Ryan W. Schloesser, Mary C. Fabrizio, Robert J. Latour, Greg C. Garman, Bob Greenlee, Mary Groves, and James Gartland
Rapid increase in abundance and expanded distribution of introduced blue catfish Ictalurus furcatus populations in the Chesapeake Bay watershed have raised regional management concerns. This study uses information from multiple surveys to examine expansion of blue catfish populations and document their role in tidal river communities. Originally stocked in the James, York, and Rappahannock River systems for development of commercial and recreational fisheries, blue catfish have now been documented in adjacent rivers and have expanded their within-river distribution to oligo- and mesohaline environments. Range expansions coincided with periods of peak abundance in 1996 and 2003 and with the concurrent decline in abundance of native white catfish I. catus. Blue catfish in these systems use a diverse prey base; various amphipod species typically dominate the diet of smaller individuals (<300 mm fork length>[FL]), and fishes are common prey for larger blue catfish (>300 mm FL). Recent studies based on stable isotope analyses suggest that adult blue catfish in these systems are apex predators that feed extensively on important fishery resources, including anadromous shads and herrings Alosa spp. and juvenile Atlantic menhaden Brevoortia tyrannus. Minimizing effects on Chesapeake Bay communities by controlling high densities of blue catfish populations is a primary goal of management, but conflicting demands of the commercial and recreational sectors must be resolved. Further, low market demand and human consumption concerns associated with purported accumulation of contaminants in blue catfish pose additional complications for regulating these fisheries.
J. D. Boon
Tidal conditions fail to explain a paradoxical similarity in water level extremes induced by Hurricane Isabel on 18 September 2003, and the 23 August 1933 storm of record at Hampton Roads, Virginia. Storm surge peaks occurred near astronomical high tide during both storms, but Isabel arrived during neap tides while tides during the 1933 storm were nearer to spring. In addition, Isabel produced a lesser storm surge, yet she yielded a storm tide, or high-water mark, roughly equal to that of the 1933 hurricane. The answer to the paradox lies in observed sea level—water level measured relative to the land—and its movement during the 70 years between these events. Water level analysis shows that the sea level change observed can be divided into three categories at three different time scales: daily (astronomical tides), monthly (seasonal change), and yearly (secular trend in sea level). At Hampton Roads, a secular rise rate of 4.25 mm⋅yr-1 (1.39 ft/century) predicted an increase of 29.8 cm in 70 years; mean sea level for the month of September stood an additional 21.9 cm above the annual mean for 2003. These numbers are comparable to the mean semirange of tide (37.0 cm) at Hampton Roads. Thus seasonal and secular change are both factors of key importance in evaluating storm tide risk at time scales attributable to major hurricanes (100 years). Adoption of a new vertical reference, projected monthly mean sea level, is proposed to facilitate their inclusion in storm tide predictions at decadal time scales.
L. H. Brasseur, A. C. Trembanis, J. M. Brubaker, and C. T. Friedrichs
After making landfall on the North Carolina coast on the morning of 18 September 2003, Category 2 Hurricane Isabel tracked northward parallel to and slightly west of the Chesapeake Bay. At Gloucester Point, near the mouth of the York River estuary, strong onshore winds with speeds in excess of 20 m⋅s-1 persisted for over 12 hours and peak winds reached over 40 m⋅s-1, causing a sustained up-estuary wind stress. Storm surge exceeded 2 m throughout most of the lower Chesapeake Bay. A 600 kHz acoustic Doppler current profiler (ADCP), deployed at a depth of 8.5 m off Gloucester Point, provided high-quality data on waves, storm surge, currents, and acoustic backscatter throughout the water column before, during, and after the storm. Pressure and salinity sensors at three additional sites further up the estuary provided information on water surface slope and saltwater excursion up the estuary. A first-order estimate of three terms of the along-channel momentum equation (barotropic pressure gradient, acceleration, and friction) showed that the pressure gradient appeared to be balanced by the wind stress and the acceleration during the storm. The storm’s path and slow speed were the primary causes of the extremely high storm surge relative to past storms in the area.
