S/S fractionation by sulfate-reducing microbial communities in estuarine sediments

Sulfur isotope fractionation during microbial sulfate reduction in brackish estuarine sediments was studied using an experimental flow-through reactor approach designed to preserve the in situ physical, geochemical and microbial structure of the sediment. Concurrent measurements of potential sulfate reduction rates and ³⁴S/³²S fractionations were carried out using intact sediment slices (2 cm thick, 4.2 cm diameter) from unvegetated, intertidal sites adjoining a salt marsh along the Scheldt estuary, The Netherlands. A total of 30 reactor experiments were performed with sediments collected in February, May and October 2006. The effects of incubation temperature (10, 20, 30 and 50 °C) and sediment depth (0-2, 4-6 and 8-10 cm) were investigated. Sulfate was supplied in non-limiting concentrations via the reactor inflow solutions; no external electron donor was supplied. Isotope fractionations (ε values) were calculated from the measured differences in sulfate δ³⁴S between in- and outflow solutions of the reactors, under quasi-steady state conditions. Potential sulfate reduction rates (SRR) varied over one order of magnitude (5-49 nmol cm⁻³ h⁻¹) and were highest in the 30 °C incubations. They decreased systematically with depth, and were highest in the sediments collected closest to the vegetated marsh. Isotope fractionations ranged from 9‰ to 34‰ and correlated inversely with SRR, as predicted by the standard fractionation model for enzymatic sulfate reduction of Rees (1973). The ε versus SRR relationship, however, varied between sampling times, with higher ε values measured in February, at comparable SRRs, than in May and October. The observed ε versus SRR relationships also deviated from the previously reported inverse trend for sediments collected in a marine lagoon in Denmark (Canfield, 2001b). Thus, isotope fractionation during sulfate reduction is not uniquely determined by SRR, but is site- and time-dependent. Factors that may affect the ε versus SRR relationship include the structure and size of the sulfate-reducing community, and the nature and accessibility of organic substrates. Whole-sediment data such as those presented here provide a link between isotopic fractionations measured with pure cultures of sulfate-reducing prokaryotes and sulfur isotopic signatures recorded in sedimentary deposits.     

Geogas transport in fractured hard rock – Correlations with mining seismicity at 3.54 km depth, TauTona gold mine, South Africa

An on-site gas monitoring study has been conducted in the framework of an earthquake laboratory (The International NELSAM–DAFGAS projects) at the TauTona gold mine, South Africa. Five boreholes up to 60 m long were drilled at 3.54 km depth into the highly fractured Pretorius Fault Zone and instruments for chemical and seismic monitoring installed therein. Over the span of 4 years sensitive gas monitoring devices were continuously improved to enable the direct observation of geogas concentration variations in the DAFGAS borehole. The major gas concentrations are constant and air-like with about 78% N₂, 21% O₂, 1% Ar. The geogas components CO₂, CH₄, He and H₂ show the most interesting trends and variations on the minute-by-minute basis and significantly correlate with seismic data, while the ²²²Rn activity remains constant. Time series and cross correlation analysis allow the identification of different gas components (geogas and tunnel air) and the identification of two processes influencing the borehole gas composition: (1) pumping-induced tunnel air breakthrough through networks of initially water-saturated fault fractures; and (2) seismicity induced permeability enhancement of fault fractures to above ∼5 × 10^-10 m². The current set-up of the gas monitoring system is sensitive enough to quantify the resulting geogas transport during periods of intense blasting activities (including recorded blasts with seismic moment ?1 × 10⁹ Nm, located within 1000 m of the cubby) and, it is suggested, also during induced earthquakes, a final goal of the project.     

Hydrogeology and groundwater flow in a basalt-capped Mesozoic sedimentary series of the Ethiopian highlands

A hydrogeological study was undertaken in the Zenako-Argaka catchment, near Hagere Selam in Tigray, northern Ethiopia, during the rainy season of 2006. A geological map was produced through geophysical measurements and field observations, and a fracture zone identified in the north west of the catchment. A perched water table was found within the Trap Basalt series above the laterized upper Aram Aradam Sandstones. A map of this water table was compiled. Water-level variation during the measurement period was at least 4.5?m. Variation in basal flow for the whole catchment for the measurement period was between 12 and 276?m³/day. A groundwater flow model was produced using Visual MODFLOW, indicating the general direction of flow to be towards the south, and illustrating that the waterways have only a limited influence on groundwater flow. The soil water budget was calculated for the period 1995?C2006, which showed the important influence of the distribution of rainfall in time. Although Hagere Selam received some 724?mm of rainfall per year over this period, the strong seasonal variation in rainfall meant there was a water deficit for on average 10?months per year.     

