Oxygen Consumption and Sulfate Reduction in Vegetated Coastal Habitats: Effects of Physical Disturbance

Brodersen, Kasper Elgetti; Trevathan-Tackett, Stacey M.; Nielsen, Daniel A.; Connolly, Rod M.; Lovelock, Catherine E.; Atwood, Trisha B.; Macreadie, Peter I.

doi:10.3389/fmars.2019.00014

Cited by 44 publications

(30 citation statements)

References 94 publications

(122 reference statements)

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“…The sediment surface was air-exposed and the top sediment was always near atmospheric O 2 concentrations (Figure 9). This is consistent with other studies demonstrating that the typical oxygen profile in the top sediment of the vegetated marsh platform follows a steady decrease from atmospheric saturation at the surface to anoxia within the first 1 cm (Holmer et al, 2002;Brodersen et al, 2019). Below the top 1 cm, the sediment was anoxic on the marsh platform (Figure 9).…”

Section: Comparison To Other Studies Of Oxygen and Ph In Salt Marsh Tsupporting

confidence: 92%

“…In situ data on oxygen fluxes for salt marsh tidal ponds are lacking in the literature, but the oxygen fluxes measured in this study were on the same order of magnitude as reported from other marsh habitats. Low marsh sediments showed a net oxygen uptake also during the day time with a net flux of 0.58 mmol m −2 h −1 in Nova Scotia marshes (Schwinghamer et al, 1991) and 0.9 mmol m −2 h −1 in Australian marshes (Brodersen et al, 2019). In tidal marsh creeks, oxygen uptake rates were found ranging from 0 to 3.2 mmol O 2 m −2 h −1 (Macpherson et al, 2007).…”

Section: Comparison To Other Studies Of Oxygen and Ph In Salt Marsh Tmentioning

confidence: 95%

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Shallow Salt Marsh Tidal Ponds–An Environment With Extreme Oxygen Dynamics

Koop-Jakobsen

Gutbrod

2019

Front. Environ. Sci.

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In marshes, tidal ponds are increasing in number and areal coverage. Getting a better understanding of their unique biogeochemistry is a prerequisite for foreseeing their future role in salt marsh ecosystems. Using in situ microprofiling, this study investigated the spatiotemporal dynamics of O 2 , pH, and CO 2 in shallow salt marsh tidal ponds in the summer time. High benthic photosynthetic activity, fueled by CO 2 from the sediment, resulted in steep vertical O 2 gradients at the sediment-water interface, increasing from anoxia to extremely supersaturated peak concentrations up to 886 ± 139 µmol L −1 (391% atmospheric O 2 saturation) over a short distance of 6 mm. These characteristic peaks developed even at low light conditions down to 150 µmol photons m −2 s −1 photosynthetically active radiation (PAR). The oxygen gradients were restricted to the layer of benthic microalgae on the sediment surface and did not extend into the water column, which was well-mixed throughout the day showing no vertical variation. The benthic photosynthesis and respiration controlled the oxygen concentration in the water column, creating net supersaturated conditions during the day and hypoxic conditions at night. The tidal ponds were generally well-buffered showing only attenuated pH fluctuations ranging from 6.2 to 7.3, and no persistent gradients built up, despite the high photosynthetic activity at the sediment water interface. CO 2 accumulated in the sediment and was present in the water column during the morning hours, but depleted in the afternoon due to the high photosynthetic uptake. Tidal ponds also experienced event-driven changes in their biogeochemistry. Sea foam developed on the water surface during the day and accumulated on one side of the pond blocking light penetration and lowering oxygen concentrations under the foam. Inundation at high tide caused a short-lived temporal variation in O 2 and pH, which was restricted to the time of the flood. As the flooding water receded, the preceding O 2 and pH conditions were immediately restored. Altogether shallow tidal ponds comprise a marsh habitat with distinctive spatiotemporal oxygen dynamics driven by benthic photosynthesis and respiration, which differ from the surrounding vegetated marsh, and could drive changes in salt marsh biogeochemistry in response to increased pond coverage.

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Section: Comparison To Other Studies Of Oxygen and Ph In Salt Marsh Tsupporting

confidence: 92%

Section: Comparison To Other Studies Of Oxygen and Ph In Salt Marsh Tmentioning

confidence: 95%

Shallow Salt Marsh Tidal Ponds–An Environment With Extreme Oxygen Dynamics

Koop-Jakobsen

Gutbrod

2019

Front. Environ. Sci.

