To investigate the factors contributing to the deterioration in water quality in Knappaghbeg Lake, Aughagower, Westport, Co. Mayo

Abstract

The investigation aims to identify the reasons why the water quality deteriorated in Knappaghbeg Lake. The lake had been monitored in the past by the EPA under the Phosphorus Regulations. These Regulations required the water quality to improve to a mesotrophic status. The initial phase of the study involved looking for any relevant datsets already available. The EPA ‘Water Quality in Ireland’ reports, provided data on previous lake sampling and the biological analysis on the Carrowbeg River; the main inflow and outflow of the lake. Details of a pollution incident which occurred in 2000, discharging 364,000 litres of slurry into the lake, was available. A fish farm had established in the lake in the early 1980’s, although operations have ceased in the last three years, the licence is still valid until 2 0 1 0 . On inspecting the catchment area the main land uses were identified to investigate possible factors which may influence the water quality. The catchment was divided up into four minicatchments, based on the stream/river draining it. The major focus of this study was to carry out a phosphorus loading to the lake, thus identifying where the highest nutrient loading was coming from. A more intensive study was carried out on one of the minicatchments, which included farm surveys, SSRS and composite sampling. Agriculture is the predominant land use in the catchment and is recognised as being responsible for causing the main deterioration of water quality in the catchment, reclaimed peatland is also used for rough grazing, only small pockets of forestry persist in the catchment. There is no wastewater treatment plant and most houses in the catchment have a septic tank. Recommendations have been made to improve the management of this catchment i.e. reduce the total phosphorus loading to the lake.