Loch Fleet is an upland loch in SW Scotland, distant from significant local pollution, and unlikely to be affected by changes during the five-year project. The underlying geology is granitic. The 111 ha catchment is 90% moorland, dominated by heather and flying bent; 10% is planted with conifers.
Rainfall is approximately 2200 mm per year, predominantly from W and SW. More than half of rain events are pH>4·7; mean pH is 4·84 (1985). Marine salts are the major solutes. Deposition of acidity is about 0·1 g H+ m−2 per year, about twice that of eastern Scotland; deposition of non-seasalt sulphur is 1·6 g S m−2 per year. Soils are shallow and comprise organic peats, peaty gleys, and peaty rankers; base saturation is 3–19%. Soils (pH 2·5 to 4·6) are most acid in the forested area.
The loch is more acid (×5) than bulk deposition; additional acidity is mobilised from soils by the predominantly (>90%) superficial drainage. Moorland drainage dominates; that from the forest is more acid, but very variable in quantity and composition.
Catchment interventions in 1986 and 1987 are designed to alter the chemistry of drainage waters and the loch, so that the fishery can be restored. In addition to the work reported, extensive soils, sediment and biological investigations are underway.