Tidal Influx Research Articles

Introducing ICEDAP: An ‘Iterative Coastal Embayment Delineation and Analysis Process’ with Applications for the Management of Coastal Change

Coastal embayments provide vital benefits to both nature and humans alike in the form of ecosystem services, access to waterways, and general aesthetic appeal. These coastal interfaces are therefore often subject to human development and modifications, with estuarine embayments especially likely to have been anthropogenically altered. Frequent alterations include damming to eliminate tidal influx, backfilling to create new land, and development for the sake of economic gain, which may cause profound damage to local habitats. By providing a record of transitions in surface waters over time, satellite imagery is essential to monitoring these coastal changes, especially on regional to global scales. However, prior work has not provided a straightforward way to use these satellite-derived datasets to specifically delineate embayed waters, limiting researchers’ ability to focus their analyses on this ecologically and economically important subset of coastal waters. Here, we created ICEDAP, a geometry-based ArcGIS toolbox to automatically delineate coastal embayments and quantify coastal surface water change. We then applied ICEDAP to the coast of South Korea, and found that coastal habitat change was particularly profound within embayed regions identified using an 8 km epsilon convexity setting (denoting a moderate distance from the coast and degree of enclosure by surrounding land areas). In the mapped coastal embayments, more than 1400 km2 of coastal habitats were lost during the past 38 years, primarily due to human modification such as large-scale land reclamation projects and the construction of impoundments. Our results suggest that anthropogenic alterations have resulted in the widespread loss of more than USD 70 million of valuable coastal ecosystem services. Together, ICEDAP provides a new innovative tool for both coastal scientists and managers to automatically identify hotspots of coastal change over large spatial and temporal scales in an epoch where anthropogenic and climate-driven changes commonly threaten the stability of coastal habitats.

Chemometric analysis and risk assessment indices to evaluate water and sediment contamination of a tropical mangrove forest

BackgroundMangroves are among the utmost productive forest residing at the interface amid terrestrial and marine environments. They play an essential role in carbon storage, nutrient cycling, and the marine food web's sustenance. Rapid land use and land cover changes have severely affected these ecosystems worldwide. Material and methodsThe present study was carried out in the mangrove forest of Kachchh district in Gujarat. This area is one of India's most swiftly growing industrialized coastal regions, embracing several ports, thermal power plants, salt production units, textile, petrochemical, cement, and fertilizer manufacturing industries. Therefore, this study aims to investigate nutrients and trace metal contamination status in mangroves. A total of 25 physicochemical parameters for water and 16 parameters for surface sediment were analysed using standard protocols. Trace metals were determined using Flame Atomic Absorption Spectrophotometry. Results and discussionImmensely higher chloride (20,116 ± 1929 mg L −1) and sulfate (2315 ± 679 mg L −1) concentrations were observed, suggesting high seawater and saltpan brine mixing in this coastal region. High tidal influx and arid-climate of the area are responsible for higher salinity (52.7 ± 5.0 PSU) in water. Cluster analysis depicts that sites M2, M3, M5, and M6 incorporate higher nutrient levels, indicating the anthropogenic origin of nutrients. The results depict the role of granulometric composition in controlling carbon, nitrogen, sulfur, and metal biogeochemistry in sediments. Results showed that mean trace metal (Fe, Cu, and Ni) content in sediment was higher than the world average shale value, indicating anthropogenic sources. Geo-accumulation index (Igeo) and Enrichment factor (EF) indicates sediment samples were moderately polluted with Cu, Zn, and Ni. ConclusionThe findings revealed that anthropogenic activities have affected the hydrogeochemistry of mangroves in the studied region, which will eventually impact flora and fauna. Therefore, there is a pressing necessity to implement pollution control, mitigation, and restoration policies for the endurable management of the mangroves.

