OS33C-01 INVITED
Estuary/ocean exchange as influenced by friction and width of cross-section
The lateral structure of estuary/ocean exchange flows is investigated theoretically as a function of friction and estuary's width. The relative contribution of friction is expressed through the Ekman number. In turn, the effects of estuary's width are explored with the Kelvin number. It is found that exchange flows are horizontally sheared under high frictional conditions independently of the width of the channel. The horizontally sheared pattern describes inflow in the channel and outflow over shoals. The exchange flow pattern is also horizontally sheared under weak friction and in wide channels. In that case, however, the outflow is concentrated on the left (looking into the estuary in the northern hemisphere) portion of the cross-section and inflow appears on the right. Also under weak friction, the exchange pattern becomes vertically sheared, with outflow at surface and inflow underneath, as the width of the channel becomes small. Under moderate friction the exchange pattern is both horizontally and vertically sheared for all widths. A horizontally sheared pattern is best defined in wide estuaries whereas a vertically sheared pattern dominates in narrow channels. Observations in tropical and subtropical systems are placed in the context of these findings.
OS33C-02
Three Dimensional Flow Dynamics Over A Hollow
Current velocity and water density profiles were measured in order to observe the effects of bathymetric depressions (hollows) on a continuously stratified flow. Data were obtained in February 2000, November 2001 and May 2002 over two hollows in the lower Chesapeake Bay. Measurements showed an acceleration of the mid- depth flow as it moved toward the deepest part of the hollow, in contrast to the deceleration expected from two- dimensional Bernoulli-type dynamics. The acceleration was attributed to lateral water intrusions that were most apparent during floods. The development of lateral water intrusions was corroborated by observations in a transverse section that crossed the deepest part of one of the hollows. The current acceleration toward the deepest part of the hollows during flood, favored by lateral water intrusions, was deflected toward the right (looking landward) owing to Coriolis accelerations. In general during ebb and flood, the dynamics over the hollows could be explained with three-dimensional Bernoulli-type dynamics (pressure gradient balanced by advection) modified by Coriolis acceleration. Outside the hollows the dynamics should be between pressure gradient and friction. The transition from frictionally dominated dynamics (outside the hollow) to advectively dominated (inside the hollow) appears at the region where the bathymetric slope equals the bottom drag coefficient. The development of lee waves with periodicities of 1.42 h was evident during flood and ebb tide periods, produced by the interaction of the increasing bottom slope and the stratified flow.
OS33C-03
Dynamics and contaminants in the coastal lagoon system of Nichupte-Bojórquez located in the Peninsula of Yucatan, Mexico
Measurements of hydrographic parameters like temperature, salinity, pH, turbidity, dissolved oxygen and determination of concentrations of contaminants like ammonia, surfactants, phosphate, nitrite and nitrate give a picture about the degradation of the lagoon system of Nichupté-Bojórquez. Numerical experiments reveal that the tidal circulation is not intense enough to induce an efficient exchange of water. Tidal currents are small and limited to regions near the two mouths which connect the lagoon system with the Caribbean Sea. The circulation induced by wind forcing is more effective in generating strong currents in the different lagoons of the system. The wind induced circulation reduces the residence time of water. To explain the observed distribution of contaminants, we also simulate numerically the dispersion of contaminants. We present a general picture of the environmental problems of this beautiful lagoon system.
OS33C-04
Tidal and Wind Driven Circulation at Huatulco Bays and Water Quality
ADCP and CTD observations performed from April 2005 to October 2006 as well as the numerical model ROMS were used to describe the circulation inside of Huatulco Bays in Oaxaca, Mexico, and asses the potential impact of the resulting transport. Tidal and residual circulations show strong dependence on the morphology of the continental shelf. To the west of Huatulco Bays, the continental shelf narrows to almost disappear. Different 25- hours velocity averages along the year collected at the entrance of the bay system show velocities around 20 cm/s to the southwest; at the interior of the system however, circulation consists mainly of eastward velocities about 14 cm/s. This pattern suggests that subtidal circulation within the bays is composed by an inflow by the western side and outflow by the eastern side. Consistent with observations, numerical experiments considering the M2 and K1 tidal components show that off the bays, though the tidal wave propagates to the west, circulation in the interior has a general orientation to the east. It is proposed that the crowding of the isobaths and the tidal wave propagation to the west of Huatulco results in a water piling and in consequence a recirculation to the east in the interior of the bays system. This type of circulation is similar to that in response to NW and SW wind, but not to that driven by wind from other directions. According to this picture, relatively diluted water from the Copalita river, 5.5 km to the east of the bays, is a source of surface water into the bays and probably an important factor for its quality. Water quality parameters collected inside of the bays during 2005 met the criteria for recreational use, except at very located points at the beginning of the rainy season, indicating no relationship with water from Copalita river.
