Interstitial Waters Research Articles

Enhancement of sediment phosphorus release during a tunnel construction across an urban lake (Lake Donghu, China).

Tunnel construction in watershed area of urban lakes would accelerate eutrophication by inputting nutrients into them, while mechanisms underlying the internal phosphorus cycling as affected by construction events are scarcely studied. Focusing on two main pathways of phosphorus releasing from sediment (enzymatic mineralization and anaerobic desorption), spatial and temporal variations in phosphorus fractionation, and activities of extracellular enzymes (alkaline phosphatase, β-1,4-glucosidase, leucine aminopeptidase, dehydrogenase, lipase) in sediment were examined, together with relevant parameters in interstitial and surface waters in a Chinese urban lake (Lake Donghu) where a subaqueous tunnel was constructed across it from October 2013 to July 2014. Higher alkaline phosphatase activity (APA) indicated phosphorus deficiency for phytoplankton, as illustrated by a significantly negative relationship between APA and concentration of dissolved total phosphorus (DTP). Noticeably, in the construction area, APAs in both sediment and surface water were significantly lower than those in other relevant basins, suggesting a phosphorus supply from some sources in this area. In parallel, its sediment gave the significantly lower iron-bound phosphorus (Fe(OOH)∼P) content, coupled with significantly higher ratio of iron (II) to total iron content (Fe(2+)/TFe) and dehydrogenase activities (DHA). Contrastingly, difference in the activities of sediment hydrolases was not significant between the construction area and other basins studied. Thus, in the construction area, subsidy of bioavailable phosphorus from sediment to surface water was attributable to the anaerobic desorption of Fe(OOH)∼P rather than enzymatic mineralization. Finally, there existed a significantly positive relationship between chlorophyll a concentration in surface water and Fe(OOH)∼P content in sediment. In short, construction activities within lakes may interrupt cycling patterns of phosphorus across sediment-water interface by enhancing release of redox-sensitive phosphate, and thereby facilitating phytoplankton growth in water column.

Platinum in salt marsh sediments: Behavior and plant uptake

Platinum is one of the least abundant elements in the earth crust with an average concentration of 0.51ngg−1, but its use in several human activities (mainly automobile catalytic converters) is leading its enrichment in surface sediments. Whereas, previous studies have assessed the Pt behavior in soils from urban areas, natural systems are still poorly studied.Accordingly, this study is aimed to characterize the behavior of the Pt released to coastal environments in sediments, ascertain the role of vegetation on the biogeochemistry of this element and assess the transference of Pt into the biological compartments. Several sediment cores were sampled in salt marshes (in unvegetated and vegetated areas) of the Tagus Estuary under different traffic pressure. Platinum concentration was analyzed in solid sediment, interstitial water and roots, leaves and stems of Sarcocornia fruticosa, a typical plant in south European salt marshes. In addition, interpretative parameters (e.g. redox potential, dissolved oxygen, pH, total reduced sulfur species, salinity and dissolved Fe and Mn in interstitial waters) were determined to better understand the biogeochemical cycle of Pt in salt marsh sediments.Although surface enrichment of Pt exists in the sediments at Low Traffic Station (2.8ngg−1), the highest enrichment was found at High Traffic Station where concentration was, in some cases, up to 40ngg−1, linked to traffic emissions. However, dissolved Pt in interstitial waters (from 0.14 to 0.70ngL−1) did not show this superficial maximum. This dissimilarity points out the unreactivity of traffic-borne Pt and the dissolution/precipitation cycle of natural Pt linked to Mn and O2 cycle, depending on the redox conditions, highly controlled by the vegetation. Platinum concentration in roots (0.9±0.6ngg−1) is reflecting the Pt concentration in the interstitial waters in each moment, even though at the two peaks of dissolved Pt (up to 2.5ngL−1) found at deeper layers, reflecting a low bioaccumulation. However, results pointed that a different Pt species (with different bioavailability) may exist in both stations. Besides, Pt mean value in stems and leaves (0.04±0.05ngg−1) indicates a low translocation of Pt from the roots to aerial parts.Therefore, the role of vegetation is fundamental on the geochemical behavior of Pt in sediments, due to the control of the redox conditions by roots in the surrounding sediments (between the O2 release and the organic matter degradation) and leading to Pt species of varying bioavailability.