A New Insight of Talang Akar Formation in the Ridho Field, North Palembang Sub-basin, Indonesia: An Integrated Approach

The synrift sandstone deposits of Eo-Oligocene Lemat (LMF) and Oligo-Miocene Talang Akar Formations (TAF) are the most well -known hydrocarbon reservoirs in the South Sumatra Basin, Indonesia. However, only limited studies on TAF in the North Palembang Sub-Basin have been published. In the Ridho field, TAF is characterized by fining-up sequences of inter bedded, fine to medium-grained sandstones and shales overlain by a coal layer as the top marker, while LMF comprises of continuous blocky-shaped, medium to coarse-grained, conglomeratic sandstones.Previous lithostratigraphy-driven sand to sand correlation between wells has created difficulties in understanding the geology and in producing consistent correlation, especially within the TAF. In order to define chronostratigraphy-based correlation and interpret the depositional environment of TAF and LMF, an integration between palynological, core study and petrophysical analysis was performed. The result of this integrated approach demonstrates aligned hypotheses. The occurrence of pollen Meyeripollis naharkotensis and Florschuetzia trilobata along the studied wells suggest Late Oligocene age. The palynology study subdivides TAF into three backmangrove-intertidal sand units with an increase of marine influence defining a transgression to the top of the TAF. The transgressive event is identified in core sample by lesser tidal influx sedimentary structures such as ripple, mudlayer, flaser and also finer grained sandstone at the top of TAF. Furthermore, based on petrophysical evaluation, better sand quality with lower NTG (net -to gross) near top TAF confirms the retrogradational event in this formation.The new sand unit definitions from the current study provide more consistent correlation in terms of sand thickness and characteristics for future modeling purposes.

Influence of hydrological factors on bacterial community structure in a tropical monsoonal estuary in India.

In the present study, we analyzed variations in bacterial community structure along a salinity gradient in a tropical monsoonal estuary (Cochin estuary [CE]), on the southwest coast of India, using Illumina next-generation sequencing (NGS). Water samples were collected from eight different locations thrice a year to assess the variability in the bacterial community structure and to determine the physico-chemical factors influencing the bacterial diversity. Proteobacteria was the most dominant phyla in the estuary followed by Bacteroidetes, Cyanobacteria, Actinobacteria, and Firmicutes. Statistical analysis indicated significant variations in bacterial communities between freshwater and mesohaline and euryhaline regions, as well as between the monsoon (wet) and nonmonsoon (dry) periods. The abundance of Betaproteobacteria was higher in the freshwater regions, while Alphaproteobacteria and Epsilonproteobactera were more abundant in mesohaline and euryhaline regions of the estuary. Gammaproteobacteria was more abundant in regions with high nutrient concentrations. Various bacterial genera indicating the presence of fecal contamination and eutrophication were detected. Corrplot based on Pearson correlation analysis demonstrated the important physico-chemical variables (temperature, salinity, dissolved oxygen, and inorganic nutrients) that influence the distribution of dominant phyla, class, and genera. The observed spatio-temporal variations in bacterial community structure in the CE were governed by regional variations in anthropogenic inputs and seasonal variations in monsoonal rainfall and tidal influx.

Examining coastal dynamics and recreational water quality by quantifying multiple sewage specific markers in a North Carolina estuary

Fecal contamination is observed downstream of municipal separate storm sewer systems in coastal North Carolina. While it is well accepted that wet weather contributes to this phenomenon, less is understood about the contribution of the complex hydrology in this low-lying coastal plain. A quantitative microbial assessment was conducted in Beaufort, North Carolina to identify trends and potential sources of fecal contamination in stormwater receiving waters. Fecal indicator concentrations were significantly higher in receiving water downstream of a tidally submerged outfall compared to an outfall that was permanently submerged (p < 0.001), though tidal height was not predictive of human-specific microbial source tracking (MST) marker concentrations at the tidally submerged site. Short-term rainfall (i.e. <12 h) was predictive of E. coli, Enterococcus spp., and human-specific MST marker concentrations (Fecal Bacteroides, BacHum, and HF183) in receiving waters. The strong correlation between 12-hr antecedent rainfall and Enterococcus spp. (r = 0.57, p < 0.001, n = 92) suggests a predictive model could be developed based on rainfall to communicate risk for bathers. Additional molecular marker data indicates that the delivery of fecal sources is complex and highly variable, likely due to the influence of tidal influx (saltwater intrusion from the estuary) into the low-lying stormwater pipes. In particular, elevated MST marker concentrations (up to 2.56 × 104 gene copies HF183/mL) were observed in standing water near surcharging street storm drain. These data are being used to establish a baseline for stormwater dynamics prior to dramatic rainfall in 2018 and to characterize the interaction between complex stormwater dynamics and water quality impairment in coastal NC.

