Effects Of Bioturbation Research Articles

Laboratory-determined phosphorus flux from lake sediments as a measure of internal phosphorus loading.

Eutrophication is a water quality issue in lakes worldwide, and there is a critical need to identify and control nutrient sources. Internal phosphorus (P) loading from lake sediments can account for a substantial portion of the total P load in eutrophic, and some mesotrophic, lakes. Laboratory determination of P release rates from sediment cores is one approach for determining the role of internal P loading and guiding management decisions. Two principal alternatives to experimental determination of sediment P release exist for estimating internal load: in situ measurements of changes in hypolimnetic P over time and P mass balance. The experimental approach using laboratory-based sediment incubations to quantify internal P load is a direct method, making it a valuable tool for lake management and restoration.Laboratory incubations of sediment cores can help determine the relative importance of internal vs. external P loads, as well as be used to answer a variety of lake management and research questions. We illustrate the use of sediment core incubations to assess the effectiveness of an aluminum sulfate (alum) treatment for reducing sediment P release. Other research questions that can be investigated using this approach include the effects of sediment resuspension and bioturbation on P release.The approach also has limitations. Assumptions must be made with respect to: extrapolating results from sediment cores to the entire lake; deciding over what time periods to measure nutrient release; and addressing possible core tube artifacts. A comprehensive dissolved oxygen monitoring strategy to assess temporal and spatial redox status in the lake provides greater confidence in annual P loads estimated from sediment core incubations.

Bioturbation Delays Attenuation of DDT by Clean Sediment Cap but Promotes Sequestration by Thin-Layered Activated Carbon

The effects of bioturbation on the performance of attenuation by sediment deposition and activated carbon to reduce risks from DDT-contaminated sediment were assessed for DDT sediment-water flux, biouptake, and passive sampler (PE) uptake in microcosm experiments with a freshwater worm, Lumbriculus variegatus. A thin-layer of clean sediment (0.5 cm) did not reduce the DDT flux when bioturbation was present, while a thin (0.3 cm) AC cap was still capable of reducing the DDT flux by 94%. Bioturbation promoted AC sequestration by reducing the 28-day DDT biouptake (66%) and DDT uptake into PE (>99%) compared to controls. Bioturbation further promoted AC-sediment contact by mixing AC particles into underlying sediment layers, reducing PE uptake (55%) in sediment compared to the AC cap without bioturbation. To account for the observed effects from bioturbation, a mass transfer model together with a biodynamic model were developed to simulate DDT flux and biouptake, respectively, and models confirmed experimental results. Both experimental measurements and modeling predictions imply that thin-layer activated carbon placement on sediment is effective in reducing the risks from contaminated sediments in the presence of bioturbation, while natural attenuation process by clean sediment deposition may be delayed by bioturbation.

Effect of Bioturbation by Tubificid Worms on Nutrient Release from the Sediment in an Agricultural Drainage Canal

Effect of Bioturbation by Tubificid Worms on Nutrient Release from the Sediment in an Agricultural Drainage Canal

Drift sands, lakes, and soils: the multiphase Holocene history of the Laarder Wasmeren area near Hilversum, the Netherlands

AbstractA unique complex of multiphased Holocene drift sands and paleosols, with at least two lacustrine phases, was discovered during a major sanitation project in the Laarder Wasmeren area near Hilversum, the Netherlands. The complex could be studied in detail, highly facilitated by the excellent and large-scale exposure of the various deposits and soils. OSL dating was used to establish ages of the phases, where possible differentiating between time of deposition and time of burial by taking into account the potential effects of bioturbation. Pollen analysis served to reconstruct the vegetation during the various phases.A first minor phase of aeolian activity already started before approx. 5,000 BC, followed around 4,000 BC by a second phase and a rather massive third phase around 3,000 BC. After a long phase of soil formation, the latest, massive drift sand phase started around the 14th to 15th century. It clearly represents the classic drift sand phase that started in the Late Middle Ages in the Netherlands. Sand drifting followed on soil forming phases during which the vegetation became increasingly dominated by ericaceous plants and culminated in heathlands. The first three aeolian phases and associated heathlands are much older than generally assumed for heathland and drift sand to occur in the Netherlands. Moreover, podzolisation was found to have started very early, true podzols already occurring before 4,000 BC.Around 3,000 BC groundwater in the area reached a maximum altitude of about 230 cm +NAP, resulting in local open water in the area. This rise is probably linked to the development of the Dutch coastal area, where at that time peat accumulated and drainage was poor, inducing a rise of the groundwater level in ‘het Gooi’. This groundwater level fell later on, to never reach this altitude again. The Groot Wasmeer was formed by local stagnation on a slowly permeable podzol and already reached a level of 320-325 cm +NAP by 400 BC, which more or less equals its 20thcentury level.The results demonstrate that earlier concepts on the occurrence and age of aeolian phases, podzols and heathland vegetations in the Netherlands are far too schematic, and that early, pre-agricultural cultures may already have had an impact on the stability of fragile cover sand landscapes, e.g. through burning. Results are in line with those from several contemporary studies on early prehistoric cultures and their impact in river dune areas in the Central and Eastern Netherlands.

