Brosens Liesa, Broothaerts Nils, Campforts Benjamin, Jacobs Liesbet, Razanamahandry Vao Fenotiana, Van Moerbeke Quinten, Bouillon Steven, Razafimbelo Tantely, Rafolisy Tovonarivo, Govers Gerard
Research Foundation Flanders (FWO), Egmontstraat 5, 1000 Brussels, Belgium; Department of Earth and Environmental Sciences, KU Leuven, Leuven, Belgium.
Department of Earth and Environmental Sciences, KU Leuven, Leuven, Belgium.
Sci Total Environ. 2022 Feb 1;806(Pt 2):150483. doi: 10.1016/j.scitotenv.2021.150483. Epub 2021 Sep 29.
Lavaka (gullies) are often considered as the prime indication of a currently ongoing human-induced environmental crisis in Madagascar's highlands. Yet, lavaka are known to have existed long before human arrival and account for the majority of the long-term sediment input into the highland rivers and floodplains. The role of anthropogenic disturbances in their formation therefore remains highly debated and it is unclear whether lavaka erosion has recently increased. Here, we address these questions by evaluating the dynamics of lavaka in the Lake Alaotra region (central Madagascar). An overall birth to stabilization ratio of 6.1 indicates a rapid lavaka population growth over the period 1949-2010s. Using data on lavaka development we calculated a mean lavaka population age of 410 ± 40 years and estimate that the disequilibrium started at 870 ± 430 cal. BP. Floodplain sedimentation starts to increase around 1000 cal. BP and peaks over the last 400 years, thereby independently confirming this time frame of increased lavaka activity. Lavaka population dynamics modelling shows that a strong increase in environmental pressure over the last centuries is needed to attain current disequilibrium levels. A general drying of the climate since 950 cal. BP in combination with the introduction of cattle and growing human presence around 1000 cal. BP will likely have triggered the increase in lavaka erosion. However, the recent acceleration cannot be explained by climatic changes alone and seems to be linked to increased anthropogenic pressure on the environment. As such, we offer a fresh and quantitatively supported perspective on lavaka dynamics and human impact in central Madagascar, where our methodology can be used in other locations where similar questions on geomorphic equilibrium need to be answered.
拉瓦卡（沟壑）通常被视为马达加斯加高地当前正在发生的人为环境危机的主要迹象。然而，众所周知，拉瓦卡早在人类到来之前就已存在，并且是高地河流和洪泛平原长期沉积物输入的主要来源。因此，人为干扰在其形成过程中的作用仍存在激烈争论，目前尚不清楚拉瓦卡侵蚀最近是否有所增加。在这里，我们通过评估阿拉奥特拉湖地区（马达加斯加中部）拉瓦卡的动态来解决这些问题。1949年至21世纪10年代期间，拉瓦卡总体的形成与稳定比例为6.1，这表明拉瓦卡数量快速增长。利用拉瓦卡发育的数据，我们计算出拉瓦卡群体的平均年龄为410±40年，并估计这种不平衡始于公元前870±430年的校准年代。洪泛平原的沉积在公元前1000年左右开始增加，并在过去400年达到峰值，从而独立地证实了拉瓦卡活动增加的这一时间框架。拉瓦卡群体动态模型表明，要达到当前的不平衡水平，需要在过去几个世纪里大幅增加环境压力。自公元前950年以来气候普遍变干，再加上公元前1000年左右引入牛以及人类活动增加，可能引发了拉瓦卡侵蚀的增加。然而，近期的加速不能仅用气候变化来解释，似乎与环境上不断增加的人为压力有关。因此，我们提供了一个全新的、有定量支持的视角，来探讨马达加斯加中部拉瓦卡动态和人类影响，我们的方法可用于其他需要回答类似地貌平衡问题的地区。
