On the contribution of the benthos to pelagic production

Annual production and consumption of oxygen were compared in large outdoor mesocosms differing only in the presence or absence of an intact benthic community and associated sediments. Both daily apparent production and nighttime respiration of oxygen were greater in tanks with a benthos. The fluxes of oxygen into, and dissolved inorganic nitrogen out of the bottom were also greater in tanks with an intact benthos. In tanks with a benthos, calculated gross system production increased 33% relative to tanks lacking a benthos. Depending on assumed O:N ratios only 45–60% of this increase was attributable to differences in the flux of inorganic nitrogen from the benthos to the water column. Nearly 40% was evidently fueled by higher rates of recycling in the water column. Between 3 and 17% of the difference in production could not be attributed to either source. The benthos apparently affects production in the water column not only by supplying nutrients directly, but also by enhancing rates of pelagic recycling

Application of filtration rate models to field populations of bivalves: an assessment using experimental mesocosms

Gross sedimentation of 14C labelled carbon was 58% greater in mesocosms (13 m3) containing the bivalve Mercenaria mercenaria (16 in m-2) relative to controls without this filter feeder. This difference was attributed to the activities of M. mercenaria and presumably due to filtration of particles from the water column. Of this increase, 32% and 47% were attributable to assimilation into clam tissue and respiration by the benthic community respectively. Permanent biodeposition by the clams contributed the least (21%). The ability of 8 filtration rate models to predict the increase in gross sedimentation was examined. Those models (4) which were based on data for bivalves filtering natural suspensions of particulate matter gave estimates which agreed well with observed differences. Those models (4) which yielded poor predictions used dues or algal monocultures to generate data and overestimated gross sedimentation due to bivalves by up to an order of magnitude. Such overestimation may exaggerate the role of bivalves in enhancing sedimentation and controlling phytoplankton biomass in shallow waters

Monitoring and modeling primary production in coastal waters: studies in Massachusetts Bay 1992-1994

During 1992-1994, we made shipboard incubations suitable for determining rates of primary production in water from Boston Harbor, Massachusetts Bay, and Cape Cod Bay (Massachusetts, USA). These measurements were part of an extensive baseline monitoring program to characterize water quality prior to diversion of effluent from Boston Harbor directly into Massachusetts Bay via a submarine outfall diffuser. Production (P) was measured using whole-water samples exposed to irradiance (I) levels from ~5 to 2000 µE m-2 s-1. P-I incubations were performed on 6 surveys a year, spaced to capture principal features of the annual production cycle. The number of stations and depths examined varied between years. There were 10 stations and 2 depths sampled in 1992-1993. In 1994, we performed in-depth studies at 2 stations (Boston Harbor\u27s edge and western Massachusetts Bay) by sampling 4 depths. Using depth-intensive 1994 data a simple empirical regression model, using information on chlorophyll biomass, incident daily light, and the depth of the photic zone, predicted integrated primary production rates derived from P-I incubations. The regression model was virtually the same as described for other coastal waters, giving confidence in general use of the model as an extrapolation tool. Using the 1994-based empirical model, we obtained favorable comparisons with production rates modeled from 1992-1993 P-I incubations. Combining the regression model with data on chlorophyll, light, and the photic zone collected on frequent hydrographic surveys (up to 16 yr-1), annual primary production was estimated for 1992-1994. Primary production in an intensively studied region of western Massachusetts Bay (21 hydrographic profile stations in an area ~100 km2) ranged from 386 to 468 g C m-2 yr-1. For a station at the edge of Boston Harbor near Deer Island extrapolations suggested production rates of 263 to 546 g C m-2 yr-1. Based on 2 stations in central Cape Cod Bay (1992-1993 only), model extrapolations suggested an annual production of 527 to 613 g C m-2 yr-1. Analyses using incubation and modeling results suggested that production variability was strongly related to fluctuations in incident irradiance, especially at daily to seasonal time scales. Chlorophyll variability secondarily influenced production, especially at seasonal to annual time scales. Finally, we provide a case where equivalent production was achieved in environments with contrasting water quality (nutrient and chlorophyll concentrations) because of variations in the depth of the photic zone (controlled by both chlorophyll and non-chlorophyll turbidity). Comparative analyses showed that our study estimates of primary production were consistent with the literature on nutrient-rich shelf environments. In conclusion, our study validated an empirical modeling approach to determining primary production in coastal marine waters

