From legacy effects of acid deposition in boreal streams to future environmental threats

Abstract Few environmental issues have resulted in such a heated policy-science controversy Sweden as the 1990s acidification debate north of country. The belief that exceptionally high stream acidity levels during hydrological events was caused by anthropogenic deposition governmentally funded, multi-million dollar surface-water liming program. This program heavily criticized large part scientific community arguing northern streams primarily naturally occurring organic acids. Here, we revisit acid legacy two decades after culmination examining long-term water chemistry trends Svartberget/Krycklan research catchment became nexus for Swedish debate. In this reference stream, acidic episodes do show modest recovery matches declines to pre-industrial levels, although continues be overwhelmingly driven acidity. Yet there are legacies related calcium losses from soils, which more pronounced than anticipated. Finally, assessment these becoming increasingly complicated new changes and threats resources must recognized avoid unnecessary, expensive, potentially counterproductive measures adapt mitigate human influences. Here make argument while era is ending, climate change, land-use transitions, long-range transport other contaminants warrant close monitoring come.