Geology Reports⌕ Search

Geology topics

Research about Maryland, Virginia

Source-linked reports with geographic coverage including Maryland, Virginia.

At least 91 records · Page 5Linked to original sources
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↗
USGS1995

Geology of the Waterford quadrangle, Virginia and Maryland, and the Virginia part of the Point of Rocks quadrangle

The bedrock geology of the Waterford quadrangle and of the Virginia part of the Point of Rocks quadrangle consists of a portion of the Middle Proterozoic basement core and its cover sequence on the eastern limb of the Blue Ridge anticlinorium and the adjacent early Mesozoic Culpeper basin. The three major rock associations in this area are: 1) Middle Proterozoic gneisses intruded by late Proterozoic metadiabase dikes, 2) unconformably overlying late Proterozoic and early Paleozoic metavolcanic and metasedimentary rocks, and 3) Upper Triassic sedimentary strata intruded by early Jurassic diabase. The Triassic and Jurassic rocks are separated from the older rocks by a major normal fault, the Bull Run fault. Late Cenozoic surficial deposits of three major types unconformably overlie the bedrock: colluvium derived from Catoctin Mountain, terrace deposits of the Potomac River, and flood plain alluvium of the Potomac River and its tributaries. -from Authors

Maryland, Virginia↗
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↗
USGS1991

Historical changes in laying date, clutch size, and nest success of American black ducks

The breeding population of American black ducks ( Anas rubripes ) on Chesapeake Bay has declined over the past 30 years. We tested whether there have been changes in laying date, clutch size, and nest success of breeding black ducks on islands in Chesapeake Bay between the 1950's and 1980's. None of these variables differed significantly between decades, suggesting that other factors must be responsible for the decline in locally breeding black ducks.

Maryland, Virginia↗
USGS1989

Nitrogen cycling between sediment and the shallow-water column in the transition zone of the Potomac River and Estuary. II. The role of wind-driven resuspension and adsorbed ammonium

During periods of sediment resuspension, desorption of ammonium from sediment solids can be the major pathway for enriching the water column with the ammonium that is produced by bacterial degradation of organic matter in the bottom material. This hyopthesis is based on a three-year study of diffusive flux in the transition zone of the Potomac River at a site 35 m from the Virginia shore where the average water-column depth is approximately 1 m over sandy sediment. A diffusion-controlled sampler was used to collect water samples at the interface between the water column and sediment and at several tens of centimeters into the sediment. Interstitial water concentration gradients showed that diffusive flux of ammonium from the sandy shallow-water sediments was approximately 1% of the diffusive flux of ammonium from the silty channel sediments in the same zone of the Potomac River. Organic nitrogen and bound or adsorbed ammonium were the predominant nitrogen forms in the sediment. Adsorbed ammonium concentrations ranged from nondetectable to 3·7 μmol g −1 of sediment. Concentrations of adsorbed ammonium per gram of sediment were one to three orders of magnitude more than interstitial water ammonium concentrations. Desorption of ammonium from sediment solids appeared to be the controlling factor in the degree of water-column ammonium enrichment. In laboratory experiments that simulated sediment resuspension, 40–80% of the adsorbed ammonium predicted to desorb did so after approximately 30 min of mixing. Based on calculations for 1 m 2 to a depth of 4 cm, one resuspenion event lasting minutes could mix more ammonium into the water column from desorption of ammonium from sediment solids than could be delivered to the water column by diffusive flux from shallow-water sediments in 10–1000 days and would be comparable to enrichment by ammonium diffusive flux for 5–50 days from channel sediments in the same river zone.

Maryland, Virginia↗
USGS1988

Nitrogen cycling between sediment and the shallow-water column in the transition zone of the Potomac River and estuary. I. Nitrate and ammonium fluxes

