Distribution and speciation of arsenic in seasonally stratified reservoirs: Implications for biotransformation mechanisms governing interannual variability.

HPLC-ICPMS was used to analyze the spatiotemporal variation of As species in different sections and tributaries of the Aha Reservoir over four seasons, and the migration and transformation mechanisms were clarified by combined analysis of hydrochemical parameters and microbial composition. The results showed that the internal release of As from the reservoir sediments is mainly due to the reduction of iron oxide and the release of adsorbed As(V). The average proportion of As(III) increased from 27.2% in autumn to 46.5% in summer, 68.9% in winter, and up to 70.8% in spring. In spring and summer, the high concentration of As(III) and organic arsenic in the epilimnion under phosphorus restriction was caused by the reductive metabolism of phytoplankton after intake of As(V). The arsenic species in the metalimnion were mainly affected by the oxidation-reduction potential (ORP). In summer and autumn, As-oxidizing bacteria used As(III) as an electron donor, and nitrate played an important role as an electron acceptor, maintaining the dominance of As(V) in the hypolimnion. However, in winter and spring, temperature-controlled ORP was the main process, which was dominated by As(III). In conclusion, As species show annual cycles in different layers of seasonally thermal stratified reservoirs. It provides a systematic mechanism of As species transformation in reservoirs, especially the effect of biological transformation mechanism.

Effects of mineral salt supplement on enteric methane emissions, ruminal fermentation and methanogen community of lactating cows.

We evaluated the effects of mineral salt supplement on enteric methane emissions, ruminal fermentation and methanogen community of dairy cows over a whole lactation period. Ten Holstein cows fed a total mixed ration (TMR) diet were randomly allocated into two groups, one supplied with mineral salts as the treatment group and the other as the control group. The methane measurement showed that the ingestion of mineral salts lowered enteric methane emissions significantly (P < 0.05), with an average of 10.5% reduction over the whole lactation period. Ruminal fermentation analysis showed the mineral salt intake could significantly decrease the acetate : propionate ratio (P < 0.05). Real-time PCR assay showed that rumen methanogen abundance significantly reduced in the treatment group (P < 0.05) but was not significantly influenced by mineral salt intake over the whole lactation period. Intergroup methanogen community composition was influenced slightly by mineral salt intake; however, significantly different intragroup profiles were apparent throughout the whole lactation period, according to denaturing gradient gel electrophoresis analysis. In conclusion, these results suggested that the effective mitigation of enteric methane emissions by mineral salt intake could be attributed to decreased density of methanogenic archaea and that fluctuations in methane emission over the lactation period might be related to Methanobrevibacter diversity.

Effect of Tai Chi on muscle strength of the lower extremities in the elderly.

OBJECTIVE: Aging is associated with a progressive decline in muscle strength, muscle mass and impaired physical function, which reduces mobility and impairs quality of life in the elderly population. The 6-12 months of exercise can enhance the muscle strength, but these improvements can only be maintained for a short period. In this study, we investigated the effects of long-term Tai Chi (TC) exercise on muscle strength of lower extremities. METHODS: A cross-sectional study was conducted in 205 long-term TC practitioners (age: 60-89 years) and 205 age and gentle matched controls who did not practice TC. Each of the activity group was further divided into three distinct age groups: G1, 60-69 years; G2, 70-79 years; and G3, 80-89 years. Hand-held dynamometery was used to measure the maximum isometric strength of iliopsoas, quadriceps femoris, tibialis anterior and hamstrings in both sides of the participants. Unpaired t tests were performed to compare the difference of strength between the TC and non-Tai Chi (NTC) groups. Multivariate analysis of variance (MANOVA) was used to compare the lower muscle strengths among the different age groups in the TC and NTC groups. Pearson's correlations were used to quantify the linear relationship between the months of TC practice and lower limbs muscle strength. RESULTS: The inter-rater reliabilities of iliopsoas, quadriceps femoris, tibialis anterior and hamstrings were intraclass correlation coeffificient (ICC) (1,1) = 0.895 (0.862-0.920), ICC (2,2) = 0.905 (0.874-0.928), ICC (3,3) = 0.922 (0.898-0.941) and ICC (4,4) = 0.930 (0.908-0.947). The strength of the muscles in the TC group did not differ among different age groups (P>0.05). The strength of iliopsoas, quadriceps femoris, tibialis anterior and hamstrings in TC group was higher than that in the NTC group (P<0.05). A correlation between muscle strength and extension of the exercise period was positive (P<0.05). CONCLUSIONS: Results shed light on the orientation and magnitude of long-term TC in preventing muscle strength loss with aging. TC might be a good form to slow down the trend of age-related decline in muscle strength in community-dwelling population.