Organically Bound Nutrients in Dissolved Organic Matter Fractions in Seepage and Pore Water of Weakly Developed Forest Soils

Previous field and laboratory studies showed that organically bound nutrients can contribute largely to the export of N, P, and S from soil into aquatic systems. One possible determinant for the losses of dissolved organic nutrients leaving the soil environment could be their distribution between dissolved organic matter (DOM) fractions of different mobility in soil. To elucidate the potential influence of DOM fractions under varying flow conditions on the vertical translocation of organically bound nutrients, we determined the concentrations and fluxes of dissolved organic C (DOC) and nutrients (DON, DOP, DOS) in soil water under a Scots pine (Pinus sylvestris L.) and a European beech (Fagus sylvatica L.) forest. We sampled seepage water from the organic forest floor layer and the mineral subsoil using zero‐tension lysimeters and soil pore water using tension lysimeters and suction cups. DOM in soil water was fractionated into hydrophilic and hydrophobic compounds by XAD‐8 at pH 2. We found that the organic forest floor layers were large sources for DOC, DON, DOP, and DOS. The dissolved organic nutrients were mainly concentrated in the hydrophilic DOM fraction which proved to be more mobile in mineral soil pore water than the hydrophobic one. Consequently, the concentrations and fluxes of dissolved organic nutrients decreased less with depth than those of DOC. Concentrations as well as fluxes in subsoil pore water of DOC and dissolved organic nutrients in the studied weakly developed soils were high as compared with literature data on deeply developed forest soils. Under conditions of rapid water flow through the strongly structured mineral soil at the beech site, almost no retention of DOM took place and thus the influence of the distribution of organically bound nutrients between the DOM fractions on the export of DON, DOP, and DOS was negligible.     

Re-assessing the nitrogen signal in continental margin sediments: New insights from the high northern latitudes

Organic and inorganic nitrogen and their isotopic signatures were studied in continental margin sediments off Spitsbergen. We present evidence that land-derived inorganic nitrogen strongly dilutes the particulate organic signal in coastal and fjord settings and accounts for up to 70% of the total nitrogen content. Spatial heterogeneity in inorganic nitrogen along the coast is less likely to be influenced by clay mineral assemblages or various substrates than by the supply of terrestrial organic matter (TOM) within eroded soil material into selected fjords and onto the shelf. The δ¹⁵N signal of the inorganic nitrogen (δ¹⁵N_inorg) in sediments off Spitsbergen seems to be appropriate to trace TOM supply from various climate- and ecosystem zones and elucidates the dominant transport media of terrigenous sediments to the marine realm. Moreover, we postulate that with the study of sedimentary δ¹⁵N_inorg in the Atlantic–Arctic gateway, climatically induced changes in catchment's vegetations in high northern latitudes may be reconstructed. The δ¹⁵N_org signal is primarily controlled by the availability of nitrate in the dominating ocean current systems and the corresponding degree of utilization of the nitrate pool in the euphotic zone. Not only does this new approach allow for a detailed view into the nitrogen cycle for settings with purely primary-produced organic matter supply, it also provides new insights into both the deposition of marine and terrestrial nitrogen and its ecosystem response to (paleo-) climate changes.     

Chloride and Organic Chlorine in Soil

Chloride is ubiquitous in soil, but the past years of research have revealed that organic matter also contains chlorine, in amounts similar to that of phosphorus. Hence, one of the major constituents of soil organic matter has previously been overlooked, and still very little is known about the turnover of organic chlorine in soil. In spite of the obvious connection between chloride and organic chlorine, organic chlorine rarely is considered when the biogeochemical cycling of chloride is in focus, and chloride rarely is taken into account when the occurrence and formation of natural organic chlorine compounds are in focus. The aim of the paper is to review ten years of research concerning the biogeochemical cycling of organic chlorine in soil, and to tie the biogeochemical cycling of organic chlorine to that of chloride.     

