Coastal ecosystems are very good at pulling carbon out of the atmosphere. But, as new research in the Baltic Sea shows, we also need to look at what they’re putting back in.
Vegetated habitats along the coast sequester huge amounts of carbon. In fact, half of all the carbon stored in ocean sediment is in three coastal “blue carbon” ecosystems: mangrove forests, seagrass meadows, and salt marshes. Seaweed, or macroalgae, also take in carbon, though it’s unclear how much of that carbon eventually ends up stored in ocean sediment.
Scientists are starting to figure out what that balance looks like in different places. In a recent study in Nature Communications, researchers from Stockholm University and the University of Finland found that habitats of bladderwrack seaweed (Fucus vesiculosus) emit methane that’s equivalent to 28% of the CO2 that they absorb. In mixed vegetation habitats, they found that methane emission amounted to 35% of the CO2 intake.
Methane is released when specialized microorganisms called methanogens break down organic matter in environments with low oxygen. Typically, those conditions are found in places where dead plant matter accumulates in the soft sediment, such as mixed vegetation and bare sediment habitats. But bladderwrack, a common brown seaweed named for the air-filled “bladders” on its fronds that allow it to float, anchors itself onto rocky areas, not soft sediment, so the team were puzzled by the higher-than-expected methane levels.
According to the latest assessment by the Baltic Marine Environment Protection Commission, better known as the Helsinki Commission (HELCOM), 97% of the Baltic Sea is affected by eutrophication, an excess of nutrients in water, with 12% in the most severe category. Caused by nitrogen and phosphorus runoff coming from agricultural fertilizer, wastewater and other sources, eutrophication favors the growth of phytoplankton and fast-growing algae, leading to low-oxygen conditions where methane-producing microorganisms thrive. Management plans to limit nutrient inputs are in place, but it will take some time before levels come down, in part because the Baltic is an inland sea, so whatever goes into the system sticks around.
— source news.mongabay.com | 29 Mar 2023
[there is nothing to worry. a part of the co2 absorbed from atmosphere is returning back to atmosphere. where as continuing burning underground coal or oil or gas, new co2 is entering to atomsphere. that is problem.]