ESTUARINE PROCESSES (IAPSO/IABO)
Location: Watson Building G23 LTA
Location of Posters: Bridge Poynting/Watson
Monday 19 July AM
Presiding Chair: M.C. Piccolo (Inst. Argentino de Oceanografia, Bahia Blanca, Argentina)
P09/W/02-A1 0910
OBSERVATION-BASED VERTICAL TURBULENT FLUXES OF MOMENTUM AND MASS IN A PARTIALLY MIXED ESTUARY
Hartmut PETERS (Rosenstiel School of Marine and Atmospheric Science, University of Miami, USA. hpeters@rsmas.miami.edu); Helmut Baumert (Hydromod Scientific Consultants, Wedel, Germany. baumert@hydromod.de)
Profiling microstructure measurements were made during 5 cruises in the Hudson River Estuary off Manhattan in 1994/95. Some 6000 drops taken in a relatively straight and uniform section of the estuary with typically 15 m depth cover fortnightly and tidal cycles in stratified and sheared flow of 1-2 m/s. Observed mixing characteristics show pronounced tidal and fortnightly variability, mixing across the estuarine halocline being strongest during ebbs on spring tide. The vertical (diapycnal) fluxes of momentum and mass can be estimated from the measured viscous dissipation rate, shear and stratification using a simple model for the flux Richardson number as function of the gradient Richardson number. The estimated turbulent momentum flux, or stress, and mass flux as well as the dissipation rate are related to the estuarine momentum, mass and energy balances.
P09/W/03-A1 0930
CIRCULATION AND MIXING IN A HYPERSALINE LAGOON
C. D. Winant, Scripps Institute of Oceanography, Centre for Coastal Studies-0209, 9500 Gilman Drive, La Jolla, CA 92093-0209. USA. E-mail: cdw@coast.ucsd.edu
Laguna San Ignacio is a coastal lagoon located along the Pacific coast of the Baja California peninsula in Mexico. Evaporation exceeds precipitation all year, and the total evaporation exceeds 2 m a year. T he concentration of salt in the lagoon has been found to remain steady, therefore a net flux of salt into the lagoon must be returned to the open ocean through circulation and mixing processes. Observations made over a year-long period reveal three mechanisms responsible for this return of salt. Near the ocean, tidal pumping dominates the mixing processes. Midway between the ocean and the closed end of the lagoon, a buoyancy-driven two-layer flow carries relatively fresh ocean water into the lagoon at the surface, while salty, denser water returns to the ocean near the bottom. Near the closed end of the lagoon, where depths are shallow and wind forcing is large, a horizontally variable circulation develops which carries relatively fresh water towards the closed end over the deeper channels near the central axis, and saltier water towards the ocean over the shallower areas near the sides of the lagoon.
P09/W/07-A1 0950
TIDAL CIRCULATION AT THE QUEQUEN GRANDE ESTUARY (ARGENTINA) MOUTH
Diana G. CUADRADO and Gerardo M.E. Perillo (both at Instituto Argentino de Oceanografía, CC 107, 8000 Bahía Blanca,Argentina, and Departamento de Geología, Universidad Nacional del Sur, San Juan 670, 8000 Bahía Blanca, Argentina, e-mail: cuadrado@criba.edu.ar, perillo@criba.edu.ar)
The Quequén Grande Estuary is located at SW of the Buenos Aires Province, Argentina. The Quequén Harbour, one of the most important harbours in Argentina, is placed at the mouth of the estuary. To accommodate the large cargo vessels that operate there, the estuary has been dredged to 12-m depth from the mouth to a distance of 2-km headward. Natural depths in the river upstream of this limit are 2-4 m. Therefore, a major step separates both reaches. We hypothesise that this abrupt change in depth introduce major disturbances in the tidal circulation within the harbour. Profiles of current velocity and direction as well as salinity and temperature were made for over a tidal cycle at three stations. One current station was placed over the step (riverside) another was placed immediately after the step (harbour side), whereas the third one was located at the harbour mouth. From the analysis of the data, we found a three layer circulation system marked by a strong stratification of the water column. T here is an upper layer (1-1.5 m thick) with almost freshwater during all the tidal cycle and with water flowing seaward. A second layer is 2-3 m thick and has salinities that vary with tidal stage and with reversing current. Whereas, on the two stations located within the harbour, there is a lower layer 6-8 m thick in which the salinity is quite homogeneous on the order of 35 and practically no currents. A situation that it is not observed in the river station. A possible explanation for the phenomena is the influence of the in the tidal wave propagation within the estuary that may induce a standing wave by reflection against the step. .
P09/W/11-A1 1010
FLOW THROUGH BATHYMETRIC CHANNELS AT THE MOUTHS OF ESTUARIES
R. P. MIED, R. A. Handler, and T. Evans, Naval Research Laboratory Remote Sensing Division Washington, D.C.20375
In-situ observation and remote sensing imagery indicate the presence of velocity convergences located over bathymetric channels in the mouths of tidal estuaries. In the Chesapeake Bay for example, there are three such features, which extend partially or completely through the mouth of the Bay. As such, strong tidal forcing drives them, and convergent features are formed over them. In this talk, we present numerical simulations performed to investigate these velocity structures in an estuary with a channel in an otherwise flat bottom.
