Responses and Tolerance Mechanisms of Mangrove Trees to the Ambient Salinity along the Egyptian Red Sea Coast

Due to the importance of mangrove forests to the ecological system, environment, climate change adaptation, mitigation and ecosystem services, it is necessary to understand the status of the mangroves in Egypt (ecology and physiology). The present study aimed to obtain the basic information needed to evaluate the photosynthetic pigments and proline mechanisms of Avicennia marina and Rhizophora mucronata mangrove to the ambient salinity. The results reached that the free proline accumulated appreciably in leaves. The functional role of proline accumulation appears to be as a cytoplasmic osmoticum to lower cell water potential, provide hydration to bipolymer and serve as an energy source under high salinity environmental conditions. Mangroves showed variations in proline content between the two species. The highest value of proline was recorded 23.56 mg/g dry wt for R. mucronata and the minimum value was recorded 17 mg/g dry wt for A. marina. In addition, the mean value of proline was recorded 18.57 mg/g dry wt for A. marina and 23.98 mg/g dry wt for R. mucronata. The contents of chlorophyll-a in different analyzed mangroves was ranged from 4.46 to 6.05 mg/gf.wt. for A. marina, and from 3.69 to 4.29 mg/gf.wt. for R. mucronata. In addition, the chlorophyll-b content was ranged from 1.46 to 1.83 mg/gf.wt. for A. marina, and from 1.27 to 1.65 mg/gf.wt. for R. mucronata. The carotenoids contents in mangroves ranged from 2.94 to 2.29 mg/gf.wt for A. marina and from 2.04 to 2.09 mg/gf.wt for R. mucronata. In the present study, A. marina was relatively more tolerant and adapted to salinity, low rainfall and extreme temperature conditions than R. mucronata. This explains the more significant local distribution of A. marina in Egypt compared to R. mucronata.

Covid-19 Pandemic in relation to levels of Pollution with PM2.5 and Ambient Salinity – An Environmental Wake-up Call

ABSTRACTINTRODUCTIONCovid-19 infection continues to be a source of great loss of life and global suffering, necessitating national lockdowns. There are however some countries and cities which appear to have contained the pandemic. Common to these countries are environmental factors including the levels of particulate matter (PM2.5) and ambient salinity.METHODPM2.5 and ambient salinity were assessed in a number of cities, differentially affected by Covid-19 infection. The cities chosen to be assessed were divided into two groups. The first group included cities having significantly high rates of Covid-19 infection, while the second group consisted of coastal cities or small island countries, all of which have low rates of Covid-19 infection. Minimum and maximum levels of PM2.5 were obtained from the Air Quality Index, one month before and one month after statutory lockdown. Salinity levels were obtained from a study that assessed chloride ion wet deposition, a surrogate for ambient salinity.RESULTSOne month prior to the statutory national lock-down or mandatory restrictions, there appear to be high levels of particulate matter, PM2.5 (min-max 67.4 - 118.7 AQI), in countries which had a high incidence of Covid-19 infection compared to lower levels in countries that have contained the infection (min-max 45.6 - 79.8) (p<0.046). One month after national restrictions there still appeared to be higher levels of particulate matter, PM2.5 (min-max 51 - 90.5 AQI), in countries which had a high incidence of Covid-19 infection compared to countries that have contained the infection (min-max 42.7 - 69.5 AQI) but this was not statistically significant.There seemed to be an inverse relationship between Covid-19 infection and ambient salinity levels. Countries that were spared high Covid-19 infection rates, besides their geographical isolation, also have higher ambient salinity levels (124 - 617mgCl/m2/TAG) compared to salinity levels noted in countries with high Covid-19 rates of infection (28.4 - 162. mgCl/m2/TAG) (p<0.003).CONCLUSIONHigh levels of PM2.5 in the presence of low ambient salinity may increase the risk of Covid-19 infection in the population. Addressing these two environmental factors may attenuate the severity of the pandemic.

Ablation of sloping ice faces into polar seawater

The effects of the slope of an ice–seawater interface on the mechanisms and rate of ablation of the ice by natural convection are examined using turbulence-resolving simulations. Solutions are obtained for ice slopes $\unicode[STIX]{x1D703}=2^{\circ }{-}90^{\circ }$, at a fixed ambient salinity and temperature, chosen to represent common Antarctic ocean conditions. For laminar boundary layers the ablation rate decreases with height, whereas in the turbulent regime the ablation rate is found to be height independent. The simulated laminar ablation rates scale with $(\sin \unicode[STIX]{x1D703})^{1/4}$, whereas in the turbulent regime it follows a $(\sin \unicode[STIX]{x1D703})^{2/3}$ scaling, both consistent with the theoretical predictions developed here. The reduction in the ablation rate with shallower slopes arises as a result of the development of stable density stratification beneath the ice face, which reduces turbulent buoyancy fluxes to the ice. The turbulent kinetic energy budget of the flow shows that, for very steep slopes, both buoyancy and shear production are drivers of turbulence, whereas for shallower slopes shear production becomes the dominant mechanism for sustaining turbulence in the convective boundary layer.