Mangrove ecosystem services under pressure: the history and future of carbon sequestration hotspots

红树林常常与臭鸡蛋的气味和成群的蚊子联系在一起。这可能是真的，但同时这些森林是独一无二的，极其宝贵。红树林生长在充满挑战的环境中，在炎热、泥泞和咸的条件下生存，因为它们在热带和亚热带的陆地和海洋边缘茁壮成长。红树林生态系统为许多动物物种提供了重要的栖息地，它们有助于过滤污染物，保护海岸免受侵蚀。此外，红树林在应对气候变化方面发挥着至关重要的作用，因为它们从大气中捕获和储存了大量碳。事实上，这些森林储存碳的速度比大多数陆地生态系统都快。树木不仅将碳储存在木材和树叶中，也储存在那些气味难闻的泥泞土壤中。尽管有这些好处，但红树林受到严重威胁，因为海平面上升可能导致森林被淹没，人们越来越多地改变沿海景观，干扰红树林赖以生存的自然过程。这种压力对红树林的影响尚不清楚，但其后果可能是红树林的严重损失和碳储量的减少。红树林在非常特殊的条件下繁茂生长。它们在潮汐的定期淹没下生长良好，但无法在长期的洪水中存活。因此，红树林需要不断抬升其生长的土壤以应对海平面上升。红树林可以通过根部捕获陆地和海洋中的沉积物来实现这一目标。此外，死根、枯叶和枯枝在泥泞的土壤中堆积。这有助于红树林海拔上升，死亡植物物质的积累产生了富含碳的沉积物。现在，基本上出现了两种可能性。如果红树林通过在土壤中积累富含碳的植物物质来跟上海平面的上升，那么碳储量实际上可以增加。然而，如果海平面上升的速度超过了红树林土壤的积累，那么树木的死亡将减少碳储量。红树林对海平面上升的适应能力存在限度，而这些限度受到人类活动的影响。例如，修建河流水坝减少了向海岸输送沉积物，而这些沉积物对于帮助红树林生长和实现持续的碳储存是必需的。显然，红树林环境非常复杂，为了保护这些宝贵的环境，迫切需要提高对红树林未来的理解和预测能力。在这个项目中，我们将揭示控制红树林中碳储存的方式和数量的过程，并开发新的计算机模型来研究海平面上升和人类活动对未来碳积累的影响。我们在哥伦比亚（南美洲）选择了三个地点，那里的红树林高达40米（!），使这些森林成为真正的碳储存热点。首先，我们将获得深度为2米的土壤样本。我们将估算它们的碳含量，过去碳积累的速度，以及碳的来源。我们还将使用保存在土壤中的微观植物遗骸来发现过去那里生长过哪些红树林物种，以及这是否影响了碳积累。第三，我们将开发一个模型，能够模拟整个红树林三角洲和河口在几十年到几百年的演变过程。最后，我们将使用这个新模型来研究海平面上升和沉积物供应变化下红树林的命运，以及对未来碳积累的影响。哥伦比亚的高中学生和教师将参加实地考察，并将在科学展览会上向公众展示他们的工作，以提高对红树林价值的认识。我们还将与项目合作伙伴共同努力，利用我们的研究结果支持制定可持续管理战略，以保护红树林环境。

Mangrove forests are often associated with the smell of rotten eggs and swarms of mosquitos. This may be true but at the same time these forests are unique and extremely valuable. Mangrove trees grow in challenging environments surviving hot, muddy and salty conditions as they thrive at the margin of land and sea in the tropics and subtropics. Mangrove ecosystems provide essential habitats for many animal species, they help filtering pollutants and protect the coast against erosion. Moreover, mangroves play a crucial role in combating climate change as they capture and store large amounts of carbon from the atmosphere. In fact, these forests store carbon faster than most land ecosystems. The trees store carbon not only in their wood and leaves, but also in those smelly muddy soils. Despite all these benefits, mangroves are heavily threatened as sea level rise may cause forest drowning and people are increasingly modifying coastal landscapes and interfering with the natural processes on which mangroves depend. The impacts of such pressures on mangrove forests are still unclear, but the consequences may be drastic mangrove loss and reductions in carbon storage.Mangrove trees flourish under very specific conditions. They grow well under regular inundation by tides, but they cannot survive prolonged flooding. Hence mangroves will need to keep raising the bed on which they grow to cope with rising sea levels. Mangroves may accomplish by trapping sediments from the land and the sea with their roots. In addition, dead roots, leaves and branches accumulate within the muddy soils. This helps mangroves to gain elevation and the build-up of dead plant material creates carbon-rich sediments. Now, essentially two possibilities emerge. If mangroves keep up with sea level rise by accumulating carbon-rich plant material in their soils, then carbon stocks can actually increase. However, if sea level rise outpaces mangrove soil buildup, then tree mortality will reduce carbon storage. Limits to the adaptability of mangrove forests to sea level rise exist and these limits are influenced by human activities. Building of river dams, for example, reduces the delivery of sediment to the coast, while this sediment is needed to help raising mangroves and enable continued carbon storage. Clearly, mangrove environments are highly complex and in order to protect these valuable environments, improved understanding and abilities to predict their future are urgently needed.In this project, we will unravel the processes that control how and how much carbon is stored in mangrove forests and develop new computer models to investigate the impacts of sea level rise and human activities on future carbon accumulation. We have selected three sites in Colombia (South America) where mangrove trees reach up to 40 meters (!) making these forests true carbon storage hotspots. First, we will obtain soil samples up to a depth of 2 meters. We will estimate their carbon content, how fast that carbon has accumulated during the past, and where the carbon is coming from. We will also use microscopic plant remains preserved in the soil to discover what mangrove species have grown there in the past and whether this has influenced carbon accumulation. Third, we will develop a model capable of simulating how entire deltas and estuaries with mangrove vegetation evolve over tens to hundreds of years. Finally, we will use this new model to investigate the fate of mangrove forests under rising sea levels and varying sediment supply, and impacts on future carbon accumulation. Colombian high-school students and teachers from will participate in fieldwork and will present their work in science fairs for the general public to increase the awareness of the values of mangrove forests. We will also work together with our project partners to use our findings to support the development of sustainable management strategies in order to safeguard mangrove environments.