Capturing of organic carbon and nitrogen in eelgrass sediments of southern Scandinavia

Abstract

The ability of seagrass meadows to filter nutrients and capture and store CO 2 and nutrients in the form of organic carbon (OC) and nitrogen (N) in their sediments may help to mitigate local eutrophication as well as climate change via meadow restoration and protection. This study assesses OC and N sediment stocks (top 50 cm) and sequestration rates within Danish eelgrass meadows. At four locations, eelgrass-vegetated and nearby unvegetated plots were studied in protected and exposed areas. The average OC and N sediment 50 cm stocks were 2.6 AE 0.3 kg OC m À2 and 0.23 AE 0.01 kg N m À2 , including vegetated and unvegetated plots. In general, OC and N stocks did not differ significantly between eelgrass meadows and unvegetated sediments. Lack of accumulation of excess 210 Pb suggested sediment erosion or low rates of sediment accumulation at most sites. OC accumulation rates ranged from 6 to 134 g m À2 yr À1 and N from 0.7 to 14 g m À2 yr À1 . Generalized additive models showed that ≥ 80% of the variation in sediment OC and N stocks was explained by sediment grain size, organic matter source, and hydrodynamic exposure. Long cores, dated with 210 Pb, showed declining OC and N densities toward present time, suggesting long-term declines in eelgrass OC and N pools. Estimates of potential nation-wide OC and N accumulation in eelgrass sediments show that they could annually capture up to 0.7% AE 0.5% of CO 2 emissions and 6.9% AE 5.2% of the total terrestrial N load.

A 2,000‐Year Record of Eelgrass (Zostera marina L.) Colonization Shows Substantial Gains in Blue Carbon Storage and Nutrient Retention

“…However, the carbon‐ (CAR: 6–8 g OC m −2 year −1 ) and nitrogen accumulation rates (NAR: 0.5–0.8 g N m −2 year −1 ) at Gåsö for the latest ∼0.7 to 1 cal ka BP (Section 3) are still lower than accumulation rates in Zostera spp. meadows in general (Martins et al., 2022; Prentice et al., 2020) and in the lower range compared to levels found in other studies in the Skagerrak‐Kattegat region, which estimated CAR between 6 and 134 g OC m −2 year −1 and NAR from 0.7 to 14 g N m −2 year −1 (Dahl et al., 2023; Leiva‐Dueñas et al., 2023). However, these studies only assessed accumulation over shorter time periods (the last decades to century), while long‐term accumulation rates tend to be lower for seagrass in general due to diagenesis and remineralization of the organic matter over time (Belshe et al., 2019).…”

“…10.1029/2023GB008039 134 g OC m 2 year 1 and NAR from 0.7 to 14 g N m 2 year 1 (Dahl et al, 2023;Leiva-Dueñas et al, 2023). However, these studies only assessed accumulation over shorter time periods (the last decades to century), while long-term accumulation rates tend to be lower for seagrass in general due to diagenesis and remineralization of the organic matter over time (Belshe et al, 2019).…”

“…For cold-temperate seagrass species, such as Z. marina, using paleoreconstructions for describing past environmental conditions and to predict future changes is lacking (but see Kindeberg et al, 2019;Leiva-Dueñas et al, 2023). There are a number of seagrass-directed paleorecords of the genus Posidonia (López-Merino et al, 2017;Macreadie et al, 2012;Mateo et al, 1997Mateo et al, , 2010Serrano et al, 2011Serrano et al, , 2016, but these are geographically constrained to Australia and the Mediterranean.…”

Short-term variation in pH in seawaters around coastal areas of Japan: characteristics and forcings

“…In such cases, not only the reduction in dissolved nutrients but also the reduction in particulate organic matter transported from rivers to coastal areas will contribute to the suppression of short-term pH drawdown. Many studies have already mentioned the contribution of seaweed/seagrass beds to the effective capture of suspended organic sediments in estuaries (e.g., Barcelona et al, 2021;Leiva-Dueñas et al, 2023;Potouroglou et al, 2017), and hence, the conservation and/or development of seaweed/seagrass beds in estuarine and coastal areas will contribute to the reduction in organic matter transport from rivers to coastal areas at times of high river flow. To specify effective measures against the current coastal acidification in Japan, further detailed observations, especially at the time of increase in water level of the river, are needed such that we can obtain a detailed understanding of practical processes that cause short-term pH variation in coastal waters.…”

The roles of seagrass litter decomposition in determining blue carbon sink capacity

“…Autochthonous C org sources include living and dead above‐ and below‐ground seagrass tissues, whereas allochthonous C org sources include imported marine algae and phytoplankton, as well as C org from terrestrial runoff and adjacent coastal ecosystems (Mcleod et al 2011; Gullström et al 2018). Notably, the contribution of autochthonous C org to the sediment C org sink exhibits considerable spatial variation across seagrass meadows (Duarte et al 2013; Leiva‐Dueñas et al 2023). Consequently, seagrass litter materials, as the dominant autochthonous source of C org , play an essential role in C org storage within seagrass meadows.…”