Recovery of acidified waters in the UK

Recovery of acidified waters in the UK

June 2001 — May 2004

The RAW-UK project, completed in May 2004, was a large research programme with the remit of tackling four key areas of research (see list below.

Report Availability

The final report is also now available for download from this website. A separate executive summary of the report may also be downloaded. Both files are available as PDF files.

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Executive Summary

Summaries of the research findings for the four work packages are available in the pages listed below:

Project Summary

The key aims of this research programme were the development of methods and models for identifying chemical and biological targets for the recovery of acidified surface waters and predicting timescales, degree and spatial extent of recovery under current and future acid deposition loads. The programme also included a pilot project for the monitoring of metal deposition and cycling in an upland catchment ecosystem.

Work Package 1 focused on the improvement of models linking water chemistry with biological status, the re-evaluation of appropriate critical chemical limits for UK critical loads and the use of analogue matching techniques to determine reference conditions from fossil remains in lake sediments, providing a basis for setting recovery targets in acidified lakes.

In Work Package 2, the national stock at risk from acidification was assessed using novel methods and datasets for both lakes and streams. The impacts of acid deposition on lakes of conservation interest were assessed through critical loads modelling and palaeolimnological techniques. The UK critical loads dataset was expanded to include regional lake and stream datasets from various sources, resulting in much better coverage of surface waters in the most impacted regions of the UK. New critical loads data based on these sites were submitted to the international mapping and modelling programme in March 2004, while biological predictive models were applied to assess the extent of biological change in terms of probability of occurrence of acid-sensitive species. Methods for the dynamic modelling of stream status and risk of acid episodes across regional stream networks were developed through the identification of hydrological response units (HRUs) and application of the PEARLS model. The links between invertebrate status and chronic or episodic acidification were explored through chemical and biological surveys with additional transplantation experiments, providing input data for the development of a biological episode response model linked to catchment characteristics through the PEARLS model.

Work Package 3 entailed the further refinement and development of the dynamic acidification model MAGIC to incorporate nitrogen dynamics and links to biological models, providing regional assessments of damage and recovery under future deposition scenarios. MAGIC reconstructions were also compared with palaeolimnological and other methods and used as the basis for the re-evaluation of appropriate critical limits for UK freshwaters.

Monitoring of trace metal deposition and cycling at Lochnagar was continued under Work Package 4, resulting in the extension of the high quality continuous monitoring dataset to 7 years. Compartments sampled included bulk deposition, lake waters, terrestrial and aquatic plants, aquatic invertebrate fauna and sediment traps, with all trend analyses being updated.