Distribution and sources of particulate organic matter in the Indian monsoonal estuaries during monsoon

Abstract

The distribution and sources of Particulate Organic Carbon (POC) and Nitrogen (PN) in 27 Indian estuaries were examined during the monsoon using the content and isotopic composition of carbon and nitrogen. Higher phytoplankton biomass was noticed in estuaries with deeper photic zone than other estuaries receiving higher suspended matter. The δ¹³C_POC and δ¹⁵N_PN data suggest that relatively higher δ¹³C_POC (−27.9 to −22.6‰) and lower δ¹⁵N_PN (0.7 to 5.8‰) were noticed in the estuaries located in the northern India, north of 16°N, and lower δ¹³C_POC (−31.4 to −28.2‰) and higher δ¹⁵N_PN (5 to 10.3‰) in the estuaries located in the southern India. This is associated with higher Chl a in the northern than southern estuaries suggesting that in situ production contributed significantly to the POC pool in the former, whereas terrestrial sources are important in the latter estuaries. The spatial distribution pattern of δ¹⁵N_PN is consistent with fertilizer consumption in the Indian subcontinent, which is twice as much in the northern India as in the south whereas δ¹³C_POC suggests that in situ production is a dominant source in the southern and terrestrial sources are important in the northern estuaries. Based on the Stable Isotope Analysis in R model, 40–90% (70–90%) of organic matter is contributed by C₃ plants (freshwater algae) in the estuaries located in the northern (southern) India.