Nitrate dynamics during impoundment and flood periods in a subtropical karst reservoir: Hongfeng Lake, Southwestern China.

Nitrogenous species, particularly nitrate, are some of the most significant contaminants in freshwater rivers and lakes in China, posing a significant threat to human and ecosystem health. To identify the major nitrate sources and transformation processes in a subtropical karst lake (Hongfeng, HF) in Southwest China, two sampling campaigns involving three lake profiles were conducted during the impoundment period (April) and flood period (August). Hydro-chemistry parameters, concentration of nitrogenous species, and dual isotopes of nitrate were analyzed. Nitrate was the major nitrogenous species in HF lake with higher proportion in April than August. The concentrations of NH4+, NO2- and dissolved organic nitrogen were below the detection limit in April, while NH4+ increased with depth in August, which may be a result of mineralization. Nitrification was detected during the impoundment period and from the surface to a depth of 10 m during the flood period. Denitrification was detected in the lake bottom waters during the flood period with isotopic fractionation of -10.7‰ for δ15N-NO3- and -4.7‰ for δ18O-NO3-. The Rayleigh distillation demonstrated denitrification showed spatial variation (53% and 89% of nitrate in the southern and northern region of the lake, respectively). The Bayesian modelling results suggest that organic nitrogen degradation and sediment make the largest contributions to nitrate (51% and 38% in April and 33% and 24% in August, respectively) to the lake. Tributaries contributed more nitrate in August (37%) than in April (10%). The results highlight that modified endogenous nitrogen contributed a high proportion of nitrate sources within the lake system during the two periods.

Lentzea guizhouensis sp. nov., a novel lithophilous actinobacterium isolated from limestone from the Karst area, Guizhou, China.

A novel filamentous actinobacterium, designated strain DHS C013(T), was isolated from limestone collected in Guizhou Province, South-west China. Morphological and chemotaxonomic characteristics of the strain support its assignment to the genus Lentzea. Phylogenetic analyses showed that strain DHS C013(T) is closely related to Lentzea jiangxiensis FXJ1.034(T) (98.7 % 16S rRNA gene similarity) and Lentzea flaviverrucosa 4.0578(T) (98.0 % 16S rRNA gene similarity), but it can be distinguished from these strains based on low levels of DNA:DNA relatedness (~44 and ~37 %, respectively). Physiological and biochemical tests also allowed phenotypic differentiation of the novel strain from these closely related species. On the basis of the evidence presented here, strain DHS C013(T) is concluded to represent a novel species of the genus Lentzea, for which the name Lentzea guizhouensis sp. nov. is proposed. The type strain is DHS C013(T) (=KCTC 29677(T) = CGMCC 4.7203(T)).

[Chemical characterization of rainwater in a karst rural site: a case study of Puding, China].

Rainwater samples of a karst rural site in Puding County, Guizhou Province, China over a period of one year (2008) were collected and the major ion concentrations were measured. The pH of samples varied from 4.6 to 7.1 and volume-weighted mean was 5.7. Ca2+ was the dominant cation in rainwater and volume-weighted mean was 303.2 microeq x L(-1). It accounted for 34%-88% of the total cations in the studied rainwater samples. SO4(2-) and NO3- were the main anions, and their volume-weighted mean were 281.2 microeq x L(-1) and 69.9 microeq x L(-1), respectively. The sum of SO4(2-) and NO3- accounted for 63%-93% of the total anions in the studied rainwater samples. Investigations of fractional acidity (FA), neutralization factors (NF), and correlation coefficients among ionic constituents indicated that high pH values were controlled by the neutralization caused by the alkaline materials but not by the absence of acidic materials. Studies of the origins of major ions showed that Ca2+ was from the terrestrial source, e. g. crustal dust and human activities, and NH4+ and K+ were from the soils and human acidities, while SO4(2-) and NO3- were mainly originated from anthropogenic sources.

Carbon biogeochemistry of ground water, Guiyang, southwest China.

Variations in the concentrations and isotopic compositions (delta13C(DIC)) of dissolved inorganic carbon (DIC) reflect contamination and biogeochemical cycling of the carbon in ground water. In order to understand contamination and biogeochemical cycling of DIC, we carried out research on the geochemistry of ground water of Guiyang, the capital city of Guizhou Province, China. Results show that ground water is mainly characterized by SO4.HCO3-Ca.Mg and HCO3-Ca.Mg chemical compositions. The hydrochemical characteristics of these types of water are mainly controlled by lithology of the aquifers. HCO3- is the dominant species of DIC in ground water and has lower concentrations and more negative values of delta13C(DIC) in the high-flow (summer monsoon) season, as compared to the low-flow season. This indicates that DIC is relatively enriched in carbon of biological origin in the high-flow season as compared to the low-flow season and that biological activities are the predominant control on shifts of stable carbon isotope values. The evidence that the delta13C(DIC) values of ground water decrease with increasing concentrations of anthropogenic species shows that the carbon isotopic composition of DIC can be a useful tracer of contamination, in addition to biogeochemical cycling of inorganic carbon in ground water. Results from this study show that ground water is impacted by significant levels of contamination from human activities, especially in the urban areas, as well as the northeast and west suburbs, in Guiyang city, southwest China.