Hydrological connectivity assessment based on solute penetration

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.