Variable sediment oxygen uptake in response to dynamic forcing

Seiche-induced turbulence and the vertical distribution of dissolved oxygen above and within the sediment were analyzed to evaluate the sediment oxygen uptake rate (JO2), diffusive boundary layer thickness (δDBL), and sediment oxic zone depth (zmax) in situ. High temporal-resolution microprofiles across the sediment-water interface and current velocity data within the bottom boundary layer in a medium-sized mesotrophic lake were obtained during a 12-h field study. We resolved the dynamic forcing of a full 8-h seiche cycle and evaluated JO2 from both sides of the sediment-water interface. Turbulence (characterized by the energy dissipation rate, ε), the vertical distribution of dissolved oxygen across the sediment-water interface (characterized by δDBL and zmax), JO2, and the sediment oxygen consumption rate (RO2) are all strongly correlated in our freshwater system. Seiche-induced turbulence shifted from relatively active (ε = 1.2 × 10-8 W kg-1) to inactive (ε = 7.8 × 10-12 W kg-1). In response to this dynamic forcing, δDBL increased from 1.0 mm to the point of becoming undefined, zmax decreased from 2.2 to 0.3 mm as oxygen was depleted from the sediment, and JO2 decreased from 7.0 to 1.1 mmol m-2 d-1 over a time span of hours. JO2 and oxygen consumption were found to be almost equivalent (within ~ 5% and thus close to steady state), with RO2 adjusting rapidly to changes in JO2. Our results reveal the transient nature of sediment oxygen uptake and the importance of accurately characterizing turbulence when estimating JO2

Application of Oxygen Eddy Correlation in Aquatic Systems

The eddy correlation technique is rapidly becoming an established method for resolving dissolved oxygen fluxes in natural aquatic systems. This direct and noninvasive determination of oxygen fluxes close to the sediment by simultaneously measuring the velocity and the dissolved oxygen fluctuations has considerable advantages compared to traditional methods. This paper describes the measurement principle and analyzes the spatial and temporal scales of those fluctuations as a function of turbulence levels. The magnitudes and spectral structure of the expected fluctuations provide the required sensor specifications and define practical boundary conditions for the eddy correlation instrumentation and its deployment. In addition, data analysis and spectral corrections are proposed for the usual nonideal conditions, such as the time shift between the sensor pair and the limited frequency response of the oxygen sensor. The consistency of the eddy correlation measurements in a riverine reservoir has been confirmed—observing a night–day transition from oxygen respiration to net oxygen production, ranging from −20 to +5 mmol m−2 day−1—by comparing two physically independent, eddy correlation instruments deployed side by side. The natural variability of the fluctuations calls for at least ∼1 h of flux data record to achieve a relative accuracy of better than ∼20%. Although various aspects still need improvement, eddy correlation is seen as a promising and soon-to-be widely applied method in natural waters

Active elderly and health-can moderate exercise improve health and wellbeing in older adults? Protocol for a randomized controlled trial

Abstract Background: Aging is marked by a progressive rise in chronic diseases with an impact on social and healthcare costs. Physical activity (PA) may soothe the inconveniences related to chronic diseases, has positive effects on the quality of life and biological rhythms, and can prevent the decline in motor functions and the consequent falls, which are associated with early death and disability in older adults. Methods: We randomized 120 over-65 males and females into groups of similar size and timing and will give each either moderate physical activity or cultural and recreational activities. Being younger than 65 years, inability to participate in physical activity for any medical reason, and involvement in a massive program of physical exercise are the exclusion criteria. The primary outcome measures are quality of life, walking speed, and postural sway. Participants are tested at baseline, post-treatment, and 6-month (24 weeks) and 12-month (48 weeks) follow-ups. Discussion: This study aims at improving the quality of life, wellness, and cognitive functioning in the elderly through a low-cost affordable program of moderate physical activity. Given the growing aging of the world population and the social and economic burden of disability in the elderly, our results might have a major impact on future practices

Boundary mixing in lakes: 2. Combined effects of shear- and convectively induced turbulence on basin-scale mixing

A detailed comparison of results from a numerical three-dimensional hydrostatic lake model with high-resolution observations of the vertical structure of the turbulent bottom boundary layer (BBL) in a medium-size lake (Lake Alpnach, Switzerland) is provided. The focus of this study is on the shear-induced generation and destruction of stratification in the BBL that may ultimately lead to unstable layers (convection). The model was shown to provide a reliable description of the internal seiching dynamics, as well as the local BBL properties, including the generation of shear-induced convection in two data sets from 2003 and 2007. Basin-scale mixing parameters, inferred from the simulations, are closely connected to the seiching motions, with the hypolimnetic mixing reacting almost immediately to the variable wind-forcing and seiching activity. During upslope flow, the BBL becomes convectively turbulent, causing low mixing efficiency on a basin-scale, whereas during downslope flow, the BBL is restratifying and shear-induced turbulence is weak but leads to a higher mixing efficiency. The overall deep-water mixing efficiency varied in the range of 5 to 10% in this system dominated by turbulent boundary processes

