A coupled flow and transport model for simulation of multi-species reactive transport in unconfined aquifer using meshless local Petrov Galerkin (MLPG) method.

An understanding of natural degradation of multiple reactive contaminants in the aquifers is essential before designing the monitoring or remediation programs for polluted aquifers. Since such reactive contaminants are ubiquitous, a number of research works has been performed in the past three decades for the modelling of multi-species reactive transport (MSRT) phenomenon. The widely used finite difference method (FDM) and finite element method (FEM)-based models suffer a drawback of relying on a grid/mesh, which makes the solution unstable. Addressing such difficulties, the latest research on the MSRT models is directed towards the meshless methods. In this study, the meshless local Petrov Galerkin (MLPG) method-based multi-species reactive transport model (MLPG-MSRT) is presented, with an objective to create a robust simulation tool for the prediction of fate of multiple contaminants of the first-order reaction network. The developed model is validated for reversible as well as irreversible reaction networks with the available analytical solutions. Also, the MLPG model for unconfined aquifer flow (UF) is developed, validated, and coupled with the MLPG-MSRT model. The MLPG-UF-MSRT model results are further compared with the established FDM-based MODFLOW-RT3D model solutions for a rectangular and a real field type study. The results showed that the proposed model can simulate MSRT as accurately as the FDM-based models with an additional advantage of simplicity and stability, and thus, is more efficient for complex field problems.

Analytical modeling of contaminant transport along sloping coastal beaches in presence of tidal waves and exponential rainfall infiltration.

Coastal beaches are the most important part of the marine environment and are highly influenced by the interactions taking place between groundwater and surface water of any form. Generally, the purity index of the groundwater is based on the concentration of Total Dissolved Solids (TDS) in it. Analytical solutions are the best tools for groundwater flow and transport modeling. However, contaminant transport along the sloping coastal beaches with complex boundaries cannot be addressed with available analytical solutions. In the present study, new analytical models are developed for groundwater flow and contaminant transport for sloping coastal beaches with continuity and tidal boundary conditions. To assess the performance of the new analytical solution and to validate the range of aquifer parameters, numerical simulation is performed using Du-Fort Frankel (DFF) Scheme. Numerical experimentation is carried out using the Tchebycheff and L2 norms. It is observed that the new analytical solution for the contaminant transport gives acceptable results over the wide range of the aquifer parameters. To show the effectiveness of the developed models, two case studies from Indian coastal aquifers namely, Kalpakkam, Tamil Nadu, and Bhavnagar, Gujarat are considered. The profiles of the contaminant concentration are obtained to study the TDS behavior along these complex coastal beaches in the spatiotemporal directions. The results are compared with numerical model results and found to be satisfactory. The combined effect of the initial rainfall and rainfall decay constants showed a significant impact on the concentration of TDS. TDS concentrations are observed to be varying highly with the variation in the tidal constituents and bed slope.

Two-step approach based multi-objective groundwater remediation using enhanced random vector functional link integrated with evolutionary marine predator algorithm.

We here propose a two-step approach-based simulation-optimization model for multi-objective groundwater remediation using enhanced random vector functional link (ERVFL) and evolutionary marine predator algorithm (EMPA). In this study, groundwater flow and solute transport models are developed using MODFLOW and MT3DMS. The ERVFL network is used to approximate the flow and transport models, enhancing the computational performance. This study also improves the robustness of the ERVFL network using a kernel density estimator (KDE) based weighted least square approach. We further develop the EMPA by modifying the marine predator algorithm (MPA) using elite opposition-based learning, biological evolution operators, and elimination mechanisms. In the multi-objective version of EMPA, the non-dominated/Pareto-optimal solutions are stored in an external repository using an archive controller and adaptive grid mechanism to promote better convergence and diversity of the Pareto front. The proposed methodologies are applied for multi-objective groundwater remediation of a hypothetical unconfined aquifer based on the two-step method. The first step directly integrates flow and transport models with EMPA and finds the optimal locations of pumping wells by minimizing the percent of contaminant mass remaining in the aquifer. In the second step, the ERVL-based proxy model is integrated with EMPA and used for multi-objective optimization while explicitly using the pumping well locations obtained in the first step. The multi-objective optimization generates a Pareto-optimal solution representing the relationship between the rate of pumping and the amount of contaminant mass in the aquifer. Further analyses show a significant advantage of the two-step approach over a traditional method for multi-objective groundwater remediation.