Noisy Wavefront Propagation in the Fisher‐Kolmogorov‐Petrovsky‐Piscounov Equation

We discuss some conjectures and open questions regarding the velocity of front propagation in the stochastic Fisher‐Kolmogorov‐Petrovsky‐Piscunov equation. © 2003 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87303/2/523_1.pd

The effects of the filter-feeding clam Mercenaria mercenaria on carbon cycling in experimental marine mesocosms

The metabolism and the fate of 14C labelled carbon was examined in 4 outdoor mesocosm (13 m3) tanks containing both benthic and pelagic compartments. Mesocosms with (16/m2) and without the clam, Mercenaria mercenaria were compared. System production, net and gross sedimentation of particulate carbon and benthic remineralization of dissolved inorganic nitrogen were all greater in mesocosms with clams. A filtration rate model, dependent on clam size and temperature, explained between 74–114% of the increased gross sedimentation in clam tanks relative to controls.The higher production in the clam tanks was at least in part due to a greater flux of dissolved inorganic nitrogen from the benthos. Despite this greater production in the clam tanks, water column biomass remained similar to controls. Calculations based on the filtration rate model indicated that clams could have consumed between 30% and 46% of the excess biomass produced during the day. Loss of particles due to processes in the water column appeared to consume most of this excess biomass. Although clams enhanced production and sedimentation, they did not limit phytoplankton biomass in the water column through filtration

Relative mobility of radioactive trace elements across the sediment-water interface in the MERL model ecosystems of Narragansett Bay

The mobilities of radioactive trace elements across the water sediment boundary of a coastal marine ecosystem were investigated. The studies carried out included chemical speciation experiments ofthe solution and solid phases, as well as verification experiments in controlled model ecosystems ( MERL tanks). The latter included backdiffusion experiments under oxic and anoxic conditions and experiments with artificially increased sediment resuspension rates. These studies have produced seven general conclusions: (1) The backdiffusion of Cs, Mn, Co, and Zn radiotracers across the sediment-water interface into oxic waters and of Mn and Co radiotracers into anoxic waters was predicted from laboratory experiments. (2) The removal from the water and the partial immobilization in the sediments of Cs, Zn and Cd tracers, during anoxic conditions, agreed with results from selective leaching experiments of surface sediments with dithionite-citrate solution, a mildly reducing agent which can reprecipitate liberated metals as sulfides. While most nuclides were leached by this solution to the same extent as by hydroxylamine, another reducing agent, Zn, Cd and Cs tracers were not, possibly due to the formation of sulfidic and other phases by the former solution. (3) Radioisotopes of particle-reactive elements (Sn, Fe, Hg and Cr) were shown by sequential extraction and ultrafiltration experiments to be involved in the dynamic cycle of colloid formation and aggregation in the water column and sediments. (4) In order to extend the information on nuclide behavior gained from the radiotracer methodology to stable trace elements, (which are often introduced into coastal water in ionic form) stable metals were added to one tank. Radiotracer behavior in the water column (removal rates and extent of uptake by suspended particles) was quite similar to that of their stable metal counterparts at ambient concentrations (Mn, Cr, Fe, Cd and Zn), added simultaneously to one tank, and to the metal behavior in other tanks operating under similar conditions. (5) The experiments with increased resuspension rates without concomitant increased bioturbation rates had, as expected, only small effects on removal rates of the radiotracers. (6) Sediment profiles of the tracers revealed both seasonal and element-specific differences in mobility near the sediment interface. Tracer profiles allowed the calculation of bioturbation (tracer microspheres) and pore water diffusion (22Na) rates, as well as an investigation of the spacial and temporal dynamics of trace element cycling near the sediment-water interface. (7) Se and Cr nuclides which were added in different oxidation states to different tanks, showed that the higher oxidation state forms (Se-VI, Cr-VI) are removed more slowly from the water column than the lower oxidation state forms (Se-IV, Cr-III). Furthermore, speciation experiments have shown that the increase in the colloidal fraction of Se may be used to calculate the characteristic times of Se-reduction to elemental or organically-bound forms

