Greater Water Depths Research Articles

Benthic Carbon Mineralization in Hadal Trenches: Insights From In Situ Determination of Benthic Oxygen Consumption

AbstractHadal trenches have been proposed as depocenters of organic material and hot spots for organic matter mineralization. In this study, we for the first time quantified the total benthic O2 uptake in hadal trenches using in situ chamber incubations. Three trenches in the tropical Pacific were targeted and exhibited relatively high diagenetic activity given the great water depths, that is, the Mariana Trench (2.0 × 102 μmol O2 m−2 d−1, 10,853 m), the Mussau Trench (2.7 ± 0.1 × 102 μmol O2 m−2 d−1, 7,011 m), and the New Britain Trench (6.0 ± 0.1 × 102 μmol O2 m−2 d−1, 8,225 m). Combined with the analyses of total organic carbon and δ13C of total organic carbon in the sediments and previously published in situ O2 microprofiles from hadal settings, we suggest that hadal benthic carbon mineralization partly is governed by the surface production and also is linked to the distance from land. Therefore, we highlight that terrestrial organic matter can be of importance in sustaining benthic communities in some hadal settings.

Effect of river confinement on depth and spatial extent of bed disturbance affecting salmon redds

ABSTRACTHuman impacts on rivers threaten the natural function of riverine ecosystems. This paper assesses how channel confinement affects the scour depth and spatial extent of bed disturbance and discusses the implications of these results for salmon-redd disturbance in gravel-bedded rivers. Two-dimensional hydrodynamic models of relatively confined and unconfined reaches of the Cedar River in Washington State, USA, were constructed with surveyed bathymetry and available airborne lidar data then calibrated and verified with field observations of water-surface elevation and streamflow velocity. Simulations showed greater water depths and velocities in the confined reach and greater areas of low-velocity inundation in the unconfined reach at high flows. Data on previously published scour depth of bed disturbance during high flows were compared to simulated bed shear stress to construct a probabilistic logistic-regression model of bed disturbance, which was applied to spatial patterns of simulated bed shear stress to quantify the extent of likely bed disturbance to the burial depth of sockeye and Chinook salmon redds. The disturbance depth was not observed to differ between confined and unconfined reaches; however, results indicated the spatial extent of disturbance to a given depth in the confined reach was roughly twice as large as in the unconfined reach.

Prediction of Deepwater FPSO responses using different numerical analysis methods

The limitations of existing wave basins present a significant challenge when modelling offshore deepwater systems, particularly due to the basin’s relatively shallow depth. Numerical simulation thus becomes valuable in predicting its behaviour during operation at sea. The coupled dynamic analysis is preferred over the traditional quasi-static method, as the former enables the inclusion of damping and added mass properties of the complete mooring line system, which becomes increasingly prominent at greater water depths. This paper investigates the motions and mooring line tensions of a turret moored Floating Production Storage Offloading (FPSO) platform using three numerical models, i.e. a dynamic system, quasi-static system and linear spring system subjected to unidirectional random wave condition. Analysis is carried out using a commercial software AQWA. The first two numerical models utilise a complete system of the same setup and configuration, while the linear spring system substitutes the mooring lines with equivalent linear springs and attempts to match the total mooring line restoring forces with that of the coupled dynamic analysis. The study demonstrates the significance of coupled dynamic analysis on the responses of an FPSO in deepwater. The numerical model of the FPSO is validated against the results of a published work.

Effect of Water Depths on the Hydrodynamic Responses of an FPSO Platform

Ship-shaped Floating Production Storage Offloading platforms (FPSO) are commonly used in the production of oil and gas in offshore deepwater regions. The vessel is held in place by mooring lines anchored to the seabed during operation, either in spread or turret mooring arrangement. When designing such systems, water depth is a main factor that needs to be considered. At greater depths, the hydrodynamic properties of mooring lines become important and may not be accurately predicted through traditional experiments or numerical quasi-static models. Numerical simulation using coupled dynamic analysis is thus recommended, as the hull-mooring behaviour is analysed simultaneously, and the damping and added mass properties of the entire mooring line system is taken into account. This paper investigates the motions and mooring line tensions of a turret-moored FPSO at various water depths ranging from 1000 m to 2000 m. The analysis focuses on numerical simulations in the fully coupled dynamic time domain. The study utilizes the commercial software AQWA, with the FPSO model subjected to a unidirectional random wave condition. The hull hydrodynamics is first solved using the 3D radiation/diffraction panel method, and the hull response equation is then coupled with the mooring line equation. The dynamic motions and mooring line tensions results are presented in terms of statistical parameters as well as response spectrum. The results highlight the significance of greater water depths on low frequency responses in surge motions and mooring line tensions, and provides insight on the increasing and decreasing trend of these responses.