A regional scale impact and uncertainty assessment of climate change in the Western Ghats in India.

The general circulation models (GCMs) and emission scenarios (RCP 4.5 and 8.5) have proven to be significantly functional in evaluating the impacts of climate change (CC) on hydrology, although their performance and accuracy varies on a regional scale. The objective of the present study is to evaluate the performance of five CMIP5 GCMs (CanESM2, BNU-ESM, CNRM-CM5, MPI-ESM-LR and MPI-ESM-MR) on a regional scale in the West Flowing River Basins-2 (WFRB-2) in India to model the impact of CC and its scenario uncertainty using reliability ensemble average (REA) method. For quantifying the results, the upper, middle and lower regions of WFRB-2 are separately analysed. The MPIMR and MPILR GCM model shows highest reliability factor range (0.3-0.6) in predicting the annual mean and annual maximum rainfall for most of the grids in the region. The GCM-simulated runoff using VIC (variable infiltration capacity) model is evaluated using statistical parameters such as root mean square error (RMSE), percentage bias (Pbias) and standard deviation (Std). The annual mean (maximum) runoff obtained using REA ensemble shows least RMSE, Pbias and Std values, i.e. 21.08%, 9.10 mm and 8.9 mm (6%, 39.1 mm, 39.1 mm), respectively for the middle region, which demonstrates higher reliability of GCM outputs in the flood-prone regions of WFRB-2. Furthermore, the future projection of annual maximum rainfall/runoff shows an increase of 50 mm/15 mm in the near future (2011-2040) for lower and 20 mm/6 mm for middle regions, which may cause flooding activities in the lower and middle region of WFRB-2.

Simulation of reactive transport in porous media using Meshless Local Petrov Galerkin (MLPG) and combination of Meshless Weak and Strong (MWS) form methods.

In this paper, two meshless methods, namely, a weak form Meshless Local Petrov Galerkin (MLPG) method, and Meshless Weak Strong (MWS) form method, obtained by combining MLPG with a strong form Radial Point Collocation Method (RPCM), are presented for simulation of advection-dispersion-reaction phenomena of the contaminants in the porous media. The first-order decay and sorption reactions are considered in this study. The Crank Nicolson scheme is applied for the time discretization. The weak form MLPG is a truly meshless and robust numerical technique, that can be applied to complex aquifer systems with derivative boundaries. However, in this method, the computational time is increased due to the integration, which is not essential for simple problems. Thus, the MLPG method is further coupled with a strong form RPCM with an aim of decreasing the background integration, by modelling only the nodes around the derivative boundaries using MLPG method and the other nodes by a direct RPCM which do not require integration. The proposed MWS model automatically converts into a complete RPCM model if there are no derivative boundaries. Thus, this model being both accurate and computationally efficient is suitable for simple and moderately complex aquifer systems and MLPG is the most stable and reliable method for modelling the most complex aquifer problems. Both the developed models are tested with available analytical solutions and applied for hypothetical case studies. The results prove the efficiency of the models and the applicability of each model is described in detail.

A microwave-based technique as a feasible method to detect plastic pollutants in experimental samples.

