Estuary Mouth Research Articles

Stable Isotopes and Bayesian Modeling Methods of Tracking Sources and Differentiating Bioavailable and Recalcitrant Phosphorus Pools in Suspended Particulate Matter

Understanding the sources of different phosphorus (P) pools and their bioavailability under imposed biogeochemical environments in a watershed is limited largely due to the lack of appropriate methods. In this research, phosphate oxygen isotope ratios and Bayesian modeling on fingerprinting elements were applied as two novel methods to identify sources and relative recalcitrancy of particulate P pools suspended in water in the continuum of sources from land to the mouth of a coastal estuary to the Chesapeake Bay. Comparative analyses of sizes, relative ratios, and oxygen isotope values of particulate P pools in the creek water suggested that the NaHCO3-P pool was bioavailable, whereas NaOH-P and HCl-P pools were recalcitrant during P transport along the creek. Agricultural field soil, streambank, and river bottom sediments were major sources of particulate P and their contributions varied significantly at the headwater and downstream regions of the creek. Bayesian modeling based on fingerprinting elements suggested that tides played a major role in forming particulate matter from estuarine sources at the creek mouth region and importing it upstream. These findings provide new insights into the origin and fate of particulate P and the fidelity of isotope and fingerprinting methods in source tracking of P in tidally influenced watersheds.

Using otolith microchemistry to assess nursery habitat contribution and function at a fine spatial scale

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 606:151-173 (2018) - DOI: https://doi.org/10.3354/meps12765 Using otolith microchemistry to assess nursery habitat contribution and function at a fine spatial scale Janet A. Ley*, Holly J. Rolls Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 Eighth Avenue Southeast, St. Petersburg, Florida 33701, USA *Corresponding author: danceswithfish.jal@gmail.com ABSTRACT: Estuarine tributaries are vital links in connectivity for transient coastal fish undergoing ontogenetic habitat shifts, yet these resources are on the frontlines of anthropogenic change. Prioritizing actions to protect valuable fisheries may require fine-scale analyses of the relative value and function of tributaries as nurseries for regional populations. For sectioned otoliths from young-of-the-year (YOY) common snook Centropomus undecimalis; snook), we used laser ablation-inductively coupled plasma-mass spectrometry and stable isotope analysis to obtain microchemical signatures distinguishing 9 tributaries (each <1.0 km2, <5 km apart) along a mangrove-to-saltmarsh gradient in the Little Manatee River (LMR), Florida, USA. Using canonical analysis of principal coordinates and jackknifed leave-one-out classification for 123 fish, 70 (56.9%) were classified correctly based on microchemical signatures, compared with 11.1% that would have been correctly classified by chance alone (χ2, p < 0.0001). Months later, 39 of 40 (98%) yr-1 snook collected from throughout the LMR were assigned to a YOY nursery tributary based on otolith core signatures. The 3 tributaries making the greatest contribution of YOY snook to the yr-1 population were in pristine, low salinity (0.5-1.5 psu) saltmarshes farthest from the estuary mouth. Since other studies have identified completely different spatial patterns in fish nursery use from year to year, this study should be replicated to assess temporal variation in snook contribution from these nurseries. Nevertheless, this fine-scale application of otolith microchemistry is encouraging for future efforts seeking to protect locations having the greatest likelihood of contributing to survival of fishes that make ontogenetic habitat shifts within coastal ecosystems. KEY WORDS: Otolith microchemistry · Mangrove · Salt marsh · Ecology · Estuary · Centropomus undecimalis · Nursery · Tampa Bay · Connectivity · Contribution analysis Full text in pdf format Supplementary material PreviousNextCite this article as: Ley JA, Rolls HJ (2018) Using otolith microchemistry to assess nursery habitat contribution and function at a fine spatial scale. Mar Ecol Prog Ser 606:151-173. https://doi.org/10.3354/meps12765 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 606. Online publication date: November 15, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Southern California Coastal Response to the 2015–2016 El Niño

