Distribution of iron in the surface and groundwaters of East Godavari district, Andhra Pradesh, India

With the progradation of Godavari delta in the east coast of India, increase in iron (Fe) concentrations in the groundwater was observed. High concentrations of Fe (> 10 mg/l) were observed in khondalite and charnockite formations. A lower portion of the Godavari river basin, viz. East Godavari district was chosen for the study of the distribution of iron with special reference to the existing geological formations and the geomorphology of the area. The concentration of iron was observed to vary from below detection limit to 69 mg/l in the groundwater while it was less than 1 mg Fe/l in river and spring waters. The Fe of river water was reduced due to seawater mixing and the electrical conductivity (EC) was increased approximately to half of the seawater conductivity. Unlike the mixing of seawater at the surface, the same seawater mixing with groundwater yielded a water having similar order of EC with relatively high Fe. Fe was inversely related with nitrate in the groundwater. Fe was found to correlate considerably better with manganese in fluvial and coastal alluvium zones. The locations having higher Fe in delta are suspected to be related to palaeo channels. The association between Fe and Mn and their negative association with NO3 may be due to the possible autotrophic denitrification that might have taken place in the subsurface.