Macroalgae form the most extensive and productive benthic marine vegetated habitats globally but their inclusion in Blue Carbon (BC) strategies remains controversial. We review the arguments offered ...to reject or include macroalgae in the BC framework, and identify the challenges that have precluded macroalgae from being incorporated so far. Evidence that macroalgae support significant carbon burial is compelling. The carbon they supply to sediment stocks in angiosperm BC habitats is already included in current assessments, so that macroalgae are de facto recognized as important donors of BC. The key challenges are (i) documenting macroalgal carbon sequestered beyond BC habitat, (ii) tracing it back to source habitats, and (iii) showing that management actions at the habitat lead to increased sequestration at the sink site. These challenges apply equally to carbon exported from BC coastal habitats. Because of the large carbon sink they support, incorporation of macroalgae into BC accounting and actions is an imperative. This requires a paradigm shift in accounting procedures as well as developing methods to enable the capacity to trace carbon from donor to sink habitats in the ocean.
Trace metal contents and fluxes in downward particulate matter and dated sediment cores of the NW Alboran Sea are analysed in this study with the aim of assessing the role of the Atlantic inflow on ...their transport. Increases in Zn, Cu and Pb were detected in downward particulate matter collected by sediment traps after river flooding events and after the Aznalcollar mining spill. Their arrival coincided within the recently estimated time range for river particles discharged into the Gulf of Cádiz to reach the Alboran Sea, indicating that their transfer is enhanced during events of increased river inputs of contaminated particulate matter. This also suggests that the effects of potential tailing dam failures in the Gulf of Cádiz watersheds could reach the Alboran Sea. These trace metals also increased in the sediment cores from the continental rise since the second half of the 19th century, suggesting that contaminated particles have been continuously transferred towards the Mediterranean Sea since that time, when mining concessions and production increased in the SW Iberian Pyrite Belt.
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•Contaminated sediment was transferred from the Gulf of Cádiz to the Alboran Sea.•The transfer of trace metal-enriched particles increased after major river flood events.•Trace metal enrichments were also detected after the Aznalcollar tailings dam failure.•Pyrite production and trace metals in Alboran Sea sediments have increased since the 1850s.•Potential tailing dam failures in the Gulf of Cádiz watersheds could affect the Alborán Sea.
Arid zone coastal wetlands provide disproportionally important ecosystem services due to their relatively high levels of productivity relative to adjacent terrestrial systems. However, these wetlands ...are vulnerable to sea level rise as sediments needed for vertical accretion are limited. In order to assess the processes important for vertical accretion in arid zone coastal wetlands, we assessed vertical accretion across an arid zone wetland landscape in Western Australia. We found that overall coastal wetlands were declining in elevation at −0.18 mm yr−1 (± standard error 0.12 mm yr−1). Vertical accretion in mangroves was evident in years of high mean sea level, but this was insufficient to counteract shallow subsidence. The high intertidal cyanobacterial mat and salt flat zones were eroding, particularly in years of high rainfall. We observed retreat of the seaward mangrove fringe associated with tree mortality caused by cyclones, but we also observed recruitment of mangroves onto the high intertidal cyanobacterial mat zone, attributed to higher sea levels. Our study found complexity in the factors causing landscape change across the intertidal zone, where variation in sea level, intense storms, and other climatic and biotic factors interact.
We assessed the influence of the intertidal and salinity gradients and mangrove forest structure on C stocks and sequestration rates in mangrove soils of an estuarine system in Todos os Santos Bay, ...Eastern Brazil. The accumulation rates of organic C (Corg) during the last century varied between and within estuarine zones, ranging from 65 to 1073 g Corg m−2 yr−1. The mean stocks of Corg and N for the top 1 m soils were 263 ± 14 Mg Corg ha−1 and 11.8 ± 0.4 Mg N ha−1, respectively. We found a less variable distribution pattern on Corg and N stocks throughout the salinity gradient than along the intertidal gradient, being significantly higher at the fringe mangroves than at the interior forest. We estimated that Brazil, one of the major reservoirs of mangroves (~ 10%) on the planet, has 207 ± 34 Tg Corg in the upper meter of soils, which represents 3–8% of the C stored in mangrove soils globally. Given that Brazil is a Blue Carbon hotspot, it is emphasized the urgent need for the establishment of better mangrove conservation practices and a comprehensive evaluation of their value in climate change mitigation and adaptation strategies for reducing CO2 emissions.