AbstractWidespread erosion associated with energetic waves of the strong 2015–2016 El Niño on the U.S. West Coast has been reported widely. However, Southern California was often sheltered from the northerly approach direction of the offshore waves. The few large swells that reached Southern California were not synchronous with the highest tides. Although west coast‐wide tidal anomalies were relatively large in 2015–2016, in Southern California, total water levels (sum of tides, anomalies, and wave superelevation) were lower than during the 1997–1998 Niño, and comparable to the 2009–2010 Niño. Airborne lidar surveys spanning 300 km of Southern California coast show the beach response varied from considerable erosion to accretion. On average, the shoreline moved landward 10 m, similar to the 2009–2010 El Niño. Some San Diego county beaches were narrower in the 1997–1998 El Niño than in 2015–2016, consistent with the higher erosion potential in 1997–1998. Beach retreat exceeded 80 m at a few locations. However, 27% of the shoreline accreted, often in pocket beaches, or near jetties. While adjacent beaches eroded, estuary mouths accreted slightly, and several estuaries remained or became closed during the study period. Only 12% of cliffs eroded (mostly at the base), and the average cliff face retreat was markedly less than historical values. Only two cliff‐top areas retreated significantly. Although some areas experienced significant change, the potential for coastal erosion and damage in Southern California was reduced compared to the 1997–1998 El Niño, because of low rainfall, a northerly swell approach, and relatively limited total high‐water levels.

Interannual and Seasonal Variations in Estuarine Water Quality

Anthropic processes degrade quality of estuarine environments, resulting in a worrying form of water pollution. The objective this study was to describe and discuss interannual and seasonal changes of water quality based on indicators monitored in Goiana River estuary, as well as identifying the main drivers of such changes. We considered three estuarine areas or habitats (upper estuary, middle estuary and lower estuary), and two seasons (dry and rainy) for anchoring sample design. The information collected for surface and bottom water include water temperature (°C), salinity, dissolved oxygen (mg L-1), saturation (%) and Secchi depth (cm) (n=864). The monthly total rainfall (mm) was compiled from public database. Multivariate analyses highlight inter dependency among these parameters. Water quality was reduced in dry periods (including episodes of hypoxia), but generally increased towards the mouth of estuary. Rainfall is the most important factor in the renewal and maintenance waters of small tropical estuaries. Regions most sensitive to climate change where water resources are depleted and/or compromised should pay even more attention to upcoming changes in rainfall (seasonal) and climatic patterns in addition to better water management practices.

Frictional interactions between tidal constituents in tide-dominated estuaries

Abstract. When different tidal constituents propagate along an estuary, they interact because of the presence of nonlinear terms in the hydrodynamic equations. In particular, due to the quadratic velocity in the friction term, the effective friction experienced by both the predominant and the minor tidal constituents is enhanced. We explore the underlying mechanism with a simple conceptual model by utilizing Chebyshev polynomials, enabling the effect of the velocities of the tidal constituents to be summed in the friction term and, hence, the linearized hydrodynamic equations to be solved analytically in a closed form. An analytical model is adopted for each single tidal constituent with a correction factor to adjust the linearized friction term, accounting for the mutual interactions between the different tidal constituents by means of an iterative procedure. The proposed method is applied to the Guadiana (southern Portugal–Spain border) and Guadalquivir (Spain) estuaries for different tidal constituents (M2, S2, N2, O1, K1) imposed independently at the estuary mouth. The analytical results appear to agree very well with the observed tidal amplitudes and phases of the different tidal constituents. The proposed method could be applicable to other alluvial estuaries with a small tidal amplitude-to-depth ratio and negligible river discharge.

Striped Bass Early Life History in the Macrotidal Shubenacadie River

AbstractThis 9‐year study (2008–2016) on the Shubenacadie River estuary in Nova Scotia yielded new insight into the only confirmed nursery habitat for the Bay of Fundy population of Striped Bass Morone saxatilis. In 7 of 9 years, the initial large spawning episode occurred between May 16 and June 1, after the accumulation of 11 to 20 degree‐days above 12°C. Most of the spawning occurred within about 3 weeks in May and June but could run into July. Egg abundance at river kilometer (rkm) 25 (measured from the estuary mouth) exceeded 1,000 eggs/m3 after the largest episodes due to the narrow estuary and high numbers of spawners. The pelagic eggs and prefeeding larvae were passively transported up and down the estuary by the strong tide, their distribution highly dependent on salinity. The salt front defined the upstream boundary of the nursery habitat, with the eggs and larvae normally distributed between 0.15‰ and 15‰ (above rkm 10). The abundance of first‐feeding larvae (5–7 mm TL) in the upper estuary (above rkm 25) was highest (&gt;500/m3) during years when May–June was warm and dry and saltwater intrusion was high (above rkm 32). Heavy rain after spawning was an important lethal factor, limiting saltwater intrusion to rkm 25 and increasing the risk of advection of eggs and larvae into Cobequid Bay. During June, a lack of copepod prey caused larvae to fail to grow, suggesting that starvation is an important lethal factor. Growth from July onwards was limited by temperature but not food: mysids were highly abundant and an important prey for young of the year (&gt;15 mm TL). By late August juvenile mean total length was &gt;9 cm in warm summers but &lt;5 cm in cooler years. Juveniles were widely dispersed in the estuary and Cobequid Bay through September; their apparent abundance each year was poorly related to larvae abundance.