The equations of motion are solved using a fully spectral code in the vertical plane (x-z) on a rotating earth. No along-channel flow variations (in the y direction) are permitted. Using a unique virtual surface approach (Goldstein et al., J. Comp Phys., 105, 1993 generates the bottom bathymetry.) in which the no-slip bottom is generated using feedback forcing. A Gaussian-shaped channel is employed to simulate typical bathymetry observed in estuarine regions. In the along-channel direction, a constant pressure gradient is imposed and the flow is integrated until steady state results.
The simulations are performed at high Rossby number (of order unity) based on the width of the groove and a typical surface velocity. Simulations show the development of a localised surface jet co-located with a bottom feature. This bottom feature takes the form of a recirculation cell, and results from the coupling of the along-channel flow with the motion in the vertical plane. The associated across-channel surface flow in the vicinity of the jet exhibits convergent and divergent regions, which correlate reasonably well with features observed in radar imagery. Their position and strength are seen to vary with the along-channel Reynolds number, Ekman layer thickness, and aspect ratio of the channel.
P09/E/04-A1 1050
STUDIES ON ESTUARINE MIXING ZONES AND CIRCULATION ON CONDUCT OF DESILTING ACTIVITIES
K.RASHEED and A.N. Balchand (Department of Physical Oceanography, Cochin University of Science and Technology, Fine Arts Avenue, Cochin 682 016,INDIA, email: oceans@md3.vsnl.net.in)
In tropical regions, large volume of freshwater and heavy loads of suspended sediments ultimately reach the coastal seas through narrow tidal inlets backed by extensive water bodies where complex estuarine processes occur. Sedimentation is one of the conundrums facing most of such locations and in cases of harbours added significant is attributed. In order to counteract sedimentation, planners and policy makers usually adopt dredging measures of varied degree and applications. Dredging operations in the mixing zone have proven effects to alter the circulation pattern, tidal flushing action, influence the bed load movement and distribution of suspended solids. As a case study, the features at Cochin estuary, the second largest port along the southwest coast of India is reviewed. This study brings out the various processes in the context of desilting at this estuarine harbour and attempts to explain particularly the changes in circulation pattern, salinity and suspended solids in the mixing zone under changing hydraulic conditions. The positive and negative aspect of dredging as well as the impact assessment for the region is comprehensively presented.
P09/E/06-A1 1110
RESIDUAL CIRCULATION IN AN ELONGATED INVERSE ESTUARINE SYSTEM: THE GULF OF SUEZ, EGYPT
MOHAMMED EL-SABH (mohammed_el-sabh@uqar.uquebec.ca), M.A. Rady (both Département d'océanographie, Université du Québec à Rimouski, Rimouski, Québec, G5L 3A1, Canada, T.S. Murty (Baird & Associates, 1145 Hunt Club Road, Suite 1, Ottawa, Ontario, K1V 0Y3, Canada, and J.O. Backhaus (Institut für Meereskunde der Universität Hamburg, Hamburg 13, Germany
A three-dimensional non-linear hydrodynamical numerical model has been used to study the water movement in the shallow Gulf of Suez at the northern end of the Red Sea. The computational grid used to schematize the Gulf has a horizontal resolution of 3x3 km and levels at 5, 15, 30 and 60m in the vertical. The simulations were carried out separately for tidal forcing and wind forcing. Further, in each case, stratified conditions were considered to represent the state of the Gulf during late summer periods. In the case of wind-induced circulations, a uniform wind speed of 5 m/s was applied over the Gulf, blowing from NW, N and NE directions. The results suggest that the dynamics of the Gulf of Suez are governed by the interaction of wind and density forcing. Only occasionally, for instance in the vicinity of headlands and islands, tidal residuals are of similar importance. For the overall residual currents, it was found that the typical (quasi) baroclinic two-layered inverse estuarine circulation observed in the Gulf of Suez can be produced under the combined action of M2-tide and winds blowing steadily from the north-eastern direction. Northwestern and northern winds produced the reverse patter.
P09/E/08-A1 1130
PHYSICAL PROCESSES IN INVERSE ESTUARINE SYSTEMS
MOHAMMED EL-SABH (Département d'océanographie, Université du Québec à Rimouski, Québec, G5L 3A1, Canada, email: mohammed_el-sabh@uqar.uquebec.ca), Than H. Aung (National Tidal Facility, The Flinders University of Australia, Adelaide, S.A.-500, Australia, T.S. Murty (W. Baird & Associates Coastal Engineers Ltd, 1145 Hunt Club Road, Suite 1, Ottawa, Ontario, K1V 0Y3, Canada
An inverse or negative estuary is a semi-enclosed sea or embayment within which loss of fresh water is more than the gain by runoff and precipitation combined. The tide-averaged internal circulation comprises as outflow of saline water near the bottom and an inflow of less saline water near the surface. Inverse estuaries are not common features of the worl's coastal environment and one can distinguish two subsets according to geographical location. The first subset includes those estuaries in which fresh water removal is the result of an excess of evaporation over precipitation. These mostly occur in low latitudes of both hemispheres and are associated with arid conditions (e.g. the Red Sea, the Mediterranean, the Arabian Gulf, the Adriatic and the South Australia gulfs). The second subset covers those estuarine systems in which fresh water removal is achieved by freezing and the production of sea ice, which involves rejection of salt from the ice crystal lattice and hence increases the salinity of the underlying fluid. This type is therefore confined to high latitudes and pricipally the polar regions (e.g. the Weddell Sea, the Ross Sea and the Beaufort Sea). Although there have been many observational and numerical studies of the dynamics of classical positive estuaries since Pritchard's pioneering work in the early 1950's, inverse estuaries have received relatively little attention. This paper reviews available literature relating to physical processes in several inverse estuarine systems and provides a framework for better understanding their characteristics and dynamics, hence providing another perspective on estuarine processes in general.
