Zuari Estuary Research Articles

Temporal variability of macrofauna from a disturbed habitat in Zuari estuary, west coast of India

Natural disturbances along with human interference make the tropical estuaries amongst the most disturbed areas globally. In spite of this, information on the seasonal variability of macrofauna from tropical estuaries is few. Temporal variability of macrofaunal community from Mormugao Bay, Zuari estuary, on the west coast of India was examined from 2003 to 2004 at seven stations. Environmental variability was assessed through physicochemical parameters of water and sediment. The changes in macrobenthic community were assessed using abundance, biomass and species diversity indices. The environmental parameters showed a significant seasonal variation influenced by monsoonal changes. The changes in the environmental conditions brought about variation in the macrobenthic community. Macrofaunal abundance, biomass and species diversity were the highest during post-monsoon influenced by recruitment. In monsoon, the macrobenthic community was dominated by polychaetes (92.17%), whereas bivalves dominated during the post-monsoon (57.7%). The macrofauna showed drastic decline during the stable pre-monsoon season, a period when the highest abundance of fauna is observed in the tropical estuary. Therefore, the macrobenthic community in the area did not follow the seasonal trend generally observed in a tropical estuary. Further, the community during pre-monsoon season was dominated by the opportunistic polychaete species indicating a possible influence of harbour activities in structuring the benthic community of the area.

Phylogenetic diversity of archaeal 16S rRNA and ammonia monooxygenase genes from tropical estuarine sediments on the central west coast of India

Phylogenetic diversity analyses of archaeal 16S rRNA and ammonia monooxygenase subunit A (A amoA) genes were carried out on sediment samples from the Mandovi and Zuari estuaries on the central west coast of India. The 16S rRNA gene libraries revealed quite high diversity of archaea in these sediments compared to previous reports from tropical and temperate estuarine sediments. Uncultured members of Crenarchaeota accounted for ∼78% of 433 archaeal 16S rRNA gene clones from both of the estuaries. We detected archaeal 16S and amoA gene-related organisms capable of ammonia oxidation. Among Crenarchaeota, marine group I (MG I) was the most predominant. Clones matching the uncultured methanobacteria were predominant among the ribogroups of Euryarchaeota. Our results indicate that archaeal diversity in tropical estuarine sediments is influenced by the mangrove vegetation bordering the lower stretches of both estuaries. Higher diversity may be related to elevated land drainage during the monsoon, particularly in the Mandovi estuary sediments. Also, the diversity of A amoA sequences was higher in Mandovi sediments than those from Zuari and other tropical and/or temperate estuaries studied previously.

Tidal Asymmetry in the Mandovi and Zuari Estuaries, the West Coast of India

Abstract Harmonic analysis of the observed and simulated tides in the Mandovi and Zuari estuaries along the west coast of India was carried out. Tidal constituents derived from this process were analyzed to study the tidal asymmetry in these estuaries. Sea level observations during March–April 2003 at 13 stations in the Mandovi and Zuari estuaries were used for the harmonic analysis. Simulations of tides were carried out using a hybrid network numerical model. The model could well simulate the amplitude and phase of five major tidal constituents (K1, O1, M2, N2, S2) in almost all stations in the Mandovi and Zuari estuaries. Both observations and simulations show that the amplitude and phase of major diurnal and semidiurnal constituents increase toward the upstream regions. The increase of this predominant species toward the upstream regions shows that the Mandovi and Zuari estuaries are not frictionally dominated estuaries because amplification due to geometrical effects cancels the decay in amplitude due...

Tidal Circulation and Salinity Distribution in the Mandovi and Zuari Estuaries: Case Study

The Mandovi and Zuari are two tropical estuaries along the west coast of India, characterized by mixed tides with semi-diurnal dominance and heavy fresh water influx during the southwest monsoon (June to September). Previous observations of tides in these estuaries show that the tidal effects in the upstream regions are subject to decay due to freshwater influx during the southwest monsoon. The longitudinal distribution of salinity in these estuaries undergoes large variations between the southwest monsoon and the dry season (February to May). The main objectives of the present study were to simulate the tidal circulation, the longitudinal distribution of salinity and the freshwater influence on tides and the salinity distribution. Another objective was to study the intra-seasonal variations of salinity during the breaks in the southwest monsoon. A hybrid network numerical model was used for the present study to simulate the tidal circulation and the salinity distribution in these estuaries. The model reproduced observed tides accurately during the dry and wet seasons. The model could reproduce the longitudinal distribution of salinity well during the dry season and the simulation of salinity distribution was reasonably well during the wet season. The simulated tidally-averaged salinities over the M2 tidal period for varying river discharges show that even a small freshwater influx can affect the longitudinal distribution of salinity to a great extent in this type of estuaries.

