Tidal Inflow Research Articles

Distribution of Recent Benthic Foraminifera from the Outer Channel in and Around Gabakund Sea Mouth of Chilika Lagoon

Chilika (19°28’ to 19°54’ N; 85°54’N to 85°38’ E) lagoon situated in the east coast of India is considered to be one of the largest tropical coastal brackish water bodies in Asia. The unique setup of 60 km long narrow strip of sand barriers and swampy islands separating the area from the sea with few mouths of interconnections in the east and draining of tributaries of the river Mahanadi in the west while its environmental condition governed by tidal inflows and the southwest monsoon.The study of features of benthic foraminiferal tests, morphology, and abundance shed light upon paleoclimatic changes like monsoon variability, salinity, temperature, etc. Ten sediment samples were collected from the outer channel of Chilika lagoon in and around the Gabakund area and processed for species level study and SEM imaging following standard procedures. Sand dominates as the substrate towards the mouth at Gabakund area and silty to clayey sand towards the southern part of the Outer Channel. A total of 13 genera of benthic foraminifera belonging to 36 species were documented at the sampling stations. In the current study the species diversity and richness on the basis of the physico-chemical attributes of sea and river water incursion during pre-monsoon time in the outer channel of the lagoon is reported. In this region calcareous benthic foraminiferal are dominant while few agglutinated foraminifera have found their unusual niche.

Zooplankton Bio-indicators Against Changing Hydrological Parameters at Bidyadhari River of Indian Sundarbans

Sundarban Estuarine System is influenced by periodic tidal input and fresh water inflow. It is surrounded by world’s largest mangrove ecosystem and harbour naturally grown fishery. The total system is intersected by a network of many rivers and creeks. Bidyadhari is one of the major rivers of Sundarbans that is surrounded by human habitation on both banks. The dynamic condition of the river due to tidal inflow and fresh water input which is further increased many folds due to human interventions. In the present study, 26 zooplankton taxa have been recorded where 16 taxa were found perennial in all three seasons. 19 species showed its highest density in the monsoon season, 4 in post-monsoon and 3 in pre-monsoon season. Considering all seasons, Pseudodiaptomus serricaudatus was found to be the most abundant species in monsoon when there was a marked increase in temperature, nitrate, phosphate, silicate and a decrease in salinity, DO, TDS, EC and chlorophyll-a concentration. On the other hand, Acrocalanus longicornis was most abundant during the post-monsoon season when pH, EC, DO, chlorophyll-a were found to be highest and temperature was lowest of all seasons. Only 3 of the 26 taxa were found in highest concentration during pre-monsoon season when salinity was found in highest concentration. The Shannon-Weiner Diversity Index, Simpson 1_D Index and Margalef Richness Index of zooplankton diversity were found highest in station 3 (nearest to the sea) during all the three seasons. Pearson Correlation Analysis showed some significant correlation between different hydrological parameters and zooplankton diversity indices. The result of the study indicates the presence of organic pollutants and eutrophication in Bidyadhari river that demands regular monitoring of water quality for maintenance of long-term sustainability of one the largest naturally grown fisheries in the world.

Always a White Christmas in the Bahamas: temperature and hydrodynamics localize winter mud production on Great Bahama Bank