A discrete-event simulation approach to evaluate the effect of stochastic parameters on offshore wind farms assembly strategies

The wind industry is facing new challenges due to the planned construction of thousands of offshore wind turbines all around the world. However, with their increasing distance from the shore, greater water depths, and increasing sizes of the plants, the industry has to face the challenge to develop sustainable installation procedures. Important limiting factors for offshore wind farm installation are the weather conditions and installation strategies. In this context, the focus of this research is the investigation of the most effective approach to installing offshore wind farms at sea, including the effects of weather conditions. This target is achieved through the implementation of a discrete-event simulation approach which includes the analysis of the environmental conditions, distance matrix, vessel characteristics, and assembly scenarios. The model maps the logistics chain in the offshore wind industry. A deterministic and a probabilistic metocean data method have been compared and cross validated. The results point to a good agreement between the two considered models, while highlighting the huge risks to the time and cost of the installation due to the stochastic nature of the weather. We suggest that simulations may improve and reduce these risks in the planning process of offshore wind farms.

Testing the applicability of a benthic foraminiferal-based transfer function for the reconstruction of paleowater depth changes in Rhodes (Greece) during the early Pleistocene.

We present paleo-water depth reconstructions for the Pefka E section deposited on the island of Rhodes (Greece) during the early Pleistocene. For these reconstructions, a transfer function (TF) using modern benthic foraminifera surface samples from the Adriatic and Western Mediterranean Seas has been developed. The TF model gives an overall predictive accuracy of ~50 m over a water depth range of ~1200 m. Two separate TF models for shallower and deeper water depth ranges indicate a good predictive accuracy of 9 m for shallower water depths (0–200 m) but far less accuracy of 130 m for deeper water depths (200–1200 m) due to uneven sampling along the water depth gradient. To test the robustness of the TF, we randomly selected modern samples to develop random TFs, showing that the model is robust for water depths between 20 and 850 m while greater water depths are underestimated. We applied the TF to the Pefka E fossil data set. The goodness-of-fit statistics showed that most fossil samples have a poor to extremely poor fit to water depth. We interpret this as a consequence of a lack of modern analogues for the fossil samples and removed all samples with extremely poor fit. To test the robustness and significance of the reconstructions, we compared them to reconstructions from an alternative TF model based on the modern analogue technique and applied the randomization TF test. We found our estimates to be robust and significant at the 95% confidence level, but we also observed that our estimates are strongly overprinted by orbital, precession-driven changes in paleo-productivity and corrected our estimates by filtering out the precession-related component. We compared our corrected record to reconstructions based on a modified plankton/benthos (P/B) ratio, excluding infaunal species, and to stable oxygen isotope data from the same section, as well as to paleo-water depth estimates for the Lindos Bay Formation of other sediment sections of Rhodes. These comparisons indicate that our orbital-corrected reconstructions are reasonable and reflect major tectonic movements of Rhodes during the early Pleistocene.

The morphodynamic responses to deposition-promoting projects in island and reef coasts of the Zhoushan Archipelago, China