Grain size, geochemistry, magnetic susceptibility: Proxies in identifying sources and factors controlling distribution of metals in a tropical estuary, India

The aim of this study is to understand the various sources and factors controlling the abundance and distribution of the metals through the analyses of selected metals (iron, manganese, chromium, copper, zinc and cobalt), sand, silt, clay, organic carbon and magnetic susceptibility of the surface sediments of Zuari estuary in three different seasons. Total suspended matter (TSM) concentration and salinity of near surface and bottom waters were also measured. The study undertaken for three seasons, based on 18 selected stations all along the estuary, indicated that the concentration of most of the metals were comparatively higher during pre-monsoon than in monsoon and post-monsoon seasons. Further, along the length of the estuary, high concentrations were observed at lower middle and lower estuary and also at few stations at the upstream end. Salinity, distribution of TSM, size of the sediment, organic matter, geomorphological setup, fresh water input from land and release of industrial waste within the estuary played a role in distribution and concentration of metals. Magnetic measurements indicated the dominance of haematite like minerals and helped in understanding the source and depositional processes.

New species of Paracalanidae along the west coast of India: Paracalanus arabiensis

A new species of copepod, Paracalanus arabiensis sp. nov. collected from Mandovi and Zuari estuaries, Goa, central west coast of India, is described. It differs from its congeners mainly in the structure of leg 5, with a row of six teeth along the edge of inner terminal spine resulting in a serrated margin and two small, stiff spines of equal length protrude in between the terminal spines.

Distribution of butyltins in waters and sediments of the Mandovi and Zuari estuaries, west coast of India

Butyltins (TBT, DBT, MBT) were measured in water and sediment samples collected from various locations in the Mandovi (ten stations) and Zuari (nine stations) estuaries during November 2007. The total butyltin (TB) in water samples varied between approximately 12 and 73 and from 0.5 to 77 ng Sn l(-1), whereas for the sediments, it varied from approximately 15 to 118 and 6 to 119 ng Sn g(-1) dry weight for the Mandovi and the Zuari estuaries, respectively. The average TB concentration in the sediments from the Zuari estuary was higher as compared to the Mandovi estuary, whereas for the water samples, it was vice versa. For both the water and sediment samples, MBT was generally the most predominant butyltin in these two estuaries. This suggests that the butyltin contamination was not freshly derived. Fairly good relationships between the concentrations of TB and organic carbon in water and sediment samples of these estuaries implicate the importance of adsorption/desorption processes in controlling the levels of TB in these estuaries.

Distribution and speciation of selected metals in surface sediments, from the tropical Zuari estuary, central west coast of India

Estuarine sediments are major reservoirs for the metals. Distribution and mobility of metals within estuaries depends strongly on their specific chemical form. In the present study, surface sediments from Zuari estuary, Goa were analysed by a sequential procedure for Fe, Mn, Cu, Zn, Cr and Co to determine their distribution in five geochemical phases (Exchangeable, carbonate, Fe-Mn oxide (reducible) organic bound (oxidisable) and residual). The total metal content, sand, silt, clay and organic carbon were also determined of the surface sediments. The total metal contents were found to be greater than the background concentrations of average shale values as well as to that of earlier studies indicating enrichment probably due to the anthropogenic origin of metals. The results obtained from sequential procedure showed that among the studied elements, Mn and Co are potentially available in the bioavailable fractions (exchangeable, carbonate and Fe-Mn oxide bound fractions) indicating their importance in toxicity whereas rest of the metals viz. Fe, Cu, Zn and to some extent Cr are largely available in residual phase although they are available in other fractions. The main source of metals to the estuary is mining and its associated activities in the study area. Chemical speciation by sequential extraction procedure has helped in assessing the mobility, bioavailability, diagenesis and toxicity of metals and hence giving a better insight into the ultimate fate of pollutants, which are introduced into the estuarine environment. To understand the risk of the metals to the sediment dwelling organisms the data were compared with the Sediment Quality Values (SQV) using SQUIRT. Also, correlation and Factor analysis were carried out to understand the associations of metals in the different fractions with sand, silt, clay, organic carbon and with other metals.