Advanced spatio-temporal modelling in long-term radiological assessment models—radionuclides in the soil column

Recent developments in the modelling of key radionuclides in long-timescale assessments of the safety of geological disposal of spent fuel and other radioactive wastes emphasise the influence of the redox conditions of the soil column. Models with higher spatial resolution than typically employed in standard modelling approaches have been shown to capture important features of experimental observations that are not otherwise manifested. Furthermore, models with monthly, rather than annually, averaged parameters and with dynamic transfers between soil and plant have been shown to lead to key differences compared with standard models employing soil–plant concentration ratios. This paper looks at the potential for the inclusion of a higher spatio-temporal resolution in models for long-timescale dose assessments and includes representations of measured plant-root distributions as well as the effects of bioturbation. Focusing here on the distribution and dynamics of radionuclides in the soil column, the effects of different spatial and temporal resolution are compared, together with an investigation of the way in which the hydrology of the soil column is represented. The approach has been successfully incorporated into a practical assessment-level model. Results indicate the potential importance of higher spatio-temporal resolution in modelling soil column dynamics, particularly of weakly sorbing radionuclides in long-timescale assessments featuring sudden transitions between ecosystem types.

The effects of bioturbation by the Venus clam Cyclina sinensis on the fluxes of nutrients across the sediment–water interface in aquaculture ponds

A mesocosm experiment was conducted to study the effects of bioturbation by the marine bivalve Cyclina sinensis in an aquatic system and to examine how the bioactivities of this clam alter the rate at which nutrients are exchanged across the sediment–water interface. A dark incubation experiment was performed to determine the fluxes of inorganic nutrients (NH4 +, NO3 − + NO2 − and PO4 3−), benthic chlorophyll a (Chl a), organic matter and sediment oxygen consumption (SOC) on days 1, 10, 20 and 30. C. sinensis destroyed the initial sediment surface and partially enhanced oxygen penetration into the sediment. The clam also increased the water content and volume of the oxic sediment. The analysis showed that increases in the clam density and time period produced higher fluxes of all the nutrients (NH4 +, NO3 − + NO2 − and PO4 3−) in the bioturbated chambers compared with the control (non-bioturbated chambers). The concentration of Chl a in the sediment increased significantly at the end of the experiment (day 30) (p < 0.05). The SOC rate increased significantly with the increase in density and with the time period from day 10 to day 30 (p < 0.05). As a result, the fluxes of nutrients increased with increased SOC, producing oxygen-induced sediment mineralization. Our findings suggest that the activities of the clams could positively influence SOC and cause an increase in the fluxes of inorganic nutrients. These effects may substantially improve the primary productivity and water quality of earthen pond ecosystems.

