| 1. |
- Asplund, Maria. E., 1970, et al.
(författare)
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Dynamics and fate of blue carbon in a mangrove-seagrass seascape : influence of landscape configuration and land-use change
- 2021
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Ingår i: Landscape Ecology. - : Springer. - 0921-2973 .- 1572-9761. ; 36, s. 1489-1509
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Tidskriftsartikel (refereegranskat)abstract
- Context Seagrass meadows act as efficient natural carbon sinks by sequestering atmospheric CO2 and through trapping of allochthonous organic material, thereby preserving organic carbon (C-org) in their sediments. Less understood is the influence of landscape configuration and transformation (land-use change) on carbon sequestration dynamics in coastal seascapes across the land-sea interface. Objectives We explored the influence of landscape configuration and degradation of adjacent mangroves on the dynamics and fate of C-org in seagrass habitats. Methods Through predictive modelling, we assessed sedimentary C-org content, stocks and source composition in multiple seascapes (km-wide buffer zones) dominated by different seagrass communities in northwest Madagascar. The study area encompassed seagrass meadows adjacent to intact and deforested mangroves. Results The sedimentary C-org content was influenced by a combination of landscape metrics and inherent habitat plant- and sediment-properties. We found a strong land-to-sea gradient, likely driven by hydrodynamic forces, generating distinct patterns in sedimentary C-org levels in seagrass seascapes. There was higher C-org content and a mangrove signal in seagrass surface sediments closer to the deforested mangrove area, possibly due to an escalated export of C-org from deforested mangrove soils. Seascapes comprising large continuous seagrass meadows had higher sedimentary C-org levels in comparison to more diverse and patchy seascapes. Conclusion Our results emphasize the benefit to consider the influence of seascape configuration and connectivity to accurately assess C-org content in coastal habitats. Understanding spatial patterns of variability and what is driving the observed patterns is useful for identifying carbon sink hotspots and develop management prioritizations.
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| 2. |
- Dahl, Martin, 1984-, et al.
(författare)
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Impacts of land-use change and urban development on carbon sequestration in tropical seagrass meadow sediments
- 2022
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Ingår i: Marine Environmental Research. - : Elsevier BV. - 0141-1136 .- 1879-0291. ; 176
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Tidskriftsartikel (refereegranskat)abstract
- Seagrass meadows store significant carbon stocks at a global scale, but land-use change and other anthropogenic activities can alter the natural process of organic carbon (Corg) accumulation. Here, we assessed the carbon accumulation history of two seagrass meadows in Zanzibar (Tanzania) that have experienced different degrees of disturbance. The meadow at Stone Town has been highly exposed to urban development during the 20th century, while the Mbweni meadow is located in an area with relatively low impacts but historical clearing of adjacent mangroves. The results showed that the two sites had similar sedimentary Corg accumulation rates (22–25 g m−2 yr−1) since the 1940s, while during the last two decades (∼1998 until 2018) they exhibited 24–30% higher accumulation of Corg, which was linked to shifts in Corg sources. The increase in the δ13C isotopic signature of sedimentary Corg (towards a higher seagrass contribution) at the Stone Town site since 1998 points to improved seagrass meadow conditions and Corg accumulation capacity of the meadow after the relocation of a major sewage outlet in the mid–1990s. In contrast, the decrease in the δ13C signatures of sedimentary Corg in the Mbweni meadow since the early 2010s was likely linked to increased Corg run-off of mangrove/terrestrial material following mangrove deforestation. This study exemplifies two different pathways by which land-based human activities can alter the carbon storage capacity of seagrass meadows (i.e. sewage waste management and mangrove deforestation) and showcases opportunities for management of vegetated coastal Corg sinks.
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| 3. |
- Dahl, Martin, et al.
(författare)
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Impacts of land-use change and urban development on tropical seagrass carbon sinks
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Seagrass meadows store significant carbon stocks at a global scale, but land-use change and anthropogenic activities can alter the natural process of organic carbon (Corg) accumulation. Here, we assessed the carbon accumulation history of two seagrass meadows in Zanzibar (Tanzania) that experienced different degrees of disturbance. The meadow at Stone Town has been highly exposed to urban development during the 20th century, while the Mbweni meadow is located in an area with relatively low impacts but historical clearing of adjacent mangroves. The results showed that the two sites had similar sedimentary Corg accumulation rates (22–25 g m-2 yr-1) since the 1940s, while during the last two decades (~1998 until 2018) they exhibited 24–30% higher accumulation of Corg, which was linked to shifts in Corg sources. The increase in the δ13C isotopic signature of sedimentary Corg (towards a higher seagrass contribution) at the Stone Town site since 1998 points to improved seagrass meadow conditions and Corg accumulation capacity of the meadow after the relocation of a major sewage outlet in the mid–1990s. In contrast, the decrease in the δ13C signatures of sediment Corg in the Mbweni meadow since the early 2010s was likely linked to Corg transport from mangrove/terrestrial material run-off following the mangrove deforestation. This study exemplifies two different pathways by which land-based human activities can alter the carbon storage capacity of seagrass meadows (i.e. sewage waste management and mangrove deforestation) and showcases opportunities for management of vegetated coastal Corg sinks
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| 4. |
- Gdaniec, Sandra, et al.
