OS23G-01 INVITED
Exposure Patterns and Health Effects Associated with Swimming and Surfing in Polluted Marine Waters
Marine bathing beaches are closed to the public whenever water quality fails to meet State and Federal standards. In this talk I will explore the science (and lack thereof!) behind these beach closures, including the health effects data upon which standards are based, shortcomings of the current approach used for testing and notification, and the high degree of spatial and temporal heterogeneity associated with human exposure to pollutants in these systems. The talk will focus on examples from Huntington Beach, where the speaker has conducted research over the past several years.
OS23G-02
Simulations of Mixing and Transport of Dissolved Waste Discharged From a Submerged Aquaculture pen
The present study focuses on understanding the transport and fate of dissolved wastes from an aquaculture pen in near-coastal environments using the hydrodynamic code SUNTANS, which uses unstructured grids to compute flows at very high resolution. Simulations of the pollutant concentration field (in time and space) as a function of the local environment (stratification, bathymetry, wind), flow conditions (tides, currents), and the location of the pen were performed. The fish-pen causes partial blockage of the water flow, causing deceleration of the approaching flow and the formation of a downstream wake. Results of both the near-field (area within 10 to 20 pen diameters of fish-pen site) as well as the far-field behavior of the pollutant field will be presented. The results provide an understanding of the impact of aquaculture fish-pens on coastal water quality.
OS23G-03
Sensitivity Analysis of Factors Influencing the Fate and Transport of Fecal Indicator Bacteria in Southern Lake Michigan
To understand the factors that influence the fate and transport of fecal indicator bacteria (FIB) in the nearshore waters of the Great Lakes, we examined two southern Lake Michigan beaches (as well as the tributaries discharging into the lake in the vicinity of the beaches). A three-dimensional, σ-coordinate Princeton Ocean Model (POM) with a nested-grid was used to describe wind-driven circulation in Lake Michigan. A biological model coupled to the hydrodynamic and temperature fields in the lake was used to describe the observed FIB levels near the beaches. We report simulation results for the summers of 2004 and 2006. Inactivation of pathogens in the nearshore region is influenced by a complex set of factors including solar insolation, water temperature, settling of particulate matter, resuspension, turbulent diffusion, loading from tributaries etc. Efforts to systematically quantify the relative contributions of these complex and often inter-related processes are somewhat limited, especially for freshwater environments. Here we describe sensitivity analyses based on our numerical simulations with the objective of ranking the various processes involved in terms of their relative importance. We also examine the performance of different mathematical formulations of inactivation in order to identify their relative merits.
OS23G-04
Transport due to Internal Waves in the San Pedro Bay Region
Field measurements and simulations of internal waves in the San Pedro Bay region indicate that they are
generated at the shelf break where the topographic slope matches that of the internal wave characteristics. This
internal wave energy radiates away from and onto the shelf in the form of first-mode waves, which steepen into
highly nonlinear waves as they propagate into shallow waters. Like surface waves, while the Eulerian mean
(time-average at a point) internal-wave induced velocity is typically small, the Lagrangian mean, which is also
known as the Stokes drift (the time-averaged velocity following a fluid particle), is not necessarily small and has
important implications for transport of pollutants and other tracers on the continental shelf. Using the
nonhydrostatic model SUNTANS, we compute the internal wave field in the San Pedro Bay Region and study the
associated transport of tracers due to the internal wave-induced Stokes drift. By simulating the flow with and
without stratification, we show that the barotropic tides have a minimal effect on transport, while internal waves
induce a complex three-dimensional Stokes drift that results in significant depth-dependent tracer transport
throughout the region. The results demonstrate that the internal wave field in coastal shelf waters is an important
contributor to cross-shelf transport, both in the short term due to the shoaling of highly nonlinear waves in
shallow waters, and in the long term due to the Stokes drift of the weakly nonlinear internal wave field throughout
the continental shelf.
http:suntans.stanford.edu
OS23G-05 INVITED
Nowcasting and Forecasting Beach Bacteria Concentration Using EPA's Virtual Beach Software
Beaches in the United States of (North) America are subject to closure when bacterial counts exceed water quality criteria. Many authorities base these decisions on water samples that typically require at least 18 hours to analyze. This persistence approach, or model, often leads to erroneous decisions due to the great variability in bacterial concentrations. Beaches are closed when they could be open and vice versa, their true status unknown until the next day. Studies show that mathematical models based on multi-variable linear regression (MLR) principles can produce better estimates, or nowcasts, using real-time explanatory variables, such as turbidity, cloud cover, and rainfall. To make such models generally available, the Environmental Protection Agency (EPA) is developing a program called Virtual Beach (VB). VB is public-domain software for developing site-specific predictive models. It features capabilities that make it possible with reasonable effort to develop, and compare the performance of, static and dynamic MLR models. The results of tests on 2006 Huntington Beach, Lake Erie beach data are presented. In addition to nowcasting, the work begins to address the question, can weather and water forecasts be used to forecast beach conditions in advance? A preliminary affirmative answer is provided based on an analysis of the Huntington Beach data, with weather forecasts for nearby Cleveland-Hopkins international airport, and NOAA lake condition forecasts. We encourage those engaged in beach monitoring and management to request VB, applying the nowcast and forecast models developed with it to their locations of interest. Disclaimer: Although this work was reviewed by EPA and approved for presentation, it may not necessarily reflect official Agency policy.
