Gustafsson, Camilla

Roth, Florian

English

Helsingin yliopiston digitaalinen arkisto

https://helda.helsinki.fiPolicy brief: Healthy coastal ecosystems are crucial to mitigateclimate changeRoth, Florian2021-08-25Roth , F & Gustafsson , C 2021 , ' Policy brief: Healthy coastal ecosystems are crucial tomitigate climate change ' , Policy Brief . <https://www.su.se/polopoly_fs/1.567417.1629364115!/menu/standard/file/PBbluecarbon.pdf >http://hdl.handle.net/10138/353664unspecifiedpublishedVersionDownloaded from Helda, University of Helsinki institutional repository.This is an electronic reprint of the original article.This reprint may differ from the original in pagination and typographic detail.Please cite the original version.Policy BriefAugust 2021Healthy coastal ecosystems are crucial to mitigate climate changeBaltic Sea CentreBaltic Sea CentreThe coastal zones are among the most effective areas on Earth at sequestering carbon from the atmosphere. Treated right, these ecosystems are important corner- stones in climate change mitigation, but if degraded, they instead release large amounts of greenhouse gases, re-enforcing global warming. Urgent action is needed to preserve and restore the Baltic Sea coasts and use these systems to work in favor of the climate – not against it.The land-ocean transition zones, the coasts, are biodiversity and productivity hotspots. In submerged coastal landscapes, a mosaic of seafloor vegetation provides habitat for numerous marine or-ganisms, but these ecosystems also play a significant role in the oceanic carbon cycle. In fact, coastal ecosystems sequester carbon – often referred to as blue carbon – from the atmosphere and oceans at significantly higher rates, per unit area, than terrestrial forests. To date, it is estimated that coastal blue carbon systems sequester 4 to 10 tons of carbon dioxide per hectare and year, thereby accounting for almost half of the total carbon sequestered in ocean sediments, despite that they cover less than two percent of the ocean floor. Healthy and diverse coastal ecosystems play an important role in climate mitigation by sequestering carbon from the atmosphere.Promote healthy coastal ecosystems by:• Reducing pollution, such as hazardous chemicals and nutrients, especially in shallow areas and bays.• Prohibiting bottom disturbing activities, such as bottom trawl fishing and dredging in coastal regions.• Stopping the ongoing exploitation of the coast by limiting new buildings and piers.Actively restore degraded but important carbon-sequestering coastal habitats, such as those of eelgrass and bladderwrack.Include managment of marine coastal ecosystems in climate policies. Support research on blue carbon ecosystem in the Baltic Sea.POLICY RECOMMENDATIONSPhoto: Mats WesterbomWith these outstanding properties, vegetated coastal ecosystems play a critical role in capturing carbon that would otherwise remain as atmospheric carbon dioxide and exacerbate climate change. Alt-hough often overlooked, it is now time to acknowledge this impor-tant ecosystem service and consider it a key argument for both the preservation and restoration of Baltic Sea coasts.Long-term storage of carbon in coastal sedimentsMangrove forests, salt marshes and seagrass meadows are typical examples of blue carbon ecosystems. Such ecosystems are found along the coastlines of every continent, except Antarctica, and they are extremely efficient in capturing carbon dioxide from the atmosphere through photosynthesis. They also trap organic matter from the water column, and their complex underground stem and root systems help binding and storing large amounts of carbon in the sediment below. The coasts of Scandinavia and the Baltic Sea are key distribution areas for eelgrass (Zostera marina L.) meadows – a seagrass with a large carbon storage capacity. In addition, other shallow submerged coastal ecosystems with mixed vegetation and salt marshes in the Baltic Sea are considered hots-pots of carbon cycling. Kept undisturbed, plants in these areas can absorb large amounts of carbon, which may be transported into the sediments, where it can remain for a long time.Coastal macroalgae also absorb large amounts of carbon. In the Baltic Sea, the bladderwrack (Fucus vesiculosus) is widespread. It has a high biomass and productivity, and often dominates shallow benthic communities with a positive effect on coastal biodiversity. Although lacking roots and, hence, the ability to directly transfer carbon into local sediments, these algae can be exported across the open ocean, and their carbon can be sequestered in long-term reservoirs like coastal sediments and the deep sea.  