ABSTRACTWhitings, or occurrences of fine-grained carbonate in the water column, have been observed in modern environments with salinities ranging from fresh to marine conditions, and thick deposits of lime mud are described throughout the geological record. Despite their ubiquity, the trigger for whitings has been debated for more than eighty years. Satellite data reveal that most whitings are restricted to the northwestern part of Great Bahama Bank (GBB) which occupies < 10% of the platform area. Even here, whitings are further focused. More than 35% of them occur in a zone which occupies just 1% of the platform. We propose a three-step process for the existence of this zone of peak whitings and why the whitings in it are both more frequent and larger in winter than summer. First, the temperature differential between on- and off-platform waters is highest in the winter, setting up a disparity between dissolved CO2 concentrations in the two water masses. Second, hydrodynamic mixing of these two water masses increases the degree of aragonite saturation of the platform-top waters, as colder on-platform waters with theoretically higher concentrations of dissolved gases are warmed via mixing with the warmer off-platform waters. Finally, spatial heterogeneity in the degree of aragonite saturation is higher in the winter, and the zone of peak whitings is situated in an area of locally enhanced saturation state. Hydrodynamic simulation suggests that the whitings zone is located by tidal inflow of off-platform waters across the western margin of GBB, as well as inflow from the Tongue of the Ocean to the north of Andros Island. Despite thermodynamic forcing mechanisms that predict higher frequency of whitings in the summer, the environmental, hydrodynamic, geochemical, and kinetic conditions in the whitings zone appear to support the Goldilocks configuration that enhances the formation of wintertime whitings on Great Bahama Bank. This phenomenon has implications for the interpretation of whitings mud in the geological record, including the geochemical signatures within it.

Import, export, and speciation of mercury in Kongsfjorden, Svalbard: Influences of glacier melt and river discharge

The major sources and sinks of total mercury (THg) and methylmercury (MeHg) in Kongsfjorden were estimated based on spreadsheet-based ecological risk assessment for the fate of mercury (SERAFM). SERAFM was parameterized and calibrated to fit Kongsfjorden using the physical properties of the fjord, runoff coefficients of Hg, transformation rate constants of Hg, partition coefficients of Hg, Hg loadings from freshwater, and solid balance parameters. The modeled Hg concentrations in the seawater matched with the measured concentrations, with a mean bias of 12% and a calibration error of 0.035. The mass budget showed that the major THg sources were tidal inflow and glacial runoff, while the major MeHg sources were tidal inflow and in situ methylation in shallow halocline water, which agreed with the distributions of THg and MeHg in seawater. The coupling of observation and fate modeling in Kongsfjorden provides a basic understanding of Hg cycles in the Arctic fjords.

Hydrodynamic stability of tidal inlet system: A case study of Pichaboni inlet, Purba Medinipur, West Bengal, India

The hydraulic geometry of tidal inlets, like, cross-sectional area, wetted perimeter and hydraulic gradient is controlled by the dynamics of tides and wave-induced littoral drift along coastlines, pushing materials into the inlet during the flood tide and flushing them out during the ebb tide. An inlet which maintains its hydraulic stability has its velocity so adjusted that it can flush out all the materials pushed into the inlet. The Pichaboni inlet situated along the Bay of Bengal coast, is a linear channel and the tidal inflow is restricted by a sluice gate. This paper investigates the impact of hydraulic geometry, morphological changes and tidal behaviour on the hydrodynamic stability of the Pichaboni inlet. The longitudinal profile shows a reverse gradient from sea to inland. The smallest cross-sectional area (throat cross-section, AC) is located 672 m inland, which is slightly smaller than the cross-sectional area required to maintain the equilibrium flow velocity. Hence, the actual flow velocity through the throat cross-section is greater than that required for the equilibrium state, and the enlargement of the cross-section area may be caused by sediment scouring which decreases the flow velocity and leads to shoaling at the mouth. The dominant west to east longshore transportation brings a huge amount of sediment influx responsible for continuous sedimentation and the associated formation of spit at the inlet mouth. Any constriction at throat due to spit formation leads to accelerated flow velocity associated with scouring at the throat area and breaching of the spit. This results in the gradual shifting of the inlet mouth by the mechanism of bar by-passing. The economic importance of the main inlet channel and its adjacent intertidal basin necessitates evaluation of the long-term stability of the tidal inlet through analysis of hydraulic and sedimentary characteristics of the inlet.

