Effects of polychaetes on silicate dynamics and fluxes in sediments: Importance of species, animal activity and polychaete effects on benthic diatoms

Laboratory experiments tested the effects of two polychaetes, a surface deposit feeder Eupolymnia heterobranchia, and a head-down deposit feeder Abarenicola pacifica, on silicate dynamics in sediment porewaters and overlying waters. Experimental chambers of sediment containing an individual deposit feeder, and controls with no macrofauna, were studied over a one month period during the summers of 1989 and 1990. Measurements included temporal changes in vertical depth profiles of pore water silicate concentrations, concurrent determinations of silicate accumulation in the water column, and the activities of experimental. organisms. A diffusion-nonlocal exchange-reaction model was devised to determine, from the pore water profiles, both the magnitude of, and variability associated with, organism effects on pore water silicate. Model results within chambers containing worms indicate that the changes in silicate concentrations due to worm activity varied by as much as an order of magnitude at a given point in the sediment column, over time periods of several days. Biologically-driven fluxes calculated from the sediment model indicate that fluxes attributable to macrofauna were positively correlated with the frequency of new burrow or tube construction, and were strongly related to the activity of the organism. Variability in the rate of silicate transport due to worms likely was related to the mechanism of habitat construction, as well as the relative distances involved in tube/burrow relocation. Silicate fluxes calculated from the model were compared with direct measures of silicate flux via the accumulation of silicate in the water column. These comparisons show that benthic diatoms at times exerted a significant effect on silicate removal from sediments and the water column. The relative importance of this effect was dictated by differences in the activity of diatoms and surrounding macrofauna between experiments, and the type of macrofaunal organisms involved. Strong interactions between the surface deposit feeder and benthic diatoms significantly affected the magnitude and direction of silicate flux across the sediment-water interface. Such interactions were lacking in experiments with the head-down deposit feeder. In combination, the sediment model and water column measurements showed that net silicate fluxes to the water column may be masked by diatom activity, even when bioirrigation serves to actively transport silicate directly from depth across the sediment-water interface

A modelling study of discontinuous biological irrigation

Irrigation of infaunal dwellings can lead to significant alteration of solute distributions in sediments. As a result, sediment-seawater fluxes of nutrients and dissolved carbon are greatly enhanced, and the biology of benthic communities is affected. The most realistic mathematical representation of irrigation and its effect on sediment geochemistry is Aller\u27s (1980) cylinder model. One critical assumption of this model is that burrows are irrigated continually, and that burrow water solute concentrations are identical to overlying water concentrations at all times. However, the vast majority of infaunal tube- and burrow-dwelling organisms irrigate periodically, i.e. in an on/off cycle. During periodic irrigation, the solute concentration at the tube wall may vary between the limits imposed by the flux from the porewater and the concentration in the overlying water. We introduce modifications to the cylinder model which allow for periodic irrigation. We assess how periodic irrigation affects solute profiles and fluxes of two chemical constituents, silica and ammonium, for different population densities (distance between burrows) and organism sizes (burrow radii). Silica and ammonium follow first and zeroth order reaction kinetics, respectively, and illustrate the behavior of two general reaction classes. Model results show that the effects of periodic irrigation vary with the class of reaction considered. For silica, radially-averaged profiles during discontinuous irrigation varied less than 15% from those with continuous irrigation for nearly all burrow sizes, burrow distances and reaction rate constants considered. However, we observed large temporal changes (as much as a factor of 6) in the areally-averaged silica flux over the irrigation cycle. Despite this time-dependence, the time-averaged silica flux was similar to that calculated for the continuous case. For ammonia, radially-averaged solute profiles were extremely sensitive to the duration of irrigation. In this case, the differences between discontinuous and continuous irrigation were greatest when the duration of irrigation was short (e.g. 5 min), and when the inter-burrow distance was small. As with silica, there was a strong time-dependence in areally-averaged ammonia flux when irrigation was periodic. However, the time-averaged ammonia flux is identical to the flux calculated for continuous irrigation. Our results suggest that irrigation behavior can affect the local burrow environment and this imposes a time dependence on solute fluxes

