Evaluation of spatial and temporal dynamics of seawater intrusion in coastal aquifers of southeast India: insights from hydrochemical facies analysis.

This study aims to investigate and understand the temporal and spatial movement of seawater intrusion into the coastal aquifers. Groundwater salinity increase has affected the entire eastern part of the study area and is primarily influenced by direct and reverse ion exchange reactions associated with intrusion and freshwater influx phases, which alternate over monsoons. To gain insights into the spatiotemporal dynamics of the seawater intrusion process, hydrochemical facies analysis utilizing the HFE-Diagram was employed. Additionally, the study considered the major ionic changes during both the monsoons. The HFE-Diagram analysis of hydrochemical facies revealed distinctions in the behaviour of each coastal aquifer concerning seawater intrusion-induced salinization. In PRM 2020, the data shows that approximately 65% of the samples fall under the freshening phase, while the remaining 35% were categorized as intrusion phase. Within the freshening phase, seven different hydrochemical facies were identified, including Na-Cl, Na-MixCl, MixNa-MixCl, Na-MixHCO3/MixSO4, MixNa-MixSO4, Na-HCO3, and MixCa-HCO3. In contrast, the intrusion phase had four facies: MixCaMixHCO3, MixNa-Cl, Ca-Cl, and Na-Cl. Especially, the Na-Cl facies (f1) within the freshening phase attributed for the largest percentage, contributing 30% of the samples. In POM 2021, the distribution of samples shifted slightly, with approximately 72.5% belonging to the freshening phase and 27.5% to the intrusion phase. Within the freshening phase of POM 2021, five hydrochemical facies were identified: Na-Cl, Na-MixCl, Na-MixHCO3/MixSO4, MixNa-MixSO4, and Na-HCO3. The intrusion phase of POM 2021 had three facies: MixNa-Cl, Na-Cl, and MixCa-Cl. Similar to PRM 2020, the Na-Cl facies (f1) remained the most predominant in the freshening phase, comprising 30% of the samples. The relation between total dissolved solids (TDS) and various ionic ratios, such as HCO3-/Cl-, Na+/Cl-, Ca2+/Cl-, Mg2+/Cl-, K+/Cl-, and SO42-/Cl-, clearly demonstrates the presence of seawater influence within the coastal aquifers of the study area.

Estimation of microplastics in sediments at the southernmost coast of India (Kanyakumari).

Increasing urbanization and anthropogenic activities of the last couple of decades have left significant amounts of plastic debris in both coastal and marine ecosystems. In this study, we estimated the abundance of microplastics (particle size < 5 mm) in the beach sediments of southernmost India at Kanyakumari by collecting sediments from harbors, coastal fishing villages/residential beaches, tourist beaches, and undisturbed coastal areas along the Indian Ocean. We recovered 343 particles (67% fiber and 33% fragment) from eight different stations by evaluating 50 g dry sediments (d.s.) from each location. All of them were secondary microplastics and most of them (i.e., 331 out of 343 particles) were transparent. Tourist beaches had the highest concentration (150 particles/50 g d.s.), followed by the harbors (99 particles/50 g d.s.). The undisturbed beach contained the least amount of microplastics, representing only 4.3% of the total recovered particles. Our study relates the abundance of microplastics to different degrees of anthropogenic activities. Further research, however, is required to identify the mechanism that influenced their transport and deposition in the coastal sediments as well as to evaluate the possible interaction between microplastic particles and marine ecosystems.