Prediction on Changes of Seabed due to Sluice Built on entrance of Haiyou Branch in Sanmen Bay

Haiyou branch is the main branch of Sanmen Bay, it is an optional plan to construct sluice at the entrance of Haiyou branch to store fresh water for the utilization of freshwater resources in the Sanmen Bay basin. Basing on the verification of historical tidal currents and seabed erosion and deposition, numerical and physical models are established. Numerical calculations and physical model test show that the impact on hydrodynamic and seabed environment after the construction of sluice will be limited to the local sea area outside the sluice, where the downstream area of sluice, Shepan waterway and Maotou waterway are located, and the siltation strength decreases from the sluice towards Maotou waterway. After the construction of the sluice, the tidal inflow volume of Shepan section will decrease by 11.3% to 17.1%, the tidal volume of Maotou section decrease by 1.7% to 4.3%, and the tidal volume of Qinshan section and Qimen section remain basically unchanged. Within one year, the downstream area of sluice will be deposited with 0.5m∼0.7m, Maotou waterway with about 0.15m, and there is also little siltation at Qimen waterway and other waterway. Due to the impact of the sluice construction of Haiyou branch, after a long time, the deposition of deep pool in Maotou waterway is 2.0m∼2.5m. A once-in-50-year flood from the upper reaches will not cause significant seabed changes in the deep pool of Maotou waterway.

Tidal Energy Flows between the Midriff Islands in the Gulf of California

The Gulf of California has many regions of potential tidal-stream energy that have been identified and characterized using in-situ measurements and numerical ocean models. The Midriff Islands region has received particular attention due to its increased current speeds and high kinetic energy. This increase in energy can be seen in the formation of internal wave packets propagating for several hundred kilometers. Here we present a brief description of internal wave measurements travel towards the Northern Gulf and explore energy generation sites. In this paper we characterize the tidal inflow and outflow that passes throughout the Midriff Islands in the central part of the Gulf. We use a three-dimensional numerical ocean model that adequately reproduces the tidal flow and the increase in speed and kinetic energy between the islands. The current flow structure shows the highest velocity cores near the shore and far from the bottom. During the rising tide, the maximum current flow (~0.6 ms−1) was found between Turón Island and San Lorenzo Island, from the surface to 200 m depth. When the currents flowed out of the Gulf, during the falling tide, the maximum negative current (−0.8 ms−1) was found between Tiburon Island and Turón Island, from near the surface to 80 m depth. Although there are favorable conditions for power generation potential by tidal flows, the vertical variability of the current must be considered for field development and equipment installation sites.

A box model to represent estuarine dynamics in mesoscale resolution ocean models

Representing the net freshwater flux at river mouths is challenging for global and regional scale ocean modelling. Although rivers are well known to affect both the coastal and basin-wide circulation and dynamics, coarse resolution ocean models cannot resolve the estuarine dynamics and are usually forced at river outlets in a simplistic way, with climatological runoff and zero or constant salinity values. The aim of this study is to provide a more realistic representation of the estuarine water inputs to a coarse but eddy-resolving regional model.First, the river volume transport and salinity values at the outlets are modelled with three different Estuary Box Models (EBMs) for stratified estuaries: the Knudsen relations model, a published EBM, called UCONN-NCAR EBM, which parameterizes the tidal inflow and mixing inside the estuary, and a new model, called CMCC-EBM. The CMCC EBM has been conceived to represent the estuarine processes coupled to a mesoscale resolving hydrodynamic model that resolves the entering flow field at the estuary mouth and it offers a new representation of the tidal inflow and a new salinity tidal mixing parameterization via horizontal diffusive processes.The Ofanto and Po rivers flowing into the Adriatic Sea (northern part of the central Mediterranean Sea) are selected as case studies. The coupling of the eddy resolving ocean model to the CMCC EBM is found to outperform the one with the UCONN-NCAR EBM in the region of freshwater influence on the shelf areas.

