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Research about Chesapeake Bay

Source-linked reports with geographic coverage including Chesapeake Bay.

At least 145 records · Page 8Linked to original sources
USGS1998

The Chesapeake Bay bolide: Modern consequences of an ancient cataclysm

During the late Eocene, the formerly quiescent geological regime of the Virginia Coastal Plain was dramatically transformed when a bolide struck in the vicinity of the Delmarva Peninsula, and produced the following principal consequences: The bolide carved a roughly circular crater twice the size of the state of Rhode Island (~6400 km 2) , and nearly as deep as the Grand Canyon (1.3 km deep). The excavation truncated all existing ground water aquifers in the impact area by gouging ~4300 km 3 of rock from the upper lithosphere, including Proterozoic and Paleozoic crystalline basement rocks and Middle Jurassic to upper Eocene sedimentary rocks. A structural and topographic low formed over the crater. The impact crater may have predetermined the present-day location of Chesapeake Bay. A porous breccia lens, 600-1200 m thick, replaced local aquifers, resulting in ground water ~1.5 times saltier than normal sea water. Long-term differential compaction and subsidence of the breccia lens spawned extensive fault systems in the area, which are potential hazards for local population centers in the Chesapeake Bay area.

Chesapeake Bay↗
USGS1998

Preliminary estimates of residence times and apparent ages of ground water in the Chesapeake Bay watershed, and water-quality data from a survey of springs

Knowledge of the residence times of the ground-water systems in Chesapeake Bay watershed helps resource managers anticipate potential delays between implementation of land-management practices and any improvements in river and estuary water quality. This report presents preliminary estimates of ground-water residence times and apparent ages of water in the shallow aquifers of the Chesapeake Bay watershed. A simple reservoir model, published data, and analyses of spring water were used to estimate residence times and apparent ages of ground-water discharge. Ranges of aquifer hydraulic characteristics throughout the Bay watershed were derived from published literature and were used to estimate ground-water residence times on the basis of a simple reservoir model. Simple combinations of rock type and physiographic province were used to delineate hydrogeomorphic regions (HGMR's) for the study area. The HGMR's are used to facilitate organization and display of the data and analyses. Illustrations depicting the relation of aquifer characteristics and associated residence times as a continuum for each HGMR were developed. In this way, the natural variation of aquifer characteristics can be seen graphically by use of data from selected representative studies. Water samples collected in September and November 1996, from 46 springs throughout the watershed were analyzed for chlorofluorocarbons (CFC's) to estimate the apparent age of ground water. For comparison purposes, apparent ages of water from springs were calculated assuming piston flow. Additional data are given to estimate apparent ages assuming an exponential distribution of ages in spring discharge. Additionally, results from previous studies of CFC-dating of ground water from other springs and wells in the watershed were compiled. The CFC data, and the data on major ions, nutrients, and nitrogen isotopes in the water collected from the 46 springs are included in this report. The apparent ages of water discharging from 30 of the 46 springs sampled were less than 20 years, including 5 that were "modern" (0-4 years). Four samples had apparent ages of 22 to 34 years, and two others from thermal springs were 40 years or greater. The remaining ten samples were contaminated with local sources of CFC and could not be dated. Nitrate concentrations and nitrate delta 15 nitrogen (d 15 N) values in water from many springs are similar to those in shallow ground water beneath fertilized fields, and some values are high enough to indicate a probable source from animal-waste components. The nitrogen data reported here highlight the significance of the springs sampled during this study as pathways for nutrient transport in the Chesapeake Bay watershed. Ground-water samples were collected from springs during an unusually high flow period and thus may not be representative of low base-flow conditions. Residence times estimated from plausible ranges of aquifer properties and results of previous age-dating analyses generally corroborate the apparent-age analysis made in the current study and suggests that some residence times could be much longer. The shortest residence times tend to be in the Blue Ridge and northern carbonate areas; however, the data are preliminary and not appropriate for statistical tests of significance or variance. Because the age distributions in the aquifer discharging to the springs are not known, and because the apparent ages of water from the springs are based on various combinations of CFC criteria, the apparent ages and calculated residence times are compared for illustrative purposes but are considered preliminary until further work is accomplished.

