Spatiotemporal variation of the nutrients and heavy metals in mangroves using multivariate statistical analysis, Gulf of Kachchh (India)

Abstract

The present study is an attempt to assess the spatial and seasonal variation of nutrients and heavy metals in mangroves water in the Gulf of Kachchh, India. The surface water samples were collected during pre- and post-monsoon to evaluate the hydrochemical processes occurring in the region. Seasonal changes and anthropogenic inputs have influenced the nutrients and metal concentrations. The results suggest high salinity (Pre-monsoon ±45.59 PSU; post-monsoon ±45.36 PSU) and chloride (Pre-monsoon ±30251 mg/L; post-monsoon ±29536 mg/L) concentration in both the seasons. Average values of Sulfate (SO₄^-), Nitrate (NO₃^-), Dissolved silica (DSi), and Phosphate (PO₄^3-) was 2503.69 mg/L, 10.47 mg/L, 35.41 mg/L and 0.85 mg/L in pre-monsoon, and 3474.50 mg/L, 13.66 mg/L, 31.54 mg/L and 0.64 mg/L in post-monsoon, respectively. Nutrient ratios indicate phosphorus limitation in both the seasons. Cluster and Principal Component analysis signifies that sampling locations in cluster 3 and factor 1 majorly impacted due to seawater mixing, high evaporation and discharge of brine from saltpans, while cluster 2, 3 and factor 2 indicates the anthropogenic source. Metal concentration was higher during pre-monsoon and among the metals, Fe, Sr, Zn and Mn were observed in high concentration. The hydrochemical characteristics of water found to be dependent on the peculiarity of sampling locations such as high tidal amplitude, less freshwater input, arid climate, extensive saltpans, tidal flushing, instinctive reducing environment and anthropogenic discharge. Gulf of Kachchh is an industrial hub of the country, where anthropogenic activities (such as fertilizer, cement, and chemicals industries, oil and petroleum refineries, metal processing units, thermal power plants and ports activities) are the prime sources of contamination, which are affecting water quality. The relatively high concentration of nutrients and metals suggests that water is in very dreadful condition, which will ultimately affect flora and fauna of this ecosystem. This study provides baseline information on mangrove water quality and impacts of ongoing anthropogenic activities on the Gulf of Kachchh.

Keywords: Anthropogenic impacts; Heavy metals; Mangroves; Multivariate statistical analysis; Nutrients.