Evidence of infaunal effects on porewater advection and biogeochemistry in permeable sediments: A proposed infaunal functional group framework

Bioturbating infauna significantly modify reaction and transport processes in permeable sediments, though most studies to date are limited in the scope of species examined. We conducted a comparative field study measuring density-dependent effects of six common bioturbating species on porewater advection and biogeochemistry, across three intertidal permeable sediment habitats. The species in this study are; head-down like deposit feeders (Abarenicola pacifica and Balanoglossus aurantiacus), surface deposit feeders (Diopatra cuprea and Onuphis jenneri) and gallery diffusers (Upogebia pugettensis and Neotrypaea californiensis). Tracer loss from gel diffusers was used to assess relative differences in porewater advection among sites, and porewater peepers were used to measure solute concentrations of carbon, nitrogen, phosphate, and silicate in experimental plots. Characteristic surface features of different infauna were counted and used as a proxy for infaunal density. Density of surface features was then used in regression analyses as an explanatory variable affecting porewater transport and chemistry. Significant infaunal density effects on porewater transport or biogeochemistry were found in all but one species, D. cuprea. The species-specific attributes and mechanisms by which these infauna affect permeable sediment processes are explored. A process based functional group framework is presented for permeable sediments. Bulk granulometric properties also were assessed. There were little to no within-site effects of porosity, hydraulic conductivity, or organic matter on porewater transport and biogeochemistry. However, significant across-site differences in granulometry and site properties were found and these are addressed in relation to infaunal effects on porewater transport and chemistry

Recruitment responses of benthic infauna to manipulated sediment geochemical properties in natural flows

Recent studies have shown that local variation in surface sediment geochemistry can have significant effects on recruitment rates of benthic invertebrates. Experiments presented here tested (1) the utility of manipulating surface porewater concentrations using spiked polyacrylamide gels and (2) the recruitment responses of the polychaete Arenicola cristata and the bivalve Mercenaria mercenaria to manipulated ammonium concentrations in realistic flows provided by a straight flume and an annular flume. Data show that successful manipulation of sediment porewater ammonium concentration is feasible in flowing waters, i.e., overlying waters remained relatively free of ammonium while manipulated concentration levels were maintained within the upper sediment layers where new recruits explore. Thus, over short experimental periods, ammonium signals can be independently modified while variables such as grain size, organic content and flow are held constant. Responses of new recruits varied as a function of experimental condition. In straight flume trials, the manipulation of ammonium concentration was successful, and within the range of concentrations tested, retention of Mercenaria was significantly reduced at the highest ammonium level. However, retention of Arenicola was uniformly low among all treatments and no significant ammonium response was detected. In annular flume runs, overall ammonium concentrations were higher than in straight flume runs, but were consistent with the intended manipulation. Mercenaria retention was uniformly low, and no differences in retention, as a function of ammonium concentration, were found. However, for Arenicola, significant differences were observed, with highest retention in lower ammonium environments. These results suggest that ammonium, isolated from other cues, plays a significant role in determining recruitment patterns, with variation in recruit responses related to signal strength

An experimental and modeling study of pH and related solutes in an irrigated anoxic coastal sediment