China׳s island and reef coasts are mainly distributed along the coasts of Zhejiang and Fujian provinces. These areas have favorable deep-water conditions and great development potential. The Zhoushan Archipelago is a typical island and reef coast. In the midst of the islands, there are many tidal channels with high water depth and high current velocity. Daishan Island is located on the northern part of the Zhoushan Archipelago. The sea north of Daishan Island can be characterized as having great water depth (generally between 10 and 20m), high current velocity (the maximum measured value is about 2m/s), and hyperconcentrated suspended sediment (annual average concentration under normal weather conditions is about 0.6kg/m3). Sediment transport is influenced by the co-action of waves and currents. Land reclamation can ease the contradiction between the desire for development and the land resource shortage on island and reef coasts. Land reclamation generally starts from deposition-promoting projects on island and reef coasts with hyperconcentration of suspended sediment with the aim of reducing the reclamation cost. Based on the morphodynamic characteristics of the sea area near north of Daishan Island, a two-dimensional mathematical model was developed to analyze the co-action of current and waves and the model was verified for spring as well as neap tides in 2007 and 2012. The simulated values of tidal stages, tidal current velocities, tidal current directions, and suspended sediment concentration at 15 stations in 2007 and 9 stations in 2012 were in good agreement with the in-situ measured values. Furthermore, the simulated magnitude and pattern of erosion and sedimentation agreed well with the observations. This model was used to evaluate the effects of a proposed siltation scheme on the hydrodynamic environment and morphological change of the study area. The results of this study can inform the protection, development, and utilization of shoal-channels on island and reef coasts, as well provide a scientific basis for comprehensive maritime protection and development.

Relationship between the occurrence of the rice water weevil and water depth in flooded rice crop

Abstract: The objective of this work was to assess the relationship between the depth of irrigation water and larval infestation by Oryzophagus oryzae in flooded rice crop. Water depth and larval infestation were evaluated in the upper levee, in between levees, and in the lower levee. The data were subjected to the descriptive statistical and geostatistical analyses. The highest larval infestation occurs in field areas with greater water depth, which is typical of the lower levee. The spatial distribution of O. oryzae larvae is of the aggregate type and depends on the greater irrigation water depth.

Shoreline Hardening Affects Nekton Biomass, Size Structure, and Taxonomic Diversity in Nearshore Waters, with Responses Mediated by Functional Species Groups

Coastal shoreline hardening is intensifying due to human population growth and sea level rise. Prior studies have emphasized shoreline-hardening effects on faunal abundance and diversity; few have examined effects on faunal biomass and size structure or described effects specific to different functional groups. We evaluated the biomass and size structure of mobile fish and crustacean assemblages within two nearshore zones (waters extending 3 and 16 m from shore) adjacent to natural (native wetland; beach) and hardened (bulkhead; riprap) shorelines. Within 3 m from shore, the total fish/crustacean biomass was greatest at hardened shorelines, driven by greater water depth that facilitated access to planktivore (e.g., bay anchovy) and benthivore-piscivore (e.g., white perch) species. Small-bodied littoral-demersal species (e.g., Fundulus spp.) had greatest biomass at wetlands. By contrast, total biomass was comparable among shoreline types within 16 m from shore, suggesting the effect of shoreline hardening on fish biomass is largely within extreme nearshore areas immediately at the land/water interface. Shoreline type utilization was mediated by body size across all functional groups: small individuals (≤60 mm) were most abundant at wetlands and beaches, while large individuals (>100 mm) were most abundant at hardened shorelines. Taxonomic diversity analysis indicated natural shoreline types had more diverse assemblages, especially within 3 m from shore, although relationships with shoreline type were weak and sensitive to the inclusion/exclusion of crustaceans. Our study illustrates how shoreline hardening effects on fish/crustacean assemblages are mediated by functional group, body size, and distance from shore, with important applications for management.

A 15.4-ka paleoclimate record inferred from δ13C and δ15N of organic matter in sediments from the sub-alpine Daping Swamp, western Nanling Mountains, South China