Low oxygen events in the Laurentian Channel during the Holocene

Geochemical and micropaleontological analyses were carried out on a 35 cm box core (CR06-TCE) spanning the last 6000 years in the Esquiman Channel, a northeast arm of the Laurentian Channel in the Gulf of St. Lawrence. A 0.6‰ decrease of δ18O in benthic foraminifer Globobulimina auriculata shells characterizes the upper 10 cm of the core and suggests a warming of the bottom waters. This change is concomitant with increased percentages of the low-oxygen tolerant benthic foraminifer species Brizalina subaenariensis and the Atlantic water species Oridorsalis umbonatus. Although a precise timing cannot be established, notably because of the smoothing effect of bioturbation, the amplitude of the trend recorded in the Esquiman Channel is coherent with that of the regional warming observed in the bottom water of the main axis of the Laurentian Channel over the last century. Warm bottom water conditions, however, are not exclusive to the recent time interval as shown by data from the lower part of the core, which are also characterized by low δ18O values in G. auriculata and occurrence of both B. subaenariensis and O. umbonatus. Such data suggest the existence of low-oxygen and relatively high temperature conditions in the bottom water of the Esquiman Channel about 4 to 6 kyrs ago likely related to enhanced inflow of Atlantic water in the Gulf of St. Lawrence through the Cabot Strait and the Laurentian Channel. These results highlight the sensitivity of bottom water properties in the Gulf of St. Lawrence to changes in the western North Atlantic circulation.

Biodiversity effects of benthic ecosystem engineers on the spatial patterns of sediment CH4 concentration in an urban Neotropical coastal lagoon

AIM: Biodiversity of sediment bioturbators has been shown to be important for to the magnitude and stability of benthic-pelagic processes. However, no study to date has evaluated the importance of the biodiversity of benthic invertebrate bioturbators to the spatial patterns of sediment CH4 concentration ([CH4]). Here we conducted a laboratorial experiment to test the following predictions: (1) Bioturbator species richness will reduce the sediment [CH4]; (2) individual bioturbator species (i.e. species composition) will have different effects on sediment [CH4]; (3) and both the effects of bioturbator species richness and composition on sediment [CH4] will be dependent on sediment depth. METHODS: We manipulated the number and composition of three functional divergent benthic invertebrate bioturbators species that are widespread in South Atlantic coastal lagoons, in laboratorial sediment chambers containing the sediment and water of an urban impacted coastal lagoon RESULTS: Bioturbator species richness had no overall significant effect on sediment [CH4] when comparisons of sediment [CH4] were made among species richness levels. However, bioturbator species richness significantly reduced sediment [CH4] when species richness levels were compared to the control (defaunated treatments), but this effect was significant only at the deepest sediment layer. Furthermore, bioturbator species composition had significant, but distinct effects on the patterns of reduction in sediment [CH4], depending on the sediment depth and the bioturbator species. CONCLUSIONS: We conclude that both the number and composition of bioturbator species are important to determine the effects of benthic bioturbators on spatial patterns of sediment [CH4], but the strength of these effects depend on species traits that determine interspecific interactions strength across the sediment vertical niche space.

Reconciling discrepancies between Uk37 and Mg/Ca reconstructions of Holocene marine temperature variability

Significant discrepancies exist between the detrended variability of late-Holocene marine temperatures inferred from Mg/Ca and Uk37 proxies, with the former showing substantially more centennial-scale variation than the latter. Discrepancies exceed that attributable to differences in location and persist across various calibrations, indicating that they are intrinsic to the proxy measurement. We demonstrate that these discrepancies can be reconciled using a statistical model that accounts for the effects of bioturbation, sampling and measurement noise, and aliasing of seasonal variability. The smaller number of individual samples incorporated into Mg/Ca measurements relative to Uk37 measurements leads to greater aliasing and generally accounts for the differences in the magnitude and distribution of variability. An inverse application of the statistical model is also developed and applied in order to estimate the spectrum of marine temperature variability after correcting for proxy distortions. The correction method is tested on surrogate data and shown to reliably estimate the spectrum of temperature variance when using high-resolution records. Applying this inverse method to the actual Mg/Ca and Uk37 data results in estimates of the spectrum of temperature variance that are consistent. This approach provides a basis by which to accurately estimate the distribution of intrinsic marine temperature variability from marine proxy records.

TURBO2: A MATLAB simulation to study the effects of bioturbation on paleoceanographic time series

Bioturbation (or benthic mixing) causes significant distortions in marine stable isotope signals and other palaeoceanographic records. Although the influence of bioturbation on these records is well known it has rarely been dealt systematically. The MATLAB program called TURBO2 can be used to simulate the effect of bioturbation on individual sediment particles. It can therefore be used to model the distortion of all physical, chemical, and biological signals in deep-sea sediments, such as Mg/Ca ratios and UK37-based sea-surface temperature (SST) variations. In particular, it can be used to study the distortions in paleoceanographic records that are based on individual sediment particles, such as SST records based on foraminifera assemblages. Furthermore, TURBO2 provides a tool to study the effect of benthic mixing of isotope signals such as 14C, δ18O, and δ13C, measured in a stratigraphic carrier such as foraminifera shells.