Assessing the Eutrophic Susceptibility of New Zealand Estuaries

We developed a method to predict the susceptibility of New Zealand estuaries to eutrophication. This method predicts macroalgae and phytoplankton responses to potential nutrient concentrations and flushing times, obtained nationally from simple dilution models, a GIS land-use model and physical estuary properties. Macroalgal response was based on an empirically derived relationship between potential nitrogen concentrations and an established macroalgal index (EQR) and phytoplankton response using an analytical growth model. Intertidal area was used to determine which primary producer was likely to lead to eutrophic conditions within estuaries. We calculated the eutrophication susceptibility of 399 New Zealand estuaries and assigned them to susceptibility bands A (lowest expected impact) to D (highest expected impact). Twenty-seven percent of New Zealand estuaries have high or very high eutrophication susceptibilities (band C or D), mostly (63% of band C and D) due to macroalgae. The physical properties of estuaries strongly influence susceptibility to macroalgae or phytoplankton blooms, and estuaries with similar physical properties cluster spatially around New Zealand’s coasts. As a result, regional patterns in susceptibility are apparent due to a combination of estuary types and land use patterns. The few areas in New Zealand with consistently low estuary eutrophication susceptibilities are either undeveloped or have estuaries with short flushing times, low intertidal area and/or minimal tidal influx. Estuaries with conditions favourable for macroalgae are most at risk. Our approach provides estuary-integrated susceptibility scores likely to be of use as a regional or national screening tool to prioritise more in-depth estuary assessments, to evaluate likely responses to altered nutrient loading regimes and assist in developing management strategies for estuaries.

Sedimentary features influencing the occurrence and spatial variability of seismites (late Messinian, Gargano Promontory, southern Italy)

Seventeen layers characterized by soft-sediment deformation structures (SSDS) were identified within the “calcari di Fiumicello”, an upper Messinian (Miocene) stratigraphic unit (30 m thick), cropping out in the northern sector of the Gargano Promontory (Apulia, southern Italy). Facies analysis was performed on the whole outcrop and detailed sedimentological investigations were carried out on the deformed beds, in order to interpret the deformation mechanism, the driving mechanism and the possible trigger agent. Deformed layers occur in some thin-bedded ooidal limestones, skeletal calcarenite, as well as in some pebble-size conglomerate, alternated with marls, deposited in a protected embayment or barrier-island-lagoon system, possibly characterized by high salinity, and tidal influx. SSDS can be classified as load- and slump/slide structures. The continuous exposures allow us to follow a single deformed layer along tens of meters, hence several types of lateral variations were observed that can be summarised as follows: (1) SSDS disappear within a few meters (with a decreasing pattern of their deformation or in an abrupt way); (2) deformed layers laterally change in thickness and morphology; and (3) a single deformed bed can laterally correspond to two deformed beds. Most of the soft sediment deformation features were identified as liquefaction and/or fluidization features related to seismic shocks (seismites). Seismites are often used as an indicator of seismic events, especially along small outcrops, trench excavation and core analysis. This study highlights the value of the sedimentological analysis for paleoseismic investigations, with the aim of improving criteria for identifying seismites in the sedimentary record, and their suitability as marker of seismic events.

Impact of 2004 co-seismic coastal uplift on the mangrove cover along the North Andaman Islands

The December 2004 earthquake and the subsequent tsunami have incurred devastating impacts on vital habitats along the Indian coastal region, where few of them are irreversible. The earthquake has uplifted the northern Andaman coast, resulting in a drastic reduction of tidal water influx into the adjoining mangrove-laden mudflats. Satellite images of the period from 2003 to 2019 were used to assess the impact of coastal upliftment on the northern Andaman mangroves. Through satellite data analysis, we report a loss of 6500 ha of northern Andaman mangroves. Tidal hydrodynamics simulation under the post-earthquake scenario showed a vast area of mudflats deprived of tidal influx. This reduction in the tidal inundation has incurred a gradual and permanent mangrove area degradation. The earthquake impact on the mangroves was not spontaneous, but a gradual process, where the mangroves were intact until Mach 2006. The earthquake and the resultant coastal uplift have significantly altered the coastal geomorphology as well as the plant demography of the study area. Field visit revealed the terrestrial vegetation growth along the erstwhile mudflats, and vast areas of mangrove peat are observed, surrounded by successions of marshy and terrestrial plants. As mangroves are preferred habitat for diverse marine and terrestrial organisms and act as a vital food source and juvenile shelters for various fish species, the extensive loss of mangrove area may adversely affect a large scale biological ecosystem.

