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 δ13CPOC and δ15NPN data suggest that relatively higher δ13CPOC (-27.9 to -22.6‰) and lower δ15NPN (0.7 to 5.8‰) were noticed in the estuaries located in the northern India, north of 16°N, and lower δ13CPOC (-31.4 to -28.2‰) and higher δ15NPN (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 δ15NPN is consistent with fertilizer consumption in the Indian subcontinent, which is twice as much in the northern India as in the south whereas δ13CPOC 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.