Impact of an extreme rainfall event on solute and sediment dynamics in a mineralised river system

2015年12月5日至6日的周末，英国有记录以来最强的降雨量落在坎布里亚郡的部分地区，在霍尼斯特山口24小时内达到341.4毫米的峰值，导致大范围洪水泛滥。现在人们普遍认为(例如，议员罗里·斯图尔特在2015年12月对媒体发表的声明)，由于气候变化的影响，这种由强降雨引发的山洪暴发(FFIR)事件在英国可能会变得更加频繁。在2015年12月5日至6日的洪水之前，纽卡斯尔大学的研究人员花了几年时间测量不同水流条件对科尔代尔贝克河排放的污染金属和沉积物的影响，科尔代尔贝克河位于霍尼斯特山口正北约10公里处。这些金属包括对鱼类有毒的锌，以及对大多数动植物有毒的镉和铅。在Coledale Beck的顶部是废弃的Force Crag金属矿(该矿的雨量计显示，2015年12月5日至6日的周末，24小时内降雨量为223.8毫米)。2014年4月完成的一种新型处理系统处理了该矿场排出的部分污水。然而，尽管处理系统工作有效，我们知道科尔代尔贝克河的一些污染仍然存在，主要是因为金属从矿场周围的其他地方排入河中。这些来源主要来自废弃渣土堆中的沉积物和河流本身。12月5日至6日的山洪暴发导致科尔代尔贝克河的地貌发生了大规模变化。大量的泥沙顺流而下，同时由于山体滑坡和侵蚀，新的泥沙暴露出来。由于我们已经掌握了Coledale Beck在不同水文条件下金属和沉积物出口的基线数据，我们现在处于独特的地位，可以研究这种极端降雨事件如何改变这种高地河流集水区金属和沉积物循环的全系统动力学。特别是，由于2015年12月洪水对Coledale Beck系统的地貌影响，将有可能评估新沉积物的暴露如何影响金属的行为。这一点很重要，因为河流中金属的形态(它们的“分配”)决定了它们被带到下游的准备程度，也影响了它们对这类河流生态的毒性。这些问题反过来又对下游的用水用户(如渔业、公用事业公司)产生影响。由于气候变化可能导致未来极端水文事件的增加，我们需要了解这些事件如何改变河流的物理和化学特征，以便有可能计划更好地应对此类事件的适应性策略。这项研究将通过在10个不同的场合采集科尔代尔贝克河沿岸的水域和沉积物样本来进行，从而确保在各种流动条件下采集样本。结果将与之前收集的基线数据进行比较，以确定极端事件导致金属和沉积物运动模式的哪些变化。这些结果将得到实验室测试和地球化学模拟的补充，以帮助我们评估河流中的沉积物和金属对水生生物可能的毒性。这项研究的预期成果将允许将工作成果转移到其他河流系统。英格兰和威尔士有450条这样的河流受到废弃矿山污染的负面影响。这项研究迫在眉睫，因为河流是动态系统，关键变化由高强度事件驱动。然而，为了正确了解2015年12月5日至6日等山洪暴发事件的影响，必须在事件发生后尽快进行抽样和分析。

Over the weekend of 5 - 6 December 2015 the most intense rainfall ever recorded in the UK fell over parts of Cumbria, peaking at 341.4 mm over a 24 hour period at Honister Pass, resulting in widespread flooding. It is now widely acknowledged (e.g. statement to the media in December 2015 by Rory Stewart MP) that such 'flash flooding from intense rainfall' (FFIR) events are likely to become more frequent in the UK due to the effects of climate change. Prior to the floods of 5-6 December 2015, Newcastle University researchers spent several years measuring the effects of varying flow conditions on the amount of polluting metal and sediment discharged from the Coledale Beck, some 10 km due north of Honister Pass. These metals include zinc which is toxic to fish along with cadmium and lead that are toxic to most flora and fauna. At the head of the Coledale Beck lies the abandoned Force Crag metal mine (a rain gauge at the mine showed that 223.8 mm of rain fell in a 24 hour period during the weekend of 5-6 December 2015). A novel treatment system, completed in April 2014, treats some of the polluted water that emerges from the mine. Nevertheless, although the treatment system works efficiently, we know that some pollution of the Coledale Beck persists, mainly as a result of metals discharged to the river from other locations around the mine site. These sources arise primarily from sediments in the abandoned spoil heaps and in the river itself. The flash flooding of 5-6 December resulted in wholesale changes to the geomorphology of the Coledale Beck. Large volumes of sediment were carried down the river, whilst new sediments were exposed due to landslides and erosion. Because we already hold baseline data relating to the export of metals and sediments under different hydrological conditions from the Coledale Beck, we are uniquely positioned to now investigate how such extreme rainfall events change the whole-system dynamics of metal and sediment cycling in such upland river catchments. In particular, due to the geomorphic impacts of the December 2015 floods on the Coledale Beck system it will be possible to evaluate how exposure of new sediments influences the behaviour of metals. This is important because the form of metals in rivers (their 'partitioning') determines the readiness with which they may be carried downstream, and also influences their toxicity to the ecology of such rivers. These issues in turn have implications for users of water further downstream (e.g. fisheries, utility companies). Because hydrological extremes are likely to increase in the future as a result of climate change, we need to understand how these events change the physical and chemical characteristics of rivers, so that it is possible to plan adaptive strategies to better deal with such events. The research will be undertaken by collecting samples of waters and sediment along the length of the Coledale Beck on 10 separate occasions, thereby ensuring that samples are collected across a range of flow conditions. The results will be compared with baseline data previously collected, to determine what changes in patterns of metal and sediment movement are caused by extreme events. These results will be complemented by laboratory tests and geochemical modelling to help us assess the likely toxicity of the sediments and metals in the river to aquatic life. The intended outcome of this research will allow transfer of the results of the work to other river systems. There are 450 such rivers in England and Wales negatively impacted by abandoned mine pollution. The research is urgent because rivers are dynamic systems with key changes being driven by high magnitude events. However to properly understand the effects of flash flooding events such as that of 5-6 December 2015, it is critical to undertake sampling and analysis as soon as possible after the event itself.