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Wetlands are sensitive, easily disturbed, and globally important ecosystems which face lots of threats, such as global climate change and local human activities. Those might result in the degradation of wetlands. The relationship between hydrological connectivity and the degradation of wetlands has gained prominence among researchers as a simple way to quickly evaluate the degradation of wetlands. This metric is responsive to preferential flow, which can, to some extent, indicate hydrological connectivity. To quantify hydrological connectivity at soil column scales, we explored the relationships between soil properties and the strength of preferential flow in samples from a degrading wetland in which Chinese tamarisk (Tamarix chinensis Lour.) grow in the Yellow River Delta. We conducted laboratory solute penetration tests through the undisturbed soil sample columns and analyzed the relationship between the solute penetration test results and preferential flow. We then verified the applicability of the dual-permeability model to predict the results of the solute penetration test. Our results revealed that the discharge rate from the soil columns was the highest in samples from 20 to 40 cm soil depth and that the flow of discharge concentration remained stable for a long time before increasing rapidly, which exhibited rich medium porosity and macroporosity. We associated this with some improvement in hydrological connectivity, which was also consistent with our dual-permeability simulation results. In the future experimental operation, we can preliminarily predict the hydrological connectivity and preferential flow intensity of soil column by using the dual-permeability model with the discharge data of solute penetration test, which can help us know quickly to what extent are wetlands degraded.

Atmospheric particulate matter is a wide-ranging environmental pollutant that can cause serious harm and poses a serious threat to public health. In this study, the near-surface particulate matter removal ability was quantitatively analyzed and compared for different land types under different pollution levels. The results showed that the concentrations of particulate matter 10 μm or less in diameter (PM10) and 2.5 μm or less in diameter (PM2.5) were higher in the morning and lower in the afternoon and that the seasonal variation was autumnwinterspringsummer at a forest site. The diurnal concentration of particulate matter at a wetland site decreased continuously, with a seasonal variation of winterautumnspringsummer. The annual variation in the particulate matter concentration was higher in 2017 than in 2016 at both the forest and wetland sites. Forests remove particulate matter via plant leaves and root absorption, and wetlands rely on the enhancement of the relative air humidity to promote the absorption and accumulation of particles. For different air pollution levels, the deposition flux of PM2.5 increased with the pollution gradient. For the same air quality pollution level, the deposition flux of PM2.5 at the forest site was approximately 1.29 times higher than that at the wetland site. Data concerning PM10 in forests and wetlands are lacking. The results show that the deposition effect of the forest on particulate matter was better than that of the wetland.

Due to human activity and global climate change, the Yellow River Delta, the youngest delta wetland in China, is suffering serious degradation. The study of hydrological connection provides new perspectives and technical support for the protection and restoration of delta wetlands. To quantify the interaction between the hydrological connection and the root–soil complex, the current study took dye-tracing experiments to examine the small-scale hydrological connectivity in soil where Phramites australis grew. The dye coverage was selected as the indicator of hydrological connectivity after preliminary analysis in this study. The main results were that (1) the strength of hydrological connectivity was negatively related to the microaggregates content, but had little to do with other soil physical properties; (2) there was a notable positive correlation between the indexes of thick root (D > 5 mm) and the dye coverage hydrological connectivity, while root biomass had little effect on hydrological connectivity; and (3) the influence of the microaggregate content dominated in the combined effect of the total surface area of the root (D > 5 mm) and the microaggregate content on hydrological connectivity in each soil layer.