The magnitude, timing and abruptness of changes in North African dust deposition over the last 20,000 yr

Reconstructions of eolian dust accumulation in northwest African margin sediments provide important continuous records of past changes in atmospheric circulation and aridity in the region. Existing records indicate dramatic changes in North African dust emissions over the last 20ka, but the limited spatial extent of these records and the lack of high-resolution flux data do not allow us to determine whether changes in dust deposition occurred with similar timing, magnitude and abruptness throughout northwest Africa. Here we present new records from a meridional transect of cores stretching from 31°N to 19°N along the northwest African margin. By combining grain size endmember modeling with 230Th-normalized fluxes for the first time, we are able to document spatial and temporal changes in dust deposition under the North African dust plume throughout the last 20ka. Our results provide quantitative estimates of the magnitude of dust flux changes associated with Heinrich Stadial 1, the Younger Dryas, and the African Humid Period (AHP; ∼11.7–5ka), offering robust targets for model-based estimates of the climatic and biogeochemical impacts of past changes in North African dust emissions. Our data suggest that dust fluxes between 8 and 6ka were a factor of ∼5 lower than average fluxes during the last 2ka. Using a simple model to estimate the effects of bioturbation on dust input signals, we find that our data are consistent with abrupt, synchronous changes in dust fluxes in all cores at the beginning and end of the AHP. The mean ages of these transitions are 11.8±0.2ka (1σ) and 4.9±0.2ka, respectively.

Influence of Chironomid Larvae on oxygen and nitrogen fluxes across the sediment-water interface (Lake Taihu, China)

The microscale distribution of oxygen, the nitrogen flux and the denitrification rates in sediment inhabited by chironomid larvae (Tanypus chinensis) were measured in eutrophic Lake Taihu, China. The presence of the chironomids in the sediment increased the oxygen diffusional flux from 10.4 ± 1.4 to 12.7 ± 2.5 mmol O2/(m2·day). The burrows of the larvae represented “hot spots” and strongly influenced the nitrogen cycles and diagenetic activity in the sediment. The results indicate that the bioturbation effects of Tanypus chinensis chironomid larvae increased the capacity of the sediment as a sink for nitrate and a source for ammonium. Nitrate influx and ammonium outflux were increased 8.8 and 1.7 times, respectively. Under bioturbation, the amount of nitrate consumed was greater than the amount of ammonium released. The total denitrification rate was also enhanced from 0.76 ± 0.34 to 5.50 ± 1.30 mmol N/(m2·day). The net effect was that the bioturbated sediments acted as a net sink for inorganic nitrogen under direct and indirect bioturbation effects compared to the control.

Is the effect of trees on soil properties mediated by soil fauna? A case study from post-mining sites

The effects of tree species differing in foliage and litter chemistry on the chemical, micro-morphological, and biological properties of soil were studied on post-mining sites afforested with one of six tree species (spruce, pine, larch, oak, lime, and alder) and also on sites left to natural succession (dominated by willow). The sites were located on a large colliery spoil heap that had been produced by the mining of coal in alkaline tertiary clays near the city of Sokolov, Czech Republic. Because no topsoil had been applied to the sites, soil development resulted from in situ interactions among the deposited overburden (spoil), trees, and soil biota. Soil formation differed markedly among sites afforested with different tree species. On sites with trees producing litter with a low C/N ratio (the deciduous species), the organic Oe layer was narrow or absent and a thick organomineral A layer was evident. On sites with trees producing litter with a high C/N ratio (the evergreen species), in contrast, a thick Oe layer and a thin A layer were evident. Besides C/N ratio, earthworm abundance and earthworm bioturbation activity (measured as the amount of earthworm casts in the topsoil) were the strongest predictors of A layer thickness and C accumulation in the mineral topsoil. Sites with higher C accumulation in mineral soil had higher microbial biomass and lower microbial respiration, which may have contributed to the higher C storage. The gradient of bioturbation was correlated with changes in the composition of the bacterial community and other soil biota, but partial correlation showed that the effects of litter quality and bioturbation were largely independent. Overall, the results indicate that the effect of tree species on soil development is substantially mediated by soil fauna activity and especially by earthworm bioturbation.

