Influences of environmental factors on the modern 14C reservoir effects in Qinghai-Tibet Plateau lakes

The establishment of reliable age in the lake sediment profile mainly depends on the AMS 14C dating technique.However,the presence of the 14C lake reservoir effects(LREs)restricted for using radiocarbon dating in lake sediment,especially in dry and cold areas with a scarce plant cover in the Qinghai-Tibet Plateau.Hence,the discussion of influence factors of LREs is crucial.This paper selected 15 lakes(17 sediment and 3 plant samples)in the Qinghai-Tibet Plateau to examine the distribution characteristics of the modern LREs and their main influencing factors.In our study area,14 lakes were all affected by the LREs.The minimum 14C year is 5900 a BP towards the deep water area,whereas the maximum 14C year is up to 7185 a BP in the margins of Lake Heihai.The maximum 14C year is up to 7750 a BP,and the minimum 14C year is present-day carbon in the 15 lakes.One further study indicated that the LRE differences in individual lake are mostly owing to the contribution of exogenous carbonate.The results displayed that the LREs tended to increase with the increase of the salinity,moreover,the LREs of saltwater lakes or salt lakes were significantly larger than freshwater lakes due to the possible supply of old total dissolved inorganic carbon with a long residence time in the lakes.Moreover,the contribution of calcite played a significant role on the LREs.Additionally,the LREs differences are affected by the source of organic matter.The lake with groundwater supply shows large LRE due to likely being influenced by crustal and ancient CO_(2) uprising.

Hydro-Chemical Characterization of Glacial Melt Waters Draining from Langtang Valley, Nepal

A detailed analytical study of the physico-chemical parameters of melt water draining from glaciers of Langtang Valley with an elevation ranging from 1395 m a s l to 4200 m a s l in Rasuwa district, Nepal was carried out in order to study the seasonal and altitudinal variation in hydro-chemistry along the Langtang River and glacial melts from the Lirung and the Khimsung Glaciers. The study was carried out during 6 - 10 April and 30 June-3 July, 2014 at 11 sites. A total of 22 composite samples were collected. The concentration of cations and anions of the Langtang Valley were found in the order Ca2+ > K+ > Na+ > Mg2+ and , respectively. Significant seasonal variation in electrical conductivity (EC), turbidity, dissolved oxygen (DO), calcium (Ca), sodium (Na), magnesium (Mg), chloride (Cl), sulphate (SO4) and total phosphorus (TP-PO4) and altitudinal variation in EC, total dissolved solids (TDS), DO and Na was found out. The concentrations of the heavy metals (As, Al, Mn, Zn, Cd, Cr) were below the detection limit except Fe (0.5 to 18.1 mg/l), which was highly variable. Calcium carbonate weathering was found out to be the major source of dissolved ions in the region. The elemental ratios (Ca/Si and K/Na) were typical of glacial melt water and the low Na/Cl and K/Cl ratios indicated major contribution from atmospheric precipitation to the observed dissolved ions of melt waters. The study showed an increase in the concentration of cations as compared to previous studies, which could be attributed to increasing weathering rates due to temperature increase. Elevated concentration of NO3 and TP-PO4 compared to previous studies show the effect of human impact in the region. Differences in the melt water composition between the debris covered and clean type glacier was found out.

Contribution of Hydrogeochemical and Isotopic Tools to the Management of Upper and Middle Cheliff Aquifers

In the alluvial aquifers of Upper and Middle Cheliff(North-West Algeria), the groundwater quality is deteriorating. The objective of this study was to characterize the physical and chemical properties of these aquifers;and to evaluate the groundwater quality and its appropriateness for drinking and agricultural use. An investigation was carried out by estimating of the physiochemical parameters(Ca^2+, Mg^2+, Na^+, K^+, Cl^-, SO4^2-, HCO3^-, NO3^-, Br^- and TDS) to identify the chemical characteristics of groundwater. Morever, the isotopic composition was examined to identify the sources of recharge of these aquifers. The groundwater geochemistry for the high water level(May, 2012 and June, 2017) and low water level(November, 2012 and October, 2017) was studied. Accordingly, water samples from 39 water sampling points were collected(October, 2017 and June, 2018), for the purpose of analyzing stable isotopes(18O, 2H). The results show that the groundwater is mainly characterized by Ca-Cl and Na-Cl type. The chemical quality of the water is from fair to poor with the presence of nitrates used in agricultural and urban discharge. Also, the Br/Cl ratio gives indications on the origin of the salinity. This salinity is due to the leaching of chlorinated fertilizers, the dissolution of evaporite deposits and the rise of deep salty water by the fault of Chellif. While, the diagram of δ2H=f(δ18O) indicates that the origin of the recharge of these aquifers is the Atlantic and Mediterranean oceanic meteoric rainwater.