Deciphering the origin and geometry of freshwater tufa barrages. From process understanding to sustainable management

并非所有的岩石都起源于火山（火成岩，如花岗岩）、沉积（沉积岩，如砂岩）或这两种类型的转化（变质岩，如大理石）。有些岩石，如石灰华，起源于温泉附近的混凝土状碳酸盐矿物的逐渐沉积。另一种奇特的石灰华叫做凝灰岩，它是在淡水环境中形成的，比如泉水、湿地和溪流。现代凝灰岩是一种多孔岩石，新鲜沉积在现存的鹅卵石、植被和原木上，它的沉淀是由藻类和苔藓等生物元素促进的。在英国的石灰岩和白垩溪流中，凝灰岩可以形成一系列类似珊瑚礁的屏障，这些环境为各种植物、大型无脊椎动物和鱼类提供了栖息地。不幸的是，凝灰岩拦河坝并不为人所知，也没有得到很好的保护，一些不明智的河流管理措施或水质变化可能会对它们产生负面影响。该项目侧重于林肯郡溪流中的凝灰岩坝序列。我们将调查凝灰岩拦河坝的几何形状，确定它们在自然环境中的形状、生长和年龄，并确定这些拦河坝是否经受住了过去的洪水。然后，我们将重点关注邓斯顿贝克的一个特定区域，这是林肯附近的一条河流，拥有丰富的凝灰岩拦河坝。在这里，我们将在河流的不同部分安装不同材料的板，我们将监测淡水凝灰岩的生长，以确定凝灰岩沉积的最佳条件。从这些实地调查中获得的结果将为我们提供设计渗漏坝（由灌木和束状木/柴堆组成）所需的信息，这些坝将促进凝灰岩的沉积。这种漏水的拦河坝经常用于河流修复和自然洪水管理项目，因为它们可以改善河流生态，减缓水流，并有助于防止下游洪水泛滥。然而，如果提供了凝灰岩沉积的条件，它们的持久性和稳定性将大大提高。此外，在凝灰岩可能存在的地方（考虑到良好的水质和苔藓的存在）建造这些漏水的堤坝可能会促进凝灰岩的沉积。我们的实地调查将指导我们设计和规划这些拦河坝的正确形状，我们将在Dunston Beck进行试点试验。凝灰岩坝是英国许多河流中隐藏的、被低估的宝藏，它们的存在需要得到承认和保护。该项目将进一步了解凝灰岩如何以及在哪里生长最多，并将通过在河流修复项目中模拟真实的凝灰岩拦河坝而超越。在这个项目中，基础的地球科学和生物学知识将为工程解决方案提供信息，以造福环境和社区，因为改善的生态系统服务支持更健康的社会。

Not all rocks originate from volcanoes (igneous, like granite), deposition (sedimentary, like sandstone) or transformation of these two types (metamorphic, like marble). Some rocks like travertine originated from the progressive deposition of concrete-like carbonate minerals near hot springs. One more peculiar type of travertine is called tufa, and it's created in freshwater environments such as springs, wetlands, and streams. Modern tufa is a porous rock that's freshy deposited over existent pebbles, vegetation and logs, and its precipitation is facilitated by biological elements such as algae and moss. In limestone and chalk streams in Britain, tufa can create series of barrages that resembles reefs, and these environments provide habitats for a variety of plants, macroinvertebrates and fish. Unfortunately, tufa barrages are not well known nor well protected, and some ill-informed river management practices or changes in water quality can affect them negatively. This project focuses on sequences of tufa barrages in streams of Lincolnshire. We will survey the geometry of tufa barrages, and determine their shape, growth and age in natural environments, as well as identify if these barrages have withstood past floods. We will then focus on a specific reach of the Dunston Beck, a stream near Lincoln with abundant tufa barrages. Here we will install slabs of different materials in different parts of the stream, and we will monitor the growth of freshwater tufa in order to determine what are the best conditions for tufa to deposit. Results obtained from these field surveys will give us the information needed to design leaky barrages (made up of brushwood and fascines/faggots) that will facilitate the deposition of tufa. Leaky barrages of these kind are often used in river restoration and natural flood management projects, as they improve the river ecology, slow down the water and help prevent flooding downstream. However, their persistence and stability could improve dramatically if tufa could grow on them given that the conditions for its deposition are provided. Also, building these leaky barrages in places where tufa could be potentially present (given the good water quality and presence of moss) may facilitate its deposition. Our field surveys will guide us in designing and planning the right shape for these barrages, and we will install a pilot trial in the Dunston Beck. Tufa barrages are a hidden and undervalued treasure of many streams in Britain, and their presence needs recognition and protection. This project will gain further understanding on how and where tufa grows the most, and will go beyond by mimicking real tufa barrages in river restoration projects. In this project, basic Earth Science and Biology knowledge will inform Engineering solutions for the benefits of the environment and communities, as improved ecosystem services support healthier societies.