Habitat heterogeneity and connectivity shape microbial communities in South American peatlands.

Bacteria play critical roles in peatland ecosystems. However, very little is known of how habitat heterogeneity affects the structure of the bacterial communities in these ecosystems. Here, we used amplicon sequencing of the 16S rRNA and nifH genes to investigate phylogenetic diversity and bacterial community composition in three different sub-Antarctic peat bog aquatic habitats: Sphagnum magellanicum interstitial water, and water from vegetated and non-vegetated pools. Total and putative nitrogen-fixing bacterial communities from Sphagnum interstitial water differed significantly from vegetated and non-vegetated pool communities (which were colonized by the same bacterial populations), probably as a result of differences in water chemistry and biotic interactions. Total bacterial communities from pools contained typically aquatic taxa, and were more dissimilar in composition and less species rich than those from Sphagnum interstitial waters (which were enriched in taxa typically from soils), probably reflecting the reduced connectivity between the former habitats. These results show that bacterial communities in peatland water habitats are highly diverse and structured by multiple concurrent factors.

Vertically-oriented trace fossil Macaronichnus segregatis from Neogene of Santa Maria Island (Azores; NE Atlantic) records vertical fluctuations of the coastal groundwater mixing zone on a small oceanic island

The trace fossil Macaronichnus segregatis is interpreted to be produced by opheliid polychaetes that feed on epigranular microbes and organic matter commonly abundant in shallow-marine foreshore sands. Resulting traces are horizontal and typically random in orientation, but sometimes perpendicular to the shoreline. However, M. segregatis in Neogene sandy sediments from Santa Maria Island in the Azores shows a vertical or sub-vertical orientation. This is explained by vertical flow of pore waters and oxygenation fluctuations within the mixing zone between interstitial marine and freshwater aquifers–where epigranular microbes and organic matter are most enriched. On reefless volcanic oceanic islands like the Azores, insular shelves are invariably steep, narrow, and exposed to strong swell. Aquifers in this setting respond rapidly to small changes on account of limited shelf space and a high potential differential that stimulates a vertical shift in habitats. Freshwater aquifers on small, low-relief oceanic islands form a thin lens, the edges of which are wedged against marine interstitial waters and migrate up and down in response to changes caused by tides, storm surges and precipitation. During the Late Miocene–Early Pliocene, Santa Maria was an island fitting this description. Due to a waning volcanism, intense marine erosion and gradual submersion, the island developed a wide shallow platform covered by sandy shoals, as exemplified by the Malbusca section with vertical Macaronichnus. The process, however, is more acute on small, reflective beaches perched on rocky island coasts. Here, sand blankets cover small ramps cut in the basaltic bedrock, resulting in very limited freshwater aquifers subject to strong changes due to the low permeability of basalts. The mixing zone is therefore forced to migrate chiefly up and down, mostly due to tides. The same response is dramatic in sandy fillings trapped in basalt fissures. As a consequence, the producer of Macaronichnus was tightly constrained in movement. Both situations occur in the “Pedra-que-pica” section on Santa Maria.

