G.V.M. Gupta

CO2 Supersaturation and Net Heterotrophy in a Tropical Estuary (Cochin, India): Influence of Anthropogenic Effect: Carbon Dynamics in Tropical Estuary

Carbon biogeochemistry of a tropical ecosystem (The Cochin Estuary, India) undergoing increased human intervention was studied during February (premonsoon), April (early monsoon) and September (monsoon) 2005. The Cochin estuary sustains high levels of pCO2 (up to 6000 μatm) and CO2 effluxes (up to 274 mmolC m−2 d−1) especially during monsoon. A first-order estimate of the carbon mass balance shows that net production of dissolved inorganic carbon is an order of magnitude higher than the net loss of dissolved and particulate organic carbon from the estuary. This imbalance is attributed to the organic inputs to the estuary through anthropogenic supplies. The bacteria-mediated mineralization of organic matter is mainly responsible for the build-up of pCO2 and increased CO2 emission to the atmosphere indicating heterotrophy. The linear correlation between excess CO2 and apparent oxygen utilization indicates respiration as the chief mechanism for CO2 supersaturation. An increase in the net negative ecosystem production (–ve NEP) between premonsoon (−136 mmolC m−2 d−1 or −376 MgC d−1) and monsoon (−541 mmolC m−2 d−1 or −1500 MgC d−1) is supported by a corresponding increase in O2 influxes from 17xa0mmol O2 m−2 d−1 (126 MgC d−1) to −128xa0mmol O2 m−2 d−1 (−946 MgC d−1) and CO2 emissions from 65 mmolC m−2 d−1 (180 MgC d−1) to 267 mmolC m−2 d−1 (740 MgC d−1). There is a significant north-south gradient in metabolic rates and CO2 fluxes attributable to the varying flow patterns and anthropogenic inputs into the estuary. The study reveals that the Cochin estuary, a previously autotrophic (CO2 sink) system, has been transformed to a heterotrophic (CO2 source) system following rapid urbanization and industrialization. Moreover, the export fluxes from the Cochin estuary appear to be quite important in sustaining net heterotrophy in the southeastern Arabian Sea.

Eutrophication induced changes in benthic community structure of a flow-restricted tropical estuary (Cochin backwaters), India

The influence of anthropogenic loading on the distribution of soft bottom benthic organisms of a tropical estuary (Cochin backwaters) was examined. The industrial activities were found to be high in the northern and central part of the estuary, where dissolved inorganic nitrogen (DINxa0> 210xa0μM) and phosphorus (DIP > 6.5xa0μM) have caused high abundance of chlorophyll a (up to 73xa0mgxa0mu2009−u20093) and accumulation of organic carbon in sediments (up to 5%). Principal component analysis distinguished three zones in the estuary. The central zone (Z1) was characterized by organic enrichment, low species diversity, and increased number of pollution tolerant species. Long-term deterioration of the estuary is indicated by an increase in the nutrients and chlorophyll a levels by sixfold during the last few decades. Flow restrictions in the lower estuary have lead to a fourfold increase in sediment organic carbon over the period of three decades. The reduced benthic diversity followed by an invasion of opportunistic polychaetes (Capitella capitata), are indicative of a stress in the estuary.

Evolution to decay of upwelling and associated biogeochemistry over the southeastern Arabian Sea shelf

Observations along 10 shelf transects in 2012 near 10°N in the southeastern Arabian Sea revealed the usual warm oligotrophic conditions during the winter monsoon and upwelling of oxygen-deficient, nutrient-rich cool water during the summer monsoon (SM). By changing an oligotrophic to a nutrient-replete condition, the upwelling is the major process that regulates the biogeochemistry of this shelf. Its onset is perceptible at 100m depth between January and March. The upwelling reaches the surface layer in May and intensifies during June–July but withdraws completely and abruptly by October. Despite the nutrient injection, the primary production during SM, integrated for euphotic zone, is comparable to that during the preceding spring intermonsoon (SIM). Again, as usual, the high oxygen demand coupled with low concentration in the upwelled subsurface waters causes severe oxygen depletion below the shallow pycnocline. The oxygen concentrations/saturations of 2012 on the midshelf are similar from those of mid-1958 to early 1960, except for marginally higher values during the peak upwelling period due to relatively weak upwelling in 2012. This implies little anthropogenic influence on coastal hypoxia unlike many other coastal regions. In 2012, the inner shelf system shifted from net autotrophy in SIM to net heterotrophy in SM but on an annual basis it was net autotrophic (gross primary production to community respiration ratio, GPP/R:1.11 ± 0.84) as organic production exceeded consumption.

