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

很少有环境问题导致瑞典像1990年代在该国北部进行酸化辩论那样引起激烈的政策科学争议。人们认为，在水文事件期间异常高的河流酸度是由人为沉积引起的，导致了一项由政府资助，耗资数百万美元的地表水石灰计划。该计划遭到了科学界很大一部分的强烈批评，认为北方溪流的酸度主要是由天然存在的有机酸引起的。在这里，我们通过争论在Svartberget / Krycklan研究流域中的长期水化学趋势，重新审视了争议结束后二十年在瑞典北部的酸沉积遗留问题，该趋势已成为瑞典争论的焦点。在此参考流中，酸性事件的趋势确实显示出适度的恢复，将酸沉降的下降与工业化前的水平相匹配，尽管物流的酸度继续受到有机酸度的压倒性驱动。然而，还有一些与土壤中钙流失有关的酸沉降现象，这比预期的更为明显。最后，由于必须认识到水资源的新变化和威胁，对这些趋势的评估变得越来越复杂，必须避免使用不必要的，昂贵的和潜在的适得其反的措施来适应和减轻人类的影响。这里我们提出一个论点，即在酸化时代即将结束之际，气候变化，土地利用过渡以及其他污染物的远距离迁移值得在未来几十年中进行密切监测。