Migration and feeding habits of juvenile Chinese sturgeon (Acipenser sinensis Gray 1835) in the Yangtze Estuary: Implications for conservation

Abstract Spatial and temporal variation in migration and feeding ecology of juvenile Chinese sturgeon (Acipenser sinensis Gray 1835) is reported for waters around Chongming Island, Yangtze Estuary, between April and August 2015. A migration survey showed that juvenile Chinese sturgeon remained within the Yangtze Estuary for a period of time preceding their onward migration to the sea; upper estuarine reaches were an important transition habitat during April and May, while nearshore coastal areas were foraging habitat during June to August. Stable isotopic analysis revealed (1) significantly lower isotope values in smaller‐sized Chinese sturgeon (≤100 mm) than larger‐ sized fish (&gt;100 mm), which indicated a dietary shift likely occurs at fork lengths greater than 100 mm; (2) the increase in values of δ13C and δ15N from May to August implied an ontogenetic dietary shift from lower to higher trophic‐level prey items; and (3) slight changes in distributional range among different coastal sites implied that individuals fed on similar food items. Coastal shallows represent major foraging areas for juvenile Chinese sturgeon in the Yangtze Estuary. In addition to the conventional conservation measures at the nature reserve, we suggest additional conservation actions to better protect juvenile Chinese sturgeon residing in the estuary; namely: (1) expanding the protected area and adding a seasonal component, from April to August, to afford better protection of juvenile Chinese sturgeon in the whole estuary, but particularly just upstream of the estuary mouth and in nearshore waters; and (2) banning all fishing activities and extending protection to the food resources (such as zoobenthos and small‐sized fishes) of juvenile Chinese sturgeon in coastal shallows.

Can Saltwater Intrusion Affect a Phytoplankton Community and Its Net Primary Production? A Study Based on Satellite and Field Observations

Net primary production (NPP) by phytoplankton is a crucial regulator of the carbon cycle and other biological processes in estuaries. Under the impacts of rising sea levels, most estuaries are experiencing increased saltwater intrusion. To determine how these changes in intrusion affect phytoplankton communities and their NPP, a study was performed in the Pearl River Estuary (PRE), China. The results based on monthly global ocean NPP satellite products from 2003 to 2015 show that NPP generally decreased from the north (the upper outlet) to the south (the estuary mouth) in the PRE, whereas temporally, NPP in the rainy season (April to September) exhibited an inverted V-shaped curve, with a maximum value in July and was generally higher than that in the dry season (October to the following March). Field observations of salinity increased from north to south in the PRE, but phytoplankton species and cell numbers decreased from outlets toward the outer estuary. Further analysis showed that NPP and phytoplankton species were positively correlated (R2 ~ 0.5), whereas NPP and salinity were negatively correlated (R2 ~ 0.4). Overall, saltwater intrusion in the dry season increased salinity and changed the phytoplankton species abundance and composition, and it may inhibit phytoplankton growth, thereby decreasing NPP.

A mass mortality of fishes caused by receding water levels in the vegetated littoral zone of the West Kleinemonde Estuary, South Africa

On 15 November 2017 the mouth of the West Kleinemonde Estuary breached following heavy catchment rains and increased river flow. The water level in the estuary following mouth opening decreased by 1.65 m within 24 h, resulting in an almost complete draining of the littoral zone where large beds of the aquatic macrophyte Ruppia cirrhosa and mats of the associated filamentous algae were present. As the water depth within the plant beds decreased, the macrophytes, together with the algal filaments, created an increasingly dense mat, trapping fish that were resident, foraging or passing through the littoral zone. By 16 November 2017 large numbers of fishes belonging to at least 20 species were trapped in pools and depressions within the littoral, as well as within the R. cirrhosa beds and filamentous algal mats in the lower reaches of this system. Other affected taxa included crustaceans, especially isopods, and large numbers of small bivalves attached to macrophyte vegetation. Beneficiaries of the fish kill, in terms of unexpected food availability, included a variety of piscivorous bird species and the Cape clawless otter Aonyx capensis. This is the first documented account of a diverse species fish kill associated with estuary mouth breaching.