(författare)
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Thorium and Protactinium isotopes as tracers of marine particle fluxes and deep water circulation in the Mediterranean Sea
- 2018
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Ingår i: Marine Chemistry. - : Elsevier. - 0304-4203 .- 1872-7581. ; 199, s. 12-23
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Tidskriftsartikel (refereegranskat)abstract
- 231Pa, 230Th and 232Th were analyzed in unfiltered sea water samples (n = 66) and suspended particles (n = 19) collected in the Mediterranean Sea during the MedSeA-GA04-S cruise along the GEOTRACES section GA04S and used to investigate mechanisms controlling the distribution and fractionation of Pa and Th in an ocean margin environment. 231Pa and230Th are particle reactive radionuclides and are often used astracers of processes such as boundary scavenging, particle transport and ocean circulation. The depth profiles of total 231Pa and 230Th concentrations in the Mediterranean Sea displayed non-linear shapes. Higher total 232Th concentrations were observed at the straits and in deepwaters pointing at lithogenic sources. Fractionation factors FTh/Pa ranged from 1.4 to 9. Application of a box-model illustrated that 94 % of the 231Pa and almost all of the 230Th (99.9 %) produced in the Mediterranean Sea is removed to the sediment by scavenging. The negligible export of 230Th to the Atlantic Ocean, leads to a reevaluation of the mean settling speed of the filtered particles, which is now estimated to 500-1000 m/y. The low FTh/Pa fractionation factors are attributed to the efficient scavenging and lack of transport of 231Pa to the Atlantic Ocean.
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| 5. |
- Olid, Carolina, et al.
(författare)
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Improving the Pb-210-chronology of Pb deposition in peat cores from Chao de Lamoso (NW Spain)
- 2013
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Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 443, s. 597-607
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Tidskriftsartikel (refereegranskat)abstract
- The natural radionuclide Pb-210 is commonly used to establish accurate and precise chronologies for the recent (past 100-150 years) layers of peat deposits. The most widely used Pb-210-dating model, Constant Rate of Supply (CRS), was applied using data from three peat cores from Chao de Lamoso, an ombrotrophic mire in Galicia (NW Spain). On the basis of the CRS-chronologies, maximum Pb concentrations and enrichment factors (EFs) occurred in the 1960s and late 1970s, consistent with the historical use of Pb. However, maximum Pb fluxes were dated in the 1940s and the late 1960s, 10 to 20 years earlier. Principal component analysis (PCA) showed that, although the Pb-210 distribution was mainly (74%) controlled by radioactive decay, about 20% of the Pb-210 flux variability was associated with atmospheric metal pollution, suggesting an extra Pb-210 supply source and thus invalidating the main assumption of the CRS model. When the CRS-ages were recalculated after correcting for the extra input from the Pb-210 inventory of the uppermost peat layers of each core, Pb flux variations were consistent with the historical atmospheric Pb deposition. Our results not only show the robustness of the CRS model to establish accurate chronologies of recent peat deposits but also provide evidence that there are confounding factors that might influence the calculation of reliable peat accumulation rates (and thus also element accumulation rates/fluxes). This study emphasizes the need to verify the hypotheses of Pb-210-dating models and the usefulness of a full geochemical interpretation of peat bog records.
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| 6. |
- Trezzi, Giada, et al.
(författare)
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Assessing the role of submarine groundwater discharge as a source of Sr to the Mediterranean Sea
- 2017
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 200, s. 42-54
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Tidskriftsartikel (refereegranskat)abstract
- Submarine groundwater discharge (SGD) has been identified as animportant source of Sr to the ocean and the SGD-driven Sr flux to theglobal ocean has been recently re-evaluated (Beck et al. 2013). However,the uncertainty of this value is still high because of the uncertaintiesrelated to the determination of SGD flow rates and the paucity of87Sr/86Sr data in SGD end-members. As carbonates have high Srconcentrations and are subjected to intense heightened weathering, theymight significantly influence the SGD input of Sr to the ocean. Here wepresent data on Sr concentrations and 87Sr/86Sr ratios in three carbonatedominated sites of the western area of the Mediterranean Sea, a semienclosedbasin characterized by abundant coastal carbonates. The87Sr/86Sr ratios in groundwater were lower compared to modern seawater (~0.70916), as expected for areas dominated by carbonate lithologies.Concentrations of Sr and 87Sr/86Sr ratios in groundwater showedconservative mixing in the studied subterranean estuaries. By using SGDflow rates reported in the literature for the study areas, a meteoricSGD-driven Sr flux of (0.12 - 2.1)·103 mol d-1 km-1 was calculated forthe region, with a fresh SGD end-member characterized by a Srconcentration of 27 - 30 μM and a 87Sr/86Sr ratio of 0.708020 - 0.707834.Integrating these Sr data with literature data (i.e. values of Srconcentration and 87Sr/86Sr ratio from other lithologies as well as SGDflow rates), we also calculated the fresh SGD-driven Sr flux to theentire Mediterranean Sea, obtaining a value of (0.34 - 0.83)·109 mol y-1,with a 87Sr/86Sr of 0.7086 - 0.7081. Thus, for the entire Mediterraneanbasin, SGD is globally a source of Sr less radiogenic compared toseawater. The SGD Sr flux to the Mediterranean Sea represents 5-6% of theSGD Sr flux to the global ocean and the Mediterranean SGD end-member hashigher Sr concentration (5.0 - 12 μM) than the global SGD end-member (2.9μM). This confirms the significant role of carbonate lithologies on SGDdrivenSr fluxes to seawater.The fresh SGD-driven Sr flux to the Mediterranean Sea is about 20 - 50%of the riverine Sr input and significantly higher than the input throughatmospheric dust deposition. Therefore SGD should be considered as animportant continental source of Sr to the basin.
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