Submarine groundwater discharge and associated nutrient fluxes in the Greater Bay Area, China revealed by radium and stable isotopes

The estuary-bay system is a common and complex coastal environment.However,quantifying submarine groundwater discharge(SGD)and associated nutrient fluxes in the complex coastal environment is challenging due to more dynamic and complicated riverine discharge,ocean processes and human activities.In this study,SGD and SFGD(submarine fresh groundwater discharge)fluxes were evaluated by combining stable and radium isotopes in the Guangdong-Hong Kong-Macao Greater Bay Area(GBA),a typical estuary-bay system.We first built a spatially distributed radium mass balance model to quantify SGD fluxes in coastal areas of GBA integrating the Pearl River Estuary(PRE),bays and shelf.We then used the stable water isotope(d2 H and d18O)end-member mixing model to distinguish submarine fresh groundwater discharge(SFGD)from SGD.Based on the 228Ra mass balance,the estimated SGD fluxes in the PRE,adjacent bay,and shelf areas were(6.14±2.74)×10^(8) m^(3) d^(-1),(3.00±1.11)×10^(7) m^(3) d^(-1),and(5.00±5.64)×10^(8) m^(3) d^(-1),respectively.Results showed that the largest area-averaged SGD was in the PRE,followed by that in the adjacent shelf and the bay.These differences may be mainly influenced by ocean forces,urbanization and benthic topographies controlling the variability of groundwater pathways.Further,the three end-member mixing model of ^(228)Ra and salinity was developed to confirm the validity of the estimated SGD using the Ra mass balance model.In the two models,groundwater endmember and water apparent age estimation were the main sources of uncertainty in SGD.The estimated SFGD flux was(1.39±0.76)108 m^(3) d^(-1),which accounted for approximately 12%of the total SGD.Combining stable and radium isotopes was a useful method to estimate groundwater discharge.Moreover,the estimated SGD associated dissolved inorganic nitrogen(DIN)flux was one order of magnitude higher than other DIN sources.SGD was considered to be a significant contributor to the DIN loading to the GBA.The findings of this study are expected to provide valuable information on coastal groundwater management and environmental protection of the GBA and similar coastal areas elsewhere.

Identifying Non-Darcian Flow and Non-Fickian Pressure Propagation in Field-Scale Discrete Fracture Networks

Non-Darcian flow has been well documented for fractured media, while the potential non-Darcian flow and its driven factors in field-scale discrete fracture networks (DFNs) remain obscure. This study conducts Monte Carlo simulations of water flow through DFNs to identify non-Darcian flow and non-Fickian pressure propagation in field-scale DFNs, by adjusting fracture density, matrix hydraulic conductivity, and the general hydraulic gradient. Numerical simulations and analyses show that interactions of the fracture architecture with the hydraulic gradient affect non-Darcian flow in DFNs, by generating and adjusting complex pathways for water. The fracture density affects significantly the propagation of hydraulic head/pressure in the DFN, likely due to fracture connectivity and flow channeling. The non-Darcian flow pattern may not be directly correlated to the non-Fickian pressure propagation process in the regional-scale DFNs, because they refer to different states of water flow and their controlling factors may not be the same. Findings of this study improve our understanding of the nature of flow in DFNs.

Impacts of permafrost degradation on streamflow in the northern Himalayas

The Himalayan water tower provides crucial water resources for Asia.Permafrost degradation is deemed to exert important impacts on streamflow in the Himalayan rivers.Yet,the magnitudes of such impacts remain poorly quantified.Here,we established a robust hydrological model that incorporated active layer deepening and ground ice melt for the drainage basin of the largest river in the northern Himalayas-the Yarlung Zangbo River(YZR).We estimated that permafrost degradation led to~0.65 km^(3)/yr decrease in surface runoff and~0.35 km^(3)/yr increase in baseflow and ground ice melt contributed~0.25% to the annual streamflow in the YZR for the period 2001-2022.The“fill-and-spill”mechanism helps explain the seeming contradiction of observed increasing versus decreasing baseflow in different permafrost regions worldwide.We propose that the dilution of riverine dissolved organic carbon(DOC)concentrations by baseflow may lead to the riverine DOC hysteresis patterns.This study not only lays solid scientific basis for water resources management in the Himalayas,but also yields new insights into how to interpret measured river discharge and nutrient flux in permafrost regions over the globe.

世界大河水沙通量变化趋势研究（英文）

河流水沙运动是地球化学循环的重要驱动力.本研究基于全球变化背景下的长序列水沙资料,对4307条世界大河(流域面积≥1000 km^2)水-沙通量的9种变化趋势及其成因进行了系统研究.结果表明,全球24%的大河呈现显著的径流变化,但年入海通量基本保持稳定;40%的大河呈现显著的泥沙通量变化,年入海通量下降20.8%;其中,亚洲大型河流的水沙通量下降趋势及南美亚马逊河的悬移质浓度上升趋势尤为突出.总体上,71%的世界大河径流变化与降水密切相关,而泥沙通量变化受大坝运行和灌溉等人类活动影响较大.

