Data and code for "Vegetation effects on delta evolution with rising sea level: Insights from experimental deltas"

Vegetation is a major control on delta evolution, but its impact over intermediate (10^2–10^3 yrs) and long (>10^3 yrs) timescales is relatively unconstrained. We particularly lack these constraints in the context of rising sea level. To address this, we conducted a set of laboratory experiments to isolate the effect of vegetation on delta evolution over intermediate-to-long timescales with sea level rise, using alfalfa (Medicago sativa) as a vegetation proxy. We found that vegetation effects promoted fixed delta shorelines that migrated more slowly and across a smaller area, preventing rapid area fluctuations and slowing area loss with sea level rise. Vegetation effects led to localized shoreline deposition and increased shoreline roughness at the landscape scale and across spatial scales. However, non-vegetated shorelines were transiently rougher during periods of rapid shoreline adjustments and area change. Vegetation promoted confined channel networks that were relatively fixed as sea level rose, resulting in a larger proportion of the delta topset characterized by longer floodplain residence times. While vegetated and non-vegetated delta channel networks had distinct channel mobility styles, the cumulative amount of geomorphic reworking was broadly equal over time, highlighting the importance of considering mass balance when assessing channel avulsion and migration hazards over timescales associated with sea level rise. These results are useful to predict how vegetation will modulate delta response to sea-level rise, climate change-induced vegetation turnover, and anthropogenic activities. More broadly, these results have implications for quantifying long-term carbon storage in delta floodplains and interpreting how modern and ancient deltas evolved.

植被是三角洲演化的核心控制因素之一，但当前学界对其在中等时长（10²–10³年）及长期（>10³年）时间尺度上的影响尚缺乏明确约束，且在海平面上升（sea level rise）背景下的相关约束尤为匮乏。为填补这一研究空白，本研究以紫花苜蓿（*Medicago sativa*）作为植被替代物（vegetation proxy），开展了一系列室内模拟实验，以分离海平面上升背景下植被对中等至长期时间尺度三角洲演化的影响。实验结果表明，植被作用可促使三角洲岸线趋于稳定：岸线迁移速度更慢、活动范围更小，能够抑制岸线面积的快速波动，并减缓海平面上升引发的岸线面积流失。植被作用会促进岸线局部沉积，并在景观尺度及各级空间尺度上提升岸线粗糙度（shoreline roughness）。但在岸线快速调整与面积变化阶段，无植被覆盖的岸线会呈现出暂时性的更高粗糙度。植被可促使形成受约束的河道网络，该网络在海平面上升过程中相对稳定，使得三角洲顶积层（delta topset）中拥有更长洪泛平原滞留时间的区域占比更高。尽管有植被与无植被覆盖的三角洲河道网络展现出截然不同的河道活动模式（channel mobility styles），但随时间推移，两者的地貌改造（geomorphic reworking）总体量大体相当。这一结果凸显了在评估海平面上升相关时间尺度下的河道决溢（channel avulsion）与迁移风险时，考虑物质平衡（mass balance）的重要性。本研究结果可为预测植被如何调节三角洲对海平面上升、气候变化引发的植被更替以及人类活动的响应提供参考。从更广泛的视角来看，本研究结果对量化三角洲洪泛平原的长期碳储量，以及解读现代与古三角洲的演化过程均具有参考价值。