Collaborative Research: Sea-level Rise and Vegetation Controls on Deltaic Landform Evolution: A Coupled Experimental and Numerical Modeling Study

三角洲是25%的人类人口的家园(Syvitski等人，2005年)。在世界各地，海平面上升速度的变化、流域的土地利用变化、饲料三角洲的土地利用变化以及三角洲上的人类活动本身正在导致三角洲地貌的快速变化，并导致宝贵的栖息地和生态系统服务的丧失。现在迫切需要预测三角洲景观、生态系统和海岸线变化的科学，以成功评估和实施改善全球三角洲可持续性的计划。然而，三角洲的变化受控于沿海河流、动植物、飓风和风暴之间的一系列相互作用，以及一系列人类操纵。这项拟议的研究将通过实验室水槽和计算实验，加强我们对三角洲如何响应气候和土地利用强迫变化的理解和预测能力，重点关注三角洲系统的物理和生物方面。三角洲物理实验将在德克萨斯大学(UT)沉积物传输和地球表面过程(STEP)盆地进行，这将允许独立和精确地控制主要地质因素：沉积物供应和相对海平面上升(RSLR)。这些实验也将是第一次研究形成三角洲的物理和生物过程之间的相互作用。实验将涉及在三角洲表面以不同的空间密度播种小型植物(紫花苜蓿)。生态系统在实验中得到了简化，但仍然自然地与不断增长和自组织的河流三角洲系统共同进化。基于物理实验结果的计算建模工作将产生一个降低复杂性的模型，该模型捕捉在工程和地质时间尺度上相对海平面快速上升时的主要生态地貌动力学反馈。由此产生的计算模型将为实验提供一个平台，以解决在不同的强迫集合(例如，以河流和波浪为主)以及在各种土地利用和气候变化情景下，一系列三角洲类型的生态地貌动态演变。通过实验室实验和计算模拟相结合的方法获得的科学见解包括：1)河流三角洲系统对RSLR的响应，特别是撕裂(洪水)频率和海岸线粗糙度的变化，2)三角洲分流河道网络与植被共同演化的自组织，3)植被密度的空间变化对河道撕裂位置和频率的影响，4)快速RSLR期间植被动力学的反馈如何影响三角洲地貌和所产生的地层。这项工作将产生第一个基于受控实验室实验的定量生态地貌动力学模型，允许探索河流三角洲地貌、河道活动和各种三角洲类型和区域单反比率的脆弱性的未来变化。

Deltas are home for 25% of the human population (Syvitski et al., 2005). Across the world, combinations of changes in sea-level-rise rates, land use changes in the watersheds the feed deltas, and human activities on deltas themselves are causing rapid changes to delta landscapes and loss of valuable habitats and ecosystem services. Science for predicting changes in delta landscapes, ecosystems, and coastlines is now urgently required to successfully evaluate and implement plans to improve sustainability for deltas globally. However, changes on deltas are controlled by an array of interactions between coastal rivers, plants and animals, hurricanes and storms, and a range of human manipulations. The proposed study will enhance our understanding of, and ability to predict how deltas will respond to changes in climate and land-use forcing, focusing on both physical and biological aspects of delta systems using laboratory flume and computational experiments.Physical delta experiments will be conducted in the University of Texas (UT) Sediment Transport and Earth-surface Processes (STEP) basin, which allows for independent and precise controls of the major geological factors: sediment supply and relative sea level rise (RSLR). These experiments will also be the first to investigate interactions between physical and biological processes in shaping deltas. Experiments will involve seeding the delta surface with small plants (Alfalfa) at different spatial densities. The ecosystem is simplified in the experiments but still naturally coevolving with a growing and self-organizing fluviodeltaic system. Computational modeling efforts, based on the results of the physical experiments, will produce a reduced complexity model that captures the main eco-morphodynamic feedbacks under rapid relative sea-level rise over engineering and geological time scales. The resulting computational models will provide a platform for experiments addressing the ecomorphodynamic evolution of a range of delta types, under disparate sets of forcing (e.g. river vs. wave dominated) and under various scenarios of land-use and climate changes. The scientific insights to be gained through the coupled laboratory experiments and computational modeling include: 1) the fluviodeltaic system's response to RSLR, in particular, changes in avulsion (flood) frequency and shoreline roughness, 2) the self-organization of the deltaic distributary channel network that coevolves with vegetation, 3) the effects of spatial variation in vegetation density on channel avulsion location and frequency, and 4) how the feedbacks from vegetation dynamics during rapid RSLR affect deltaic landforms and resulting stratigraphy. This work will produce the first quantitative eco-morphodynamic model based on controlled laboratory experiments, allowing exploration of future changes in fluviodeltaic landscapes, channel activity, and vulnerability for a range of delta types and RSLR rates.