Utilisation of different carbon sources in a shallow estuary identified through stable isotope techniques

Organic carbon in estuarine sediments can have many different sources. Terrestrial, riverine, estuarine and marine C pools may all contribute to and influence the organic C (C_org) inventory of the estuarine sediments and the differing stable isotope signatures of the sources are reflected in the sediment's overall ¹³C content. Ecological interpretations of sedimentary isotope data may, however, be limited by the fact the total C_org inventory of a sediment may not be an accurate representation of the fraction that is labile and being actively turned over by the sedimentary community. To gain a better understanding of sedimentary C_org dynamics in estuaries and the relationship between the sedimentary C pool and the C_org undergoing mineralisation, we studied three components of an estuarine system: (1) the sedimentary C_org inventory on a transect from the mouth to the upper end of the estuary, (2) temporal changes of sedimentary C_org at one station throughout a year, and (3) the δ¹³C of respired CO₂ compared to the δ¹³C of available source material and sedimentary C_org in a novel application of methods developed for soil science. Our experiments demonstrated that material of marine origin dominated the studied estuary. At the time-series station, material of marine origin dominated the sedimentary C_org throughout the 1-yr study period. δ¹³C values of CO₂ released from the sediment differed significantly from the sedimentary C_org inventory at all study sites, but also clearly reflected differences between the main sections of the estuary. These results suggest that δ¹³C measurements of respired CO₂ are promising as a tool to advance our understanding of C cycling in estuaries, and highlight that the sedimentary C_org pool alone may not be a satisfactory indicator of OM utilisation in estuarine sediments.     

Organic carbon isotope gradient and ocean stratification across the late Ediacaran-Early Cambrian Yangtze Platform

Organic carbon isotope(δ13Corg) data from two well-preserved sections across a shallow-to-deep water transect of the late Ediacaran-Early Cambrian Yangtze Platform in South China show significant temporal and spatial variations. In the shallow-water Jiulongwan-Jijiapo section, δ13Corg values of the late Ediacaran Dengying Formation range from -29‰ to -24‰. In the deep-water Longbizui section, δ13Corg values from time-equivalent strata of the Dengying Formation are mostly between –35‰ and -32‰. These new data, in combination with δ13Corg data reported from other sections in South China, reveal a 6‰–8‰ shallow-to-deep water δ13Corg gradient. High δ13Corg values(-30‰) occur mostly in shallow-water carbonate rocks, whereas low δ13Corg values(-32‰) dominate the deep-water black shale and chert. The large temporal and spatial δ13Corg variations imply limited buffering effect from a large dissolved organic carbon(DOC) reservoir that was inferred to have existed in Ediacaran-Early Cambrian oceans. Instead, δ13Corg variations between platform and basin sections are more likely caused by differential microbial biomass contribution to total organic matter. High δ13Corg values(-30‰) documented from shallow-water carbonates are within the range of typical Phanerozoic δ13Corg data and may record the isotope signature of organic matter from primary(photosynthetic) production. In contrast, low δ13Corg values(-32‰) from deep-water sections may have resulted from higher chemoautotrophic or methanotrophic biomass contribution to bulk organic matter in anoxic environments. The δ13Corg data provide indirect evidence for ocean stratification and episodic chemocline fluctuations in the Ediacaran-Early Cambrian Yangtze Platform.     

Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation,Flin Flon Belt,Canada

The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ¹³C_org) and sulfur isotopes (δ³⁴S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ¹³C_org (?36 ‰ to ?27 ‰) and δ³⁴S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.     

Two episodes of C-depletion in organic carbon in the latest Permian: Evidence from the terrestrial sequences in northern Xinjiang, China

New analyses reveal two intervals of distinctly lower δ¹³C values in the terrestrial organic matter of Permian–Triassic sequences in northern Xinjiang, China. The younger negative δ¹³C_org spike can be correlated to the conspicuous and sharp δ¹³C drops both in carbonate carbon and organic carbon near the Permian–Triassic event boundary (PTEB) in the marine section at Meishan. The geochemical correlation criteria are accompanied by a magnetic susceptibility pulse and higher abundances of distinctive, chain-like organic fossil remains of Reduviasporonites.The older negative δ¹³C_org spike originates within a latest Permian regression. Significant changes in organic geochemical proxies are recorded in the equivalent interval of the marine section at Meishan. These include relatively higher concentrations of total organic carbon, isorenieratane, C₁₄–C₃₀ aryl isoprenoids and lower ratios of pristane/phytane that, together, indicate the onset of anoxic, euxinic and restricted environments within the photic zone. The massive and widespread oxidation of buried organic matter that induced these euxinic conditions in the ocean would also result in increased concentrations of ¹³C-depleted atmospheric CO₂. The latest Permian environmental stress marked by the older negative δ¹³C_org episode can be correlated with the distinct changeover of ostracod assemblages and the occurrences of morphological abnormalities of pollen grains. These observations imply that biogeochemical disturbance was manifested on the land at the end of the Permian and that terrestrial organisms responded to it before the main extinction of the marine fauna.     