Nitrate Removal by a Permeable Reactive Barrier of Fe0:A Model-Based Evaluation

Permeable reactive barrier(PRB) filled with zero valent iron(ZVI, Fe^0) can be an effective option to remove nitrate from contaminated groundwater. The long-term performance of such PRBs, however, might be compromised by the problem of declining reactivity and permeability, which could cause a decrease in the nitrate removal efficiency. In this study we explored suitable model formulations that allow for a process-based quantification of the passivation effect on denitrification rates and tested the model for a 40 years long operation scenario. The conceptual model underlying our selected formulation assumes the declining reactivity of the ZVI material through the progressing passivation caused by the precipitation of secondary minerals and the successive depletion of the ZVI material. Two model scenarios, i.e., the base model scenario which neglects the explicit consideration of the passivation effect and one performed with the model in which the impact of the passivation effect on denitrification was considered, were compared. The modeling results illustrate that nitrate removal in the model of considered passivation started to be incomplete after 10 years, and the effluent nitrate concentration of PRB rose up to 86% of the injected water concentration after 40 years, in contrast to the base scenario, corresponding well with the field observations of successively declining nitrate removal efficiencies. The model results also showed that the porosity of the PRB increased in both models. In order to improve and recover the reactivity of ZVI, pyrite was added to the PRB, resulting in completely nitrate removal and lower consumption of ZVI.

Contaminant transport in heterogeneous aquifers: A critical review of mechanisms and numerical methods of non-Fickian dispersion

Natural aquifers usually exhibit complex physical and chemical heterogeneities,which are key factors complicating kinetic processes,such as contaminant transport and transformation,posing a great challenge in the remediation of contaminated groundwater.Aquifer heterogeneity usually leads to a distinct feature,the so-called“anomalous transport”in groundwater,which deviates from the phenomenon described by the classical advection-dispersion equation(ADE)based on Fick’s Law.Anomalous transport,also known as non-Fickian dispersion or“anomalous dispersion”in a broad sense,can explain the hydrogeological mechanism that leads to the temporally continuous deterioration of water quality and rapid spatial expansion of pollutant plumes.Contaminants enter and then are retained in the low-permeability matrix from the high-permeability zone via molecular diffusion,chemical adsorption,and other mass exchange effects.This process can be reversed when the concentration of pollutants in high-permeability zones is relatively low.The contaminants slowly return to the high-permeability zones through reverse molecular diffusion,resulting in sub-dispersive anomalous transport leading to the chronic gradual deterioration of water quality.Meanwhile,some contaminants are rapidly transported along the interconnected preferential flow paths,resulting in super-dispersive anomalous transport,which leads to the rapid spread of contaminants.Aquifer heterogeneity is also an important factor that constrains the efficacy of groundwater remediation,while the development,application,and evaluation of groundwater remediation technologies are usually based on the Fickian dispersion process predicted by the ADE equation.Comprehensive studies of the impacts of non-Fickian dispersion on contaminant transport and remediation are still needed.This article reviews the non-Fickian dispersion phenomenon caused by the heterogeneity of geological media,summarizes the processes and current understanding of contaminant migration and transformation in highly heterogeneous aquifers,and evaluates mathematical methods describing the main non-Fickian dispersion features.This critical review also discusses the limitations of existing research and outlines potential future research areas to advance the understanding of mechanisms and modeling of non-Fickian dispersion in heterogeneous media.

Antibiotic enhanced dopamine polymerization for engineering antifouling and antimicrobial membranes

In this work,we adopt a new tobramycin(TOB)-dopamine coating system to endow thin film composite membranes with excellent antifouling and antimicrobial properties.Combining the hydrophilic and antibiofouling properties of both TOB and polydopamine,the TOB-dopamine modified membrane exhibits improved antifouling and antimicrobial properties compared with the conventional dopamine modified and unmodified membranes.The TOB-dopamine system has two advantages over the conventional modification with dopamine and tris buffer solution.First,TOB-dopamine modification is more efficient than the conventional dopamine modification due to the accelerating effect of TOB on dopamine polymerization.Second,the TOB-dopamine modified membranes exhibit better hydrophilicity,and enhanced antifouling and antimicrobial properties than the conventional dopamine modified membrane.Beyond engineering membranes,the proposed TOB-dopamine system can also be extended for wider surface hydrophilic and antimicrobial modifications.

Transcriptomic analysis of bisphenol AF on early growth and development of zebrafish(Danio rerio)larvae

Bisphenol AF(BPAF),an alternative to bisphenol A,is widely detected in aquatic environments.Owing to health concerns,the toxic effects of BPAF on organisms are drawing attention.The present study aims to evaluate the toxicity of BPAF,combining the results of omics techniques and experiment.Employing transcriptome sequencing(RNA-seq),we obtained 391,648,512,and 545 differentially expressed genes(DEGs)in 0.1,1,10,and 100 mg/L BPAF-exposed zebrafish larvae,respectively.Gene ontology(GO)analysis and Kyoto Encyclopedia of Genes and Genomes(KEGG)enrichment revealed the early development,stimulus-response,and MAPK signaling pathway were significantly affected by BPAF.In addition,five hub genes(fgf3,fgf4,map2k1,myca,and casp3b)were highlighted as the key genes in MAPK signaling pathway using the protein-protein interaction network.Therefore,the RNA-seq results showed that early development and stimulus-response were the main processes affected by BPAF,which was consistent with our morphological and pathological results.The hatching rate of zebrafish embryos in 1 and 10 mg/L BPAF groups was significantly inhibited,and the oxidative stress indexes,including the level of total antioxidant capacity(T-AOC),superoxide dismutase(SOD),and lipid peroxidation(LPO),were significantly increased by the 100 mg/L BPAF treatment.Moreover,the activity of alkaline phosphatase(AKP)was significantly decreased in all BPAF exposure groups.In conclusion,exposure to BPAF at environmental relevant concentrations affected the early development and immune system of zebrafish larvae by modulating MAPK signaling pathway,and our results provide solid evidence for the future studies on the toxicity of bisphenols.