Quaternary surface processes indicated by the magnetic fabric of undisturbed, reworked and fine-layered loess in Hungary

Statistical analytical methods were applied to classify the magnetic fabric of samples from different Hungarian loess profiles. A previous study of the anisotropy of magnetic susceptibility (AMS) of Hungarian loess suggested that ‘typical’ (wind-blown or undisturbed) and ‘redeposited’ loess were well differentiated by known statistical methods. The analyses of new samples require a review of previous results and the terms like ‘typical’ (wind-blown), ‘reworked’ and ‘redeposited’ loess.The type of magnetic fabric of fine-layered loess is classified by a new mathematical method in AMS study of loess: hierarchical cluster analysis. The following Quaternary surface processes were revealed by characteristics of the magnetic fabric of Hungarian loess:The primary magnetic fabric preserves the possible transport or accumulation direction of dust (direction of maximum susceptibility, NE/SW axis) and the structure of the fabric was affected by compaction. In the case of loess, the deviation of the inclination from vertical indicates the accumulation of dust on a sloping surface.The secondary magnetic fabric (fabric of the material after reworking or redeposition) of loess shows the magnetic fabric characteristics of reworked or redeposited material. Scattered values of the principal susceptibilities indicate the effect of bioturbation. Redeposition (fine-layered loess samples) is indicated by the alignment of the direction of maximum and intermediate susceptibilities on a stereographic plot and the degree of alignment possibly indicates the energy of the surface process (lower or higher degree of energy connected to different kind of surface process can produce different kind of magnetic fabric).The magnetic mineralogy of the pilot samples is determined by isothermal remanent magnetisation (IRM) measurements. No differences between loess samples with different sedimentary structure could be shown. The dominant phase in the magnetic fabric that determined the magnetic character of samples was magnetite/maghemite.

Modeling the vertical soil organic matter profile using Bayesian parameter estimation

Abstract. The vertical distribution of soil organic matter (SOM) in the profile may constitute an important factor for soil carbon cycling. However, the formation of the SOM profile is currently poorly understood due to equifinality, caused by the entanglement of several processes: input from roots, mixing due to bioturbation, and organic matter leaching. In this study we quantified the contribution of these three processes using Bayesian parameter estimation for the mechanistic SOM profile model SOMPROF. Based on organic carbon measurements, 13 parameters related to decomposition and transport of organic matter were estimated for two temperate forest soils: an Arenosol with a mor humus form (Loobos, the Netherlands), and a Cambisol with mull-type humus (Hainich, Germany). Furthermore, the use of the radioisotope 210Pbex as tracer for vertical SOM transport was studied. For Loobos, the calibration results demonstrate the importance of organic matter transport with the liquid phase for shaping the vertical SOM profile, while the effects of bioturbation are generally negligible. These results are in good agreement with expectations given in situ conditions. For Hainich, the calibration offered three distinct explanations for the observations (three modes in the posterior distribution). With the addition of 210Pbex data and prior knowledge, as well as additional information about in situ conditions, we were able to identify the most likely explanation, which indicated that root litter input is a dominant process for the SOM profile. For both sites the organic matter appears to comprise mainly adsorbed but potentially leachable material, pointing to the importance of organo-mineral interactions. Furthermore, organic matter in the mineral soil appears to be mainly derived from root litter, supporting previous studies that highlighted the importance of root input for soil carbon sequestration. The 210Pbex measurements added only slight additional constraint on the estimated parameters. However, with sufficient replicate measurements and possibly in combination with other tracers, this isotope may still hold value as tracer for SOM transport.

Effect of reoxygenation and Marenzelleria spp. bioturbation on Baltic Sea sediment metabolism

