Compounds In Pore Water Research Articles

Dissolved organic matter and nutrient processing in organic-rich subterranean estuaries: Implications for future land use and climate scenarios

The subterranean estuary (STE) is a recognized reactive biogeochemical zone at the groundwater–seawater interface in coastal regions. However, few studies have explored dissolved organic matter (DOM) and nutrient processes in buried organic-rich STEs (with up to 20 % of organic matter content), despite their potential contributions to coastal water hypoxia and greenhouse gas emissions. This study conducted controlled laboratory experiments to investigate the physicochemical controls on DOM and nutrient processing in organic-rich STEs, considering variations in groundwater nitrate (NO3–) concentrations, salt concentration, seawater ions, and incubation times. Results showed elevated levels of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in pore water, primarily from particulate organic matter (POM) degradation that originated from decayed vascular plants. POM-to-DOM degradations further resulted in the accumulation of ammonium (NH4+) and highly unsaturated compounds in all treatments. The addition of high-ionic-strength treatments (e.g., seawater and sodium chloride [NaCl] solution) reduced DOC solubility and selectively removed dissolved aromatic compounds in porewater. The cation-rich seawater shifted the porewater NH4+ generation pathway from predominantly biological (re)mineralization in freshwater to abiotic (desorption via ion exchange) pathways in the saline water setup. Orthophosphate (PO43−) dynamics were likely to be influenced by the iron-rich sediment surface in both freshwater and saline water scenarios. Our experiments further indicated that the long-term incubation enriched DOM concentration with a high degradation state. This work demonstrated that organic-rich STEs are significant sources of less labile DOM and NH4+ to coastal waters. In the context of global climate change, our results illustrate the sensitivity of DOM and nutrient biogeochemical cycling in STEs to salinization and altered residence time, consequently affecting the quantity and quality of DOM and nutrients transported to coastal waters.

Dissolved Solute Sampling Across an Oxic-Anoxic Soil-Water Interface Using Microdialysis Profilers.

Biogeochemical processes shift rapidly in both spatial (millimeter scale) and temporal (hour scale to day scale) dimensions at the oxic-anoxic interface in response to disturbances. Deciphering the rapid biogeochemical changes requires in situ, minimally invasive tools with high spatial and temporal sampling resolution. However, the available passive sampling devices are not very useful in many cases either due to their disposable nature or the complexity and extensive workload for sample preparation. To address this problem, a microdialysis profiler with 33 individual polyethersulfone nanomembrane tubes (semipermeable, <20 nm pore size) integrated into the one-dimensional skeleton (60 mm) was established to iteratively sample the dissolved compounds in porewater across the soil-water interface at a high resolution of 1.8 mm (outer diameter plus one spacing, i.e., 0.1 mm between probes). The sampling mechanism is based on the principle of concentration gradient diffusion. The automatic loading of degassed water allows minimal disturbance to the chemical species across the oxic-anoxic interface. This paper describes the procedures of device setup and continuous porewater sampling across the soil-water interface on a daily basis. Concentration-depth profiles were selectively measured before (on Day 6) and after (on Day 7) disturbances induced by irrigation. The results showed that concentration-depth profiles were undergoing rapid changes, especially for redox-sensitive elements (i.e., iron and arsenic). These protocols can help investigate the biogeochemical responses across the soil-water interface under various disturbances caused by physical, chemical, and biological factors. The paper thoroughly discusses the advantages and disadvantages of this method for potential use in the environmental sciences.

Characterization of dissolved organic matter processing between surface sediment porewater and overlying bottom water in the Yangtze River Estuary

Dissolved organic matter (DOM) exchange in the sediment-water interface of estuaries is essential for the global elemental cycle. To clarify the interface DOM processing, this study applies optical techniques and ultrahigh-resolution mass spectrometry to assess DOM composition of surface sediment porewater and bottom (overlying) water across the Yangtze River Estuary (YRE). Results suggested that DOM exchange in the sediment-water interface mainly followed from sediment porewater to bottom water driven by a significant dissolved organic carbon concentration gradient and hydrodynamic force. We also characterized two porewater DOM sources, including microbial production and byproducts of processed sediments. High microbial activities resulted in the enrichment of protein-like fluorescent components and N-bearing compounds in porewater, potentially decreasing the oxygen concentration of bottom water due to the high lability. And the deamination of N-bearing compounds in the sediment-water interface could likely serve as a N-bearing nutrient source to bottom water. Moreover, due to sediment-specific features in different areas driven by hydrologic sorting and local phytoplankton supply, porewater DOM of muddy areas accumulated more aromatic substances from the degradation of terrestrial organic matter. The release and oxic transformation of oxygen-deficient aromatic compounds could contribute to the refractory carbon pool of estuarine water (carboxyl-rich alicyclic molecules, CRAM), modulating the quality of organic carbon mobilized from the land to the coastal ocean. Considering strong hydrodynamic force in numerous estuaries worldwide, DOM exchange and processing at the sediment-water interface has a meaningful influence on the biogeochemistry of estuarine water columns, which warrants further studies.

