Distribution of trace metals and organic matter in the sediments of Godavari estuary of Kakinada bay, East Coast of India

In Godavari estuary, the enhanced metal concentration in the sediment is localized, and is accompanied by marked enrichment in organic carbon, Kjeldahl nitrogen, and humic acid. High concentration of organic carbon was observed near the riverside sampling stations. A similar pattern was found for the humic acid concentrations. Relatively high organic carbon content was observed in pre-monsoon/monsoon compared to post-monsoon seasons which can be attributed to higher productivity due to upwelling in the former and land runoff due to excessive rainfall in the later seasons. The trace metals in the sediments were found to be in the following order of their abundance Fe>Mn>Zn>Pb>Ni>Cu>Cd. In monsoon season relatively high levels of trace metals were reported in surface sediments which are transported by currents. The dominant process controlling the metal enrichment may be either precipitation of metal-humic acid type of complexes. Our results indicate that in the Godavari estuary, the metal distribution is mainly influenced by sedimentary dynamics, while the contamination effect is very limited.