We inferred past climate conditions from the δ13C and δ15N of organic matter (OM) in a sediment core (DP-2011-02) from the sub-alpine Daping Swamp, in the western Nanling Mountains, South China. In the study region, a 1000-m increase in altitude results in a ~0.75‰ decrease in δ13C and a ~2.2‰ increase in δ15N. Organic carbon stable isotope (δ13C) values of the dominant modern vegetation species, surface soils, and the core samples taken in the swamp exhibit a strong terrestrial C3 plant signature. Comprehensive analysis of the core indicates both terrestrial and aquatic sources contribute to the OM in sediment. Temperature and precipitation are most likely the critical factors that influence δ13C: warm and wet conditions favor lower δ13C, whereas a dry and cool climate leads to higher δ13C values. Higher δ15N values may result from greater water depth and increased primary productivity, promoted by large inputs of dissolved inorganic nitrogen, induced by high surface runoff. Lower δ15N values are associated with lower lake stage and reduced productivity, under drier conditions. Therefore, stratigraphic shifts in these stable isotopes were used to infer past regional climate. Measures of δ13C and δ15N in deglacial deposits, in combination with total organic carbon (TOC) and nitrogen (TN) concentrations, the TOC/TN ratio, coarse silt and sand fractions, dry bulk density and low-frequency mass magnetic susceptibility, reveal two dry and cold events at 15,400–14,500 and 13,000–11,000 cal a BP, which correspond to Heinrich event 1 and the Younger Dryas, respectively. A pronounced warm and wet period that occurred between those dry episodes, from 14,500 to 13,000 cal a BP, corresponds to the Bolling–Allerod. The δ13C and δ15N data, however, do not reflect a warm and wet early Holocene. The Holocene optimum occurred between ~8000 and 6000 cal a BP, which is different from inferences from the nearby Dongge cave stalagmite δ18O record, but consistent with our previous results. This study contributes to our understanding of climate-related influences on δ13C and δ15N in OM of lake sediments in South China.

Methane in shallow subsurface sediments at the landward limit of the gas hydrate stability zone offshore western Svalbard

Offshore western Svalbard plumes of gas bubbles rise from the seafloor at the landward limit of the gas hydrate stability zone (LLGHSZ; ∼400m water depth). It is hypothesized that this methane may, in part, come from dissociation of gas hydrate in the underlying sediments in response to recent warming of ocean bottom waters. To evaluate the potential role of gas hydrate in the supply of methane to the shallow subsurface sediments, and the role of anaerobic oxidation in regulating methane fluxes across the sediment–seawater interface, we have characterised the chemical and isotopic compositions of the gases and sediment pore waters. The molecular and isotopic signatures of gas in the bubble plumes (C1/C2+=1×104; δ13C-CH4=−55 to −51‰; δD-CH4=−187 to −184‰) are similar to gas hydrate recovered from within sediments ∼30km away from the LLGHSZ. Modelling of pore water sulphate profiles indicates that subsurface methane fluxes are largely at steady state in the vicinity of the LLGHSZ, providing no evidence for any recent change in methane supply due to gas hydrate dissociation. However, at greater water depths, within the GHSZ, there is some evidence that the supply of methane to the shallow sediments has recently increased, which is consistent with downslope retreat of the GHSZ due to bottom water warming although other explanations are possible. We estimate that the upward diffusive methane flux into shallow subsurface sediments close to the LLGHSZ is 30,550mmolm−2yr−1, but it is <20mmolm−2yr−1 in sediments further away from the seafloor bubble plumes. While anaerobic oxidation within the sediments prevents significant transport of dissolved methane into ocean bottom waters this amounts to less than 10% of the total methane flux (dissolved+gas) into the shallow subsurface sediments, most of which escapes AOM as it is transported in the gas phase.

Experimental study on the hydrodynamic behaviour of an FPSO in a deepwater region of the Gulf of Mexico

As offshore oil and gas exploration moves progressively toward greater water depths, it becomes more challenging to predict the environmental forces and global responses of floating production storage and offloading (FPSO) systems and the dynamic behaviour of the mooring lines and risers. The validation of complex numerical models through scale model experimental testing is restricted by the physical limits of the test facilities. It is not feasible to install the equivalent full length mooring lines and riser systems and select an appropriate scale model for reducing the uncertainties in the experimental test programme for deepwater and ultra-deepwater conditions. The combination of an appropriate scale FPSO model with a suitable level of equivalent effect reduced depth using a hybrid passive truncated experimental methodology for the mooring lines and risers is a practical approach.Following recent discoveries, FPSO has been proposed for a portion of the planned development in the southern Gulf of Mexico (GOM) in water depth ranging from 1000 to 2000m. Based on a scale model and a hybrid passive truncated experimental method for mooring lines and risers, this paper investigates the global response of an FPSO, as well as the dynamics of mooring lines and risers in the context of prevailing environmental conditions for field development in a specific deepwater location in GOM. The experiments revealed that the main horizontal motion response of the FPSO (surge) under non-collinear loading condition is almost two-times that of the collinear loading condition. The mooring lines in the non-collinear condition are more sensitive to the dynamic response and risers appear to have an important influence on the low frequency damping.