Nitrogen Uptake Dynamics in a Tropical Eutrophic Estuary (Cochin, India) and Adjacent Coastal Waters

Quantification of nitrogen (N) transformation rates in tropical estuarine-coastal water coupled systems undergoing anthropogenic disturbances is scant. A thorough understanding of these metabolic rates is required to evolve a mitigation strategy to save such systems from further degradation. Here, we report the first measurements of ammonium (NH4+) and nitrate (NO3−) uptake along with N2 fixation rates in the Cochin estuary, a tropical eutrophic ecosystem along the west coast of India, and two transects (off Cochin and off Mangalore) in the coastal Arabian Sea. In general, the Cochin estuary sustained higher uptake rates of NH4+ (0.32–0.91xa0μmol N l−1 h−1) and NO3− (0.01–0.38xa0μmol N l−1 h−1) compared to coastal waters. The N uptake in the nearshore waters of Cochin transect (NH4+u2009:u20090.34xa0μmol N l−1 h−1 and NO3−u2009:u20090.18xa0μmol N l−1 h−1) was influenced more by estuarine discharge than was the Mangalore transect (NH4+u2009:u20090.02xa0μmol N l−1 h−1 and NO3−u2009:u20090.03xa0μmol N l−1 h−1). Despite high dissolved inorganic nitrogen (DIN) concentrations, the Cochin estuary also showed higher N2 fixation rates (0.59–1.31xa0nmol N l−1 h−1) than the coastal waters (0.33–0.55xa0nmol N l−1 h−1). NH4+ was the preferred substrate for phytoplankton growth, both in the Cochin estuary and coastal waters, indicating the significance of regenerative processes in primary production. A significant negative correlation between total nitrogen (TN): total phosphorus (TP), and NH4+ uptake (as well as N2 fixation) rates in the estuary suggests that nutrient stoichiometry plays a major role in modulating N transformation rates in the Cochin estuary.

Effect of vertical stability and circulation on the depth of the chlorophyll maximum in the Bay of Bengal during May-June, 1996

Abstract A two-gyre circulation system consisting of an anticyclonic gyre (ACG) in the northwestern Bay of Bengal and a cyclonic gyre (CG) west of the Andaman Islands is shown by the hydrographic data collected during May–June, prior to the southwest monsoon of 1996. This circulation system leads to an intense southwestward flow in the central Bay. The circulation pattern characterizes the transition from the pre-monsoon (spring season) ACG to the southwest monsoon CG. A deep chlorophyll maximum (DCM) is found in the depth range 30–50xa0m in the coastal region and 50–100xa0m in the open sea. The DCM is located below the surface mixed layer, in the oxycline and nutricline, and above the seasonal thermocline/pycnocline, which coincides with the deep stability maximum (DSM). In the ACG, the DCM is located at 100xa0m when DSM is at 140xa0m deep, whereas in the CG, the DCM and DSM rise to 50 and 80xa0m, respectively. The magnitude of the chlorophyll maximum (CMAX) is nearly twice as high in the CG zone as in the ACG zone. The depths of both DCM and DSM, however, are twice as large in the ACG zone as in the CG zone. This shows that the meso-scale circulation patterns affect the spatial distribution of chlorophyll a (both DCM and CMAX) in the Bay of Bengal.

Testing the efficiency of temperate benthic biotic indices in assessing the ecological status of a tropical ecosystem

The objectives of the present study were to evaluate the ecological status of tropical coastal waters using the temperate benthic indices and examine the effect of seasonal variability on the performance of benthic indices. Macrobenthic samples were collected from northwest to southeast coast of India during 2003-2012 and we tested different univariate indices, ecological strategies, indicator species and multimetric indices. AMBI and multimetric indices performed satisfactorily in evaluating the ecological status. Seasonal variability on the biotic indices was observed during the southwest monsoon and fall intermonsoon period due to recruitment. Therefore, we recommended the non-monsoon period (January-May) as a suitable time of the year to use the indices for effective assessment of the Indian coastal waters. Results show that, the temperate benthic indices are efficient in assessing the tropical environmental status. However, complementary use of different indices is suggested for accurate assessment of the environmental status.

