Abstract:
The present study investigates processes and factors which determine the distribution of grain size, organic carbon and metals in mudflat sediment cores collected from lower regions of three tropical estuaries, viz., Mandovi, Sharavathi and Gurupur. The three rivers are similar in terms of monsoonal characteristics and discharge pattern, but are different in tidal range, catchment area geology and anthropogenic activities. The data revealed increase in finer sediments, organic carbon and metals in the recent years in Mandovi and Sharavathi estuaries, while the data revealed decrease in the Gurupur estuary. The increase in finer sediments in Mandovi and Sharavathi estuaries was attributed to catchment area activities, rainfall and runoff and mixing behaviour within estuaries. The change in the morphology of the Mangalore spit led to an increase in coarser sediments in the recent years in the Gurupur estuary. The similarity in distribution pattern of metals to that of finer sediments and organic carbon in three estuaries indicated the role of finer sediments and organic carbon in distribution of metals. In addition, correlation, factor and cluster analyses suggested the role of Fe and/or Mn oxide in adsorption of metals onto sediments. However, the factors regulating distribution of metals varied among the three estuaries, which are attributed to variations in rock types in their basins, in addition to changes in response to natural forces and human activities.