P09/P/02-A1 1150
ESTUARINE PROCESSES AND GEOMORPHOLOGY, KARNATAKA COAST, INDIA
K S JAYAPPA (Marine Geology Faculty, Mangalore University, Mangalagangotri-574199, Karnataka, India, email:jayappa@mnglr.ernet.in).
Estuarine siltation especially during SW monsoon is a common processes of southern Karnataka coast. The two main sources of sediment input are river discharge and littoral drift. Because of continuous accumulation of sediment, the draft required for navigation is reduced and capsizing of fishing boats and loss of lives has become a frequent phenomenon. To achieve minimum depth for navigation, the channels need to be dredged regularly. To avoid littoral drift entering the estuaries, construction of breakwaters is necessitated.
Erosion of beaches close to river mouths is more complex than that of open beaches. It is more complex due to the presence of forces like tidal and fluvial currents in addition to storm waves, longshore currents and influence of man–made structures. Most of the marshy and swampy zones bordering the estuaries are getting silted. Mangroves covering tidal creeks and estuarine borders act as land builders, natural buffers and give protection to the coastline against stormy winds and floods.
Migration of estuaries and confluence of two or three of them before debauching into the sea and occurrence of various types of spits are the peculiarities of this coast. Spits indicate secreting tendency of beaches. Migrations of estuaries are mainly due to longshore drift while evolution of spits are due to longshore and river drifts. The net drift has been inferred to be southerly on the basis of accretion on updrift and erosion on downdrift directions of barriers, shifting of estuarine mouths, heavy mineral distribution, length of drift sectors and longshore sediment transport studies.
Monday 19 July PM
Presiding Chair: C.D. Winant (Scripps Inst. of Oceanografy, La Jolla, CA, USA)
P09/W/01-A1 1420
CURRENT OBSERVATIONS OFFSHORE BAHIA BLANCA ESTUARY, ARGENTINA
M. Cintia Piccolo and Gerardo M. E. Perillo (both at Instituto Argentino de Oceanografía, CC 107, 8000 Bahía Blanca, Argentina and Universidad Nacional del Sur, email pIccolo@criba.edu.ar)
Continuous current measurements at two stations offshore Bahía Blanca Estuary (Argentina) in late spring, 1993 were employed to analyse the magnitude and relative importance of tidal and wind driven motion in the area. Hourly wind and tides were obtained from an oceanographic tower located at the mouth of the estuary and from three coastal navigation lights that cover all the coast of the study region.
Subtracting the tidal components from the original records revealed non-tidal flow. Instantaneous motion is characterised by semidiurnal tidal currents of 5-56 cm s-1amplitudes. Mean velocities at both stations (located at both sides of the estuarine mouth) were 22.6 and 22.1 cm s-1, respectively. Winds were strong practically during all the measurement period being always higher than 18-m s-1 from the SE. Tidal and higher frequencies motions were smaller than the instantaneous and well correlated with the prevailing winds.
P09/W/04-A1 1440
EFFECT OF THE EARTH fS ROTATION ON THE CIRCULATION IN ROFIS
AKIHIDE KASAI (Graduate School of Agriculture, Kyoto University, 606-8502, Japan, email kasai@kais.kyoto-u.ac.jp) Edward Hill (School of Ocean Sciences, University of Wales, Bangor, LL59 5EY, U.K.) Tateki Fujiwara (Graduate School of Agriculture, Kyoto University, 606-8502, Japan) John Simpson (School of Ocean Sciences, University of Wales, Bangor, LL59 5EY, U.K.)
Recent surveys in various channel-type ROFIs (regions of freshwater influence) have shown considerably different flow patterns in each. A simple model including viscous effects and the Earth_fs rotation is proposed to explain these differences and to examine the along-channel flow pattern. Model results show that the flow pattern is strongly dependent on the Ekman number. With a large Ekman number, the system is governed by gravitational circulation and thus the along-channel density gradient is important. However, the contribution by the baroclinic component becomes large when the Ekman number is small. Density structure and residual currents were observed on the two sections in the Kii Channel, Japan. Since the Ekman number is O(10^-2) in the channel and the current is highly dependent on the across-channel density structure, the flow pattern was different from those observed in many classical drowned river valley estuaries. The along channel flow in the Kii Channel was successfully reproduced by the model based on the observed density field. The model can be applied to the other ROFIs and satisfactorily explained their flow patterns. In Delaware Bay or Chesapeake Bay, contrary to the Kii Channel, shallow depth makes large Ekman numbers (~1) and the barotropic flow penetrates in the whole water.