Plastic-derived pollutants are hazardous and pervasive in the environment, and their detection is a challenge due to observational constraints of various dimensions. Physical, chemical, thermal, and spectroscopic methods are extensively used to identify microplastics in environmental systems, but fundamental challenges exist in the isolation and analysis of nanoplastics from environmental samples. The promising practices are often destructive, rendering the samples inutile for further investigations. In this paper, a technique based on the measurement of the dielectric properties of the samples, carried out using the rectangular cavity perturbation technique at the S-band of microwave frequency of 2-4 GHz is proposed. The ability of this method to identify some of the most abundant types of plastics found in the environment, polypropylene, low-density polyethylene, high-density polyethylene, and cross-linked polyethylene, is demonstrated. Electrical characteristics at microwave frequencies such as absorption factor, dielectric constant, and dielectric loss tangent are found useful in the identification of various polymers in the samples. Further, this method can be applied to identify other environmentally stable performance and engineering polymers, which are not often investigated in the environmental matrices for their hazardous effects. This non-destructive measurement method is quick and straightforward and can be further developed to identify a wide range of plastic materials present in various environmental compartments.

On the emergence of a health-pollutant-climate nexus in the wake of a global pandemic.

COVID-19 has wreaked havoc throughout the planet within a short time frame, inducing substantial morbidity and mortality in the global population. The primary procedures commonly used to manage the pandemic can produce various environmental pollutants, primarily contaminants of emerging concern such as plastics, chemical disinfectants, and pharmaceutical waste. There is a huge influx of various environmental pollutants due to the pandemic effect. We, therefore, introduce the term "envirodemics" depicting the exacerbated surge in the amount of pandemic-induced pollutants. The general toxicity pattern of common chemical ingredients in widely used disinfectants shows negative impacts on the environment. We have identified some of the significant imprints of the pandemic on localizing the Sustainable Development Goals-environment interaction and their implications on achieving the goals in terms of environmental benefits. Climate change impacts are now widespread and have a profound effect on pollutant fluxes and distribution. The climate change signatures will impact the pandemic-induced enhanced fluxes of pollutants in the global waters, such as their transport and transformation. In this study, possible interactions and emerging pathways involving an emerging climate-health-pollutant nexus are discussed. The nexus is further elaborated by considering plastic as an example of an emerging pollutant that is produced in huge quantities as a by-product of COVID management and disaster risk reduction. Additionally, regulatory implications and future perspectives concerning the unleashed nexus are also discussed. We hope that this communication shall call for incisive investigations in the less explored realm concerning the health-pollutant-climate nexus.

Conflicting trajectories of landscape transformation in the humid tropical agricultural plantations of the Western Ghats, India.

The forest-agricultural landscapes of the humid tropics are transforming in their physical and socio-cultural spaces. Even though the processes of landscape transformation are highly contextual, their drivers, impacts and implications fan out across multiple scales from the local to the global. In the present study, the processes of landscape change, their multi-scalar actors and trajectories are examined in the agricultural plantations of tea, coffee and cardamom within a humid tropical forest of the Western Ghats, India. It employs an integrated multiple-source analysis of data collected through household surveys and interviews, secondary datasets, satellite imageries and litigation documents. The landscape change processes identified in the physical, social and cultural spaces include confiscation of plantations by the state, simplification of agricultural practices or abandonment of cultivation altogether, casualisation and feminisation of labour and non-agricultural diversions such as land speculation and tourism, driven by the global plantation crisis and changes in national and state forest policies. Post-globalisation, there was a high out-migration of labour and a significant decline (43%) of the population in the region. The prominent institutional actors of the state, the planters and the judiciary make these forest-enclosed plantations a highly contested space, with 75% of the area under various conflicts of tenure. These processes and actors had resulted in contrasting trajectories of incipient forest regeneration on the one hand and increased degradation on the other. A contextualized analysis of these trajectories of landscape change in these globally important humid tropical landscapes can valuably inform sustainable natural resource management frameworks.

Assessing the impacts of historical and future land use and climate change on the streamflow and sediment yield of a tropical mountainous river basin in South India.

