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，英国坎布里亚郡的部分地区出现了有记录以来最强的降雨，在24小时内，Honister山口的降雨量达到了341.4毫米，导致了大范围的洪水。现在人们普遍承认（例如，2015年12月罗里·斯图尔特议员向媒体发表的声明），由于气候变化的影响，这种“强降雨引发的山洪暴发”（FFIR）事件可能会在英国变得更加频繁。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的水流条件对Coledale Beck排放的污染金属和沉积物数量的影响，Coledale Beck位于Honister Pass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的顶端是废弃的Force峭壁金属矿山（矿山的雨量计显示，2015年12月5日至6日周末的24小时内降雨量为223.8毫米）。一个新的处理系统于2014年4月完成，用于处理从矿井中流出的一些污水。然而，尽管处理系统有效地工作，我们知道，科莱代尔贝克的一些污染仍然存在，主要是由于金属从矿区周围的其他地方排放到河中。这些来源主要来自废弃的废土堆和河流本身的沉积物。12月5日至6日的山洪导致Coledale Beck的地貌发生了大规模的变化。大量的沉积物被顺流而下，同时由于山体滑坡和侵蚀，新的沉积物暴露出来。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，我们现在有独特的优势来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整个系统动态。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，因为金属在河流中的形态（它们的“分配”）决定了它们被顺流而下的可能性，也影响了它们对河流生态的毒性。这些问题反过来又影响到下游的用水者（例如渔业、公用事业公司）。由于气候变化，未来水文极端事件可能会增加，因此我们需要了解这些事件如何改变河流的物理和化学特征，以便有可能制定适应策略来更好地应对此类事件。这项研究将沿着Coledale Beck的长度在10个不同的场合收集水和沉积物样本，从而确保在一系列流动条件下收集样本。结果将与先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。这些结果将由实验室测试和地球化学模型加以补充，以帮助我们评估河流中的沉积物和金属对水生生物的可能毒性。这项研究的预期结果将允许将工作结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井污染的负面影响。这项研究很紧迫，因为河流是动态系统，其关键变化是由高强度事件驱动的。然而，要正确理解2015年12月5日至6日等山洪事件的影响，至关重要的是在事件发生后尽快进行采样和分析。

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.