Porewater CO2–carbonic acid system chemistry in permeable carbonate reef sands

Porewater was collected from highly permeable, carbonate-rich, sandy sediments at two locations on Oahu, Hawai'i, CRIMP-2 on the Kaneohe Bay barrier reef and Ala Wai on a fringing coral reef nearshore to the Ala Wai canal and urban Honolulu. Samples were collected at the sediment–water interface and from porewater wells installed at sediment depths of 2, 4, 6, 8, 12, 16, 20, 30, 40, and 60cm. Total alkalinity and dissolved inorganic carbon were enriched, relative to the overlying water column, and ratios of TA:DIC at the two sites (0.80 and 0.93) suggest that aerobic respiration and sulfate reduction – both coupled with carbonate mineral dissolution – in the oxic and anoxic layers, respectively, are the major controls on the biogeochemistry of the sediment–porewater system. The porewater was approaching thermodynamic saturation with respect to aragonite with increasing depth (Ω=1.2–3.5) and was found to be undersaturated with respect to all phases of magnesian calcite (Ω=0.3–0.9) containing greater than 12mol% MgCO3. In addition to microbial controls on porewater diagenesis, transient physical events in the water column, such as swells and changing bottom current speeds, appear to exert a strong influence on the porewater chemistry due to the highly permeable and porous nature of the sediments. Profiles collected before and after swell events at each location show an apparent flushing of the porewater system, replacing low pH, high DIC interstitial waters with seawater from the overlying water column. Based partially on the results of our porewater analysis, we hypothesize that future changes in surface water DIC and pH resulting from ocean acidification (OA) could have a very significant impact on the dissolution rates of metastable skeletal and abiotic carbonate phases of varying magnesian calcite compositions (Mg-calcite) and aragonite. This is especially important in sandy reef sediments like those of this study, which are greatly influenced by the overlying water column. As the carbonate mineral saturation state of the overlying water column continues to decrease due to OA, an increase in carbonate mineral dissolution is expected and the high advective rate of water exchange between the porewater of sandy sediments and the overlying water column, as observed in this study and others, along with increased rates of dissolution of metastable carbonate phases, could lead to significantly higher future rates of mass transfer of TA and DIC between the sediments and the overlying water column. This may result in a deficit of the CaCO3 balance in some reef ecosystems and a decrease in accretion rates. Analysis of our porewater work in conjuction with previous studies of the porewater chemistry of Kaneohe Bay, Oahu in both siliciclastic-rich and siliciclastic-poor carbonate sediments leads to the conclusion that the porewaters of the former are more strongly buffered with respect to pH than those of the latter due to reverse weathering reactions. Thus carbonate-rich sandy sediments of reefs with little terrestrial influence and aluminosilicate detritus may become more susceptible to calcium carbonate loss due to the enhanced environmental and microbial dissolution of carbonate substrates expected due to OA.

New water mites species (Acariformes: Hydrachnidia) from interstitial waters of the Russian Far East.

Illustrated descriptions of three water mite species, Wandesia sokolowi sp. n., Frontipodopsis cuspidata sp. n. and Chappuisides orientalis sp. n. from interstitial waters of the Russian Far East are presented. The male of Wandesia reducta Tuzovskij, 1987 is described for the first time. An identification key of Russian species from the genus Wandesia, based on adults, is given.

The environmental impacts and health hazards of abandoned boats in estuaries

Decaying boats are a common sight in the coastal zone and yet the practice of abandonment appears to be exempt from any clear or enforceable regulation. In the present study we surveyed two estuaries in eastern England hosting an abundance and variety of abandoned vessels. An inventory of items and materials associated with or adjacent to each boat was recorded in order to gain an insight into the hazards and pollution risks related to abandonment. Materials most commonly observed were paints, plastics, timber,expanded-extruded polystyrene and masonry, while items logged included ropes, tyres, canisters, electronic equipment and a variety of metal objects that were either fixed to or contained by the boats. As well as representing an eyesore and inhibiting access to the shore, decaying boats are a hazard to human health and safety and are a source of pollution (e.g. plastics, heavy metals, oil-related hydrocarbons) to local sediment and interstitial waters. Recommendations to deal with the problem of boat abandonment include compulsory boat registration, making boaters aware of (and providing incentives for) safe disposal, and providing authorities and landowners with clear information on existing or new agencies and legislation.

Analysis of Dissolved Organic Nutrients in the Interstitial Water of Natural Biofilms

In biofilms, the matrix of extracellular polymeric substances (EPSs) retains water in the interstitial region of the EPS. This interstitial water is the ambient environment for microorganisms in the biofilms. The nutrient condition in the interstitial water may affect microbial activity in the biofilms. In the present study, we measured the concentrations of dissolved organic nutrients, i.e., saccharides and proteins, contained in the interstitial water of biofilms formed on the stones. We also analyzed the molecular weight distribution, chemical species, and availability to bacteria of some saccharides in the interstitial water. Colorimetric assays showed that the concentrations of saccharides and proteins in the biofilm interstitial water were significantly higher (ca. 750 times) than those in the surrounding lake waters (p < 0.05). Chromatographic analyses demonstrated that the saccharides in the interstitial waters were mainly of low molecular-weight saccharides such as glucose and maltose, while proteins in the interstitial water were high molecular-weight proteins (over 7000Da). Bacterial growth and production of EPS occurred simultaneously with the decrease in the low molecular-weight saccharide concentrations when a small portion of biofilm suspension was inoculated to the collected interstitial water, suggesting that the dissolved saccharides in the interstitial water support bacterial growth and formation of biofilms.