Inorganic and methylmercury: do they transfer along a tropical coastal food web?

Methylmercury (MeHg) and inorganic mercury (Hg_inorg) were evaluated in the water of a Brazilian estuary, with two size classes of plankton and seven fish species of different feeding habits. Water partition coefficients (PCs) in microplankton were fourfold higher for MeHg than for Hg_inorg; and water PCs in mesoplankton were 26 times higher for MeHg than Hg_inorg. Difference between microplankton and mesoplankton MeHg bioaccumulation factor (BAF) was higher (0.60 log units) than Hg_inorg BAF (0.24 log units), indicating that trophic transfer of MeHg between planktonic organisms is more efficient than Hg_inorg transference. MeHg concentrations, proportion of mercury as MeHg and its biotransference factors (BTFs) in the microplankton, mesoplankton and fish increased with increasing trophic level while biotic concentrations of Hg_inorg and proportion of mercury as Hg_inorg decreased thus indicating that MeHg was indeed the biomagnified species of mercury. MeHg reflected the vertical trophic guilds distribution, due to the fact that the top predator fish presented the highest concentration (0.77 μg g⁻¹ d.w.), followed by the less voracious species (0.43 μg g⁻¹ d.w.); while planktivorous fish presented the lowest concentrations (0.044 μg g⁻¹ d.w.). Hg_inorg did not present the same behavior. Results suggest that feeding habits and trophic guild are important parameters, influencing biotransference and biomagnification processes.     

Biomarker evidence for biotic and environmental change across the Cambrian Series 2–Series 3 boundary at the Wuliu- Zengjiayan section,Guizhou, China

The Wuliu-Zengjiayan section in Jianhe County, Guizhou Province, China has been suggested as a potential Global Stratotype Section and Point(GSSP) for the defined base of Cambrian Series 3. A molecular organic geochemical study on the Cambrian Series 2Series 3 boundary interval was carried out to reveal the biotic and environmental change during this transition. The hydrocarbons extracted from the Kaili Formation were proved to be indigenous. The various geochemical proxies such as biomarker parameter, δ13Corg, atomic H/C value of kerogen, and TOC content, co-vary along with the sedimentary column, and show a quick and significant change just across the Cambrian Series 2Series 3 boundary. The less abundance of isoprenoid hydrocarbons, the relative enrichment of midchain monomethyl branched alkanes(mmb-alkanes), the relatively negative value of δ13Corg, and the higher TOC contents may suggest that the upper Cambrian Series 2 was deposited in a relatively reducing environment with a higher organic input from cyanobacteria-predominated benthic microbial mats. On the other hand, the relative enrichment of isoprenoid hydrocarbons, the less abundance of mmb-alkanes, the relatively positive value of δ13Corg, the lower TOC contents, and the lower atomic H/C values of kerogen are combined to indicate an enhanced phytoplankton production and an increased oxygen content and nutrients in the ocean during the early Cambrian Series 3, which could have benefited the explosion of the Kaili Biota. The Wuliu-Zengjiayan section may provide a typical case to understand the co-variation of marine microbe, animal, and environment.     