Organic matter decomposition at a constructed fen in the Athabasca Oil Sands region: Effect of substrate type and environmental conditions

Fen construction has recently been tested in the Athabasca Oil Sands Region, Alberta, Canada in an effort to return peatlands to the post-mining landscape. Understanding the drivers of organic matter decomposition in constructed fens will improve our capacity to evaluate the return of ecosystem function while also helping to inform management activities that could optimize peat accumulation. At a four year old constructed fen, we measured the decomposition of Carex aquatilis and Juncus balticus tissue over one year along with soil physical and chemical properties including concentrations of phenolic compounds in pore water, and potential phenol oxidase and hydrolase enzyme activities. Results were compared to three reference fens. Averaged across both species, decomposition of aboveground plant tissue was significantly slower at the constructed fen than the reference fens. Across the reference fens, a positive relationship between phenolic compound concentrations and decomposition constant (k) suggests microbial use of phenolic compounds as substrates. We found no evidence that phenolic compounds suppressed decomposition. At the constructed fen, a negative relationship between total potential hydrolase activity and k was observed, suggesting that nutrient limitation may suppress microbial activity at the site. There was little evidence that mulch or planting treatments altered short-term litter decomposition rate at the constructed fen, indicating that future research should focus on differences in biomass production between species, below ground nutrient cycling and the longer term preservation of litter as peat to determine strategies for optimizing peat accumulation.

DDT and related compounds in pore water of shallow sediments on the Palos Verdes Shelf, California, USA

Abstract For nearly two and a half decades following World War II, production wastes from the world's largest manufacturer of technical DDT (1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene) were discharged into sewers of Los Angeles County. Following treatment, the wastes were released via a submarine outfall system to nearshore coastal waters where a portion accumulated in shallow sediments of the Palos Verdes Shelf (PVS). An investigation of the pore-water geochemistry of DDT-related compounds (DDX) was undertaken in an effort to understand factors controlling the rate of reductive dechlorination (RDC) of the major DDT degradate, 4,4′-DDE (1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethenyl]benzene). Equilibrium matrix-solid phase microextraction (matrix-SPMEeq) combined with automated thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) was used to determine freely dissolved concentrations of ten DDX analytes in sediment cores collected from three locations on the PVS (stations 3C, 6C, 8C, which are 7 km, 2 km, and 0 km, respectively, downcurrent from the outfall system). Pore-water concentrations (pM) of the principal DDX compounds involved in RDC were: 3C-DDE: 6.0–24, DDMU (1-chloro-4-[2-chloro-1-(4-chlorophenyl)ethenyl]benzene): 11–160, DDNU (1-chloro-4-[1-(4-chlorophenyl)ethenyl]benzene): 1.8–68; 6C-DDE: 5.6–170, DDMU: 5.6–177, DDNU: 1.7–87; 8C-DDE: 27–212, DDMU: 31–403, DDNU: 5.5–89. Variations in the spatial distribution of DDX analytes in pore water reflect several factors including proximity to the outfalls, RDC reaction rates, and natural variability in sedimentation and post-depositional transport processes. A comparison of pore-water data produced using matrix-SPMEeq/TD-GC/MS and whole-core squeezing/solvent extraction/liquid injection-GC/MS indicates that the majority of the DDE in the upper sediment column (≤about 10 cm) is associated with dissolved/colloidal organic matter. Below that depth, freely-dissolved DDE predominates. The principal organic geochemical phase controlling sorption of DDE in PVS sediments are residual hydrocarbons, the vast majority of which originated from petroleum refinery wastes. Organic carbon-normalized sediment-water distribution coefficients (KOC) were calculated from solid-phase and pore-water concentrations of DDX and organic carbon. Log KOC values (L/kg) were relatively invariant across the shelf and with depth in the sediment column. Shelf-wide compound-specific coefficients (log KOC) were: DDE: 7.5 ± 0.11, DDMU: 6.92 ± 0.13, DDNU: 6.37 ± 0.19. The spatial uniformity of KOC means that biological exposure and availability of the DDX compounds can, in principle, be estimated from solid-phase chemical measurements.

