Per- and polyfluoroalkyl substances (PFAS) have become a well-known class of anthropogenic pollutants in coastal regions. It is known that PFAS primarily enter the sea from nearshore sources, dry deposition, and wet deposition. However, the contribution of offshore sources to PFAS pollution in the sea remains poorly understood. Our study aims to investigate the occurrence of 74 PFAS across 15 groups in a coastal region of eastern China and to characterize their spatial distribution by focusing on the critical roles of both nearshore and offshore sources. Results revealed that 26 PFAS were detected in the coastal region (i.e., Ou River and Wenzhou Bay), with detection frequencies ranging from 4.3% to 100.0%. Notably, over 10 PFAS were detected for the first time in the region, such as perfluorooctane sulfonamide (FOSA), hexafluoropropylene oxide dimer acid (HFPO-DA), and 6:2 fluorotelomer sulfonic acid (6:2 FTSA), among others. The concentrations of detected PFAS ranged from 0.0018 to 76.31 ng/L, with perfluorooctanoic acid (PFOA) as the dominant congener. Spatial analysis indicated that the nearshore area was more severely polluted compared to the offshore area, with specific hotspots identified near industrialized areas. However, the distribution of certain PFAS, such as perfluorobutane sulfonic acid (PFBS) and perfluoro-3,6-dioxaheptanoic acid (PFDHA), exhibited a contrasting pattern, with higher concentrations observed in the offshore area and near island perimeters. These findings suggest that PFAS pollution in Wenzhou Bay originates from both nearshore and offshore sources, highlighting a complex interplay between nearshore and island-related activities.

The spatial variability of soil NO⁻ ₃–N, NH⁺ ₄–N and total nitrogen (TN), which can be greatly affected by farmland use types, are vital for agricultural management and environmental protection. To data, only few studies have been down to investigate the spatial patterns of soil NO⁻ ₃–N, NH⁺ ₄–N and TN in topsoil and their relationships with vadose zone soil nitrogen and groundwater NO⁻ ₃–N under different types of farmland use (vegetable field, orchard and cropland). We collected 61 topsoil (0–25 cm) samples, 162 vadose zone (0–200 cm) soil samples and 35 groundwater samples from Haidian district of Beijing, China. Geostatistical method and ArcGIS were used to characterize and compare the spatial heterogeneities of topsoil NO⁻ ₃–N, NH⁺ ₄–N and TN and to study the nitrogen content relationships among topsoil, vadose zones and groundwater under different types of farmland use. The results indicated that the contents of topsoil NO⁻ ₃–N and NH⁺ ₄–N were normally distributed, while TN was lognormally distributed. Both topsoil NH⁺ ₄–N and TN showed moderate variability, while NO⁻ ₃–N showed strong variability under different types of farmland use. The greatest influence on soil NO⁻ ₃–N was from human activity like fertilization and irrigation. The type of farmland use had significant (P − ₃–N, NH⁺ ₄–N and TN contents in soils, and NO⁻ ₃–N concentrations in groundwater. The NO⁻ ₃–N content in topsoil and NO⁻ ₃–N concentration in groundwater under different types of farmland use showed the same descending order (vegetable field > orchard > cropland), and the soil NH⁺ ₄–N content showed the same descending order in topsoil and 0–200 cm vadose zone (cropland > orchard > vegetable). However, the soil TN content didn't follow that order. Vegetable fields had the highest N fertilizer rates, and consequently they also had the highest contents in topsoil and vadose zones and highest concentrations in groundwater. Thus, vegetable fields had the biggest pollution potential in groundwater. At last, a logarithmical relationship between NO⁻ ₃–N concentrations and groundwater depths was found in farmland areas. Taking environment and the types of farmland use into account, we propose sandy areas and areas without water-resisting soil layers are not suitable for planting vegetables.

Rainfall-driven non-point source (NPS) pollution has become a critical issue for water environment management in urban watershed systems. However, single-model use is limited to fully represent the intricate processes of rainfall-correlated NPS pollution generation and dispersion for effective decision-making. This study develops a novel cross-scale, multi-factor coupled model framework to characterize hydrologic and NPS pollution responses to different rainfall events in Shenzhen, China, a representative worldwide metropolis facing challenges from rapid urbanization. The calibrated and validated coupled model achieved remarkable agreements with observed hydrologic (Nash–Sutcliffe efficiency, NSE > 0.81) and water quality (NSE > 0.85) data in different rainfall events and demonstrated high-resolution dynamic changes in flow and pollutant transfer within the studied watershed. In an individual rainfall event, heterogeneous spatial distributions of discharge and pollutant loads were found, highly correlated with land use types. The temporal change pattern and risk of flooding and NPS pollution differed significantly with rainfall intensity, and the increase in the pollutants (mean 322% and 596%, respectively) was much larger than the discharge (207% and 302%, respectively) under intense rainfall conditions. Based on these findings, a decision-support framework was established, featuring land-use-driven spatial prioritization of industrial hotspots, rainfall-intensity-stratified management protocols with event-triggered operational rules, and integrated source-pathway-receiving end intervention strategies. The validated model framework provides quantitative guidance for optimizing infrastructure design parameters, establishing performance-based regulatory standards, and enabling real-time operational decision-making in urban watershed management.

Long-term irrigation with reclaimed water may change soil physical properties and solute transport rate due to C and N in reclaimed water and the particularity of reclaimed water. Ordinary water, reclaimed water and mixed water which added C and N into reclaimed water were used as background water, then potassium bromide was added to background water and mixed them into three kinds of solutions whose bromide concentrations were all 0.5 mol/L, then soil column breakthrough experiments were conducted. The results showed that bacteria quantity increased both in sandy soil and loam after soil column experiments, and bacteria quantity in sandy soil and loam were all in the following descending order: breakthrough solution using mixed water as background water, breakthrough solution using reclaimed water as background water, and breakthrough solution using ordinary water as background water. However, fungi quantity had no significant difference. Cumulative infiltration in sandy soil and loam can be properly described by power function and logarithm function, respectively. The amount of cumulative infiltration in sandy soil and loam in the same infiltration time were all showed a descending order as: breakthrough solution using ordinary water as background water, breakthrough solution using reclaimed water as background water, and breakthrough solution using mixed water as background water. Breakthrough curves can be well described by CXTFIT 2.1 code, it can be seen from the values of V and D that reclaimed water and the addition of C and N made solute transport more difficult in soils and increased diffusion coefficient, and these impacts were greater on loam than sandy soil. Reclaimed water and the added C and N increased soil bacteria, complicated soil pore system, and decreased soil hydraulic conductivity.