Local acoustic habitat relative to hearing sensitivities in beluga whales (Delphinapterus leucas)

Background noise can have a substantial effect on communication signals, however far less is known about how natural soundscapes may influence hearing sensitivity. Here we compare the audiograms of 26 wild beluga whales measured in their natural environment to a series of ecoacoustic measurements within a primary portion of their Bristol Bay summer habitat, the Nushagak Estuary in Bristol Bay, AK, USA. Environmental acoustic measurements were made during 2012 and 2016 using two different methods: a moored recorder and drifter buoys. Environmental noise curves varied substantially. Drifter recordings from the middle of Nushgak Estuary had the highest spectrum levels during ebb tides with acoustic energy from sediment transport extending well into higher frequencies (ca. 60 kHz), likely due to rapidly moving tidal flow and shifting sediment in that location. Drifter recordings near the estuary mouth and shallow tidal flats were lower amplitude. Noise levels generally varied during drifts (in one case up to ca. 6 dB) reflecting acoustic cues available to the local belugas. The moored recorder showed a substantially different spectral profile, especially at lower frequencies, perhaps due to its attachment to a pier piling and subsequent pier noise. Hearing sensitivity varied by individual and thresholds often fell above 1/3 octave-band noise levels, but not overall noise spectral density. Audiograms of the most sensitive animals closely paralleled the lowest ambient noise power spectral density curves, suggesting that an animal’s auditory dynamic range may extend to include its habitat’s quietest conditions. These data suggest a cautious approach is necessary when estimating the sound-sensitivity of odontocetes found in quiet environments as they may have sensitive auditory abilities that allow for hearing within the lowest noise-level conditions. Further, lower level ambient noise conditions could provide a conservative estimate of the maximal sensitivity of some cetacean populations within specific environments.

Seasonal hydrodynamic interactions between tidal waves and river flows in the Yangtze Estuary

Estuaries are transition regions between marines and inland rivers where hydrodynamic processes are controlled by oceanic tidal waves and fluvial discharges. Moreover, human activities, such as the growing number of water conservancy projects, have an increasing impact on estuarine hydrodynamics. However, these natural variations and anthropogenic impacts are not yet fully understood, especially for large estuaries. In this study, the interactions between tidal waves and riverine flows in the Yangtze Estuary were investigated using the methods of numerical modelling and harmonic analysis. The focus of this study is on the characteristics of tides in the coastal area, seasonal variations in hydrodynamic process and impacts of reservoir regulation on tidal constituents in the tidal river. The results indicate that in the coastal area, semi-diurnal and diurnal tidal constituents propagate in different directions along the coast and that the tidal waves in the coastal area are stationary, i.e. the amplitude and phase do not change in time. However, in the tidal river, significant seasonal variations in the water surface slope, water level fluctuations and damping process can be identified. In the dry season, the tidal signal can reach Datong station, >600 km from the estuary mouth, whereas in the wet season, the signal's reach is approximately 350 km. From the dry to wet seasons, the maximum decrease in the amplitude of the dominant M2 tide is approximately 0.3 m. The amplitudes of the tidal constituents do not decrease monotonically because of the complex interactions among the bed friction, river discharge and channel width convergence as well as energy transmission between the tidal constituents. Because the Three Gorges Reservoir is used to regulate seasonal discharge, the increase in the accumulated amplitudes of the six major tides can reach up to 0.1 m in the tidal river reach.

