Contact angle hysteresis in the clay-water-air system of soils

The purpose of this research is to study the change in wettability of clays due to the influence of mesophilic soil microorganisms' activity when adding model contaminants: water-in-oil emulsion, glycerol and oleic acid. During the experiments, the objectives of this study were to specify peculiarities of wetting contact angle hysteresis of clays with substrates of different mineral composition and microbial activity. Hydrophilicity/hydrophobicity of the stimulator for microbial activity does not have a clear effect on clay properties. The surface heterogeneity mostly increases with time, perhaps, due to biofilm exudates whatever was a type of microbial stimulator. Chemical and geometric heterogeneities played comparable roles in the surface hydrophilic-hydrophobic balance. Results obtained prove that microbial communities and/or the Fe chemical state alteration (pyrite, hematite or goethite) were responsible for both hydrophilization and hydrophobization of the surface. The equation for the drop spreading rate was presented and verified by well comparison of experimental results with simulations.179-19

Aquifers and hyporheic zones: Towards an ecological understanding of groundwater

Ecological constraints in subsurface environments relate directly to groundwater flow, hydraulic conductivity, interstitial biogeochemistry, pore size, and hydrological linkages to adjacent aquifers and surface ecosystems. Groundwater ecology has evolved from a science describing the unique subterranean biota to its current form emphasising multidisciplinary studies that integrate hydrogeology and ecology. This multidisciplinary approach seeks to elucidate the function of groundwater ecosystems and their roles in maintaining subterranean and surface water quality. In aquifer-surface water ecotones, geochemical gradients and microbial biofilms mediate transformations of water chemistry. Subsurface fauna (stygofauna) graze biofilms, alter interstitial pore size through their movement, and physically transport material through the groundwater environment. Further, changes in their populations provide signals of declining water quality. Better integrating groundwater ecology, biogeochemistry, and hydrogeology will significantly advance our understanding of subterranean ecosystems, especially in terms of bioremediation of contaminated groundwaters, maintenance or improvement of surface water quality in groundwater-dependent ecosystems, and improved protection of groundwater habitats during the extraction of natural resources. Overall, this will lead to a better understanding of the implications of groundwater hydrology and aquifer geology to distributions of subsurface fauna and microbiota, ecological processes such as carbon cycling, and sustainable groundwater management