Report No SR3408/1

Oct 1993

Peat deposits are common in Scotland and Northern Ireland and extraction for horticultural and fuel use, by a variety of methods, is concentrated in the Highlands and Islands of Scotland and in Northern Ireland. This review of the effects of the extraction process on receiving waters includes experience gained in Scotland and Northern Ireland, and in other parts of the world where peat extraction is more widespread.

The available information indicates that, in general, drainage and subsequent peat extraction activities result in an increase in the amount of water emanating from the catchment as both baseflow and stormflow. The quality of this runoff also changes as a result of drainage and extraction. In general the export of suspended material and dissolved organic matter is enhanced and increases in the nutrient content, metal content, colour and pH are observed under certain conditions.

The impact on receiving watercourses is highly site specific and is dependent on the scale of the extraction operation in relation to the size of the receiving watercourse. Increases in the biomass of bacterio-plankton and changes in the phytoplankton and periphyton have been observed in Finland and in macrophytes in Eire. Impacts on invertebrates and fish are less clear cut but are subjects of further ongoing investigations in Finland.

Pollution control measures commonly used to improve the quality of the runoff are aimed primarily at the removal of suspended solids and include settlement ponds, suitably designed drainage networks and overland flow areas. The Finnish National Board of Waters and the Environment have produced a set of guidelines for the protection of waters in peat mining areas in Finland. These guidelines have been reproduced in full in an Appendix as an example of the application of the pollution control measures as part of a wider strategy for the protection of waters in a peat mining area.

Discharge consents for drainage waters from peat extraction sites should always include suspended solids and pH, and additionally nutrients and colour where local conditions dictate. Discharge consents are not set in all areas of Scotland. Monitoring of discharges for compliance must take into account the rainfall related nature of the discharge events, particularly for suspended solids. Chemical monitoring using automatic samplers triggered by increases in flow and complementary biological monitoring may be considered.

As a result of the review a further study is recommended including an assessment of the toxicity of discharges from peat extraction sites. Both the harmonisation of consenting policy and the development of some guidelines for the protection of receiving waters in Scotland and Northern Ireland are also recommended. KEY WORDS Peat extraction; pollution control measures; water quality; discharge consents

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