Chabazite and dolomite formation in a dolocrete profile: An example of a complex alkaline paragenesis in Lanzarote, Canary Islands

This paper studies the weathering and soil formation processes operating on detrital sediments containing alkaline volcanic rock fragments of the Mirador del Río dolocrete profile. The profile consists of a lower horizon of removilised weathered basalts, an intermediate red sandy mudstones horizon with irregular carbonate layers and a topmost horizon of amalgamated carbonate layers with root traces. Formation occurred in arid to semiarid climates, giving place to a complex mineralogical association, including Mg-carbonates and chabazite, rarely described in cal/dolocretes profiles. Initial vadose weathering processes occurred in the basalts and in directly overlying detrital sediments, producing (Stage 1) red-smectites and dolomicrite. Dominant phreatic (Stage 2) conditions allowed precipitation of coarse-zoned dolomite and chabazite filling porosities. In Stages 3 and 4, mostly pedogenic, biogenic processes played an important role in dolomite and calcite accumulation in the profile. Overall evolution of the profile and its mineralogical association involved initial processes dominated by alteration of host rock, to provide silica and Mg-rich alkaline waters, suitable for chabazite and dolomite formation, without a previous carbonate phase. Dolomite formed both abiogenically and biogenically, but without a previous carbonate precursor and in the absence of evaporites. Dominance of calcite towards the profile top is the result of Mg/Ca decrease in the interstitial meteoric waters due to decreased supply of Mg from weathering, and increased supply of Ca in aeolian dust. Meteoric origin of the water is confirmed by C and O isotope values, which also indicate lack of deep sourced CO2. The dolocrete studied and its complex mineral association reveal the complex interactions that occur at surface during weathering and pedogenesis of basalt-sourced rocks.

Chemical and textural controls on the formation of sepiolite, palygorskite and dolomite in volcanic soils

A 3-m deep soil profile from Gran Canaria, Canary Islands, has been studied. The profile is interesting because soil development on mafic tephra produced a pattern of clay mineral and carbonate distribution. Carbonates precipitated abundantly, increasingly towards the bottom, making up 20–90wt.% of the soil. Sepiolite and calcite are dominant at the top, whereas palygorskite and dolomite are the major components at the lower part of the profile. Quartz is present in low amounts in most of the profile, and smectite and non-crystalline partially altered tephra occur in low amounts towards the bottom. Mineralogical, chemical and textural investigations indicate that sepiolite and calcite precipitated in the space between the original tephra grains, from Ca, Mg and Si dissolved in situ and transported in the runoff. Palygorskite and smectite precipitated within tephra grains, from in situ tephra weathering, as well as dolomite. The distribution of the clay minerals is due to clay composition and ion mobility. Sepiolite, consisting only of Si and Mg, precipitated outside tephra grains, where the mobile Si and Mg ions were abundant in the interstitial waters. Palygorskite and smectite contain Si, Al, Fe, and Mg and only precipitated within the tephra grains, where the immobile Al and Fe were available. Calcite precipitation in solution is kinetically favored over that of dolomite and thus calcite precipitated between the grains. Dolomite precipitated within altering tephra grains and spherical clay structures because tephra and clay generated a viscous medium where dolomite supersaturation increased and the kinetic barrier for precipitation was overcome. These results are relevant to the “dolomite problem”, as they illustrate how dolomite can precipitate in surface conditions, and to CO2 sequestration, because dolomite can immobilize higher CO2 amounts (both Ca and Mg are involved and not only Ca) and in a much more stable manner (dolomite is eight orders of magnitude less soluble than calcite).

Sediment chemistry and flooding exposure: a fatal cocktail forPhragmites australisin the Mediterranean basin?