Unlike terrestrial soils, the sediments of marine ecosystems are lar-gely anaerobic (without oxygen). This means that the carbon in-corporated into the sediments decomposes very slowly and that it takes a long time until it is eventually released back to the water as carbon dioxide. If more sediment is continuously accumulated, the organic matter can be sequestered over geological timescales. The carbon found in coastal sediments is often thousands of years old.Degraded coasts emit greenhouse gasesCoastal ecosystems worldwide bring an enormous value in eco-system services. However, they face increasing pressures due to climate change and other anthropogenic environmental stressors, such as eutrophication, chemical pollution, and physical explo-itation. The rates of loss of coastal blue carbon ecosystems are estimated to be twice that of forests: 0.03 – 1 percent of the total area is lost annually. When these ecosystems are degraded, disappear, or converted to other uses, their carbon sink capacity is lost. But the degradation of coastal blue carbon habitats does not only slow the uptake of carbon from the atmosphere. When degraded or destroyed, these ecosystems start emitting the carbon they have stored for centu-ries into the atmosphere and oceans. Consequently, they become sources of climate-relevant greenhouse gases, both in the form of carbon dioxide and methane – the latter is a potent greenhouse gas with a sustained flux global warming potential 45 times that of carbon dioxide. Currently there is, however, a major knowled-ge gap in our understanding of the variability of such emissions over various spatial and temporal scales, particularly in Baltic Sea coastal environments.It is hypothesized that healthy coastal ecosystems with a high biodiversity work as effective carbon sinks. Coastal ecosystems in a degraded state with lower biodiversity have a limited carbon sink capacity and can be net sources of the climate-relevant greenhouse gases carbon dioxide (CO2) and methane (CH4). Nevertheless, the potential of different types of coastal ecosystems to sequester carbon and the influence of disturbance on this process has not been quantified. Similarly, the role of coastal biodiversity is not well under-stood, neither in the Nordic countries nor elsewhere in the world. Illustration: Jerker Lokrantz/Azote A degraded ecosystem suffering from eutrophication and loss of biodiversity loses its carbon-sequestering potential and might, instead, emit carbon dioxide and methane to the atmosphere.COASTAL BLUE CARBONBlue carbon is a concept describing carbon captured from the atmosphere and water and stored in coastal and marine ecosystems. It highlights that coastal ecosystems, in addition to terrestrial forests (coined as ‘green carbon’), contribute significantly to carbon sequestration.The carbon uptake in coasts and oceans can both result in a short-term storage in plants and algae (i.e., in their biomass), but more importantly, to a long-term sequestra-tion within the seafloor. Through continuous sedimen-tation, organic material may be buried in the sediments where it can remain for millennia. Conservation and restoration of coastal ecosystems, speci-fically salt marshes, seagrass meadows, mangrove forests, and macroalgae habitats are, therefore, excellent examp-les of nature-based solutions for climate mitigation.Photo: Mats WesterbomThe Baltic Sea coast – already a carbon source?There is growing concern that warming in high-latitude regions may lead to a release of stored methane from hot spots such as the Arctic tundra, further exacerbating climate change. Less recogni-zed is the fact that the same may apply to shallow coastal zones in the Baltic Sea, too. Already to date, emissions of methane partially offsets coastal blue carbon burial around the world, and the emissions are likely to increase due to continued urbanization, eutrophication, and global warming. Likewise, measurements in the Baltic Sea during the heatwave in 2018 showed record-high levels of released me-thane from the coastal zone.As extreme weather events are predicted to become more frequent in a changing climate, and eutrophic conditions are characteris-tic for coastal Baltic Sea habitats, it is of uttermost importance to protect Baltic Sea coastal habitats from further degradation that may turn these systems into greenhouse gas hot-spots. At the same time, further knowledge is needed to resolve the scale and drivers of variable methane emissions in heterogeneous and dyna-mic coastal environments – both in healthy and disturbed ecosys-tem-states. Performing such research in the Baltic Sea would be of broad interest since the Baltic Sea is considered a ‘time machine’ for the world’s coastal zones, experiencing the effects of climate change at an accelerated rate while also suffering from multiple other human stressors.Right measures can restore the ecosystemsUnlike the expected release of methane from the Arctic tundra, the release of greenhouse gases from coastal ecosystems is not an irreversible process. Although heating enhances the release of methane from coastal sediments temporarily, it can be prevented by moderating other