Hydrogeochemical balance of forest umbrisol profiles (‘Sierra de Gata’, central western Spain)

Three techniques for obtaining soil water solutions (gravitational and matrical waters extracted using both in situ tension lysimeters and in vitro pressure chambers) and their later chemical analysis were performed in order to know the evolution of the soil‐solution composition when water moves down through the soil, from the Ah soil horizon to the BwC‐ or C‐horizons of forest soils located in western Spain. Additionally, ion concentrations and water volumes of input waters to soil (canopy washout) and exported waters (drainage solutions from C‐horizons) were determined to establish the net balance of solutes in order to determine the rates of leaching or retention of ions. A generalized process of sorption or retention of most components (even Cl^?) was observed, from the soil surface to the C‐horizon, in both gravitational and matrical waters, with H₄SiO₄, Mn²⁺, Na⁺, and SO₄^2? being the net exported components from the soil through the groundwater. These results enhance the role of the recycling effect in these forest soils. The net percentages of elements retained in these forest soils, considering the inputs and the outputs balance, were 68% K⁺, 85% Ca²⁺, 58% Mg²⁺, 7% Al³⁺, 5% Fe³⁺, 34% Zn²⁺, 57% Cl^?, and 20% NO₃^?, and about 75% of dissolved organic carbon was mineralized. Copyright © 2007 John Wiley & Sons, Ltd.     

Interactions of Chlorine with Natural Organic Matter and Formation of Intermediates: Evidence by Differential Spectroscopy

This communication describes the use of differential absorbance spectroscopy to explore the intermediates formed during halogenation of natural organic matter (NOM). The differential spectra of chlorinated NOM comprise two contributions. The primary component is negative and has a peak near 270 nm. The shape of this band is independent of chlorine dose, and its intensity increases monotonically with Cl₂ dose. The second component is positive, with a well‐defined peak near 280 nm and another, broader band in the 340...380 nm range. The second component is noticeable at low chlorine concentrations but disappears with increasing Cl₂ dose. We attribute this component to aromatic chlorinated intermediates formed prior to the release of identifiable smaller species such as haloacetic acids. We believe that this component of the differential spectra can be used to probe the identity, formation and breakdown of the halogenated intermediates.     

Spatial-temporal variations in organic matter of the Sea of Azov

The spatial-temporal variations in the amount and biochemical composition of organic matter and the rates of its transformations in the ecosystems of the Russian part of the Sea of Azov are analyzed. Maximum OM concentrations are typical for Taganrog Bay. A characteristic feature of the Sea of Azov is a large proportion of particulate organic matter, which in summer in Taganrog Bay exceeded 35%. It is shown that not only the concentration of organic matter changes from season to season, but also its elementary (C_org, N_org, and P_org) and biochemical composition (proteins, carbohydrates, and lipids). The major biochemical compound of dissolved organic matter is shown to be carbohydrates (13–28%), and that of particulate matter is protein (44–51%). The hydrolytic (phosphatase and protease) and oxidation-reduction enzymes of electron-transport system demonstrate a high activity in summer. The estimated short turnover times of phosphates and protein suggest the rapid and complete utilization of organic matter in the Sea of Azov.     

The fluvial flux of particulate organic matter from the UK: the emission factor of soil erosion

Soil erosion has been identified as a potential global carbon sink since eroded organic matter is replaced at source and eroded material is readily buried. However, this argument has relied on poor estimates of the total fate of in‐transit particulates and could erroneously imply soil erosion could be encouraged to generate carbon stores. These previous estimates have not considered that organic matter can also be released to the atmosphere as a range of greenhouse gases, not only carbon dioxide (CO₂), but also the more powerful greenhouse gases methane (CH₄) and nitrous oxide (N₂O). As soil carbon lost by erosion is only replaced by uptake of CO₂, this could represent a considerable imbalance in greenhouse gas warming potential, even if it is not significant in terms of overall carbon flux. This work therefore considers the flux of particulate organic matter through UK rivers with respect to both carbon fluxes and greenhouse gas emissions. The results show that, although emissions to the atmosphere are dominated by CO₂, there are also considerable fluxes of CH₄ and N₂O. The results suggest that soil erosion is a net source of greenhouse gases with median emission factors of 5.5, 4.4 and 0.3 tonnes CO_2eq/yr for one tonne of fluvial carbon, gross carbon erosion and gross soil erosion, respectively. This study concludes that gross soil erosion would therefore only be a net sink of both carbon and greenhouse gases if all the following criteria are met: the gross soil erosion rate were very low (<91 tonnes/km²/yr); the eroded carbon were completely replaced by new soil organic matter; and if less than half of the gross erosion made it into the stream network. By establishing the emission factor for soil erosion, it becomes possible to properly account for the benefits of good soil management in minimizing losses of greenhouse gases to the atmosphere as a by‐product of soil erosion. Copyright © 2015 John Wiley & Sons, Ltd.     

