[Effect of hydrochemistry characteristics under impact of human activity: a case study in the upper reaches of the Xijiang River basin].

In this paper, observation and sampling were taken three times a month in a hydrological year for three typical sections of the middle and upper reaches of the Xijiang River basin, based on the data of hydrochemistry and flow, the article mainly discusses the evolution process of hydrochemistry in river under natural process and impact of human activity. Hydrochemical characteristics of 116. samples were analyzed in the study area. The hydrochemistry type in the middle and upper reaches of the Xijiang River basin belonged to HCO3- -Ca2+ type, and the chemical weathering type mainly came from carbonate rock weathering. Ca2+ and HCO3- were the main cations and anions, which reflected that hydrochemical characteristics of river in karst area mainly affected by the dissolution of carbonate rock. Na, Mg2, Ca2+ and Cl- mainly affected by natural conditions, the impact of human activity was little. K+, NO3-, SO4(2-) and HCO3- were affected by human activity in different degrees, and it showed different influence ways. This study had an important significance for the change of river hydrochemistry, water quality characteristics, and the effect on substance transported fluxes in the downstream of Pearl River and water quality protection in South China Monsoon Area.

Radiation induces acid tolerance of Clostridium tyrobutyricum and enhances bioproduction of butyric acid through a metabolic switch.

BACKGROUND: Butyric acid as a renewable resource has become an increasingly attractive alternative to petroleum-based fuels. Clostridium tyrobutyricum ATCC 25755T is well documented as a fermentation strain for the production of acids. However, it has been reported that butyrate inhibits its growth, and the accumulation of acetate also inhibits biomass synthesis, making production of butyric acid from conventional fermentation processes economically challenging. The present study aimed to identify whether irradiation of C. tyrobutyricum cells makes them more tolerant to butyric acid inhibition and increases the production of butyrate compared with wild type. RESULTS: In this work, the fermentation kinetics of C. tyrobutyricum cultures after being classically adapted for growth at 3.6, 7.2 and 10.8 g·L-1 equivalents were studied. The results showed that, regardless of the irradiation used, there was a gradual inhibition of cell growth at butyric acid concentrations above 10.8 g·L-1, with no growth observed at butyric acid concentrations above 3.6 g·L-1 for the wild-type strain during the first 54 h of fermentation. The sodium dodecyl sulfate polyacrylamide gel electrophoresis also showed significantly different expression levels of proteins with molecular mass around the wild-type and irradiated strains. The results showed that the proportion of proteins with molecular weights of 85 and 106 kDa was much higher for the irradiated strains. The specific growth rate decreased by 50% (from 0.42 to 0.21 h-1) and the final concentration of butyrate increased by 68% (from 22.7 to 33.4 g·L-1) for the strain irradiated at 114 AMeV and 40 Gy compared with the wild-type strains. CONCLUSIONS: This study demonstrates that butyric acid production from glucose can be significantly improved and enhanced by using 12C6+ heavy ion-irradiated C. tyrobutyricum. The approach is economical, making it competitive compared with similar fermentation processes. It may prove useful as a first step in a combined method employing long-term continuous fermentation of acid-production processes.