Ecology & Environmental Science

Effectiveness of measures to tackle diffuse pollution

Diffuse pollution from agriculture is a major cause for the failure to achieve objectives set out in the EU Water Framework Directive. A Programme of measures have been introduced with the aim of achieving good ecological status in surface water bodies; evidence is required to assess the effectiveness of these measures.

In 2006-7 a series of monitoring stations was established in sub-catchments of the Lunan Water in Angus, to collect data and to allow the effect of such measures to be separated from other factors, including hydrology and changes in land use, which can also have influenced water quality. In collaboration with the James Hutton Institute, BioSS looked at trends in concentrations and loads of nitrate, soluble reactive phosphorus, suspended solids and turbidity. Nutrient concentrations were obtained from fortnightly samples, but as flow was measured continuously, we were able to estimate quarterly loads using the modelled relationship between flow and concentration obtained from those occasions when concentrations were measured.

Although evidence for downward trends in nitrate concentrations was found, evidence for corresponding data in nitrate loads was not found. This apparent discrepancy is most likely due to the concentration data being more sensitive to change, since load estimates are greatly influenced by temporal variability in hydrology. Downward trends in concentrations might be interpreted by policy makers as demonstrating that regulations are having an impact, but a longer time frame would be needed to confirm the effectiveness of measures on loads.

nitrate concentrations Observed nitrate concentrations in the Lunan Water at Hatton, Angus, with fitted model incorporating seasonal variation and long-term trend.

Further details from: Luigi Spezia

Article date 2015

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