Multi-scale European Soil Information System (MEUSIS): a multi-scale method to derive soil indicators

The Multi-scale Soil Information System (MEUSIS) can be a suitable framework for building a nested system of soil data that could facilitate interoperability through a common coordinate reference system, a unique grid coding database, a set of detailed and standardized metadata, and an open exchangeable format. In the context of INSPIRE Directive, MEUSIS may be implemented as a system facilitating the update of existing soil information and accelerating the harmonization of various soil information systems. In environmental data like the soil one, it is common to generalize accurate data obtained at the field to coarser scales using either the pedotransfer rules or knowledge of experts or even some statistical solutions which combine single values of spatially distributed data. The most common statistical process for generalization is averaging the values within the study area. In this paper, we do not present a simple averaging of numerical values without any further processed information. The upscaling process is accompanied with significant statistical analysis in order to demonstrate the method suitability. The coarser resolution nested grids cells (10??? 10?km) represent broad regions where the calculated soil property (e.g., organic carbon) can be accurately upscaled. Multi-scaled approaches are urgently required to integrate different disciplines (such as Statistics) and provide a meta-model platform to improve current mechanistic modeling frameworks, request new collected data, and identify critical research questions. Past papers have described in detail the upscaling methodology while our present approach is to demonstrate an important application of this methodology accompanied with statistical evidence.     

Predictability of bacterial activity and denitrification in aquatic sediments with continuous measurements of redox potential

Redox potential has been adopted as a qualitative parameter for interpreting solubility changes of nutrients and contaminants and the biological activity within wetland systems for several decades. The majority of studies considering the redox geochemistry in sediments used measurements of bulked material and single point measurement of biogeochemical parameters for interpretation, yet it remains questionable whether this information is reliable for environments that are very dynamic, such as wetlands. In this study it is evaluated whether variations in redox potential reflect dynamics of denitrification and overall bacterial respiration using continuous measurements of redox potential in time-series experiments in laboratory microcosms, in which the biogeochemical variation was enhanced by bioturbation. The results presented here suggest that measurements of redox potential have predictive potential in approximating rates of denitrification and overall bacterial respiration in aquatic sediments. The data clearly suggest that, while sediment bulk measurements and measurements of single profiles of redox potential, denitrification and bacterial activity often fail to provide ecological relevant information in dynamic systems, measurements of spatial and temporal redox potential profiles provide a useful parameter that reflects biogeochemical processes and functioning of sediments.     

Effect of nitrogen loading rates on nitrogen removal by using a biological filter proposed for ventilated improved pit latrines

Pit latrines are the most frequently used sanitation systems in developing countries because of weak infrastructure and poor economic wealth. A modified ventilated improved pit latrine, with a biological filter beneath is proposed to stabilize and to remove the bulk of the nitrogen from the liquid phase. Although the hydraulic loading rate in the proposed biological filter system was calculated to be ca 36 L/m²/d, significantly lower than the rates that are typical applied in standard rate biological filters (in the range of 1000–4000 L/m²/d) used to treat domestic wastewater; the total Kjeldahl nitrogen and chemical oxygen demand concentrations are significantly higher in faecal sludge, namely 3–5 g /L and 20–50 g /L, respectively compared to ca 60 mg/L and 500 mg/L in standard rate biological filters. The biological filter was operated at nitrogen loading rates of 72, 145, 290 and 435 g/m²/d, respectively, until stable state conditions were obtained. The biological filter showed effective nitrogen removal between 72 and 434 g/m²/d and the best total nitrogen removal was obtained at 145 g/m²/d, namely 92 %. These results suggest that it should be possible to remove nitrogen effectively using a biological filter beneath a modified ventilated improved pit latrine.     