Sudden enhancement of sedimentation flux of <Superscript>210</Superscript>Pb<Subscript>ex</Subscript> as an indicator of lake productivity as exemplified by Lake Chenghai

The fundamental assumption of ²¹⁰Pb sediment dating is the stable flux of ²¹⁰Pb_ex, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the ²¹⁰Pb_ex activity in sediments will be exponentially reduced with sedimentation age. ²¹⁰Pb_ex in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly increased, ²¹⁰Pb_ex will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of ²¹⁰Pb dating; on the other hand, the sudden enhancement of ²¹⁰Pb_ex flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of ²¹⁰Pb_ex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of ¹³⁷Cs activity is characterized by a tree-peak pattern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of ²¹⁰Pb_ex activity displays a specific distribution of peaks, and is similar to the vertical profile of C_org. This phenomenon seems to be related to the mechanism of constraining the transfer of ²¹⁰Pb_ex into lake sediments. The average atomic ratios of H_org/C_org and C_org/N_org in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition-de-composition-accumulation”, the sedimentation fluxes (F(C_org)) of organic carbon (C_org) since 1970 were calculated by modeling. The sedimentation fluxes of ²¹⁰Pb_ex (F(²¹⁰Pb_ex)) in different years display good synchronous relations with the sedimentation flux of organic carbon (F(C_org)), especially in the years of 1972–1974 and 1986–1989. The variation of F(C_org) led to the variation of F(²¹⁰Pb_ex); the variation of F(²¹⁰Pb_ex) reflects, to some extent, the historical variation of lake productivity.     

New assessment of organic mercury formation in highly polluted sediments in the Lenga estuary,Chile

Anomalously high levels of mercury in sediment in the Lenga estuary, Chile are comparable to the most contaminated sites previously reported elsewhere. Total mercury (Hg_total) concentrations range from 0.5 to 129 mg kg⁻¹ and organic mercury (Hg_org) from 11 to 53 μg kg⁻¹. The highest levels are in areas near the previous wastewater outfall of a chlo-alkali plant. The results show that the proportion of Hg_org/Hg_total in the sediment varies by more than two orders of magnitude (0.02–5.7%) according to the concentration of Hg_total. No correlation between the concentration of Hg_org and Hg_total was found. The lack of correlation does contrast with the findings of other authors in culture media. Our results indicate that even at very high concentrations of Hg_total and organic matter do not influence organic mercury formation in estuary sediments. The disparity in Hg_total and Hg_org concentrations also attests to environmental differences in the formation.     

Carbon remineralization in the Amazon–Guianas tropical mobile mudbelt: A sedimentary incinerator