Averting danger under the bridge: video confirms that adult small-toothed morays tolerate salinity before and during tidal influx

Safety considerations for researchers shape ecological research approaches in dangerous aquatic environments. A series of recent studies has demonstrated that the moray Gymnothorax polyuranodon (Family Muraenidae) occupies freshwater in the adult phase. However, its potential use of tidal habitat remains largely unexplored, due partly to the challenges of performing underwater research within estuarine crocodile territories. In September 2017, opportunistic snorkel-based observations revealed individuals of this species occupying lairs at an upper tidal creek site during low tide (under freshwater conditions). This provided an opportunity to tailor field-based measurements of the salinity tolerance of this species a fortnight later during a more substantial high tide. Specifically, remote underwater video, snorkel and above-water observations of morays, combined with salinity measurements, reveal that G. polyuranodon is capable of tolerating salinity of at least 14.4 for several hours and can inhabit salinity of 19 for a period of several minutes. This finding, when viewed in synergy with other relevant studies of G. polyuranodon, indicates that the species is either catadromous or amphidromous or capable of either strategy.

Character of extreme high tide level variations response to coastline deformation in Taizhou Bay

Taizhou Bay, which locates in the southern coast of China, is frequently influenced by human activities, leading coastline changes frequently in coastline changes visible from space. Coastline deformation in this area will obviously affect the character of extreme high tide level variations in Jiaojiang River and Estuary especially during flood and typhoon periods. Statistic data showed that 54.5% of the extreme high tide levels of Jiaojiang River were caused by typhoon and 27.3% by flood in the past twenty-two years. So, a two-dimensional (2-D) hydrodynamic numerical model including Jiaojiang River and East China Sea was established based on the Mike21 FM model. The model was calibrated with field data and then was employed to predict the extreme flood and storm high tide level changes under three different assumption plans of coastline deformation. 100-year return discharge upstream with 2-year return tide level downstream conditions were set in the model to simulate extreme flood level changes, while Typhoon 0414 with actual discharge upstream were considered to simulate extreme storm high tide level variations. According to the flood level changes simulating results, an increase of 0.01∼0.03 m in extreme flood level will happen in river section and estuarine section and a decrease of 0.01∼0.06 m will occur outside estuarine section. Predictions of the typhoon conditions show that an increase of 0.01∼0.15 m in extreme storm high tide level will happen in both river and estuarine sections with a decrease of 0.01∼0.03 m outside of the Jiaojiang Estuary. Further analysis from tide wave point illustrates that propagation direction of nearshore tide wave in Taizhou Bay will be turned by coastline deformation, thus reflection effect of tide wave will be weakened, while distribution of storm tide currents field changes shows that tidal influx of Jiaojiang Estuary increases due to the blocking effect of the seawalls, causing this kind of special extreme high tide level changing formation.

Long-Term Geomorphic Changes in the Coastal Profile of Lingding Bay in the Pearl River Estuary and the Response to Tides Since 1906

Lingding Bay in the Pearl River Estuary, located on the north coast of the South China Sea, experiences frequent storm surges caused by typhoons. The geomorphic features of the Pearl River Estuary have changed tremendously due to natural processes and human activities over the last century, and these changes have led to changes in the hydrodynamic environment, such as a reduced capacity for holding tides in the coastal zone. In this paper, the relation between geomorphic features and the capacity for holding tides is analyzed. In order to ascertain how historical landform change affects this capacity, we study the spatial morphology change of Lingding Bay in the Pearl River Estuary (since 1906) through the analysis of historical topographic maps and nautical charts. The shape index and fractal dimension were introduced as indicators to reflect coastline changes that have affected the tides. The tidal dissipation rate and tidal influx were found to describe a bay’s capacity to hold tides. The results show that, since 1906, the tidal influx and the tidal dissipation rate have decreased by about 14.11% and 23%, respectively, in the study area. We suppose that these changes could be attributed to geomorphic changes, primarily changes brought about by land reclamation projects.

