Prosenjit Pramanick

RISING WATER SALINITY: A THREAT TO MANGROVES OF INDIAN SUNDARBANS

Abstract Mangroves constitute an important ecosystem because of their global extent and high productivity. These plants thrive in the intertidal zones of the tropics and subtropics that are characterized by regular tidal inundation and fluctuating salinity. Mangrove species are well adapted, both morphologically and physiologically, to survive under saline conditions, but in hypersaline environment their growth is reduced. The present chapter is a critical analysis on the impact of salinity on the growth of a common mangrove species (Hertiera fomes). The analysis has been carried out in the framework of Indian Sundarbans, which has contrasting salinity profiles in different segments owing to barrage discharge and siltation phenomena. Analysis of the decadal profile of salinity indicates a gradual lowering in the western Indian Sundarbans due to Farrakka barrage discharge and run-off from catchments. The central sector, however, exhibits a contrasting picture of increment of aquatic salinity through time, mainly due to disconnection of the Bidyadhari River with the Ganga–Bhagrirathi–Hooghly River system (in the western part). This has made the Matla River in the central Indian Sundarbans hypersaline in nature (that used to get water from the Bidyadhari River) finally leading to an insecure ecological condition for the growth and survival of mangroves. The possible remedial measures to combat the situation have also been listed considering the ecological framework of the study zone.

Decadal Variation of Nutrient Level in Two Major Estuaries in Indian Sundarbans

The impact of the nutrient level on the water quality in the Hooghly and Matla estuarine complex in Indian Sundarbans was assessed for three decades (1984-2014). Nitrate, phosphate and silicate were used as indicators of nutrient related water quality in the estuarine water. Our first order analysis reflects significant spatio-temporal variations of selected nutrients with relatively higher values in the Hooghly estuary (in the western Indian Sundarbans) compared to the Matla estuary (in the central Indian Sundarbans). Significant variations were observed in dissolved nitrate, phosphate and silicate concentrations between stations and years (p < 0.01). Such pronounced variations may be attributed to the location of highly industrialized and urbanized city of Kolkata, Howrah and Haldia port-cum-industrial complex adjacent to the Hooghly estuary. The sudden rise of selected nutrients during premonsoon, 2009 (irrespective of sampling stations) is directly related to AILA, a super-cyclone that occurred in the lower Gangetic delta during 22nd 25th May, 2009.

Signal of Climate Change through Decadal Variation of Aquatic pH in Indian Sundarbans

Repeat hydrographic and time series data for 30 years in the western Indian Sundarbans exhibit direct evidence for acidification of estuarine water. The long-term trend in surface water pH is interpreted as signal of climate change and its possible causes are briefly outlined in this first-order analysis. The significant spatio-temporal variation of surface water pH can be attributed to factors like seawater intrusion into the estuary from Bay of Bengal, sewage discharge (from point and nonpoint sources) and photosynthetic activity by the mangrove vegetation that exhibit variable biomass and area around the selected stations. The sudden rise of surface water pH during 2009 in all the stations is a direct consequence of sea water intrusion during AILA, a super cyclone that hit Sundarbans on 25th May, 2009. The significant negative correlation of mangrove vegetation pool (assessed from AwiFS data for June 2010) with percentage of pH fall (r = - 0.6978; p <0.01) strongly supports the positive influence of mangrove photosynthetic activity in shifting the equilibrium towards alkalinity.

Baseline Data of Stored Carbon in Spinifex littoreus from Kadmath Island, Lakshadweep

Sand dune vegetations have several ecosystem services of which carbon storage and sequestration play a major role in the domain of climate change. Stored Carbon in the Above Ground Biomass and Below Ground Biomass of Spinifex littoreus collected from Kadmath Island (U.T. of Lakshadweep) were estimated during March 2016. Soil Organic Carbon was also monitored simultaneously to evaluate the stored organic carbon in the underlying soil. The observed data shows that density or biomass per unit area of the species plays a crucial role in regulating the carbon pool in the coastal zone.