Temporal variation of diatom benthic propagules in a monsoon-influenced tropical estuary

Temporal variations in the diatom benthic propagule (DBP) community and their role in the phytoplankton community in a monsoon-affected tropical estuary, Zuari estuary, Goa (India) are presented. The DBP from the sediments was enumerated using an extinction dilution method (most probable number method), which allows estimation of resting stages through examination of germinated vegetative cells in culture. The DBP community was dominated by planktonic species belonging to the genera Skeletonema, Fragilariopsis, Thalassiosira, and Chaetoceros. Benthic propagules (BPs) of Skeletonema costatum and Fragilariopsis sp. were dominant throughout the year. Between these two species, only S. costatum showed a linear relationship between the BP and planktonic cells, indicating that this species is particularly important in coupling of pelagic and benthic ecosystems. During the onset and restart of monsoon after an intermittent break, water column was stratified, with a low-salinity layer arising from riverine discharge and precipitation at the surface and relatively cold, saline, low-oxygen waters at the bottom. Stratification favored blooming of S. costatum and Fragilariopsis sp. in nutrient-rich surface and bottom waters, respectively. The decline in these blooms ensuing nitrate depletion and salinity change resulted in an increased abundance of BP. Chaetoceros bloom was observed during the monsoon break as well as during non-monsoon period and on both the occasions the decline in bloom was coupled with freshwater discharge. During the non-monsoon season, Thalassiosira blooms were encountered subsequent to high nitrate inputs. These findings suggest that in such shallow tropical regions, physical processes during monsoon (freshwater discharge) and non-monsoon seasons (currents, waves and tides) cause resuspension of diatom BP. Since light is not a limiting factor for germination in such regions, the blooming of resuspended BP depends on nutrient availability.

Bacterial Growth Efficiency in a Tropical Estuary: Seasonal Variability Subsidized by Allochthonous Carbon

Bacterial growth efficiency (BGE) is a key factor in understanding bacterial influence on carbon flow in aquatic ecosystems. We report intra-annual variability in BGE, and bacteria-mediated carbon flow in the tropical Mandovi and Zuari estuaries (southwest India) and the adjoining coastal waters (Arabian Sea). BGE ranged from 3% to 61% and showed clear temporal variability with significantly (ANOVA, p < 0.01) higher values in the estuaries (mean, 28 +/- 14%) than coastal waters (mean, 12 +/- 6%). The greater variability of BGE in the estuaries than coastal waters suggest some systematic response to nutrient composition and the variability of dissolved organic matter pools, as BGE was governed by bacterial secondary production (BP). Monsoonal rains and its accompanied changes brought significant variability in BGE and bacterial productivity/primary productivity (BP/PP) ratio when compared to nonmonsoon seasons in the estuaries and coastal waters. High BP/PP ratio (>1) together with high carbon flux through bacteria (>100% of primary productivity) in the estuarine and coastal waters suggests that bacterioplankton consumed dissolved organic carbon in excess of the amount produced in situ by phytoplankton of this region, which led to the mismatch between primary production of carbon and amount of carbon consumed by bacteria. Despite the two systems being subsidized by allochthonous inputs, the low BGE in the coastal waters may be attributable to the nature and time interval in the supply of allochthonous carbon.

Analysis of estuarine colour components during non-monsoon period through Ocean Colour Monitor

Simultaneous acquisition of water samples, radiance and irradiance measurements were carried out from 40 stations in the Mandovi–Zuari estuaries during February to May 2002. From the samples collected, inherent and apparent optical properties (IOP and AOP) such as absorption coefficient ( a), upwelling diffuse attenuation coefficient ( k u) and subsurface reflectance ( R) were derived. Using these optical properties, radiative transfer at each water column is examined. On the basis of the radiative transfer outcome, band-ratio algorithms are derived for three optically active substances (OAS), viz, chlorophyll- a, suspended sediment and coloured dissolved organic matter (CDOM). The respective algorithms are 670/555, 490/670 and 412/670 nm for chlorophyll- a, suspended sediment and CDOM. These algorithms are applied to Ocean Colour Monitor (OCM), onboard Indian Remote Sensing Satellite (IRS)-Polar Satellite Launch Vehicle (P4), scenes (digital data), to synoptically analyze these OAS. The synoptic analysis of OAS revealed different hydrodynamic characteristics of the estuaries during non-monsoon seasons.

Tides in the Mandovi and Zuari estuaries, Goa, west coast of India

Mandovi and Zuari are two estuaries located in Goa, west coast of India. Variation of water level in the estuaries was monitored for a month at 13 locations using tide-poles during March–April 2003. Analysis of this data has provided for the first time, characteristics of how tidal constituents vary in the narrow and shallow estuaries, typical of those found along the west coast of India. At a distance of 45 km from the mouth the tidal range increased in both estuaries by approximately 20%. The tidal range at the upstream end of the two channels at the stations dropped sharply because of the increase in elevation of the channels.

