STREAM ACIDIFICATION TRENDS IN THE WELSH UPLANDS - A MODELING STUDY OF THE LLYN-BRIANNE CATCHMENTS

Historical reconstructions and predictions of streamwater acidification are presented for moorland and afforested catchments in the Welsh Uplands at Llyn Brianne, [UK]. The model MAGIC (Model of Acidification of Groundwater in Catchments) is calibrated using data from a moorland catchment and validated by application to a forested catchment. While atmospheric deposition is shown to be the primary cause of stream acidification, conifer afforestation can enhance stream acidity. The historical trends determined by the model indicate that acidification has been present since the turn of the century and will continue unless either deposition levels are reduced significantly or other land management actions such as liming are undertaken on a major scale.