Environmental Factors as Predictors of Seagrass Soil Carbon Stocks in the Solent, UK

Seagrass ecosystems have high carbon storage potential, acting as important global carbonsinks. However, seagrass soils are increasingly under threat from erosion, with meadowsexperiencing a global estimated decline of 7% per year, potentially leading to CO2 emissions.This decline has been driven by disturbances related to eutrophication, shading, erosion,warming, and physical removal, particularly over the last 100 years. This studyevaluates the relationship between a range of variables and carbon storage potential inseagrass meadows from the Solent, UK. By establishing relationships betweenparameters, this study provides important information on the main environmental factorsimpacting seagrass carbon storage potential, providing useful information for restorationprojects. Six fieldwork sites were selected within the Solent region, in southern England. Selectedsampling sites encompass seagrass habitats on both muddy and sandy substrates,incorporating Zostera marina (Eelgrass), Zostera noltii, Zostera angustifolia, andRuppia spp. meadows, thus providing comparable environmental data between thesehabitats. Relationships between soil carbon stocks, edaphic, and ecological factorswere examined to determine which factors were correlated with seagrass carbonstorage (Corg) potential. Environmental factors were grain size, dry bulk density,sorting, %silt, salinity, pH, nutrients, elevation, seagrass species diversity, and shootdensity. A test for analysis of variance showed that, soil Corg (MgCha−1), Dry bulk density(DBD) (g/cm3), mean grain size (φ), sorting coefficient, %Silt, pH, salinity (0/00) andelevation (m) were significantly different between sites. The relationship between soil Corg(MgCha−1) and the predictor variables was explained in a Partial least square regressionmodel (PLS). The first five components selected explained 88.7% of the variation in the data,with the most important variables responsible for the variation in soil Corg being DBD,followed in a ranking order by NO2− (μmolL−), SO4−2 (μmolL−), pH, sorting coefficient(φ) and salinity (). The first five predictors appointed by PLS as main drivers for variation in soil Corg, wereselected for inclusion in a PCA analysis. Edaphic characteristics showed the largestinfluences on the model, with sorting (φ), and DBD (g/cm3) closely correlated to soil Corg(MgCHa−1). PCA also showed that the concentration of nutrients (NO2− (μmolL−) andSO4−2 (μmolL−), pH, and DBD (g/cm3), were the main drivers in Ryde (RYST), Cowes(CWST) and Farlington Marshes (FMST), while soil Corg (MgCha−1) and sorting coefficient(φ) were the most influential variables for Creek Rythe (CRST), Hayling Island (LGST) and Porchester (PMST). Correlation tests to identify individual associations between the main five environmental predictors and soil Corg (MgCha−1) corroborated PCA’s results, with DBD (g/cm3)presenting a strong negative relationship, and sorting (φ) a strong positive relationship, with soil Corg (MgCHa−1). This shows that edaphic variables, mainly related to grain size and percentage of fine particles, were the most relevant for seagrass carbon storage (Corg).However, all 11 parameters presented different degrees of effect in soil Corg stocks across sites, indicating the importance of considering environmental factors when addressing monitoring needs with the aim of conserving and protecting these ecosystems and their role as carbon sinks