Holistic monitoring of increased pollutant loading and its impact on the environmental condition of a coastal lagoon with Ammonia as a proxy for impact on biodiversity

Abstract. Eutrophication poses a serious threat to the ecological functioning of marginal marine habitats in the era of Anthropocene. Coastal lagoons are particularly vulnerable to nutrient enrichment and associated changes in environmental condition due to their limited marine connection and longer water residence time. Benthic organisms are more susceptible to the impacts of nutrient enrichment as organic carbon produced in water column production gets sequestered in the sediment compartment leading to increased bacterial degradation that may cause hypoxia. Apart from nutrient enrichment, addition of different heavy metals as Potential Toxic Elements (PTE) from industrial sources also impacts the biota. In the present study, the concentrations of different nutrients and PTEs have been measured from the water profile of the World’s second largest coastal lagoon, Chilika. Alongside characterization of the sedimentary organic carbon was also carried out. The globally present coastal benthic foraminiferal genera Ammonia was also tested for its applicability as a biotic indicator of pollution in this habitat. The study was conducted for a period of twelve months. The investigation revealed that concentration of dissolved nitrate in the water column was extremely high along with increased values of sedimentary organic carbon deposit, both of which are characteristics of coastal eutrophication. Intermittent hypoxia within the pore space was also recorded. Characterization of stable isotopes from the sedimentary carbon revealed the origin of it to be autochthonous in nature, thus supporting the idea of nutrient driven increased primary production. Concentrations of PTEs were in most cases below bioavailable values, however occasional high values were also observed. The number of specimens belonging to Ammonia spp. also appeared to be a potent biotic proxy of eutrophication as it displayed significant correlation with both nitrate and concentration of organic carbon.