Direct measurement of dissolved inorganic nitrogen exchange and denitrification in individual polychaete (Nereis virens) burrows

The burrows of macroinfauna are significant sites of sediment-water nitrogen exchange and associated microbial activity. In this study, the exchange of dissolved inorganic nitrogen (DIN) and nitrogen cycle reaction rates were quantified in individual burrows of the estuarine polychaete Nereis virens. Burrow ventilation rate and DIN (NH4+, NO2−, NO3− and N2O) exchange were determined at 22°C in individual, inhabited burrows with and without the presence of C2H2 (an NH4+ oxidation, N2O reduction block). Ventilation cycles were unaffected by C2H2, but worm metabolism (O2 uptake) and excretion of NH4+ were enhanced by ∼100% and ∼50%, respectively. Time-specific DIN exchange patterns were quantitatively modeled by relating burrow water concentration changes, excretion, and ventilation rates. The highest rates were at the start of ventilation periods and decreased or increased (depending on the solute) exponentially to a steady state level. The presence of C2H2 increased NH4+ release from burrows and changed the NO2− flux from a high release (∼300 nmol h−1) to an uptake (∼–30 nmol h−1). Nitrate uptake was independent of C2H2, presumably because overlying water NO3− concentration was high (∼100 μM). Indirect estimates of nitrification corresponded to the burrow release of NO2− without C2H2. Approximately half of the NO2− + NO3− uptake in burrows was due to denitrification. In microcosms with and without N. virens (875 m−2), denitrification was stimulated 3-fold by N. virens and the ratio denitrification/nitrification increased from 0.61 to 1.11. The changes in DIN flux and denitrification caused by N. virens corresponded well to the rates extrapolated from individual burrows to the appropriate worm density of 875 m−2. At the abundance used, N. virens burrows were responsible for 37% and 66% of the total sediment nitrification and denitrification, respectively

Sleep duration modifies effects of free ad libitum school meals on adiposity and blood pressure

Insufficient sleep can potentially affect both energy intake and energy expenditure, resulting in obesity and reduced cardiometabolic health. The objective of the study was to investigate if habitual sleep duration of 8- to 11-year-olds modifies the effect of free ad libitum school meals on cardiometabolic markers, body composition, dietary intake, and physical activity. For 2 consecutive 3-month periods, this cluster-randomized, controlled, cross-over trial provided 530 children with school meals or usual lunch brought from home. Dietary intake, activity, and sleep were measured simultaneously for 7 consecutive days using dietary records and accelerometers. Short- and long-sleeping children were defined as lower and upper tertile of sleep duration. Body composition, blood pressure, blood lipids, and homeostatic model assessment of insulin resistance (HOMAIR) were measured/calculated. Overall, school meals compared with lunch from home had positive effects on physical activity and blood pressure in long-sleeping children and negative effects on body fat in short-sleeping children. Short-sleeping children increased fat mass compared with long-sleeping children by 0.21 (95% confidence interval 0.03–0.38) kg, android fat mass by 0.02 (0.001–0.04) kg, waist circumference by 0.73 (0.23–1.24) cm, blood pressure by 1.5 (0.4–2.6) mm Hg, fat intake by 1.1 (0.2–2.0) percentage of energy, and decreased total physical activity by 7.2 (1.6–12.7) % (all P ≤ 0.04), while HOMAIR and blood lipids were not modified by sleep duration (all P ≥ 0.32). In conclusion, the susceptibility to increase abdominal adiposity and blood pressure when exposed to dietary changes can potentially be explained by too little sleep, which results in increased caloric intake and reduced physical activity. </jats:p

Acute oil exposure reduces physiological process rates in Arctic phyto- and zooplankton

Arctic shipping and oil exploration are expected to increase, as sea ice extent is reduced. This enhances the risk for accidental oil spills throughout the Arctic, which emphasises the need to quantify potential consequences to the marine ecosystem and to evaluate risk and choose appropriate remediation methods. This study investigated the sensitivity of Arctic marine plankton to the water accommodated fraction (WAF) of heavy fuel oil. Arctic marine phytoplankton and copepods (Calanus finmarchicus) were exposed to three WAF concentrations corresponding to total hydrocarbon contents of 0.07 mg l−1, 0.28 mg l−1 and 0.55 mg l−1. Additionally, the potential phototoxic effects of exposing the WAF to sunlight, including the UV spectrum, were tested. The study determined sub-lethal effects of WAF exposure on rates of key ecosystem processes: primary production of phytoplankton and grazing (faecal pellet production) of copepods. Both phytoplankton and copepods responded negatively to WAF exposure. Biomass specific primary production was reduced by 6, 52 and 73% and faecal pellet production by 18, 51 and 86% with increasing WAF concentrations compared to controls. The phototoxic effect reduced primary production in the two highest WAF concentration treatments by 71 and 91%, respectively. This experiment contributes to the limited knowledge of acute sub-lethal effects of potential oil spills to the Arctic pelagic food web