The 20,000-years-long sedimentary record of the Lesina coastal system (southern Italy): From alluvial, to tidal, to wave process regime change

The present-day Lesina area (Adriatic coast of southern Italy) preserves in the subsurface the stratigraphic signature of a recent sedimentary process regime change, which was responsible for the conversion of a former alluvial plain into a back-barrier tidal flat and, finally, into the modern barrier island. Facies-based analyses of the first 55 m of the upper Pleistocene–Holocene stratigraphic record, integrated with biostratigraphic sampling, radiocarbon data, and aerial observations of some diagnostic relict morphologies, allowed us to reconstruct the history of the last 20,000 years of this area. The succession investigated is adjacent to a salt dome, which uplifted in recent times, forming the easternmost boundary of the present-day Lesina lagoon. Three main stratigraphic intervals were detected in the subsurface: the lowermost unit is made up of conglomerates, sandstones, and mudstones of terrestrial origin, belonging to a complex system of alluvial plain filling a pre-existing Last Glacial Maximum (LGM) topography. The second interval consists of sands and muds, with subordinate conglomerates of brackish and marine origin, and lies on the previous one through a wide ravinement. Its composing lithofacies exhibit a strong tidal signature preserved in tidal rhythmites belonging to a net of tidal channels, associated with marshes, mud flat, and lagoonal deposits. These sediments record the emplacement of a back-barrier tidal flat, which developed under the strong influence of a tidal influx enhanced by the late post-LGM transgression. The third uppermost interval resulted from the deposition of coastal-marine sands and gravels accumulated during the ensuing modern normal regression, under the dominance of a wave-dominated coastal dynamics, which was responsible for the progradation of the present-day beach barrier and the closure of the Lesina lagoon. The paleogeography of the back-barrier tidal flat preceding the onset of the modern barrier island is thus reconstructed based on the results of our facies analysis, biostratigraphy, and AMS dating. Many of the elements composing this mid-Holocene tide-influenced system were also interpreted from the aerial-photograph observation of several relict morphologies, which are still preserved in many parts of the modern Lesina barrier island. We propose some new interpretation on the origin some of these elements, which possibly developed under sedimentary process regimes different from the modern ones, including some flood-tidal deltas, previously interpreted as tsunami-derived washover fans.

The impact of large-scale reclamation on hydro-dynamic environment–A case study of Xinghua Bay

A hydro-dynamic model is established on basis of MIKE21FM to simulate the hydro-dynamic characteristics of Xinghua Bay and investigate the influence of reclamation project on the tidal elevation and tidal currents. Tidal elevation data was obtained at the six tide gauge stations around the Xinghua Bay, and another six current stations were established to observe the tidal current velocity and direction. Validation shows that the model-simulated tidal elevation and tidal currents agree well with observations made at different stations. Predictions are made according to the reclamation project proposed in the regional marine planning of Hanjiang Industrial Park around the port in Putian City. The variations of hydro-dynamic factors, such as tide, current velocity and direction and tidal influx are obtained, and the adverse effect of reclamation on marine environment is discussed. It is shown that the tidal level inside the Xinghua Bay during high tide decreases after the reclamation project is completed. The tidal currents during flooding tide generally decrease in the southeast of the reclamation region, with the maximum decreasing amplitude reaching 0.44 m s−1. On the other hand, the tidal currents during flooding tide increase around the southeast and southwest corners of the reclamation region. The tidal currents during ebb tide increase around the southeast and southwest corners of the reclamation region, with the maximum increasing amplitude attaining 0.18 m s−1. The results in this paper can give some guidance for the marine environment management and the effective utilization of land in Putian.

Going with the flow: Tidal influence on the occurrence of the harbour porpoise (Phocoena phocoena) in the Marsdiep area, The Netherlands

One of the most important factors explaining the distribution and behaviour of coastal marine mammals are tides. Tidal forces drive a large number of primary and secondary processes, such as changes in water depth, salinity, temperature, current velocity and direction. Unravelling which tidal process is the most influential for a certain species is often challenging, due to a lack of observations of all tide related covariates, strong correlation between them, and the elusive nature of most marine organisms which often hampers their detection.In the Marsdiep area, a tidal inlet between the North Sea and the Dutch Wadden Sea, the presence of harbour porpoises (Phocoena phocoena) was studied as a function of tide related covariates. Observations were carried out in early spring from a ferry crossing the inlet on a half hourly basis. Environmental and sightings data were collected by one observer, while an on-board Acoustic Doppler Current Profiler (ADCP) and temperature sensor continuously recorded current velocity profiles and temperature, respectively. Sea surface temperature and salinity were measured at a nearby jetty. Sightings (n=134) were linked to tidal elevation, geographical position, local depth-averaged current velocity, water temperature (with and without trend correction) and salinity.Variation in sighting rate was best described by salinity, with highest sighting rate at high levels of salinity (>30gkg−1), indicating that porpoises enter the area in bodies of (more saline) North Sea water. Second best variable was time of day, with the highest sighting rate early morning, and decreasing during the day. However, surveys in the morning happened to coincide more often with high water and hence, the apparent time of day effect could be due to collinearity. Most porpoises were present in the northern part of the Marsdiep, particularly during high tide.Tide dependent sighting rates confirmed that porpoises reside in the North Sea, and enter the western Wadden Sea during the flood and leave during ebb. This tidal influx is most likely related to prey availability, which corresponds to other recent studies in this area showing higher fish abundance during high tide. Documenting information on tide related patterns could be used in practice, when e.g. planning anthropogenic activities or assessing critical habitats for this species.

