Temporal and spatial variation of pH and related paramters in Bastuån, Jämtland

Anthropogenic emissions of acidifying substances, mainly sulfur dioxide, during the second half of the 20th century caused a widespread acidification of many European freshwater environments. Even relatively remote areas, such as inland northern Sweden, experienced reduced pH-values, much due to low buffering capacity in the environment. Extensive liming has taken place in Sweden over the past fifty years to counteract negative effects on limnic ecosystems. Despite a general increase in pH over the last decades, problems with acidification still occur. However, this can be hard to separate from natural acidity due to a large landscape variability. This study aims at describing the temporal and spatial variation of pH and pH-related parameters in Bastuån, a 46 km2 watershed in Jämtland, Sweden, which is being investigated for future liming measures. Existing water chemistry data sets were analyzed and extended with an additional field study, sampling the twelve largest tributaries to Bastuån. Results show that pronounced high and low pH values has become increasingly rare while the average is basically unchanged between 1999 and 2017. Low pH is mainly associated with high discharge during snowmelt or rain events. Anthropogenic SO42- concentrations seems to contribute relatively little to pH-depressions while organic acids plays a more important role. Large water chemical variations in the tributaries indicate that several different biological and physical properties within the watershed regulates pH. However, any credible function that can predict pH using such properties remains to be found