The groundwater of low-temperature geothermal systems located in the Mexican Highlands is used as an urban water supply owing to water scarcity in the area. In the Juventino Rosas (JR) area, central Mexico, the highest well temperature is 50°C; most of the hot waters range from 24°C to 48°C. The aquifer systems are formed mainly by Oligocene-Pliocene rhyolite-ignimbrite rocks, basaltic-andesitic rocks of the Trans Mexican Volcanic Belt (TMVB), and Quaternary sediments that filled the valleys. The groundwater of these aquifers contains hazardous elements such as arsenic at 0.0026–0.045 mg/L, fluoride at 0.569–3.03 mg/L, and radon at 1,000–52,300 Bq/m3. Tectonic and subsidence faults and fractures allow rapid ascension of geothermal flow. The presence of this flow was corroborated by the water geochemistry and the water table behavior. Hydrogeochemical modeling was used to define this system as low temperature rather than geothermal.
The major chemical and stable isotopic compositions of hydrogen, oxygen, and sulfur (δD, δ18O, δ34S) were analyzed from water samples of wells and natural springs in the northern foot area of Mt. Fuji and the adjacent Misaka and Tanzawa Mountains to investigate the origin of deep well waters and water-rock interactions that affect the water quality. The water in the samples was considered to have originated through the mixing of meteoric water with very small amounts of altered seawater that had been trapped in the pore spaces in the basement rock, the so-called green tuff formations. The major chemical components of the original waters are considered to be affected by the dissolution of anhydrite and/or gypsum, the weathering of plagioclase, precipitation of calcite, and the cation exchange reaction of smectite. In the distributed volcanic products of Mt. Fuji, the weathering of olivine appears to be an important factor in water quality. The δ34S values of the SO42– ions of well water were higher in the Misaka and Tanzawa Mountains and lower at the foot of Mt. Fuji, indicating the presence of anhydrite/gypsum of different origins.
The carbon isotope ratios of organic carbon in settling particles collected in the highly-diatom-productive Bering Sea were determined. Wet decomposition was employed to oxidize relatively fresh organic matter. The amount of unoxidised organic carbon in the residue following wet decomposition was negligible. The δ13C of organic carbon in the settling particles showed a clear relationship against SiO2/CaCO3 ratio of settling particles: approximately –26‰ and –19‰ at lower and higher SiO2/CaCO3 ratios, respectively. The δ13C values were largely interpreted in terms of mixing of two major plankton sources. Both δ13C and compositional data can be explained consistently only by assuming that more than 98% of diatomaceous organic matter decays and that organic matter derived from carbonate-shelled plankton may remain much less remineralized. A greater amount of diatom-derived organic matter is discovered to be trapped with the increase of SiO2/CaCO3 ratio of the settling particles. The ratio of organic carbon to inorganic carbon, known as the rain ratio, therefore, tends to increase proportionally with the SiO2/CaCO3 ratio under an extremely diatom-productive condition.
Understanding the transport of branched glycerol dialkyl glycerol tetraethers (brGDGTs) along the soil-river-lake transect is of vital importance, which helps discriminate the autochthonous from allochthonous contribution of brGDGTs in lake and river environment and favors the application of brGDGT-based proxies in paleo-reconstruction. We collected the sediment samples from the Qinghai Lake, the largest saline lake in China, as well as the river sediments and catchment soils, to examine the difference in the distribution of 5- vs. 6-methyl brGDGTs along the soil-river-lake transect. The brGDGT distributions were found to show a large variation along the transect, which can be reflected by the MBTʹ-derived indices and IR indices. There is a considerable difference in brGDGT distributions between soil and the river sediment. The inflowing rivers likely receive terrestrial brGDGT input to a variable degree. BrGDGTs in the Buha river are primarily of autochthonous origin whereas other ephemeral streams, like the Heima river, exhibit a similar brGDGT distribution to the surrounding soils, reflecting that these compounds are likely derived from soils. A higher quantity of 6-methyl brGDGTs and brGDGT-Ia was observed in the lake than in the river sediments, pointing to a preferential degradation of 5-methyl brGDGTs and/or an increase of in situ production of 6-methyl brGDGTs in the lake. In addition, in arid and alkaline soils, both CBTʹ and IR indices have strong correlations with soil pH even within the narrow pH range. Furthermore, we find a clear relationship of CBT with water salinity in Buha river. The difference in soil and river leads to a complicated interpretation for the CBT (CBTʹ) index. In the lake, the MBTʹ (specially represented by MBTʹ5ME and MBTʹ6ME), defined mainly by the fractional abundance of GDGT-Ia, increases with lake water depth, suggesting the maximum water depth is likely to impact the use of MBTʹ/CBT proxy in the Qinghai Lake.
