| 1. |
- Dahl, Martin, et al.
(författare)
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Increased current flow enhances the risk of organic carbon loss from Zostera marina sediments: Insights from a flume experiment
- 2018
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 63:6, s. 2793-2805
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Tidskriftsartikel (refereegranskat)abstract
- Hydrodynamic processes are important for carbon storage dynamics in seagrass meadows, where periods of increased hydrodynamic activity could result in erosion and the loss of buried carbon. To estimate hydrodynamic impacts on the resuspension of organic carbon (Corg) in seagrass-vegetated sediments, we exposed patches (0.35 × 0.35 cm) of Zostera marina (with different biomass, shoot densities, and sediment properties) to gradually increased unidirectional (current) flow velocities ranging from low (5 cm s−1) to high (26 cm s−1) in a hydraulic flume with a standardized water column height of 0.12 m. We found that higher flow velocities substantially increased (by more than threefold) the proportion of Corg in the suspended sediment resulting in a loss of up to 5.5% ± 1.7% (mean ± SE) Corg from the surface sediment. This was presumably due to increased surface erosion of larger, carbon-rich detritus particles. Resuspension of Corg in the seagrass plots correlated with sediment properties (i.e., bulk density, porosity, and sedimentary Corg) and seagrass plant structure (i.e., belowground biomass). However, shoot density had no influence on Corg resuspension (comparing unvegetated sediments with sparse, moderate, and dense seagrass bed types), which could be due to the relatively low shoot density in the experimental setup (with a maximum of 253 shoots m−2) reflecting natural conditions of the Swedish west coast. The projected increase in the frequency and intensity of hydrodynamic forces due to climate change could thus negatively affect the function of seagrass meadows as natural carbon sinks. © 2018 The Authors. Limnology and Oceanography published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and Oceanography
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| 2. |
- de Smit, J. C., et al.
(författare)
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Wind exposure and sediment type determine the resilience and response of seagrass meadows to climate change
- 2022
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 67:51, s. S121-S132
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Tidskriftsartikel (refereegranskat)abstract
- Seagrasses and bare sediment represent alternative stable states, with sediment resuspension being a key driver of system stability via the Seagrass-Sediment-Light (SSL) feedback. We explore the SSL feedback by quantifying the sediment stabilization by seagrass, and using these measurements to calculate under which conditions seagrass ends up in a turbid environment. We quantified in-situ sediment resuspension velocity thresholds (u(cr)) for Zostera marina growing in medium to fine sand, using a field flume inducing near-bed wave motion. u(cr) was determined for full length shoots, shoots clipped to 0.08 m, and removed shoots. We found that rhizomes did not influence u(cr) of the top sediment layer. Overall, u(cr) was linearly related to blade area, which became independent for sediment type when normalizing u(cr) for the resuspension threshold after shoot removal. Comparing measured u(cr) against natural wave conditions showed that the seagrass meadow at the study site is currently stable. Exploring the effects of changing hydrodynamic conditions revealed that effects of increasing storminess has limited influence on sediment resuspension and thus the SSL-feedback. Increasing mean wind velocity had a stronger influence on SSL-feedback dynamics by causing more frequent exceedance of u(cr). The response of seagrasses to increasing wind pressure depends on bay topography. A fully exposed Z. marina meadow under low initial turbidity pressure trended toward bistability, as turbidity pressure increased mainly on bare sediments. The study site and a fully exposed Z. marina meadow under high initial turbidity pressure saw an increase in turbidity across all blade areas.
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| 3. |
- Marin-Diaz, B., et al.
(författare)
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Role of eelgrass on bed-load transport and sediment resuspension under oscillatory flow
- 2020
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 65:2, s. 426-436
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Tidskriftsartikel (refereegranskat)abstract
- Coastal vegetation is widely attributed to stabilize sediment. While most studies focused on how canopy causes flow reduction and thereby affects sediment dynamics, the role of roots and rhizomes on stabilizing the surface sediment has been less well studied. This study aims to quantify interactions between above- and belowground biomass of eelgrass (i.e., living Zostera marina plants and mimics) with surface sediment erosion (i.e., bed load and suspended load), under different hydrodynamic forcing that was created using a wave flume. Belowground biomass played an important role preventing bed-load erosion, by roughly halving the amount of sediment transported after being exposed to maximal orbital velocities of 27 cm s−1, with and without canopy. Surprisingly, for suspended sediment transport, we found opposite effects. In the presence of eelgrass, the critical erosion threshold started at lower velocities than on bare sediment, including sand and mud treatments. Moreover, in muddy systems, such resuspension reduced the light level below the minimum requirement of Z. marina. This surprising result for sediment resuspension was ascribed to a too small eelgrass patch for reducing waves but rather showing enhanced turbulence and scouring at meadow edges. Overall, we conclude that the conservation of the existent eelgrass meadows with developed roots and rhizomes is important for the sediment stabilization and the meadow scale should be taken into account to decrease sediment resuspension. © 2019 The Authors. Limnology and Oceanography published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and Oceanography.
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| 4. |
- Meysick, L., et al.
(författare)
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Coastal ecosystem engineers and their impact on sediment dynamics: Eelgrass–bivalve interactions under wave exposure
- 2022
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 67:3, s. 621-633
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Tidskriftsartikel (refereegranskat)abstract
- Habitat forming ecosystem engineers play critical roles in structuring coastal seascapes. Many ecosystem engineers, such as seagrasses and epifaunal bivalves, are known to have positive effects on sediment stability and increase coastal protection and ecosystem resilience. Others, such as bioturbating infaunal bivalves, may instead destabilize sediment. However, despite the common co-occurrence of seagrasses and bivalves in coastal seascapes, little is known of their combined effects on sediment dynamics. Here, we used wave flumes to compare sediment dynamics in monospecific and multispecific treatments of eelgrass, Zostera marina, and associated bivalves (infaunal Limecola balthica, infaunal Cerastoderma edule, epifaunal Magellana gigas) under a range of wave exposures. Eelgrass reduced bedload erosion rates by 25–50%, with digital elevation models indicating that eelgrass affected the sediment micro-bathymetry by decreasing surface roughness and ripple sizes. Effects of bivalves on sediment mobilization were species-specific; L. balthica reduced erosion by 25%, C. edule increased erosion by 40%, while M. gigas had little effect. Importantly, eelgrass modified the impacts of bivalves: the destabilizing effects of C. edule vanished in the presence of eelgrass, while we found positive additive effects of eelgrass and L. balthica on sediment stabilization and potential for mutual anchoring. Such interspecific interactions are likely relevant for habitat patch emergence and resilience to extreme wave conditions. In light of future climate scenarios where increasing storm frequency and wave exposure threaten coastal ecosystems, our results add a mechanistic understanding of sediment dynamics and interactions between ecosystem engineers, with relevance for management and conservation.
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