Global-scale human impact on delta morphology has led to net land area gain
Global-scale human impact on delta morphology has led to net land area gain
复制标题
DOI：
10.1038/s41586-019-1905-9
复制
发表时间：
2020-01-01
期刊：
影响因子：
64.8
通讯作者：
Tornqvist, T. E.
中科院分区：
文献类型：
--
作者：
Nienhuis, J. H.;Ashton, A. D.;Tornqvist, T. E.
河流三角洲是地球上最具经济和生态价值的环境之一。即使在没有海平面上升的情况下，三角洲也越来越容易受到沿海灾害的影响，因为沉积物供应减少和气候变化改变了三角洲的沉积物预算，影响了三角洲的形态，并可能导致侵蚀（1-3）。然而，三角洲沉积物预算，波浪和潮汐的海洋力量，三角洲形态之间的关系仍然很难量化。在这里，我们展示了全球约11，000个沿海三角洲的形态，从小型海湾三角洲到大型三角洲，都受到了河流筑坝和森林砍伐的影响。我们介绍了一个模型，该模型表明，当今的三角洲形态变化之间的连续波（约80%），潮汐（约10%）和河流（约10%）的优势，但大多数大型三角洲潮汐和河流为主。过去30年来，尽管海平面上升，全球各三角洲每年净增加土地面积54 +/- 12平方公里（2个标准差），其中最大的1%三角洲占所有净增加土地面积的30%。人类是这些净土地收益的重要驱动力-三角洲增长的25%可归因于森林砍伐引起的河流沉积物供应增加。然而，在近1,000个三角洲中，拦河筑坝（4）导致人为沉积物通量严重减少（50%以上），迫使三角洲土地每年集体损失12 +/- 3.5平方公里（2个标准差）。并非所有的三角洲都会因筑坝而失去土地：向潮汐优势过渡的三角洲目前正在获得土地，可能是通过河道填充。然而，随着预期的海平面加速上升（5），最近的土地收益不太可能在整个世纪持续下去。了解波浪和潮汐对沉积物的重新分布对于成功预测人类活动对三角洲的影响至关重要，无论是在当地还是全球范围内。一项全球河流三角洲研究显示，在过去30年中，三角洲面积净增加了约54 km（2）yr（-1），部分原因是森林砍伐导致的沉积物输送增加。
River deltas rank among the most economically and ecologically valuable environments on Earth. Even in the absence of sea-level rise, deltas are increasingly vulnerable to coastal hazards as declining sediment supply and climate change alter their sediment budget, affecting delta morphology and possibly leading to erosion(1-3). However, the relationship between deltaic sediment budgets, oceanographic forces of waves and tides, and delta morphology has remained poorly quantified. Here we show how the morphology of about 11,000 coastal deltas worldwide, ranging from small bayhead deltas to mega-deltas, has been affected by river damming and deforestation. We introduce a model that shows that present-day delta morphology varies across a continuum between wave (about 80 per cent), tide (around 10 per cent) and river (about 10 per cent) dominance, but that most large deltas are tide- and river-dominated. Over the past 30 years, despite sea-level rise, deltas globally have experienced a net land gain of 54 +/- 12 square kilometres per year (2 standard deviations), with the largest 1 per cent of deltas being responsible for 30 per cent of all net land area gains. Humans are a considerable driver of these net land gains-25 per cent of delta growth can be attributed to deforestation-induced increases in fluvial sediment supply. Yet for nearly 1,000 deltas, river damming(4) has resulted in a severe (more than 50 per cent) reduction in anthropogenic sediment flux, forcing a collective loss of 12 +/- 3.5 square kilometres per year (2 standard deviations) of deltaic land. Not all deltas lose land in response to river damming: deltas transitioning towards tide dominance are currently gaining land, probably through channel infilling. With expected accelerated sea-level rise(5), however, recent land gains are unlikely to be sustained throughout the twenty-first century. Understanding the redistribution of sediments by waves and tides will be critical for successfully predicting human-driven change to deltas, both locally and globally.A global study of river deltas shows a net increase in delta area by about 54 km(2) yr(-1) over the past 30 years, in part due to deforestation-induced sediment delivery increase.