Modeling the migration of the American eel in the Gulf of St. Lawrence

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 549:183-198 (2016) - DOI: https://doi.org/10.3354/meps11706 Modeling the migration of the American eel in the Gulf of St. Lawrence Mélanie Béguer-Pon1,2,*, Kyoko Ohashi2, Jinyu Sheng2, Martin Castonguay3, Julian J. Dodson1 1Département de Biologie, Université Laval, Québec City, Québec G1V 0A6, Canada 2Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada 3Institut Maurice-Lamontagne/Fisheries and Oceans Canada, CP 1000, Mont-Joli, Québec G5H 3Z4, Canada *Corresponding author: melanie.beguer@gmail.com ABSTRACT: Telemetry experiments allow documentation of aquatic animal movements in the ocean, and numerical models can contribute to our understanding of the mechanisms underlying the observed movement patterns. In this study, we used mature (silver-stage) American eel Anguilla rostrata migration out of the St. Lawrence Estuary (SLE)-Gulf of St. Lawrence (GSL) system to illustrate how an individual-based model coupled with a 3-dimensional ocean circulation model can help us understand fish behaviour, and complement ongoing and future telemetry experiments. A suite of 23 numerical simulations that combined various vertical and horizontal swimming behaviours of virtual eels (‘v-eels’) was conducted to evaluate which behaviours most closely matched the observed migratory patterns of silver eels in the GSL. Results indicated that v-eels migrating through the SLE-GSL must employ active swimming and complex orientation strategies in order to migrate in the time suggested by telemetry experiments. The use of selective tidal stream transport is sufficient for v-eels to escape entrapment in the Estuary; however, this behaviour requires active swimming rather than simply drifting in the direction of the appropriate currents in the Estuary in order to eventually exit the GSL within the time frame observed in the field. Orientation towards higher salinity and/or greater water depths in the Gulf was not sufficient for v-eels to successfully escape the GSL, suggesting the use of other variables such as the geomagnetic field gradient is required. The model also allows exploration of the potential effects of climate change on the duration of migration, through changes in hydrological conditions. KEY WORDS: Orientation cues · Telemetry · Particle-tracking · Spawning migration · Ocean Tracking Network · Ocean circulation model · Anguilla rostrata Full text in pdf format PreviousNextCite this article as: Béguer-Pon M, Ohashi K, Sheng J, Castonguay M, Dodson JJ (2016) Modeling the migration of the American eel in the Gulf of St. Lawrence. Mar Ecol Prog Ser 549:183-198. https://doi.org/10.3354/meps11706 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 549. Online publication date: May 10, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Causes and deterrent of SWF in deep water of Mississippi prodelta areas

Shallow water flow (SWF) represents a costly drilling challenge in deep water. Establishing the differential pressure between the sand and the shale beds is the main objective. This is because most of the SWFs take place while penetrating the shale-sand boundaries. During compaction, sand's formation water influxes rapidly upward, whereas shale's dewatering is very sluggish. The differential pressure (ΔP) value ranges from 670 psi (1.2 ppg) to 50 psi (0.2 ppg) at variable depths. All ΔP's show high values at depth between 1000 ft and 3000 ft below mudline at any water depth, which is where most SWF takes place. ΔP noticeably increases near the mudline at greater water depth and can be the reason for the occasional conductor and wellhead sinking in the extra-deep water. Choosing correct mud-up values (ΔP) at depth is essential to combat SWF and avoid loss of circulation. The safe mud weight is calculated at different water depth and below the mudline depth. Algorithm and tabulations are systematically presented. Case histories from the Gulf of Mexico, where the upper Pleistocene-recent depositional fan was and is still active, are utilized.

High-resolution phylogenetic microbial community profiling.

