Atmospheric nitrogen deposition is of great concern to both air quality and the ecosystem, particularly in northern China, which covers one-quarter of China’s cultivated land and has many heavily air polluted cities. To understand the characteristics of wet N deposition at rural sites in northern China, one-year wet deposition samples were collected in the Daheitin reservoir region. Due to the intense emissions of gaseous nitrogen compounds from heating activities during cold seasons and distinct dilution effects under different rainfall intensities and frequencies, the volume weighted mean concentrations of wet N deposition showed higher levels in dry seasons but lower levels in wet seasons. In contrast, the wet N deposition rates varied consistently with precipitation, i.e., high during the wet season and lower during the dry season. The annual wet deposition rate of total inorganic ions (the sum of NO₃⁻–N and NH₄⁺–N) at the rural site in North China from July 2019 to June 2020 was observed at 18.9 kg N ha⁻¹ yr⁻¹, still remained at a relatively high level. In addition, biomass burning activities are ubiquitous in China, especially in northern China; however, studies on its impact on wet N deposition are limited. Non-sea salt potassium ion (nss-K⁺) was employed as a molecular tracer to investigate the characteristics of biomass burning activities as well as their impact on the chemical properties of wet N deposition. Three precipitation events with high nss-K⁺ levels were captured during the harvest season (June to July). The variations in the patterns of nss-K⁺, deposited N species, and ratios of nss-K⁺ to nitrogen species as well as their relationships all indicated that biomass burning emissions contributed remarkably to NO₃⁻–N but had a minor influence on NH₄⁺–N.

Microplastics (MPs) in the water environment pose a potential threat to aquatic organisms. The Species Sensitivity Distribution (SSD) method was used to assess the ecological risks of microplastics on aquatic organisms in this study. However, the limited toxicity data of aquatic organisms made it impossible to derive water quality criteria (WQC) for MPs and difficult to implement an accurately ecological risk assessment. To solve the data gaps, the USEPA established the interspecies correlation estimation (ICE) model, which could predict toxicity data to a wider range of aquatic organisms and could also be utilized to develop SSD and HC₅ (hazardous concentration, 5th percentile). Herein, we collected the acute toxicity data of 11 aquatic species from 10 families in 5 phyla to fit the metrical-based SSDs, meanwhile generating the ICE-based-SSDs using three surrogate species (Oncorhynchus mykiss, Hyalella Azteca, and Daphnia magna), and finally compared the above SSDs, as well as the corresponding HC₅. The results showed that the measured HC₅ for acute MPs toxicity data was 112.3 μg/L, and ICE-based HC₅ was 167.2 μg/L, which indicated there were no significant differences between HC₅ derived from measured acute and ICE-based predicted values thus the ICE model was verified as a valid approach for generating SSDs with limited toxicity data and deriving WQC for MPs.

As a new type of water source, reclaimed water is used to replenish the landscape water bodies of urban river courses, which can alleviate the problem of insufficient water in river courses. However, due to the large amount of reclaimed water input, the water quality of the downstream river is obviously different from that of the upstream river. In this study, with the recharge of reclaimed water, the water conductivity increased gradually from upstream to downstream of the Wenyu River river, while the pH decreased gradually. In terms of nutrient concentration, TN, NO₃-N and NO₂-N of river water showed an obvious upward trend from upstream to downstream.