Performance evaluation of a submerged tidal energy device with a single mooring line

A submerged tidal energy device with contra-rotating Diffuser Augmented Tidal Turbines (DATTs) has been investigated in this paper. The device is moored to the seabed with a single mooring line, which limit it to operate at mean water depth, but otherwise allows it to float freely with the tidal current, like a kite in the wind, to harness tidal current energy. This research focuses on the evaluation of stability and power generation of the submerged tidal energy device based on 1:5th scaled model tests and the full-scaled prototype sea trials.A 1:5th scaled model had been manufactured and tested in a circulating water channel to observe the power generation performance and working attitude around the designed inflow velocity. A full-scaled prototype was manufactured and tested near the CHU Island in Shandong Province, China. The results show that the device can change its direction automatically to make the DATTs face the tidal inflow, as the tidal current changes direction. The device has a good stability in pitch and roll motions. But the device's stability in yaw motions is worse than the other two, which will significantly affect the power generation performance and introduce more demanding structural requirements.

Regional-scale paleobathymetry controlled location, but not magnitude, of tidal dynamics in the Late Cretaceous Western Interior Seaway, USA

Abstract Despite extensive outcrop and previous sedimentologic study, the role of tidal processes along sandy, wave- and river-dominated shorelines of the North American Cretaceous Western Interior Seaway remains uncertain, particularly for the extensive mid-Campanian (ca. 75–77.5 Ma) tidal deposits of Utah and Colorado, USA. Herein, paleotidal modeling, paleogeographic reconstructions, and interpretations of depositional process regimes are combined to evaluate the regional-scale (hundreds to thousands of kilometers) basin physiographic controls on tidal range and currents along these regressive shorelines in the “Utah Bight”, southwestern Western Interior Seaway. Paleotidal modeling using a global and astronomically forced tidal model, combined with paleobathymetric sensitivity tests, indicates the location of stratigraphic units preserving pronounced tidal influence only when the seaway had a deep center (∼400 m) and southern entrance (>100 m). Maximum tidal velocity vectors under these conditions suggest a dominant southeasterly ebb tide within the Utah Bight, consistent with the location and orientation of paleocurrent measurements in regressive, tide-influenced deltaic units. The modeled deep paleobathymetry increased tidal inflow into the basin and enhanced local-scale (tens to hundreds of kilometers) resonance effects in the Utah Bight, where an amphidromic cell was located. However, the preservation of bidirectional, mudstone-draped cross-stratification in fine- to medium-grained sandstones requires tides in combination with fluvial currents and/or local tidal amplification below the maximum resolution of model meshes (∼10 km). These findings suggest that while regional-scale controls govern tidal potential within basins, localized physiography exerts an important control on the preservation of tidal signatures in the geologic record.

Sediment deposition in the central Hauraki Gulf, New Zealand

Based on the analysis of 14 short sediment cores, we present new insights into the distribution of surficial sediments in the central Hauraki Gulf, a semi-enclosed coastal embayment on the northeast coast of New Zealand’s North Island. We identify and discuss the effects of interaction of modern wind-generated waves and currents with regard to deposition and reworking of sediments in the Gulf. The modern hydrodynamic regime is controlled by tidal currents, oceanic inflows, and wave-induced currents and it is responsible for a N-S gradient in sediment texture and elemental concentrations in the central Hauraki Gulf sediments. The present-day sediment input into the system is generally low and consists of fine-grained fluvial sediments mostly deposited in the southern study area and comparatively high inputs of relict carbonate material to the northern study sites. The central Hauraki Gulf sediments, which show numerous age reversals in the sedimentary record, can be characterised as palimpsest sediments, as a consequence of continuous reworking and storm-induced sediment transport. In view of the new data, a previously assumed significant post-transgression accumulation of sediments of > 10 m in the central Hauraki Gulf appears to be very unlikely.

Denitrification rates across a temperate North Pacific estuary, Yaquina Bay, Oregon.