Seasonal Drivers of Carbon Dioxide Dynamics in a Hydrologically Modified Subtropical Tidal River and Estuary (Caboolture River, Australia)

AbstractEstuaries are dynamic hot spots for carbon cycling and atmospheric evasion. Here we assess the dynamics and drivers of CO2 in a hydrologically modified subtropical Australian estuary. Over 1 year, 10 high‐resolution spatial surveys of pCO2, radon, chromophoric dissolved organic matter, chlorophyll a, and physicochemical parameters were conducted from the estuary mouth to a weir located 25 km upstream. The riverine respiratory quotient revealed that processes besides water column respiration were driving high CO2 within the tidal river (salinity &lt; 2) but not in the estuary (salinity &gt; 2). Conservative mixing plots for pCO2 and 222Rn implied that groundwater may be a contributing source of CO2 during most surveys, but not during dry conditions. A multiple linear regression model explained 88% of the annual pCO2 variability, indicating that mixing, metabolism, temperature, and groundwater inputs were key drivers of CO2. Inputs from an upstream wastewater outfall potentially fuel observed seasonal algal blooms, resulting in the lowest daytime CO2 emissions periods. Postbloom surveys had the highest daytime CO2 emissions. The average tidal river CO2 atmospheric flux rate was 379 ± 53 mmol m−2 day−1. The average estuarine CO2 flux was 78 ± 17 mmol m−2 day−1, equating to 28 ± 6 mol m−2 yr−1. Although the tidal river surface area was ~10 times smaller than the estuary, about one third (35%) of the CO2 emissions were derived from the tidal river. Our results suggest that CO2 emissions along the tidal river‐estuary continuum are dynamic over small temporal and spatial scales and that a combination of hydrological and biological processes is a controlling factor of this variability.

Stable isotopes demonstrate the effectiveness of a tidally-staged sewage release system

Nutrient loading from sewage wastewater discharge contributes to the eutrophication of coastal waters. Wastewater from the Gold Coast, Australia is discharged into the Gold Coast Seaway (GCS) for 13.5 h d−1 primarily on the ebbing tide to disperse wastewater seawards. Nitrogen stable isotopes were used to assess how effectively the tidally staged release system dispersed wastewater out of the GCS and identified pathways by which sewage-N was incorporated into food webs. Turf algae, limpets and barnacles were sampled at the GCS, at two coastal sites and at the mouth of a control estuary that lacked point-source discharge. In the GCS δ15N values of algae and limpets returned to coastal baseline levels within 250 m of the diffusers. In contrast, δ15N of filter-feeding barnacles did not significantly vary indicating wastewater-N does not dominate the pelagic food web. Nitrogen stable isotopes clearly demonstrated that the tidally-staged wastewater release system effectively disperses wastewater offshore.

Suspended sediment dynamics in a well-mixed estuary: The role of high suspended sediment concentration (SSC) from the adjacent sea area

Understanding the sediment transport processes, especially the formation and maintenance of the estuarine turbidity maximum (ETM) in estuaries is essential for dealing with harbour siltation and the related estuarine environmental issues. To gain insight into the mechanism of sediment dynamics and ETM formation in the Yongjiang estuary (YE), which is well-mixed and features abundant suspended sediment sourced from the adjacent sea area, field observations were conducted in June 2015. The flow velocity, salinity, and suspended sediment concentration (SSC) were synchronously measured over a 25-h tidal cycle along the YE and its adjacent sea area. Observations showed that there was abundant suspended sediment exchanging between the YE and its adjacent sea area. In particular, there existed an obvious difference in the single or twin peak SSC signals in different stations during a semi-diurnal tidal cycle, especially between the inner-estuary and outer-estuary regions. Detailed analyses on the processes of sediment transport showed that, in the outer sea area, the tidal-driven advection of suspended sediment was dominant to the temporal distribution of SSC, which was featured by a single peak signal in a semi-diurnal tidal cycle. For the estuarine channel, the landward transport of high-concentration suspended sediment by the flood current from the sea region was the major inducement of peak SSC signals in the lower reach of the YE, while the effect of bed sediment resuspension was mainly responsible for the peak signals during the ebb period. Unlike the formation of ETM in highly stratified or partially mixed estuaries, the ETM in the YE, which is located approximately 7 km upstream from the estuary mouth, was mainly controlled by the effect of tidal asymmetry, together with the contributions made by local resuspension of bed sediment and possible fluid mud. Some other possible factors, such as deflocculation, may also impact the formation and maintenance of the ETM in the YE, but further study is needed in the future.