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 482:43-55 (2013) - DOI: https://doi.org/10.3354/meps10232 Effect of reoxygenation and Marenzelleria spp. bioturbation on Baltic Sea sediment metabolism S. Bonaglia1,*, M. Bartoli2, J. S. Gunnarsson3, L. Rahm4, C. Raymond3, O. Svensson3, S. Shakeri Yekta4, V. Brüchert1 1Department of Geological Sciences, and 3Department of Systems Ecology, Stockholm University, 10691 Stockholm, Sweden 2Department of Environmental Sciences, University of Parma, 43124 Parma, Italy 4Department of Thematic Studies—Water and Environment, Linköping University, 58183 Linköping, Sweden *Email: stefano.bonaglia@geo.su.se ABSTRACT: Nutrient reduction and the improvement of bottom water oxygen concentrations are thought to be key factors in the recovery of eutrophic aquatic ecosystems. The effects of reoxygenation and bioturbation of natural hypoxic sediments in the Baltic Sea were studied using a mesocosm experiment. Anoxic sediment box cores were collected from 100 m depth in Kanholmsfjärden (Stockholm Archipelago) and maintained in flow-through mesocosms with 3 treatments: (1) hypoxic: supplied with hypoxic water; (2) normoxic: supplied with oxic water; and (3) Marenzelleria: supplied with oxic water and the polychaete Marenzelleria spp. (2000 ind. m–2). After a 7 wk long conditioning period, net fluxes of dissolved O2, CH4, Fe2+, Mn2+, NH4+, NO2-, NO3-, PO43- and H4SiO4, and rates of nitrate ammonification (DNRA), denitrification and anammox were determined. Phosphate was taken up by the sediment in all treatments, and the uptake was highest in the normoxic treatment with Marenzelleria. Normoxic conditions stimulated the denitrification rate by a factor of 5. Denitrification efficiency was highest under normoxia (50%), intermediate in bioturbated sediments (16%), and very low in hypoxic sediments (4%). The shift from hypoxic to normoxic conditions resulted in a significantly higher retention of NH4+, H4SiO4 and Mn2+ in the sediment, but the bioturbation by Marenzelleria reversed this effect. Results from our study suggest that bioturbation by Marenzelleria stimulates the exchange of solutes between sediment and bottom water through irrigation and enhances bacterial sulfate reduction in the burrow walls. The latter may have a toxic effect on nitrifying bacteria, which, in turn, suppresses denitrification rates. KEY WORDS: Hypoxia · Macrofauna · Mesocosm · Denitrification · Dissimilatory nitrate reduction to ammonium · DNRA · Benthic Flux · Baltic Sea Full text in pdf format PreviousNextCite this article as: Bonaglia S, Bartoli M, Gunnarsson JS, Rahm L and others (2013) Effect of reoxygenation and Marenzelleria spp. bioturbation on Baltic Sea sediment metabolism. Mar Ecol Prog Ser 482:43-55. https://doi.org/10.3354/meps10232 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 482. Online publication date: May 22, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Stress features in Terra Rossa soil under traditional olive cultivation: a micromorphological and mineralogical characterization

This study analyzes the micromorphological and mineralogical properties of a Terra Rossa soil under a traditional Mediterranean olive grove. It highlights the microscopic and sub-microscopic features generated by the permanent crop cover. The study area, where the land use has remained unchanged for the last 150 years, is near Sassari (Sardinia, Italy) and is characterized by dominant Terra Rossa developed on Miocene marine limestone. Two soil profiles were opened and described in July 2009, 1 under the canopy of an olive tree and 1 between the trees. Chemical and physical analyses were carried out. Undisturbed aggregates were collected from all the sampled horizons for thin section and scanning electron microscope (SEM) analysis, complemented by mineralogical analyses (X-ray diffractometry, XRD). The results obtained highlighted the effects of vigorous bioturbation and stress actions that have occurred on the pedogenetic features inherited from complex genetic processes.

Biogenically enhanced reservoir properties in the Medicine Hat gas field, Alberta, Canada

Spot-minipermeametry and micro-CT analytical techniques were employed to evaluate the effect(s) of bioturbation on porosity and permeability distributions in reservoir facies of the highly prolific Medicine Hat gas field of Alberta, Canada. This study focuses on five cm-scale samples that occur at different stratigraphic positions and intersect discrete bioturbated horizons within the Medicine Hat Member. Spot-minipermeability results demonstrate that permeability in bioturbated sandstones is up to two orders of magnitude greater than those of the muddy matrix, thus corresponding to a dual-porosity fluid flow system. Graphing bioturbation intensity versus measured permeability indicates that burrows are well connected horizontally and provide flow conduits. Micro-CT models reveal that burrowed sandstones are isolated and planiform in character; rare interpenetrations from vertically oriented trace fossils serve to interconnect these hydraulically isolated strata. Results show that bioturbated sandstones possess reservoir properties comparable to those associated with laminated sandstones, yielding an anisotropic porous medium. Understanding the impact of trace fossils on porosity–permeability distributions in the Medicine Hat gas field can be used to identify potential reservoir from previously interpreted non-reservoir rock, and, ultimately, improve reserve estimations.