The common reed die-back syndrome was formerly reported mostly in Central Europe and more recently in the Mediterranean basin. This study investigates a case of reed die-back in Central Italy through a Geographic Information System (GIS) diachronic survey and the analysis of macromorphological and ecological parameters. Data were recorded during field activities on ten plots randomly distributed according to two ecological statuses, permanently and temporarily flooded. Culm density, height and diameter, clumping habit, flowering head and dead apical bud number and rate were measured; for each plot, chemical parameters of sediments were analyzed. Information on interstitial waters for the flooded plots was also provided. Floristic-vegetational features of the reed-bed community such as the total vegetation cover, the species composition and abundance were estimated. Univariate and multivariate analyses were used to demonstrate differences between morphological traits of flooded and emerged stands and their relationships with the chemical features of sediment. Macromorphological traits differed according to the ecological status, with flooded stands showing patterns related to poor health status of Phragmites australis , such as high rates of clumping habit and dead apical bud rate, high culm density and, to a lesser extent, low culm diameter and flowering head rate. Sulfates were relatively abundant in the sediment of flooded stands and, together with some heavy metals, resulted in some of the mentioned traits. Our results showed a relationship between reed die-back and prolonged flooding and highlighted the potential role of some chemical parameters in affecting the growth of permanently flooded reeds.

Two hyporheic species of the genus Cerconeotes Huys, 1992: C. euryhalinus (Krishnaswamy, 1957) and C. huysi n. sp. (Copepoda, Harpacticoida, Leptastacidae) from India

To date, the genus Cerconeotes Huys, 1992, has seven nominal species, all known mostly from marine interstitial waters. Here, Cerconeotes euryhalinus (Krishnaswamy, 1957), an incompletely described and little-known species, is redescribed in detail after designating the neotype, and an illustrated description is given for Cerconeotes huysi n. sp. Both species were collected from freshwater as well as brackish water hyporheic habitats in southeastern India. The morphological relationships of these species with their congeners are discussed, and two criteria of the original generic definition emended. Cerconeotes huysi n. sp. is unique in the genus in the shape and armature of leg 5 in both sexes, in the male leg 3 second endopodal segment with two smooth, spine-like reduced elements (one apical and one subapical), and the long caudal rami and their armature elements. It closely resembles C. euryhalinus. A brief note on the ecology of the species is also added.

Navigating the tmdl process: sediment toxicity

A key step in the development of Total Maximum Daily Load (TMDL) allocations for water bodies impaired due to sediment toxicity is the identification of chemicals responsible for toxicity. Sediment toxicity identification evaluation procedures (TIEs) are one of the primary tools used in this process. This project evaluated standardized and recently developed sediment TIE methods developed by the US EPA and others, to determine their utility for identifying chemicals responsible for toxicity. In this study, formulated sediments were spiked with five chemicals: copper, fluoranthene, tetrachlorobenzene, nonylphenol and ammonia. Experiments were conducted using sediments spiked with single chemicals and chemical mixtures. Toxicity tests used the estuarine amphipod Eohaustorius estuarius and the freshwater amphipod Hyalella azteca. TIEs were conducted using solid-phase (whole sediment) and sediment interstitial waters. Our results indicate that the TIE methods are sufficient to characterize and identify toxicity due to single and multiple chemicals using spiked sediments. One key finding from the spiked sediment experiments is that methods to elute chemicals from extraction media used in solid-phase and interstitial water TIEs require further refinement to ensure complete and consistent elution of sorbed chemicals. An additional finding is that both solid-phase and interstitial water TIE procedures provide useful lines of evidence and that both approaches should be used in a weight-of-evidence approach in the sediment TIE process. In the final phase of this project, we evaluated the TIE procedures using ambient samples collected from three marine sites and three freshwater sites. Marine sediments were collected from Switzer Creek in San Diego Bay, Upper Newport Bay in Newport Beach, and Consolidated Slip, in Long Beach Harbor, all of which are sites in southern California. Freshwater sediments were collected from two additional sites in California: San Diego Creek, in Newport Beach, and Alisal Slough, in Salinas. The final freshwater sediment was collected from a site in Indiana Harbor. Multiple solid-phase and interstitial water TIEs were conducted on each sediment and results of these were combined with chemical analyses and other lines-of-evidence to evaluate the methods. The results indicate that sediment TIE methods are sufficiently developed to characterize toxicity due to general classes of chemicals such as cationic metals, organic chemicals, and ammonia. Methods to improve extraction and elution of metal and organic chemicals in highly toxic sediments require further refinement in order to allow identification of specific chemicals responsible for toxicity as part of the Phase II TIE process. These refinements include determining the appropriate masses of solid-phase extraction media to allow complete removal of toxic chemicals from sediments and interstitial waters. In addition, we recommend that additional studies be designed to determine optimal equilibration periods to maximize removal of toxic chemicals using resin amendments in solid-phase sediment TIEs. As in the spiked-sediment TIEs, we observed inconsistent elution of toxic chemicals from extraction media used in solid-phase and interstitial water Phase II TIEs with the ambient samples. These procedures require additional work to ensure that chemicals responsible for toxicity are completely eluted from extraction media. Improvement of the Phase II TIE elution and solvent handling steps should facilitate better identification of chemicals responsible for toxicity, particularly in situations where toxicity is due to highly insoluble chemicals. When these considerations are satisfactorily addressed, the methods evaluated are capable of providing useful lines of evidence that can be combined to successfully identify sediment toxicants. This title belongs to WERF Research Report Series ISBN: 9781843397663 (Print) ISBN: 9781780403786 (eBook)

