Processes Impacting on Estuarine Turbidity Zones in tidal estuaries

河口最大浑浊度（ETM）是由悬浮颗粒物（SPM）在水体中和底部的累积引起的，是潮汐河口中普遍存在的现象。ETM的一阶动力学在几十年前就已经被理解了：在纵向盐梯度区域，SPM净输送是指向上游的，而在淡水范围内，SPM净输送通常是指向下游的，导致SPM输送收敛，从而积累盐侵入的向陆端，这是经典的ETM位置。在强动态潮汐的情况下，洪水更强，但短于退潮，上游SPM运输也产生在淡水范围内，导致ETM在（无盐）潮汐河以及。最近的一项国家的最先进的审查的提议者和同事揭示了大量的知识差距，在ETM动态，限制了理解的自然和人为过程相关的ETM及其生态后果，阻碍了河口的可持续管理。拟议项目的一个重点是扩展总交换流量（TEF）分析框架，以SPM运输每盐度级（Q1）。利用这一分析工具和其他分析工具，将研究以下主要研究问题。问题2：水体中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？问题3：SPM动态和ETM形成的调整时间尺度是什么？问题4：ETM中河流和海洋SPM类的比例是多少？调查这些问题的方法是一个数值模型实验室，包括一个理想化的模型设置的三维收敛河口。模型设置将被校准，以再现从易北河河口和斯海尔德河的纵向盐度和SPM剖面的多年观测数据。数值实验室将首先被用来系统地研究ETM动态的敏感性，以现实的潮汐和淡水强迫条件下观察易北河河口和Scheldt在几十年。之后，将研究覆盖多维参数空间的理想化强迫条件的情景，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.