P09/W/10-A1 1500
OBSERVATIONS OF FRONTOGENESIS IN DIFFERENT ESTUARINE SYSTEMS
Arnold Valle-Levinson, Center for Coastal Physical Oceanography, old Dominion University, Crittenton Hall, 768 52nd Street, Norfolk, Virginia 23529 USA, email: arnoldo@ccpo.odu.edu
Underway current velocity profiles obtained in two different estuaries (the James River and the lower Chesapeake Bay) and one coastal lagoon (Yavaros Bay in Mexico) are used to depict the appearance of surface lateral flow convergences during both flood and ebb stages of the tidal cycle. Lateral surface flow convergences appear over the edges of the channels and are produced by the phase lag of the flow in the channel relative to the shoals. In the three systems studied, flood convergences consistently develop on the right edge of the channel (looking into the estuary) in the late tidal stages. Ebb convergences appear over the left edge of the channel soon after maximum currents. Most of these convergences cause fronts in the density field and flotsam lines that also appear over the edges of the channel and that last less than two hours. In the lower Chesapeake Bay, the position of the fronts is compared to concentrations of measured near-surface chlorophyll and optical backscatter (a proxy for zooplankton). This work shows that the strength of lateral convergences along the estuary is proportional to the tidal amplitude and the channel steepness. It also suggests that the convergences are produced mainly by the tidal flow interacting with the channel-shoal bathymetry, i.e., that they do not require the presence of density gradients.
P09/W/14-A1 1520
UPWELLING IN A SEMI-ENCLOSED COASTAL SEA INDUCED BY INTERMITTENT INTRUSION OF OCEANIC WATER
SHIGEHO KAKEHI (Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan, email kakehi@kais.kyoto-u.ac.jp) Tateki Fujiwara (Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan, email fujiwara@kais.kyoto-u.ac.jp) Satoshi Sato (Hydrographic Department Maritime Safety Agency, Japan, Minato-ku, Nagoya, 455-8528, Japan, email stssato@cue.jhd.go.jp) Sugiyama Youichi (Electric Technology Research Department, Chubu Electric Power Co., Inc., Midri-ku, Nagoya, 459-8522 Japan, email Sugiyama.Youichi@chuden.co.jp)
Estuaries are affected by not only river but also ocean. Estuarine circulation, one of the dominant flows in estuaries, is the mechanism which steadily transports and lifts nutrient-rich deep water to the euphotic zone. In contrast, oceanic water may intrude intermittently into estuaries and induce sporadic upwelling. Because of the difficulty of observing the intermittent intrusion of oceanic water, its magnitude and its effect on estuarine ecosystems remain unknown.
CTD and ADCP surveys were conducted in Ise Bay, Japan, on 29 and 30 October 1994. The data observed by mooring system in center of the bay showed that oceanic water flowed into the bay on 29 October. The water, influenced by earth's rotation, flowed in along the bottom along the eastern edge of the bay. The upwelling velocity at each 1m is estimated from volume flux by residual current at 5.7m/d on 29 October, the day on which large scale intrusion occurred. This value exceeds 10 times the upwelling velocity estimated from salt budget under the steady state assumption. This suggests that upwelling induced by intermittent intrusion is lager in magnitude than that driven by the mean estuarine circulation. It is considered that large amounts of nutrients are supplied to the upper layer by this upwelling. This indicates that the intermittent intrusion plays an important role on the primary production in estuaries.
P09/W/08-A1 1600
INTERNAL SEICHES IN THE QUEQUEN RIVER ESTUARY, ARGENTINA
Gerardo M. E. PERILLO and M. Cintia Piccolo (both at Instituto Argentino de Oceanografía, CC 107, 8000 Bahía Blanca, Argentina and Universidad Nacional del Sur, email perillo@criba.edu.ar)
Quequén River Estuary is one of the largest of the Buenos Aires Province (Argentina) containing one of the most important grain and fisheries harbour of the country. The last 2000 m of the estuary have been dredged to 12 m to accommodate the large cargo vessels. The average river headward of the dredging border is almost 4 m, which resulted in a 8 m step between them.
Historical tidal records from the gage located at mid distance from the mouth and the step present short period (3-25 min) fluctuations superimposed over the regular tide. These fluctuations are almost permanent with and amplitude of 4-10 cm. However, there are examples of large fluctuations up to 1.5 m that have produced serious consequences to loaded vessels.
Two tide gages sampling at 1-min interval were located at the mouth and at the step (on the harbour side) for a period of 1 month. Although no major fluctuations occurred both gages have registered the same fluctuations but displaced 3-6 min being earlier at the step. CTD data gathered at 1.5 m depth for one tidal cycle presented a similar fluctuation that occurs at a strong halocline that is present almost all the time at that depth.
