Clam harvesting decreases the sedimentary carbon stock of a Zostera marina meadow

Duque-Núñez

et al. 2019

Sci Rep

Coastal vegetated ecosystems are major organic carbon (OC) and total nitrogen (TN) sinks, but the mechanisms that regulate their spatial variability need to be better understood. Here we assessed how superficial sedimentary OC and TN within intertidal vegetated assemblages (saltmarsh and seagrass) vary along a flow gradient, which is a major driver of sediment grain size, and thus of organic matter (OM) content. A significant relationship between flow current velocity and OC and TN stocks in the seagrass was found, but not in the saltmarsh. OC and TN stocks of the saltmarsh were larger than the seagrass, even though that habitat experiences shorter hydroperiods. Mixing models revealed that OM sources also varied along the flow gradient within the seagrass, but not in the saltmarsh, showing increasing contributions of microphytobenthos (17–32%) and decreasing contributions of POM (45–35%). As well, OM sources varied vertically as microphytobenthos contribution was highest at the higher intertidal saltmarsh (48%), but not POM (39%). Macroalgae, seagrass and saltmarsh showed low contributions. Local trade-offs between flow current velocities, hydroperiod and structural complexity of vegetation must be considered, at both horizontal and vertical (elevation) spatial dimensions, for better estimates of blue carbon and nitrogen in coastal ecosystems.

Section: Discussionmentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Superficial sedimentary stocks and sources of carbon and nitrogen in coastal vegetated assemblages along a flow gradient

Duque-Núñez

et al. 2019

Sci Rep

Limnology & Oceanography

“…Furthermore, the molecular composition and recalcitrance of OC sources (litter quality), sediment mineralogy, temperature, and microbial community composition are also important in determining the quantity and quality of carbon sequestered in seagrass meadows (Belshe et al ; Trevathan‐Tackett et al ). Benthic disturbances, such as shading, bioturbation by infauna, and wave action, can also influence OC stocks (Barañano et al ; Trevathan‐Tackett et al ). On the Central Coast of British Columbia, bioturbation by sea otters ( Enhydra lutris ) digging for prey, the dynamics of active infaunal communities, and human activities including dredging, log boom shading, increasing sedimentation, and erosion should be investigated further to determine their impacts on the carbon sequestration and storage capacity of nearshore systems.…”

Section: Discussionmentioning

confidence: 99%

Reduced water motion enhances organic carbon stocks in temperate eelgrass meadows

Prentice

Hessing‐Lewis

Sanders‐Smith

et al. 2019

Organic carbon (OC) storage in coastal vegetated ecosystems is increasingly being considered in carbon financing and climate change mitigation strategies. However, spatial heterogeneity in these “blue carbon” stocks among and within habitats has only recently been examined, despite its considerable implications. Seagrass meadows have potential to store significant amounts of carbon in their sediments, yet studies comparing sediment OC content at regional and meadow scales remain sparse. Here, we collected sediment cores from six temperate eelgrass (Zostera marina) meadows on the coast of British Columbia, Canada, to quantify sediment OC stocks, accumulation rates, and sources, and to examine local and regional drivers of variability. Sediment OC content was highly variable—across all sites, stocks in the top 0–5 cm ranged from 83 to 1089 g OC m−2, while the 15–20 cm stocks exhibited a 24‐fold difference, from 59 to 1407 g OC m−2. Carbon accumulation rates ranged from 4 to 33 g OC m−2 yr−1. Isotopic mixing models revealed that sediment OC was primarily terrestrial carbon (41.3%) and canopy‐forming kelps (33.3%), with a smaller contribution of eelgrass (25.3%). Here, we show that regional variability in OC content exceeds meadow‐scale variability. This result is likely driven by landscape factors, most notably relative water motion, representing a more dominant control on seagrass OC accumulation than meadow‐scale factors such as canopy complexity. These findings elicit caution when scaling up seagrass meadow OC content and demonstrate that measures of the hydrodynamic environment could improve estimates of carbon storage in temperate soft sediment habitats.

“…Despite the environmental and socio-economic importance of seagrass ecological services, these habitats are strongly declining worldwide 13,14 . Natural and anthropogenic drivers have led to coastal wetlands degradation 14 and sediment-stored C release to the atmosphere and ocean, shifting these ecosystems from C sinks to C sources 14–16 . Some of the main triggers for wetland loss are sediment erosion and physical impacts (e.g.…”

Section: Introductionmentioning

confidence: 99%

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

Sousa

Silva

Azevedo

et al. 2019

Sci Rep

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.