Effects of Tidal-Forcing Variations on Tidal Properties Along a Narrow Convergent Estuary

A 1D analytical framework is implemented in a narrow convergent estuary that is 78 km in length (the Guadiana, Southern Iberia) to evaluate the tidal dynamics along the channel, including the effects of neap-spring amplitude variations at the mouth. The close match between the observations (damping from the mouth to ∼ 30 km, shoaling upstream) and outputs from semi-closed channel solutions indicates that the M2 tide is reflected at the estuary head. The model is used to determine the contribution of reflection to the dynamics of the propagating wave. This contribution is mainly confined to the upper one third of the estuary. The relatively constant mean wave height along the channel (< 10% variations) partly results from reflection effects that also modify significantly the wave celerity and the phase difference between tidal velocity and elevation (contradicting the definition of an “ideal” estuary). Furthermore, from the mouth to ∼ 50 km, the variable friction experienced by the incident wave at neap and spring tides produces wave shoaling and damping, respectively. As a result, the wave celerity is largest at neap tide along this lower reach, although the mean water level is highest in spring. Overall, the presented analytical framework is useful for describing the main tidal properties along estuaries considering various forcings (amplitude, period) at the estuary mouth and the proposed method could be applicable to other estuaries with small tidal amplitude to depth ratio and negligible river discharge.

An evaluation of factors controlling the abundance of epiphytes on Zostera marina along an estuarine gradient in Yaquina Bay, Oregon, USA

Epiphytes on seagrass (Zostera marina) growing in the lower intertidal were examined along an estuarine gradient within Yaquina Bay, Oregon over a period of 4 years. The Yaquina Estuary receives high levels of nutrients from the watershed during the wet season and from the ocean during the dry season. Mean epiphyte biomass per unit seagrass leaf surface area (epiphyte load) peaked during the summer, and thus epiphyte load was higher during dry season than wet season in both marine and riverine dominated regions. Epiphyte load was greater in marine than in riverine dominated areas in both wet and dry seasons, although only dry season differences were significant. There was no evidence that grazers controlled epiphyte load differences. Annual DIN concentration was inversely related to epiphyte load, principally because of elevated wet season dissolved inorganic nitrogen from river inputs. While there was a positive annual relation of epiphyte load to PO4 concentration, it is not clear that phosphorus becomes a limiting nutrient for epiphyte growth. Water column light attenuation tends to increase linearly with distance from the estuary mouth, while both epiphyte load and Z. marina biomass tend to decrease. Both seagrass and seagrass epiphytes may be increasingly light limited in the upper estuary, and thus, epiphyte loads may have proportionally more impact on seagrass occurrence in this estuarine region.

Factors influencing marked variations in the frequency and timing of bar breaching and salinity and oxygen regimes among normally-closed estuaries

The aim of this study was to determine the factors that influence the breaching of the bar at the mouth of estuaries that are normally-closed to the ocean and the trends exhibited by salinity and oxygen concentration in those systems during protracted periods of closure. Collated data for 1972 to 2016 demonstrate that the frequency and timing of bar breaching of three normally-closed estuaries, located along ~100 km of coastline in a low rainfall region of temperate south-western Australia, differ markedly. Breaching occurred in 12 years in Stokes Inlet, ≥ eight in Hamersley Inlet and only three in Culham Inlet. Breaching in each estuary was related to relatively very high volumes of fluvial discharge. Although breaching typically occurred following exceptional winter rainfall in Stokes Inlet, whose catchment received by far the greatest winter rainfall, it usually took place in Hamersley and Culham inlets following atypically high summer and autumn rainfall, often associated with cyclonic activity. Salinity, oxygen concentration and water temperature were measured seasonally between summer 2002 and spring 2004, during which period each of these estuaries was closed to the ocean following major natural breaches of each system and the influx of substantial volumes of oceanic water. Mean salinities in the estuary basins rose by markedly different extents during the three years of closure. They thus increased from 30 in Stokes Inlet, 35 in Hamersley Inlet and 52 in Culham Inlet, to maxima of 64, 143 and 293, respectively, with the highest individual salinity of 313 in the latter estuary the greatest yet recorded for any estuary worldwide. In contrast, oxygen concentrations declined to minima of 5.5, 2.5 and 0.6 mg L−1, respectively, and were inversely related to salinity in the basin of each estuary (r = −0.7 to −0.8). Although salinities in the main river of each estuary did not become as highly elevated as in its basin, they still reached 221 in that of Culham Inlet. The very different extents to which salinity increased and oxygen concentration declined among the three estuaries reflect variations in amount of rainfall and thus fluvial discharge, the area and depth of basin relative to discharge and resilience of the bar at the estuary mouth. Thus, while a suite of factors contribute to bar breaching and the physico-chemical characterstcs of normally-closed estuaries, variations in their importance as ‘drivers’ among estuaries should be considered when studying the ecology of a given system.

