ABSTRACT A high concentration of hydrogen gas occurs in fracture zones of active faults that are associated with historical earthquakes. To explain the described phenomenon, we propose the piezoelectrochemical (PZEC) effect as a mechanism for the direct conversion of mechanical energy to chemical energy. When applied to natural piezoelectric crystals including quartz and serpentine, hydrogen and oxygen are generated via direct water decomposition. Laboratory experiments show H 2 gas is generated from strained piezoelectric material due to the extremely low solubility of H 2 , suggesting that the deformed or strained mineral surfaces can catalyze water decomposition. If the strain-induced H 2 production is significant, hydrogen measurements at monitoring sites can offer information on deformation of rocks operating at depth prior to earthquakes. Oxygen can be measured in water due to its high solubility compared to hydrogen. Our experimental results demonstrate that dissolved oxygen generated from the PZEC effect can oxidize dissolved organic dye and ferrous iron in an aqueous Fe(II)–silicate metal complex. The hydrogen and oxygen formed through stoichiometric decomposition of water in the presence of strained or deformed minerals in fault zones (including subduction zones and transform faults) may be referred to as tectonic hydrogen and tectonic oxygen. Tectonic hydrogen could be a potential energy source for deep subsurface and glacier-bedrock interface microbial communities that rely on molecular hydrogen for metabolism. Tectonic oxygen may have been an important oxidizing agent when dissolved in water during times in early Earth history when atmospheric oxygen levels were extremely low. Reported “whiffs” of dissolved oxygen before the Great Oxidation Event might have been related to tectonic activity.

Abstract Water, the vital element of the environment, considered for long time an inexhaustible and renewable resource, can have a limiting or favourable potential in the socioeconomic development of a region. Given that Romania's NE (Eastern Carpathians and the northwestern part of the Moldova Plateau) is undergoing increased competition for water resources, triggered by the intensification of agriculture and industrial development, better knowledge of the hydrological processes and the quality of surface water is required. The main purpose of the present study was to identify the hydrological processes determining the quality of surface waters based on analyses of the stable isotopic composition of water from precipitation, rivers and lakes and its quality parameters. For this, water samples were collected from 29 river sections, two lakes and a precipitation monitoring point over a period of 12 months (January to December 2019). The results show that the changes in the isotopic composition of precipitation and surface water are mainly controlled by air temperature, which, in turn, is influenced by the large-scale atmospheric circulation and other factors (e.g. precipitation amount, season, altitude). At the same time, the chemical analyses indicate that the water resources of the study area are predominantly characterized by a good chemical and ecological state, except for two sampling points with a moderate state and three with a poor ecological state.