Blue Carbon stock in Zostera noltei meadows at Ria de Aveiro coastal lagoon (Portugal) over a decade

Abstract

This work assessed the Blue Carbon (C) stock in the seagrass meadows (Zostera noltei) of Ria de Aveiro coastal lagoon (Portugal), and evaluated its spatio-temporal trend over the 2003–2005 to 2013–2014 period. Zostera noltei spatial distribution, restricted to intertidal areas in 2014, was mapped by remote sensing using an unmanned aerial vehicle (UAV) and aerial photography. Zostera noltei biomass was also monitored in situ over a year and its Blue C stock was estimated. By 2014, intertidal meadows covered an area of 226 ± 4 ha and their Blue C stock ranged from 227 ± 6 to 453 ± 13 Mg C. Overall, Ria de Aveiro Z. noltei intertidal meadows increased in extent over the 2003–2005 to 2013–2014 period, corroborating the recent declining trend reversal observed in Europe and contrary to the global decline trend. This spatio-temporal shift might be related to a natural adjustment of the intertidal meadows to past human intervention in Ria de Aveiro, namely large-scale dredging activities, particularly in the 1996–1998 period, combined with the more accurate assessment performed in 2014 using the UAV. This recovery contributes to the effective increase of the Blue C stock in Ria de Aveiro and, ultimately, to supporting climate regulation and improving ecosystem health. However, major dredging activities are foreseen in the system’s management plan, which can again endanger the recovery trend of Z. noltei intertidal meadows in Ria de Aveiro.

Sediment Characteristics Determine the Flowering Effort of Zostera noltei Meadows Inhabiting a Human-Dominated Lagoon

“…The above-mentioned anthropogenic activities can cause, among others, mechanical impacts across the seagrass meadows and changes in their sediment composition [13][14][15]. Nevertheless, recent studies suggest that some seagrass species, especially of the genus Zostera, are currently adapting to human-modified environments [16][17][18][19][20][21][22].…”

“…In addition, the species inhabits a wide range of salinities (7-35 psu) [24,25], can tolerate elevated seawater temperatures (above 37 • C) [26] and adapts to high light exposure conditions during low tide [27]. Thus, Z. noltei is suited to intertidal areas of estuaries and lagoons, such as Ria de Aveiro, which are also environments dominated by several human activities [16,20]. Numerous studies have shown that there is a positive trend in this seagrass expansion amidst environments dominated by human activities during recent decades (i.e., shellfish harvesting and dredging) [16,20].…”

“…Thus, Z. noltei is suited to intertidal areas of estuaries and lagoons, such as Ria de Aveiro, which are also environments dominated by several human activities [16,20]. Numerous studies have shown that there is a positive trend in this seagrass expansion amidst environments dominated by human activities during recent decades (i.e., shellfish harvesting and dredging) [16,20]. Moreover, the flowering effort of Z. noltei can increase under the influence of certain anthropogenic perturbations such as mechanical, sedimentary and hydrodynamic impacts [28][29][30].…”

High Seasonal Variability in Sediment Carbon Stocks of Cold‐Temperate Seagrass Meadows

“…However, most studies assessing seagrass carbon storage in temperate regions have been performed during the summer and to our knowledge only two studies have examined TOC stock variation across seasons in seagrass meadows. These studies were performed in subtropical or warm‐temperate seagrass meadows and revealed only minor to moderate variation in sedimentary carbon stocks (Samper‐Villarreal et al, ; Sousa et al, ). However, as seasonality is stronger in cold‐temperate areas with larger seasonal variation in environmental conditions, the influence on the carbon stocks will likely be stronger compared to the subtropical and warm‐temperate regions, where the seasonal variation in seagrass growth and productivity, although existing, is not as pronounced (Pérez et al, ; Sousa et al, ; Thorhaug & Roessler, ).…”

“…These studies were performed in subtropical or warm‐temperate seagrass meadows and revealed only minor to moderate variation in sedimentary carbon stocks (Samper‐Villarreal et al, ; Sousa et al, ). However, as seasonality is stronger in cold‐temperate areas with larger seasonal variation in environmental conditions, the influence on the carbon stocks will likely be stronger compared to the subtropical and warm‐temperate regions, where the seasonal variation in seagrass growth and productivity, although existing, is not as pronounced (Pérez et al, ; Sousa et al, ; Thorhaug & Roessler, ). In this study, we measured the sedimentary TOC content during the course of a year in two Z. marina meadows (in both the shallow and deeper parts of the meadow within each site) to examine the effect of seasonality on the carbon storage capacity.…”