Modeling Spatio-Temporal Shoreline Shifting of a Coastal Island in Bangladesh Using Geospatial Techniques and DSAS Extension

Abstract The study attempted to assess the changes in shoreline and erosion-accretion of newly formed island at the mouth of the Meghna river estuary in Bangladesh using multi temporal satellite images and GIS techniques. The current study used NDWI an MNDWI to delineate land and water boundary to extract the shoreline and also used some overlay analysis to measure the erosion-accretion. DSAS extension is used for analyzing the shifting of the shoreline. The results (1990-2015) show that the island has 1192 hectares of land accreted during this time period, and about 1 km of its shoreline lost during this time period as it has broken in few places. Most accretion found in the northwestern part and erosion in southeastern and southwestern part. The study area was divided into four different segments and about 115 transects were constructed, of which about 74 shows the seaward movement and 44 shows landward movement. Seaward movement and rate of shoreline shifting is higher in the northwestern part where net shoreline movement (NSM) is +1897 meters and end point rate (EPR) is +73 m/year. Landward movement and the rate of shoreline shifting are higher in southeastern and southwestern part of which net shoreline movement (NSM) is about -2680 meters and end point rate (EPR) is about -129 m/year. The highest landward movement is found as -2680 meters and highest seaward movement as +1897 meters. Accretion process is dominant while erosion process discontinued the shoreline in some places.

Subtidal variability of the Tagus river plume in winter 2013

The subtidal variability of surface plume response to local wind and river runoff is studied off central Portugal using a hindcast model for the Tagus Estuary (TE) plume. In addition to the model, the main patterns of variability of the TE plume were extracted in an automated mode using Self Organizing Maps (SOM). Three characteristic spatial patterns are extracted in a 3 × 2 SOM array: in synoptic time scales, northward and southward propagation of the plume and transitional periods. Results suggest that river runoff and wind induce strong variability in the coastal ocean, and that the TE plume has a rapid response to their changes. Under high river runoff there is a southern propagation of the plume, even during downwelling favorable winds, revealing bi-directional patterns due to the combined effect of estuarine outflow, wind direction and coastline in establishment the plume direction. The same is found during transitional periods, revealing that the TE plume has significant influence both north and south of the estuary mouth. SOM was applied for the first time to extract spatial and temporal features of the TE plume and prove to be a reliable tool to study large quantities of data in addition to the model results analysis.

Coupling End‐Member Mixing Analysis and Isotope Mass Balancing (222‐Rn) for Differentiation of Fresh and Recirculated Submarine Groundwater Discharge Into Knysna Estuary, South Africa

AbstractQuantification of submarine groundwater discharge (SGD) is essential for evaluating the vulnerability of coastal water bodies to groundwater pollution and for understanding water body material cycles response due to potential discharge of nutrients, organic compounds, or heavy metals. Here we present an environmental tracer‐based methodology for quantifying SGD into Knysna Estuary, South Africa. Both components of SGD, (1) fresh, terrestrial (FSGD) and (2) saline, recirculated (RSGD), were differentiated. We conducted an end‐member mixing analysis for radon (222Rn) and salinity time series of estuary water over two tidal cycles to determine fractions of seawater, riverwater, FSGD, and RSGD. The mixing analysis was treated as a constrained optimization problem for finding the end‐member mixing ratio that is producing the best fit to observations at every time step. Results revealed highest FSGD and RSGD fractions in the estuary during peak low tide. Over a 24 h time series, the portions of FSGD and RSGD in the estuary water were 0.2% and 0.8% near the estuary mouth and the FSGD/RSGD ratio was 1:3.3. We determined a median FSGD of 41,000 m³ d−1 (1.4 m³ d−1 per m shoreline) and a median RSGD of 135,000 m³ d−1 (4.5 m³ d−1 per m shoreline) which suggests that SGD exceeds river discharge by a factor of 1.0–2.1. By comparison to other sources, this implies that SGD is responsible for 28–73% of total DIN fluxes into Knysna Estuary.