Macrofaunal irrigation is an important process in nearshore sediments, facilitating greater exchange between sediments and seawater and imparting significant lateral heterogeneity to the porewater profiles of many constituents. Like many macrofaunal activities, irrigation is a transient behavior, i.e. tubes and burrows are flushed periodically, at frequencies that generally are species-specific. As a result, transient concentrations within the dwelling arise, potentially impacting gradients, fluxes and reaction rates in the vicinity of the dwelling. We investigated the impact of periodic burrow irrigation on the distribution of several diagenetically important porewater constituents. Laboratory experiments evaluated irrigation periodicity using artificially irrigated tubes embedded in nearshore organic-rich sediments, and microdistributions of oxygen and pH in laboratory experiments were measured with microelectrodes. To help interpret our results, we also constructed a simplified time and space-dependent transport-reaction model for oxygen, pH and sulfide in irrigated sediments. Laboratory results show substantial differences in the pH field of sediments surrounding an irrigated tube as a function of irrigation frequency. Higher pH values, indicative of an overlying water signature, were observed in the vicinity of the tube wall with increasing duration of irrigation. Conversely, oxygen concentrations did not vary significantly with the amount of irrigation, most likely a result of extremely high sediment oxygen demand. Model results are consistent with laboratory findings in predicting differences in the measured variables as a function of irrigation frequency. However, the nature and extent of the model-predicted differences are often at variance with the experimental data. Overall, experimental and modeling results both suggest irrigation periodicity can substantially influence porewater distributions and diagenetic processes in sediments. Future studies should examine the influence of irrigation periodicity on the types and rates of reactions, and the attendant biological features, in the environment encompassing the tube or burrow wall

Process-specific cues for recruitment in sedimentary environments: Geochemical signals?

The most biologically and geochemically active marine sediments are characterized by steep chemical gradients within the top centimeters of sediment (Berner, 1980). A common feature of these environments is disruptions of surface sediments by both physical and biotic forces. Growth and mortality rates for new recruits are affected by many of these surface perturbations. At the same time, these disturbances also impose a discontinuity in concentration across the sediment-water interface, and accordingly, a change in surface chemistry. In this paper we present evidence that the cue used by juveniles to distinguish between recently disturbed and undisturbed surfaces may be disruption of geochemical gradients that are typical of nearshore benthic systems. New juveniles exposed to ammonium concentrations typical of disturbed surface sediments exhibit behaviors consistent with rejection of the habitat. Conversely, new juveniles placed onto sediments containing ammonium levels typical of undisturbed surficial sediments rapidly initiate burrowing activity, a sign of acceptability. We also present a numerical model, which assesses the dynamics of small-scale chemical shifts that accompany sediment disruption, to determine (a) what is the magnitude of surface chemistry changes associated with disturbance (i.e. what is the signal strength)? and (b) what are the spatial and temporal scales associated with the return to the undisturbed condition ( recovery )? Model results show that the signal strength, and the return to acceptable conditions, are strongly influenced by the initial gradient. Model predictions of the time required to recover indicate that times to recovery are longer than the interval between disturbance events, but are of the same temporal scale (minutes to hours). Thus, our results suggest that the dynamics of surficial gradients provide a strong signal over appropriate time scales that may reveal the intensity of disturbance and the likelihood of mortality for juveniles. As such, transport-reaction processes which govern porewater concentrations in surficial sediments may also play a role in recruitment processes

Evidence of infaunal effects on porewater advection and biogeochemistry in permeable sediments: A proposed infaunal functional group framework

Bioturbating infauna significantly modify reaction and transport processes in permeable sediments, though most studies to date are limited in the scope of species examined. We conducted a comparative field study measuring density-dependent effects of six common bioturbating species on porewater advection and biogeochemistry, across three intertidal permeable sediment habitats. The species in this study are; head-down like deposit feeders (Abarenicola pacifica and Balanoglossus aurantiacus), surface deposit feeders (Diopatra cuprea and Onuphis jenneri) and gallery diffusers (Upogebia pugettensis and Neotrypaea californiensis). Tracer loss from gel diffusers was used to assess relative differences in porewater advection among sites, and porewater peepers were used to measure solute concentrations of carbon, nitrogen, phosphate, and silicate in experimental plots. Characteristic surface features of different infauna were counted and used as a proxy for infaunal density. Density of surface features was then used in regression analyses as an explanatory variable affecting porewater transport and chemistry. Significant infaunal density effects on porewater transport or biogeochemistry were found in all but one species, D. cuprea. The species-specific attributes and mechanisms by which these infauna affect permeable sediment processes are explored. A process based functional group framework is presented for permeable sediments. Bulk granulometric properties also were assessed. There were little to no within-site effects of porosity, hydraulic conductivity, or organic matter on porewater transport and biogeochemistry. However, significant across-site differences in granulometry and site properties were found and these are addressed in relation to infaunal effects on porewater transport and chemistry