A three-year study of seasonal variation in water-column and sediment nitrogen species was conducted in the transition zone of the Potomac River 35 m from the Virginia shore at a site with an average water-column depth of approximately 1 m over sandy sediment. A diffusion-controlled sampler was used to collect water samples from the water column, at the interface between the water column and sediment, and at several tens of centimeters into the sediment. Nitrate was the predominant dissolved nitrogen species in the water column. The importance of denitrification was inferred by nitrate fluxes which were directed into the sediment from the water column during approximately 75% of the sampling periods and ranged from 0·02 to 0·69 mmol m −2 day −1 . Flux of nitrate from the sediment into the water column, ⩾0·1 mmol m −2 day −1 , due possibly to nitrification in surficial sediment, occurred during one spring and two summer sampling periods. Ammonium fluxes were less than 0·1 mmol m −2 day −1 during 90% of the sampling periods. Of the ammonium fluxes that were >0·05 mmol m −2 day −1 , all were fluxes into the sediment during sampling periods when sediment resuspension occurred, and all were into the water column during periods of calm. The mean value of ammonium flux (0·005 ± 0·05 mmol m −2 day −1 ) from the sandy, shallow-water sediments was two orders of magnitude less than the ammonium fluxes from the deeper, silty channel sediments in the same reach of the river. Diffusive flux calculations suggest that approximately one order of magnitude more nitrate than ammonium is cycled between the shallow-water column and the sandy sediment in the transition zone of the Potomac River.

Maryland, Virginia↗
USGS1988

Food habits and distribution of wintering canvasbacks, Aythya valisineria, on Chesapeake Bay

Baltic clams ( Macoma balthica ) were the predominant food items of 323 canvasbacks ( Aythya valisineria ) collected throughout Chesapeake Bay during 1970–1979. Natural vegetation constituted 4% of the food volume. Widgeongrass ( Ruppia maritima ) and redhead grass ( Potamogeton perfoliatus ) constituted the greatest percent volume and frequency of occurrence among the plant species, whereas wild celery ( Vallisneria americana ) constituted only a trace of the food volume. These results contrast with historical records of food habits of canvasbacks in Chesapeake Bay. Canvasback population estimates during the 1970’s were examined to detect annual and seasonal changes in distribution. Linear regression analyses of winter canvasback populations in the bay showed a significant decline in the upper-bay and middle-bay populations, but no significant changes in the lower-bay and Potomac River populations. The changes in winter distribution and abundance of the canvasback appear related to changes in natural food availability, which is the result of altered environmental conditions.

Maryland, Virginia↗
USGS1987

In situ striped bass (Morone saxatilis) contaminant and water quality studies in the Potomac River

The objectives of this study were to evaluate survival of striped bass ( Morone saxatilis ) prolarvae and yearlings in the Potomac River by using in situ test chambers; correlate survival of both striped bass life stages with the presence of water quality conditions, inorganic contaminants, and organic contaminants and conduct histological examinations of surviving yearling striped bass. Survival of striped bass prolarvae ranged from 4.5–22.5% at three field locations during three 96-h experiments; control survival was ≥81%. Yearling survival ranged from 0–77.5% at three river stations during two 7-d experiments; highest mortality occurred at the upriver station. Control survival was 100%. Poor survival of striped bass prolarvae was likely related to the presence of inorganic contaminants (monomeric aluminum, cadmium, and copper) acting singly or synergistically and sudden decreases in water temperature (< 11°C). Yearling mortality at the upriver station was likely correlated with high pH conditions from a point source discharge and perhaps inorganic contaminants. Histological examinations of yearlings suggested that test organisms exposed to Potomac River water exhibited adverse changes in the kidney.

Maryland, Virginia↗
USGS1987

The distribution of nitrogen species and adsorption of ammonium in sediments from the tidal Potomac River and estuary

The distribution of dissolved ammonium, adsorbed ammonium and residual, organic and total nitrogen was measured in Potomac River tidal, transition zone and lower estuary sediments to a depth of 66 cm. For these sediments, exchangeable ammonium, and thereby adsorbed ammonium concentrations, were determined directly using an ammonia electrode in alkaline sediment suspensions. Ammonia electrode data were comparable to data obtained by KCl extraction of fresh sediment. The conventional unitless ammonium adsorption coefficient, calculated as the slope of the regression line drawn when sediment-adsorbed ammonium (μmol g −1 dry wt of sediment) is plotted against interstitial water ammonium (μmol g −1 dry wt sediment), is 1·5 for this system. When a modified ammonium adsorption coefficient is calculated from sediment-adsorbed ammonium concentrations and a ratio of interstitial water ammonium and potassium concentrations, the regression equation through the data has a zero intercept and is more nearly linear than the regression equation of data based on conventional calculations. The use of a ratio including ammonium and potassium concentrations in the interstitial water term takes into account ionic strength variations in the estuary and competition between ammonium and potassium for adsorption sites.

Maryland, Virginia↗