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The effect of tidal forcing on biogeochemical processes in intertidal salt marsh sediments.

Taillefert M, Neuhuber S, Bristow G - Geochem. Trans. (2007)

Bottom Line: Monitoring wells deployed to observe the effects of the tides on the vertical component of porewater transport reveal that creek sediments, because of their confinements, are exposed to much higher hydrostatic pressure gradients than mud flats.Our study indicates that iron reduction can be sustained in intertidal creek sediments by a combination of physical forcing and chemical oxidation, while intertidal mud flat sediments are mainly subject to sulfate reduction.These processes likely allow microbial iron reduction to be an important terminal electron accepting process in intertidal coastal sediments.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0340, USA. mtaillef@eas.gatech.edu

ABSTRACT

Background: Early diagenetic processes involved in natural organic matter (NOM) oxidation in marine sediments have been for the most part characterized after collecting sediment cores and extracting porewaters. These techniques have proven useful for deep-sea sediments where biogeochemical processes are limited to aerobic respiration, denitrification, and manganese reduction and span over several centimeters. In coastal marine sediments, however, the concentration of NOM is so high that the spatial resolution needed to characterize these processes cannot be achieved with conventional sampling techniques. In addition, coastal sediments are influenced by tidal forcing that likely affects the processes involved in carbon oxidation.

Results: In this study, we used in situ voltammetry to determine the role of tidal forcing on early diagenetic processes in intertidal salt marsh sediments. We compare ex situ measurements collected seasonally, in situ profiling measurements, and in situ time series collected at several depths in the sediment during tidal cycles at two distinct stations, a small perennial creek and a mud flat. Our results indicate that the tides coupled to the salt marsh topography drastically influence the distribution of redox geochemical species and may be responsible for local differences noted year-round in the same sediments. Monitoring wells deployed to observe the effects of the tides on the vertical component of porewater transport reveal that creek sediments, because of their confinements, are exposed to much higher hydrostatic pressure gradients than mud flats.

Conclusion: Our study indicates that iron reduction can be sustained in intertidal creek sediments by a combination of physical forcing and chemical oxidation, while intertidal mud flat sediments are mainly subject to sulfate reduction. These processes likely allow microbial iron reduction to be an important terminal electron accepting process in intertidal coastal sediments.

No MeSH data available.


Average concentrations of Fe2+ and ΣH2S measured in situ during tidal cycles as a function of depth at: a) the mud flat site; and b) the creek bank site. The standard deviations represent temporal variations from the average concentration during tidal cycles. The number of tidal cycles during which concentrations were measured and the date of these measurements are provided above each data set.
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Figure 8: Average concentrations of Fe2+ and ΣH2S measured in situ during tidal cycles as a function of depth at: a) the mud flat site; and b) the creek bank site. The standard deviations represent temporal variations from the average concentration during tidal cycles. The number of tidal cycles during which concentrations were measured and the date of these measurements are provided above each data set.

Mentions: Similar in situ measurements were conducted over three years and at different seasons at the same sites. To compare the behavior of the different sites over tidal cycles, the average Fe2+ and ΣH2S concentrations measured as a function of time at each depth and both sites was represented with the temporal deviation from their average concentrations as a function of depth in the sediment (Figure 8). This comparison confirmed the high temporal variations linked to tidal changes and revealed two main differences between MF and CB sediments. First, MF sediments displayed higher concentrations of dissolved sulfide compared to the CB site, which could produce relatively high concentrations of Fe2+ (Figure 8). Second, the concentration of dissolved sulfides increased regularly with depth in MF sediments, while concentrations were much more variable with depth in CB sediments.


The effect of tidal forcing on biogeochemical processes in intertidal salt marsh sediments.

Taillefert M, Neuhuber S, Bristow G - Geochem. Trans. (2007)

Average concentrations of Fe2+ and ΣH2S measured in situ during tidal cycles as a function of depth at: a) the mud flat site; and b) the creek bank site. The standard deviations represent temporal variations from the average concentration during tidal cycles. The number of tidal cycles during which concentrations were measured and the date of these measurements are provided above each data set.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1904194&req=5

Figure 8: Average concentrations of Fe2+ and ΣH2S measured in situ during tidal cycles as a function of depth at: a) the mud flat site; and b) the creek bank site. The standard deviations represent temporal variations from the average concentration during tidal cycles. The number of tidal cycles during which concentrations were measured and the date of these measurements are provided above each data set.
Mentions: Similar in situ measurements were conducted over three years and at different seasons at the same sites. To compare the behavior of the different sites over tidal cycles, the average Fe2+ and ΣH2S concentrations measured as a function of time at each depth and both sites was represented with the temporal deviation from their average concentrations as a function of depth in the sediment (Figure 8). This comparison confirmed the high temporal variations linked to tidal changes and revealed two main differences between MF and CB sediments. First, MF sediments displayed higher concentrations of dissolved sulfide compared to the CB site, which could produce relatively high concentrations of Fe2+ (Figure 8). Second, the concentration of dissolved sulfides increased regularly with depth in MF sediments, while concentrations were much more variable with depth in CB sediments.

Bottom Line: Monitoring wells deployed to observe the effects of the tides on the vertical component of porewater transport reveal that creek sediments, because of their confinements, are exposed to much higher hydrostatic pressure gradients than mud flats.Our study indicates that iron reduction can be sustained in intertidal creek sediments by a combination of physical forcing and chemical oxidation, while intertidal mud flat sediments are mainly subject to sulfate reduction.These processes likely allow microbial iron reduction to be an important terminal electron accepting process in intertidal coastal sediments.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0340, USA. mtaillef@eas.gatech.edu

ABSTRACT

Background: Early diagenetic processes involved in natural organic matter (NOM) oxidation in marine sediments have been for the most part characterized after collecting sediment cores and extracting porewaters. These techniques have proven useful for deep-sea sediments where biogeochemical processes are limited to aerobic respiration, denitrification, and manganese reduction and span over several centimeters. In coastal marine sediments, however, the concentration of NOM is so high that the spatial resolution needed to characterize these processes cannot be achieved with conventional sampling techniques. In addition, coastal sediments are influenced by tidal forcing that likely affects the processes involved in carbon oxidation.

Results: In this study, we used in situ voltammetry to determine the role of tidal forcing on early diagenetic processes in intertidal salt marsh sediments. We compare ex situ measurements collected seasonally, in situ profiling measurements, and in situ time series collected at several depths in the sediment during tidal cycles at two distinct stations, a small perennial creek and a mud flat. Our results indicate that the tides coupled to the salt marsh topography drastically influence the distribution of redox geochemical species and may be responsible for local differences noted year-round in the same sediments. Monitoring wells deployed to observe the effects of the tides on the vertical component of porewater transport reveal that creek sediments, because of their confinements, are exposed to much higher hydrostatic pressure gradients than mud flats.

Conclusion: Our study indicates that iron reduction can be sustained in intertidal creek sediments by a combination of physical forcing and chemical oxidation, while intertidal mud flat sediments are mainly subject to sulfate reduction. These processes likely allow microbial iron reduction to be an important terminal electron accepting process in intertidal coastal sediments.

No MeSH data available.