Spatiotemporal Assessment of Water and Sediment Quality in the Sasihithlu Mangrove Ecosystem

Abstract

Mangrove ecosystems are ecologically important coastal habitats that are influenced by seasonal changes in hydrology, sediment characteristics and vegetation composition. The present study assessed the spatiotemporal variations in water and sediment quality and documented mangrove diversity in the Sasihithlu mangrove region, Mangaluru, Karnataka. Monthly sampling was conducted at five stations from October 2024 to September 2025. Surface water was analysed for air and water temperature, pH, salinity, dissolved oxygen, biological oxygen demand, chemical oxygen demand, alkalinity, nutrients and chlorophyll-a. Sediment samples were analysed for temperature, pH, organic carbon and textural composition, while mangrove flora was recorded using morphological observations. Rainfall showed clear seasonal variability, with a total of 4423.9 mm during the study period. Water temperature ranged from 26.8 to 32.5°C, pH from 6.5 to 8.3, salinity from 7.0 to 33.0 PSU, dissolved oxygen from 4.01 to 7.64 mg/L, BOD from 0.97 to 3.99 mg/L and COD from 20.76 to 70.02 mg/L. Nutrient concentrations and chlorophyll-a also varied across months and stations. Sediment temperature ranged from 26.0 to 32.8°C, sediment pH from 6.1 to 8.1 and organic carbon from 0.60% to 3.24%. The sediment was dominated by silt, followed by sand and clay. Six true mangrove species and four mangrove-associated species were recorded, with Rhizophora mucronata as the dominant species. Diversity indices indicated moderate diversity, with Shannon-Wiener values ranging from 1.70 to 1.86, Simpson values from 0.45 to 0.72, evenness from 0.85 to 0.93 and richness from 0.06 to 0.14. The findings indicate seasonal variation in water and sediment conditions and provide baseline information for continued monitoring of the Sasihithlu mangrove ecosystem.