Impact of Aquatic Salinity on Mangrove Seedlings: A Case Study on Heritiera fomes (Common Name: Sundari)

Mangroves are the characteristic littoral plant formation of tropical and subtropical sheltered coastlines [1]. Being on the land sea interface, they are always associated with and subjected to saline seawater. However saline condition is not a prerequisite for their development, rather mangroves choose saline condition to avoid the competition with the more vigorous terrestrial plants. Based on the physiological studies, Bowman [2] and Davis [3] concluded that mangroves are not salt lovers, rather salt tolerants. But excessive saline conditions retard seed germination, impede growth and development of mangroves. Indian Sundarbans, the famous mangrove chunk of the tropics is gradually losing Heritiera fomes (commonly known as Sundari) owing to increase of salinity in the central sector of the delta complex around the Matla River. Reports of alteration of growth in mangroves due to difference in salinity between western and central sectors of Indian Sundarbans are available [4]. However no study has yet been carried on the effect of salinity fluctuation on the photosynthetic pigments and carotenoid level of mangroves under culture conditions from this part of the Indian sub-continent. The effects of salinity on mangroves have been studied in relation to antioxidative enzymes [5,6], leaf structure, rates of transpiration, stomatal conductance and rates of photosynthesis [7,8] and changes in chloroplast structure and function [5,9]. Reported that Na+/H+ antiport catalyzed exchange of Na+ for H+ across the vacuolar membrane of the cells of Bruguiera sexangula offered tolerance to ionic stress imposed by NaCl and this mechanism was important for cellular salinity adjustments. Also, the mechanism of acclimation to salt in mangroves was suggested to be linked to the changes in the vacuolar size in B. sexangula [10]. Further, one of the biochemical mechanisms by which mangroves counter the high osmolarity of salt was accumulation of compatible solutes [5].

How Bruguiera gymnorhizza seedlings respond to climate change induced salinity rise

A study was undertaken during August 2017 to evaluate the effect of salinity on chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid and proline contents of hydroponically grown seedlings of Bruguiera gymnorhizza. The primary aim was to observe its tolerance to changing salinity. The selected seedlings were exposed to fi ve different salinity levels (2,5,10,15 and 20psu) for a period of 30 days and observations were done at a regular interval of 7,14,21 and 30 days respectively. The concentrations of chlorophyll exhibited signifi cant positive correlations with salinity (p<0.01). The chlorophyll a:b ratio in the plant varied between 2.39 to 3.71 throughout the period of investigation. The salinity fl uctuation did not affect the carotenoid level and proline content in the leaves of the species as evidenced from the insignifi cant r values. The results show that Bruguiera gymnorhizza of Indian Sundarbans region can tolerate and adapt to high saline condition as witnessed in the central sector of the deltaic complex around the Matla River. Research Article How Bruguiera gymnorhizza seedlings respond to climate change induced salinity rise? Prosenjit Pramanick1, Subrata Trivedi2, Sufi a Zaman1 and Abhijit Mitra3* 1Department of Oceanography, Techno India University West Bengal, Salt Lake Campus, Kolkata 700091, India 2Department of Biology, Faculty of Science, University of Tabuk, Ministry of Higher Education, Kingdom of Saudi Arabia 3Department of Marine Science, University of Calcutta, 35 B.C. Road, Kolkata 700019, India *Address for Correspondence: Abhijit Mitra, Department of Marine Science, University of Calcutta, 35 B.C. Road, Kolkata 700019, India, Email: abhijit_mitra@hotmail.com Submitted: 15 September 2017 Approved: 20 September 2017 Published: 22 September 2017 Copyright:

Monitoring Condition Factor of the Dominant Fin Fishes in the Estuaries of Lower Gangetic Delta in the Backdrop of Climate Change