The Amazon River spawns a vast mobile mudbelt extending ∼1600 km from the equator to the Orinoco delta. Deposits along the Amazon–Guianas coastline are characterized by some of the highest C_org remineralization rates reported for estuarine, deltaic, or shelf deposits, however, paradoxically, except where stabilized by mangroves or intertidal algal mats, they are usually suboxic and nonsulfidic. A combination of tides, wind-driven waves, and coastal currents forms massive fluid muds and mobile surface sediment layers ∼0.5–2 m thick which are dynamically refluxed and frequently reoxidized. Overall, the seabed functions as a periodically mixed batch reactor, efficiently remineralizing organic matter in a gigantic sedimentary incinerator of global importance. Amazon River material entering the head of this dynamic dispersal system carries an initial terrestrial sedimentary C_org loading of ∼ 0.7 mg C m⁻² particle surface area. Total C_org loading is lowered to ∼ 0.2 mg C m⁻² in the proximal delta topset, ∼60–70% of which remains of terrestrial origin. Loading decreases further to 0.12–0.14 mg C m⁻² (∼60% terrestrial) in mudbanks ∼600 km downdrift along French Guiana, values comparable to those found in the oligotrophic deepsea. DOC/ΣCO₂ ratios in pore waters of French Guiana mudbanks indicate that >90% of metabolized organic substrates are completely oxidized. Within the Amazon delta topset at the head of the dispersal system, both terrestrial and marine organic matter contribute substantially to early diagenetic remineralization, although reactive marine substrate dominates (∼60–70%). The conditional rate constant for terrestrial C_org in the delta topset is ∼0.2 a⁻¹. As sedimentary C_org is depleted during transit, marine sources become virtually the exclusive substrate for remineralization except very near the mangrove shoreline. The δ¹³C and Δ¹⁴C values of pore water ΣCO₂ in mudbanks demonstrate that the primary source of remineralized organic matter within ∼1 km of shore is a small quantity of bomb signature marine plankton (+80‰). Thus, fresh marine organic material is constantly entrained into mobile deposits and increasingly drives early diagenetic reactions along the transit path. Relatively refractory terrestrial C_org is lost more slowly but steadily during sedimentary refluxing and suboxic diagenesis. Amazon Fan deposits formed during low sea level stand largely bypassed this suboxic sedimentary incinerator and stored material with up to ∼3X the modern high stand inner shelf C_org load (Keil et al., 1997b. Proceedings of the Ocean Drilling Program, Scientific Results. Vol. 155. pp. 531–537). Sedimentary dynamics, including frequency and magnitude of remobilization, and the nature of dispersal systems are clearly key controls on diagenetic processes, biogeochemical cycling, and global C storage along the continental margins.     

Pump‐and‐Treat Groundwater Remediation Using Chlorine/Ultraviolet Advanced Oxidation Processes

Comparative studies of the use of chlorine/ultraviolet (Cl₂/UV) and hydrogen peroxide/ultraviolet (H₂O₂/UV) Advanced oxidation processes (AOPs) to remove trichloroethylene (TCE) from groundwater in a pump‐and‐treat application were conducted for the first time at the full‐scale operational level at two water treatment facilities in Northern California. In these studies, aqueous chlorine replaced hydrogen peroxide in the AOP treatment step, where the oxidant is exposed to UV light to produce highly reactive radical species that degrade groundwater contaminants. TCE removal rates as a function of initial chlorine dose and pH were then determined. At the site where the natural pH of the water was 7.1, TCE was removed (to a concentration of less than 0.5 µg/L) for nearly every chlorine dose point tested, and pH adjustment slightly enhanced the treatment process at this facility. The second site had a high natural pH of 7.7, and here, TCE was not completely removed for any chlorine dose up to 5.7 mg/L, although TCE removal did increase when the chlorine dose increased between 0.9 and 3.6 mg/L. Residual TCE remaining in the water post‐Cl₂/UV was readily removed using active carbon filtration, which is part of the overall treatment train at this facility. These studies also verified that Cl₂/UV AOP did not interfere with the photolysis of N‐nitrosodimethylamine or result in an effluent acutely toxic toward Ceriodaphnia dubia. Comparative economic analysis revealed that the chemical costs associated with Cl₂/UV AOP were 25 to 50% of the costs associated with in place H₂O₂/UV AOP treatment.     

Geochemical characterization of the organic matter, pore water constituents and shallow methane gas in the eastern part of the Ulleung Basin, East Sea (Japan Sea)