Environmental heterogeneity affects input, storage, and transformation of coarse particulate organic matter in a floodplain mosaic

Quantifying spatial and temporal dynamics of organic matter (OM) is critical both for understanding ecosystem functioning and for predicting impacts of landscape change. To determine the influence of different habitats and coarse particulate OM (CPOM) types upon floodplain OM dynamics, we quantified aerial input, lateral surface transfer, and surface storage of CPOM over an annual cycle on the near-natural floodplain of the River Tagliamento in NE-Italy. Using these data, we modelled floodplain leaf dynamics, taking account of the spatial distribution and hydrologic connectivity of habitats, and using leaf storage as a response variable. Mean aerial CPOM input to the floodplain was similar from riparian forest and islands, but surface transfer was greater from islands, supporting the suggestion that these habitats act as "islands of fertility” along braided rivers. Leaves were the lateral conveyor of energy to more open parts of the floodplain, whereas CPOM was mainly stored as small wood in vegetated islands and riparian forest. Simulating the loss of habitat diversity (islands, ponds) decreased leaf storage on the whole floodplain, on exposed gravel and in large wood accumulations. In contrast, damming (loss of islands, ponds and floods plus floodplain overgrowth) greatly increased storage on exposed gravel. A random shuffle of habitats led to a storage increase on exposed gravel, while that in large wood accumulations and ponds declined. These results disentangle some of the complexities of CPOM dynamics in floodplain ecosystems, illustrate the value of models in understanding ecosystem functioning at a landscape level, and directly inform river management practic

Implementation of the S100 Calcium-Binding Protein B Biomarker in a Clinical Setting:A Retrospective Study of Benefits, Safety, and Effectiveness

Recent years have seen the emergence of the S100 calcium-binding protein B (S100B) biomarker used in the initial management of minor traumatic brain injury (TBI) patients. S100B has been found to reduce cerebral computed tomography (CT-C) scans and was recently implemented in the Scandinavian Neurotrauma Committee (SNC) guidelines. In a clinical setup, we retrospectively investigated the use of the S100B biomarker in relation to the SNC guidelines in the respective year before and after implementation. Accordingly, minor TBI patients with the International Classification of Diseases, Tenth Revision diagnostic code of S06.0 commotio cerebri were included in 2018 (n = 786) and 2019 (n = 709) for comparison of emergency department time (EDT) and CT-Cs. In 2019, we included all patients with an S100B sample (n = 547; 348/199 male:female; median age, 52 years). We found an S100B sensitivity of 92% and negative predictive value (NPV) of 99% (cutoff, 0.10 μg/L) regardless of SNC guideline compliance. With strict SNC guideline management, sensitivity and NPV increased to 100%, even at a 0.20-μg/L cutoff that increased the specificity from 49% to 76%. After S100B implementation, we found the median EDT to significantly increase from 196 min (interquartile range [IQR] = 127–289) in 2018 to 216 min (IQR = 134.0–309.5) in 2019 (p = 0.0148), which may have resulted from poor guideline compliance (53.9%). Contrarily, the proportion of CT-C scanned patients decreased from 70% to 56.3% equal to a relative 27.5% decrease of scanned patients (p < 0.0001). Conclusively, our study supported the safe and efficient clinical use of the S100B biomarker, albeit with a minor EDT increase. S100B combination with the SNC guidelines improved clinical potential

