Northern Chesapeake Bay Research Articles

Seasonal and annual loads of hydrophobic organic contaminants from the Susquehanna River basin to the Chesapeake Bay

Water from the Susquehanna River was collected and analyzed for polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyl (PCB) congeners to estimate seasonal and annual riverine loads to the Chesapeake Bay. Temporal variations in the chemical loads resulted from the large changes in the water flow rates and in the particle-associated contaminant concentrations. Concentrations of PCBs and PAHs in river particles (ng/g) were twice as great as those in the northern Chesapeake Bay, indicating that the Susquehanna River is an important source of these contaminants to the bay. The river carries a majority of its hydrophobic organic contaminants (HOCs) in the particulate phase. During periods of high flow, large amounts of suspended particles in the river result in elevated HOC levels and increased loadings of these contaminants to the bay. From 1997 to 1998, 60% of the total annual HOC loading occurred in the early spring coincident with high river flows. The total PCB and PAH annual loadings from the Susquehanna River to the Chesapeake Bay were 76 and 3160 kg/year, respectively and 75% of the loaded organic contaminants were in the particulate phase. Principal component analysis of PAH and PCB congener patterns in the particles reveals that the river suspended particles were dominated by autochthonous production in the summer and by resuspended sediment and watershed erosion during the winter and early spring.

Predictability of Vibrio cholerae in Chesapeake Bay.

Vibrio cholerae is autochthonous to natural waters and can pose a health risk when it is consumed via untreated water or contaminated shellfish. The correlation between the occurrence of V. cholerae in Chesapeake Bay and environmental factors was investigated over a 3-year period. Water and plankton samples were collected monthly from five shore sampling sites in northern Chesapeake Bay (January 1998 to February 2000) and from research cruise stations on a north-south transect (summers of 1999 and 2000). Enrichment was used to detect culturable V. cholerae, and 21.1% (n = 427) of the samples were positive. As determined by serology tests, the isolates, did not belong to serogroup O1 or O139 associated with cholera epidemics. A direct fluorescent-antibody assay was used to detect V. cholerae O1, and 23.8% (n = 412) of the samples were positive. V. cholerae was more frequently detected during the warmer months and in northern Chesapeake Bay, where the salinity is lower. Statistical models successfully predicted the presence of V. cholerae as a function of water temperature and salinity. Temperatures above 19 degrees C and salinities between 2 and 14 ppt yielded at least a fourfold increase in the number of detectable V. cholerae. The results suggest that salinity variation in Chesapeake Bay or other parameters associated with Susquehanna River inflow contribute to the variability in the occurrence of V. cholerae and that salinity is a useful indicator. Under scenarios of global climate change, increased climate variability, accompanied by higher stream flow rates and warmer temperatures, could favor conditions that increase the occurrence of V. cholerae in Chesapeake Bay.

Seasonal and annual air-water exchange of polychlorinated biphenyls across Baltimore Harbor and the northern Chesapeake Bay.

As part of the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS), air-water exchange fluxes of polychlorinated biphenyls (PCBs) were determined along a transect in the Baltimore Harbor from the Inner Harbor of Baltimore, MD, to the mainstem of the northern Chesapeake Bay to assess the overall contributions of urban source PCBs through air-water exchange and their impacts on coastal waters. Six sites were sampled during three intensive sampling periods in June 1996, February 1997, and July 1997 and at two sites (urban and rural) every ninth day between March 1997 and March 1998 to measure spatial and temporal variability in the PCB air-water exchange fluxes. During the intensive sampling campaigns, net total PCB (t-PCBs) volatilization fluxes ranged between 5 and 2120 ng m(-2) day(-1), varying on both temporal and spatial scales. Volatilization fluxes were highest in February, driven by high winds and elevated dissolved PCB concentrations. Throughout the annual sampling period, t-PCB volatilization fluxes were similar between urban (130 microg m(-2) yr(-1)) and rural (120 microg m(-2) yr(-1)) sites. Approximately 10% of the dissolved t-PCB inventory in the water column in Baltimore Harbor exchanges with the atmosphere each day. From air-water exchange alone, the estimated residence time of dissolved t-PCBs in the harbor is approximately 10 days (estimated hydraulic residence time of water in the harbor is between 7 and 14 days), indicating that air-water exchange is an efficient removal mechanism of t-PCBs from urban coastal waters. Furthermore, the annual flux of t-PCBs volatilizing from Baltimore Harbor is approximately 12% of the gas-phase t-PCB inventory over the water, and at the northern Chesapeake Bay site, the t-PCB flux is approximately 40% of the gas-phase t-PCB inventory. This suggests that air-water exchange of t-PCBs has the potential to be a significant source of PCBs to the rural atmosphere.

Herbicide and insecticide loadings from the Susquehanna River to the northern Chesapeake Bay.