An Unprecedented Scientific Community Response to an Unprecedented Event: Tropical Storm Agnes and the Chesapeake Bay
M. P. Lynch
In June 1972, the remnants of Hurricane Agnes brought destructive floods to the watershed of the Chesapeake Bay basin. Unlike Hurricane Isabel, Agnes did not strike Chesapeake Bay directly, but deposited a record amount of rainfall on the watershed. The evening that the Agnes rainfall began in earnest coincided with a meeting of the Citizens Program for the Chesapeake Bay. The directors of the three largest Chesapeake Bay research institutions, Drs. Donald W. Pritchard, L. Eugene Cronin, and William J. Hargis Jr., were in attendance at this meeting. The potential magnitude of the Agnes rainfall was readily apparent at the meeting as one of the planned evening events had to be moved due to a foot of water in the meeting room. The following morning at breakfast, the three directors committed their institutions to “Operation Agnes,” extensive studies of the biological, chemical, and physical impacts of this event. Hargis, Cronin, and Pritchard were good friends and strong competitors of long standing. Since 1949, Pritchard had been the first full-time director of the Chesapeake Bay Institute (CBI); Cronin had headed the Chesapeake Biological Laboratory (CBL) since 1951; and Hargis had been director of the Virginia Institute of Marine Science (VIMS) (and its predecessor the Virginia Fisheries Laboratory-VFL) since 1959. In 1964, the three directors had set up an informal Chesapeake Bay Research Council (CBRC) to coordinate some of their Chesapeake Bay research activities. They used the CBRC mechanism to coordinate “Operation Agnes,” a commitment that was made without any assurance of financial support for these studies. The gamble taken by the three laboratory directors was successful, eventually resulting in a peer-reviewed book published by The Johns Hopkins University Press entitled The Effects of Tropical Storm Agnes on the Chesapeake Bay Estuarine System. Operation Agnes was the last project undertaken by the CBRC. Reorganization by two of the parent institutions and incorporation of the Chesapeake Research Consortium (CRC) resulted in a realignment of Chesapeake Bay scientific leadership and the leadership of Operation Agnes moved from CBRC to CRC. The scientific community’s response to Tropical Storm Agnes—an unprecedented event— was in itself unprecedented. A number of coincidences came into play: recent (1969) experience with flooding from Hurricane Camille; fortuitous attendance of the leaders of the three largest Chesapeake Bay research institutions at a meeting directly affected by Agnes; and the prior mobilization of the three institutions to conduct extensive hydrographic studies throughout Chesapeake Bay. The most important factor, however, was the strong commitment of three laboratory directors to the understanding of the Chesapeake Bay system.
M. M. Montane and H. M. Austin
Few studies have focused on the effects of climatic perturbations, such as hurricanes, on finfish recruitment and behavior. The Virginia Institute of Marine Science (VIMS) Trawl Survey has sampled continuously throughout the Virginia portion of Chesapeake Bay for 50 years. While hurricanes have impacted Chesapeake Bay during this time, three periods of hurricane activity— September and November 1985 (hurricanes Gloria and Juan), September 1989 (Hurricane Hugo), and September 2003 (Hurricane Isabel)—coincided with the largest spikes in juvenile recruitment of Atlantic croaker (Micropogonias undulatus) for half a century. The fall (October–December) croaker young-of-year indices for 1985, 1989, and 2003 were seven, five, and eight times greater, respectively, than the 50-year average. Typically Atlantic croaker display great interannual variability in Chesapeake Bay, with these fluctuations shown to be weather related. The timing of Atlantic croaker recruitment to Chesapeake Bay is such that late summer/fall hurricanes are most likely to affect them, as opposed to other shelf spawners. Understanding the effects of hurricanes on species, such as croaker, that have enormous ecological, commercial, and recreational importance is essential for prudent fisheries management.