Over the past decade, high-throughput short-read 16S rRNA gene amplicon sequencing has eclipsed clone-dependent long-read Sanger sequencing for microbial community profiling. The transition to new technologies has provided more quantitative information at the expense of taxonomic resolution with implications for inferring metabolic traits in various ecosystems. We applied single-molecule real-time sequencing for microbial community profiling, generating full-length 16S rRNA gene sequences at high throughput, which we propose to name PhyloTags. We benchmarked and validated this approach using a defined microbial community. When further applied to samples from the water column of meromictic Sakinaw Lake, we show that while community structures at the phylum level are comparable between PhyloTags and Illumina V4 16S rRNA gene sequences (iTags), variance increases with community complexity at greater water depths. PhyloTags moreover allowed less ambiguous classification. Last, a platform-independent comparison of PhyloTags and in silico generated partial 16S rRNA gene sequences demonstrated significant differences in community structure and phylogenetic resolution across multiple taxonomic levels, including a severe underestimation in the abundance of specific microbial genera involved in nitrogen and methane cycling across the Lake's water column. Thus, PhyloTags provide a reliable adjunct or alternative to cost-effective iTags, enabling more accurate phylogenetic resolution of microbial communities and predictions on their metabolic potential.

Consequences and Implications of Anthropogenic Desalination of Salt Marshes on Macrobenthos

Coastal wetlands are important natural habitats. Wetland restoration and creation projects are often conducted, in part to mitigate for habitat loss, but the factors leading to the success of such projects are not fully understood. A management project was examined in the Yellow River Delta Natural Nature Reserve where large impounded salt marshes were flooded with freshwater with the goal of creating fresh marsh habitat. Areas flooded with freshwater had greater water depth, lower salinity, and bulk density, and more porous and softer soils than unmanipulated areas. The freshwater plant Phragmites australis replaced the salt marsh species Suaeda salsa and Tamarix chinensis at high elevations, but flooding with freshwater led to an extinction of plants at middle elevations. Freshwater flooding reduced densities and the diversity of macrobenthos in high marsh, and macrobenthos were almost absent in the middle marsh. There was no overlap of macrobenthic species between treated and control areas, and the macrobenthic species richness in treated areas was very low. The results suggest that this management technique is more likely to achieve its goals at higher marsh elevations. The success of future projects may be improved by selecting high elevation sites or improving techniques to better reduce salinities in middle elevation sites. As the project replaced salt marshes with fresh marshes that are only partially functional, future projects of this type should only proceed after identifying better techniques that will produce better results.

Modelling the Potential of Integrated Vegetation Bands (IVB) to Retain Stormwater Runoff on Steep Hillslopes of Southeast Queensland, Australia

Rainfall intensity is predicted to increase under a changing climate, leading to increased risks of hillslope erosion, downstream sedimentation and flooding. For many catchments used for grazing and agricultural land uses, it will become increasingly important to maintain ecohydrological functioning despite climatic extremes. One means to achieve this is through strategic reforestation using locally endemic species, in spatial configurations that effectively intercept, retain or and redistribute overland flows. This paper adopts a modelling approach for investigating the potential of one such design termed “integrated vegetation bands” (IVB), to increase the retention of runoff across steep hillslopes, particularly in the sub-tropics where rainstorms are becoming increasingly intense. A spatially distributed simulation model (MIKE-SHE) was applied to a steep, grazed catchment (Maronghi Creek catchment, Southeast Queensland, Australia) to compare stormwater runoff characteristics between: (1) the existing pasture land cover; and (2) a series of hypothetical IVB added across this pasture land. The IVB were approximately 20 m wide, and configured at 5% gradient towards ridgelines. Results for estimates of overland flow depth and infiltration (spatial), and accumulative water balance (temporal), confirm that the area of hillslope retaining &gt; 10 mm/day more runoff increased by 22% under IVB compared to the pasture land use. Excluding the IVB themselves, the area of hillslope where runoff retention increased was 11%. During the most intense rainfall, IVB held up to 25% greater water depth and had 10% greater infiltration at the hillslope scale. At the sub-catchment scale, discharge decreased by 7% and infiltration increased by 23%. The findings for sub-tropical landscapes presented here are consistent with studies conducted in temperate regions. Based on the results of this preliminary modelling work, the IVB concept has been established as a paired-catchment field trial in a high rainfall catchment in Southeast Queensland, Australia.

