ESTIMATING VERTICAL EDDY DIFFUSIVITY IN A SMALL LAKE: A COMPARISON OF METHODS

估算小湖中的垂直涡流扩散率：方法比较

• 批准号: NE/D008298/1
• 负责人: Andrew Folkard
• 金额: $ 7.02万
• 依托单位: Lancaster University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FD008298%2F1
• 关键词: ESTIMATING; VERTICAL; EDDY; DIFFUSIVITY; SMALL

Turbulence is a pre-eminently important phenomenon in water, largely because it is the most effective way of spreading particles, heat and dissolved substances from one place to another. As well as its obvious importance in the atmosphere and oceans, where it plays a crucial role in the world's health and climate by transferring heat, pollutants and many other things around the globe, turbulence is also central to understanding lakes. Lakes are very important both as water resources for humans and as locations of remarkably high levels of biodiversity, especially at the microbiological level which forms the foundation stone of natural ecosystems. In lakes, turbulence performs a multitude of roles: it provides nutrients from the lakebed to the upper levels of the lake where most plankton exist; it mixes oxygen down to lower levels in the lake allowing organisms to exist there that otherwise would suffocate; it spreads heat through the lake water enabling biological activity; and it is central to the cycling of many key chemicals and the diffusion of pollutants. Although it also mixes things horizontally, its key role is to mix vertically, connecting the nutrient supply - the food source - at the lake bed with the light, warm, oxygen rich waters near the surface which most organisms inhabit. Clearly, therefore, measuring the rate of vertical mixing caused by turbulence (which we call the 'vertical diffusivity' and denote Kz) is of crucial importance for understanding how lakes work and thus enabling us to manage them effectively. Nevertheless, this is very difficult to do, and moreover the techniques that have been used have largely been developed in lakes much larger than those found in the UK, as well as in the oceans. In smaller lakes, the fact that the water is in general much closer to the nearest bit of lake bed, and turbulence in a fluid is in general highest near a solid boundary, because of its creation by the fluid scraping against the boundary, means that the patterns of Kz in small lakes are likely to be quite different from those in larger lakes or oceans. So techniques that work well in large lakes may not work so well in smaller ones, and vice versa. Our aim in this project, therefore, is to test several of these techniques in a lake typical of those found in the UK (and of a size and type very common around the world) to find a method that is appropriate, transferrable to other lakes and cheap and easy to use. We are particularly interested in looking at a technique that uses the natural emission of the radioactive gas radon from the lake bed, as this has not previously been tried in UK lakes to our knowledge.

湍流是水中一种极其重要的现象，很大程度上是因为它是将颗粒、热量和溶解物质从一个地方传播到另一个地方的最有效方式。湍流在大气和海洋中的重要性显而易见，它通过在全球范围内传递热量、污染物和许多其他东西，在世界健康和气候中发挥着至关重要的作用，湍流也是理解湖泊的核心。湖泊既是人类的水资源，也是生物多样性水平非常高的地点，特别是在构成自然生态系统基石的微生物层面。在湖泊中，湍流扮演着多种角色：它将营养物质从湖床提供到湖的上层，那里是大多数浮游生物的栖息地；它将氧气向下混合到湖中的较低水平，使原本会窒息的生物体得以存在；它通过湖水传播热量，使生物活动得以实现；它是许多关键化学物质循环和污染物扩散的核心。尽管它也在水平方向上混合，但它的关键作用是在垂直方向上混合，将湖床上的营养物质供应--食物来源--与大多数生物栖息的水面附近明亮、温暖、富含氧气的水域连接起来。因此，很明显，测量湍流引起的垂直混合速率(我们称之为‘垂直扩散系数’，记为Kz)对于了解湖泊如何工作，从而使我们能够有效地管理它们是至关重要的。然而，这很难做到，而且已经使用的技术在很大程度上是在比英国发现的大得多的湖泊和海洋中开发出来的。在较小的湖泊中，水一般离最近的湖床更近，流体中的湍流通常在固体边界附近最高，因为它是由流体刮过边界而产生的，这意味着小湖泊中的Kz模式可能与较大的湖泊或海洋中的模式非常不同。因此，在大型湖泊中奏效的技术可能在较小的湖泊中就不那么奏效，反之亦然。因此，我们在这个项目中的目标是在一个典型的英国湖泊(其大小和类型在世界上非常常见)中测试这些技术中的几种，以找到一种合适的、可转移到其他湖泊的、廉价且易于使用的方法。我们特别感兴趣的是一种利用湖床自然释放的放射性气体氡的技术，因为据我们所知，这项技术以前从未在英国的湖泊中尝试过。