Effect-directed analysis of Elizabeth River porewater: developmental toxicity in zebrafish (Danio rerio).

In the present study, effect-directed analysis was used to identify teratogenic compounds in porewater collected from a Superfund site along the Elizabeth River estuary (VA, USA). Zebrafish (Danio rerio) exposed to the porewater displayed acute developmental toxicity and cardiac teratogenesis, presumably because of elevated sediment levels of polycyclic aromatic hydrocarbons (PAHs) from historical creosote use. Pretreatment of porewater with several physical and chemical particle removal methods revealed that colloid-bound chemicals constituted the bulk of the observed toxicity. Size-exclusive chromatography and normal-phase high-performance liquid chromatography were used to fractionate Elizabeth River porewater. Acute toxicity of porewater extracts and extract fractions was assessed as the pericardial area in embryonic zebrafish. The most toxic fraction contained several known aryl hydrocarbon receptor (AhR) agonists (e.g., 1,2-benzofluorene and 1,2-benzanthracene) and cytochrome P450 A1 (CPY1A) inhibitors (e.g., dibenzothiophene and fluoranthene). The second most toxic fraction contained known AhR agonists (e.g., benzo[a]pyrene and indeno[1,2,3-cd]pyrene). Addition of a CYP1A inhibitor, fluoranthene, increased toxicity in all active porewater fractions, suggesting synergism between several contaminants present in porewaters. The results indicate that the observed acute toxicity associated with Elizabeth River porewater results from high concentrations of AhR agonistic PAHs and mixture effects related to interactions between compounds co-occurring at the Elizabeth River site. However, even after extensive fractionation and chemical characterization, it remains plausible that some active compounds in Elizabeth River porewater remain unidentified.

Modern applications for a total sulfur reduction distillation method - what's old is new again.

BackgroundThe use of a boiling mixture of hydriodic acid, hypophosphorous acid, and hydrochloric acid to reduce any variety of sulfur compounds has been in use in various applications since the first appearance of this method in the literature in the 1920’s. In the realm of sulfur geochemistry, this method remains a useful, but under-utilized technique. Presented here is a detailed description of the distillation set-up and procedure, as well as an overview of potential applications of this method for marine sulfur biogeochemistry/isotope studies. The presented applications include the sulfur isotope analysis of extremely low amounts of sulfate from saline water, the conversion of radiolabeled sulfate into sulfide, the extraction of refractory sulfur from marine sediments, and the use of this method to assess sulfur cycling in Aarhus Bay sediments.ResultsThe STrongly Reducing hydrIodic/hypoPhosphorous/hydrochloric acid (STRIP) reagent is capable of rapidly reducing a wide range of sulfur compounds, including the most oxidized form, sulfate, to hydrogen sulfide. Conversion of as little as approximately 5 micromole sulfate is possible, with a sulfur isotope composition reproducibility of 0.3 permil.ConclusionsAlthough developed many decades ago, this distillation method remains relevant for many modern applications. The STRIP distillation quickly and quantitatively converts sulfur compounds to hydrogen sulfide which can be readily collected in a silver nitrate trap for further use. An application of this method to a study of sulfur cycling in Aarhus Bay demonstrates that we account for all of the sulfur compounds in pore-water, effectively closing the mass balance of sulfur cycling.

LMWOA (low molecular weight organic acid) exudation by salt marsh plants: Natural variation and response to Cu contamination

This work aimed to evaluate, in vitro, the capability of roots of two salt marsh plants to release low molecular weight organic acids (LMWOAs) and to ascertain whether Cu contamination would stimulate or not organic acids exudation. The sea rush Juncus maritimus and the sea-club rush Scirpus maritimus, both from the lower Douro river estuary (NW Portugal), were used. Plants were collected seasonally, four times a year in 2004, during low tide. After sampling, plant roots were washed for removal of adherent particles and immersed for 2 h in a solution that matched salinity (3) and pH (7.5) of the pore water from the same location to obtain plant exudates. In one of the seasons, similar experiments were carried out but spiking the solution with different amounts of Cu in order to embrace the range between 0 and 1600 nM. In the final solutions as well as in sediment pore water LMWOAs were determined by high performance liquid chromatography. Plants were able to release, in a short period of time, relatively high amounts of LMWOAs (oxalate, citrate, malate, malonate, and succinate). In the sediment pore water oxalate, succinate and acetate were also detected. Therefore, plant roots probably contributed to the presence of some of these organic compounds in pore water. Exudation differed between the plant species and also showed some seasonally variation, particularly for S. maritimus. The release of oxalate by J. maritimus increased with Cu increase in the media. However, exudation of the other LMWOAs did not seem to be stimulated by Cu contamination in the media. This fact is compatible with the existence of alternative internal mechanisms for Cu detoxification, as denoted by the fact that in media contaminated with Cu both plant species accumulated relatively high amounts (29–83%) of the initially dissolved Cu. This study expands our knowledge on the contribution of globally dominant salt marsh plants to the release of LMWOAs into the environment.

