Dippers (Cinclus cinclus) as bioindicators of health and resilience of freshwater ecosystems in the face of complex ecological change

淡水生态系统至关重要，因为它们综合了环境压力对景观和集水区的影响，就单位面积提供的生态系统服务而言，它们的重要性是其他广泛生境类型的两倍以上(自然资本资产指数)。然而，有效监测淡水并了解它们对多种环境压力的反应是具有挑战性的。北斗七星是英国典型的河鸟，作为捕食者，它可能为我们的河流生态系统的健康及其对各种形式的环境管理的反应提供一个方便而有效的哨兵。勺子被证明是人为压力的敏感指标，例如空气污染造成的酸化(例如，Vickery，1992)。然而，在过去30年中，在控制排放之后，酸沉降量大幅下降，而更多对环境无害的林业做法可能有助于减轻针叶林对旱地溪流酸化的影响。工业和城市点源的水污染也得到了严格的管制，从而改善了水质。因此，Bird Atlas 2007-11年揭示的北斗七星种群以及其他河岸鸟类(例如灰辫子、普通琵琶、鹅尾鸟)的种群下降是一个谜。虽然北斗七星受到严冬的不利影响，但近几十年来温和潮湿的冬季使这些不利影响黯然失色，这反映在河流流量和变化量的总体增加，最明显的是在该国西部。随着酸化对有机碳分解速率和溶解度的制约作用解除，再加上降水和温度的升高，高地淡水的水色普遍增加(“褐化”)(Battarbee等人，2014年)。有越来越多的案例表明，更多的河流流态变化和水色增加对水生无脊椎动物猎物和北斗七星觅食效率的影响可能正在影响北斗七星种群比率(例如Taylor&O‘Halloran，2001)，从而导致该河鸟和其他河鸟数量的下降。最后，虽然有很好的证据表明酸化高地淡水的化学改善，但大多数评估表明，对酸敏感的无脊椎动物和鱼类的生物恢复滞后了一段时间(Battarbee等人，2014年)。北斗七星的现状可能是这一趋势的延伸，在这种趋势上，其他压力源已经逐渐叠加。苏格兰拥有丰富的档案，包括详细的气候预测、土地覆盖图、最近的管理历史，以及关于河流流量、化学物质和无脊椎动物种群的高质量历史和当前数据。结合国家不同地区对北斗七星生态和人口学的多项详细的历史研究，这提供了一个独特的机会，可以测试不断变化的淡水环境压力平衡如何融入到对一个有魅力和可接近的生物指示物种的影响中。它还提供了一个机会，以探索各种地方和集水区规模的管理干预措施，最终旨在惠及生物多样性和生态系统服务交付，是否体现在改进的北斗业绩中。例如，当地的河岸树木种植和泥炭地恢复是可以预期的措施，通过一系列机制，使北斗七星受益。

Freshwater ecosystems are of critical importance because they integrate effects of environmental pressures across landscapes and catchments and are more than twice as important as other broad habitat types in terms of ecosystem service delivery per unit area (Natural Capital Asset Index). Monitoring freshwaters effectively and understanding their response to multiple environmental stressors is, however, challenging.Dippers are the quintessential river bird of Britain and, as a predator, are likely to provide a convenient and effective sentinel of the health of our riverine ecosystems and their response to various forms of environmental management. Dippers are proven sensitive indicators of anthropogenic pressures such as acidification from air pollution (e.g. Vickery, 1992). However, in the past 30 years, acid deposition has declined greatly following controls on emissions, while more environmentally benign forestry practices may have helped to mitigate impacts of conifer plantations on upland stream acidification. Water pollution from industrial and urban point sources has also been strictly regulated leading to improved water quality. The declines in dipper populations, and those of other riparian birds (e.g. grey wagtail, common sandpiper, goosander) revealed by Bird Atlas 2007-11, are therefore a conundrum.Dippers are predicted to be highly responsive to the changes in temperature and flow regimes that will arise from climate change over the 21st century (Saether et al., 2000). While Dippers are adversely affected by severe winters these have been eclipsed by mild wet winters in recent decades which are reflected in overall increases in river flow and variability, most notably in the west of the country. Water colour is generally increasing ('brownification') in upland freshwaters as the constraining effects of acidification on decomposition rates and solubility of organic carbon are lifted, alongside increasing precipitation and temperature (Battarbee et al., 2014). There is a growing case that effects of more variable river flow regimes and increased water colour on aquatic invertebrate prey and Dipper foraging efficiency may be affecting Dipper demographic rates (e.g. Taylor & O'Halloran, 2001), and thus contributing to declines in this and other river birds. Finally, while there is good evidence for chemical improvement of acidified upland freshwaters, most assessments suggest that biological recovery of acid-sensitive invertebrates and fish is lagging some way behind (Battarbee et al., 2014). The current status of Dippers may be an extension of this trend upon which other stressors have gradually been superimposed.Scotland has a rich archive of detailed climate projections, land cover maps, recent management histories, and high quality historical and current data on river flow, chemistry and invertebrate populations. Combined with the multiple detailed historical studies of Dipper ecology and demography from different parts of the country this provides a unique opportunity to test how the changing balance of environmental pressures on freshwaters is integrated in its impact on a charismatic and accessible bio-indicator species. It also presents an opportunity to explore if various local and catchment scale management interventions, ultimately intended to benefit biodiversity and ecosystem service delivery, are captured in improved Dipper performance. Native riparian tree planting and peatland restoration, for example, are measures that might be expected, via a range of mechanisms, to benefit Dippers.