Multivariate statistical techniques for the evaluation of spatial and temporal variations in water quality of the Mahanadi river–estuarine system (India) – a case study

Spatial and temporal distributions of water quality using multivariate statistical techniques for the evaluation of nutrients (NO₂-N, NO₃-N, NH₄-N, PO₄-P, SiO₄-Si, total N, total P) in relation to some physico-chemical features (DO, BOD, TSS, TDS, SO₄²⁻, Cl⁻) were studied for 31 different stations of the Mahanadi river–estuarine system in the eastern part of India. The seasonal nutrient variations (except SiO₄-Si) exhibit higher values during monsoon season in unpolluted stations and the reverse trends for polluted stations, which are related to agricultural run-off and regional anthropogenic activities respectively. Silicate shows a well defined pattern of distribution with a higher concentration during the monsoon, which is slightly removed from the estuarine water of Mahanadi during the pre-monsoon season. The results of R-mode factor analyses revealed that anthropogenic contributions are responsible for the increase in nutrients and the decrease in DO and pH levels of the water. The magnitude of BOD with respect to total N and P demonstrates the intensity of organic pollution in the system. The removal of silicate in the saline system is clearly visible through factor analysis and the different mode of association of TSS is reflected seasonally. The relationships among the stations are highlighted by cluster analysis, represented in dendograms to categorize different levels of contamination.