Oscillatory porewater bioadvection in marine sediments induced by hydraulic activities of Arenicola marina

We employed real‐time pressure recording and high temporal resolution two‐dimensional oxygen imaging to characterize the porewater bioadvection related to hydraulic activities of Arenicola marina, a widespread representative of benthic macrofauna. Behavior‐specific positive and negative pressure oscillations and hydraulic pulses resulted in bidirectional porewater flow and highly dynamic redox oscillations on the scale of minutes. Pumping of water by the worm into its blind‐ending burrow pressurized the sediment and caused sediment oxygenation at depth and the exit of anoxic porewater into the overlying water. The sediment volume that was affected by bioadvective transport of oxygen and the porewater flow patterns varied strongly among sediment types. In low‐permeability sediments, localized plumes of anoxic porewater ascended from the sediment, presumably through sedimentary cracks, while porewater flowed evenly through highly permeable sediments. Hydraulic behaviors that moved water out through the open tail shaft caused a reduction of porewater pressures below the hydrostatic baseline which resulted in the collapse of plumes and enhanced oxygen penetration into the surficial sediments. Porewater bioadvection and the related perfusing and oscillatory phenomena will affect a variety of biogeochemical and ecological processes, including organic matter mineralization, benthic recruitment, and prey localization. We suggest that bidirectional porewater bioadvection and the associated transient geochemical conditions are prevalent features of biogenically active sediments

Beam Test with a GridGEM TPC Prototype Module

The International Large Detector (ILD) --a detector concept for the International Linear Collider (ILC)-- foresees a Time Projection Chamber (TPC) as its main tracking detector. Currently, the R&D efforts for such a TPC focus on studies using a large prototype that can accommodate up to seven read-out modules which are comparable to the ones that would be used in the final ILD TPC. The DESY TPC group has developed such a module using GEMs for the gas amplification, which are mounted on thin ceramic frames. The module design and first results of a test beam campaign are presented.Comment: 6 pages, 11 figures, prepared for LCWS 2011 proceeding

A bioturbation classification of European marine infaunal invertebrates

Bioturbation, the biogenic modification of sediments through particle reworking and burrow ventilation, is a key mediator of many important geochemical processes in marine systems. In situ quantification of bioturbation can be achieved in a myriad of ways, requiring expert knowledge, technology, and resources not always available, and not feasible in some settings. Where dedicated research programmes do not exist, a practical alternative is the adoption of a trait-based approach to estimate community bioturbation potential (BPc). This index can be calculated from inventories of species, abundance and biomass data (routinely available for many systems), and a functional classification of organism traits associated with sediment mixing (less available). Presently, however, there is no agreed standard categorization for the reworking mode and mobility of benthic species. Based on information from the literature and expert opinion, we provide a functional classification for 1033 benthic invertebrate species from the northwest European continental shelf, as a tool to enable the standardized calculation of BPc in the region. Future uses of this classification table will increase the comparability and utility of large-scale assessments of ecosystem processes and functioning influenced by bioturbation (e.g., to support legislation). The key strengths, assumptions, and limitations of BPc as a metric are critically reviewed, offering guidelines for its calculation and application

Activity-independent screening of secreted proteins using split GFP

The large-scale industrial production of proteins requires efficient secretion, as provided, for instance, by the Sec system of Gram-positive bacteria. Protein engineering approaches to optimize secretion often involve the screening of large libraries, e.g. comprising a target protein fused to many different signal peptides. Respective high-throughput screening methods are usually based on photometric or fluorimetric assays enabling fast and simple determination of enzymatic activities. Here, we report on an alternative method for quantification of secreted proteins based on the split GFP assay. We analyzed the secretion by Bacillus subtilis of a homologous lipase and a heterologous cutinase by determination of GFP fluorescence and enzyme activity assays. Furthermore, we identified from a signal peptide library a variant of the biotechnologically relevant B. subtilis protein swollenin EXLX1 with up to 5-fold increased secretion. Our results demonstrate that the split GFP assay can be used to monitor secretion of enzymatic and non-enzymatic proteins in B. subtilis in a high-throughput manner