In this study, the impacts of land use/land cover (LULC) and climate change on the streamflow and sediment yield were investigated for the Payaswani River Basin, Western Ghats, India. The LULC was determined using Landsat images, and climate data were procured from five general circulation models for representative concentration pathway (RCP) 4.5 (moderate emission) and 8.5 (high emission). The land change modeler was used to derive the future LULC and its changes from 1988 (historical) to 2030 (future) by using the transition matrix method. The SWAT model was used to assess the impacts of LULC and climate change for the streamflow and sediment yield. The results showed that decrease in forests and grasslands and increase in plantation, agricultural, and urban areas from 1988 to 2030 would lead to an increase in the mean streamflow (11.23%) and sediment yield (17.41%). Under RCP 4.5, climate change would decrease the streamflow by 2.38% in 2030. However, under RCP 8.5, climate change would increase the streamflow by 0.12% in 2030. The sediment yield under RCP 4.5 and 8.5 would increase by 1.23% and 3.33%, respectively. In comparison with the baseline condition, by 2030 future changes in the LULC and climate would increase the streamflow by 7.05% and 11.71% under RCP 4.5 and 8.5, respectively. The sediment yield would increase by 7.92% and 27.11% under RCP 4.5 and 8.5, respectively. The streamflow and sediment yield were predicted to increase in the summer and winter but decrease in the monsoon season.

Meshfree radial point collocation-based coupled flow and transport model for simulation of multispecies linked first order reactions.

Mesh/grid-based methods such as the Finite element method (FEM) and Finite difference method (FDM) are extensively used for simulation of contaminant species transport in groundwater. However, these methods in their standard form are susceptible to instabilities such as oscillations and numerical dispersion in the solution. Further, due to the use of mesh/grid, these methods are also computationally expensive. In this study, a meshfree method named Radial point collocation method (RPCM) is demonstrated for simulating reactive transport involving linked first-order reactions in a coupled flow environment. Multiquadrics radial basis functions (MQ-RBF) are used for approximation of the state variables. The model uses local support domains which produce sparse matrix systems that efficiently deal with the ill-conditioning problem which generally occurs while using global support domains. The model developed is verified against the semi-analytical solutions and its performance is compared with FEM for case studies. It is observed that the model provides accurate solutions for the problems considered and also handles advective flow conditions better than FEM. The proposed model successfully simulates the fate of contaminants in linked chain reactions.

Reactive contaminant transport simulation using the analytic element method, random walk particle tracking and kernel density estimator.

In this study, we propose a simulation model to solve the two-dimensional groundwater flow and advection-dispersion-reaction equation (ADRE) by coupling analytic element method (AEM), random walk particle tracking (RWPT) and kernel density estimator (KDE). In the AEM-RWPT-KDE model, AEM solves the groundwater flow equation, RWPT solves the advection-dispersion-reaction equation and KDE enhances the accuracy and computational efficiency of RWPT. AEM generates a continuous velocity distribution which is suitable for RWPT. An analytic expression is modified to simulate radioactive decay for discrete transport time steps and is embedded in the RWPT model. Linear adsorption is also incorporated in the RWPT model by tracking particles with a retarded velocity. Unlike Eulerian transport models such as finite element or finite difference methods, RWPT is completely free from numerical dispersion. The comparison of results illustrates the superiority of the RWPT model over accurate Eulerian-Lagrangian models with reference to the analytical solution. Further, the AEM-RWPT-KDE model is used to simulate the transport processes of Radium-228 and Trichloroethene (TCE) in two hypothetical aquifer cases. Both case studies reflect the practical applicability of the proposed methodology.

Can plastics affect near surface layer ocean processes and climate?

