Water quality degradation and eutrophication risk in the Ashtamudi wetland: role of physicochemical factors and microplastics

Coastal wetlands, unique ecosystems situated at the interface of land and coastal waters, are the principal retention pools for environmental microplastics, which can be degraded at higher rates by their anomalous hydrological characteristics. The Ashtamudi coastal wetland, a Ramsar wetland, is increasingly affected by anthropogenic and natural microplastic pollution and nutrient enrichment. To evaluate the present status and spatial heterogeneity in this ecosystem, water quality and microplastic distribution were studied at seven sites. Extensive physicochemical analysis was carried out with key physicochemical parameters such as BOD, potassium, nitrogen, phosphorus, TDS, turbidity, and chloride, and microplastic characterization using FTIR spectroscopy, zeta potential, and UV-visible analysis. Statistical analysis showed significant spatial heterogeneity in water quality and microplastic characteristics. CPCB limit exceedance was found at all the sites for BOD, chloride, and water quality index (WQI), suggesting extreme organic pollution, salinity stress, and overall water quality impairment. High levels of nitrogen (~ 5.5 mg/L) and phosphorus (~ 1.2 mg/L) at all the sites, particularly at Thekkumbhagam, suggest advanced eutrophication, leading to algal blooms, oxygen depletion, and aquatic ecosystem disturbance. Mukkadu and Ashtamudi presented relatively lower values, but all the sites exceeded wetland nutrient thresholds. FTIR detected microplastic polymers like polypropylene (PP), polyethene (PE), polyvinyl chloride (PVC), and polyethene terephthalate (PET), with differences in particle size and distribution. Besides identification, microplastics are carriers of toxic pollutants, alter aquatic food chains, and produce ingestion-related health risks to organisms. The current study points out the interlinked consequences of nutrient enrichment, salinity, ecological concerns and microplastic dispersal, suggesting the ecological vulnerability of the Ashtamudi wetland. The study outlines the future scope and possible solutions for the mitigation of microplastic pollution in wetlands. These implications need immediate pollution control and conservation measures to ensure the long-term environmental sustainability of this critical wetland ecosystem.