Maryland, Virginia↗
USGS1997

The Chesapeake Bay bolide impact: A convulsive event in Atlantic Coastal Plain evolution

Until recently, Cenozoic evolution of the Atlantic Coastal Plain has been viewed as a subcyclical continuum of deposition and erosion. Marine transgressions alternated with regressions on a slowly subsiding passive continental margin, their orderly succession modified mainly by isostatic adjustments, occasional Appalachian tectonism, and paleoclimatic change. This passive scenario was dramatically transformed in the late Eocene, however, by a bolide impact on the inner continental shelf. The resultant crater is now buried 400–500 m beneath lower Chesapeake Bay, its surrounding peninsulas, and the continental shelf east of Delmarva Peninsula. This convulsive event, and the giant tsunami it engendered, fundamentally changed the regional geological framework and depositional regime of the Virginia Coastal Plain, and produced the following principal consequences. (1) The impact excavated a roughly circular crater, twice the size of Rhode Island (∼6400 km 2 ) and nearly as deep as the Grand Canyon (∼1.3 km deep). (2) The excavation truncated all existing ground-water aquifers in the target area by gouging ∼4300 km 3 of rock from the upper lithosphere, including Proterozoic and Paleozoic crystalline basement rocks and Middle Jurassic to upper Eocene sedimentary rocks. (3) Synimpact depositional processes, including ejecta fallback, massive crater-wall failure, water-column collapse, and tsunami backwash, filled the crater with a porous breccia lens, 600–1200 m thick, at a phenomenal rate of ∼1200 m/hr. The breccia lens replaced the truncated ground-water aquifers with a single 4300 km 3 reservoir, characterized by ground water ∼1.5 times saltier than normal sea water (chlorinities as high as 25,700 mg/l). (4) A structural and topographic low, created by differential subsidence of the compacting breccia, persisted over the crater at least through the Pleistocene. In the depression are preserved postimpact marine lithofacies and biofacies (upper Eocene, lower Oligocene, lower Miocene) not known elsewhere in the Virginia Coastal Plain. (5) Long-term differential compaction and subsidence of the breccia lens spawned extensive fault systems in the postimpact strata. Many of these faults appear to reach the bay floor, and may be potential hazards for motion-sensitive structures in population centers around Chesapeake Bay. Near-surface fracturing and faulting generated by the impact shock may extend as far as 90 km from the crater rim. (6) Having never completely filled with postimpact sediments, the sea-floor depression over the crater appears to have predetermined the location of Chesapeake Bay. (7) As large impact craters are principal sources for some of the world's precious metals, it is reasonable to expect that metal-enriched sills, dikes, and melt sheets are present in the inner basin of the crater. In addition to these specific consequences, the crater and the convulsive event that produced it, have widespread implications for traditional interpretations of certain structural and depositional features of the Atlantic Coastal Plain, particularly in southeastern Virginia.

Chesapeake Bay↗
USGS1997

Avian cholera in ospreys: first occurrence and possible mode of transmission

In 1994, six Ospreys (Pandion haliaetus) were recovered during the later stages of an epizootic of avian cholera (Pasteurella multocida) in diving ducks and seabirds on Chesapeake Bay in Maryland and Virginia. Pasteurella multocida was isolated from four Ospreys submitted for bacterial examination. This is believed to be the first report of avian cholera in Ospreys. The same isolate, serotype 3,4, was isolated from the Ospreys, diving ducks,and seabirds collected during the epizootic. Possible modes of transmission of avian cholera in Ospreys were either the ingestion of sick waterfowl or use of infected carcasses or bones as nest material.

Maryland, Virginia↗
USGS1997

Climate control

April showers bring May flowers. Well, not always. The climate of the Chesapeake Bay area, as elsewhere, varies from year to year as anyone living in the watershed the last few years can attest. That variability, though, is more than just a conversation ice-breaker. Fluctuations in seasonal rainfall affect river flows into the Bay and can hinder nutrient reduction efforts aimed at restoring the Chesapeake ecosystem because nutrient flows into the Bay are closely tied to river discharge.

Delaware, Maryland, New York, Pennsylvania, Virgin↗
USGS1996

Impact origin of the Chesapeake Bay structure and the source of the North American tektites

Seismic profiles, drill core samples, and gravity data suggest that a complex impact crater ~35.5 million years old and 90 kilometers in diameter is buried beneath the lower Chesapeake Bay. The breccia that fills the structure contains evidence of shock metamorphism, including impact melt breccias and multiple sets of planar deformation features (shock lamellae) in quartz and feldspar. The age of the crater and the composition of some breccia clasts are consistent with the Chesapeake Bay impact structure being the source of the North American tektites.

