Hypolimnetic oxygenation is an increasingly common lake management strategy for mitigating hypoxia/anoxia and associated deleterious effects on water quality. A common effect of oxygenation is increased oxygen consumption in the hypolimnion and predicting the magnitude of this increase is the crux of effective oxygenation system design. Simultaneous measurements of sediment oxygen flux (J O2) and turbulence in the bottom boundary layer of two oxygenated lakes were used to investigate the impact of oxygenation on J O2. Oxygenation increased J O2 in both lakes by increasing the bulk oxygen concentration, which in turn steepens the diffusive gradient across the diffusive boundary layer. At high flow rates, the diffusive boundary layer thickness decreased as well. A transect along one of the lakes showed J O2 to be spatially quite variable, with near-field and far-field J O2 differing by a factor of 4. Using these in situ measurements, physical models of interfacial flux were compared to microprofile-derived J O2 to determine which models adequately predict J O2 in oxygenated lakes. Models based on friction velocity, turbulence dissipation rate, and the integral scale of turbulence agreed with microprofile-derived J O2 in both lakes. These models could potentially be used to predict oxygenation-induced oxygen flux and improve oxygenation system design methods for a broad range of reservoir systems.
The present study aimed at developing a new vesicular formulation capable of promoting the protective effect of ascorbic acid and tocopherol against intestinal oxidative stress damage, and their efficacy in intestinal wound healing upon oral administration. A pH-dependent copolymer (Eudragit® L100), a water-soluble prebiotic fibre (Nutriose® FM06), a phospholipid mixture (Lipoid S75), and two natural antioxidants (ascorbic acid and tocopherol) were combined to fabricate eudragit-nutriosomes by a simple, solvent-free procedure. The vesicles were spherical and oligolamellar, with some multicompartment structures in Eudragit-nutriosomes, small in size (~100 nm), with highly negative zeta potential. The effect of Eudragit® and Nutriose® on the stability on storage and in simulated gastrointestinal fluids were confirmed by the Turbiscan® technology and in vitro studies, respectively. Eudragit-nutriosomes exhibited a protective effect against H2O2-induced oxidative stress, and a proliferative effect in Caco-2 cells, as they provided the closure of the scratched area after 96 h of incubation.
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