Authors: Michael Bruen, Anna Rymszewicz, John O’Sullivan, Jonathan Turner, Damian Lawler, Elizabeth Conroy and Mary Kelly-Quinn
Summary: The SILTFLUX project addressed three major objectives related to sediment pollution in rivers.
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The SILTFLUX project measured sediment flux at high temporal resolution and studied the biological response in selected river catchments of common typologies found in Ireland (focussing, on siliceous and calcareous geologies in combination with pasture and tillage land-uses). While sediment loads delivered by Irish rivers were low in comparison with many European rivers, deposited sediment was more closely associated with biological impact, although disentangling the impacts of sediment from other influences, such as nutrients, is challenging.
While further study is required before definitive sediment thresholds for impact can be established, a precautionary deposited sediment cover target not exceeding 20% is recommended for the upper reaches of river networks. However, for areas with sediment-sensitive species, a lower target may be advisable. Coordination of methods between agencies collecting sediment data is recommended to facilitate inter-comparison of datasets. SILTFLUX produced a checklist of measures to reduce and mitigate sediment effects in sensitive habitats.
SILTFLUX showed that, with care, turbidity can be used to estimate suspended sediment flux in Irish rivers, but that site and instrument specific calibration equations are required. Long term datasets of these variables are required to establish reliable relationships. The project produced a list of measures for reducing sediment loads and mitigating their effects. The project developed a modelling approach from its own data that could be extended with additional data to estimate sediment flux from ungauged small catchments which can contribute to a national sediment yield map.
The project showed that visual methods for estimating deposited sediment are useful and recommends that the methodology be standardised to enhance the usefulness of such data and in particular their relationship with reference conditions.