Integrating morphodynamic and ecological processes to understand and predict the response of salt marshes to sea-level change and reduced sediment supply

盐沼是海岸沉积体系，对波浪衰减和海岸保护具有重要作用。一般来说，许多盐沼可以适应海平面上升(SLR)，因为淹没频率的增加会导致沉积物沉积和淤积的增加。然而，在十年的时间尺度上，由于泥沙沉积速率的时空变化，潮汐沼泽的复杂形态响应可能在全球变化的时代演变。盐沼中的泥沙淤积、淤积速率和模式受潮差、风暴频率和泥沙供应等外部环境因素的影响，其中许多因素会因环境变化而改变。内部因素，如海拔和到泥沙来源的距离，会影响当地尺度上的泥沙沉积速率和模式。此外，还发现植被通过降低水流速度来增加泥沙淤积。泥沙淤积增加和由此引起的地表高程变化反过来又促进植被变化和增加生物量生产，从而导致更多的泥沙捕获，从而形成沉积物动力学和植被的正反馈循环。各种考虑这些因素的地貌动力学模型已经被提出用来预测潮汐沼泽表面高程的变化。这些模型从零维点模型到景观尺度模型。此外，基于经验现场测量和统计分析的模型和基于水动力学方程的物理模型都是可用的。其中许多模型还试图包括植被对水流和泥沙沉积的影响。然而，沼泽植被与水文地貌过程之间的许多生物物理相互作用以及异质植被格局对沉积物通量的影响还知之甚少。例如，模型大多集中在均匀的低洼沼泽，但沼泽地带之间的植被结构差异很大，形成了异质格局。最重要的是，模型通常假定植被是静态的，而形态沼泽的发展确实也是植被演替的主要驱动因素，导致植被特性的变化，进而也影响如上所述的沉积物动力学。我们建议通过整合沉积物和植被动力学之间的反馈环来改进瓦登海盐沼的地貌动力学模型。这些模型将能够更好地预测沼泽对不同气候变化情景的响应(WPA/B)。此外，它们将是在沿海保护措施(WPC)背景下进行决策的有用工具。我们建议两名博士生参加一个为期三年的项目。博士生A将专注于泥沙淤积和淤积的经验和物理模型。博士生B将为盐沼植被开发一个可预测的生境分布模型。

Salt marshes are coastal sedimentary systems which are important for wave attenuation and coastal protection. In general, many salt marshes can adjust to sea level rise (SLR), because increased inundation frequencies lead to enhanced sediment deposition and accretion. However, on a decadal time scale complex morphological responses of tidal marshes might evolve in times of global change due to spatial and temporal variable sediment deposition rates. Sediment deposition and accretion rates and patterns in salt marshes are affected by external environmental factors such as the tidal range, storm frequency and sediment supply, many of which will be altered by environmental change. Internal factors such as elevation and distance to the sediment source affect sediment deposition rates and patterns on the local scale. Additionally, vegetation was found to increase sediment deposition by reducing flow velocity. Increased sediment deposition and the resulting surface-elevation change in turn promote vegetation change and increase biomass production, which leads to more sediment trapping and thus to a positive feedback loop of sediment dynamics and vegetation. Various morphodynamic models considering these factors have been proposed to predict changes in surface elevation of tidal marshes. These models reach from zero-dimensional point models to landscape scale models. Furthermore, both models based on empirical field measurements and statistical analysis, and physical models based on hydrodynamic equations are available. Many of these models also attempt to include the effect of vegetation on flow and sediment deposition. Yet, many biophysical interactions between marsh vegetation and hydro-morphological processes, and effects of heterogeneous vegetation patterns on sediment fluxes are poorly understood. For example, models mostly focus on homogeneous low marshes, but vegetation structure strongly differs between marsh zones and forms heterogeneous patterns. Most importantly, models generally assume that vegetation is static, while morphological marsh development is indeed also a main driver of vegetation succession, leading to changes in vegetation properties which in turn also affect sediment dynamics as outlined above. We propose to improve morphodynamic marsh models by integrating feedback loops between sediment and vegetation dynamics for salt marshes in the Wadden Sea. These models will be better able to predict marsh response to different climate change scenarios (WP A/B). Furthermore, they will be a useful tool for decision making in the context of coastal protection measures (WP C). We propose a three year project for two PhD-students. PhD-student A would focus on empirical and physical modelling of sediment deposition and accretion. PhD-student B would develop a predictive habitat distribution model for salt marsh vegetation.