A foraminiferal testimony for the reduced adverse effects of mining in Zuari Estuary, Goa

This paper demonstrates the potentiality of foraminifera in detecting mining pollution. Goa’s Mandovi–Zuari estuarine complex is most vulnerable to deterioration caused by the mining industry. The objective of the present study is to estimate the health of the Zuari through foraminiferal distribution in its surface sediments. The foraminiferal data generated was compared with the three‐decade‐old foraminiferal data collected in 1972 and total suspended matter (TSM) data over the years. There has been a substantial increase in the maximum total foraminiferal number (TFN), from 1143 specimens in 1972 to 3057 specimens per gram sand in 2003. Even the Total Species Number (TSN) has increased from 24 in 1972 to 50 in 2003. This is in compliance with the TSM data collected over the years, which has considerably decreased. The foraminiferal data, TSM data and reduction in mining activities in the catchment area of the Zuari Estuary suggest an improvement in the environmental health of the estuary. This study also strengthens the view that foraminifera can be used as a tool to monitor marine pollution.

Recruitment of the barnacle Balanus amphitrite in a tropical estuary: implications of environmental perturbation, reproduction and larval ecology

Phytoplankton blooms are known to influence barnacle recruitment and in boreal regions spring blooms work as an important trigger. Close to the west coast of the sub-continent of India, blooms tend to be triggered by breaks in the monsoon and the recurrence of the monsoon after a short break can stress the new recruits. The recruitment of Balanus amphitrite, an acorn barnacle, at Dona Paula Bay at the mouth of Zuari estuary, Goa, India was studied. Observations included variations in recruitment, larval abundance, development and reproduction. Adult conditioning and inter-brood variations were important factors in the larval ecology of this organism. The results indicate that the impulsive release of larvae during breaks between monsoons could be a short-sighted luxury for Balanus amphitrite in these waters. Temporal variations or recruitment failure in such environments can be attributed to inappropriate cue synchronization.

Seasonal shift in net ecosystem production in a tropical estuary

Net ecosystem production was examined in the Mandovi and Zuari estuaries (southwestern India) and the adjoining coastal waters for a period of 1 yr (January to December 1998). The study period encompassed premonsoon, monsoon, and postmonsoon seasons. At the estuarine stations, net ecosystem production showed monthly variation and a transition from net autotrophy of 49 mmol C m−2 d−1 during the nonmonsoon seasons (premonsoon and postmonsoon) to net heterotrophy of —46 mmol C m−2 d−1 in the monsoon season. Seasonal monsoon‐driven changes such as increased allochthonous inputs resulted in enhanced heterotrophic respiration and reduced primary production in the estuaries. In the coastal station, the monthly variation in net ecosystem production was not significant, and net heterotrophy was prevalent whenever measurements were made, thereby potentially serving as the net source of carbon dioxide to the atmosphere. Results suggest that the excess organic matter from these tropical estuaries supports heterotrophy in the adjacent coastal ecosystem.

Temporal variations in dimethylsulphoniopropionate and dimethyl sulphide in the Zuari estuary, Goa (India).

Despite tropical estuarine systems representing important sites for active biogeochemical processes, studies on dimethyl sulphide (DMS) in these systems are sparse. Here we report on DMS and dimethylsulphoniopropionate (DMSP) variability in relation to physicochemical and biological parameters for a period of 14 months in a tropical estuarine environment. DMS and DMSP showed high temporal variations with maximal concentrations during the southwest monsoon coinciding with a dinoflagellate bloom. Dinoflagellates appear to be the major contributors to the DMSP pool. Average DMS and DMSP concentrations (surface and bottom) suggested that much of the DMSP produced is converted to forms other than DMS. Surface DMS varied between 0.3 and 15.4 nmol dm(-3) while DMSP ranged from 0.8 to 419.5 nmol dm(-3). The DMS flux was 0.03-1.9 microM m(-2) d(-1) (average=0.6 microM m(-2) d(-1)) during the study period, that concurs well with the values reported for temperate estuaries.

