River deltas are the major repositories of terrestrial sediment fl ux into the world's oceans. Reduction in riverine inputs into the deltas due to upstream damming might lead to a relative dominance of waves, tides and currents that are especially exacerbated by coastal subsidence and sea-level rise ultimately affecting the delta environment. Analysis of multi-date satellite imagery and maps covering the Krishna and Godavari deltas along the east coast of India revealed a net erosion of 76 km 2 area along the entire 336-km-long twin delta coast during the past 43 years 2000-2005. In the case of the Godavari delta, although the water discharge data do not show any major change, there was almost a three-fold reduction in its suspended sediment loads from 150·2 million tons during 1970-1979 to 57·2 million tons by [2000][2001][2002][2003][2004][2005][2006]. A comparison of data on annual sediment loads recorded along the Krishna and Godavari Rivers showed consistently lower sediment quantities at the locations downstream of dams than at their upstream counterparts. Reports based on bathymetric surveys revealed considerable reduction in the storage capacities of reservoirs behind such dams. Apparently sediment retention at the dams is the main reason for the pronounced coastal erosion along the Krishna and Godavari deltas during the past four decades, which is coeval to the hectic dam construction activity in these river basins.

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The mid- to late-Holocene monsoon decline led to aridification of the Indian Peninsula impacting the early agricultural practices in the region. Our analysis of organic carbon, mineral magnetic properties and AMS 14C dating of a 54.2-m-long sediment core (CY) from the Godavari Delta, India, showed changes in the organic carbon source and sediment provenance, which are linked to the changes in vegetation and soil/rock erosion caused by widespread aridification and associated human adaptation in central India. Our results show a decline in the concentration of ferrimagnetic minerals, indicating reduced input from the basalts of the Deccan Plateau after ~6.0 cal. ka BP in response to the weaker Indian monsoon. δ13C values show a distinct increase from ~4.9 cal. ka BP, indicating an increase in C4 plant sources under the continued weak monsoon phase, whereas a higher ferrimagnetic mineral concentration in the sediment suggested an increased Deccan basalt source. Abrupt increase in δ13C values and decrease in TOC content accompanied with a significant increase in ferrimagnetic mineral concentration from ~3.2 to 3.1 cal. ka BP reflected a shift of organic carbon and sediment source and a severe decline in vegetation coverage. Such phenomena indicate intensified deforestation and soil/rock erosion in the Deccan Plateau producing higher ferrimagnetic mineral inputs, which is in agreement with significant expansion of agricultural activities in the Deccan Chalcolithic cultural period. In addition, C3 plants recovered and magnetic concentration declined during the wet events (4.6 and 4.0 cal. ka BP) of Neolithic time, while both C3 plants and magnetic parameters increased during the wet events (3.1–2.8 and 2.1 cal. ka BP) of the Chalcolithic cultural period. This implies increased agricultural activity and the onset of human modification of the ecosystem.

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