Climate change in salt marshes - Effects of hydrodynamic forcing and higher temperatures on coastal vegetation

盐沼和其他沿海生态系统提供了重要的生态系统服务，如海岸保护，因为植被对水动力起到阻碍作用，从而导致波浪衰减。到目前为止，大多数研究都集中在植被对水动力学的影响上，而关于水动力学如何反过来影响和潜在损害盐沼植物的关键知识却缺失了。此外，全球变暖对沼泽植物生物物理特性的影响尚不清楚，这些特性决定了它们的波衰减能力。我们将(i)利用瓦登海盐沼边缘的波浪记录站量化水动力，并确定其在不同暴露地点的时空变化。同时，植被结构和生物量的最终损失将被非破坏性地确定，并与记录的水动力条件相关联。在受控的实验条件下（ii），水动力的阈值将在真正按比例的水槽研究中进行评估，超过该阈值，盐沼植物将遭受物理损害。我们期望阈值是特定于物种的，因为盐沼中的植物物种在其生物物理特性（如植物灵活性）方面存在显著差异。此外，这些阈值的季节性变化是由于植物发育阶段的不同，以及某些物种的单个个体与复杂植被冠层中相关个体的阈值差异。最后，我们将（iii）在一个世界独特的全生态系统盐沼变暖实验中分析温度上升对沼泽植物生物物理特性的影响，从而分析沼泽植物的波衰减能力。我们预计，气候变暖将增加地上和地下生物量，延长生长季节，增加植物的木质素含量。总的来说，这可能会增加盐沼在温暖世界中的海岸保护功能。研究结果将用于海浪对陆地海防系统影响的水动力模型，以及不同气候变化和海平面上升情景下的沼泽演变模型。研究结果将有助于今后充分评价盐沼的海岸保护功能，更好地应对生态随机性和风暴潮等极端事件对沿海盐沼的影响。

Salt marshes and other coastal ecosystems provide important ecosystem services such as coastal protection, as the vegetation acts as an obstruction to hydrodynamic forces, thus leading to wave attenuation. While most studies so far have focused on the effects of vegetation on hydrodynamics, crucial knowledge on how hydrodynamics in turn affect and potentially damage salt marsh plants are missing. Additionally, effects of global warming on biophysical properties of marsh plants, which determine their wave attenuation capacity, are unknown. We will (i) quantify hydrodynamic forces using wave recording stations at the margin of Wadden Sea salt marshes and determine its spatial and temporal variation at sites differing in exposure. In parallel, vegetation structure and the eventual loss of biomass will be non-destructively determined and correlated to the recorded hydrodynamic conditions. Under controlled experimental conditions (ii) thresholds of hydrodynamic forces beyond which salt marsh plants suffer physical damage will be assessed in a true to scale flume study. We expect thresholds to be species specific, as plant species in salt marshes significantly differ in their biophysical properties such as plant flexibility. Furthermore, seasonal changes in these thresholds due to different plant development stages and differences in thresholds between single individuals of certain species and those associated in complex vegetation canopies will be determined. Finally, we will (iii) analyse effects of rising temperatures on biophysical properties and thus wave attenuation capacity of marsh plants in a world-unique whole ecosystem salt-marsh warming experiment. We expect that warming will increase above- and belowground biomass, prolong the growing season and increase the lignin content of plants. Overall, this might increase the coastal protection function of salt marshes in a warmer world. The results will be made available to be fed into both hydrodynamic models of wave impact on land-ward lying sea defences as well as into models of marsh evolution under different climate change and sea level rise scenarios. The findings will thus help to assess the coastal protection function of salt marshes adequately in the future and to better deal with impacts of ecological stochasticity and extreme events such as storm surges on coastal salt marshes.