The Susquehanna River watershed has a large drainage area (71200 km(2)) containing heavy agricultural land usage. The river provides approximately half the total freshwater input to the Chesapeake Bay. Water samples were collected at Conowingo Dam near the mouth of the river every 9 days from February 1997 through March 1998. Atrazine, its transformation product 6-amino-2-chloro-4-(isopropylamino)-s-triazine (CIAT), and metolachlor were found in the highest concentrations with maximums of 500, 150, and 330 ng/L, respectively. The annual mass loads for atrazine, CIAT, metolachlor, simazine, and 6-amino-2-chloro-4-(ethylamino)-s-triazine (CEAT) from the Susquehanna River to the Chesapeake Bay were 1600, 1600, 1100, 820, and 720 kg/year, respectively. Annual loadings of insecticides and organochlorine compounds ranged from 2.8 kg/year for alpha-HCH to 34 kg/year for diazinon. Strong correlations between loading data from this and previous studies and total annual water discharge through the dam were used to estimate total metolachlor and atrazine loads (12400 and 9950 kg, respectively) to the northern Chesapeake Bay from 1992 to 1997.

Processes driving the short-term variability of polycyclic aromatic hydrocarbons in the Baltimore and northern Chesapeake Bay atmosphere, USA

Polycyclic aromatic hydrocarbons (PAHs) were measured in the Baltimore and adjacent Chesapeake Bay in July 1997. Time series of 4- and 12-h samples were taken at two sites 15 km apart in order to evaluate the influence of a number of processes on the short-term variability of PAH in the Baltimore and northern Chesapeake Bay atmospheres. PAH concentrations were 2–3-fold higher in the Baltimore atmosphere than in the adjacent Chesapeake Bay atmosphere. For example, gas-phase phenanthrene and pyrene concentrations were 12.5 and 2.14 ng m −3 in the Baltimore site and 5.57 and 0.548 ng m −3 in the Chesapeake Bay, respectively. The influence of wind direction, wind speed and temperature was evaluated by multiple linear regressions which indicated that atmospheric gas-phase PAH concentrations over the Chesapeake Bay were significantly higher when the air mass was from the urban/industrial Baltimore area. Furthermore, the increase of gas-phase low-MW PAH concentrations with temperature and wind speed suggests that volatilization from the bay is an important source of pollutants to the atmosphere, at least when air masses are not influenced by the Baltimore urban and industrial area. Indeed, while on the long-term, the Chesapeake Bay is a receptor of atmospherically deposited PAHs, on the short-term and during appropriate meteorological conditions, the bay acts as a source of pollutants to the atmosphere. Aerosol-phase PAH concentrations and temporal trends showed a strong dependence on aerosol soot content due to the high affinity of PAHs to the graphitic structure of soot. These results confirm the important influence of urban areas as a source of pollution to adjacent aquatic environments and as a driving factor of the short-term variability, either directly by transport of urban-generated pollutants or by volatilization of previously deposited pollutants. Conversely, the complex diurnal trends of gas-phase PAHs at the Baltimore site suggests that degradation processes dominate the diurnal trends of PAHs in urban atmospheres. This conclusion is supported by estimated rate constants for PAH reaction with OH radicals which show good agreement with reported values within a factor of two.

Polychlorinated biphenyls and particulate organic/elemental carbon in the atmosphere of Chesapeake Bay, USA

Polychlorinated biphenyls (PCBs) and particulate organic/elemental carbon (OC/EC) differ as to sources, but are both elevated in major urban areas leading to loadings of proximate terrestrial and aquatic systems. Because of the dramatic difference in speciation, sources, and sinks of these compunds, gas+particulate phase PCBs and particulate OC/EC were measured in urban Baltimore, MD and over Chesapeake Bay at 4 and 12 h frequencies in July 1997. Gas phase ∑PCBs averaged 1180 pg m −3 for Baltimore and 550 pg m −3 for northern Chesapeake Bay. PCB homolog distributions in the gas phase differed between the land and over-water sites whereby the trichlorobiphenyls were higher in Baltimore compared to Chesapeake Bay. Autocorrelation analysis yielded a diurnal cycle for gas phase PCBs at Baltimore with the lowest concentrations observed during the day. Particulate organic and elemental carbon constituted 12.4% (17.4% organic matter) and 2.8% of total suspended particles (TSP) in Baltimore, and 15.0% (21.0% organic matter) and 5.3% over the Chesapeake Bay, respectively. Variability in PCB concentrations was not related to the variability in OC/EC concentrations. OC/EC ratios suggest that particulate organic carbon was mostly primary aerosol. Emissions of both classes of compounds into the Baltimore atmosphere and vicinity are major sources to the Bay.

An index of ecosystem integrity for Northern Chesapeake Bay

We propose a theoretical approach to evaluating the quality of large ecosystems under anthropogenic stress, and present a partial application of these ideas. We synthesized data from a variety of Chesapeake Bay monitoring programs into composite variables expressing ecosystem integrity. The analysis spanned most of the larger Maryland tributaries to the Bay (tidal fresh to mesohaline areas) for nine years (1986–1994). An index modeled on the Index of Biotic Integrity (IBI) and a multivariate ordination and ranking method combined information on aquatic plant, plankton, benthic and fish assemblages with water quality-based habitat goals. The multivariate method proved superior to the IBI approach in discriminating ecosystem integrity. A logistic regression model with watershed land use characteristics and water depth as independent variables explained a significant amount of variation in the multivariate rank index. Urban land use had the most negative effect on the index, whereas forested land had the most positive effect.

