Late Holocene mangrove dynamics and coastal environmental changes in the Northeastern Cauvery River Delta, India

Abstract A palaeoclimate and palaeoecological study was carried out using sedimentological, palynological and thecamoebian evidence in a 5 m deep sediment core deposited since ∼3630 cal BP from TSpettai mangrove wetland, northeastern part of Cauvery River Delta. Textural analysis shows the overall predominance of fine clay with intermittent phases of sand. The palynological climatic period inferred in Phase I (∼3630–3170 cal BP) shows a stabilized estuarine ecosystem conducive for mangroves along with a good percentage of hinterland forest indicating a warm and humid climate with strengthened monsoon. Phase IIa (∼3170–2600 cal BP) shows abundance of salt-tolerant mangroves along with a mixed forest suggesting climatic amelioration from warm and humid to dry and arid. Phase IIb (∼2600–1300 cal BP) shows the dominance of salt tolerant species indicating enhanced dry and arid climate coupled with weakened monsoon. Phase III (since ∼1300 cal BP) is characterized by rejuvenation of true mangroves and high percentages of salinity tolerant mangroves with a low percentage of thecamoebians, thereby indicating increased salinity induced by weakened monsoon and enhanced anthropogenic activity. It is inferred that during the past 3 millennia, climate changed from warm and humid to cool and arid conditions, with an evolution of vegetation from moist to dry deciduous forest. The qualitative and quantitative study shows a decline in the true mangroves and an increase in the salt tolerant vegetation, which is attributed to the increased salinity in the wetland due to high salt accumulation in the root zone which is vulnerable for mangroves.