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One of the most important questions in the science of global carbon cycle is how to balance the atmospheric CO2 budget. However, there is a large terrestrial carbon sink is missing. The locations, magnitudes, variations, and mechanisms responsible for this terrestrial missing carbon sink are uncertain and the focus of much continuing debate. In order to provide a basis for the assessment of carbonate weathering-related carbon sink, this study investigated the spatial and temporal variations of dissolved inorganic carbon (DIC) and particulate organic carbon (POC), and used stable carbon isotopes and hydrochemical data to quantitatively estimate the proportion of DIC transformation to POC and analyze the potential influence of the transformation of DIC into OC on the carbon isotope composition in the Lijiang River (typical karst surface water), Southwest China. The results showed that DIC concentrations are high in winter and low in summer and increase from upstream to downstream. POC concentrations are high in summer and low in spring. δ13CPOC and δ13CDIC are negatively correlated in the Lijiang River. The δ13CDIC values are high in spring and low in summer, compared with the estimated δ13CDIC(cal.); the observed δ13CDIC values have a maximum positive shift in spring and similar in the summer; the δ13CPOC values decrease from upstream to downstream, and are high in summer and low in spring. These observations indicate that the isotopic compositions of both DIC and POC are significantly affected by aquatic photosynthesis that transforms DIC into OC. In-river primary production contribute 12–54% of POC, and the contributions of carbonate rock-sourced DIC to the riverine POC range from 7 to 30%, which suggests an important sink of atmospheric CO2 in river systems and should be taken into account in global carbon cycle. [ABSTRACT FROM AUTHOR]

We analysed precipitation and river water samples from the Lijiang River basin with the aim of understanding the important role of acid rain components, especially NH 4 , in chemical weathering of karst areas. First, analysis of the hydrochemical characteristics revealed the following: In the precipitation samples, the volume-weighted mean pH was 4.91, and the acid rain rate was 65%. The major ion composition was characterized by a dominance of NH 4 , Ca, SO 4 and NO 3 , accounting for 40.0%, 35.3%, 46.3% and 30.5%, respectively, of the total cation and anion concentrations. In the river water samples, the pH ranged from 6.75 to 9.16, with an average of 7.55. The major hydrogeochemical species in the river water samples were Ca–HCO 3 and Mg–HCO 3. Second, by employing chloride-normalized ratios of the other major ions in precipitation, we estimated that the contributions of SO 4 and NO 3 from the atmosphere to the river were53.6% and 35.0%, respectively. Third, combining the hydrochemical index with the value of δ13C DIC and using the hydrochemical composition method showed that the proportion of carbonate weathered (R) by NH 4 , H 2 SO 4 and HNO 3 from acid rain accounted for 9.3%, 9.4% and 3.1% of the total weathering rate, respectively, and the proportions in the upper reaches were significantly higher than those in the lower reaches of the river. The average values of the carbonate weathering proportion (R) and the carbonate weathering rate (CWR) due to acid rain were approximately 22.0% and 2.1 t/km2/yr, respectively. Taken together, our results revealed that carbonate weathering by acid rain can significantly increase the carbonate weathering rate, which is essential information for accurate estimation of the carbon cycle (namely, inorganic carbon sources and sinks). Image 1 • Analysis of hydrochemical characteristics of precipitation and river water. • NH 4 (H), H 2 SO 4 and HNO 3 may provide the required protons for weathering reactions. • Carbonate weathering by acid rain can significantly increase weathering rate. [ABSTRACT FROM AUTHOR]

Surface water suffering from nitrate (NO 3 - ) contamination in karst area is not only harmful to human health as drinking water but can also affect the process of carbonate rock weathering, so it is crucial to trace the sources and transformations of NO 3 - in karst surface water. In this study, an investigation of water chemical data and NO 3 - isotopes (δ 15 sources of individual potential sources (incl. soil organic nitrogen (SON), atmospheric precipitation (AP), manure and sewage wastes (M&S), and chemical fertilizer (CF)) in the Lijiang River (typical karst surface water), Guilin, Southwest China. δ 18 O) was used to elucidate the transformations of NO 3 - and quantify a proportional apportionment of NO 3 - sources of individual potential sources (incl. soil organic nitrogen (SON), atmospheric precipitation (AP), manure and sewage wastes (M&S), and chemical fertilizer (CF)) in the Lijiang River (typical karst surface water), Guilin, Southwest China. δ 15 N-NO 3 - and δ 18 O-NO 3 - values of water samples from the Lijiang River range from 2.14 to 13.50‰ (mean, 6.59‰) and from - 2.44 to 6.97‰ (mean, 3.76‰), respectively. A positive correlation between Cl - and NO 3 - but no correlations between NO 3 - and δ 15 N-NO 3 - or δ 18 O-NO 3 - are found and the δ 18 O-NO 3 - values fitted the theoretical δ 18 O-NO 3 - values produced from nitrification, suggesting that the genesis of NO 3 - in waters of the Lijiang River is affected by nitrification processes and the mixing process has a major effect on NO 3 - transportation. Results of the Bayesian stable isotope mixing model show that the M&S and SON are the main NO 3 - source through the whole year (accounting for ~ 61% and 65% of the total NO 3 - in the wet and dry season, respectively), followed by CF (~ 29%). Furthermore, we find that nitrification of nitrogen in fertilizers, soil, and manure and sewage can promote the carbonate rock weathering. The estimated contribution of such nitrification to the weathering of carbonate rocks accounts for about 11% of the total carbonate rock weathering flux (calculated by HCO 3 - ) in the Lijiang River. This finding indicates that the weathering of carbonate rock is probably affected by nitrogen nitrification processes in karst catchment.

Central core disease is a rare inherited neuromuscular disorder caused by mutations in ryanodine receptor type 1 gene. The clinical phenotype of the disease is highly variable. We report a Chinese pedigree with central core disease confirmed by the gene sequencing. All 3 patients in the family presented with mild proximal limb weakness. The serum level of creatine kinase was normal, and electromyography suggested myogenic changes. The histologic analysis of muscle biopsy showed identical central core lesions in almost all of the muscle fibers in the index case. Exon 90-106 in the C-terminal domain of the ryanodine receptor type 1 gene was amplified using polymerase chain reaction. One heterozygous missense mutation G14678A (Arg4893Gln) in exon 102 was identified in all 3 patients. This is the first report of a familial case of central core disease confirmed by molecular study in mainland China.