The extent and temporal variability of denitrification activity was measured in Yaquina Bay, Oregon, over a year using sediment cores collected approximately monthly from August 2003 through August 31, 2004. Denitrification rates in sediments from a marine-dominated intertidal sand flat near the mouth of the estuary averaged 0.181 ±0.114 mmol m-2 d-1 whereas sediments in the estuary (5 stations) and river averaged 0.626 ±0.141 mmol m-2 d-1. Sediment cores from all estuarine sites indicated denitrification activity throughout the year and were within the values reported for other temperate estuaries. Denitrification rates decreased with depth from 0.4 mmol m-2 d-1 in the upper 2 to 5 cm of sediment to 0.006 mmol m-2 d-1 at 28 cm sediment depth, indicating denitrification occurred primarily in the upper 5 cm. There was no relationship between denitrification rate and nitrate concentrations in the overlying water column (r2 = 0.16). Denitrification rates were lowest in areas with low sediment carbon content, particularly in the sandy intertidal areas at the mouth of the estuary (r2 = 0.78). The results suggest that denitrification rates in this estuary were influenced primarily by the availability of organic carbon. The amount of nitrogen removed by denitrification was estimated to be 8.7 percent of the annual Yaquina River load for August 2003 through August 2004. The relatively low percent lost via denitrification may be due to high river discharge when the nitrogen load was greatest during winter storm events and dissolved nitrogen was exported directly from the estuary into the Pacific Ocean. Stable isotopes were used to investigate the carbon source. The carbon isotope data increased from -27 δ13C in the freshwater river to -21.5 δ13C at the seawater site, reflecting a typical change from terrestrial plant vegetation to phytoplankton carbon sources. Similar values for δ13C between suspended and benthic sediments indicated resuspension and mixing occurred during tidal inflow.

HYDRAULIC INVESTIGATIONS FOR THE ENVIRONMENTAL IMPACTS DUE TO TIDAL ENERGY DEVELOPMENT

New ocean renewable energy has been developing around the world for a goal of reducing greenhouse gas emission. Tidal energy is more powerful and it has potential for future electricity generation among several ocean renewable energies even though not yet widely used. Also tides are more predictable than wind energy and solar energy. SIHWA Lake Tidal Power Plant in South Korea is the largest tidal power installation in the world, with the total power output capacity of 254MW. The project was opened in 2012 and a 12.5km long seawall constructed in 1994 for flood mitigation and agricultural purpose. Power is generated on tidal inflows into the 30km² basin with the help of ten 25.4MW submerged bulb turbines. Eight culvert type sluice gates are used for the water outflow from the barrage. The amount of discharge flow in total ten of turbines is 3,000 m3/sec, and discharge flow in eight of water gate is 8,500 m3/sec. At the time when SIHWA Lake Tidal Power Plant was designed for construction, its flow velocity was predicted as less than 2m/sec in front of water gate. Accordingly, discharge flow should have no significant impact on navigation channels and several berth facilities. It also should not affect on ship navigation. However, within a year after the first run on April 2012, more than 2.5m/sec of flow velocity was generated and it damaged on navigation channels and berth facilities. Increased flow velocity at SIHWA sea area is directly impacting on ship navigation. In severe case, it will cause human and physical damages. In order to prevent these damages, it is necessary to find the causes and countermeasures of increased flow velocity for reduction in flow velocity of discharge.

Controls on tidal sedimentation and preservation: Insights from numerical tidal modelling in the Late Oligocene–Miocene South China Sea, Southeast Asia

