Pollution status of the Yellow River tributaries in middle and lower reaches.

To determine the water quality status of the primary tributaries in middle and lower reaches of the Yellow River Basin, water collected from the confluence of the ten tributaries and some physical, chemical and biological parameters were analyzed, and then water quality index and health risk were evaluated. Of the ten main tributaries in the middle and lower reaches, only the Qingshui River had water of medium quality in the upper reaches, while all the other tributaries contributed water of poor quality. The Jindi and Dawen rivers in the lower reaches had the poorest water quality, especially the Jindi River. TP, TN, BOD5, COD, TOC and coliform bacteria exceeded the national criteria by 155%, 1%, 97.5%, 35.5%, 114.2%, and 80%, respectively. Cluster analysis indicated that industrial, agricultural, and domestic sewage, along with industrial waste gas, were the main sources of pollution in these tributaries. An analysis of the bacterial community structure showed that the Jindi River was the most polluted and had the largest species diversity and richness of bacteria. Also, its number of pathogenic microorganisms was much higher than that of other areas, and the bacterial functional genes of related metabolic pathways were significantly enriched. This was in sharp contrast with that of the Qingshui River, which had the best water quality. We suggest more specifics policy should be taken for different tributaries, and poor water quality of Jindi and Dawen River should be further studied to explore the most suitable pollution control methods.

Three kinds of ammonia oxidizing microorganisms play an important role in ammonia nitrogen self-purification in the Yellow River.

To develop the microbial resources of the Yellow River, seven water samples were collected along the Lanzhou region of the river from upstream to downstream for testing. Analysis of various physico-chemical indexes was conducted, and key parameters influencing the water quality were selected through principal component analysis, after which the decisive factors impacting water quality were determined by correlation and regression analysis. The results indicated that (1) DO, NH3-N, NO2--N, TN, TC, As, Cr6+ and Pb were the main physico-chemical factors influencing water quality in the Lanzhou region, with NH3-N having the greatest effect. (2) Ammonia-oxidizing microorganisms [ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and anaerobic ammonia-oxidizing bacteria (AMX)] were found to mediate the transformation of NH3-N in the studied section. AOA was the primary microbe community among the two aerobic ammonia-oxidizing microorganisms (AOA and AOB) in the Yellow River. (3) Phylogenetic analysis showed that there were some known groups, and there were still many unknown species in the water of the studied section, especially within the AMX population. (4) Correlation analysis revealed that AOA has strong adaptability to unhealthy environments, and that some environmental factors (higher concentrations of carbon, nitrogen and some heavy metals) could increase the AOA gene abundance. Overall, these results suggested there are rich ammonia-oxidizing microbial resources, especially AOA, in the Lanzhou section of the Yellow River, which have the potential for application in nitrogen sewage treatment.

Greater health risk in wet season than in dry season in the Yellow River of the Lanzhou region.

The Yellow River flows through Lanzhou city and is the only drinking water source for 3.6 million residents. Yet, little is known regarding the safety and quality of the Yellow River for resident consumption. To address this knowledge-gap, water samples were collected from different sites within this section during the dry and wet seasons. Physico-chemical parameters and microbial community metrics were analyzed to assess the health risk associated with this Chinese mother river. Water quality of the river was better during the dry season (March-April) than in the wet season (September-October). Fifteen conventional physico-chemical and biological indices, such as NH3-N, NO2--N, total nitrate (TN), five day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), volatile phenol (VP), and coliform abundances, generally exceeded acceptable standards. The average abundance of coliforms was 2.8 times that of acceptable standards in the dry season and 4.6 times the standards in the wet season. The concentration of the toxic metal As was more than two times than that of the national standard in waters from the wet season. Microbial community analysis also indicated that community diversity and species richness were positively correlated with the concentrations of several physico-chemical parameters. The results indicate that As and Cr6+ pose potential risk for human health through consumption by residents. Further, the results indicated that human activities are the main causes of water pollution, and that long-term strict monitoring should be conducted to ensure the safety of drinking water consumption and the health of the environment.