Stable Isotope Ratio and Elemental Analysis (CNS) in Mangrove Leaves in the Creek Ecosystem: An Indicator of Coastal Marine Pollution

Abstract

The stable isotopes ratio and elemental composition in the mangrove leaves are excellent indicators for coastal marine pollution. The present study investigated the composition of Carbon, Nitrogen, and Sulfur, δ¹³C and δ¹⁵N values in mangrove leaves to identify the source of pollution and energy to the mangroves in the creek ecosystem of Mumbai Harbour Bay. The oxygen and hydrogen stable isotope ratios (δ¹⁸O and δ²H) of leaf water were estimated to understand the relative contribution of freshwater and seawater to the mangrove's water source. The Carbon, Nitrogen and Sulfur contents were found to vary from 37.79 to 42.55% (Average: 40.06 ± 1.54%), 2.13–3.79% (Average: 2.94 ± 0.45%) and 0.37–0.81% (Average: 0.53 ± 0.14%) in the mangrove leaves, respectively. The δ¹³C and δ¹⁵N values were found to vary from − 30.43 to − 28.41‰ (Average: − 29.46 ± 0.74‰) and from − 2.67 to 5.54‰ (Average: 2.21 ± 3.20%), respectively. The δ¹⁸O and δ²H values were found to vary from − 2.7 to 0.83‰ and − 6.86 to 5.43‰ with an average of − 0.94 ± 0.83 and − 2.03 ± 3.52‰ respectively. According to the observed δ¹⁸O and δ²H values, mangroves in the northern part had a relatively higher contribution of freshwater input compared to southern part of the study area. The lower values of δ¹⁵N towards the northern end of the creek indicate a relatively higher contribution of nitrogen from industrial discharges. Similar values of δ¹³C in mangrove in the region suggest a common source of carbon. Mangroves found near discharge locations have different elemental composition and δ¹⁵N values compared to those mangroves that are not located near discharge location. These differences can be used as potential markers to identify the coastal marine pollution. The results of the present study may be used for developing rational approaches for protection and conservation of the mangrove ecosystem in the bay.