权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

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/G020302/1
负责人：
Colin Jago
金额：
$ 75.53万
依托单位：
Bangor University
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%2FG020302%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.

河口具有生物生产力，易受气候变化的影响，易受营养物质富集的影响。这些特性通过它们捕获、过滤和回收颗粒物质的能力得到加强。因此，供应河口的颗粒物质的处理是重要的，并取决于河口的主要物质来源。在这方面，悬浮微粒物质（SPM）及其固有的化学特性有助于控制从河流集水区到沿海地区的物质的反应性、运输和生物影响。在向海岸的运输过程中，SPM的物理性质（粒度、密度、沉降速度）在短时间和长度尺度上发生变化，特别是当陆地颗粒遇到河流-河口过渡带（RETZ）特征的陡峭水动力、化学和生物梯度并进入河口时。这是因为SPM主要以絮凝体的形式存在：无机物、有机物和水的聚集体。絮凝体生长到比单个无机组分大得多的尺寸。当淡水在RETZ内遇到盐水时，就会发生聚集，并进一步受到生物效应的介导。当单个粒子在弱湍流中碰撞时，就会产生絮凝体，并在强湍流中破裂。较大的絮凝体沉降迅速，从而将物质转移到沉积物床上。因此，陆地SPM的命运（即，它是被河流保留，转移到河口，还是出口到沿海海洋）受到浮冰性质的强烈影响，而浮冰性质又取决于它们的来源和成因。由于絮凝体易碎，取样时容易破裂，因此很难对其进行研究。由于絮凝体在短时间和长度尺度上改变其性质，因此需要高分辨率的测量。这是很难实现的，但现在有了光学技术，可以对絮凝体特性（尺寸、体积浓度）进行高分辨率的原位测量，再加上质量浓度和沉降速度的测量，就可以对絮凝体强度进行评估。本项目研究了从河流集水区到河口的SPM及其颗粒成分（碳、氮、重金属）的转移。这些陆地成分对沿海地区的水质、生态系统功能和健康都很重要，而且很可能因气候变化导致的河流状况变化（大洪水事件频率增加）而严重改变。目的是确定(i)河流SPM的不同来源，它随季节和偶然的洪水事件而变化，当物质被调动时，以前沉积在空中暴露的洪泛平原和高堤岸上。我们将使用多种地球化学指标，如C:N比、稳定碳同位素和木质素衍生的有机物单体产率，以及重金属形式的无机地球化学示踪剂。（ii）通过RETZ和入海口时，浮冰的性质和地球化学组成如何演变。（三）絮凝体和物质转移如何对海洋强迫（潮汐、风暴）和河流强迫，特别是短时间（偶发）事件作出反应。来自集水区、RETZ和河口的仪器采样点的高分辨率观测数据集将用于验证1-D垂直交换模型，该模型将嵌入到3-D水动力模型中，用于情景测试间歇性河流洪水和风暴对河流-河口系统物质转移的影响。实地研究区域是大潮汐Dyfi系统（西威尔士），那里有一个由集水区和海岸研究中心建立的示范项目，该中心将为该项目提供后勤基础设施支持。该项目将在环境局和中欧经济合作中心的参与下进行，它们将是产出的重要最终用户。