Impacts of Saltwater Incursion on Plant Communities, Anaerobic Microbial Metabolism, and Resulting Relationships in a Restored Freshwater Wetland

Hopfensperger, Kristine N.; Burgin, Amy J.; Schoepfer, Valerie A.; Helton, Ashley M.

doi:10.1007/s10021-014-9760-x

Cited by 43 publications

(38 citation statements)

References 66 publications

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“…A third potential pool, free sulfide (H 2 S) can build up under certain conditions, but free sulfide was not observed in our concurrent monitoring of shallow (15 cm deep) groundwater wells (data not shown). We did occasionally observe pore water sulfide in very near-surface areas (e.g., <3 cm depth) in areas under persistent salt water incursion; this, however, was relatively rare and isolated to areas near the salt water source on the site [Hopfensperger et al, 2014].…”

Section: 1002/2014jg002739mentioning

confidence: 76%

“…Sampling sites represent the longitudinal (salt to fresh) gradient at the larger site (Figure 1). Vegetation along the channel ranges from (Site 1) sparsely forested, (Sites 2 and 3) densely herbaceous, and slightly shrubby to (Site 4) slightly shrubby [Hopfensperger et al, 2014]. Cores were sectioned under anaerobic conditions (Coy Anaerobic Chamber, Coy Products) and homogenized into the 0-3, 3-6, and 6-9 cm depths.…”

Section: Field Site Description and Sample Collectionmentioning

confidence: 99%

“…Practically, it is the CRS concentration divided by two to represent the molar amount of iron present in FeS 2 plus the AVS concentration multiplied by one (FeS) divided by the total iron content of the sediment [Boesen and Postma, 1988;Burton et al, 2006]. Here we make the simplifying assumption that H 2 S and elemental sulfur are negligible; we know that pore water H 2 S is relatively low on the site due to previous work [Hopfensperger et al, 2014]. This fraction ranges from 0 to 1; a value above 1 indicates excess free sulfide (e.g., site is in a "sulfidic" state), while DOS < 1 implies that there is still available iron left for binding.…”

Section: Degree Of Sulfidization (Dos) Calculationsmentioning

confidence: 99%

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Iron clad wetlands: Soil iron‐sulfur buffering determines coastal wetland response to salt water incursion

2014

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Coastal freshwater wetland chemistry is rapidly changing due to increased frequency of salt water incursion, a consequence of global change. Seasonal salt water incursion introduces sulfate, which microbially reduces to sulfide. Sulfide binds with reduced iron, producing iron sulfide (FeS), recognizable in wetland soils by its characteristic black color. The objective of this study is to document iron and sulfate reduction rates, as well as product formation (acid volatile sulfide (AVS) and chromium reducible sulfide (CRS)) in a coastal freshwater wetland undergoing seasonal salt water incursion. Understanding iron and sulfur cycling, as well as their reduction products, allows us to calculate the degree of sulfidization (DOS), from which we can estimate how long soil iron will buffer against chemical effects of sea level rise. We show that soil chloride, a direct indicator of the degree of incursion, best predicted iron and sulfate reduction rates. Correlations between soil chloride and iron or sulfur reduction rates were strongest in the surface layer (0-3 cm), indicative of surface water incursion, rather than groundwater intrusion at our site. The interaction between soil moisture and extractable chloride was significantly related to increased AVS, whereas increased soil chloride was a stronger predictor of CRS. The current DOS in this coastal plains wetland is very low, resulting from high soil iron content and relatively small degree of salt water incursion. However, with time and continuous salt water exposure, iron will bind with incoming sulfur, creating FeS complexes, and DOS will increase.

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Section: 1002/2014jg002739mentioning

confidence: 76%

Section: Field Site Description and Sample Collectionmentioning

confidence: 99%

Section: Degree Of Sulfidization (Dos) Calculationsmentioning

confidence: 99%

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Iron clad wetlands: Soil iron‐sulfur buffering determines coastal wetland response to salt water incursion

2014

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“…We acknowledge that our experiment simulated short-term consequences of seawater intrusion, such as increased sulfate availability, and the addition of other marine nutrients and microbial communities, but we were not simulating longer-term changes such as differences in plant communities and production that may result from increased salinity (Neubauer, 2013;Hopfensperger et al, 2014;Herbert et al, 2015). Nevertheless, many other short-term studies conducting similar seawater addition experiments have observed a decrease in CH 4 production rates with elevated salinity (DeLaune et al, 1983;Marton et al, 2012;Chambers et al, 2011Chambers et al, , 2013Neubauer et al, 2013;van Dijk et al, 2015).…”