W. G. Reay and K. A. Moore
Water quality impacts from Tropical Cyclone Isabel on the York River estuary were assessed based on long-term, near-continuous, shallowwater monitoring stations along the York River proper (poly- and mesohaline regimes) and its two tidal tributaries—the Mattaponi and Pamunkey rivers (oligohaline and tidal freshwater regimes). Regional rainfall from 18 to 19 September 2003 ranged from 5.8 to 11.7 cm. Peak mean daily stream flow occurred on 21 September 2003 and represented a 20- and 30-fold increase over prestorm conditions on the Mattaponi and Pamunkey rivers, respectively. Isabel produced a storm surge of 1.7 m near the mouth of the estuary and 2.0 m in the upper tidal freshwater regions. The tidal surge resulted in a short-term (12- to 36-hour) pulse of high salinity water (approximately 10 ppt greater than pre-storm conditions) within the oligohaline portion of the estuary. In comparison, salinity levels within the upper tidal fresh water and down-river poly-and mesohaline regions remained relatively unchanged. Following the storm surge, salinity levels within lower portions of the estuary declined 1.5 to 4.5 ppt for an extended period in response to freshwater runoff. Elevated turbidity—in some cases extreme—was in direct response to the storm surge and waves associated with Tropical Cyclone Isabel. With the exception of a single station, maximum storm-associated turbidity levels varied between 192 and >1000 NTUs (nephelometric turbidity units). Turbidity levels returned to prestorm conditions within a 24- to 30-hour period at most stations. Perhaps the most significant environmental impact associated with the passage of Isabel was the persistent low dissolved oxygen (DO) levels (3–4 mg⋅L-1) that occurred at the tidal freshwater stations. Low DO at these stations coincided with increased freshwater inflow to the Mattaponi and Pamunkey rivers, suggesting augmented loadings of readily degradable organic material from the watershed. Mean daily DO levels took approximately two weeks to return to prestorm levels at these sites. Dissolved oxygen levels at the poly- and mesohaline stations within the York River proper remained at or above 5 mg⋅L-1 prior to, during, and after the storm’s passage.
J. Shen, W. Gong, and H. Wang
Hurricane Isabel made landfall near Drum Inlet, about 240 km south of the Chesapeake Bay mouth, on the Outer Banks of North Carolina at 17:00 UTC (GMT 12:00), 18 September 2003. Hurricane Isabel is considered one of the most significant tropical cyclones to affect portions of northeastern North Carolina and east-central Virginia. The ADvanced CIRCulation Model (ADCIRC) model was applied to the Chesapeake Bay to simulate Hurricane Isabel. High-resolution grids were placed inside the Bay and tributaries; coarse grids were placed outside the Bay. The spatial grid resolution in the Bay mainstem is about 200–1000 m and the spatial grid resolution in the tributaries ranges from 50–700 m. A parametric wind model was used to drive the model. The model results show that, with the use of a parametric wind model, the model can predict the peak surge and storm tide histories along the Bay mainstem and tributaries. The model was used to analyze the impact of sea level rise on surge and inundation prediction.
H. Wang, J. Cho, J. Shen, and Y. P. Wang
An unstructured grid hydrodynamic model was used to study storm surge in the Chesapeake Bay during Hurricane Isabel. The model-simulated, storm-induced water level compared reasonably well with the measured data collected around the Bay. Calibrated water level was extracted from the model to further analyze the dynamics of the surge as it formed and propagated along the mainstem Chesapeake. Based on time-series analysis, formation of the surge due to the pumping of coastal waters (hereafter called the primary surge) into the Chesapeake was first identified at the Bay mouth with a peak height of 1.5 m above mean sea level (MSL). Once formed, it propagated northward with gradually diminishing amplitude at a speed of about 5 m⋅sec-1 until reaching Windmill Point, near the mouth of the Rappahannock River in Virginia. Beyond Windmill Point, the surge height increased monotonically toward the northern part of the Chesapeake Bay. Spatial analysis of surge height revealed that a second-stage surge was induced directly by the southerly wind following Hurricane Isabel’s passage inland. The persistent southerly wind induced a setup and a set-down in the upper and lower Chesapeake respectively, with the dividing line near Windmill Point where the water level stayed at approximately 0.5 m above MSL during the event. Space-time analysis provided further evidence that the abnormally high water in the upper Chesapeake Bay was the result of the primary surge wave as well as the second-stage surge caused by the southerly wind-induced setup.
Ann Hayward Rooney-Char and Maurice P. Lynch
Harold J. Humm
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