Nutrient Reduction in Rivers

Currently the EPA is reviewing IPPC licenses with a view to ensuring compliance with the Surface Water Regulations (S.I. 272 of 2009). The regulations set new ambient concentration limits which include stricter limits on nutrient (Nitrogen & Phosphorus) concentrations in surface waters.

Over the past 20 years strenuous efforts have been made to reduce nutrient inputs to our rivers, lakes and coastal waters. Excess levels of nutrients can lead to eutrophication which in turn damages ecosystems. Emissions to waters include both point source (industry, municipal wastewater treatment plants etc.) and so called diffuse sources such as those from agriculture.

However there is little information available on the impact on rivers of reductions in nutrient inputs over time. A recent report has shed some light on this issue.

The scientists (Bouraoui F. & Grizzetti B., 2011) found that some river basins experienced increases in nutrient concentrations despite reduced anthropogenic input. Looking closely at two case studies, the Elbe in Germany and the Loire in France, they found that this could be partly explained by a time lag in the transport of excess nitrate into the groundwater as well as by storage of nutrients in soil and aquifers.

For the Elbe and the Loire, the scientists calculated time lags of 8 and 14 years, respectively, but previous research suggests this could be up to 40 years for some rivers.

The targets for Ireland, set under the Water Framework Directive, are to achieve ‘good’ nutrient status by 2015, 2021 or 2028. These targets may not be met based on the above research. It is accepted that for most cases in an Irish context, nutrient inputs from diffuse sources (eg agriculture) account for the majority of nutrient discharges to surface waters.

The agricultural sector was encouraged by Teagasc to spread excessively high P loadings on land up until the 1990s. If the impact of this poor advice will really take 40 years to flush through the system then we can expect that ‘good’ nutrient status may not be achieved in some lakes and rivers until the 2030s, regardless of what limits are placed on point source emissions.