AbstractNumerical tidal modelling, when integrated with other geological datasets, can significantly inform the analysis of physical sedimentation processes and the depositional and preservational record of ancient tide‐influenced shoreline–shelf systems. This is illustrated in the Oligo–Miocene of the South China Sea, which experienced significant changes in basin physiography and where tide‐influenced, shoreline–shelf deposition is preserved in ca 10 sub‐basins. Palaeogeographic reconstructions, palaeotidal modelling and regional sedimentary facies analysis have been integrated in order to evaluate the spatial–temporal evolution and physiographic controls on tidal sedimentation and preservation during the ca 25 Myr Oligo–Miocene record in the South China Sea. Palaeotidal modelling, using an astronomically‐forced and global tidal model (Fluidity) at a maximum 10 km resolution, indicates that spring tides along Late Oligocene to Middle Miocene coastlines were predominantly mesotidal–macrotidal and capable of transporting sand, which reflects two main conditions: (i) increased tidal inflow through wider ocean connections to the Pacific Ocean; and (ii) tidal amplification resulting from constriction of the tidal wave in a ‘blind gulf’ type of basin morphology. Since the Middle to Late Miocene, a reduction in the amplitude and strength of tides in the South China Sea was mainly due to diminishing tidal inflow from the Pacific Ocean caused by the northward movement of the Philippines and Izu–Bonin–Mariana arc. Sensitivity tests to palaeogeographic and palaeobathymetric uncertainty indicate that regional‐scale (hundreds to thousands of kilometres) palaeogeographic changes influencing tidal inflow versus outflow can override local‐scale (one to hundreds of kilometres) changes to tidal resonance and convergence effects (funnelling and shoaling), such as shelf width and shoreline geometry. Palaeotidal model results compare favourably to the distribution and sedimentary fabric of Oligo–Miocene, tide‐influenced, shoreline–shelf successions in peripheral South China Sea basins. However, the preservation potential of tidal deposits is lower in open coastline environments, probably due to enhanced reworking during storms and river floods.

Evaluation of the entry of white shrimp postlarvae (Decapoda: Penaeidae) to a nursery area in the southern Gulf of Mexico

The immigration of white shrimp Penaeus setiferus (Decapoda: Penaeidae) postlarvae (Pls) into the Terminos Lagoon was studied to determine the annual pattern of abundance and its relationship with temperature, salinity, tidal current velocity, and river discharge. Zooplankton samples were simultaneously obtained fortnightly at surface, mid-water, and bottom. The nets used were 50 cm in diameter, 1.5 m in length and 505 μm mesh size. The results indicated a postlarval seasonal immigration pattern, with the lowest average density values from March to May and October to November, and significantly higher values from June to September; maximum peaks occurred in June and September. High Pls densities were obtained between one and three hours after the tidal inflow started. Temperature and salinity varied little during each sampling period and had no apparent effect on immigration, but did have an effect on the seasonal abundance cycle. The multiple regression models indicated that the tidal current velocity and the temperature explained 86% of the variation in Pls abundance during immigration to the Terminos lagoon. The larval migration varied at different levels, with highest densities occurring at a medium depth of 5 m. The Pls entered an optimal range of tidal current velocity (between 0.6 and 0.9 m 3 s -1 ). The main entry mechanism was through the tide current of the Selective Tide Stream Transport, where the Pls could also select an optimum current velocity, avoiding the strata of higher turbulence that would imply higher energy expenditures.

Hydrographic maintenance of deep anoxia in a tidally influenced saline lagoon

Low dissolved oxygen concentrations are of increasing concern in aquatic ecosystems, particularly at the interface between freshwater and marine environments. Oxygen depletion occurs naturally in many perennially stratified systems and it remains to be seen how climate change will affect these habitats. This is due, in part, to a lack of high-resolution, long-term data describing interannual variability in dissolved oxygen concentrations within stratified basins. Physicochemical parameters for Lough Furnace, an ecologically important tidal lagoon, were assessed using daily measurements (2009–14) from an undulating CTD (conductivity, temperature and depth) profiler and observations of tidal exchange flow. Continuous vertical saline stratification existed, with anoxia (<0.1mgL–1) typically persisting below 6m. Tidal inflows were generally restricted, with deep-water renewal events by intrusions of denser spring tidal water occurring episodically (three times in 6 years), following prolonged periods of low freshwater input. Although wind forcing alone was not sufficient to generate basin-scale mixing, the conditions that led to deep-water renewals may also be conducive to wind-driven upwelling events in nearshore areas. These findings have wider application to larger-scale two-layered stratified systems with deep anoxia because the ability to forecast such dynamic events is important for assessing the ecological implications of dissolved oxygen depletion.