Wildfire magnitude and frequency have greatly escalated on a global scale. Wildfire products rich in biogenic elements can enter the ocean through atmospheric and river inputs, but their contribution ...to marine phytoplankton production is poorly understood. Here, using geochemical paleo-reconstructions, a century-long relationship between wildfire magnitude and marine phytoplankton production is established in a fire-prone region of Kimberley coast, Australia. A positive correlation is identified between wildfire and phytoplankton production on a decadal scale. The importance of wildfire on marine phytoplankton production is statistically higher than that of tropical cyclones and rainfall, when strong El Niño Southern Oscillation coincides with the positive phase of Indian Ocean Dipole. Interdecadal chlorophyll-a variation along the Kimberley coast validates the spatial connection of this phenomenon. Findings from this study suggest that the role of additional nutrients from wildfires has to be considered when projecting impacts of global warming on marine phytoplankton production.
Submarine canyons are preferential pathways for transport of particulate matter and contaminants from the shelf to the deep sea. The Gulf of Palermo continental margin has a very narrow shelf (about ...2–3 km wide on average) and is incised by several submarine canyons that favour shelf-slope sediment transfer. A sediment core collected on the outer shelf and six sediment cores taken at different depths along the Oreto, Eleuterio and Anerella submarine canyons were analysed to study the transfer and historical record of trace metal contamination in the Gulf of Palermo continental margin. Trace metals, major elements, organic carbon and sediment grain size were analysed in these cores, which were dated with 210Pb to assess their historical compositional evolution since the late 19th century. Hg, Pb, Cu, Zn and Cd content increased until the 1970s and 1980s, associated with the increase in urbanization and industrial activities in the Palermo area, and Hg was the contaminant that reached the highest enrichments. However, the increasing trend of these metals contamination was reversed in the 1970s and 1980s, coinciding with drastic changes in the terrigenous content and grain size of sediments in the canyon axes. These changes occurred when bottom trawling fleets expanded to deeper fishing grounds equipped with powerful trawlers around the Gulf of Palermo canyon heads and flanks and along the Oreto canyon axis. Bottom trawlers have resuspended large amounts of sediment, which have been transferred into the canyons since the 1970s and 1980s and have thus increased sediment accumulation rates. This resuspended sediment has been mixing with the sediment transferred and accumulated along the canyons, diluting and reducing its trace metal contamination levels since the expansion of the bottom trawling fleets.
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•Submarine canyons transfer trace metal contamination downslope.•Submarine canyons can preserve the historical sediment record of trace metal contamination.•Trace metal contamination in the sedimentary record increased until the 1970s and 1980s.•Contamination decreased after the expansion of trawling fleets to deeper fishing grounds.•Resuspension induced by trawling decreased sediment trace metal contamination levels.
The future of Blue Carbon science Macreadie, Peter I; Anton, Andrea; Raven, John A ...
Nature communications,
09/2019, Letnik:
10, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The term Blue Carbon (BC) was first coined a decade ago to describe the disproportionately large contribution of coastal vegetated ecosystems to global carbon sequestration. The role of BC in climate ...change mitigation and adaptation has now reached international prominence. To help prioritise future research, we assembled leading experts in the field to agree upon the top-ten pending questions in BC science. Understanding how climate change affects carbon accumulation in mature BC ecosystems and during their restoration was a high priority. Controversial questions included the role of carbonate and macroalgae in BC cycling, and the degree to which greenhouse gases are released following disturbance of BC ecosystems. Scientists seek improved precision of the extent of BC ecosystems; techniques to determine BC provenance; understanding of the factors that influence sequestration in BC ecosystems, with the corresponding value of BC; and the management actions that are effective in enhancing this value. Overall this overview provides a comprehensive road map for the coming decades on future research in BC science.
