The weakened connectivity of wetland systems is the key factor leading to the destruction, degradation, and disappearance of wetlands. The study of the change of wetland system connectivity enables understanding the hydrological process in wetland system and providing significant support for the study of ecological water demand. However, research on the connectivity of wetland systems has primarily focused on the intuitive connectivity in terms of hydrology and geomorphology in recent years, while the impact of wetland systems on habitat has been ignored. In this study, an innovative method was applied to evaluate and regulate the stereoscopic spatial connectivity (SSC) of the wetland system in the Heilongjiang River Basin in China (HRBC). In this method, the water requirements of typical organisms in the region were considered, and the hydrological trend in the wetland system as well as the health conditions of the SSC were analyzed using remote sensing image. A regulation mode for improving the stereoscopic spatial connectivity index (SSCI) was proposed. The results revealed that over the past 35 years, the wetland system in the study area shrank significantly, with the SSCI decreasing from 41.30% in 1980 to 35.08% in 2015. By comparing the correlation among temperature, precipitation, agricultural land, construction land, and the wetland system during the same period, it was proven that human activity is the major driving force behind the observed wetland system shrinkage. Subsequently, the key protected areas required to maintain the SSC of the wetland system were clarified, and the key recovery areas were determined according to the three scenarios of ‘high–medium–low’ feasibility, which greatly improved the SSCI and generalization route (GR) after regulation. In general, the proposed SSC evaluation methods can fully reflect the ecohydrological process of wetland systems. The methods also scientifically quantify the significant effects of the regulation mode, which has certain relevance for the evaluation and regulation of wetland systems in other regions.
Taking hydrophilic and water-repellent soils from the Guishui River Basin as the research object, one-dimensional infiltration experiments were conducted to study the effects of soil water repellency on cumulative infiltration (CI) and the infiltration rate (IR). The test results show that, for the hydrophilic soil (HS) sample, the CI increases monotonously with time and the IR decreases monotonously. For the water-repellent soil (W-RS), however, the following characteristics were observed: (1) There is an inflection point in the CI and a sudden increase in IR. Larger values of the initial soil water content produce an earlier and more significant inflection point in CI, and a larger peak value of IR. (2) The post-peak stable IR is greater than that the pre-peak value, ignoring the beginning of rapid infiltration, and the overall IR presents a single peak. The applicability of various water infiltration models was analyzed for the two soil types. Numerical analysis suggests the following conclusions: (1) For both HS and W-RS, the Kostiakov function, Gamma function, and Beta function (BF) models exhibit good applicability. (2) For W-RS, the Gauss function model not only reflects the monotonous decrease in IR, but also produces a steady IR in the initial stage, a gradual increase before the peak value, and a gradual decrease after the peak value. Similarly, the BF model reflects the monotonous decrease in IR. A piecewise BF can also reflect the U-shaped change in rapid infiltration before the inflection point, as well as the gradual increase and right-skewed distribution curve of W-RS infiltration before and after the inflection point. The BF model achieves the best simulation accuracy and has the widest applicability.