OS23G-06
Fresh Submarine Groundwater Discharge from a Contaminated Beach Aquifer is Enhanced During Neap Tide
Experiments were carried out to assess the fortnightly effects of mixed semi-diurnal tides and tidally-induced aquifer overheight on the timing, magnitude, and quality of submarine groundwater discharge (SGD) from an unconfined beach aquifer impacted by septic tank effluent at Stinson Beach, California. Groundwater- and ocean elevations, salinity, and nutrient concentrations were monitored throughout a 14-day neap/spring cycle. A freshening of the surf zone coupled with an increase in nutrient concentrations was observed at neap tide and attributed to discharge of fresh, nutrient-rich groundwater during that part of the fortnight. Nutrient concentrations in the surf zone returned to near-offshore levels during the spring tide. Estimates of SGD were made with chemically- and physically-based methods. Fresh SGD was maximal during the neap tide although total SGD was maximal during the spring tide. An overheight of time-averaged piezometric head was observed in the aquifer near the beach face throughout the 14-day experiment. This overheight varied significantly with tidal range, thereby controlling the seaward hydraulic gradient across the fresh part of the aquifer and, thus, the flow of nutrient-rich fresh groundwater to the coastal ocean. We discuss the role of aquifer overheight in controlling submarine discharge of fresh groundwater and related non-point source pollution from unconfined aquifers in similar environments.
OS23G-07
Beach Sands Along the California Coast are Diffuse Sources of Fecal Bacteria to Coastal Waters
Fecal indicator bacteria (FIB) are nearly ubiquitous in California (CA) beach sands. Sands were collected from 55
beaches along the CA coast. Ninety-one percent of the beaches had detectable enterococci (ENT) while 62%
had detectable E. coli (EC) in their sands. The presence of a putative bacterial source (such as a river),
the degree of wave shelter, and surrounding land use explained a significant (p<0.05) fraction of the variation in
both ENT and EC densities between beaches. Sand characteristics including moisture content, organic carbon,
and percent fines, significantly (p<0.05) influenced only EC densities in beach sand. We assayed 34 of 163
sand samples for salmonellae, but did not detect this bacterial pathogen. The potential for FIB to be transported
from the sand to sea was investigated at a single wave-sheltered beach with high densities of ENT in beach
sand: Lovers Point, CA (LP). We collected samples of exposed and submerged sands as well as water over a 24
h period in order to compare the disappearance or appearance of ENT in sand and the water column. Exposed
sands had significantly higher densities of ENT than submerged sands with the highest densities located near
the high tide line. Water column ENT densities began low, increased sharply during the first flood tide and slowly
decreased over the remainder of the study. During the first flood tide, the number of ENT that entered the water
column was nearly equivalent to the number of ENT lost from exposed sands when they were submerged by
seawater. The decrease in nearshore ENT concentrations after the initial influx can be explained by ENT die-off
and dilution with clean ocean water. A source tracking study at LP indicated that ENT were likely of human origin
because they were positive for the esp gene.
http:www.stanford.edu/~aboehm/research.htm
OS23G-08
Spatio-Temporal Variability in Fecal Indicator Bacteria Concentrations at Huntington Beach: Connections to Physical Forcing
Two major factors determine the spatial and temporal distributions of fecal indicator bacteria (FIB) at a given beach: local circulation & mixing patterns, and bacterial inactivation rates. High frequency and spatial resolution bacterial sampling combined with measurements of physical processes can be used to infer inactivation rates, enabling differentiation between dilution & mortality as factors driving variability in nearshore FIB abundance. A FIB sampling experiment (HB06) took place on 16 October 2006, at Huntington State Beach, a site selected due to its persistent problems with FIB pollution. Water samples were taken at 20-minute intervals (from 6:50am to 11:50am) at ten locations; four in an alongshore transect spanning 1 km at the shoreline, and the remainder in a 300-m long cross-shore transect. All samples were analyzed for FIB concentration (Total Coliforms, E. coli & Enterococci) and, for a subset, species level Enterococcus composition was determined. As part of the HB06 experiment, currents, temperature, waves, and chlorophyll fluorescence were measured simultaneously in the cross-shore direction with rapid CTD casts 300 m offshore. Results indicate that E. coli and Enterococcus concentrations exhibit exponential decreases with time, with smaller decay rates associated with depth and with sites in the Talbert Marsh and Santa Ana River. FIB concentrations are also noticeably lower farther offshore (300 m). Spatio-temporal patterns in FIB concentration will be presented in conjunction with the nearshore physical data allowing the relationship between physical dynamics and biological variability to be addressed.