Plastics in the ocean are of great concern nowadays, and are often referred to as the apocalyptic twin of climate change in terms of public fear and the problems they pose to the aquatic and terrestrial environment. The number of studies focusing on the ecological effects and toxicity of plastics has substantially increased in the last few years. Considering the current trends in the anthropogenic activities, the amount of plastics entering the world oceans is increasing exponentially, but the oceans have a low assimilative capacity for plastics and the near-surface layer of it is a finite space. If loading of the oceans with plastics continues at the current rate, the thin sea surface microlayer can have a substantial amount of plastics comparable to the distribution of phytoplankton, at least in the major oceanic gyres and coastal waters in the future. Also, processes like biofouling can cluster microplastics in dense fields in the near-surface layer. Plastics can contribute to the warming or cooling of the water column by scattering and attenuating incoming solar radiation, leading to a potential change in the optical and other physico-chemical properties of the water column. We propose a new notion that changes in solar radiation in the water column due to the plastics have the potential to affect the physical processes in the ocean surface and near-surface layers, and can induce climate feedback cycles. The future can be very different, if plastics evolve as one of the key players affecting the ocean physical processes and hence this is the time to tackle this puzzle with appropriate strategies or let the genie out of the bottle.

Assessment of the environmental health of an ecologically sensitive, semi-enclosed, basin - A water quality modelling approach.

Semi-enclosed basins are environmentally dynamic and some of the most anthropogenically affected components of the coastal realm. They can reflect various environmental impacts, thus qualifying as natural laboratories to study these impacts. The Gulf of Khambhat (GoK) is such a system where analysis of in situ parameters indicated polluted conditions. The sources of various contaminants were deciphered. Though there are considerable inputs of pollutants, the assimilative capacity of the GoK holds good with high Dissolved Oxygen (DO) (6-9.3 mg/L) content as revealed in situ and in silico. High Biochemical Oxygen Demand (BOD) and marginal ammonia contamination prevail in the region. Simulations revealed that the rivers bring in a considerable amount of nitrate, organic material and phosphate into the Gulf. Considering the prevailing environmental condition, the current study posits to have regular water quality monitoring; and the carrying capacity of the Gulf should be assessed before the authorization of anthropogenic activities.

Climate change impact assessments on the water resources of India under extensive human interventions.

Climate change is a major concern in the twenty-first century and its assessments are associated with multiple uncertainties, exacerbated and confounded in the regions where human interventions are prevalent. The present study explores the challenges for climate change impact assessment on the water resources of India, one of the world's largest human-modified systems. The extensive human interventions in the Energy-Land-Water-Climate (ELWC) nexus significantly impact the water resources of the country. The direct human interventions in the landscape may surpass/amplify/mask the impacts of climate change and in the process also affect climate change itself. Uncertainties in climate and resource assessments add to the challenge. Formulating coherent resource and climate change policies in India would therefore require an integrated approach that would assess the multiple interlinkages in the ELWC nexus and distinguish the impacts of global climate change from that of regional human interventions. Concerted research efforts are also needed to incorporate the prominent linkages in the ELWC nexus in climate/earth system modelling.

Transforming river basins: Post-livelihood transition agricultural landscapes and implications for natural resource governance.

The agricultural and livelihood transitions post globalization are redefining resource relations and redrawing landscapes in the Global South and have major implications for nascent natural resource governance regimes such as Integrated River Basin Management (IRBM). A mosaic of divergent reciprocations in resource relations were noticed due to livelihood transitions in the rural areas where previous resource uses and relations had been primarily within agriculture. The reconstitution of rural spaces and the attendant changes in the resource equations are observed to be creating new sites of conformity, contestation and conflicts that often move beyond local spaces. This paper critically reviews studies across the Global South to explore the nature and extent of changes in resource relations and agricultural landscapes post livelihood diversification and the implication and challenges of these changes for natural resource governance. Though there is drastic reduction in agricultural livelihoods throughout the Global South, changes in agricultural area are found to be inconsistent and heterogeneous in the region. Agriculture continues in the countrysides but in widely differentiated capacities and redefined value systems. The transformed agrarian spaces are characterized by a mosaic of scenarios from persistence and sustainable subsistence to differentiation and exploitative commercial practices to abandonment and speculation. The reconfigured resource relations, emergent multiple and multi-scalar interest groups, institutional and policy changes and altered power differentials in these diversified landscapes are yet to be incorporated into natural resource governance frameworks such as IRBM.