We studied the effects of pumping surface water down through the pycnocline (i.e. artificial ventilation) on hydrodynamics, oxygen concentrations, hydrogen sulfide, and nutrients in two anoxic coastal basins (Lannerstasundet and Sandofjarden). In addition, in a corresponding laboratory aquarium experiment, pumping of less saline surface water entrained dense bottom water with a mixing ratio of 6.8 and illustrated dispersal below the pycnocline. Oxygen saturation increased from 0 to 20%; oxygen penetrated poorly into the sediment of the aquarium. In the salinity-stratified Lannerstasundet basin, ventilation also oxidized the anoxic bottom water. The ventilation removed hydrogen sulfide and decreased the sub-pycnocline water pools of phosphorus and ammonium, which was not observed in a neighboring reference basin. The summertime ventilation warmed and made the sub-pycnocline water less saline. In the autumn, the inflows of cooled water from the surroundings with equal or higher salinity promoted its sinking in the relatively warm ventilated basin. The inflows maintained oxygen concentrations between 4 and 8 mg L-1 for months after the ventilation ended. In contrast to Lannerstasundet, ventilation did not prevent formation of anoxia and release of nutrients in the temperature stratified Sandofjarden. Here, the ventilation capacity was less than that in Lannerstasundet and ventilation expanded the sub-thermocline bottom area, warmed the bottom sediments, and probably displaced oxic water from the experimental area. The ventilation did not promote density conditions for inflows and no marked inflow-induced oxidation was observed after midsummer. We conclude that a significant amount of anoxic water was entrained into the ascending plume which reduced the oxygen content below the pycnocline ventilation in aquarium experiment. Additionally, summertime ventilation may improve the status of the salinity-stratified basins for further oxidation. The improvement occurs due to autumn cooling and favorable basin topography, which promote inflows of oxic water with larger density and thereby, renewal of bottom water in the pumped basin. The semi-enclosed and temperature-stratified basin cannot form such favorable density conditions for inflows and thus ventilation is less efficient.

Effects of hypolimnetic aeration (pumping of epilimnetic water into the hypolimnion) on the quantity of settling material in eutrophied Lake Vesijarvi, Finland were studied by comparing spatially comprehensive gross sedimentation rates as dry and organic matter prior to aeration activity and during two aerated years. Possible changes in the organic matter (as loss on ignition, LOI), carbon (C) and nitrogen (N) contents and changes in the C/N ratio of the settling material and surface sediment were quantified. Thermal stratification broke up earlier due to aeration and was followed by sedimentation peaks. The absolute amount of dry and organic matter as well as C and N settling to the lake bottom were significantly higher in the aerated years. Increased sedimentation rates were especially pronounced in the deep zones indicating enhanced sediment focusing. Increased sedimentation of C and N reflected higher primary production during the aerated years, which most likely was associated with increased temperature and turbulence and the subsequent regeneration and recycling of nutrients in the water body. Aeration seemed to slightly enhance degradation, but contrary to its ultimate aim, it failed to decrease the phosphorus content of the water column and deposits of organic material in the deep zones of the lake.

Background Hypotension is common after cardiac arrest (CA), and current guidelines recommend using vasopressors to target mean arterial blood pressure (MAP) higher than 65 mmHg. Pilot trials have compared higher and lower MAP targets. We will review the evidence on whether higher MAP improves outcome after cardiac arrest. Methods This systematic review and meta-analysis will be conducted based on a systematic search of relevant major medical databases from their inception onwards, including MEDLINE, Embase and the Cochrane Central Register of Controlled Trials (CENTRAL), as well as clinical trial registries. We will identify randomised controlled trials published in the English language that compare targeting a MAP higher than 65-70 mmHg in CA patients using vasopressors, inotropes and intravenous fluids. The data extraction will be performed separately by two authors (a third author will be involved in case of disagreement), followed by a bias assessment with the Cochrane Risk of Bias tool using an eight-step procedure for assessing if thresholds for clinical significance are crossed. The outcomes will be all-cause mortality, functional long-term outcomes and serious adverse events. We will contact the authors of the identified trials to request individual anonymised patient data to enable individual patient data meta-analysis, aggregate data meta-analyses, trial sequential analyses and multivariable regression, controlling for baseline characteristics. The certainty of the evidence will be assessed by the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system. We will register this systematic review with Prospero and aim to redo it when larger trials are published in the near future. Conclusions This protocol defines the performance of a systematic review on whether a higher MAP after cardiac arrest improves patient outcome. Repeating this systematic review including more data likely will allow for more certainty regarding the effect of the intervention and possible sub-groups differences.