Section: Seawater Addition Experimentsmentioning

confidence: 99%

“…In contrast, the freshwater sediments used in this simulation had lower sulfate availability, and the sulfatereducing bacteria abundances were an order of magnitude lower than methanogens. In some cases, however, sulfate reduction can increase without a corresponding decrease in CH 4 production (Hopfensperger et al, 2014), especially if seawater intrusion increases both sulfate and organic matter availability (Weston et al, 2011).…”

Section: Seawater Addition Experimentsmentioning

confidence: 99%

Regulators of coastal wetland methane production and responses to simulated global change

et al. 2017

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Abstract. Wetlands are the largest natural source of methane (CH 4 ) emissions to the atmosphere, which vary along salinity and productivity gradients. Global change has the potential to reshape these gradients and therefore alter future contributions of wetlands to the global CH 4 budget. Our study examined CH 4 production along a natural salinity gradient in fully inundated coastal Alaska wetlands. In the laboratory, we incubated natural sediments to compare CH 4 production rates between non-tidal freshwater and tidal brackish wetlands, and quantified the abundances of methanogens and sulfate-reducing bacteria in these ecosystems. We also simulated seawater intrusion and enhanced organic matter availability, which we predicted would have contrasting effects on coastal wetland CH 4 production. Tidal brackish wetlands produced less CH 4 than non-tidal freshwater wetlands probably due to high sulfate availability and generally higher abundances of sulfate-reducing bacteria, whereas non-tidal freshwater wetlands had significantly greater methanogen abundances. Seawater addition experiments with freshwater sediments, however, did not reduce CH 4 production, perhaps because the 14-day incubation period was too short to elicit a shift in microbial communities. In contrast, increased organic matter enhanced CH 4 production in 75 % of the incubations, but this response depended on the macrophyte species added, with half of the species treatments having no significant effect. Our study suggests that CH 4 production in coastal wetlands, and therefore their overall contribution to the global CH 4 cycle, will be sensitive to increased organic matter availability and potentially seawater intrusion. To better predict future wetland contributions to the global CH 4 budget, future studies and modeling efforts should investigate how multiple global change mechanisms will interact to impact CH 4 dynamics.

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Causal mechanisms of soil organic matter decomposition: deconstructing salinity and flooding impacts in coastal wetlands

Stagg

Schoolmaster

Krauss

et al. 2017

Ecology

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Coastal wetlands significantly contribute to global carbon storage potential. Sea-level rise and other climate-change-induced disturbances threaten coastal wetland sustainability and carbon storage capacity. It is critical that we understand the mechanisms controlling wetland carbon loss so that we can predict and manage these resources in anticipation of climate change. However, our current understanding of the mechanisms that control soil organic matter decomposition, in particular the impacts of elevated salinity, are limited, and literature reports are contradictory. In an attempt to improve our understanding of these complex processes, we measured root and rhizome decomposition and developed a causal model to identify and quantify the mechanisms that influence soil organic matter decomposition in coastal wetlands that are impacted by sea-level rise. We identified three causal pathways: (1) a direct pathway representing the effects of flooding on soil moisture, (2) a direct pathway representing the effects of salinity on decomposer microbial communities and soil biogeochemistry, and (3) an indirect pathway representing the effects of salinity on litter quality through changes in plant community composition over time. We used this model to test the effects of alternate scenarios on the response of tidal freshwater forested wetlands and oligohaline marshes to short- and long-term climate-induced disturbances of flooding and salinity. In tidal freshwater forested wetlands, the model predicted less decomposition in response to drought, hurricane salinity pulsing, and long-term sea-level rise. In contrast, in the oligohaline marsh, the model predicted no change in response to drought and sea-level rise, and increased decomposition following a hurricane salinity pulse. Our results show that it is critical to consider the temporal scale of disturbance and the magnitude of exposure when assessing the effects of salinity intrusion on carbon mineralization in coastal wetlands. Here, we identify three causal mechanisms that can reconcile disparities between long-term and short-term salinity impacts on organic matter decomposition.

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Impacts of Saltwater Incursion on Plant Communities, Anaerobic Microbial Metabolism, and Resulting Relationships in a Restored Freshwater Wetland

Cited by 43 publications

References 66 publications

Iron clad wetlands: Soil iron‐sulfur buffering determines coastal wetland response to salt water incursion

Iron clad wetlands: Soil iron‐sulfur buffering determines coastal wetland response to salt water incursion

Regulators of coastal wetland methane production and responses to simulated global change

Causal mechanisms of soil organic matter decomposition: deconstructing salinity and flooding impacts in coastal wetlands

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