pressures. TO BRIDGE THE GAP BETWEEN SCIENCE AND POLICYThis policy brief is produced by Stockholm University Baltic Sea Centre.Scientists, policy and communication experts work together to bridge the gap between science and policy. We compile, analyse and synthesise scientific research on Baltic Sea related issues and communicate it at the right moment to the right actor in society. Follow our policy news at @balticseacentre CONTACTFlorian Roth, ResearcherStockholm University and University of Helsinkiflorian.roth@su.seCamilla Gustafsson, ResearcherUniversity of Helsinkicamilla.gustafsson@helsinki.fiScience and communication with focus on the sea+46-8-16 37 18     |    ostersjocentrum@su.se     |    su.se/ostersjocentrumBaltic Sea CentreBaltic Sea CentreCO-BENEFITS OF COASTAL PROTECTION AND RESTORATIONBiodiversity: Healthy coastlines host biodiverse ecosys-tems.Water quality: Wetlands and coastal vegetation can filter water, take up nutrients, enhance the water quality, and produce oxygen.Ocean acidification: Coastal vegetation can locally alle-viate low pH conditions, thereby representing a possible tool to mitigate the consequences of ocean acidification. Food security: Coastal ecosystems are breeding grounds for commercially important fish species.Recreation and tourism: Coasts provide attractive set-tings for outdoor activities.BALTIC BRIDGETaking measures to reduce eutrophication and stop physical disturbance in shallow waters can help re-establish carbon se-questering systems such as seagrasses. Also, methods to actively restore degraded coastal habitats, such as eelgrass and bladder-wrack, are already in use and ready for broader adoption.Need for implementing blue carbon to policiesConserving and restoring coastal habitats has been recognized as an essential component of climate change mitigation. In a recent report of the World Resources Institute, the global mitigation po-tential of healthy coastal marine ecosystems has been estimated to 0.5 billion tons carbon per year. This can be compared to the total annual reductions of greenhouse gas emissions needed by 2050 to fulfill the Paris agreement of 13 billion tons of carbon.  As assets for carbon sequestration, the coasts also have a mone-tary value. For example, the asset value of carbon sequestration by blue carbon ecosystems in the coastal waters of the United Kingdom has been estimated to 60 billion British pounds for the year 2019, which is about ten times as much as the estimated asset This policy brief has been produced within Baltic Bridge - a collaboration between Stockholm University and the University of Helsinki. The collaboration combines the strong ecological and process-oriented research perfor-med at Tvärminne Zoological Station with Stockholm University Baltic Sea Center's expertise in biogeoche-mistry, modeling, and communication. An important part of the Baltic Bridge collaboration has been the research on coastal ecology and climate interactions. This research is now extended with quantifying the carbon sequestra-tion potential of Baltic Sea coastal ecosystems and how greenhouse gas emissions from these areas counteract this important ecosystem service. The overall goal is to help decision-makers and the business community to act for the benefit of the Baltic Sea.value of fish captures in the same waters. Such national assess-ments of blue carbon resources are required to develop policies aiming at preserving vegetated coastal ecosystems to enhance car-bon sequestration and mitigate greenhouse gas emissions. For the Nordic countries there are, however, large uncertainties regarding the carbon stocks and sequestration rates of coastal ecosystems, and limited data is available on the loss and fate of carbon after disturbance. As this knowledge deficit currently hinders the adop-tion of these systems into policies, carbon trading, and national inventories, it is important to rapidly start filling these knowledge gaps, especially considering the fast rate of decline reported for many blue carbon ecosystems.Thus, maintaining the health of coastal ecosystems is not only beneficial for livelihoods, food security, recreational opportunities and biodiversity, but it is also an effective strategy for climate mitigation. To have a chance to reach the goals of the Paris agre-ement, we cannot afford to lose more of the high carbon seques-tering coastal ecosystems or let important habitats degrade into greenhouse gas sources. Instead, we have to make all effort to bre-ak the cycle, restore damaged habitats and return the Baltic Sea coasts to the long-term carbon sinks they have the potential to be.Photo: Kennerth Kullman

Policy brief: Healthy coastal ecosystems are crucial to mitigate climate change

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Policy brief: Healthy coastal ecosystems are crucial to mitigate climate change

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