Measurements of eddy correlation oxygen fluxes in shallow freshwaters: Towards routine applications and analysis

Benthic fluxes of dissolved oxygen are measured in a shallow reservoir using the eddy correlation technique. Flux variations depict the diurnal production-consumption cycle, with daytime oxygen release following the solar radiation trend. The average nighttime uptake of -40 +/- 11 mmol m-2 d-1 is in excellent agreement with the rate of -35 +/- 3 mmol m-2 d-1 derived from sediment oxygen microprofiles. Separating large-scale advective and turbulent fluctuations is a crucial and uncertain component of the flux computation and the largest source of error. To compensate for the 2.25 s oxygen sensor response time, the oxygen flux calculations are corrected by only ~5% using a first-order spectral enhancement. This work demonstrates that only a slightly faster oxygen sensor would be needed to resolve the entire flux spectrum. The 18 hours of data are the first measurements obtained in a freshwater reservoir that capture the diurnal oxygen production-consumption cycle

Evaluating oxygen fluxes using microprofiles from both sides of the sediment-water interface

Sediment-water fluxes are influenced by both hydrodynamics and sediment biogeochemical processes. However, fluxes at the sediment-water interface (SWI) are almost always analyzed from either a water-or sediment-side perspective. This study expands on previous work by comparing water-side (hydrodynamics and resulting diffusive boundary layer thickness, delta(DBL)) and sediment-side (oxygen consumption and resulting sediment oxic zone) approaches for evaluating diffusive sediment oxygen uptake rate (J(O2)) and delta DBL from microprofiles. Dissolved oxygen microprofile and current velocity data were analyzed using five common methods to estimate J(O2) and delta(DBL) and to assess the robustness of the approaches. Comparable values for J(O2) and delta(DBL) were obtained (agreement within 20%), and turbulence-induced variations in these parameters were uniformly characterized with the five methods. J(O2) estimates based on water-side data were consistently higher (+1.8 mmol m(-2) d(-1) or 25% on average) and delta(DBL) estimates correspondingly lower (-0.4 mm or 35% on average) than those obtained using sediment-side data. This deviation may be attributed to definition of the sediment-water interface location, artifacts of the methods themselves, assumptions made on sediment properties, and/or variability in sediment oxygen-uptake processes. Our work emphasizes that sediment-side microprofile data may more accurately describe oxygen uptake at a particular location, whereas water-side data are representative of oxygen uptake over a broader sediment area. Regardless, our overall results show clearly that estimates of J(O2) and delta(DBL) are not strongly dependent on the method chosen for analysis

Suppressing effect of CMPPE, a new positive allosteric modulator of the GABAB receptor, on alcohol self-administration and reinstatement of alcohol seeking in rats

Positive allosteric modulators (PAMs) of the GABAB receptor constitute a class of pharmacological agents gaining increasing attention in the alcohol research field because of their ability to suppress several alcohol-related behaviors in rodents. CMPPE is a novel GABAB PAM, still limitedly characterized in vivo. It was therefore of interest to test its ability to affect operant, oral self-administration of alcohol and cueinduced reinstatement of alcohol seeking in alcohol-preferring rats. To this end, female Sardinian alcohol-preferring (sP) rats were trained to lever-respond for alcohol (15% v/v) under the fixed ratio (FR) 5 (FR5) schedule of reinforcement. Once lever-responding had stabilized, rats were exposed to test sessions (under the FR5 [Experiment 1] and progressive ratio [PR; Experiment 2] schedules of reinforcement) preceded by treatment with CMPPE (0, 2.5, 5, and 10 mg/kg; intraperitoneally [i.p.]). In Experiment 3, once lever-responding had stabilized, rats underwent an extinction responding phase and then a single reinstatement session during which lever-responding was resumed by the non-contingent presentation of a complex of alcohol-associated cues; CMPPE (0, 2.5, 5, and 10 mg/kg; i.p.) was administered before the reinstatement session. Selectivity of CMPPE actionwas assessed by evaluating the effect of CMPPE (0, 2.5, 5, and 10 mg/kg; i.p.) on self-administration of a chocolate solution in male Wistar rats (Experiment 4). In Experiments 1 and 2, treatment with 5 and 10 mg/kg CMPPE reduced lever-responding and breakpoint for alcohol. In Experiment 3, treatment with 5 and 10 mg/kg CMPPE suppressed reinstatement of alcohol seeking. In Experiment 4, no dose of CMPPE affected lever-responding for the chocolate solution. These results extend to CMPPE the ability of all previously tested GABAB PAMs to affect alcohol-motivated behaviors in rodents and confirm that these effects are a shared feature of the entire class of GABAB PAMs. This conclusion is of relevance in view of the forthcoming transition of GABAB PAMs to clinical testing

