6 research outputs found
Sulfate Reduction and Sulfur Cycles at Two Seagrass Beds Inhabited by Cold Affinity Zostera marina and Warm Affinity Halophila nipponica in Temperate Coastal Waters
Role of carbonate burial in Blue Carbon budgets
Calcium carbonates (CaCO3) often accumulate in mangrove and seagrass sediments. As CaCO3 production emits CO2, there is concern that this may partially offset the role of Blue Carbon ecosystems as CO2 sinks through the burial of organic carbon (C-org). A global collection of data on inorganic carbon burial rates (C-inorg, 12% of CaCO3 mass) revealed global rates of 0.8 TgC(inorg) yr(-1) and 15-62 TgC(inorg) yr(-1) in mangrove and seagrass ecosystems, respectively. In seagrass, CaCO3 burial may correspond to an offset of 30% of the net CO2 sequestration. However, a mass balance assessment highlights that the C-inorg burial is mainly supported by inputs from adjacent ecosystems rather than by local calcification, and that Blue Carbon ecosystems are sites of net CaCO3 dissolution. Hence, CaCO3 burial in Blue Carbon ecosystems contribute to seabed elevation and therefore buffers sea-level rise, without undermining their role as CO2 sinks
The effects of manipulation of sedimentary iron and organic matter on sediment biogeochemistry and seagrasses in a subtropical carbonate environment
The microbial metabolism of organic matter (OM) in seagrass beds can create sulfidic conditions detrimental to seagrass growth; iron (Fe) potentially has ameliorating effects through titration of the sulfides and the precipitation of iron-sulfide minerals into the sediment. In this study, the biogeochemical effects of Fe availability and its interplay with sulfur and OM on sulfide toxicity, phosphorous (P) availability, seagrass growth and community structure were tested. The availability of Fe and OM was manipulated in a 2 × 2 factorial experiment arranged in a Latin square, with four replicates per treatment. The treatments included the addition of Fe, the addition of OM, the addition of both Fe and OM as well as no addition. The experiment was conducted in an oligotrophic, iron-deficient seagrass bed. Fe had an 84.5% retention efficiency in the sediments with the concentration of Fe increasing in the seagrass leaves over the course of the experiment. Porewater chemistry was significantly altered with a dramatic decrease in sulfide levels in Fe addition plots while sulfide levels increased in the OM addition treatments. Phosphorus increased in seagrass leaves collected in the Fe addition plots. Decreased sulfide stress was evidenced by heavier δ34S in leaves and rhizomes from plots to which Fe was added. The OM addition negatively affected seagrass growth but increased P availability; the reduced sulfide stress in Fe added plots resulted in elevated productivity. Fe availability may be an important determinant of the impact that OM has on seagrass vitality in carbonate sediments vegetated with seagrasses
The carbonate factory continuum, facies mosaics and microfacies: an appraisal of some of the key concepts underpinning carbonate sedimentology
Natural patches in Posidonia oceanica meadows: the seasonal biogeochemical pore water characteristics of two edge types
peer reviewedSeagrass meadows can be assimilated to seascape
matrixes encompassing a mosaic of natural and
anthropogenic patches. Natural patches within the Mediterranean
Posidonia oceanica meadows show a structural
particularity which consist in a duality of their edge types.
One edge is eroded by bottom currents, while the adjacent
meadow colonizes the bare sediments. This study aims to
study the dynamics of these two edges through the investigation
of the biogeochemistry (pH, total alkalinity, dissolved
inorganic carbon, CO2,
CH4,
N2O,
H2S,
dissolved
inorganic nitrogen, PO4
3−) within vegetated and unvegetated
sediments. These observations are compared with
the adjacent meadow to have a better understanding of the
colonization processes. Our results reveal that the P. oceanica
matrix shows differences from the vegetated edges of
sand patches, especially with regard to nutrient availability,
which is generally more important at the colonized edge
(dissolved inorganic nitrogen up to 65.39 μM in June). A
clear disparity also occurs between the eroded and colonized
edge with both a seasonal and bathymetrical variation of leaf
biomass with higher disparities at 10 m in June (colonized
edge 1415 gDW m−2; eroded edge 1133 gDW m−2). Themost important contrasts during this study were assessed in
June, suggesting that the warm period of the year is more
suitable for sampling to highlight disparate characteristics in
temperate seagrass meadows. These findings put into light
the potential importance of biogeochemical processes in
the dynamics of natural patch edges. We hypothesize that
they may influence the structural dynamics of P. oceanica
seascapes