Historical biogeography of the genus Polycopissa (Ostracoda: Myodocopa: Cladocopina), with the description and DNA barcode of the second Indo-Pacific species from the Seto Inland Sea

A new cladocopid ostracod species, Polycopissa okadai n. sp., is described from the marine interstitial environment of the Seto Inland Sea, western Japan. This is the second representative of this genus identified from the Indo-Pacific region. A detailed morphological observation of the carapace and appendage was performed using a scanning electron microscope. In particular, the results showed that the morphology of the pore system on the outer surface of the carapace could be utilised for generic-level identification and for taxonomic classification of fossil species. In addition, the DNA barcode sequence of this new species was also determined, which was the first such determination within the suborder Cladocopina. Species belonging to Polycopissa Chavtur 1981 show a transoceanic distribution and have been reported from cryptic habitats such as interstitial waters or anchialine caves. The historical biogeography of Polycopissa is the subject of this study, based on previously suggested hypotheses. It is highly likely that the species of Polycopissa are a Tethyan relict and must have recently dispersed from an adjacent habitat to the current distribution area.

Simulation of aromatic polycyclic hydrocarbons remobilization from a river sediment using laboratory experiments supported by passive sampling techniques.

Resuspension of bedded sediments was simulated under laboratory-controlled conditions in order to assess the amount of polycyclic aromatic hydrocarbons (PAH) remobilized in the dissolved fraction during one short and vigorous mixing. The desorbed amount of PAH was compared to the exchangeable fraction, the total amount of PAH sorbed on the sediment particles, and the dissolved PAH amount contained in the interstitial pore waters in order to evaluate the contribution of each fraction to the total amount of PAH released. To monitor the desorption of PAH and measure low trace level concentrations, passive samplers were used in an experimental open flow through exposure simulator. Results show that for the selected sediment, a substantial fraction of sorbed PAH (69 % of the total amount) is not available for remobilization in a depleted medium. Obtained data pinpoint that over 9 days, only 0.007 % of PAH are desorbed by passive diffusion through a water-sediment interface area of 415 cm(2) and that an intense resuspension event of 15 min induces desorption of 0.015 % of PAH during the following 9 days. Results also highlight that during resuspension simulation, modifications of the sediment and the water body occurred since partitioning constants of some pollutants between sediment and water have significantly decreased.