Laboratory study for pore pressures in sandy deposit under wave loading

This paper presents the results of an experimental study of wave-induced pore pressures in marine sediments. A one-dimensional facility was set up with a vertical cylinder, and a 1.8m thick sandy deposit with 0.2m of water above the deposit. Unlike the previous experiments of Zen and Yamazaki (1990a), additional static water pressures were added onto the harmonic dynamic wave pressure, which allowed us to simulate a case with a greater depth of water. Furthermore, more pore pressure gauges were installed to better resolve the distribution of the pore pressure. A series of experiments with 3000 wave cycles in each test were conducted under various wave and soil conditions. This allowed examining the influence of the wave and soil parameters on the wave-induced pore pressures as well as liquefaction. The experimental results show the significant influence of liquefaction on sandy deposits in shallow water. Furthermore, the thickness of the sandy deposit was usually considered to be unchanged in theoretical calculations, while the thickness was observed to change periodically with the loadings.

Nest-Site Selection and Reproductive Success of the Little GrebeTachybaptus ruficollisin Northeast Algeria

We studied the phenology, habitat selection, and interannual and seasonal changes in breeding performance of the little grebe Tachybaptus ruficollis in relation to the spatial structure of a shallow lake during three breeding seasons (2010–2012). Nests were mostly located in shallow waters, close to the shore (98.3 ± 37.9 cm), in vegetation dominated by Scirpus lacustris. The egg-laying period started at the end of March and extended for four months until the end of July. Overall, the mean clutch size was 4.7 ± 1.1 (N = 154) with a modal clutch of 5. There was a seasonal decline in both egg volume and clutch size. The overall nesting success was 60% and the chief causes of nest failure were predation (52%) and adverse weather (20%). Breeding outcome was influenced by water depth, nest size and year of breeding. Predation and nest flooding markedly varied between years. Larger nests had a higher nesting success than smaller ones. Likewise, nests located at greater water depth (further from the shore) succeeded better than ones located in shallower water. As the little grebe forages preferentially in shallow waters, these results suggest that optimal nesting locations may be the result of a trade-off between conflicting selection pressures such as foraging efficiency (better in shallow waters) and nest predation risk (greater in shallow waters).

Dissolved amino acids in oceanic basaltic basement fluids

The oceanic basaltic basement contains the largest aquifer on Earth and potentially plays an important role in the global carbon cycle as a net sink for dissolved organic carbon (DOC). However, few details of the organic matter cycling in the subsurface are known because great water depths and thick sediments typically hinder direct access to this environment. In an effort to examine the role of water–rock–microorganism interaction on organic matter cycling in the oceanic basaltic crust, basement fluid samples collected from three borehole observatories installed on the eastern flank of the Juan de Fuca Ridge were analyzed for dissolved amino acids. Our data show that dissolved free amino acids (1–13nM) and dissolved hydrolyzable amino acids (43–89nM) are present in the basement. The amino acid concentrations in the ridge-flank basement fluids are at the low end of all submarine hydrothermal fluids reported in the literature and are similar to those in deep seawater. Amino acids in recharging deep seawater, in situ amino acid production, and diffusional input from overlying sediments are potential sources of amino acids in the basement fluids. Thermodynamic modeling shows that amino acid synthesis in the basement can be sustained by energy supplied from inorganic substrates via chemolithotrophic metabolisms. Furthermore, an analysis of amino acid concentrations and compositions in basement fluids support the notion that heterotrophic activity is ongoing. Similarly, the enrichment of acidic amino acids and depletion of hydrophobic ones relative to sedimentary particulate organic matter suggests that surface sorption and desorption also alters amino acids in the basaltic basement. In summary, although the oceanic basement aquifer is a net sink for deep seawater DOC, similar amino acid concentrations in basement aquifer and deep seawater suggest that DOC is preferentially removed in the basement over dissolved amino acids. Our data also suggest that organic carbon cycling occurs in the oceanic basaltic basement, where an active subsurface biosphere is likely responsible for amino acid synthesis and degradation.