No abstract

Unsaturated flow is an important factor that affects groundwater motion. Among various drainage models, the nonlinear Hillslope-storage Boussinesq (HSB) model has been commonly used to predict water flux along a slope. In this study, we improved this model by considering lateral flow in the unsaturated zone. Using modified van Genuchten functions, we analytically expressed the concept of equivalent propagation thickness in the vadose zone. This analytical expression was then incorporated into the HSB model to reflect two different stages of the drainage process and to simulate the hillslope drainage process more accurately. The model results indicated that lateral flow has significant effects in the unsaturated zone during the hillslope drainage process. Even in sandy aquifers, the amount of water contributed by the unsaturated zone is a key factor that enables a decrease in the water table during the middle and late stages of the process. A comparison between the measured and simulated results based on both convergent-type and divergent-type hillslope drainage processes revealed that the thickness of the saturated zone decreases as the unsaturated flow increases. This study emphasizes the necessity of considering unsaturated flow in the HSB model to improve the accuracy of predicting groundwater outflow rates and develop more accurate hydrographs. The concept of equivalent propagation thickness also provides a criterion for assessing the importance of unsaturated lateral flow for future drainage research.

Recession flow analysis is usually conducted to infer hydraulic parameters of hillslope aquifers. Various Boussinesq equation‐based models, both linear and nonlinear, have been used to analyze the recession curves for sloping aquifers, with a focus on the long‐time recession behavior. Based on a modified Boussinesq equation with capillarity incorporated, we demonstrate the significant effect of unsaturated flow on the recession curve, which result in three (instead of two) power law regimes with two transition points (instead of one) corresponding to the formation of a fully unsaturated zone at the adjacent area of the upslope boundary and across the whole domain, respectively. The results show that the power of the second and third recession regime is variable, depending on the slope angles, soil types, and hillslope geometries. The unsaturated flow effects also lead to the absence of drastic drop of −dQ/dt at the transition between the first and second regime, which was predicted by previous numerical models but has not been observed in the field or laboratory experiments. These findings have important implications for recession flow analysis in studies of hillslope aquifers.

No abstract

No abstract

No abstract

Global-change drivers that alter tidal amplitude or sea level could directly impact coastal aquifers' seawater-microbe interactions. The semidiurnal or diurnal tide can have consequences for chemical redistribution, because it deepens oxygen and nutrients penetration depth, thereby increasing O 2 depletion via microbial respiration in sediments during groundwater circulation. However, chemical and microbial distributions in tidal aquifers remain unclear, in deference to their link with depth and lateral location. By combining the microbes-accumulated equation with the traditional groundwater flow model in coastal aquifers, we explicitly unravelled the heterotrophic zonation, the salinity zonation, and the oxic zonation of tidal aquifers. According to the model estimates, salt penetrates deeper than reactive chemicals, and the heterotrophic high biomass zone is presumably 2-3 m deep. Such depth of heterotrophic distribution is 2-3 orders of magnitude higher than phototrophic distribution.Additionally, heterotrophic biomass can exhibit faint oscillations, even under the tide forces, whereas dissolved chemicals fluctuate significantly with tidal pumps. Due to

A novel mechanism-based fluorescent probeRhod-CHOwhich involved the initial nucleophilic addition of H2S to aldehyde followed by the subsequent intramolecular nucleophilic addition process.