Source of sediment components and processes with time in middle regions of tropical estuaries along west coast of India

Abstract

To understand the source of materials and processes operating, the sediment cores collected from mudflats representing middle region of Sharavathi and Gurupur estuaries were analysed for grain size, organic carbon, clay mineralogy, bulk metals and clay chemistry. Relatively higher concentration of sand in the Sharavathi and higher clay and organic carbon content in the Gurupur estuary indicated variations in the depositional environment between the two estuaries. Further, higher sand in middle section and silt in the upper section in Sharavathi and Gurupur estuaries respectively indicated variations in the depositional conditions with time in both the estuaries. The kaolinite was the most abundant clay mineral, and the abundance and distribution of clay minerals in the two estuaries revealed the role of catchment area geology and river-sea water mixing conditions as major factors in sediment deposition. All the metals showed similar distribution pattern to finer sediments and organic carbon in the Sharavathi estuary, indicating their role in distribution of metals. Also, significant association of metals with Al suggested their natural source in this estuary. Similar distribution pattern of metals with Al in the clay fraction also supported lithogenic source of metals in the Sharavathi estuary. In the Gurupur estuary, role of sediment components was limited in the distribution of metals and insignificant association of metals with Al suggested their non-natural source. Non-similar distribution pattern of metals to that of Al in the clay fraction of the Gurupur estuary and their insignificant association with Al indicated metals source as anthropogenic.