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“…The blue reference line shows the approximate relationship expected for aerobic respiration and productivity, which consumes approximately 0.15 mol of TA for every mole of DIC respired. (Holmer et al, 2003;Brodersen et al, 2019) and denitrification (Welsh et al, 2001) rates, suggesting that our NEC determinations were indeed largely driven by CaCO 3 precipitation and dissolution. Still, other studies have found relatively high rates of SO 2− 4 reduction in seagrass sediments (Hines and Lyons, 2007), especially those with high seagrass shoot density (Holmer and Nielsen, 1997), so we express caution in the interpretation of our NEC results.…”

Section: Nep and Necmentioning

confidence: 81%

Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows

et al. 2019

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Abstract. The net ecosystem productivity (NEP) of two seagrass meadows within one of the largest seagrass ecosystems in the world, Florida Bay, was assessed using direct measurements over consecutive diel cycles during a short study in the fall of 2018. We report significant differences between NEP determined by dissolved inorganic carbon (NEPDIC) and by dissolved oxygen (NEPDO), likely driven by differences in air–water gas exchange and contrasting responses to variations in light intensity. We also acknowledge the impact of advective exchange on metabolic calculations of NEP and net ecosystem calcification (NEC) using the “open-water” approach and attempt to quantify this effect. In this first direct determination of NEPDIC in seagrass, we found that both seagrass ecosystems were net heterotrophic, on average, despite large differences in seagrass net above-ground primary productivity. NEC was also negative, indicating that both sites were net dissolving carbonate minerals. We suggest that a combination of carbonate dissolution and respiration in sediments exceeded seagrass primary production and calcification, supporting our negative NEP and NEC measurements. However, given the limited spatial (two sites) and temporal (8 d) extent of this study, our results may not be representative of Florida Bay as a whole and may be season-specific. The results of this study highlight the need for better temporal resolution, accurate carbonate chemistry accounting, and an improved understanding of physical mixing processes in future seagrass metabolism studies.

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“…This result would have been even stronger if not for one study showing a large increase in biomass following mangrove clearing, driven by elevated algal biomass compared to the reference sites (Granek & Ruttenberg, ). However, the response of soil carbon storage to deforestation showed an even greater decrease than biomass, likely caused by increased remineralization of the carbon stored in the sediment as a result of exposure to oxic conditions (Brodersen et al, ), but also leaching, erosion and reduced soft sediment accretion levels (Castillo, Apan, Maraseni, & Salmo, ; Duncan et al, ). This confirms that the loss of carbon sequestration potential in BCE sediments due to deforestation is far more substantial than the loss of carbon from biomass, which is predicted by the relatively higher sequestration potential of sediment compared to biomass (McLeod et al, ).…”

Section: Discussionmentioning

confidence: 99%

Impacts of land management practices on blue carbon stocks and greenhouse gas fluxes in coastal ecosystems—A meta‐analysis

O’Connor

Fest

Sievers

et al. 2020

Global Change Biology

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Global recognition of climate change and its predicted consequences has created the need for practical management strategies for increasing the ability of natural ecosystems to capture and store atmospheric carbon. Mangrove forests, saltmarshes and seagrass meadows, referred to as blue carbon ecosystems (BCEs), are hotspots of atmospheric CO2 storage due to their capacity to sequester carbon at a far higher rate than terrestrial forests. Despite increased effort to understand the mechanisms underpinning blue carbon fluxes, there has been little synthesis of how management activities influence carbon stocks and greenhouse gas (GHG) fluxes in BCEs. Here, we present a global meta‐analysis of 111 studies that measured how carbon stocks and GHG fluxes in BCEs respond to various coastal management strategies. Research effort has focused mainly on restoration approaches, which resulted in significant increases in blue carbon after 4 years compared to degraded sites, and the potential to reach parity with natural sites after 7–17 years. Lesser studied management alternatives, such as sediment manipulation and altered hydrology, showed only increases in biomass and weaker responses for soil carbon stocks and sequestration. The response of GHG emissions to management was complex, with managed sites emitting less than natural reference sites but emitting more compared to degraded sites. Individual GHGs also differed in their responses to management. To date, blue carbon management studies are underrepresented in the southern hemisphere and are usually limited in duration (61% of studies <3 years duration). Our meta‐analysis describes the current state of blue carbon management from the available data and highlights recommendations for prioritizing conservation management, extending monitoring time frames of BCE carbon stocks, improving our understanding of GHG fluxes in open coastal systems and redistributing management and research effort into understudied, high‐risk areas.

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Oxygen Consumption and Sulfate Reduction in Vegetated Coastal Habitats: Effects of Physical Disturbance

Cited by 44 publications

References 94 publications

Shallow Salt Marsh Tidal Ponds–An Environment With Extreme Oxygen Dynamics

Shallow Salt Marsh Tidal Ponds–An Environment With Extreme Oxygen Dynamics

Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows

Impacts of land management practices on blue carbon stocks and greenhouse gas fluxes in coastal ecosystems—A meta‐analysis

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