The influence of salt on dissolved organic matter from peat soils

Strehse, Robert; Bohne, H.; Amha, Yosef; Leinweber, Peter

doi:10.1016/j.orggeochem.2018.10.001

Cited by 21 publications

(10 citation statements)

References 34 publications

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“…The lower DOC concentrations under saline water conditions can be explained by the coagulation of a certain fraction of DOC to particles larger than 0.45 µm, which would not pass the 0.45 µm filter. This is a reversible process as has been documented previously [12,13,43]. The impact of water salinity on DOC release is related to carbon quality.…”

Section: Effect Of Salinity On C N and P Releasesupporting

confidence: 54%

Short Term Effects of Salinization on Compound Release from Drained and Restored Coastal Wetlands

Liu

Lennartz

2019

Water

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Over the past two decades, great efforts have been made to restore coastal wetlands through the removal of dikes, but challenges remain because the effects of flooding with saline water on water quality are unknown. We collected soil samples from two adjacent coastal fen peatlands, one drained and diked, the other open to the sea and rewetted, aiming at assessing the mobility and export of various compounds. Microcosm experiments with constant flow-through conditions were conducted to determine the effluent concentrations of dissolved organic carbon (DOC), ammonium ( NH 4 + ), and phosphate ( PO 4 3 − ) during saline–fresh water cycles. Sodium chloride (NaCl) was used to adjust salinity (saline water, NaCl concentration of 0.12 mol L−1; fresh water, NaCl concentration of 0.008 mol L−1) and served as a tracer. A model analysis of the obtained chloride ( Cl − ) and sodium ( Na + ) breakthrough curves indicated that peat soils have a dual porosity structure. Sodium was retarded in peat soils with a retardation factor of 1.4 ± 0.2 due to adsorption. The leaching tests revealed that water salinity has a large impact on DOC, NH 4 + , and PO 4 3 − release. The concentrations of DOC in the effluent decreased with increasing water salinity because the combination of high ionic strength (NaCl concentration of 0.12 mol L−1) and low pH (3.5 to 4.5) caused a solubility reduction. On the contrary, saline water enhanced NH 4 + release through cation exchange processes. The PO 4 3 − concentrations, however, decreased in the effluent with increasing water salinity. Overall, the decommissioning of dikes at coastal wetlands and the flooding of once drained and agriculturally used sites increase the risk that especially nitrogen may be leached at higher rates to the sea.

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Section: Effect Of Salinity On C N and P Releasesupporting

confidence: 54%

Short Term Effects of Salinization on Compound Release from Drained and Restored Coastal Wetlands

Liu

Lennartz

2019

Water

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“…

{SO}_{4}^{2 -}

reduction and oxic respiration are responsible for the major share of DOC oxidation in marine endobenthic environments (Bender and Heggie 1984; Henrichs and Reeburgh 1987) and we assume that this is also true for the peat‐derived DOC in our experiment. Highly decomposed peat has only small quantities of organic carbon that can still be turned into decomposable DOC (Strehse et al 2018). The peat in deeper layers exhibits significantly lower degrees of decomposition and higher C org contents, thus we assume this peat may still contain significant amounts of decomposable DOC.…”

Section: Discussionmentioning

confidence: 99%

“…Until today, the peatland drains through an extensive channel system towards the south. In the last decades, the onshore area has been subject to a wide range of investigations, including gas emissions and the investigations of landside biogeochemical processes, hydrology monitoring programs as well as geologic surveys (Voigtländer et al 1996; Lasak et al 2010; Koch et al 2014; Koebsch et al 2015; Miegel et al 2016; Jurasinski et al 2018; Strehse et al 2018; Wen et al 2018). The beach area has been subject to beach nourishments, wooden groynes were installed to retain the sand and a dyke was constructed after several wash‐over events (Kolp 1957; Voigtländer et al 1996).…”

Section: Study Sitementioning

confidence: 99%

Carbon release and transformation from coastal peat deposits controlled by submarine groundwater discharge: a column experiment study