Coastal vegetated ecosystems such as saltmarshes and seagrasses are important sinks of organic carbon (OC) and total nitrogen (TN), with large global and local variability, driven by the confluence ...of many physical and ecological factors. Here we show that sedimentary OC and TN stocks of intertidal saltmarsh (
Sporobolus maritimus
) and seagrass (
Zostera noltei
) habitats increased between two- and fourfold along a decreasing flow velocity gradient in Ria Formosa lagoon (south Portugal). A similar twofold increase was also observed for OC and TN burial rates of
S. maritimus
and of almost one order of magnitude for
Z. noltei
. Stable isotope mixing models identify allochthonous particulate organic matter as the main source to the sedimentary pools in both habitats (39–68%). This is the second estimate of OC stocks and the first of OC burial rates in
Z. noltei
, a small, fast-growing species that is widely distributed in Europe (41,000 ha) and which area is presently expanding (8600 ha in 2000s). Its wide range of OC stocks (29–99 Mg ha
−1
) and burial rates (15–122 g m
2
y
−1
) observed in Ria Formosa highlight the importance of investigating the drivers of such variability to develop global blue carbon models. The TN stocks (7–11 Mg ha
−1
) and burial rates (2–4 g m
−2
y
−1
) of
Z. noltei
were generally higher than seagrasses elsewhere. The OC and TN stocks (29–101 and 3–11 Mg ha
−1
, respectively) and burial rates (19–39 and 3–5 g m
−2
y
−1
) in
S. maritimus
saltmarshes are generally lower than those located in estuaries subjected to larger accumulation of terrestrial organic matter.
The majority of the carbon stored in seagrass sediments originates outside the meadow, such that the carbon storage capacity within a meadow is strongly dependent on hydrodynamic conditions that ...favor deposition and retention of fine organic matter within the meadow. By extension, if hydrodynamic conditions vary across a meadow, they may give rise to spatial gradients in carbon. This study considered whether the spatial gradients in sediment and carbon accretion rates correlated with the spatial variation in hydrodynamic intensity within a single meadow. Field measurements were conducted in three depth zones across a Zostera marina L. (eelgrass) meadow in Nahant Harbor, Massachusetts. Four sediment cores were collected in each zone, including one outside the meadow (control) and three within the meadow at increasing distances from the nearest meadow edge. Sedimentation and carbon accretion rates were estimated by combining the measurements of dry bulk density, organic carbon fraction (%OC), 210Pb, and 226Ra. Tilt current meters measured wave velocities within each zone, which were used to estimate turbulent kinetic energy (TKE). Both sediment and carbon accretion rates exhibited spatial heterogeneity across the meadow, which were correlated with the spatial variation in near-bed TKE. Specifically, both accretion rates increased with decreasing TKE, which was consistent with diminished resuspension associated with lower TKE. A method is proposed for using spatial gradients in hydrodynamic intensity to improve the estimation of total meadow accretion rates.
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•Spatial gradients in carbon and wave intensity were compared across a Zostera marina (L.) meadow.•Higher near-bed turbulence was correlated with lower sediment and carbon accretion rates.•Storm events may dominate resuspension and therefore carbon storage.•Wave dissipation by the seagrass meadow influenced the spatial variation in carbon.
Nutrient reduction is an essential environmental policy for water quality remediation, but climate change can offset the ecological benefits of nutrient reduction and lead to the difficulty of ...environmental evaluation. Here, based on the records of three lipid microalgal biomarkers and stable isotopes of carbon and nitrogen in two sediment cores from the embayment of Perth, Australia, we reconstructed the microalgal biomasses (diatoms, dinoflagellates and coccolithophores) over the past century and evaluated the ecological effects of nutrient reduction on them, using Change Point Modeling (CPM) and redundancy analysis (RDA). The CPM result showed that total microalgal biomarkers increased by 25% and 51% in deep and shallow areas, respectively, due to nutrient enrichment caused by industrial wastewater in the 1950s and the causeway construction in the 1970s, and dinoflagellates were beneficiaries of eutrophication. The nutrient reduction policy since the 1980s had not decreased total microalgal biomass, and diatoms were beneficiaries of this period. RDA based on time series of sediment cores and water monitoring data revealed that the increase of sea-surface temperature and the decrease of rainfall since the 1980s may be important factors sustaining the high total microalgal biomass and increasing the degree of diatom dominance. The result also indicated that the variations of microalgal assemblages may better explain the effect of nutrient reduction rather than total microalgal biomass.
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•The decadal patterns of microalgae have been reconstructed.•Dinoflagellates profited from the eutrophic conditions.•Diatoms benefited from nutrient reduction.•Microalgal biomass did not decrease following nutrient reduction.•Climate change can cause non-linear responses in primary producers.
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