The impact of vegetation on meandering rivers

The relationships between the evolution of land plants, meandering-river dynamics and global biogeochemical fluxes remain poorly understood. This Review explores the relationships between vegetation and the stability and dynamics of meandering rivers and will serve anthropogenic stressors on Earth's rivers.The Palaeozoic evolution of land plants revolutionized river geomorphology. However, the relationships between biotic forcing and channel dynamics are still debated and, as such, the impacts of anthropogenic stressors such as climate change, reduced biodiversity and aridification on modern meandering rivers and their biogeochemical fluxes remain poorly understood. In this Review, we propose a unifying framework based on field and modelling data that describes the stability and dynamics of meandering rivers in both the presence and the absence of land plants. Based on evidence from the pre-vegetation rock record and from modern systems, we emphasize that meandering streams can indeed arise in the absence of land plants. However, plant evolution provided widespread settings suitable for stable meandering systems through retention of floodplain mud, sediment baffling and mechanical strengthening of channel banks. Altogether, these processes slowed the characteristic rates of meander growth and floodplain-soil reworking by up to an order of magnitude. Continued anthropogenic removal of riparian and watershed vegetation due to increased urbanization, deforestation, aridification and pollution could revert streams to pre-vegetation functioning, thereby increasing their channel and sediment mobility. Future research can use this framework to constrain the pace of ancient landscape processes on Earth and Mars, in addition to modern terrestrial rivers impacted by humans.

陆地植物的演化、曲流河动力学以及全球生物地球化学通量之间的关系仍知之甚少。本综述探讨了植被与曲流河的稳定性和动力学之间的关系，并将涉及地球河流面临的人为压力因素。陆地植物在古生代的演化彻底改变了河流地貌。然而，生物作用力与河道动力学之间的关系仍存在争议，因此，诸如气候变化、生物多样性减少和干旱化等人为压力因素对现代曲流河及其生物地球化学通量的影响仍不太清楚。在本综述中，我们基于野外和模拟数据提出了一个统一的框架，该框架描述了有陆地植物和无陆地植物情况下曲流河的稳定性和动力学。基于无植被岩石记录和现代系统的证据，我们强调在没有陆地植物的情况下确实可能出现曲流河。然而，植物的演化通过保留洪泛平原的淤泥、阻挡沉积物以及对河岸进行机械加固，为稳定的曲流系统提供了广泛的环境。总体而言，这些过程将曲流增长和洪泛平原土壤再造的特征速率减缓了多达一个数量级。由于城市化加剧、森林砍伐、干旱化和污染，河岸和流域植被持续受到人为清除，这可能使河流恢复到无植被时的功能状态，从而增加其河道和沉积物的流动性。未来的研究可以利用这个框架来限制地球和火星上古代地貌过程的速度，以及受人类影响的现代陆地河流的相关情况。