Processes Impacting on Estuarine Turbidity Zones in tidal estuaries

由于悬浮颗粒物（SPM）在水柱和底部积聚而引起的河口最大浊度（ETMs）是潮汐河口普遍存在的现象。早在几十年前，人们就已经了解了ETM的一阶动力学：在纵向盐梯度区域，净SPM向上游输送，而在淡水区域，净SPM向下游输送，导致SPM输运汇聚，从而导致盐侵入的陆地端积聚，这是经典的ETM位置。在涨潮比退潮强而短的强动力潮汐情况下，淡水区也会产生上游SPM输运，导致（无盐）潮河也会产生etm。最近对倡导者及其同事进行的最新研究表明，在ETM动力学方面存在巨大的知识差距，这限制了对与ETM有关的自然和人为过程及其生态后果的理解，并阻碍了河口的可持续管理。拟议项目的一个重点是将总交换流量（TEF）分析框架扩展到每个盐度类别（Q1）的SPM传输。使用这个和其他的分析工具，以下主要的研究问题将被调查。Q2：水柱中SPM的快速动态和底池的缓慢动态如何相互作用，以确定ETM的位置和变化？Q3：随着水动力条件的变化，SPM动力学和ETM形成的调整时间尺度是什么？问4：在东热带气旋中，河流和海洋SPM类别的比例是多少？研究这些问题的方法是一个数值模型实验室，由一个理想的三维辐合河口模型组成。该模型设置将被校准，以重现易北河口和斯海尔德河的纵向盐度和SPM剖面的多年观测数据。数值实验室将首先用于系统地研究易北河口和斯海尔德河近几十年来观测到的ETM动力学对实际潮汐和淡水强迫条件的敏感性。随后，将研究覆盖多维参数空间的理想强迫条件情景，以系统地回答上述研究问题。

Estuarine turbidity maxima (ETMs) due to accumulation of suspended particulate matter (SPM) in the water column as well as at the bottom are an ubiquitous phenomenon in tidal estuaries. The first-order dynamics of ETMs have been understood already a few decades ago: in the region of longitudinal salt gradients, net SPM transport is directed upstream whereas in the freshwater range, net SPM transport is generally directed downstream, leading SPM transport convergence and consequently accumulation of the landward end of the salt intrusion, which the classical ETM location. In the case of strongly dynamic tides with the flood being stronger but shorter than the ebb, an upstream SPM transport is also generated in the freshwater range, leading to ETMs in the (salt-free) tidal river as well. A recent state-of-the-art review of the proponent and co-workers revealed substantial knowledge gaps in ETM dynamics which limit the understanding of natural and anthropogenic processes related to ETMs and their ecological consequences and which hamper the sustainable management of estuaries. One focus of the proposed project is the extension of the Total Exchange Flow (TEF) analysis framework towards SPM transport in per salinity class (Q1). Using this and other analysis tools, the following major research questions will be investigated. Q2: How do the fast dynamics of SPM in the water column and the slow dynamics of the bottom pool interact to determine ETM locations and variability? Q3: What are the adjustment timescales of SPM dynamics and ETM formation in response to changing hydrodynamic conditions? Q4: What are the fractions of fluvial and marine SPM classes in ETMs? The method to investigate these questions is a numerical model laboratory consisting of an idealised model setup of a three-dimensional convergent estuary. The model setup will be calibrated to reproduce multi-decadal observational data of longitudinal salinity and SPM profiles from the Elbe estuary and the Scheldt. The numerical laboratory will first be used to systematically study sensitivities of ETM dynamics to realistic tidal and freshwater forcing conditions as observed for the Elbe estuary and the Scheldt over several decades. Afterwards, scenarios with idealised forcing conditions covering a multi-dimensional parameter space will be studied to systematically answer the above research questions.