Maryland, Virginia↗
USGS1996

Review of factors affecting the distribution and abundance of waterfowl in shallow-water habitats of Chesapeake Bay

Long-term trends of waterfowl populations in Chesapeake Bay demonstrate the importance of shallow-water habitats for waterfowl species. Although recent increases in field feeding by geese and swans lessened the importance of shallow-water areas for these species, most duck species depend almost exclusively on shallow-water habitats. Many factors influenced the distribution and abundance of waterfowl in shallow-water habitats. Habitat degradation resulted in the decline in numbers of most duck species and a change in distribution of some species. Increased numbers of mallards ( Anas platyrhynchos ) in recent decades probably resulted from release programs conducted by the Maryland Department of Natural Resources and private individuals. Studies of food habits since 1885 showed a decline in submerged-aquatic vegetation in the diet of some species, such as the canvasback ( Aythya valisineria ), and an increase in the proportions of invertebrates in the diet. Diversity of food organisms for many waterfowl species has declined. Surveys of vegetation and invertebrates in the Chesapeake Bay generally reflect a degradation of shallow-water habitat. Human population increases in the Chesapeake Bay watershed directly and indirectly affected waterfowl distribution and abundance. The increase of exotic plant and invertebrate species in the bay, in most cases, benefited waterfowl populations. Increased contaminants have reduced the quality and quantity of habitat, although serious attempts to reverse this trend are underway. The use of shallow-water habitats by humans for fishing, hunting, boating, and other recreational and commercial uses reduced the use of shallow-water habitats by waterfowl. Humans can lessen the adverse influences on the valuable shallow-water habitats by restricting human population growth near these habitats and improving the water quality of the bay tributaries. Other affirmative actions that will improve these areas for waterfowl include greater restrictions on boat traffic in shallow-water habitats and establishing more sanctuaries in shallow-water areas that have complete protection from human disturbance.

Maryland, Virginia↗
USGS1995

Effects of diet on rate of body mass gain by wintering canvasbacks

Because habitat degradation has led to the loss of submerged vegetation in Chesapeake Bay, wintering canvasbacks ( Aythya valisineria ) have shifted from a plant diet of American wildcelery ( Vallisneria americana ) to an animal diet of Baltic clams ( Macoma balthica ). We conducted experiments with pen-reared canvasbacks ( n = 32, 1990; n = 32, 1991) to assess the effect of this diet change on mass recovery rate following a simulated period of food deprivation. During the recovery phase, canvasbacks were fed ad libitum either (1) Baltic clams (1991 only), (2) tubers of wildcelery, 3) corn, or (4) commercial control diet. Initial body mass of ducks did not differ between years ( P = 0.754) or among pens ( P > 0.264) or diets within years (1990, P = 0.520; 1991, P = 0.684). Body mass decline during food deprivation ( x̄ = 26.0 g/day ± 0.6 SE) did not differ among diets (1990, P = 0.239; 1991, P = 0.062) or between sexes in 1990 ( P = 0.197), but was greater ( P = 0.039) for males ( x̄ = 28 g/day ± 0.8 SE) than females ( x̄ = 25 g/day ± 0.9) in 1991. Mass recovery rate differed between diets (clams excluded) in 1990 ( P = 0.003) and 1991 (clams included) ( P = 0.011); mean = 42 g • bird -1 /day -1 ± 3.8 (SE) control diet, mean = 32 g • bird -1 /day -1 ± 2.8 wildcelery tubers, mean = 24 g • bird -1 /day -1 ± 4.9 whole corn, and mean = 23 g • bird -1 /day -1 ± 1.0 Baltic clams. Canvasbacks consumed an average of 2,169 g • bird -1 /day -1 of Baltic clams, 1,158 g • bird -1 /day- 1 of wildcelery tubers, 152 g • bird -1 /day -1 whole corn, and 208 g • bird -1 /day -1 (dry mass) control diet during recovery. Managers should restore and maintain aquatic plant foods that enhance winter survival of canvasbacks and other waterfowl in response to declining habitat quality.