P09/E/07-A1 1620
LOW FREQUANCY RESPONSE OF BAIE DES CHALEURS, CANADA, TO WIND FORCING
MOHAMMED EL-SABH (Département d'océanographie, Université du Québec à Rimouski, Rimouski, Québec, G5L 3A1, Canada, email mohammed_el-sabh@uqar.uquebec.ca) Diane Lavoie (Institut Maurice-Lamontagne, B.P. 1000, Mont-Joli, Québec, G5H 3Z4, Canada
The response of the Baie des Chaleurs (BdC), a large-scale stratified estuarine system in eastern Canada, to the passage of three storms in 1990 is discussed. Current meter, sea-level data and time-series temperature observations are analyzed and compared with output from a 3-layer numerical model. The model incorporates realistic coastal geometry and is driven by wind stress calculated from observed winds. The results show that the kintetic energy is dominated by a low frequency periods of 5-12 d, with the strongest signal at 10-12 d. This corresponds to similar variability in the synoptic wind forcing due to the rapid propagation of extratropical cyclones and the passage of pressure systems over the Gulf of St. Lawrence, including the BdC. The spectra for temperature show similar features, with the strongest signal near the density interface. The 5-12 d peak may also be related to fluctuations in the Gaspe Current, near the entrance of BdC, which are likewise correlated with wind stress at the NW of the Gulf of St. Lawrence. Further data analysis show a relationship between upwelling coastal wave propagation and alongshore wind stress in the north shore of the bay. The corresponding wave, with phase speed of 0.50 m/s, can be interpreted as a coastally trapped wave with the characteristics of a baroclinic Kelvin wave. Results from the numerical model show good agreement with observed currents in the bay during the height of the storms.
P09/W/05-A1 1640
OBSERVATIONS AND MODEL STUDY OF THE DNIEPER-BOOG ESTUARY
V. Serenko and V. Kovba (both at Main Ecological Inspection, Kiev, Ukraine) J. Greenfield (EPA, Athens, GA, USA) and J. Marlar (EPA, Athens, GA, USA, retired) R. Demchenko, V. Maderich, N. Margvelashvily, M. ZHELEZNYAK (all at Institute of Problems of Mathematical Machines and Systems, Glushkov pr., 42, Kiev, 252187, Ukraine; E-mail: mark@immsp.kiev.ua)
The Dnieper-Boog Estuary (DBE) located on the north-west coast of the Black Sea, is the sea's largest estuary. It is plagued with problems caused by the man-made alterations. The most important factor, which changed state of whole ecosystem, was construction of the Kakhovka Reservoir dam at approximately 60 km from the mouth of the Dnieper. Industrial and agricultural development are also significant factors. The results of observations and simulations of water quality using 1985-1998 data are presented. The, two- and three-dimensional real time models, consisting of linked hydrodynamic and water quality models were applied to the DBE. The submodel of water quality simulates the transport and transformation reactions of four interacting systems: phytoplankton kinetics, the phosphorus cycle, the nitrogen cycle, and the dissolved oxygen balance. The models were calibrated using historical data from 1985 and 1987. New field data collected in 1998 by the joint USA-Ukraine project were used for verification of the models. The models reproduced the behavior of the main nutrients as well as the summer hypoxia. A set of numerical experiments was carried out to predict and assess the impact of the Kakhovka Reservoir operational mode on the environmental situation in the downstream river/estuary system. The preliminary results of this study demonstrate that decisions involving complex environmental problems can be addressed with the coupled hydrodynamic and water quality models.
Tuesday 20 July AM
Presiding Chair: G.M.E. Perillo (Inst. Argentino de Oceanografia, Bahia Blanca, Argentina)
P09/W/06-A2 0850
HYPOXIA IN THE GULF OF MEXICO: POLITICAL MANIFESTATIONS OF SCIENTIFIC AMBIGUITY
TODD M. KENNEDY and Timothy W. Lyons (Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA, Email: c694575@showme.missouri.edu)
Seasonal occurrence of hypoxia has been observed in the Gulf of Mexico since 1985. The hypoxic zone extends for up to 18,000 sq. km and encompasses up to 80% of the total water column. Hypoxia has already caused massive fish kills, significantly impacting the economy of the Gulf region and disturbing the trophically linked aquatic community. While the magnitude of hypoxia and its effects are well documented and undisputed within the scientific community, and although fertilizer usage has been identified as a contributor, there is significant scientific uncertainty in the causal relationship between upstream nutrient sources and downstream eutrophication.
Separation between cause and effect and uncertainty in the linkages between complex coupled systems is manifested in the current approaches to remediation: (1) treatment of symptoms rather than causes, (2) allocation of limited resources to address hypoxia in the context of related coastal issues [e.g., harmful algal blooms] that are politically more visible but may ultimately represent red herrings, and (3) failure to co-ordinate currently isolated efforts to address what is likely a diverse nonpoint-source pollution issue. Most intriguing about the latter is that lack of co-ordination may exacerbate hypoxia. Insular upstream efforts to reduce the flux of a specific nutrient may shift biological production downstream, facilitating accelerated oxygen consumption in the Gulf. The dilemma lies with co-ordinating the regulatory response within the time frame of the problem in an atmosphere of scientific uncertainty and disparate political and societal agendas.
