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Growing demands on water supply worldwide have resulted in aquifer overdraft in many regions, especially in alluvial basins under intensive irrigation. This further leads to serious deterioration of groundwater quality. Managed aquifer recharge (MAR) has been shown to mitigate groundwater overdraft, but whether MAR can actually stabilize or reverse the ongoing declines in regional groundwater quality caused by non-point sources has not been demonstrated. This study was intended to address the question by investigating impacts of different MAR strategies on regional groundwater quality. A geostatistical model was first used to characterize a heterogeneous alluvial aquifer system in a portion of the Tulare Lake Basin. Three-dimensional numerical models were then employed to simulate groundwater flow and mass transport. Next, MAR strategies were applied in locations with different geological conditions or joint with different irrigation activities, and their performances were evaluated. Results demonstrate the potential of significant, long-term benefits for regional groundwater quality by applying strategic, high-intensity recharge operations on geologically favorable subregions. Siting MAR above the incised valley fill (IVF) deposit, a near-surface paleochannel containing unusually coarse, high-conductivity hydrofacies, leads to more extensive improvement in the groundwater quality in terms of salinity due to significant vertical flow and lateral outward flow from the IVF. Overall, decades would be required to alleviate groundwater quality concerns in the studied 189 km2 region. The simulations indicate that the deep concentrations remain below the secondary maximum contaminant level as the solute mass migrates downward with the prominent contribution from the attenuation via dispersion and matrix diffusion.

Regional scale transport models are needed to support the long-term evaluation of groundwater quality and to develop management strategies aiming to prevent serious groundwater degradation. The transport dominant process, advection or diffusion, was identified for flow fields with different primary flow directions. The capacities of Multi-Rate Mass Transfer (MRMT) and adaptive Multi-rate Mass Transfer (aMMT), modified from MRMT by updating mass transfer rates with changing velocities, to adequately describe the main solute transport processes, including the capture of late-time tails under changing boundary conditions were evaluated. Advective-dispersive contaminant transport simulated in a 3D heterogeneous medium was used as a reference solution. Equivalent transport under homogeneous flow conditions was then evaluated by applying the MRMT or aMMT models for upscaling. Results indicated that for advection-dominated transport, both the MRMT and aMMT methods can upscale the anomalous transport dynamics affected by sub-grid heterogeneity under transient flow conditions. Whereas, for diffusion-dominated systems, the MRMT model failed to capture the tails of tracer breakthrough curves (BTCs) after the boundary condition changed, but the results from the aMMT model were significantly improved. However, if the overall flow direction changed, both MRMT and aMMT failed to represent the BTC tail generated by the heterogeneous system. In this study, an indicator that describe the primary flow direction in anisotropic heterogeneous domain was developed, and the relationship between the flow direction and the dominant transport process was investigated. The ranges of the indicator, within which the advection or diffusion is dominant, are determined. Therefore, this study not only show the capability of upscaling methods on describing the transport that dominated by different processes, but provides a guide on choosing upscaling methods in field site, which supports long-term management of groundwater.

Low doses of antibiotics are ubiquitous in the marine environment and may exert negative effects on non-target aquatic organisms. Using primary macrophages of common carp, we investigated the mechanisms of action following exposure to several common antibiotics; cefotaxime, enrofloxacin, tetracycline, sulfamonomethoxine, and their mixtures, and explored the immunomodulatory effects associated with the nuclear factor-κB (NF-κB) signaling pathway. A KEGG pathway analysis was conducted using the sixty-six differentially expressed genes found in all treatments, and showed that exposure to 100 μg/L of antibiotics could affect regulation of the NF-κB signaling pathway, suggesting that activation of NF-κB is a common response in all four classes of antibiotics. In addition, the four antibiotics induced nf-κb and NF-κB-associated cytokines expression, as verified by qPCR, however, these induction responses by four antibiotics were minor when compared to the same concentration of LPS treatment (100 μg/L). Antagonists of NF-κB blocked many of the immune effects of the antibiotics, providing evidence that NF-κB pathways mediate the actions of all four antibiotics. Moreover, exposure to environmentally relevant, low levels (0.01-100 μg/L) of antibiotics induced a NF-κB-mediated immune response, including endogenous generation of ROS, activity of antioxidant enzymes, as well as expression of cytokine and apoptosis. Moreover, exposure to mixtures of antibiotics presented greater effects on most tested immunological parameters than exposure to a single antibiotic, suggesting additive effects from multiple antibiotics in the environment. This study demonstrates that exposure of fish primary macrophages to low doses of antibiotics activates the NF-kB pathway.

Regional scale transport models are needed to support the long-term evaluation of groundwater quality and to develop management strategies aiming to prevent serious groundwater degradation. The transport dominant process, advection or diffusion, was identified for flow fields with different primary flow directions. The capacities of Multi-Rate Mass Transfer (MRMT) and adaptive Multi-rate Mass Transfer (aMMT), modified from MRMT by updating mass transfer rates with changing velocities, to adequately describe the main solute transport processes, including the capture of late-time tails under changing boundary conditions were evaluated. Advective-dispersive contaminant transport simulated in a 3D heterogeneous medium was used as a reference solution. Equivalent transport under homogeneous flow conditions was then evaluated by applying the MRMT or aMMT models for upscaling. Results indicated that for advection-dominated transport, both the MRMT and aMMT methods can upscale the anomalous transport dynamics affected by sub-grid heterogeneity under transient flow conditions. Whereas, for diffusion-dominated systems, the MRMT model failed to capture the tails of tracer breakthrough curves (BTCs) after the boundary condition changed, but the results from the aMMT model were significantly improved. However, if the overall flow direction changed, both MRMT and aMMT failed to represent the BTC tail generated by the heterogeneous system. In this study, an indicator that describe the primary flow direction in anisotropic heterogeneous domain was developed, and the relationship between the flow direction and the dominant transport process was investigated. The ranges of the indicator, within which the advection or diffusion is dominant, are determined. Therefore, this study not only show the capability of upscaling methods on describing the transport that dominated by different processes, but provides a guide on choosing upscaling methods in field site, which supports long-term management of groundwater.

The long-term evaluation of regional-scale groundwater quality needs efficient upscaling methods for transient flow. Upscaling techniques, such as the Multirate Mass Transfer (MRMT) method with constant upscaling parameters, have been used for transport with steady-state flow, yet the upscaling parameters (i.e., rate coefficients) may be time dependent. This study proposed and validated an adaptive MRMT (aMMT) method by allowing the mass transfer coefficients in MRMT to change with the flow field. Advective-dispersive contaminant transport simulated in a 3-D heterogeneous medium was used as a reference solution. Equivalent transport under homogeneous flow conditions was evaluated by applying the MRMT and aMMT models for upscaling. The relationship between mass transfer coefficients and flow rates was fitted under steady-state flow driven by various hydraulic gradients. A power law relationship was obtained, which was then used to update the mass transfer coefficients in each stress period under transient flow conditions in the aMMT method. Results indicated that for advection-dominated transport, both the MRMT and aMMT methods can upscale the anomalous transport dynamics affected by subgrid heterogeneity under transient flow conditions. Whereas for diffusion-dominated systems, the MRMT model failed to capture the tails of tracer breakthrough curves after the boundary condition changed, but the results from the aMMT model were significantly improved. However, if the overall flow direction changed, both MRMT and aMMT failed to represent the breakthrough curve tail generated by the heterogeneous system. The results point toward a promising path for upscaling transport in complex aquifers with transient flow.