Hyperspectral imaging of the microscale distribution and dynamics of microphytobenthos in intertidal sediments

We describe a novel, field-deployable hyperspectral imaging system, called Hypersub, that allows noninvasive in situ mapping of the microphytobenthos (MPB) biomass distribution with a high spatial (sub-millimeter) and temporal (minutes) resolution over areas of 1 x 1 m. The biomass is derived from a log-transformed and near-infrared corrected reflectance hyperspectral index, which exhibits a linear relationship (R-2 > 0.97) with the chlorophyll a (Ch1 a) concentration in the euphotic zone of the sediment and depends on the sediment grain size. Deployments of the system revealed that due to factors such as sediment topography, bioturbation, and grazing, the distribution of MPB in intertidal sediments is remarkably heterogeneous, with Ch1 a concentrations varying laterally by up to 400% of the average value over a distance of 1 cm. Furthermore, due to tidal cycling and diel light variability, MPB concentrations in the top 1 mm of sediments are very dynamic, changing by 40-80% over a few hours due to vertical migration. We argue that the high-resolution hyperspectral imaging method overcomes the inadequate resolution of traditional methods based on sedimentary Ch1 a extraction, and thus helps improve our understanding of the processes that control benthic primary production in coastal sediments

Intermittent bioirrigation and oxygen dynamics in permeable sediments: An experimental and modeling study of three tellinid bivalves

To explore the dynamic nature of geochemical conditions in bioirrigated marine permeable sediments, we studied the hydraulic activity of three tellinacean bivalve molluscs (the Pacific species Macoma nasuta and Macomona liliana, and the northern Atlantic and Pacific species Macoma balthica). We combined porewater pressure sensing, time-lapse photography and oxygen imaging to quantify the durations and frequencies of tellinid irrigation activity and the associated oxygen dynamics in the sediment. Porewater pressure records of all tellinids were dominated by intermittent porewater pressurization, induced by periodic water injection into the sediment through their excurrent siphons, which resulted in intermittent oxygen supply to subsurface sediments. The irrigation (two–12 minutes long) and intervals between subsequent irrigation bouts (1.5–13 minutes) varied among tellinid species and individual sizes. For large M. liliana and M. nasuta, the average intervals between irrigation bouts were sufficiently long (10 minutes and four minutes, respectively) to allow complete oxygen consumption in between irrigation bouts in all tested sediment types. Irrigation patterns of smaller conspecifics and the smaller species M. balthica were characterized by significantly shorter separation of irrigation bouts, which resulted in more continuous oxygenation of the sediment. Transport-reaction modeling confirmed these species- and size-specific geochemical signatures and indicated that the geochemical character of the sediment is largely conditioned by the interplay between temporal irrigation patterns and sedimentary oxygen consumption rates. For large tellinids, model simulations indicated that oscillatory rather than stationary geochemical conditions are prevalent in a wide range of sediment types, with oxic pockets collapsing completely between periods of active irrigation. Based on the model results we developed analytical approximations that allow estimation of spatio-temporal characteristics of sediment oxygenation for a wide range of sediment types and infaunal activity patterns. Our results emphasize the need to consider the intermittent nature of bioirrigation when studying the geochemical impact of infauna in permeable sediments

Global Carbon Cycling on a Heterogeneous Seafloor

Diverse biological communities mediate the transformation, transport, and storage of elements fundamental to life on Earth, including carbon, nitrogen, and oxygen. However, global biogeochemical model outcomes can vary by orders of magnitude, compromising capacity to project realistic ecosystem responses to planetary changes, including ocean productivity and climate. Here, we compare global carbon turnover rates estimated using models grounded in biological versus geochemical theory and argue that the turnover estimates based on each perspective yield divergent outcomes. Importantly, empirical studies that include sedimentary biological activity vary less than those that ignore it. Improving the relevance of model projections and reducing uncertainty associated with the anticipated consequences of global change requires reconciliation of these perspectives, enabling better societal decisions on mitigation and adaptation.Peer reviewe