Abstract Geochemical analyses of sediments, pore water and headspace gas of the piston cores taken from the eastern part of Ulleung Basin of the East Sea (Japan Sea) were carried out to assess the origin of the sedimentary organic matter and interstitial fluid. Several tephra layers within the core are identified as the Ulleung‐Oki (10.1 ka), the Aira‐Tanzawa (23 ka) and the Ulleung‐Yamato (30.9 ka) tephras. With the exception of these volcanic layers, the cores consist predominantly of muddy sediments that contain >0.5% total organic carbon. Atomic C/N ratios and δ¹³C_org values suggest that the organic matter originated from marine algae rather than from land vascular plants, whereas Rock‐Eval pyrolysis suggests that the organic matter is thermally immature and comes from a land vascular plant (Type III). These conflicting results seem to be caused by the heavy oxidization of the marine organic matter. Sulphate concentration profiles of pore waters show strongly linear depletion (r² > 0.97) with sediment depth. The estimated sulphate–methane interface (SMI) depth using the sulphate concentration gradient was nearly 3.5 m below seafloor (mbsf) in the southern part of the study area, and deeper than 6 mbsf in the northern part of the area. The difference in SMI depths is likely associated with the amount of the methane flux. The methane concentration below the SMI in the two southern cores increases rapidly, implying the occurrence of methanogenesis and anaerobic methane oxidation (AMO). In contrast, the two northern cores have a low methane concentration below the SMI. values measured from all cores were in the range of −83.5 to −69.5‰, which suggests that the methane derives from a methanogenic microbe. values become decreased toward SMI, but increased below SMI; therefore, has eventually the minimum value near the SMI. The values are also decreased when the methane concentration is increased. These phenomena support the typical occurrence of AMO in the study area.     

Siliceous productivity changes in Gulf of Ancud sediments (42°S, 72°W), southern Chile,over the last ∼150 years

We evaluated changes in siliceous export production and the source of organic matter preserved in sediment core MD07-3109H recovered from the Gulf of Ancud, Chiloé Inner Sea (42°S, 72°W, water column depth: 328 m), southern Chile. We analyzed the abundance of siliceous microfossils (diatoms, silicoflagellates, sponge spicules, Chrysophyte cysts, phytoliths), geochemical proxies (weight percent silicon %Si_OPAL, organic carbon, total nitrogen, C/N molar), and sediment stable isotopes (δ¹³C_org, δ¹⁵N). Chronology based on ²¹⁰Pb and ¹⁴C provided an accumulated age of 144 years at the base of the core.Sediments of core MD07-3109H are predominantly marine in origin, averaging δ¹³C_org=–20.75‰±0.82, δ¹⁵N=8.7±0.35‰, and C/N=8.76±0.36. Marine diatoms compose 94% of the total assemblage of siliceous microfossils. Our record of productivity based on the mass accumulation rates of organic carbon, total nitrogen, Si_OPAL, and total diatoms showed high values between 1863 and 1869 AD followed by a declining trend until 1921 AD, a transition period from 1921 to 1959 AD with fluctuating values, and a clear decreasing pattern from 1960 AD to the present. This marked reduction in productivity was associated with decreased precipitation and Puelo River streamflow (41°S), as well as a warmer and more stratified water column, especially since the 1980s.     

Characterizing Water Flow in Vegetated Lysimeters with Stable Water Isotopes and Modeling

We have used stable water isotopes (δ¹⁸O, δ²H) in combination with lumped-parameter modeling for characterizing unsaturated flow in two lysimeters vegetated with maize. The lysimeters contained undisturbed soil cores dominated by sandy gravel (Ly1) and clayey sandy silt (Ly2). Stable water isotopes were analyzed in precipitation and lysimeter outflow water over about 3 years. The mean transit time of water T and dispersion parameter P_D, obtained from modeling, were higher for the silt soil in Ly2 than for the gravel soil in Ly1 (T of 362 vs. 129 d, P_D of 0.7 vs. 0.12). The consideration of preferential flow (PF) paths could substantially improve the model curve fits, with 13 and 11% contribution of PF for Ly1 and Ly2 as best estimates. Different assumptions were compared to estimate the input function, that is, stable water isotope content in the recharging water. Using the isotopic composition of precipitation as input (no modification) resulted in reasonable model estimations. Best model fits for the entire observation were obtained by weighting the recharging isotopes according to average precipitation within periods of 3 and 6 months, in correspondence to changing vegetation phases and seasonal influences. Input functions that consider actual evapotranspiration could significantly improve modeling at some periods, however, this led to deviations between modeled and observed δ¹⁸O at other periods. This may indicate the influence of variable flow, so that dividing the whole observation period into hydraulically characteristic sub-periods for lumped-parameter modeling (which implements steady-state flow) is recommended for possible further improvement.