Operant, oral alcohol self-administration: Sex differences in Sardinian alcohol-preferring rats

Sardinian alcohol-preferring (sP) rats have been selectively bred, over almost forty years and for more than 100 generations, for high alcohol preference and consumption. Rats of the sP line have served as animal model of excessive alcohol consumption for more than 120 published studies. With very few exceptions however, these studies have always employed male sP rats, and little is known on alcohol-related behaviors in female sP rats. The present study was designed to fill, at least in part, this gap. To this end, operant self-administration of alcohol under the fixed ratio 4 schedule of reinforcement was compared between male, intact female, and ovariectomized female sP rats. Additional aims were (i) investigation of whether, and to which extent, estrous cycle influenced alcohol self-administration in sP rats and (ii) investigation of whether alcohol selfadministration in male, intact female, and ovariectomized female sP rats differed in sensitivity to pharmacological manipulation. Lever-responding for alcohol resulted to be steadily higher in male than intact and ovariectomized female sP rats; conversely, because of large sex differences in rat body weight, estimated amount of self-administered alcohol (expressed in g/kg) did not differ among the 3 sP rat groups or occasionally resulted to be higher in intact female than male and ovariectomized female sP rats. Blood alcohol levels deriving from self-administered alcohol (i) did not differ among the 3 sP rat groups, (ii) achieved values known to result in measurable psychopharmacological effects, and (iii) positively correlated with both number of lever-responses for alcohol and estimated amount of self-administered alcohol. Treatment with both the opioid receptor antagonist, naloxone (0, 0.3, 1, and 3 mg/kg, i.p.), and the positive allosteric modulator of the GABAB receptor, GS39783 (0, 25, 50, and 100 mg/kg, i.g.), reduced alcohol self-administration with comparable potency and efficacy in the 3 sP rat groups. Impact of estrous cycle on alcohol self-administration was relatively modest, limited to a tendency toward a reduction in number of lever-responses for alcohol and estimated amount of self-administered alcohol in estrus and metestrus. Together, the results of the present study provide the first characterization of alcoholseeking and -taking behavior in female sP rats

Measurements of eddy correlation oxygen fluxes in shallow freshwaters: Towards routine applications and analysis

Benthic fluxes of dissolved oxygen are measured in a shallow reservoir using the eddy correlation technique. Flux variations depict the diurnal production-consumption cycle, with daytime oxygen release following the solar radiation trend. The average nighttime uptake of -40 +/- 11 mmol m(-2) d(-1) is in excellent agreement with the rate of -35 +/- 3 mmol m(-2) d(-1) derived from sediment oxygen mic-roprofiles. Separating large-scale advective and turbulent fluctuations is a crucial and uncertain component of the flux computation and the largest source of error. To compensate for the 2.25 s oxygen sensor response time, the oxygen flux calculations are corrected by only similar to 5% using a first-order spectral enhancement. This work demonstrates that only a slightly faster oxygen sensor would be needed to resolve the entire flux spectrum. The 18 hours of data are the first measurements obtained in a freshwater reservoir that capture the diurnal oxygen production-consumption cycle

Variable sediment oxygen uptake in response to dynamic forcing

Seiche-induced turbulence and the vertical distribution of dissolved oxygen above and within the sediment were analyzed to evaluate the sediment oxygen uptake rate (J(O2)), diffusive boundary layer thickness (delta(DBL)), and sediment oxic zone depth (z(max)) in situ. High temporal-resolution microprofiles across the sediment-water interface and current velocity data within the bottom boundary layer in a medium-sized mesotrophic lake were obtained during a 12-h field study. We resolved the dynamic forcing of a full 8-h seiche cycle and evaluated J(O2) from both sides of the sediment-water interface. Turbulence (characterized by the energy dissipation rate, epsilon), the vertical distribution of dissolved oxygen across the sediment-water interface (characterized by delta(DBL) and z(max)), J(O2), and the sediment oxygen consumption rate (R(O2)) are all strongly correlated in our freshwater system. Seiche-induced turbulence shifted from relatively active (epsilon = 1.2 x 10(-8) W kg(-1)) to inactive (epsilon = 7.8 x 10(-12) W kg(-1)). In response to this dynamic forcing, delta(DBL) increased from 1.0 mm to the point of becoming undefined, z(max) decreased from 2.2 to 0.3 mm as oxygen was depleted from the sediment, and J(O2) decreased from 7.0 to 1.1 mmol m(-2) d(-1) over a time span of hours. J(O2) and oxygen consumption were found to be almost equivalent (within similar to 5% and thus close to steady state), with R(O2) adjusting rapidly to changes in J(O2). Our results reveal the transient nature of sediment oxygen uptake and the importance of accurately characterizing turbulence when estimating J(O2)