Using 224Ra/228Th disequilibrium to quantify benthic fluxes of dissolved inorganic carbon and nutrients into the Pearl River Estuary

The 224Ra/228Th disequilibrium that was recently observed in coastal sediments has been proven to be an excellent proxy for tracing the benthic processes that regulate solute transfer across the sediment–water interface. In order to better utilize this proxy, there is a need to understand the reaction kinetics of 224Ra in sediments. In this study, depth profiles of 224Ra and 228Th in bulk sediments were collected along a transect in the Pearl River Estuary (PRE). Together with bulk sediment measurements, dissolved 224Ra, dissolved inorganic carbon (DIC), and nutrients (NO2−+NO3−, NH4+) in pore water and in the overlying waters were also determined. A marked deficit of 224Ra with respect to 228Th with large spatial variations was observed in the PRE sediments. By use of a diagenetic model for the distributions of dissolved and adsorbed 224Ra in sediments, we infer that adsorption removes 224Ra from aqueous phase at a rate of 0.1±1.1–2000±400d−1. In addition, adsorption of 224Ra exhibits a rate sequence of oxic freshwater>anoxic freshwater>anoxic brackish water, probably reflecting the effect of the redox conditions and ionic strength on the adsorption–desorption kinetics of 224Ra.Benthic fluxes of 224Ra were estimated from the observed deficit of 224Ra in the sediments using a one-dimensional (1D) mass balance exchange model. We demonstrated that irrigation was the predominant process that controls solute transfer across the sediment–water interface, whereas molecular diffusion and sediment mixing together contributed <5% of the total 224Ra fluxes from bottom sediments. We then utilized the 224Ra/228Th disequilibrium approach to quantify the benthic fluxes of DIC and nutrients. We showed that sediment interstitial waters delivered approximately 42±6×109mol of DIC and ∼16±1×109mol of NH4+ into the PRE in the dry season. In contrast, it removed about 13±1×109mol of NO3− from the overlying water column. The benthic flux of DIC is equivalent to ∼18% of the riverine input in this season. In terms of nutrients, our results suggest that bottom sediments are a major sink of water column NO3−, and are a predominant source of NH4+ in the PRE. Overall, this study indicates that irrigation is an important process and must be considered in the mass balance of DIC and nutrients in estuaries.

Origin of the unique geochemical anomaly in the continent/ocean transition zone between Spitsbergen and Knipovich Ridge

The paper is devoted to the interpretation of published data on the geochemical anomaly detected in interstitial water within a thick (about 1 km) Pliocene—Quaternary marine sequence recovered by Hole 986 (ODP Leg 162). Salinity of interstitial water in the core from this hole decreases downward the section and the value at the bottom becomes 1.5 times lesser, relative to the normal marine value at the top. Nature of this geochemical anomaly remains enigmatic so far. We examine this issue under a more general scope of the origin of the inverse interstitial and fissure waters in sedimentary rocks. We support the opinion of hydrogeologists who attribute the super-low mineralization of these waters to the influx of high-temperature CO2-rich fluids into the sedimentary cover from magma sources in the basement. This inference is confirmed by not only the distribution of TDS content in the interstitial water, but also its alkalinity, Li content, and Na/Cl ratio in the hole core. The obtained results should be considered in the analysis of the nature of the Knipovich Ridge, as well as the type, and age of the Earth’s crust in the vicinity.

Influence of Cladophora-Quagga Mussel Assemblages on Nearshore Methylmercury Production in Lake Michigan.

Recent spread of invasive mussels in Lake Michigan has altered primary productivity in the nearshore zone, resulting in proliferation of filamentous benthic green algae (Cladophora glomerata). In areas of dense Cladophora and quagga mussel (Dreissena bugensis) assemblages, as well as in regions where sloughed Cladophora accumulates, methylmercury (MeHg) production is enhanced. A shoreline transect from a river mouth through waters overlying Cladophora/quagga-rich zones showed that aqueous MeHg concentrations increased, despite river dilution. Cladophora, as primary producers, ranged from 0.6 to 7.5 ng g(-1) MeHg [4-47% of total mercury (Hg) as MeHg], and were higher than MeHg concentrations in offshore-collected seston. Concentrations of MeHg in decaying Cladophora accumulated onshore ranged from 2.6 to 18.0 ng g(-1) MeHg (18-41% as MeHg) and from 0.1 to 3.0 ng g(-1) MeHg (2-21% as MeHg) in deposits of recently sloughed and accumulated Cladophora in a nearshore topographical depression. Relative to offshore open waters, interstitial waters within decaying Cladophora from onshore and nearshore deposits were elevated in MeHg concentration, 1000- and 10-fold, respectively. Percent Hg as MeHg was also elevated (65-75% and 9-19%, respectively for onshore interstitial water and nearshore interstitial water, compared to 0.2-3.3% as MeHg for open water). Quagga mussels collected within growing Cladophora beds in the nearshore zone were significantly higher in MeHg than offshore counterparts. Our combined results suggest that recent changes in nearshore primary production contributes to MeHg production and bioaccumulation in Lake Michigan.

