Vegetation history and salinity gradient during the last 3700 years in Pichavaram estuary, India

Abstract

Palaeoclimate, palaeoecological and palaeoshoreline studies were carried out for a 2.5 m deep sediment core deposited since ∼3700 yrs BP in the central part of Pichavaram mangrove wetland, Cauvery river delta. Presently, the study area is dominated by Avicennia officinalis, A. marina and Suaeda sp. with fringes of Rhizophora sp. along the backwater channel. Based on sedimentology, palynological and thecamoebian analysis, it is inferred that since 2100 yrs BP the climate amelioration took place from warm and humid with strengthened monsoon to a dry and arid climate coupled with weakened monsoon condition inducing changes in ecology vulnerable for mangroves. Consequently, the vegetation too evolved from moist deciduous/evergreen forest to mixed deciduous forest and a reduction in mangrove diversity. The qualitative and quantitative study show a decline in the mangroves since the last millennium which may be attributed to the increased salinity along with enhanced anthropogenic activities in Pichavaram estuary. This is reflected by the dominance of salt tolerant mangrove associates since the last millennium.

Coastal vegetation dynamics in response to climatic and relative sea level changes in Mahanadi River delta, NE coast of India

“…The sedimentation rate between 1420–770 cal yr BP was highest at Mahanadi delta as compared to the other sites along the east coast. The vertical stack of sediment deposited at that time period as at 0.9 m below the mean sea level (msl) in the northern part of Mahanadi delta (present study) whereas the same is at 0.9 m above msl in Pichavaram (Cauvery delta) (Srivastava et al 2012), 0.25 m above msl in TS pettai (Cauvery delta) (Srivastava and Farooqui 2013) and 1.3 m above msl in Chilika lagoon (southern part of Mahanadi delta) (Pandey et al 2014). A fall in the relative sea level between ∼3980–200 cal yr BP and 3530–950 cal yr BP and the subsequent ingression of sea water after 200 cal yr BP and 950 cal yr BP was recorded in the northeastern part of Krishna Delta (Farooqui et al 2016) from a 500 cm core at Kanuru and a 118 cm core at Machilipatnam, respectively.…”

“…The sedimentation rate between 1420-770 cal yr BP was highest at Mahanadi delta as compared to the other sites along the east coast. The vertical stack of sediment deposited at that time period as at 0.9 m below the mean sea level (msl) in the northern part of Mahanadi delta (present study) whereas the same is at 0.9 m above msl in Pichavaram (Cauvery delta) (Srivastava et al 2012) elevation trends would clarify how the sea level is changing relative to the mangrove surface in different sectors of the Indian coastline and prioritize the target areas for conservation strategies.…”

“…Palynological record from Pichavaram estuary, east coast of India marks the presence of salt tolerant plant like Suaeda sp. and other mangrove-associated species along with high percentage of foraminiferal linings during 2100-200 cal yr BP, suggesting less fluvial input corresponding to a weak monsoon and relatively drier environment whereas after 200 cal yr BP, presence of true mangroves along with thecamoebians indicate rejuvenation of mangroves in a warm and humid climate (Srivastava et al 2012).…”

Genome Sequence Analysis of Exiguobacterium sp. Strain TBG-PICH-001, Isolated from Pichavaram Mangrove Forest in South India

“…strain TBG-PICH-001 was isolated from a soil sample from Pichavaram Mangrove Forest (11.4226°N, 79.7748°E) ( 2 ). The world’s second-largest mangrove wetland, Pichavaram is situated on the southeastern coast of South India in the Cuddalore District of Tamil Nadu State ( 3 ). The bacterium was isolated following the dilution plate method, using skim milk agar plates containing casein hydrolysate (0.5%), yeast extract (0.25%), skimmed milk powder (1.0%), and agar (1.0%), with a pH of 7.0.…”

Multiscale Diagnosis of Mangrove Status in Data-Poor Context Using Very High Spatial Resolution Satellite Images: A Case Study in Pichavaram Mangrove Forest, Tamil Nadu, India

“…Unless a policy for regulating freshwater inflow into the mangroves is implemented, such persistent hypersaline conditions may prove to be detrimental to newly planted mangrove saplings, resulting in reduced mangrove growth or even sapling mortality. Historically, hypersaline conditions have severely affected the existing plant diversity in Pichavaram, with extreme halophytic plants becoming dominant in the mangrove landscape, thus reducing the distribution of the less halophytic plant species [42,43,48]. Low plant diversity may be a precursor for ecosystem collapse, especially in an event of a widespread dieback or disease, from which mangroves may not recover from.…”