Trace metals in street dust originate from many natural and anthropogenic sources and may directly or indirectly affect daily life and health. Here, the enrichment factor (EF), an efficient parameter to assess the contamination by trace metals, was evaluated and compared in four different zones of the urban area of Nanchang city during different seasons. Results showed that EFs of trace metals have regional seasonal variations. The EF range of Cr, Ni, Cu, Zn, As, Cd and Pb were found to be (0.76-16.38), (0.66-9.06), (1.09-169.58), (1.52-36.16), (0.44-7.17), (2.07-78.38), (0.95-20.94), respectively. These values indicate minimal to significant pollution. The EF values of Zn, Cd and Pb in street dust show very similar variations as their median and mean values of EF are higher in certain zones, and their seasonal variations are similar. The Ni and As results suggest that anthropogenic influences for these elements are not significant. The Ni may be influenced by land use type rather than point sources and As may be attributed to natural sources. The Principal Component Absolute Scores - Multivariate Linear Regression (PCAS-MLR) model was used to identify the types and contributions of trace metal sources. The main sources of trace metals in dust were found to be industrial discharges and traffic emissions. However, the percentages of their contributions have significant regional differences. The relationship between the EF of trace metals and the ecological risk index (ERI) was also investigated, and indicates that seriously polluted areas correspond to high ERI regions. The land use types and characteristics of the source jointly affects the relationship between EFs and ERI.

Soil microbes play a crucial role in ecosystem function. Here, the effects of soil and water conservation measures on soil microbial community structures, biodiversity, and co-occurrence networks are investigated and compared. We sampled soils at three different depths (0–10 cm, 10–20 cm and 20–40 cm) in a citrus orchard that uses long-term soil and water conservation measures, which includes Bermuda grass strip intercropping (BS), Bermuda grass full coverage (BF), Radish–soybean crop rotation strip intercropping (RS) and clear tillage orchards (CT). Results demonstrated that BS and BF yields a significant increase in bacterial richness and diversity of fungal in soils, while BF contains more beneficial microbial taxa, especially those with degrading and nutrient cycling capabilities. Microbial community structures differed significantly among the applied measures. In addition, co-occurrence networks under BS, BF and RS were more complex and robust than that of CT, and the stability of the network in BF was the highest. Microbial interactive stability and potential interactions in bacterial networks were stronger than those of fungi. The distribution of dominant phyla showed that Chloroflexi and Ascomycota dominated the different soil and water conservation measures. Proteobacteria and Ascomycota are revealed to be keystone species in bacterial networks and fungal networks, respectively, while Proteobacteria was the keystone species in microbial networks. Though the relative abundance of Chloroflexi turned out to have increased among the four measures, the relative abundance for Proteobacteria, Acidobacteria and Actinobacteria all decreased along the soil profile, with Acidobacteria under BS to be an exception. Soils under BS and BF had higher total nitrogen, microbial biomass carbon and organic carbon than CT and RS. Organic carbon(C) and total nitrogen(N) in soil were the major drivers of these bacterial community patterns, while there was no significant correlation between them and fungi. Overall, BF increases soil nutrients and microbial diversity, and also promotes ecological stability and interrelations among microbial taxa that collectively improve soil quality in the citrus orchard studied. Therefore, we recommended BF to be an ideal application for citrus orchards of southeast China.