P09/W/12-A2 0910
INTRUSION OF OCEANIC WATER INTO ISE BAY AND ITS INFLUENCE ON HYPOXIA
TETSUYA TAKAHASHI (Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan, email tetsuya@kais.kyoto-u.ac.jp) Tateki Fujiwara (Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan, email fujiwara@kais.kyoto-u.ac.jp)
Ise Bay is a semi-enclosed sea connected with the Pacific Ocean through Irako Strait and has an area of 1700 square km and mean depth of 30 m. A large amount of fresh water(annual mean: 600 cubic m/s) flows into the head of the bay and water in the bay is strongly stratified. In contrast the water column is well mixed at the bay mouth (Irako Strait) because of strong tidal stirring. This heterogeneity of stratification leads to a horizontal density gradient and strong estuarine gravitational circulation.
Below the pycnocline in the bay, severe hypoxia occurs during the summertime every year. This hypoxic water mass is cold and isolated from the surrounding waters. The supply of oxygen to the hypoxic water mass is restricted to the intrusion of the well mixed water in Irako Strait. The mixed water intrudes into the bay along isopycnals. We define the intrusion depth as the depth where the water density equals that of the intruding mixed water. The temporal variation of the intrusion depth explains the temporal and spatial variation of hypoxia. When the mixed water intrudes into the middle layer in the bay, the hypoxia progresses below the intrusion depth, and when it intrudes into the bottom layer, the hypoxia disappears. The age of the intruded water, which is defined as elapsed time after the intrusion, is estimated from the water temperature. The age explains 80% of variance in the concentration of oxygen in the bay. This indicates that physical processes can explain the major part of the behaviour of hypoxia and that the seasonal variation indensity difference between the bay and shelf waters plays an important role in the development of hypoxia in Ise Bay.
P09/W/13-A2 0930
INFLUX OF NITROGEN AND PHOSPHORUS FROM THE OUTER OCEAN INTO EUTROPHIC ESTUARIES DRIVEN BY ESTUARINE CIRCULATION
Tateki FUJIWARA, Tetsuya Takahashi and Natsuko Uno (all at Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto 606-8502, Japan, email: fujiwara@kais.kyoto-u.ac.jp, tetsuya@kais.kyoto-u.ac.jp, uno@kais.kyoto-u.ac.jp)
Nitrogen and phosphorus from human activity make estuaries eutrophic. In highly populated bay areas, such as Tokyo Bay, Ise Bay and Osaka Bay in Japan, red tide may occur throughout the year near the bay head, where large amounts of terrestrial N and P collect. Until recently it has been widely believed that the greater part of this inflow of N and P is transported to the open ocean by water exchange between the bay water and oceanic water. However, the research necessary to verify this hypothesis has not been carried out because of the difficulty of observation.
We developed a method to directly measure the flux of N and P, and applied it to surveys at various cross-sections in Osaka Bay-Kii Channel System, and obtained results contrary to the previous hypothesis. We found that N and P flow into the System from the outer ocean, and their fluxes exceed the terrestrial N and P loads.
The inflow of these oceanic nutrients is caused by the coexistence of two factors: the estuarine circulation (inflow in the lower layer and outflow in the upper layer) and nutrient depletion in the upper layer by the photosynthesis. Both phenomena are common in many stratified estuaries. We can therefore estimate that the inflow of the oceanic nutrients is not a unique but rather common phenomena.
P09/E/02-A2 0950
A MULTI AND INTERDISCIPLINARY APPROACH IN STUDY OF ESTUARINE PROCESSES IN A TROPICAL WATERBODY
A. N. BALCHAND, K. J. Ajith, K. Rasheed, M. G. Sreedevi, M.S. Madhusoodanan, J. K. Jossia, T.K. Anujee, P.R.Saritha and T.T.M. Asharaf (Department of Physical Oceanography, Cochin University of Science and Technology, Fine Arts Avenue, Cochin 682 016, India, email: oceans@md3.vsnl.net.in)
Tropical waterbodies exemplify complex biogeochemical processes coupled with extensive geomorphological variability capable of signaturing sensitive land sea boundary changes and (hydrological) impacts of any climate change. In addition, anthropogenic demands and varied uses have now left a very clear impression on the aquatic scenario with distinguishable marks of past two decades or more of activities. The estuarine system is currently subjected to a systems approach methodology to unravel the environmental features that has a bearing on the coastal seas. The steps covered include (1) periodic update on embank features (2) land use and practices in hinterland development (3) water resources and management plans (4) hydrological impact assessment (5) assessment of geomorphologic features (6) study of biogeochemical processes (7) identifying sensitive variables and (8) prospective planning and developmental measures. The scenario of the Cochin estuary on the tropical maritime boundary of southwest coast of India is drawn up as an illustrative case study to impress the complexities of these coastal environments.