Maryland, Virginia↗
USGS1994

Problems of stock definition in estimating relative contributions of Atlantic striped bass to the coastal fishery

Stock contribution studies of mixed‐stock fisheries rely on the application of classification algorithms to samples of unknown origin. Although the performance of these algorithms can be assessed, there are no guidelines regarding decisions about including minor stocks, pooling stocks into regional groups, or sampling discrete substocks to adequately characterize a stock. We examined these questions for striped bass Morone saxatilis of the U.S. Atlantic coast by applying linear discriminant functions to meristic and morphometric data from fish collected from spawning areas. Some of our samples were from the Hudson and Roanoke rivers and four tributaries of the Chesapeake Bay. We also collected fish of mixed‐stock origin from the Atlantic Ocean near Montauk, New York. Inclusion of the minor stock from the Roanoke River in the classification algorithm decreased the correct‐classification rate, whereas grouping of the Roanoke River and Chesapeake Bay stock into a regional (“southern”) group increased the overall resolution. The increased resolution was offset by our inability to obtain separate contribution estimates of the groups that were pooled. Although multivariate analysis of variance indicated significant differences among Chesapeake Bay substocks, increasing the number of substocks in the discriminant analysis decreased the overall correct‐classification rate, Although the inclusion of one, two, three, or four substocks in the classification algorithm did not greatly affect the overall correct‐classification rates, the specific combination of substocks significantly affected the relative contribution estimates derived from the mixed‐stock sample, Future studies of this kind must balance the costs and benefits of including minor stocks and would profit from examination of the variation in discriminant characters among all Chesapeake Bay substocks.

Maryland↗
USGS1994

Tag recovery estimates of migration of striped bass from spawning areas of the Chesapeake Bay

In 1988–1991 striped bass Morone saxatilis were collected for tagging from various spawning areas within the Hudson River (New York) and the Chesapeake Bay (Maryland). The fish were tagged and released during traditional periods of spawning and recovered by commercial and recreational fishermen. The proportion of fish that migrated in spring–fall from spawning areas in Chesapeake Bay to more northern waters of mid‐Atlantic and New England states was estimated from the geographically stratified tag returns. Most of the tagged fish were 40–100 cm total length (TL). The estimated proportion of migrant striped bass increased with body size, and nearly all fish larger than 100 cm TL left the bay during the spring–fall migration. Sex‐specific differences in migration appear to be associated with the differences in body size of mature males and females, thus lending support to previously hypothesized patterns of striped bass migration.

Maryland↗
USGS1994

Flock sizes and sex ratios of canvasbacks in Chesapeake Bay and North Carolina

Knowledge of the distribution, size, and sex ratios of flocks of wintering canvasbacks ( Aythya valisineria ) is fundamental to understanding the species' winter ecology and providing guidelines for management. Consequently, in winter 1986-87, we conducted 4 monthly aerial photographic surveys to investigate temporal changes in distribution, size, and sex ratios of canvasback flocks in traditional wintering areas of Chesapeake Bay and coastal North Carolina. Surveys yielded 35mm imagery of 194,664 canvasbacks in 842 flocks. Models revealed monthly patterns of flock size in North Carolina and Virginia, but no pattern of change in Maryland. A stepwise analysis of flock size and sex ratio fit a common positive slope (increasing proportion male) for all state-month datasets, except for North Carolina in February where the slope was larger ( P < 0.001). State and month effects on intercepts were significant ( P < 0.001) and confirmed a previously identified latitudinal gradient in sex ratio in the survey region. There was no relationship between flock purity (% canvasbacks vs. other species) and flock size except in North Carolina in January, February, and March when flock purity was related to flock size. Contrasting characteristics in North Carolina with regard to flock size (larger flocks) and flock purity suggested that proximate factors were reinforcing flocking behavior and possibly species fidelity there. Of possible factors, the need to locate foraging sites within this large, open-water environment was hypothesized to be of primary importance. Comparison of January 1981 and 1987 sex ratios indicated no change in Maryland, but lower ( P < 0.05) canvasback sex ratios (proportion male) in Virginia and North Carolina.

