Controlling factors and health risks of groundwater chemistry in a typical alpine watershed based on machine learning methods.

Groundwater is a key water resource in alpine watersheds, but its quality is deteriorating due to human activities. The Golmud River watershed is a representative alpine watershed in Northwest China, and it was chosen to explore groundwater chemistry, associated controlling factors, source contributions, and potential health risks. The analysis includes the use of a self-organizing map (SOM), positive matrix factorization (PMF), ionic ratios, and a Monte Carlo simulation. The content of total dissolved solids in phreatic water was higher in the dry season and increased from the mountainous zone to the fine-soil plain-overflowing zone. Additionally, the water type varied from HCO3- to Cl- types whereas confined groundwater was chemically stable and of a HCO3- type. The SOM results showed a visual correlation between the ions in groundwater. The combination of SOM, PMF, and ionic ratios identified water-rock action as a dominant factor of groundwater chemistry. It was also found that Clusters I and III were mainly influenced by silicate weathering (a total contribution of 38.4 %), whereas evaporation was dominant in Cluster VI (a contribution of 32.5 %). Anthropogenic pollution was mainly associated with clusters V and IV and was related to industrial and agricultural activities during the snowmelt and wet seasons, and fluorine deposition formed by residential coal heating during the dry season (contributions of 1.4 % and 23.8 % in Clusters V and IV, respectively). The sudden increases in B3+ and Li+ in Cluster II were due to inputs from small tributaries (a contribution of 3.9 %). The probabilistic health risk assessment showed that fluoride posed a greater non-carcinogenic risk to human health than Sr2+, B3+, and NO3-, and its potential threat to children was more significant during the dry season than in other seasons. It is necessary for local governments to establish urgent fluoride emission control policies within the Golmud River watershed.

Total sediment transport from an urbanizing watershed in the upper Yellow River, China.

For many event-based, high-sediment yield rivers draining arid zones, where erosion activities in the watershed and fluvial erosion in the stream channel are nearly equally important in sediment transport, determination of fluvial sediment dynamics are of great importance in establishing reliable strategies to manage environmental changes in watershed scale. Wash load rating curve indicating watershed characteristic changes and Ackers and White's bed load function (wash load excluded) used for determining bed load transport dynamics are distinguished for the first time to recognize the true sediment transport mode in the lower Huangshui River, which is the largest tributary of the upper Yellow River, contributing a lot to the wash load of the Inner Mongolia desert reach of the Yellow River and causing complicated water-sediment response. Based on the continuous and detailed hydrological data monitored at the Minhe gauge station, our results indicated that the sediment transport regime has altered since the 1980s in response to the eco-environmental changes mainly due to urbanization, with suspended sediment concentration (SSC) decreased by 50% on average compared with the natural state (1950-1980). The combined use of wash load rating curve and theoretical bed load function derived an estimate of total sediment transport due to comprehensive ecological management since the 2000s to be 3.43 × 107 t for the lower Huangshui River, among which the total bed load is 1.40 × 107 t, and the wash load is 2.03 × 107 t. The transport ratio of wash load to total bed load is 1.45:1.

Gaseous and particulate air pollution in the Lanzhou Valley, China.

Gaseous and particulate matter measurements were performed from January 1999 to December 2001 to assess seasonal and diurnal patterns of air pollutions in the Lanzhou Valley, China. The objectives are the determination of the temporal variability of total suspended particulate (TSP) matter and PM10 levels, and their relationship with the SO2 and NOx emissions and desert dust intrusions from the dust sources in the Hexi Corridor in Gansu Province. The results showed that concentrations of gaseous and particulate pollutants undergo seasonal variations characterized by a winter maximum levels for SO2 (0.094-0.208 mg/m3) and NO2 (0.068-0.089 mg/m3) and a spring maximum levels for TSP (0.885-1.037 mg/m3). Linear regression analysis indicated that the diurnal mean TSP/PM10 ratio may approximate to 3.0, and that the annual NO2/NOx ratio was approximately 0.86, with its highest monthly average of 0.91 in June and its lowest monthly average of 0.788 in January. The origin of PM10 episodes was investigated by correlating the PM10 episodes in the Lanzhou Valley with the high wind speeds in Jinchang (dust sources) in the Hexi Corridor, and also, by comparing the PM10 levels with the SO2 and NOx concentrations. Most of the 'high PM10 episodes' (1-h mean maximum >1.0 mg/m3) were attributed to the desert dust intrusions from the Hexi Corridor. The influence of the industrial and domestic emissions in the PM10 levels was evidenced during most of the periods with the PM10 levels less than 1.0 mg/m3.