Kreuzburg

Rezanezhad

Milojevic

et al. 2020

Limnology & Oceanography

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Although the majority of coastal sediments consist of sandy material, in some areas marine ingression caused the submergence of terrestrial carbon-rich peat soils. This affects the coastal carbon balance, as peat represents a potential carbon source. We performed a column experiment to better understand the coupled flow and biogeochemical processes governing carbon transformations in submerged peat under coastal fresh groundwater (GW) discharge and brackish water intrusion. The columns contained naturally layered sediments with and without peat (organic carbon content in peat 39 AE 14 wt%), alternately supplied with oxygen-rich brackish water from above and oxygen-poor, low-saline GW from below. The low-saline GW discharge through the peat significantly increased the release and ascent of dissolved organic carbon (DOC) from the peat (δ 13 C DOC − 26.9‰ to − 27.7‰), which was accompanied by the production of dissolved inorganic carbon (DIC) and emission of carbon dioxide (CO 2 ), implying DOC mineralization. Oxygen respiration, sulfate (SO 2 − 4 ) reduction, and methane (CH 4 ) formation were differently pronounced in the sediments and were accompanied with higher microbial abundances in peat compared to sand with SO 2 − 4 -reducing bacteria clearly dominating methanogens. With decreasing salinity and SO 2− 4 concentrations, CH 4 emission rates increased from 16.5 to 77.3 μmol m −2 d −1 during a 14-day, low-saline GW discharge phase. In contrast, oxygenated brackish water intrusion resulted in lower DOC and DIC pore water concentrations and significantly lower CH 4 and CO 2 emissions. Our study illustrates the strong dependence of carbon cycling in shallow coastal areas with submerged peat deposits on the flow and mixing dynamics within the subterranean estuary.Sea-level rise is considered to be one of the main impacts of climate change, with significant implications for mineralization processes within coastal wetlands (Nicholls and Cazenave 2010;Neubauer 2013;Plag and Jules-Plag 2013;Hahn et al. 2015;Wang et al. 2016). In particular, coastline retreat may cause submergence of terrestrial, organic carbonrich peat sediments. The extent of submarine peat and the process-based impacts on carbon transformation processes and exchange of trace gases in shallow coastal areas have been poorly addressed. Sediment column experiments are powerful tools to investigate subprocesses and simulate changes of environmental and hydrological conditions. These changes are accelerated by land subsidence of peatland caused by their large-scale drainage for agricultural use. Land subsidence alters the hydrologic exchange processes across the land-sea interface (Nieuwenhuis and Schokking 1997;Hooijer et al. 2012) including changes in surficial runoff, subsurface mixing, and submarine groundwater discharge (SGD).SGD is comprised of all flow of water from the seabed into the coastal ocean, predominantly recirculated seawater (SW), driven by wave action, density gradients, and sea-level dynamics (Robinson et al.

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“…Likewise, we observed a negative correlation between SO 4 -2 concentrations and CH 4 emissions across all treatments. Both salinity treatments decreased DOC concentrations, likely due to salt-induced flocculation which promotes particle aggregation [27,28], hence exclusion during filtration. We found no correlation between DOC and CH 4 emissions as found in other studies [61].…”

Section: Biomass and C Process Responsesmentioning

confidence: 99%

“…Elevated salinity associated with seawater intrusion and road deicing salts can induce osmotic stress, altering growth and composition of plant and microbial communities [24,25]. Further, saline conditions change the availability of terminal electron acceptors [26], and promote organic matter flocculation [27,28], which alter microbial respiration rates. Intrusion of sulfate-rich seawater into freshwater wetlands reduces soil CH 4 emissions, as sulfate reduction can be thermodynamically favored over methanogenesis [29,30].…”

Section: Introductionmentioning

confidence: 99%

Nitrogen enrichment stimulates wetland plant responses whereas salt amendments alter sediment microbial communities and biogeochemical responses

et al. 2020

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Freshwater wetlands of the temperate north are exposed to a range of pollutants that may alter their function, including nitrogen (N)-rich agricultural and urban runoff, seawater intrusion, and road salt contamination, though it is largely unknown how these drivers of change interact with the vegetation to affect wetland carbon (C) fluxes and microbial communities. We implemented a full factorial mesocosm (378.5 L tanks) experiment investigating Crelated responses to three common wetland plants of eastern North America (Phragmites australis, Spartina pectinata, Typha latifolia), and four water quality treatments (fresh water control, N, road salt, sea salt). During the 2017 growing season, we quantified carbon dioxide (CO 2) and methane (CH 4) fluxes, above-and below-ground biomass, root porosity, light penetration, pore water chemistry (NH 4 + , NO 3-, SO 4-2 , Cl-, DOC), soil C mineralization, as well as sediment microbial communities via 16S rRNA gene sequencing. Relative to freshwater controls, N enrichment stimulated plant biomass, which in turn increased CO 2 uptake and reduced light penetration, especially in Spartina stands. Root porosity was not affected by water quality, but was positively correlated with CH 4 emissions, suggesting that plants can be important conduits for CH 4 from anoxic sediment to the atmosphere. Sediment microbial composition was largely unaffected by N addition, whereas salt amendments induced structural shifts, reduced sediment community diversity, and reduced C mineralization rates, presumably due to osmotic stress. Methane emissions were suppressed by sea salt, but not road salt, providing evidence for the additional chemical control (SO 4-2 availability) on this microbial-mediated process. Thus, N may have stimulated plant activity while salting treatments preferentially enriched specific microbial populations. Together our findings underpin the utility of combining plant and microbial responses, and highlight the need for more integrative studies to predict the consequences of a changing environment on freshwater wetlands.

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The influence of salt on dissolved organic matter from peat soils

Cited by 21 publications

References 34 publications

Short Term Effects of Salinization on Compound Release from Drained and Restored Coastal Wetlands

Short Term Effects of Salinization on Compound Release from Drained and Restored Coastal Wetlands

Carbon release and transformation from coastal peat deposits controlled by submarine groundwater discharge: a column experiment study

Nitrogen enrichment stimulates wetland plant responses whereas salt amendments alter sediment microbial communities and biogeochemical responses

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