Influence of the carbon isotopic composition of methane and the proportion of methane-derived bicarbonate on the 13C/12C ratio of dissolved inorganic carbon at the sulfate–methane transition in the Joetsu Basin area, eastern margin of the Sea of Japan

The geochemistry of interstitial waters associated with active marine hydrocarbon seepage provides insight into the source and ongoing dynamics of such systems. In this investigation of interstitial waters obtained from sediments in a gas hydrate region of the Sea of Japan, we compare carbon isotopic composition (δ13C) of dissolved inorganic carbon (DIC) at the sulfate–methane transition (SMT) with δ13C of deeply sourced methane (as inferred from the deepest samples obtained beneath the SMT). Based on this comparison, we distinguish two causes for lower values of δ13CDIC at the SMT. In Group A (17 piston cores), δ13CDIC values at the SMT (−30.0 to −9.7‰ VPDB) correlate positively with δ13C of deep methane (−90.7 to −61.4‰ VPDB). Lowering of these δ13CDIC values was independent of methane flux, which controls the generation rate of methane-derived bicarbonate by anaerobic oxidation of methane, owing to the influence of a high alkalinity flux from depth. In the Group B core samples, δ13CDIC at the SMT (−41.6 to −14.2‰ VPDB) relative to δ13C of deep methane (−68.2 to −40.5‰ VPDB) is lower than that of Group A, implying a greater contribution of methane-derived HCO3−. With only two exceptions, the Group B core sites were located at areas of active gas seepage. The admixture of methane from migrating methane bubbles with deep methane in the interstitial waters of sediments has the potential to significantly increase the overall methane flux at gas seep sites. Although the admixture may reflect higher δ13C values of deep methane, the increase in methane flux results in a higher proportion of methane-derived HCO3− and lower δ13CDIC at the SMT. Recovery of two group B cores adjacent a dormant pockmark suggests that the depression with seismic blanking beneath it, similar to that of the gas seep sites, is a previous gas seepage site.

Diagenesis of bivalves from Jurassic and Lower Cretaceous lacustrine deposits of northeastern China

AbstractIn contrast to the numerous excellently preserved arthropods, vertebrates and plants from the Mesozoic lacustrine fossil lagerstätten of northeastern China, which have calcium phosphate or organic skeletons, the preservation of taxa with a calcareous skeleton is fairly poor. Here we investigate, using a scanning electron microscope and energy dispersive X-ray spectrometer, the preservational modes of bivalves from the Jurassic Daohugou Fossil Beds of Inner Mongolia and the Lower Cretaceous Yixian Formation of eastern Liaoning. The Jurassic bivalve Ferganoconcha sibirica is preserved as strongly compressed composite moulds which contain remains of the organic periostracum. In the Yixian Formation, the bivalves Sphaerium anderssoni and Arguniella ventricosa occur as compacted internal, external or composite moulds or are preserved with a silicified shell, and rarely with a shell consisting of iron hydroxides, which had replaced pyrite during late diagenesis/weathering. Silicification produced partly fabric-replacive microcrystalline quartz and partly void-filling megaquartz crystals after the carbonate shell had been dissolved. Films of authigenic aluminosilicate minerals, partly secondarily silicified, cover the exterior and interior shell surfaces. Occasionally, early diagenetic pyrite crystals, now oxidized to iron hydroxides, filled shell cavities forming internal moulds and rarely replaced the bivalve shell. The poor preservation of the bivalves reflects the environment and water chemistry of these lakes, which were heavily influenced by volcanic processes. Frequent ash deposition and decomposition of volcanic glass particles created acidic and alkaline lake and interstitial waters, which led to early diagenetic formation of authigenic aluminosilicate minerals, ferruginous internal moulds, dissolution of shell carbonate and silicification of shells.