P09/E/03-A2 1010
ORGANIC CONTAMINANTS AND HEAVY METALS IN THE CONWY ESTUARY, NORTH WALES
Yang P Liu, JUN L ZHOU, Tim Dunn School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Anglesey LL59 5EY, UK
The Conwy Estuary is one of the largest and most westerly of the major estuaries of the North Wales coast, and drains an area of about 660 square kilometres from its source at Llyn Conwy in the mountains of Snowdonia. The estuary has rarely been studied for the presence of organic and inorganic contaminants, which may arise from the surronding farming and mining activities, and sewage discharges. The present project aims to fill in gap in our knowledge by determining the levels of heavy metals and polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine insecticides in water, suspended particulate matter and sediments. Results show the levels of heavy metals and organic contaminants in water are seasonally dependent, with high levels in summer and relatively low levels in winter. Metal levels suggest strong influence from mining activities, while PAH levels indicate the importance of river and sewage inputs as well as atmospheric deposition. Contaminant levels in sediments exhibit homogeneous distributions suggest strong circulations of sediment population within the estuary. The ratios of individual PAHs in sediment point to the dominance of inputs by urban activities. Finally the results are incorporated into the Estuarine Contaminant Simulator (ECoS) for simulation and prediction purpose.
P09/W/09-A2 1050
BIOGEOCHEMICAL LOADING VIA GROUNDWATER DISCHARGE TO ESTUARIES: BARATARIA BASIN, LOUISIANA (USA)
Jaye E. CABLE (Department of Oceanography & Coastal Sciences, Coastal Ecology Institute, Louisiana State University, Baton Rouge, Louisiana, USA 70803, email jcable@unix1.sncc.lsu.edu) L.V. Inniss (Institute for Environmental Studies and Department of Oceanography & Coastal Sciences, Louisiana State University, Baton Rouge, Louisiana, USA 70803; email linniss@unix1.sncc.lsu.edu) E.M. Swenson and R.E. Turner (both at Coastal Ecology Institute, Louisiana State University, Baton Rouge, Louisiana, USA 70803)
Submarine groundwater inputs to marine and fresh waters are receiving increasing attention within the United States and other countries as techniques are developed to better assess this elusive component of hydrologic budgets. Techniques that have been applied to quantify this flow include seepage meters, piezometers, and naturally occurring tracers. Several studies have demonstrated the importance of groundwater inputs to estuaries and coastal waters. In fact, these subsurface flows to estuarine surface waters can be surprisingly high. Biogeochemical budgets in estuaries often neglect groundwater inputs due to the difficulty associated with quantifying this input. The overall objective of this research is to contribute to our understanding of nutrient inputs to Barataria Basin via subsurface waters using the natural tracers, 222Rn (t1/2 = 3.83 days) and 226Ra (t1/2 = 1620 years). A geochemical mass balance of these tracers, in conjunction with standard hydrological techniques, provides an estimate of the magnitude of groundwater inputs to the water budget of this important estuarine watershed. Nutrient concentrations (N, P) measured at each station during the study provide an assessment of the nutrient loading from groundwaters to surface waters in the basin. Key questions include (1) what are the regional magnitudes and variations (temporal and spatial) of groundwater inputs to the estuary; and (2) how does temporal variability in groundwater input affect the nutrient loading to wetlands and lakes within the Barataria Basin?
P09/L/04-A2 1110
LINKING OFFSHORE IMPACTS TO MAINLAND WITHDRAWALS FROM REGIONAL AQUIFERS
Sydney T. Bacchus (Institute of Ecology, University of Georgia, Athens, Georgia, 30602-2202; e-mail: sbacchus@arches.uga.edu)
Adverse impacts to surface resources beyond the points unsustainable groundwater withdrawals from the Floridan aquifer have been documented throughout Florida. Unsustainable withdrawals from the same regional karst aquifer on the mainland of southeast Georgia have resulted in an estimated decline in the potentiometric surface of approximately 9 m on Cumberland Island. The majority of this largest, barrier island off the coast of Georgia was designated as a National. Seashore in 1972, with 3,600 ha of the federally owned tract identified as a "Wilderness Area", to "preserve the scenic, scientific, and historical values" of this natural resource. A ground reconnaissance conducted in the vicinity of the interior "Wilderness Area" wetlands on Cumberland Island, where the greatest potential for adverse impacts related to groundwater withdrawals was predicted to occur, revealed extensive environmental damage and sinkhole-like depressions.
Groundwater discharges from submarine springs and seeps are known to have decreased due to groundwater mining on the mainland, but quantification is difficult. The hypothesis is proposed that the documented damage to the National Seashore, in addition to large scale damage to estuarine and marine resources are linked to wide-spread fluid extraction throughout the Atlantic and Gulf Coastal Plains. Detailed, multidisciplinary investigations are recommended to determine the magnitude and extent of the damage and what corrective measures can be taken.
P09/L/01-A2 1130
BAROTROPIC CIRCULATION IN BAHÍA BLANCA ESTUARY (ARGENTINA).
