SUMMARYThe roles of nitric oxide synthase activity (NOS), nitrite and myoglobin (Mb) in the regulation of myocardial function during hypoxia were examined in trout and goldfish, a hypoxia-intolerant and hypoxia-tolerant species, respectively. We measured the effect of NOS inhibition, adrenaline and nitrite on the O 2 consumption rate and isometric twitch force development in electrically paced ventricular preparations during hypoxia, and measured O 2 affinity and nitrite reductase activity of the purified heart Mbs of both species. Upon hypoxia (9% O 2 ), O 2 consumption and developed force decreased in both trout and goldfish myocardium, with trout showing a significant increase in the O 2 utilization efficiency, i.e. the ratio of twitch force to O 2 consumption, suggesting an increased anaerobic metabolism. NOS inhibition enhanced myocardial O 2 consumption and decreased efficiency, indicating that mitochondrial respiration is under a tone of NOS-produced NO. When trout myocardial twitch force and O 2 consumption are enhanced by adrenaline, this NO tone disappears. Consistent with its conversion to NO, nitrite reduced O 2 consumption and increased myocardial efficiency in trout but not in goldfish. Such a difference correlates with the lower O 2 affinity measured for trout Mb that would increase the fraction of deoxygenated heme available to catalyze the reduction of nitrite to NO. Whereas lowaffinity trout Mb would favor O 2 diffusion within cardiomyocytes at high in vivo O 2 tensions, goldfish Mb having higher O 2 affinity and higher nitrite reductase activity appears better suited to facilitate O 2 diffusion and nitrite reduction in the heart during severe hypoxia, a condition particularly well tolerated by this species.
BACKGROUND: H 2 S and methanethiol, which are important odorants from pig facilities, were unsatisfactorily removed in field biological air filters with short residence time. For a better understanding of the process, this study established a dynamic model for simulation of H 2 S and methanethiol removal in a three-stage biological air filter (two stages of biotrickling filter and one stage of biofilter), based on experimental determined mass transfer coefficients and partition coefficients from previous studies. RESULTS: The maximum biodegradation rates for both H 2 S and methaetniol were estimated to be relatively low, with differences observed for different stages. Further, H 2 S removal was also observed to be limited by mass transfer, while other parameters such as active water content, biofilm thickness and diffusioncoefficient were also shown to affect model performance, indicating the relevance of proper estimation of these parameters. For methanethiol, on the other hand, the model is mainly limited by maximum biodegradation rate. CONCLUSION: Overall, the established model can properly simulate the performance of the field biological air filter for the removal of volatile sulfur compounds. Calibration of model parameters in field conditions may further improve the model precision and robustness for predicting performance of the field biological air filter. NOTATION a specific surface area (m 2 m −3 ) a e effective specific interfacial area (m 2 m −3 ) C g ,C l gas and liquid Contaminant concentration (g m −3 ) D GL diffusion coefficient in liquid (m 2 s −1 ) D p dispersion-diffusion coefficient (m 2 s −1 ) H dimensionless Henry's law constant (-) K G a e overall volumetric air-water mass transfer coefficientMaximum degradation rate (g m −3 h −1 ) z the absorption column depth (m)Greek letters porosity (-) a active water content (-)
Regime shifts are likely to have strong impacts on all trophic levels and their interactions. In addition, weather conditions and sea level rise together with tidal currents may change sediment morphology in coastal areas and estuaries. Here, we studied the effects of these drivers of ecosystems on abundance of seven wader species feeding on macrozoobenthos in the German sector of the Wadden Sea. We hypothesized that regime shift caused decreases in wader abundance and that changes in sediment morphology driven by sea level rise and tidal amplitude affected these changes. We analyzed numbers of waders on a short term, 1998–2016, that matched a large-scale geographical study of sediment morphology in the German sector, and at a long term, 1987–2019. Changes in numbers of waders were estimated as slope of coefficients of the trends of wader species numbers in the two periods. The average (se) year of decreases in numbers of waders was initiated for most species and tidal basins in the year 1992 (± 0.4) that followed a regime shift in the Southern North Sea and in the Wadden Sea in 1988–1989. There were no statistical differences between the years when numbers of waders started to decrease between the northern and the southwestern tidal basins of the German sector, indicating that the drives affected both coastal sections simultaneously. Significant relationships were found between slopes of coefficients of wader species and sediment morphology and physical features as sea level rise and tidal amplitude. Relationships were most pronounced for the long term, 1987–2019 compared to the short term, 1998–2016. We conclude that regime shift and changes in sediment morphology driven by sea level rise and sediment change can affect abundance of migratory wader species in large estuaries and shallow coastal waters.
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