlton, Evidence Directorate
Research Collaborator:
Centre for Ecology and Hydrology
Research Contractor:
Amec Foster
Wheeler Environment & Infrastructure UK Limited,
Cannon Court,
Abbey Lawn,
Abbey Foregate,
Shrewsbury
SY2 5DE, UK
Tel +44 (0) 1743 342000
This project was funded by the Environment Agency’s Evidence Directorate, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.
E: research@environment-agency.gov.uk
© Environment Agency.