A geochemical study of trace elements in soil profiles developed on basaltic parent materials of unknown ages along the slopes of Mt. Cameroon was carried out. The study objectives included vertical description of element dispersion, element mobility and relating element distribution to weathering intensity. Twenty five soil samples from 6 sites (between 30 to 1017 m a.s.l.) were collected and analysed for trace element concentrations by ICP-MS technique. The weathering status of these soils, (derived from chemical weathering indices) indicate that the most weathered profiles are located at higher elevations with lower mean annual precipitation. Higher losses in Cu, Co and Zr in the moderately weathered profiles in the zones of high leaching are linked to the comparatively higher dissolution of Fe-bearing minerals such as magnetite to which resulted in higher Fed/FeT ratios. Organic matter may account for low mobility of Cu and Pb, while for Zn, the Mn-Al system may control Zn retardation at low elevations. Ni and Sr were highly mobilised at all elevations while Pb, Rb and Sr showed evidence of atmospheric deposition. Comparatively higher inputs of dust-derived minerals in the lower elevation could also affect the distribution of TE. Suggestions are therefore made for the existence of an inflection point within this elevational bracket marked by incongruent dissolution of primary silicate minerals (particularly Fe-minerals).
Concentrations of acid volatile sulfides (AVS) as metal sulfides in three different size fractions (<30 nm, 30–200 nm, >200 nm) at Lake Teganuma were measured using a nano-filtration followed by a purge-trap gas chromatography with a flame photoionization detector (GC-FPD). Fresh water samples were collected at four sites in the lake and sequentially filtered with 30 nm and 200 nm pore size filters on site immediately after the sampling. The concentrations of unfiltered AVS (AVStotal) ranged from 0.6 to 1.4 nmol/kg, among which the highest concentration was found in a lotus colony site. Except for the lotus colony site, the relative AVS abundances in the three size-fractions were quite similar. It was found that >80% of AVStotal existed in the <30 nm size fraction, while only 10~20% in 30–200 nm and >200 nm size fractions. In the lotus colony site, on the other hand, <30 nm fraction contributed only ~5% but the 30–200 nm size fraction exhibited most dominant contribution (~80%), although the AVStotal concentration in the lotus colony site was similar to those in other sites. Present observation shows that metal sulfides exist in fresh water environment and mainly reside in <30 nm size fraction, but even larger metal sulfide nanoparticles with the size of 30–200 nm can be formed, which seem to be formed from <30 nm size fraction through a relatively rapid process.
This paper reports iodine (127I and 129I) and cesium (137Cs) isotope concentrations in groundwater of confined and unconfined aquifers in the vicinity of the Fukushima Dai-ichi nuclear power plant (FDNPP). 127I and 129I concentrations range from 2–13 μg/L and 5 × 107–8 × 1010 atom/L respectively, resulting in 129I/127I atomic ratios from 5 × 10–9 to 2 × 10–6. In all samples, 137Cs concentrations were below detection limit. The deep-sealed groundwater from the confined aquifer did not contain significant quantities of Fukushima-derived 129I compared to the groundwater in the unconfined aquifer. The minimal 129I/137Cs activity ratios in the groundwater are more than 2–500 times higher than the FDNPP source ratio. These data can be explained by rainwater infiltrating through the surface soils, with the more water-soluble 129I preferentially extracted into the aqueous phase and the 137Cs preferentially retained in the soil.