Benthic Foraminifera Response to Ecosystem Pollution in the Uppanar Estuary, Tamil Nadu Coast, India

Abstract

A total of 14 surface (0-1cm) sediment grab samples and bottom water samples were collected at water depths varying from 0.8 to 2.5m in the Uppanar estuary. All the samples were analyzed to recognize the spatial distribution of benthic foraminifer assemblages and their relationship with environmental variables. The values of physicochemical parameters of bottom waters revealed that normal marine to hyposaline, low DO and high pH conditions were prevailing at the water-substrate interface at the time of sampling. The pH varies from 8.3 to 7.8, salinity from 32.46 PSU to 20.24 PSU, the DO from 5.4ml/L to 2ml/L from estuarine mouth to upstream direction. A total of 54 benthic foraminifer species belonging to 18 genera are identified and the faunal assemblages are dominated by Ammonia parkinsoniana, A. beccarii, A. tepida and Quinqueloculina spp. The dominance of Ammonia at all stations infer that it has a high tolerance to environmental variables and also reproduces more periodically than other taxa. The abundance and diversity (species richness) of living and total benthic foraminifera roughly corroborate the trends of salinity, pH and DO, indicating that these ecological variables largely affect the distribution of foraminiferal assemblages. The relative richness of species is high in lower estuary (stns.1–3), moderate in the middle estuary (stns. 4–7) and low in upper estuary (stns.8–14). The species richness in comparable samples is an indicator of environmental health, thus low values signifying deteriorated environmental conditions in the middle and upper estuarine zones. These estuarine zones are proximal to outfall of industrial effluents, resulting in low species richness and frequency. Four biotopes are recognized by cluster analysis of the total (live+dead) foraminiferal abundance data and their distribution are closely related to variations in salinity, DO and other parameters related to the hydrodynamics of the region. The unsystematic grouping of stations as disclosed by cluster analysis for total foraminifera suggests that the middle and upper estuarine zones are severely stressed due to industrial pollution. The FORAM index (FI) ranging from 1 to 1.45 indicates that estuary is environmentally stressed and inhospitable for symbiotic foraminifera. The Foram Stress Index (FSI) ranges from 0 to 4.23 and the decreasing trend of values indicate that severity of pollution increases in the upstream direction. Stations 1,2 and 4 are moderately polluted and the remaining are highly polluted. Ammonia-Elphidium index (AEI) with >90 at stns. 3–13 indicates increased hypoxic conditions, probably prevailed due to the mixing of industrial effluents. The species diversity indices (H’, M, D and J) show a positive correlation with each other and low values of these indices clearly denote serious environmental degradation of the ecosystem. The foraminifer distribution data of this study will form the baseline against which future environmental monitoring of the Uppanar estuary will be compared.