Measuring and Modeling Flow Rates in Tidal Creeks: A Case Study from the Central Coast of South Carolina

The purpose of this study was to collect site- and condition-specific hydrology data to better understand the water flow dynamics of tidal creeks and terrestrial runoff from surrounding watersheds. In this paper, we developed mathematical models of tidal creek flow (discharge) in relation to time during a tidal cycle and also estimated terrestrial runoff volume from design storms to compare to tidal creek volumes. Currently, limited data are available about how discharge in tidal creeks behaves as a function of stage or the time of tide (i.e., rising or falling tide) for estuaries in the southeastern United States, so this information fills an existing knowledge gap. Ultimately, findings from this study will be used to inform managers about numeric nutrient criteria (nitrogen-N and phosphorus-P) when it is combined with biological response (e.g., phytoplankton assemblages) data from a concurrent study. We studied four tidal creek sites, two in the Ashepoo-Combahee-Edisto (ACE) Basin and two in the Charleston Harbor system. We used ArcGIS to delineate two different watersheds for each study site, to classify the surrounding land cover using the NOAA Coastal Change Analysis Program (C-CAP) data, and to analyze the soils using the NRCS Soil Survey Geographic database (SSURGO). The size of the U.S. Geological Survey’s Elevation Derivatives for National Application (EDNA) watersheds varied from 778 to 2,582 ha; smaller geographic watersheds were delineated for all sites (except Wimbee) for stormwater modeling purposes. The two sites in Charleston Harbor were within the first-order Horlbeck Creek and the second-order Bulls Creek areas. The ACE Basin sites were within the third-order Big Bay Creek and the fourth-order Wimbee Creek areas. We measured the stage and discharge in each creek with an acoustic Doppler current profiler (ADCP) unit for multiple tide conditions over a 2-year period (2015–2016) with the goal of encompassing as large of a range of tide stage and discharge data measurements as possible. The Stormwater Runoff Modeling System (SWARM) was also used to estimate the potential water entering the creeks from the land surface; this volume was very small relative to the tide water volume except for the more-developed Bulls Creek watershed. The results show that the peak discharge occurred on the ebb tide and that the duration of the flood tide spanned a longer period of time; both of these observations are consistent with traits associated with an ebb-dominated tidal creek system. The tidal inflow and outflow (flood and ebb tides, respectively) showed an asymmetrical pattern with respect to stage and discharge; peak discharge during the flood (rising) tide occurred at a higher stage than for the peak discharge during the ebb (falling) tide. This is not an unexpected result, as the water on an ebb tide is moving down gradient funneled through the creek channel toward the coast. Furthermore, water moving with the rising flood tide must overcome frictional losses due to the marsh bank and vegetation; i.e., the peak discharge can only happen when the water has risen above these impediments. We infer from the flow dynamics data that faster water velocities during ebb tide imply that more erosive energy could transport a larger mass of suspended solids and associated nutrients (e.g., orthophosphate) from the estuary to the coastal ocean. However, the discharge and runoff modeling indicate that land-based flux was important in the developed Bulls Creek watershed, but not at the larger and less-developed Big Bay Creek watershed. At Big Bay Creek, the relatively large tidal discharge volume compared to the smaller potential runoff generated within the watershed indicates that the creek could potentially dilute terrestrial runoff contaminants. Smaller, more-urbanized tidal wetland systems may not benefit from such dilution effects and thus are vulnerable to increased runoff from adjacent developed landscapes.

Hydrochemical variability associated with rainfall regime: a case study in the coastal wetland of the outer Río de la Plata Estuary, Argentina