I: TIDAL RESPONSE
Elbio D. PALMA (Dpto. de Física, Universidad Nacional del Sur. Avda. Alem 1253. (8000). Bahía Blanca)
The Bahía Blanca Estuary lodges in its margins a major petrochemical industrial park, a thermoelectric plant, and an important deep-water harbor system. A better understanding of the physical properties of the estuary will certainly help in solving the pollution and dredging problems of the region. In this study the tidal wind driven response of the estuary is analyzed with a finite difference two-dimensional barotropic model which has an embedded algorithm that handles tidal flat covering and uncovering. The model is verified by comparing observed and computed water elevations in some stations. The model results show that the incident tidal wave from the Atlantic is delayed considerably as it enters the estuary channels. The wave amplitude is amplified towards the head, with channel convergence prevailing over bottom and lateral friction A comparative study between sea surface elevation and currents lag confirms the existence of a standing wave in the main navigation channel. Experiments with the prevailing NW winds show minor modifications of surface elevations in the outer estuary and of tidal currents in the inner main channel. The simulation with the strongest SE winds (‘sudestadas’) produce the highest sea level changes in coastal areas, with important consequences for harbor activities.
P09/L/02-A2 1135
BAROTROPIC CIRCULATION IN BAHÍA BLANCA ESTUARY (ARGENTINA).
II: RESIDUAL CURRENTS.
Elbio D. PALMA (Dpto. de Física, Universidad Nacional del Sur. Avda. Alem 1253. (8000). Bahía Blanca)
Tidally driven residual circulations are persistent features that contribute to the overall long-term distribution and transport of water properties. In this study we develop a depth-averaged model that includes tidal flats covering and uncovering to examine the residual circulation in Bahía Blanca estuary (Argentina). The model is integrated with appropriate boundary conditions to study the residual through-flow and the generation of residual eddies. The qualitative nature of the residual gyres is consistent with those discussed by several authors for similar coastal locations. Sensibility of the results to spatial resolution and horizontal mixing parameters are also analyzed by numerical experimentation. The dominant physical mechanism is explained by transport of vorticity from the oscillating flow to the mean field by barotropic rectification of the tidal wave. Finally, the effects of the dominant winds on the residual currents are discussed. The results stressed the importance of the open boundary treatment when studying wind driven residuals.
P09/L/03-A2 1140
MODELLING OF THE VERTICAL CIRCULATION IN QUEQUEN HARBOR (ARGENTINA)
Elbio D. Palma1 and G.M. E. Perillo2,3 (1Dpto. de Física, Universidad Nacional del Sur. Avda. Alem 1253. (8000). Bahía Blanca.2Instituto Argentino de Oceanografía Florida 400 Edificio E1. (8000) Bahía Blanca. Argentina3.Dpto. de Geología, Universidad Nacional del Sur. San Juan 870, 8000 Bahía Blanca, Argentina).
It has been observed that the vertical circulation in Quequén Harbor is strongly influenced by a steep bathymetric slope (step) located at the junction of the main harbor with the river. In this study a numerical model is used to examine the dynamics induced by tides and freshwater discharge in the system and to investigate the influence of the step on the circulation. Residual currents and salinity distribution obtained with the model show a two-layer circulation pattern where relatively low salinity water flows out at the surface and compensating high salinity waters from the shelf flows at the bottom. However, the model results also show that the presence of the steep slope can generate internal waves that modified the two-layer circulation mode. Sensibility experiments conducted changing the step position and depth confirms its strong influence on the harbor dynamics. During slack water time the model results show a re-circulation pattern at the base of the step. Further numerical experiments including passive tracers in the model show that this re-circulation modifies the vertical distribution of dissolved and suspended estuarine constituents.
P09/E/01-A2 1145
THE INFLUENCE OF THE TIDES ON THE CIRCULATION OF A TWO-SILLED FJORD
Michael W. STACEY (Department of Physics, Royal Military College of Canada, Kingston, Ontario, K7K 7B4, Canada. Email: stacey-m@rmc.ca) Yves Gratton (INRS-Oceanologie, 310 Allee des Ursulines, Rimouski, Quebec, G5L 3A1, Canada. Email: yves_gratton@uqar.uquebec.ca)
A laterally integrated, two-dimensional numerical model has been used with observations of velocity, temperature and salinity to study the influence of the M2 tide on the circulation in the Saguenay Fjord. The fjord has two sills, an outer sill (approx. 30 m deep) near its mouth,and an inner sill (approx. 60 m deep) about 20 km further up-fjord. The inner sill separates the inner and outer basins of the fjord. Both basins are about 250 m deep. The fjord is highly stratified, so vigorous internal motions are generated by the interaction of the tide with the sills of the fjord. The M2 tidal velocity near the surface, and over the deepest part of the outer basin, can be greater than 1 m/s.
The M2 tide has a very significant influence on the sub-tidal circulation because much of the energy associated with the tidally-generated internal motions is dissipated in the outer basin, so there is significantly more vertical mixing there than in the inner basin. The resulting horizontal pressure gradient causes a significant (10-20 cm/s) mean bottom flow of water from the inner into the outer basin across the inner sill. Upon entering the outer basin, this water sinks almost to the bottom. This 'reverse renewal', caused by the excessive tidal mixing in the outer basin, is evident in both the observations and the simulation.
According to the numerical model, M2 tidal energy is withdrawn from the surface tide at a rate of about 50 MW. The rate of withdrawal would be about five times less if the fjord were unstratified. Most of the energy withdrawn from the surface tide is fed into the internal tide.