Deposit-Feeding Sea Cucumbers Enhance Mineralization and Nutrient Cycling in Organically-Enriched Coastal Sediments

BackgroundBioturbators affect multiple biogeochemical interactions and have been suggested as suitable candidates to mitigate organic matter loading in marine sediments. However, predicting the effects of bioturbators at an ecosystem level can be difficult due to their complex positive and negative interactions with the microbial community.Methodology/Principal FindingsWe quantified the effects of deposit-feeding sea cucumbers on benthic algal biomass (microphytobenthos, MPB), bacterial abundance, and the sediment–seawater exchange of dissolved oxygen and nutrients. The sea cucumbers increased the efflux of inorganic nitrogen (ammonium, NH4 +) from organically enriched sediments, which stimulated algal productivity. Grazing by the sea cucumbers on MPB (evidenced by pheopigments), however, caused a net negative effect on primary producer biomass and total oxygen production. Further, there was an increased abundance of bacteria in sediment with sea cucumbers, suggesting facilitation. The sea cucumbers increased the ratio of oxygen consumption to production in surface sediment by shifting the microbial balance from producers to decomposers. This shift explains the increased efflux of inorganic nitrogen and concordant reduction in organic matter content in sediment with bioturbators.Conclusions/SignificanceOur study demonstrates the functional role and potential of sea cucumbers to ameliorate some of the adverse effects of organic matter enrichment in coastal ecosystems.

Distribution of Foraminifera of the Poverty Continental Margin, New Zealand: Implications for Sediment Transport

ABSTRACT Foraminiferal assemblages were used to investigate the nature of sedimentation on the tectonically active Poverty continental margin (PCM) of New Zealand. Recent research around the world has been focused on understanding the sedimentary functioning of small mountainous rivers to the global sediment budget, and this study is part of a greater effort to define the processes that link sediment source and sink of such a system in New Zealand. Fifty-five surface samples from box, gravity, and multi-cores from the shelf and slope of the PCM were used to document the distribution of modern benthic foraminifera. Also, twenty samples from two gravity cores retrieved from Poverty Canyon, a hypothesized conduit of sediment to the deep ocean, were analyzed to evaluate the record of down-slope sediment transport. Seven biofacies, recognized by cluster analysis of benthic foraminiferal abundance data from surface and core samples, are strongly related to water depth and continental margin morphology: inner-shelf biofacies (26–43 m), shelf biofacies (~30–130 m) (this biofacies contained all samples from a canyon-head core taken at 359-m water depth), outer-shelf biofacies (60–250 m), upper-slope biofacies (230–350 m), shallow lower-slope biofacies (870–1255 m), Lachlan Anticline biofacies (40–63 m on the PCM shelf), and a mid-canyon thalweg biofacies from a core taken at 891-m water depth. Foraminiferal assemblages of the Lachlan Anticline biofacies are characterized by the largest foraminifera (mostly inner-and mid-shelf species), the most diverse assemblages, and the highest percentage of reworked planktonic tests in the dataset. Many planktonic and benthic specimens have probably been derived from the outcropping Miocene-Pliocene rock of the anticline. A high percentage of reworked (fossil) planktonic foraminifera at the mouth of Poverty Bay likely results from sediments shed from rapidly uplifting Plio-Pleistocene strata within the Waipaoa River drainage basin. Assemblages throughout the canyon-head (359 m) and mid-canyon (891 m) cores from Poverty Canyon contained higher percentages of shallower-water indicator taxa than other samples at similar depths outside the canyon, thus supporting the hypothesis that Poverty Canyon is channeling sediment from the shelf and upper slope to the deep ocean. However, different patterns of down-core distributions between the canyon head and mid-slope thalweg sites indicate that the nature of sedimentation varies down canyon. Abundances of shallower-water foraminifera suggest that shelf taxa are being supplied from a more consistent source to the canyon head, while shelf and upper-slope taxa are more variably supplied to the deeper-canyon thalweg. The effects of bioturbation appear to be greater in the canyon head.