Chemical characteristics of Central Indian Basin waters during the southern summer

Abstract Chemical properties of the water column were examined at the Indian Deep-sea Environment Experiment (INDEX) site in the Central Indian Basin (CIB), as a part of baseline studies prior to the benthic disturbance experiment for the environmental impact assessment of mining of polymetallic nodules. The study shows three equatorward moving water masses. (a) The Subsurface Salinity Maximum in the depth range 125–200xa0m, characterized by high salinity (34.74–34.77xa0psu) and oxygen minimum associated with weak maxima in nutrients. (b) The Deep Oxygen Maximum (234–245xa0μM) in the depth range 250–750xa0m, associated with minima in nutrients and relatively high pH. (c) The Salinity Minimum Water (34.714–34.718xa0psu) corresponding to the Antarctic Intermediate Water (AAIW) at depths 800–1200xa0m in the density (σθ) range 27.2–27.5. Progressive changes in these characteristics are attributed to mixing with waters above and below, and to oxidation of organic detritus en route. Among the three water masses, the oxygen maximum water shows the lowest changes in its properties, which may suggest that this water mass is moving the fastest.

Hydrobiological responses of the North Eastern Arabian Sea during late winter and early spring inter-monsoons and the repercussions on open ocean blooms

Winter cooling and persistent mixing for more than a quarter of year (November to early March) along the North Eastern Arabian Sea (NEAS) results in nutrient enrichment of the euphotic column thereby triggering biological production. Hydrographic characteristics of NEAS during Late Winter Monsoon (LWM) and Early Spring Inter Monsoon (ESIM) and the influence on biological production are overviewed here. Winter convective mixing signatures were evident during LWM with low SST (24°C), high SSS (36.4), deep mixed layers (>100 m) and increased surface nitrate (~1 µM). Open ocean waters observed high chlorophyll a (1–2 mg m −3 ) and microphytoplankton abundance (1.2–1.5 × 10 4 cells l −1 ). Diatoms and green Noctiluca scintillans were the major microphytoplankton identified. ESIM observed gradual stabilization of water column with curtailment of winter signatures and strengthening of Noctiluca scintillans blooms. Mesozooplankton biomass was higher during LWM and decreased towards ESIM with intensification of Noctiluca blooms. However during ESIM, abundance of gelatinous zooplankton occurred in the bloom region. Inter-annual variations were observed in the biological responses along with the hydrographic changes. Thus the convective process during winter monsoon and stabilization of the water column during ESIM plays a significant role in the production pattern of NEAS.

Chronic invasive fungal rhinosinusitis by Paecilomyces variotii: A rare case report

Fungal infection of the paranasal sinuses is an increasingly recognised entity, both in normal and immunocompromised individuals. The recent increase in mycotic nasal and paranasal infections is due to both improved diagnostic research and an increase in the conditions that favour fungal infection. Aspergillus, Candida, and Mucor species are the most common causative agents of fungal sinusitis, but infection with lesser known species have been reported across the world infrequently. This article reviews and presents a case report of chronic fungal sinusitis in an immunocompetent adult male infected with Paecilomyces variotii which is opportunistic soil saprophyte, uncommon to humans.

Characteristics of a cyclonic eddy and its influence on mesozooplankton community in the northern Bay of Bengal during early winter monsoon

Characteristics of a cold-core eddy and its influence on the mesozooplankton community were studied along the central (87° E) Bay of Bengal during winter monsoon (November 2008) based on in situ data. The thermo-haline structure and the satellite-derived sea level anomaly maps showed the presence of a cyclonic eddy between 16° N and 20° N. The nutrient enhancement due to the eddy pumping in the euphotic column (∼50xa0m) had resulted in high chlorophyll a concentration, a factor of 8 times higher than that outside the eddy, which led to higher mesozooplankton biovolume (0.35u2009±u20090.36xa0mlxa0m−3) and abundance (276u2009±u2009184xa0indxa0m−3). The northern cyclonic eddy (NCE) seems to exist for approximately 6xa0months between July and January. During summer, the NCE is forced by local wind stress curl and the resultant Ekman pumping, whereas during fall and early phase of the winter, it is sustained by westward propagating semi-annual Rossby waves. The longer existence of NCE in the study region, which originated 6xa0months prior to the present observation, provides a favourable environment for the mesozooplankton community to grow and reproduce, resulting in noticeable increase in the biovolume. Hence, the persistent and longer existence of NCE significantly influences the biological production of the generally oligotrophic BoB, making it locally biologically ‘active’.