Nordic Blue Carbon Ecosystems: Status and Outlook

Abstract

Vegetated coastal and marine habitats in the Nordic region include salt marshes, eelgrass meadows and, in particular, brown macroalgae (kelp forests and rockweed beds). Such habitats contribute to storage of organic carbon (Blue Carbon – BC) and support coastal protection, biodiversity and water quality. Protection and restoration of these habitats therefore have the potential to deliver climate change mitigation and co-benefits. Here we present the existing knowledge on Nordic BC habitats in terms of habitat area, C-stocks and sequestration rates, co-benefits, policies and management status to inspire a coherent Nordic BC roadmap. The area extent of BC habitats in the region is incompletely assessed, but available information sums up to 1,440 km2 salt marshes, 1,861 (potentially 2,735) km2 seagrass meadows, and 16,532 km2 (potentially 130,735 km2, including coarse Greenland estimates) brown macroalgae, yielding a total of 19,833 (potentially 134,910) km2. Saltmarshes and seagrass meadows have experienced major declines over the past century, while macroalgal trends are more diverse. Based on limited salt marsh data, sediment C-stocks average 3,311 g Corg m-2 (top 40-100 cm) and sequestration rates average 142 g Corg m-2 yr-1. Eelgrass C-stocks average 2,414 g Corg m-2 (top 25 cm) and initial data for sequestration rates range 5-33 g Corg m-2, quantified for one Greenland site and one short term restoration. For Nordic brown macroalgae, peer-reviewed estimates of sediment C-stock and sequestration are lacking. Overall, the review reveals substantial Nordic BC-stocks, but highlights that evidence is still insufficient to provide a robust estimate of all Nordic BC-stocks and sequestration rates. Needed are better quantification of habitat area, C-stocks and fluxes, particularly for macroalgae, as well as identification of target areas for BC management. The review also points to directives and regulations protecting Nordic marine vegetation, and local restoration initiatives with potential to increase C-sequestration but underlines that increased coordination at national and Nordic scales and across sectors is needed. We propose a Nordic BC roadmap for science and management to maximize the potential of BC habitats to mitigate climate change and support coastal protection, biodiversity and additional ecosystem functions.

First assessment of seagrass carbon accumulation rates in Sweden: A field study from a fjord system at the Skagerrak coast

“…The cumulative accumulation of C org stocks showed a relatively small variation between cores with similar C org stocks at 50 cm, ranging from about 4.6 to 5.9 kg C org m -2 , which are comparable to previous assessments in the Skagerrak-Kattegat region [14,19,29,58]. The main difference in C org stocks between the cores was due to the variation in seagrass sediment depth thickness resulting in a storage from 0.7 kg C org m -2 at Va ¨stra Korsvik (with a seagrass sediment depth of 11 cm) up to 20.6 kg C org m -2 in the Kristineberg 2 core (accumulated in 149 cm thick seagrass sediment).…”

Arctic kelp forest decline -- a consequence of melting glaciers?

“…Together with the kelp forest retreat at our study site, this might resemble the predicted decline in kelp forest contribution to marine carbon cycles under the negative impacts of increasing water turbidity (Blain et al, 2021). However, the potential contribution of kelp forests in general to natural carbon sequestration remains a controversially discussed topic in current research (Hurd et al, 2022;Krause-Jensen et al, 2022;Pedersen et al, 2020).…”

Are Nordic Saltmarshes Europe’s Way to ‘Live in Harmony with Nature’? Scientists Driven Future Scenarios via a Participatory Workshop

“…They provide invaluable benefits (i.e., ecosystem services) such as retention and transforming nutrients and pollutants, controlling floods, and providing protection from storm surges and erosion [2][3][4][5]. The area of known data on saltmarshes' coverage in Nordic countries is estimated to be nearly 1440 km 2 [6], which has been on the decline since the end of the last ice age when the ecosystems were formed over 12,000 years ago. Moreover, reduction in the area has accelerated due to dredging and draining the marshes to build roads and houses or even using them as landfills [7] while recent studies show that home values increase when saltmarshes are preserved [8].…”