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The recruitment potential and the ability of Ulva flexuosa Wulfen zoospores to survive darkness were tested under different conditions in the present study. The dark preserved zoospore was cultured under a two-factor experimental design to test the effect of salinity and nitrate, effect of salinity and phosphate, effect of light and salinity, and effect of light and phosphate. The recruitment (germination and growth) of zoospores was significantly affected by light and salinity. The nitrate concentration of 20 μmol.l -1 was found to initiate the process of germination and its subsequent growth and, its effect appeared greatest under 25 psu condition. While nitrate enhances the growth of biomass more than phosphate, both show a positive interactive effect on biomass increase when crossed with salinity. The combined effect of 25 psu salinity and 8 μmol.l -1 phosphate exhibited higher biomass growth. There was a significant effect of light and salinity on the biomass of zoospore, though there was no significant interaction between the two factors. There was an increase in biomass of growing zoospores to increase in light intensity and 80 μmol.m -2.s -1 of light intensity was considered optimal. Similarly, high light intensity condition favored higher biomass growth and there was significant interaction between light (80 μmol. m -2. s -1) and phosphate (4 μmol. l -1) in high salinity (35 psu) condition. The result of this study showed that dark preserved zoospores of U. flexuosa have the potential for recruitment and it gives us an understanding how different factors play a role in the process of recruitment. © 2012 Temjensangba Imchen. Source

Manoj N.T.,National Institute of Oceanography of India
Natural Hazards

Estimation of flushing time (T F) in an estuary is important for water quality analysis, and it is one of the major transport time scales used in estuaries to quantify the hydrodynamic processes and for water resources management strategies. Thus, the main objective of the present study was to estimate the T F in the Mandovi estuary (a monsoonal estuary) on the west coast of India. In the study, field observations of salinity (FOS) and a numerical model are used to describe the T F during the south-west monsoon (heavy river discharge), post-monsoon (moderate river discharge) and pre-monsoon (negligible river discharge). T F was calculated for 12 (months) river discharge scenarios (the calculation was done under monthly mean flow conditions). Among the 12 scenarios, four scenarios were within an extremely low flow range: 0. 8-2. 2 m 3s -1; four were in a moderate flow range: 4. 3-67 m 3s -1; and the remaining four were in a high flow range: 119. 0-506. 6 m 3s -1. The T F calculated from FOS and numerical model showed good matches during the periods of heavy river discharge and moderate river discharge. The results from FOS (numerical model) showed that the T F was 1. 12 (1. 11) days for a river flow of 506. 6 m 3s -1 (during the south-west monsoon), and the T F reached 251. 28 (592. 38) days under extreme low flow of 0. 8 m 3s -1 (during the pre-monsoon). Regression equations fitted by power and exponential functions were derived from FOS and numerical model simulations to correlate T F with monthly mean river discharges. The power regression equation derived from FOS (numerical model) showed good statistical fit with data (r = -0. 997 (-1. 0)) for any given river discharge compared to the exponential regression equation (r = -0. 81 (-0. 80)). Hence, the power regression equation can be used for the rapid evaluation of the impact of drought (during the pre-monsoon) and flood (during the SW monsoon) scenarios in the estuary. © 2012 Springer Science+Business Media B.V. Source

Diatoms are abundant in biofilms developed on surfaces immersed in sunlit waters. In both the planktonic and the biofilm mode of growth, diatoms produce carbohydrate polymers which perform several functions including motility, protection, production of macro-aggregates and detoxification. However, little is known about the differences, if any, in the production and characterization at the molecular level of carbohydrates in planktonic and biofilm cells. In order to identify the differences in these two modes of growth, the concentration of total carbohydrates, carbohydrate fractions, neutral carbohydrates, uronic acids and amino sugars in planktonic and biofilm cells of Amphora rostrata were measured. The results showed that the distribution of carbohydrate fractions, uronic acids and amino sugars was different in biofilm and planktonic cells. Cell normalized concentrations of these components were two to five times greater in planktonic cells compared with biofilm cells. The concentrations of glucose and glucosamine decreased, whereas fucose increased in planktonic cells over the period of cultivation. Conversely, the concentrations of glucose and glucosamine increased while that of fucose decreased in attached cells. The study suggests that marked differences exist between the carbohydrates of the planktonic and the biofilm cells of A. rostrata. Source

Diffusion coefficients of Cd-humate complexes are dependent on pH and [Cd]/[Humic] Acid (HA)] ratio in a Cd-HA system. These two factors mainly control the mass transport and complexation kinetics of Cd that may influence bioavailability and toxicity of Cd species in environmental systems. Determination of diffusion coefficients of Cd-HA systems by Scanned stripping voltammetry and dynamic light scattering techniques can provide a better understanding of the systems and can be very useful for extracting other speciation parameters of the systems. This study revealed that Cd2+ ion along with small dynamic Cd complexes was predominantly present in a Cd-HA system at pH 5 with high diffusion coefficients. HA molecules were in aggregated form at pH 5. However, HA molecules were in disaggregated form at pH 6 and concentrations of Cd2+ ion and small Cd-dynamic complexes decreased with a decrease in diffusion coefficients of Cd complexes at this pH due to formation of Cd-humate complexes. No further decrease in the hydrodynamic radii of HA was observed with the increase of pH from 6 to 7. The Cd-humate system partially lost its lability at pH 7. Conditional stability constants were calculated for Cd-humate complexes by combining the diffusion coefficient data obtained by two techniques. The log K values calculated in this study are in good agreement with the data available from the literature. © 2009 Elsevier B.V. All rights reserved. Source

Roy R.,National Institute of Oceanography of India
Estuarine, Coastal and Shelf Science

Halocarbons released from oceans are known to be important in the atmospheric processes. Their abundance in seawater is influenced by water column conditions and phytoplankton community. In the present study halocarbon abundances together with pigment composition were monitored in the coastal waters of the central eastern Arabian Sea. Short-term variability for the period December 2005-March 2007 was studied for chlorinated hydrocarbons (CHCl3, CCl4) and bromocarbons (CH2Br2 and CHBr3) for the first time in the Arabian Sea. Variability in pigments was used to understand the influence of phytoplankton community composition on halocarbon concentrations in this region. Halocarbons and phytoplankton pigments showed strong short-term variability, with maximal values generally associated with southwest (summer) monsoon high productivity. Decreased chlorocarbon abundances in sub-surface layers indicate their possible consumption under oxygen deficient conditions, particularly during the summer monsoon and Fall-Intermonsoon periods. Halocarbon abundances were in the order: CHCl3, CH2Br2, CHBr3 and CCl4. The CHCl3 showed significant positive relationship with fucoxanthin (r = 0.93, p = 0.001, n = 155) suggesting the importance of diatoms and prymnesiophytes in the Arabian Sea. Among the phytoplankton pigments chlorophyll-a showed a positive relationship with marker pigment fucoxanthin. Of the four phytoplankton groups studied, the percent dominance was in the order: diatoms > nanoflagellates > cyanobacteria > dinoflagellates. Our study shows that the utilization of halocarbons during microbial oxidation of organic matter could be a significant sink of these compounds although they might be produced in significant quantities by biochemical processes during high productivity periods, as can be seen from our observations in summer monsoon in the Arabian Sea. © 2010 Elsevier Ltd. All rights reserved. Source

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