Origin of freshwater and polynya water in the Arctic Ocean halocline in summer 2007

Extremely low summer sea-ice coverage in the Arctic Ocean in 2007 allowed extensive sampling and a wide quasi-synoptic hydrographic and δ¹⁸O dataset could be collected in the Eurasian Basin and the Makarov Basin up to the Alpha Ridge and the East Siberian continental margin. With the aim of determining the origin of freshwater in the halocline, fractions of river water and sea-ice meltwater in the upper 150 m were quantified by a combination of salinity and δ¹⁸O in the Eurasian Basin. Two methods, applying the preformed phosphate concentration (PO^*) and the nitrate-to-phosphate ratio (N/P), were compared to further differentiate the marine fraction into Atlantic and Pacific-derived contributions. While PO^*-based assessments systematically underestimate the contribution of Pacific-derived waters, N/P-based calculations overestimate Pacific-derived waters within the Transpolar Drift due to denitrification in bottom sediments at the Laptev Sea continental margin.Within the Eurasian Basin a west to east oriented front between net melting and production of sea-ice is observed. Outside the Atlantic regime dominated by net sea-ice melting, a pronounced layer influenced by brines released during sea-ice formation is present at about 30–50 m water depth with a maximum over the Lomonosov Ridge. The geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the Transpolar Drift.The ratio of sea-ice derived brine influence and river water is roughly constant within each layer of the Arctic Ocean halocline. The correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea-ice formation within the Arctic Ocean. Over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found, sea-ice formation results in a linear correlation between brine influence and river water at salinities of about 32–34. In coastal polynyas in the shallow regions of the Laptev Sea and southern Kara Sea, sea-ice formation transports river water into the shelf’s bottom layer due to the close proximity to the river mouths. This process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30–32. Our study indicates which layers of the Arctic Ocean halocline are primarily influenced by sea-ice formation in coastal polynyas and which layers are primarily influenced by sea-ice formation over the open ocean. Accordingly we use the ratio of sea-ice derived brine influence and river water to link the maximum in brine influence within the Transpolar Drift with a pulse of shelf waters from the Laptev Sea that was likely released in summer 2005.     

Spatial distribution and general population characteristics of mysid shrimps in the Westerschelde estuary (SW Netherlands)

The distribution and general population characteristics of five mysid shrimps were investigated in the period 2003–2005 in the Westerschelde estuary, a tidal temperate estuary situated along the Dutch–Belgian border. Multivariate analyses revealed that salinity predominantly governs the spatial distribution of Neomysis integer, Gastrosaccus spinifer, Schistomysis kervillei and Schistomysis spiritus while temperature, and to a lesser extent turbidity, control the distribution of Mesopodopsis slabberi. N. integer is a resident species in the mesohaline zone of the estuary, i.e. all life stages of the species are present in the estuary throughout the year. For the first time since decades N. integer inhabits the oligohaline zone of the estuary supposedly as a consequence of improved oxygen conditions in the upstream reaches. M. slabberi, the most abundant mysid in the Westerschelde, dominates the hyperbenthos of the mesohaline zone of the estuary. The polyhaline zone of the estuary is, most abundantly inhabited by M. slabberi, G. spinifer, S. kervillei and to a lesser extent by S. spiritus. The abundance of the latter four species is low in winter, probably due to a migration towards coastal waters to avoid colder temperatures in the estuary combined with an increased mortality after breeding. The sex ratio of all the mysid populations corresponds to the expected 1:1 female:male ratio and no salinity governed segregation is found between the different life stages of each mysid population. A seasonal variation exists in brood size in the N. integer population regardless of the body size, with a larger number of broods during winter and spring compared to the summer. In the other mysid populations the brood sizes vary only with the length of the ovigerous females.     

Bioturbation effects of Corophium volutator: Importance of density and behavioural activity

Bioturbation is one of the major processes influencing ecosystem functioning. Population parameters such as species density, burrow density and species-specific life modes, determine the impact of bioturbation on the ecosystem. A laboratory experiment was developed, using microcosms mimicking a marine intertidal sediment–water interface which allowed for quantification of different population parameters. The vertical redistribution, bioturbation rate and maximum penetration depth of two sizes (41 and 129 μm) of luminophores were measured in five treatments (control, low density of burrows with and without Corophium (1989 ind./m²), and high density of burrows with and without Corophium (14,921 ind./m²)) after 1, 7 and 14 days. Results indicate that the behavioural activities of Corophium are of the utmost importance in sediment reworking, since they contributed to a five-fold increase in bioturbation rate compared to the passive transport induced by the static structure of the burrows. Furthermore, density is an important parameter because only high densities play a prominent role in particle transport and hence in organic matter processing, while the role of low Corophium densities is limited in sediment reworking. No evidence for differentiation in sediment size fractions was observed. Finally, bioturbation rates in this study were low compared to other studies, and these results suggest an influence of the tidal rhythmicity in the behavioural activity of Corophium on the bioturbation rate.