Hydrodynamic characteristics and sediment transport of a tidal river under influence of wading engineering groups

By taking the Yong River for example in this paper, based on the multiple measured data during 1957 to 2009, the change process of runoff, tide feature, tidal wave, tidal influx and sediment transport are analyzed. Then a mathematical model is used to reveal the influence mechanism on hydrodynamic characteristics and sediment transport of the wading engineering groups such as a tide gate, a breakwater, reservoirs, bridges and wharves, which were built in different periods. The results showed the hydrodynamic characteristics and sediment transport of the Yong River changed obviously due to the wading engineering groups. The tide gate induced deformation of the tidal wave, obvious reduction of the tidal influx and weakness of the tidal dynamic, decrease of the sediment yield of flood and ebb tide and channel deposition. The breakwater blocked estuarine entrances, resulting in the change of the tidal current and the reduction of the tidal influx in the estuarine area. The large-scale reservoirs gradually made the decrease of the Yong River runoff. The bridge and wharf groups took up cross-section areas, the cumulative affection of which caused the increase of tidal level in the tidal river.

Beverley Park water reuse plant: getting the salt just right

The extraction type wastewater recycling systems are those where wastewater is taken from the collection system en route to the central treatment plant. This paper discusses a case study of Sydney’s first ever extraction type scheme, the Beverley Park water reuse scheme. Primary applications of recycled water from this case study site include: parks and ovals, green-belt and golf course irrigation. Given the plant’s location on a major interceptor sewer along Kogarah Bay, tidal influx posed a significant challenge due to high salt levels. Salt sensitive grass on golf course greens meant that treated water had to meet stringent quality requirements with regards to salt. The design involved modelling the process of diurnal fluctuations in salt levels and to provide an optimised process design. A non-membrane, design based solution was also chosen to resolve this high salinity challenge. This Case Study highlights the significant challenges in planning, design and commissioning of water reuse plant intercepting sewer carriers prone to salt water intrusion. The study provides valuable knowledge that will assist in providing viable extraction type water reuse schemes for tidal impacted areas.

Effect of Freshwater Influx on Phytoplankton in the Mandovi Estuary (Goa, India) during Monsoon Season: Chemotaxonomy

The Mandovi estuary is a prominent water body that runs along the west coast of India. It forms an estuarine network with the adjacent Zuari estuary, connected via the Cumbharjua canal. The physico-chemical conditions seen in the Mandovi estuary are influenced by two factors: the fresh water runoff during the monsoon season (June-September) and the tidal influx of coastal seawater during the summer (October to May) season. However, the effects of monsoon related changes on the phytoplankton of the Mandovi estuary are not yet fully understood. An attempt to understand the same has been made here by applying the process of daily sampling at a fixed station throughout the monsoon season. It was noticed that the onset of the monsoon is responsible for an increase in nitrate levels upto 26 μM from <1 µM during pre-monsoon and enhancement of chlorophyll a (chl a) as high as 14 µg·L −1 during the same period. The phytoplankton population was observed through both chemotaxonomy and microscopy and was found to be composed mainly of diatoms. CHEMTAX analysis further uncovers the presence of several other groups of phytoplankton, the presence of which is yet to be reported in many other tropical estuaries. It includes chrysophytes, cyanobacteria, prasinophytes, prymnesiophytes and chlorophytes. The appearance of phytoplankton groups at various stages of the monsoon was recorded, and this data is discussed in relation to environmental changes in the Mandovi estuary during the monsoon season.

