In-situ anatomical and elemental response of aquatic macrophytes against nutrient enrichment in freshwater tropical lakes

Abstract

Nutrient enrichment in lakes due to municipal wastewater discharge and agricultural run-off leads to excessive growth of algae and aquatic macrophytes leading to their altered trophic states. This paper presents the effect of wastewater-induced nutrient enrichment on the anatomical changes and elemental profiling in three common aquatic macrophytes of freshwater lakes in India’s Central Gangetic Plain. It is observed that with increase in trophic state, biomineral depositions are seen in the leaf anatomy of aquatic macrophytes. Elemental variations in free-floating (Eichhornia crassipes), submerged (Hydrilla verticillata) and emergent (Typha latifolia) macrophytes collected from three different lakes with different catchment characteristics and trophic state using EDS (Energy-Dispersive X-Ray Spectroscopy) spectra show that with increasing trophic state, elemental constituent in the aquatic macrophytes also increases. The rhizome of Eichhornia crassipes showed the formation of calcium oxalate crystals in SEM (Scanning Electron Microscope) images and EDS analysis. Among macrophytes, floating and submerged macrophytes show a greater number of elemental constituents as compared to the emergent macrophytes. The findings of this study show that the anatomical and elemental responses of macrophytes are dependent both on the water quality and trophic state of the lakes. In-situ responses of macrophytes are based on their tolerance level against the pollution load and environmental changes. This study has important implications for understanding the response mechanism of macrophytes with changing water quality and increasing trophic state, which may help in proper management of freshwater ecosystem.