Assessment and Attribution of Mangrove Forest Changes in the Indian Sundarbans from 2000 to 2020
Assessment and Attribution of Mangrove Forest Changes in the Indian Sundarbans from 2000 to 2020
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DOI：
10.3390/rs13244957
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发表时间：
2021-12-01
期刊：
影响因子：
5
通讯作者：
Nicholls, Robert J.
中科院分区：
文献类型：
--
作者：
Samanta, Sourav;Hazra, Sugata;Nicholls, Robert J.
印度孙德尔本斯与孟加拉国一起构成了世界上最大的红树林。该地区红树林的开垦活动于 20 世纪 30 年代停止。然而，它们仍然受到不利的环境影响，例如过去几个世纪恒河-雅鲁藏布江三角洲主要河道迁移造成的沉积物匮乏、气旋登陆、孟加拉湾的波浪作用（由于上游引水而改变水文）以及相对海平面上升的普遍影响。这项研究建立在早期工作的基础上，通过执行最大似然监督分类，使用来自 Landsat 和 MODIS 卫星图像的各种植被指数来评估 2000 年至 2020 年红树林范围、属组成和红树林“健康”指标的变化。我们发现，保护区内约 110 km(2) 的红树林因侵蚀而消失，而孙德尔本斯生物圈保护区 (SBR) 的有人居住区则通过种植和再生增加了 81 km(2) 的红树林。收益都在邻近的红树林之外。然而，它们部分补偿了邻近红树林的碳损失。通过合并已发表的文献和地面实况调查的数据进行分析，发现属的组成发生了向更耐盐的属的变化，同时喜淡水的 Heiritiera、Nypa 和 Sonneratia 组合的流行率也在减少。增强植被指数（EVI）和归一化植被指数（NDVI）等健康指标在过去二十年中呈现出单调恶化的趋势，这在红树林临海部分更为明显。季风前和季风后时期盐度的增加、气温的升高和降雨量的减少似乎导致了这种退化。总的来说，这些结果表明红树林面积和健康状况下降，从长远来看，这对印度孙德尔本斯构成了生存威胁，特别是在气候变化和海平面上升的情况下。鉴于其独特的价值，政策过程应该承认并解决这些威胁。
The Indian Sundarbans, together with Bangladesh, comprise the largest mangrove forest in the world. Reclamation of the mangroves in this region ceased in the 1930s. However, they are still subject to adverse environmental influences, such as sediment starvation due to migration of the main river channels in the Ganges-Brahmaputra delta over the last few centuries, cyclone landfall, wave action from the Bay of Bengal-changing hydrology due to upstream water diversion-and the pervasive effects of relative sea-level rise. This study builds on earlier work to assess changes from 2000 to 2020 in mangrove extent, genus composition, and mangrove 'health' indicators, using various vegetation indices derived from Landsat and MODIS satellite imagery by performing maximum likelihood supervised classification. We show that about 110 km(2) of mangroves disappeared within the reserve forest due to erosion, and 81 km(2) were gained within the inhabited part of Sundarbans Biosphere Reserve (SBR) through plantation and regeneration. The gains are all outside the contiguous mangroves. However, they partially compensate for the losses of the contiguous mangroves in terms of carbon. Genus composition, analyzed by amalgamating data from published literature and ground-truthing surveys, shows change towards more salt-tolerant genus accompanied by a reduction in the prevalence of freshwater-loving Heiritiera, Nypa, and Sonneratia assemblages. Health indicators, such as the enhanced vegetation index (EVI) and normalized differential vegetation index (NDVI), show a monotonic trend of deterioration over the last two decades, which is more pronounced in the sea-facing parts of the mangrove forests. An increase in salinity, a temperature rise, and rainfall reduction in the pre-monsoon and the post-monsoon periods appear to have led to such degradation. Collectively, these results show a decline in mangrove area and health, which poses an existential threat to the Indian Sundarbans in the long term, especially under scenarios of climate change and sea-level rise. Given its unique values, the policy process should acknowledge and address these threats.