Report No SR 97 (01) F

August 1997

The Loch Dee Project was established in 1979 to assess the relative role of acid deposition and coniferous afforestation on surface water ecology. To undertake such a study, three sub-catchments under differing land-uses and the loch outflow have been sampled and monitored on a regular basis. This report reviews and considers the data collected, the changes in hydrochemistry and suggests options for the future of the Project.

The analysis of the seventeen years weekly spot sample data and selected continuous water quality data from the three sub-catchments and loch outflow at Loch Dee have illustrated the relative role of atmospheric deposition and land management practices on water quality.

The major findings and results of the review are:

• There is a decline in streamwater sulphate which is of the same order as the reduction in the atmospheric deposition of non-marine sulphate.
• Streamwater nitrate indicates no trend over the record.
• There is a large response to the incidence of atmospheric sea-salt incursions. These episodes are somewhat random in occurrence. However. the impact of several episodes over one winter can have an influence on several years water chemistry.
• The impact and magnitude of this atmospheric deposition is influenced by the differing land management in the three sub-catchments. The forested sub-catchments capture more of the atmospheric aerosols and consequently the streams have higher concentrations. For sulphate, this process may be slowing the recovery of surface waters to declining depositions of sulphur. The greater requirement of nitrogen by the forest. in comparison to shorter vegetation types. reduces the amount of nitrate lost to the surface waters.
• The calcium and pH response of the limed sub-catchment is significantly different to the other sub-catchments. However. some of the difference will be due to sub-catchment differences in geology and hydrological routing.
• Use of the MAGIC model to predict future change in water quality in the catchment suggests recovery under existing sulphur abatement strategies will be slow and limited. particularly in the presence of forestry.

It is suggested that for the future:

• The weekly sampling programme of bulk precipitation and water quality is continued.
• The hydrochemical data are supplemented with data on aquatic invertebrates.
• Judged against the maintenance and replacement costs of the continuous pH and conductivity monitors and other resource requirements of the project (eg. invertebrate data collection) it is suggested SEPA give careful consideration to their continued deployment.
• The Project and SEPA maintain and foster further collaborative links with other organisations actively involved with the aspects of environmental monitoring and research.

KEY WORDS: Upland water quality trends (annual. seasonal, episodes). acid deposition. afforestation. Acidification.

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