The current global fisheries production is ~160 million tonnes. The quantum is gradually rising as a result of increases in aquaculture production. A number of climate-related threats to capture both the fisheries and aquaculture are identified, but we have high uncertainty in predictions of the future fisheries production because of uncertainty over the future global aquatic net primary production and the transfer of this production through the food chain to human consumption. Recent changes in the distribution and productivity of a number of fish species can be ascribed with high confidence to regional climate variability, such as the El Nino–Southern Oscillation. The future production may increase in some high-latitude regions because of warming and decreased ice cover, but the dynamics in low-latitude regions are governed by different processes, and production may decline as a result of reduced vertical mixing of the water column and, hence, reduced recycling of nutrients. There are strong interactions between the effects of fishing and the effects of climate because fishing reduces the age, size and geographic diversity of populations and the biodiversity of marine ecosystems, making both more sensitive to additional stresses such as climate change-induced salinity oscillation. The estuaries in the lower Gangetic delta at the apex of Bay of Bengal are noted for contrasting spatial variation of salinity. The Hooghly estuary in the western sector is relatively low saline compared to the Matla estuary in the central sector on account of receiving the fresh water discharge from the Farakka barrage. The central sector is hyper saline due to siltation of the Bidyadhari River since the late fifteenth century. The present study evaluates the condition factor of fourteen commercially important fin fish species (that constitute ~75 % of the fishes in the catch basket) collected from the Hooghly and Matla estuaries in the western and central sectors of the lower Gangetic delta, respectively. Relatively higher values of condition factor of all the species collected from the Hooghly estuary (compared to those collected from the Matla estuary) confirm the adverse effect of hyper salinity on the growth and condition factor of the species.

Green patches as carbon reservoir: A case study from Dhruba Chand Halder College, West Bengal

In the context of Climate change, greenhouse gas mitigation is one of the major concerns of the present era. Carbon sequestration by green plants is one of the most important processes for the reduction of carbon dioxide emission. Trees are the major sinks for atmospheric carbon. In the present study we evaluated the stored carbon in the dominant trees of Dhruba Chand Halder College (formerly Dakshin Barasat College) campus through the assessment of Above Ground Stem Biomass (AGSB) and Above Ground Stem Carbon (AGSC) of each species. AGSB ranged from 0.631 tonnes (Delonix regia) to 21.343 tonnes (Swietenia macrophylla) and AGSC ranged from 0.291 tonnes (Delonix regia) to 10.437 tonnes (Swietenia macrophylla) during study period. The assessment of the carbon dioxide equivalent for the species reveals considerable potential of the trees in off-setting atmospheric carbon dioxide.

Mangrove Health Card: A Case Study on Indian Sundarbans

Relative abundance and Shannon-Weiner species diversity index of true mangrove species were estimated in 10 sampling stations of Indian Sundarbans during 2013. The mangrove patches in the selected stations were categorized into a 4-point scale depending on the values of Shannon-Weiner species diversity index. The health of the mangrove forest as per our constructed 4-point scale was found to be regulated primarily by anthropogenic factors, although in station like Sagar South, the natural erosion may be the key player in determining the mangrove floral diversity.

Decadal Variation of Dissolved Oxygen in the Lower Gangetic Delta

We analyzed the Dissolved Oxygen (DO) level in the surface water off Namkhana, a sampling station in the lower Gangetic delta region. Our three decade analysis in three different seasons (premonsoon, monsoon and postmonsoon) exhibits a decrease in the DO value with the passage of time. Based on the DO value we carried out a premilinary Water Quality Index (WQI) analysis using the average seasonal temperature of the study region. This index can be used as proxy to aquatic health in the study site, provided other relevant variables remain within the optimum range. The DO level varies as per the sequence monsoon > postmonsoon > premonsoon. The sudden rise of DO level and WQI during premonsoon 2009 is attributed to Aila, a super cyclone that passed across the lower Gangetic delta on 25th May, 2009 with a speed of ~110 km/hr.