Impacts of hydrological variability on material transfers through the River-Estuary Transition Zone

水文变率对河流-河口过渡区物质转移的影响

基本信息

批准号：
NE/G01860X/1
负责人：
Christopher Vane
金额：
$ 10.89万
依托单位：
British Geological Survey
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2009
资助国家：
英国
起止时间：
2009 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FG01860X%2F1
关键词：
Impacts hydrological variability material transfers

项目摘要

Estuaries are biologically productive, susceptible to climatic variability, and vulnerable to nutrient enrichment. These characteristics are reinforced by their ability to trap, filter, and recycle particulate matter. The processing of particulate matter supplied to estuaries is therefore important and dependent on the major sources of material to estuaries. In this respect, suspended particulate matter (SPM) and its inherent chemical characteristics are instrumental in controlling the reactivity, transport, and biological impact of substances from river catchments to the coastal zone. During transport to the coast, the physical properties of SPM (particle size, density, settling velocity) change on short time and length scales, especially when terrestrial particles encounter the steep hydrodynamic, chemical, and biological gradients that characterise the River-Estuarine Transition Zone (RETZ), and enter the estuary. This is because SPM is largely in the form of flocs: aggregates of inorganic matter, organic matter, and water. Flocs grow to a much larger size than their individual inorganic components. Aggregation occurs when fresh water meets salt water in the RETZ and is further mediated by biological effects. Flocs are created when individual particles collide due to weak turbulence, and are ruptured by strong turbulence. Large flocs sink rapidly, thus transferring material to the sediment bed. So, the fate of terrestrial SPM (i.e., whether it is retained by rivers, transferred to estuaries, or exported to the coastal ocean) is strongly influenced by floc properties, which, in turn, are dependent on their provenance and genesis. Since flocs are fragile and ruptured by sampling, they are difficult to study. High resolution measurements are needed since flocs change their properties on short time and length scales. This has been difficult to achieve, but optical techniques are now available which allow high resolution in situ measurement of floc properties (size, volume concentration), which, coupled with measurements of mass concentration and settling velocity, provide assessment of floc strength. This project investigates the transfer from river catchments to estuaries of SPM and its particulate components (carbon, nitrogen, heavy metals). These terrestrial components are important for water quality and ecosystem functioning and health in the coastal zone, and are likely to be severely altered by changes to the fluvial regime - increased frequency of major flood events - driven by climate change. The aims are to determine (i) The varying provenance of riverine SPM, which changes seasonally and during episodic flood events, when material is mobilised, previously deposited on aerially exposed floodplains and high banks. We will use multiple geochemical proxies in the form of the C:N ratio, stable carbon isotopes, and the lignin-derived monomer yields of organic matter, as well as inorganic geochemical tracers in the form of heavy metals. (ii) How floc properties and geochemical composition evolve as they pass through the RETZ and the estuary. (iii)How flocs and material transfers respond to marine forcings (tidal, storm) and fluvial forcings, especially short duration (episodic) events. High resolution observational datasets from instrumented sampling sites in the catchment, RETZ, and estuary will be used to validate a 1-D vertical exchange model, which will be embedded in a 3-D hydrodynamic model for scenario testing of impacts of episodic river floods and storms on material transfers through the river-estuary system. The field study area is the macrotidal Dyfi system (West Wales), where there is a demonstration project set up by the Centre for Catchment and Coastal Research, which will provide a logistical infrastructure in support of this project. The project will be carried out with the participation of the Environment Agency and CEFAS, who will be important end users of the outputs.

河口在生物学上具有生产力，容易受到气候变异的影响，并且容易受到营养富集的影响。这些特征通过捕获，过滤和回收颗粒物的能力来增强。因此，提供给河口的颗粒物的处理非常重要，并且取决于河口的主要材料来源。在这方面，悬浮的颗粒物（SPM）及其固有的化学特性对控制从河流流到沿海地区物质的反应性，运输和生物学影响有用。在运输到海岸期间，SPM（粒径，密度，沉降速度）的物理性能在短时间和长度尺度上发生变化，尤其是当陆地颗粒遇到陡峭的水动力学，化学和生物学梯度时，这些梯度表征了河流 - 经历过渡区（RETZ）的表征，并进入河口。这是因为SPM在很大程度上以泡沫的形式：无机物质，有机物和水的聚集体。比单个无机成分的絮凝物的大小要大得多。当淡水在RETZ中遇到盐水时会发生聚集，并由生物学作用进一步介导。当单个颗粒由于湍流弱而碰撞并因湍流破裂时，会产生泡沫。大型泡沫迅速下沉，从而将材料转移到沉积物床上。因此，陆地SPM的命运（即，无论是由河流保留，转移到河口或出口到沿海海洋的命运）受群絮状特性的强烈影响，这反过来依赖于其出处和创世记。由于絮凝物是脆弱的，并因采样而破裂，因此很难研究。需要高分辨率的测量值，因为絮凝物在短时间和长度尺度上更改其性能。这很难实现，但是现在可以使用光学技术，从而可以高分辨率原位测量泡沫特性（尺寸，体积浓度），并与质量浓度和沉降速度的测量相结合，提供了对逆变强度的评估。该项目研究了从河流流域到SPM及其颗粒成分（碳，氮，重金属）的转移。这些陆地成分对于沿海地区的水质和生态系统功能和健康非常重要，并且可能会因河流政权的变化而严重改变 - 由气候变化驱动的重大洪水事件的频率增加。目的是确定（i）Riverine SPM的不同来源，河流SPM的季节性变化和情节性洪水事件发生了变化，当材料被动员时，以前存放在空中裸露的洪泛区和高库中。我们将以C：N比，稳定的碳同位素和有机物的木质素衍生的单体产量以及以重金属形式使用多种地球化学代理。（ii）泡沫特性和地球化学成分如何通过RETZ和河口发展。（iii）泡沫和物料转移如何响应海洋强迫（潮汐，风暴）和河流强迫，尤其是持续时间短（情节）事件。来自集水区，RETZ和河口的仪器采样位点的高分辨率观察数据集将用于验证1-D垂直交换模型，该模型将嵌入3-D流体力学模型中，以测试通过河流系统通过河流系统进行情节性河流洪水和风暴对物质转移的影响。现场研究区域是大型Dyfi系统（西威尔士），那里有一个由集水区和沿海研究中心建立的示范项目，该项目将提供一个后勤基础设施以支持该项目。该项目将与环境局和CEFA的参与一起进行，CEFA将是输出的重要最终用户。