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Objective: This study investigated the relationships between PM2.5 and 5 criteria air pollutants (SO2, NO2, PM10, CO, and O3) in Heilongjiang, China, from 2015 to 2018 using global and geographically and temporally weighted regression models. Methods: Ordinary least squares regression (OLS), linear mixed models (LMM), geographically weighted regression (GWR), temporally weighted regression (TWR), and geographically and temporally weighted regression (GTWR) were applied to model the relationships between PM2.5 and 5 air pollutants. Results: The LMM and all GWR-based models (i.e., GWR, TWR, and GTWR) showed great advantages over OLS in terms of higher model R2 and more desirable model residuals, especially TWR and GTWR. The GWR, LMM, TWR, and GTWR improved the model explanation power by 3%, 5%, 12%, and 12%, respectively, from the R2 (0.85) of OLS. TWR yielded slightly better model performance than GTWR and reduced the root mean squared errors (RMSE) and mean absolute error (MAE) of the model residuals by 67% compared with OLS; while GWR only reduced RMSE and MAE by 15% against OLS. LMM performed slightly better than GWR by accounting for both temporal autocorrelation between observations over time and spatial heterogeneity across the 13 cities under study, which provided an alternative for modeling PM2.5. Conclusions: The traditional OLS and GWR are inadequate for describing the non-stationarity of PM2.5. The temporal dependence was more important and significant than spatial heterogeneity in our data. Our study provided evidence of spatial–temporal heterogeneity and possible solutions for modeling the relationships between PM2.5 and 5 criteria air pollutants for Heilongjiang province, China.

Water is an indispensable commodity for the survival of all living beings and for their well-being. The objective of this work is to evaluate the level of pollution of different drinking water sources consumed and its link with health in Pelengana commune, Mali. Samples of water were taken from various sources, namely, hand pumps, boreholes, dug wells, and shallow wells for physical, chemical, heavy metals, and bacteriological analyses, using American Public Health Association (APHA) Standard Techniques. Results revealed that the nitrate-nitrogen (NO3−N) values of the water samples from the different water sources had concentrations exceeding the United States Environmental Protection Agency's (US-EPA) regulation of 10 mg/L, as well as World Health Organization Guideline for Drinking Water Quality (WHO GDWQ) (11 mg/L). The same applies to heavy metals such as Cd, Pb, and Fe, in which, concentrations exceed their allowable limits in certain locations. Moreover, apart from water samples from some different boreholes, total coliform, and Escherichia coli have been detected in all selected water sources, which indicates fecal contamination. In all, there is a pressing need to stop the consumption of drinking water from contaminated sources and to effect appropriate treatment.

Many studies have well reported nutrient deficiency and soil degradation focusing on soil N in pure plantations. However, few papers focused on soil P deficiency during pure plantation afforestation. We examined the variations in P fractions and phosphatase (P‐ase) activities in the rhizosphere and bulk soils in Larix olgensis plantations of 16, 23, 34, and 49 y. Correlation analysis was applied to identify the relationships between available P and other P fractions and P‐ase activities in the rhizosphere soil at different developmental stages. The stepwise regression models were established to explore their relationships with tree growth. The results showed that the deficiency of available P occurred in the rhizosphere micro‐region relative to the bulk soil in the 34‐ and 49‐y‐old stands, which was related to the lower acid phosphatase activity, the deficient Fe‐bound P, and occluded phosphate, as well as to soil pH in the rhizosphere soil during these periods. In addition, tree growth in the young and near‐mature stands was significantly correlated with soil P fractions, and the main P fractions closely related to tree growth were total P, organic P, available P and inorganic P, followed by Ca‐bound P and Fe‐bound P. The decreases in average DBH and average height growth in the near‐mature stand were related to the deficiency of available P in this period. Our results indicate that the development of Larix olgensis plantations affects the bioavailability of P through dynamic changes of P fractions and P‐ase activities, which provides a theoretical base in future afforestation with Larix olgensis plantations.

Microenvironmental heterogeneity of soil physical properties in 0-20 cm and 20-40 cm soil layers in a broad-leaved Pinus koraiensis forest gap in Xiao Xing'anling Mountains were analyzed by geostatistical method. The results show that the amount of soil water, saturation water capacity, capillary water capacity and porosity in the top layer were greater than those in the lower layer, except for bulk density, where the opposite applied. Soil physical properties in the top soil layer had relatively higher ranges and coefficients of variation. The total and auto correlation spatial heterogeneity of soil physical properties in the top layer were larger than those in the lower layer. The soil water had a strong anisotropic structure in an easterly and northerly direction, but porosity shows isotropy in the same directions. With increasing spatial distance, the other three physical factors exhibited anisotropic structures. The mutual effect between semi-variograms of soil physical properties in the top layer within the spatial autocorrelation range was not significant. For spatial distribution of physical properties within different layers, the patches at the middle and lower ranks in the forest gap dominated. Patches at higher rank were only distributed in the 0-20 cm soil layer and were located north of the forest gap center.