Chemical Blocking of Zinc Ions in CNS Increases Neuronal Damage Following Traumatic Brain Injury (TBI) in Mice

Traumatic brain injury (TBI) is one of the leading causes of disability and death among young people. Although much is already known about secondary brain damage the full range of brain tissue responses to TBI remains to be elucidated. A population of neurons located in cerebral areas associated with higher cognitive functions harbours a vesicular zinc pool co-localized with glutamate. This zinc enriched pool of synaptic vesicles has been hypothesized to take part in the injurious signalling cascade that follows pathological conditions such as seizures, ischemia and traumatic brain injury. Pathological release of excess zinc ions from pre-synaptic vesicles has been suggested to mediate cell damage/death to postsynaptic neurons.In order to substantiate the influence of vesicular zinc ions on TBI, we designed a study in which damage and zinc movements were analysed in several different ways. Twenty-four hours after TBI ZnT3-KO mice (mice without vesicular zinc) were compared to littermate Wild Type (WT) mice (mice with vesicular zinc) with regard to histopathology. Furthermore, in order to evaluate a possible neuro-protective dimension of chemical blocking of vesicular zinc, we treated lesioned mice with either DEDTC or selenite. Our study revealed that chemical blocking of vesicular zinc ions, either by chelation with DEDTC or accumulation in zinc-selenium nanocrystals, worsened the effects on the aftermath of TBI in the WT mice by increasing the number of necrotic and apoptotic cells within the first 24 hours after TBI, when compared to those of chemically untreated WT mice.ZnT3-KO mice revealed more damage after TBI compared to WT controls. Following treatment with DEDTC or selenium an increase in the number of both dead and apoptotic cells were seen in the controls within the first 24 hours after TBI while the degree of damage in the ZnT3-KO mice remained largely unchanged. Further analyses revealed that the damage development in the two mouse strains was almost identical after either zinc chelation or zinc complexion therapy

Kupffer cells are central in the removal of nanoparticles from the organism

<p>Abstract</p> <p>Background</p> <p>The study aims at revealing the fate of nanoparticles administered intravenously and intraperitoneally to adult female mice, some of which were pregnant. Gold nanoparticles were chosen as a model because these particles have been found to be chemically inert and at the same time are easily traced by autometallography (AMG) at both ultrastructural and light microscopic levels.</p> <p>Results</p> <p>Gold nanoparticles were injected intravenously (IV) or intraperitoneally (IP) and traced after 1, 4 or 24 hours. For IV injections 2 and 40 nm particles were used; for IP injections 40 nm particles only. The injected nanoparticles were found in macrophages only, and at moderate exposure primarily in the Kupffer cells in the liver. IV injections resulted in a rapid accumulation/clustering of nanoparticles in these liver macrophages, while the uptake in spleen macrophages was moderate. IP injections were followed by a delayed uptake in the liver and included a moderate uptake in macrophages located in mesenteric lymph nodes, spleen and small intestine. Ultrastructurally, the AMG silver enhanced nanocrystals were found in lysosome-like organelles of the Kupffer cells and other macrophages wherever located.</p> <p>Accumulations of gold nanoparticles were not found in any other organs analysed, i.e. kidneys, brain, lungs, adrenals, ovaries, placenta, and fetal liver, and the control animals were all void of AMG staining.</p> <p>Conclusion</p> <p>Our results suggest that: (1) inert gold nanoparticles do not penetrate cell membranes by non-endocytotic mechanisms, but are rather taken up by endocytosis; (2) gold nanoparticles, independent of size, are taken up primarily by Kupffer cells in the liver and secondarily by macrophages in other places; (3) gold nanoparticles do not seem to penetrate the placenta barrier; (4) the blood-brain barrier seems to protect the central nervous system from gold nanoparticles; (5) 2 nanometer gold particles seem to be removed not only by endocytosis by macrophages, and we hypothesize that part of these tiny nanoparticles are released into the urine as a result of simple filtration in the renal glomeruli.</p