River ecosystem responses to decreasing glacier cover

气候变化对高海拔生态系统的生物多样性构成了相当大的威胁，世界各地的北极高寒地区已经开始对变暖表现出明显的反应（Milner et al., 2017）。冰川质量平衡研究表明，在上个世纪，大多数地区的冰川持续减少，有人认为，在许多地方，冰川退缩甚至可能正在加速。持续的负冰川质量平衡将导致冰川和积雪融化减少（Barnett et al., 2005），地下水贡献按比例增加（Brown et al., 2006）和前冰期河景动态的变化（Malard et al., 2006）。这些水文变化将显著改变高山河流群落（Brown et al., 2007; Brown & Milner, 2012; Jacobsen et al., 2012）。然而，迄今为止，大多数研究都集中在大型无脊椎动物上，没有对更高层次组织（即整个食物网；Clitherow等人，2013年；Fell等人，2017年）的响应进行详细评估，我们对初级生产或呼吸等生态系统过程的重要程度知之甚少。这些都是主要的研究空白，因为复杂系统中潜在的涌现特性意味着很难预测生态系统的反应，因此很难通过简单地从较低的组织水平（即种群反应；Woodward等人，2010）进行推断来准确地为保护和管理策略提供信息。该主题相对广泛，并将重点放在适合成功候选人的专业知识和兴趣上。例如，可以对食物网的组成部分（如微生物/藻类/大型无脊椎动物等特定群体）、它们通过进食环节的联系和/或与水生生态系统相关的功能过程（如养分吸收、初级生产）如何与冰川退缩联系进行实地调查。该项目将确定一个连续的河流进行研究，从那些高度冰川化的流域到那些没有冰川影响的流域。通过检查来自不同水源的河流，这个项目的一个主要成果将是预测河流生态系统如何响应未来的气候变化而发生变化。学生将受益于全球许多地区已经存在的大量数据（例如Brown et al., 2018, Fell et al., 2018），例如允许使用相同方法进行比较研究。与利兹大学正在进行的项目的链接或通过合作者将允许学生在秘鲁（例如https://gtr.ukri.org/projects?ref=NE%2FS013296%2F1），斯堪的纳维亚（通过挪威水研究所，NIVA）或喜马拉雅山（http://gotw.nerc.ac.uk/list_full.asp?pcode=NE%2FP016146%2F1）进行实地活动。项目目标本研究预计将允许详细评估：(1)大型无脊椎动物/藻类和/或微生物群落组成，(2)流食物网结构（例如Clitherow et al., 2013）。可以采用描述性和实验性相结合的方法。成功的申请者将有机会进行实地考察，从冰川河流中收集自己的原始数据集。这项研究设计将允许比较来自不同盆地和可能不同山脉的冰川河流，并分析来自更密集监测的河流的季节动态。

Climate change poses a considerable threat to the biodiversity of high altitude ecosystems, with Arctic alpine regions across the world already beginning to show clear responses to warming (Milner et al., 2017). Glacier mass-balance studies show consistent decreases over the last century in most regions and it has been suggested that retreat may even be accelerating in many locations. Continued negative glacier mass-balance will lead to glacier- and snow-melt reductions (Barnett et al., 2005), proportionally greater groundwater contributions (Brown et al., 2006) and changes in proglacial riverscape dynamics (Malard et al., 2006). These hydrological changes will dramatically alter alpine river communities (Brown et al., 2007; Brown & Milner, 2012; Jacobsen et al., 2012). However, to date most studies have focused on macroinvertebrates, there have been no detailed assessments of responses at higher levels of organisation (i.e. whole food webs; Clitherow et al., 2013; Fell et al., 2017) and we know little about how important ecosystem processes such as primary production or respiration will change. These are major research gaps because the potential for emergent properties in complex systems means it is difficult to predict ecosystem responses, and therefore to accurately inform conservation and management strategies, by simply extrapolating from lower levels of organization (i.e. population responses; Woodward et al., 2010).The topic is relatively broad and would be focused to suit the expertise and interests of the successful candidate. Example approaches could be to undertake field surveys of how components of food webs (e.g. specific groups such as microbes/algae/macroinvertebrates), their connections via feeding links, and/or functional processes associated with aquatic ecosystems (e.g. nutrient uptake, primary production) are linked to glacier retreat. The project would identify a continuum of rivers to work on, from those draining highly glacierized basins to those with no glacial influence. By examining rivers fed from different water sources, a major output from this project will be predictions about how river ecosystems can be expected to change in response to future climate change. The student will benefit from access to extensive data that already exists for many locations globally (e.g. Brown et al., 2018, Fell et al., 2018), for example allowing comparative studies using the same methods. Links to ongoing projects at Leeds or via collaborators would allow the student to conduct a field campaign in either Peru (e.g. https://gtr.ukri.org/projects?ref=NE%2FS013296%2F1), Scandinavia (via the Norwegian Institute for Water Research, NIVA) or the Himalayas (http://gotw.nerc.ac.uk/list_full.asp?pcode=NE%2FP016146%2F1).Project GoalsThis research is anticipated to allow detailed assessments of: (1) macroinvertebrate/algal and/or microbial community composition, (2) stream food web structure (see e.g. Clitherow et al., 2013). A combined approach of descriptive and experimental approaches may be utilised. The successful applicant will have opportunities to undertake fieldwork to collect their own primary datasets from glacier-fed rivers. This study design will allow comparisons of glacier-fed rivers from different basins and potentially different mountain ranges, and analyses of seasonal dynamics from more intensively monitored rivers.