Particle-associated bacterial dynamics in a tropical tidal plain (Zuari estuary, India)

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 33:29-40 (2003) - doi:10.3354/ame033029 Particle-associated bacterial dynamics in a tropical tidal plain (Zuari estuary, India) Maria-Judith B. D. De Souza, Shanta Nair, P. A. Loka Bharathi*, D. Chandramohan Biological Oceanography Division, National Institute of Oceanography, Dona Paula, 403-004 Goa, India *Corresponding author. Email: loka@darya.nio.org ABSTRACT: The dynamics of particle-associated bacteria (PAB) in a tropical estuary, Zuari, in Goa on the west coast of India, was studied for a year from September 1997 to October 1998. Bacterial abundance, productivity and enzymatic activities were measured at a fixed station in the estuary. The study period covered pre-monsoon (February to May), southwest monsoon (June to September) and post-monsoon (October to January) seasons. Particulate organic carbon ranged from 0.5 to 17.5 mgC l-1. Particles of size range >3 to <220 μm were the most abundant, were rich in organic carbon (~60%), and formed 55% of the suspended load (ave. ~0.1 g l-1) in the estuary. PAB ranged from 8.8 x 107 to 3.9 x 1010 l-1 and the waters close to the sediment had a higher abundance than the surface waters. PAB varied seasonally and accounted for 20 to 80% of the total bacterial population. The mean rate of production as measured by 3H-thymidine incorporation was 70 μg C l-1 d-1 in the surface and 35 μg C l-1 d-1 in the bottom waters. Monthly production varied by 2 orders and was not coupled to abundance. However, high production during the monsoon was fuelled by allochthonous input of organic matter. No linear relationship was observed between biological parameters and other measured environmental parameters except for temperature, which showed a linear relationship with PAB and particle numbers. The bacterial carbon demand (BCD) at the station was higher than the primary production (PP) and was met by allochthonous input. Our study demonstrates that the PAB dynamics were determined by the availability of substrates and resuspension of sedimented materials. KEY WORDS: Particle-associated bacteria · Biomass · Productivity · Tropical · Estuary Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 33, No. 1. Online publication date: August 21, 2003 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2003 Inter-Research.

Ecology of the Wood-boring Bivalve Martesia striata (Pholadidae) in Indian Waters

Martesia striata (Linnaeus) is one of the dominant wood-boring organisms found in Indian waters. Incidence of this organism in the Zuari estuary (Goa) was evaluated by exposing wooden panels (Mangifera indica) to the marine environment between January 1996 and January 1997. Effects of salinity variation on embryonic and larval development were evaluated (salinity 0, 10, 20, 30, 35, 40 and 50, temperature 25 °C) and maximum metamorphic success was observed at 30 salinity. Results of the rearing experiments, destruction pattern of wood in the environment and reproductive biology indicate that although recruitment is halted during the monsoon, adults survive and become reproductively mature in the following post-monsoon, leading to increased recruitment during pre-monsoon months.

Propagation of tides in the Mandovi and Zuari estuaries

The Mandovi and the Zuari are two shallow estuaries that are located in Goa and join the Arabian Sea. The main channel of each is about 50 km long, has its cross-sectional area decreasing rapidly in the upstream direction, and receives large amounts of riverine freshwater during the southwest Monsoon and little during the rest of the year. Tides in the channels exhibit the following characteristics: (a) The speed of propagation is about 6.5 m s−1; (b) tidal amplitude remains unchanged over a distance of about 40 km from the mouth; (c) mean water level near the head increases with increase in runoff; (d) tidal amplitude decays rapidly over ≈ 10 km near the head, the decay is more rapid during periods of higher runoff.

Tidal Propagation in the Mandovi–Zuari Estuarine Network, West Coast of India: Impact of Freshwater Influx

The Mandovi–Zuari estuarine network on the west coast of India consists of shallow strongly converging channels, that receive large seasonal influx of fresh water due to the monsoons. The main channels, the Mandovi and Zuari estuaries, connect the network to the Arabian Sea. Observations show that tidal amplitude in the channels remains unchanged over large distances (|mS40km) from the mouths of the main channels and then decays rapidly over approximately 10km near the head. To understand the dynamics behind this behaviour, a numerical model for tidal propagation has been used that simulates the observed tidal elevations well. Momentum balance in the model is predominantly between pressure gradient and friction. In the region of undamped propagation, the model behaviour is consistent with the theory that geometric amplification balances frictional decay leaving the tide unchanged. This balance breaks down near the upstream end, where channels are narrowest, and mean velocity associated with freshwater influx is sufficiently large to prevent upstream propagation of tide. This leads to rapid decay in tidal amplitude. The model also shows that the mean water-level rises in the upstream direction, in the region of the decay.