In coastal wetlands, the interaction between groundwater, surface water and marine or estuarine water determines the water chemistry; variations in the water balance may be of influence as well. The objective of this work was to assess how the rainfall regime affects the hydrological and geochemical processes that regulate the quality of surface and groundwater in the Samborombon Bay coastal wetland. We analyzed the water balances and chemical data of surface and groundwater during a dry and a wet period. Results show that the rainfall regime regulates water quality in the three hydrological units defined for the region (i.e., groundwater in the coastal plain, groundwater in the shell ridges and surface water in the coastal plain). In the water balance corresponding to a dry period, real evapotranspiration is similar to precipitation. In such conditions, in the coastal plain, the halite and gypsum salts precipitate. Subsequently, the rain or the tidal flow dissolves them, and they enter the water table by infiltration. The lowering of the water table favors the oxidation of sedimentary pyrite and the contribution of sulfates. The oversaturation of calcium carbonates in groundwater causes their precipitation, both in the coastal plain and in the shell ridges. The chemistry of surface water depends on the influence generated by the tidal inflow and groundwater discharge. During the wet periods, precipitation is higher than real evapotranspiration, leading to the infiltration of water excess toward the water table and the increase in surface runoff; this causes a decrease in the concentration of ions dissolved by dilution. This rainfall regime hinders the formation of evaporite salts (gypsum and halite) and leads to the undersaturation of groundwater with respect to calcite, allowing the dissolution of carbonates. As regards the chemical composition of the surface water in the coastal plain, the surface runoff in the drainage basin is more significant than the groundwater discharge and the tidal inflow. It can be concluded that the alternation of dry and wet periods in the Samborombon Bay wetland causes the rainfall regime to be a determining factor in the different hydrological and geochemical processes affecting the quality of surface and groundwater.

Marsh accretion and sediment accumulation in a managed tidal wetland complex of Delaware Bay

Wetland impoundments are created to provide ecological benefits such as water quality improvement, mosquito control, and migratory bird habitat. Prime Hook National Wildlife Refuge, located on the southwestern shore of the Delaware Bay, is composed of four interconnected wetland management units. Tidal inflow from Delaware Bay to Units I and IV occurs naturally, whereas flow to Units II and III has been restricted by tidal gates since the mid-1980s. To assess the accretionary status of Refuge marshes and inform an ongoing restoration, we investigated soil physical properties and developed 137Cs and 210Pb radiochronologies for cores collected at twelve sites. Results indicate that marsh accretion is driven by a combination of mineral sediment and organic matter accumulation, the relative proportions of which vary among and within the wetland units. Accretion rates (0.11–0.54cm/y) were found to be significantly correlated with organic matter accumulation but not with mineral sediment accumulation. These relationships demonstrate that biotic contributions to marsh accretion, such as belowground biomass productivity, must be considered in marsh restoration strategies, in addition to the supply of mineral sediment. At eight of the sites, the contribution of mineral sediment to the total volume of the soils has decreased significantly since the early 1900s, predating the impoundment works, perhaps in association with closure of two tidal inlets by natural processes. By comparison, changes in organic soil volume were relatively small over the same time span. At seven of the sites the marsh is accreting at, to just below, the rate of local relative sea-level rise (0.34±0.03cm/y) with potential for submergence on the long term. Additional research at the Refuge is needed to better align measurements of marsh accretion, relative sea-level from tide gauges, and wetland elevation change.

Influence of Oceanic Features around Inlet on the Thermohaline Variability in the Cochin Estuary during 2011 and 2012

Thermohaline variability in the Cochin estuary primarily depends on the mixing of fresh water downstream and sea water intrusion upstream. Knowledge of sea water intrusion into the estuary is important for functioning of ecological systems. Therefore this study explored the possibility of monitoring sea water intrusion into the estuary using open ocean thermohaline properties obtained from satellite data. Recently, an extensive observational program has been carried out during 2011 and 2012 in the Cochin estuary to collect temperature and salinity profiles on a fortnightly interval with a station spacing of approximately 100m. Notable temporal variability in salinity is observed in the depth time plots constructed using profiles collected during high tide.Salinity intrusion into Harbor Mouth, during summer and winter monsoon period, exhibits considerable year to year variability. The retreat of summer monsoon rainfall and reduction in the freshwater water discharge resulted in a gradual increase in the salinity both in the surface and bottom. Earlier studies reported that the thermohaline variability on semi-diurnal and diurnal scales is solely due to tidal inflow and out flow.The present study looked into the influence of open ocean thermohaline properties around inlet as observed in the Sea Surface Salinity and Sea Surface Temperature derived from satellite data on the salinity variability in the estuary.