Maryland, North Carolina, Virginia↗
USGS1993

Resource protection for waterbirds in Chesapeake Bay

Many living resources in the Chesapeake Bay estuary have deteriorated over the past 50 years. As a result, many governmental committees, task forces, and management plans have been established. Most of the recommendations for implementing a bay cleanup focus on reducing sediments and nutrient flow into the watershed. We emphasize that habitat requirements other than water quality are necessary for the recovery of much of the bay's avian wildlife, and we use a waterbird example as illustration. Some of these needs are: (1) protection of fast-eroding islands, or creation of new ones by dredge deposition to improve nesting habitat for American black ducks(Anas rubripes), great blue herons(Ardea herodias), and other associated wading birds; (2) conservation of remaining brackish marshes, especially near riparian areas, for feeding black ducks, wading birds, and wood ducks(Aix sponsa); (3) establishment of sanctuaries in open-water, littoral zones to protect feeding and/or roosting areas for diving ducks such as canvasbacks(Aythya valisineria) and redheads(Aythya americana), and for bald eagles(Haliaeetus leucocephalus); and (4) limitation of disturbance by boaters around nesting islands and open-water feeding areas. Land (or water) protection measures for waterbirds need to include units at several different spatial scales, ranging from ?points? (e.g., a colony site) to large-area resources (e.g., a marsh or tributary for feeding). Planning to conserve large areas of both land and water can be achieved following a biosphere reserve model. Existing interagency committees in the Chesapeake Bay Program could be more effective in developing such a model for wildlife and fisheries resources.

Chesapeake Bay↗
USGS1993

Survival of hatching-year female canvasbacks wintering on Chesapeake Bay

Low annual survival of hatching-year (HY) females is a critical management concern for canvasbacks ( Aythya valisineria ), and may contribute substantially to reduced reproductive potential and the male-biased sex ratio of the species. To evaluate the contribution of mortality on a traditional wintering area to low annual survival, we estimated survival rates of HY female canvasbacks during 3 winters (1987-89) on Chesapeake Bay. We implanted radio transmitters in 204 HY and 44 after-hatching-year (AHY; 1989 only) female canvasbacks and tracked them from mid-December to early March. Ten-week survival rates did not differ ( P > 0.05) among years for HY females; estimates ranged from 0.833 to 0.930 and averaged 0.887. Of 17 mortalities recorded for HY females during the 3-year study, 14 of 15 dated deaths occurred during the duck hunting season (first 3 weeks of the study), even though the hunting season on canvasbacks was closed. As a result, survival rates were lower during hunting versus posthunting periods ( P ≤ 0.05 for 2 of 3 yr). Illegal hunting was the single largest source of mortality for HY females. Shot ducks accounted for a loss of 4% and suspected crippling losses (ducks scavenged by shoreline predators) may have increased hunting-associated losses to as high as 7%. In 1989, no deaths were observed for AHY females, and their survival was higher (P = 0.02) than HY females. High winter survival for HY females indicates that substantial mortality occurs at some other time of the annual cycle.

Maryland↗
USGS1992

Distribution and effects of shallow gas on bulk estuarine sediment properties

Gas bubble are present in sediments covering approximately 30% of the main stem of Chesapeake Bay, with bubbles occurring at the sediment-water interface in 18% of the main stem sediments. This biogenic gas is found either in the sediments in the lower salinity reaches of the Bay, or confined to sediments which overline infilled palaeodrainage channels formed during the Wisconsinan low sea level stand (approximately 18 ka). Gas associated with the old drainage network does not correlate with present bathymetry or sedimentological patterns. Some differences between the gas-charged and gas-free sediments are: (1) gas-charged sediments have water contents 10-20% higher than comparable gas-free cores; (2) organic matter is better presented with depth in the gas-charged sediments (upwards of 60% more at one depth); (3 monosulphides are dominant sulphide mineral phase within the gas-charged sediments, comprising over 40% of the total sulphur. Within the gas-free sediments monosulphides are significant only near the sediment-water interface and rapidly become negligible with depth, and; (4) cores of gas-charged sediments are highly colour-banded due to preservation of sulphide mineral variations, while gas-free cores are diagenetically altered to pyrite.

Maryland↗
USGS1992

Implanting radio transmitters in wintering canvasbacks

To conduct telemetry studies of wintering canvasbacks ( Aythya valisineria ) on Chesapeake Bay [Maryland, USA], we needed to devise a suitable method of radio transmitter attachment. We describe as aseptic, intraabdominal surgical technique, using the inhalation anesthetic isoflurane, to implant 20-g radio transmitters in free-ranging canvasbacks. We evaluated the technique over 3 winters (1987-89), when an annual average of 83 female canvasbacks received implant surgery during a 9-day period in mid-December. Of 253 ducks, 248 (98%) were implanted successfully, and 200 (80.65) completed the 70-day study until early March. No mortality or abnormal behavior from surgery was identified post-release.

Maryland, Virginia↗