Dual character of Sundarban estuary as a source and sink of CO2 during summer: an investigation of spatial dynamics.

A comprehensive attempt has been made to evaluate the diurnal and spatial pattern of CO2 exchange between the atmosphere and water along the estuarine track of Indian Sundarbans during the two summer months, April and May, 2011. Rigorous field observations were carried out which included the hourly measurements of total alkalinity, pH, fugacity of CO2 in ambient air and water surface, dissolved oxygen, and chlorophyll a. The estuarine water was found rich in total alkalinity and was oversaturated with CO2 throughout the diurnal cycle in the two stations situated at the inner and middle estuary, respectively, whereas an entirely reverse situation was observed in the outer fringes. The fugacity of CO2 in water ranged from 152 to 657 µatm during the study period. The percentage of over-saturation in inner and middle estuary varied from 103 to 168 and 103 to 176 %, respectively, whereas the degree of under-saturation in the outer estuary lied between 40 and 99 %. Chlorophyll a concentrations were found higher in the outer estuary (12.3 ± 2.2 mg m(-3)) compared to the middle (6.4 ± 0.6 mg m(-3)) and inner parts (1.6 ± 0.2 mg m(-3)), followed by a similar decreasing pattern in nutrient availability from the outer to inner estuary. The sampling stations situated at the inner and middle estuary acted as a net source of 29.69 and 23.62 mg CO2 m(-2) day(-1), respectively, whereas the outer station behaved as a net sink of -33.37 mg CO2 m(-2) day(-1). The study of primary production and community respiration further supports the heterotrophic nature of the estuary in the inner region while the outer periphery was marked by dominant autotrophic character. These contrasting results are in parity with the source characters of many inner estuaries and sinking characters of the outer estuaries situated at the distal continental shelf areas.

Comparative study of heavy metals in selected mangroves of Sundarban ecosystem, India.

Accumulation and partitioning of eight heavy metals Cr, Pb, Zn, Cd, Ni, Cu, Co and Fe were studied in the root, stem and leaf of mangrove species (Sonneratia caseolaris, Acanthus ilicifolius and Excoecaria agallocha) for comparison and in mangrove sediments for calculation of bio concentration factor (BFC) in Sundarban India. Magnitude of Fe was found highest in the sediments (35371.71 mg kg(-1)) and plant parts of the three species (a maximum of 11428.0 mg kg(-1) in the root of S. caseolaris). For other heavy metals, plants showed exclusion and selection mainly based on utilization, regardless of their level in the sediments. In most of the cases significant variation of absorption was found between the three species (F = 11.48 to 157.37; p < 0.001) and between their plant parts (F = 10.98 to 338.03; p < 0.001). S. caseolaris was found to be a less potential heavy metal accumulator than the other two species, except for Fe and Zn in the root. Irrespective of the magnitude of the heavy metals, other species showed significant correlations (r = 0.509 to 0.961; p < 0.001) between heavy metal accumulations, exclusively due to chemical reason, whereas S. caseolaris showed significant correlations (r = 0.554 to 0.926; p < 0.001) between each and every heavy metal, which signifies similar mode of absorption pattern regardless of their utilization. This nonbiased manner of heavy metal accumulation pattern may help the species to withstand in the polluted areas.