Effects of the Large-Scale Reclamation Project on Hydro-Dynamic Environment in the Estuary

The hydro-dynamic environment will be changed after reclamation project building. It will affect the navigation, estuary regime, tidal prism, flood controlling, storm surge and so on. Taking the shore reclamation between Oujiang and Feiyunjiang estuary as example, a tidal current mathematical model is used to study the effects of the large-scale reclamation on the hydro-dynamic environment. Based on triangle grid and finite volume method, the shallow flow model is examined by 9 tidal level stations and 9 observed synchronous vertical lines. And the comparison between computed result and measured solution demonstrates very good agreement. After the project building, the high tide level reduces to a certain extent and the flow of front reclamation line reduces by a big margin. But it is a little influence to the core ports of Wenzhou. And the tidal influx through Feiyunjiang Estuary decreases. The result can provide important reference and inspiration for the effects of hydro-dynamic environment due to the large-scale reclamation projects.

Physicochemical and biological factors controlling water column metabolism in Sundarbans estuary, India

BackgroundSundarbans is the single largest deltaic mangrove forest in the world, formed at estuarine phase of the Ganges - Brahmaputra river system. Primary productivity of marine and coastal phytoplankton contributes to 15% of global oceanic production. But unfortunately estuarine dynamics of tropical and subtropical estuaries have not yet received proper attention in spite of the fact that they experience considerable anthropogenic interventions and a baseline data is required for any future comparison. This study is an endeavor to this end to estimate the primary productivity (gross and net), community respiration and nitrification rates in different rivers and tidal creeks around Jharkhali island, a part of Sundarbans estuary surrounded by the mangrove forest during a period of three years starting from November’08 to October’11.ResultsVarious physical and chemical parameters of water column like pH, temperature, conductivity, dissolved oxygen, turbidity, suspended particulate matter, secchi disc index, tidal fluctuation and tidal current velocity, standing crop and nutrients were measured along with water column productivity. Relationship of net water column productivity with algal biomass (standing crop), nutrient loading and turbidity were determined experimentally. Correlations of bacterial abundance with community respiration and nitrification rates were also explored. Annual integrated phytoplankton production rate of this tidal estuary was estimated to be 151.07 gC m-2 y-1. Gross primary productivity showed marked inter annual variation being lowest in monsoon and highest in postmonsoon period.ConclusionAverage primary production was a function of nutrient loading and light penetration in the water column. High aquatic turbidity, conductivity and suspended particulate matter were the limiting factors to attenuate light penetration with negative influence on primary production. Community respiration and nitrification rates of the estuary were influenced by the bacterial abundance. The estuary was phosphorus limited in postmonsoon whereas nitrogen-limited in premonsoon and monsoon period. High algal biomass and primary productivity indicated the estuary to be in eutrophic state in most of the time throughout the year. Our study also indicated a seasonal shifting between autotrophic and heterotrophic conditions in Sundarban estuarine ecosystem and it is a tropical, well mixed (high tidal influx) and marine dominated (no fresh water connection) system.

Assessment of Organic Matter Sources in the Tropical Mangrove Ecosystems of Cochin, Southwest India

The sources of organic matter in three typical mangrove systems of Cochin estuary were assessed for the first time with help of sediment bulk parameters and fatty acid biomarkers. The C/N and δ13C analysis showed intermediate values to that of autochthonous and terrestrial inputs of organic matter, signaling to a mixed origin. The biochemical composition of sedimentary organic matter revealed a dominance of lipids over proteins and carbohydrates, indicating the nutritive or energetic value as well as the freshness of organic matter in all the systems. Fatty acids ranging from C8 to C24 were identified in the study. C20:5n-3 was one of the major fatty acids at station 1, indicating significant benthic phytoplankton contribution. The zooplankton biomarkers C20:1 and C24:1 were also present in appreciable levels, suggesting the tidal influx. Principal fatty acids at station 2 were the zooplankton biomarkers C20:1 and C24:1 implying significant estuarine contribution through tidal influx. The major fatty acids at station 3 were diatom marker C20:5n-3 and the higher plant marker C24:0. Dominant fatty acids in mangrove leaves; C18:2n-6 and C18:3n-3 were also present at station 3. The low contributions of C20:1 and C24:1 confirms the limited tidal exchange at this station. Presence of significant amount polyunsaturated fatty acids in the mangrove sediments confirms the freshness of organic matter. Thus, fatty acid biomarker study of the three mangrove systems of Cochin estuary could substantiate the bulk parameter approaches effectively; distinguishing the multiple sources of the organic matter and the observed spatial variations.