The effects of infaunal biodiversity on biogeochemistry of coastal marine sediments

We tested the role of benthic infaunal functional diversity in regulating the biogeochemistry of nearshore sediments using laboratory microcosms. Single and multispecies assemblages of deposit-feeding polychaetes (Clymenella torquata, Spio setosa, and Leitoscoloplos fragilis) were used, and fluxes of oxygen and phosphate, as well as profiles of oxygen and pH in the sediment pore water, were measured. Significant differences in flux rates were found among treatments that were unrelated to polychaete abundance or biomass alone. Multispecies assemblages had lower flux rates of both oxygen and phosphate than rates calculated from the single-species treatments. Depthintegrated oxygen and pH profiles also showed significant differences between multispecies assemblages and selected single-species treatments. These differences were most likely from species-specific feeding and burrowing behavior and species-related interactions. Coefficients of variance for both oxygen and pH were highest for microcosms with no polychaetes and lowest for the assemblages, indicating a dampening effect of multispecies assemblages on porewater heterogeneity. When oxygen flux data was incorporated into a model of oxygen dynamics in Long Island Sound, results indicated that shifts in the benthic community composition could change sediment oxygen consumption rates sufficiently to disrupt the balance between the physical supply of oxygenated water and biological oxygen demand. The results of this study confirm the importance of benthic functional biodiversity to nearshore sedimentary processes and suggest that losses of functional diversity can have significant effects on ecosystem function

EFAS/EAN survey on the influence of the COVID-19 pandemic on European clinical autonomic education and research

© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.Purpose: To understand the influence of the coronavirus disease 2019 (COVID-19) pandemic on clinical autonomic education and research in Europe. Methods: We invited 84 European autonomic centers to complete an online survey, recorded the pre-pandemic-to-pandemic percentage of junior participants in the annual congresses of the European Federation of Autonomic Societies (EFAS) and European Academy of Neurology (EAN) and the pre-pandemic-to-pandemic number of PubMed publications on neurological disorders. Results: Forty-six centers answered the survey (55%). Twenty-nine centers were involved in clinical autonomic education and experienced pandemic-related didactic interruptions for 9 (5; 9) months. Ninety percent (n = 26/29) of autonomic educational centers reported a negative impact of the COVID-19 pandemic on education quality, and 93% (n = 27/29) established e-learning models. Both the 2020 joint EAN-EFAS virtual congress and the 2021 (virtual) and 2022 (hybrid) EFAS and EAN congresses marked higher percentages of junior participants than in 2019. Forty-one respondents (89%) were autonomic researchers, and 29 of them reported pandemic-related trial interruptions for 5 (2; 9) months. Since the pandemic begin, almost half of the respondents had less time for scientific writing. Likewise, the number of PubMed publications on autonomic topics showed the smallest increase compared with other neurological fields in 2020-2021 and the highest drop in 2022. Autonomic research centers that amended their trial protocols for telemedicine (38%, n = 16/41) maintained higher clinical caseloads during the first pandemic year. Conclusions: The COVID-19 pandemic had a substantial negative impact on European clinical autonomic education and research. At the same time, it promoted digitalization, favoring more equitable access to autonomic education and improved trial design.info:eu-repo/semantics/publishedVersio

Search for New Physics in the Multijet and Missing Transverse Momentum Final State in Proton-Proton Collisions at √s=7 TeV

A search for physics beyond the standard model is performed in events with at least three jets and large missing transverse momentum produced in proton-proton collisions at sqrt(s) = 7 TeV. No significant excess of events above the expected backgrounds is observed in 4.98 inverse femtobarns of data collected with the CMS detector at the Large Hadron Collider. The results are presented in the context of the constrained minimal supersymmetric extension of the standard model and more generically for simplified models. For the simplified models of gluino-gluino and squark-squark production, gluino masses below 1.0 TeV and squark masses below 0.76 TeV are excluded in case the lightest supersymmetric particle mass is below 200 GeV. These results significantly extend previous searches