OS33C-05
Monitoring of Water Quality by Satellite Imagery and In-Situ Sediments Componentsf at the Ishikari Bay, Hokkaido, Japan
To monitor the water quality of the Ishikari Bay, we studied the diffusion pattern of the fresh water from the Ishikari River using satellite-derived imagery and, verified the water pollution change from the fluctuation of sedimentsf components during the period 1999-2001. All along winter season, icebergs and rough weather prevent us from monitoring the water quality around Hokkaido coastal sea areas. A practical way to conduct the monitoring of this coastal water quality is to use sophisticated remote-sensing techniques. But there are many controversial issues to be solved before using these techniques. Especially the sensor, detecting primary production as chlorophyll sometimes mistakes suspended substance for chlorophyll in the vicinity of river mouth. Because of these problems, there is a need for a new algorithm to make proper interpretations at coastal waters. For this purpose, and to get reasonable information from the high-resolution satellite imagery, the sea-truth data representing chemical species and, their relation with satellite-derived imagery was first of all investigated. The field of study was the Ishikari Bay. At this field, a blooming phytoplankton covering a wide area of the bay was observed when a large quantity of fresh water involved a lot of nutrients discharged from the Ishikari River during a heavy rain event as 100mm of precipitation. The migration of this blooming around the Ishikari Bay was observed in time series till the Okhotsk Sea, by satellite. The results indicate the possibility of the transport of pollutants such as chemical compounds from the Ishikari River basin to the Okhotsk Sea through the medium of plankton. The relationship between satellite-derived imagery (SeaWifs) and chemical species (taken as the sea-truth) was investigated on suspended solids, chlorophyll-a, salinity and water temperature. There is a good relationship between suspended solids and the satellite-derived imagery. The relationship between chlorophyll-a and the satellite- derived imagery was not as obvious, with sometimes the presence of water plumes. Nevertheless, satellite imagery was useful to monitor the influence of fresh water. Furthermore, we investigated the components of sediments sampled in the vicinity of the Ishikari river mouth. The fluctuation of the sedimentsf components around 70 years was observed in organic carbon, Cr, Pb and Cu using the Pb and Cs dating methods. The result indicated that the high concentration (more than 1%) of organic carbon changed during the period of high economic growth, and sometimes there were discharges of high Cr concentration from the abolition mine. And, from the result of fluctuation of the diatom frustules in the sediment, the river and the coastal water had a high primary productivity during the period of the high economic growth. This agrees with the result of the above- mentioned fluctuation of organic matter.
OS33C-06
Submarine Groundwater Discharge (SGD) in Barbados Linking Population and the Environment
Population and economic activity, like agriculture and tourism, both demand freshwater and supply nutrients, like nitrate, to the freshwater reserves. Freshwater and its pollutant load are delivered to the coastal zone via SGD with consequent impacts on tourism and fisheries thus linking the land-based and marine economic sectors. The spatial and temporal variations in SGD were investigated at two sites on the west coast of Barbados during both the wet season, with average rainfalls above 140 mm/month, and the dry season with an average rainfall of 40 mm/month. The SGD flow was modulated by the tide. As a result, measurements must be averaged over a tidal cycle. At Alleynes Bay, characterized by exposed seepage springs at low tide, the average SGD flow rate dropped from 49 cm/d in the wet season to 26 cm/d in the dry season; also, the component of freshwater in the SGD also decreased from 33% to 21%, indicating a three-fold increase in the freshwater flow to the lagoon during the wet season. The NOx concentrations of the SGD were more than 25 times higher than ambient. NOx varied inversely with salinity from 2.5 mg/L at 3 psu to less than 0.1 mg/L at 34 psu. At Queens Fort Beach, where springs are absent, there was no increase in SGD between the seasons. The difference from 14 cm/d in wet season to 20 cm/d in the dry season was not significant. Neither was there a difference in salinity, or NOx, between the ambient water and SGD. SGD at Queens Fort Beach appeared to be composed entirely of recirculated sea water driven by oceanographic processes. About 60% of the western shoreline of Barbados was estimated to have freshwater component to SGD providing an important source of NOx to the lagoon. The source of NOx to the groundwater would increase with population; during the dry season the population may increase due to a peak in tourism. At the same time, reduced rainfall would reduce dilution thus increasing the NOx concentrations of the freshwater end member. Simultaneously, however, the SGD outflow decreases. Our SGD measurements suggest that the NOx input to the lagoon is decreased as a result of these competing factors during the dry period and is increased during the wet period.
OS33C-07
Understanding a Century of Change in an Estuary: Tampa Bay. Florida
During the 20th century, Tampa Bay on the west coast of Florida changed from a largely pristine subtropical
estuary to a busy waterway with commercial ports and extensive coastal urbanization. The estuary has been
physically altered through dredging and construction and its biogeochemical, sedimentary and hydrological
balances have been changed. Environmental indicators show that the health of the estuary has been significantly
impacted. Long-term restoration and conservation efforts in the next decades will need to be made in the
presence of sustained population expansion, increased use of water resources, developments of ports, bay-wide
dredging, construction of pipelines, and increased large ship traffic.
The Tampa Bay integrated modeling program has helped rationalize, and organize our understanding of the ways
that the ecosystem has changed and we have simulated the bay as it was at the ends of the 19th and 20th
centuries. This involves submodels of hydrodynamics, hydrology, wave climate, sediment transport, and
biogeochemical processes. A key element in this research is the recognition by the USGS Integrated Science
Study that estuarine systems function as a dynamic interplay among biologic, geologic, hydrologic, atmospheric,
and chemical processes. Integrated modeling also relies heavily on synthesis modeling of historical and modern
data for the estuary and the Tampa Bay study has included a major collection program for physical data between
2004 and 2006. An important part of the integrated modeling program has been public outreach including training
in the development of submodels by state agencies, universities and community groups.
The present paper reviews the Tampa Bay Integrated Coastal Models with conclusions about some of the major
anthropogenic impacts. Examples include restoration projects based on the predictions of submodels developed
by local agencies for wetland habitats around the Bay and studies by port authorities using submodels of short
episodic events such as ship wakes and contaminant spills. Planners have found major application of
submodels in coastal hazard prediction especially from severe storms.
http:gulfsci.usgs.gov