Concentrations, sulfur isotopic compositions and origin of organosulfur compounds in pore waters of a highly polluted raised peatland

Sulfur cycling in peatlands plays a key role in their response to atmospheric deposition of acid sulfate; however, the role of dissolved organic sulfur species has received little attention. In this study, we assess the quantitative importance of dissolved organic sulfur species in a heavily polluted peatland and their role in sulfur cycling. Surface and pore waters from a raised peat bog have been analyzed for dissolved organic and inorganic species. Except in the surface water, organically bound sulfur dominates over sulfate sulfur and the organosulfur is predominantly in the humic fraction, which is not GC amenable. Two organosulfur compounds are present in the GC amenable fraction at all depths; a compound containing a benzene ring, sulfone and amide groups dominates while a compound closely similar to either benzothiazole or 1,2-benzisothiazole is present at 100–1000 times lower concentrations. Other organosulfur species were detected in some samples by GC–AED (gas chromatography–atomic emission detection) at similar or yet lower concentrations but not identifiable with GC–MS. In the shallowest parts of the peat, sulfur isotopic data on the humic and non-humic dissolved organic sulfur fractions show a pronounced difference, implying different sources for these organosulfur compounds. Humic organosulfur is 34S enriched, indicating a source for this component from breakdown of plant materials, which have similar δ34S (0.1‰ and 4.2‰). By contrast, the non-humic organosulfur is more 34S depleted at shallow depths (−11.7‰ in surface water), indicating an origin from reaction of bacterially produced sulfide (−9.9‰ in surface water) with dissolved organic material. Deeper in the peat the non-humic organosulfur becomes more 34S enriched (up to +6.8‰), which may result from either: (i) reactions between organic material and more 34S enriched sulfide; or (less likely) (ii) a shift to production of non-humic organosulfur by breakdown of humic compounds or plant material in the peat matrix.These data highlight the importance of organosulfur species relative to inorganic species in peatland groundwaters. Organosulfur species comprise the bulk of the dissolved sulfur budget and are involved in the bacterial cycling of sulfur in the peatland ecosystem.

Distribution of volatile organic compounds in porewater of the seasonally unsaturated Chalk aquifer

Abstract The Chalk aquifer is contaminated at many sites at outcrop by volatile organic compounds (VOCs). Most studies of VOCs concentrate on the saturated zone, ignoring potentially significant accumulations of dissolved contaminants within porewaters of the unsaturated zone. Of particular interest in the Chalk is the large zone of the aquifer over which seasonal fluctuation of the water table occurs. VOCs accumulated in this zone (resulting from vertical migration and diffusion from contaminated ground water at seasonal high water levels) can form a reservoir of contaminants which will be released into the aquifer over a long period. Better understanding of the VOC behaviour in the seasonally unsaturated zone is needed to improve risk assessment and optimize remediation response. Determination of VOC occurrence and concentration in the seasonally unsaturated zone at a contaminated site on the Chalk outcrop is described. Some 500 samples of chalk have been taken from cores drilled in the unsaturated zone over a depth interval of 20 m. Headspace analysis has been used to determine porewater chemistry for a range of VOCs. Vertical profiles of contaminant con- centration are presented and interpreted in terms of VOC transport mechanisms. Hydrocarbon contamination at the site poses an additional element of complexity. The presence of chloride associated with VOC contamination provides a conservative comparison for the distribution behaviour of the VOCs.

Methylated arsenic species in estuarine porewaters

AbstractInorganic arsenic, monomethylarsenic and dimethylarsenic species have been observed in samples of sediment porewater collected from the Tamar Estuary in South‐West England. Porewater samples were collected using in situ dialysis. The arsenic species were separated by hydride generation and concentrated by liquid nitrogen trapping, prior to analysis by directly coupled gas chromatography‐atomic absorption spectroscopy. The predominant dissolved arsenic species present was inorganic arsenic (5‐62 m̈g dm−3). However, this is the first time significant concentrations of methylated arsenic species have been quantified in estuarine porewaters (0.04–0.70 m̈g dm−3), accounting for between 1 and 4% of the total dissolved arsenic. The presence of methylated arsenic compounds in porewaters is attributed to in situ environmental methylation, although the possibility of methylated arsenic species being derived from biological debris cannot be excluded.