Movement of Largemouth Bass in Northern Chesapeake Bay: Relevance to Sportfishing Tournaments

Abstract Largemouth bass Micropterus salmoides have been displaced as far as 50 km from where they were caught in Chesapeake Bay tidewater angling tournaments. Two concerns are whether largemouth bass return to capture areas or whether they stockpile at tournament release sites. To answer these questions, movements of 82 largemouth bass tagged with radio transmitters and 146 largemouth bass tagged with streamer tags were observed during 1991–1995. Fish were collected by boat electrofishing near two disparate tournament weigh-in stations on the eastern and western shores of northern Chesapeake Bay. Some largemouth bass (43 radio-tagged, 58 streamer-tagged) were displaced 15–21 km to the other station; controls (39 radio-tagged, 88 streamer-tagged) were released where they were caught. Movement patterns were similar for displaced largemouth bass: 43% from the Susquehanna River (western shore) and 33% from the Northeast River (eastern shore) exhibited directed movement towards initial capture areas by return...

Seasonal concentrations of organic contaminants at the fall line of the Susquehanna River basin and estimated fluxes to northern Chesapeake Bay, USA

Riverine fluxes of several pesticides and other organic contaminants from above the fall line of the Susquehanna River basin to northern Chesapeake Bay, USA, were quantified in 1994. Base flow and storm flow samples collected at the fall line of the river from February to December 1994 were analyzed for both dissolved and particulate phase contaminants. Measured concentrations of the organonitrogen and organophosphorus pesticides varied mainly in response to the timing of their application to agricultural fields. Conversely, the concentrations of the more particle-sorptive contaminants such as polychlorinated biphenyls (PCBs), organochlorine (OC) insecticides, and polycyclic aromatic hydrocarbons (PAHs) were more directly correlated with river flow throughout the year. Annual fluxes were almost entirely in the dissolved phase for the organonitrogen and organophosphorus pesticides, distributed between the dissolved and particulate phases for the PCBs and OC insecticides, and primarily in the particulate phase for the PAHs.

ANNE ARUNDEL COUNTY, MARYLAND MANAGES SEWER SYSTEM WITH DIGITAL ORTHOPHOTO/GIS/CMMS INTEGRATION

ANNE ARUNDEL COUNTY, MARYLAND MANAGES SEWER SYSTEM WITH DIGITAL ORTHOPHOTO/GIS/CMMS INTEGRATIONAnne Arundel County, Maryland is located in the scenic and historic Northern Chesapeake Bay Area, and provides sanitary sewer service to over 450,000 citizens through the Department of Public Works, Bureau of Utilities. The Department of Public Works also includes the Bureaus of Highways and Parks, Waste Management, Engineering, Finance, and Administration.The County is currently implementing an...Author(s)Robert A. SnodgrassSourceProceedings of the Water Environment FederationSubjectSession 9 – GISDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2000ISSN1938-6478SICI1938-6478(20000101)2000:4L.506;1-DOI10.2175/193864700785140601Volume / Issue2000 / 4Content sourceCollection Systems ConferenceFirst / last page(s)506 - 511Copyright2000Word count270

Influence of Baltimore's Urban Atmosphere on Organic Contaminants over the Northern Chesapeake Bay

ABSTRACT Air and precipitation samples were collected along an urban to over-water to rural transect across the northern Chesapeake Bay as a preliminary investigation into the spatial extent of elevated atmospheric concentrations of urban-derived persistent organic pollutants. Air samples were collected daily from June 3–9, 1996, along the transect as part of the Atmospheric Exchange over Lakes and Oceans project. Total (gas + particle bound) atmospheric polycy-clic aromatic hydrocarbon concentrations [∑-PAH] ranged from 0.4 to 114 ng/m3, and gas phase polychlorinated bi-phenyl concentrations [∑-PCB] ranged from 0.02 to 3.4 ng/m3. Strong concentration gradients were found for both PAHs and PCBs, with the highest concentrations in the city and the lowest at the downwind rural site. Gas and particle bound PAHs varied independently in the city, possibly due to strong but geographically separated emission sources. A precipitation event collected during westerly winds contained fourfold higher ∑-PAH and twelvefold higher ∑-PCB concentrations at the over-water site than at the rural background location, further indicating that the urban plume extends from Baltimore, MD, over the northern Chesapeake Bay over a spatial scale of approximately 30 km.

Diffusive Exchange of Polycyclic Aromatic Hydrocarbons across the Air−Water Interface of the Patapsco River, an Urbanized Subestuary of the Chesapeake Bay

Air−water exchange fluxes of 13 polycyclic aromatic hydrocarbons (PAHs) were determined along a transect in the Patapsco River from the Inner Harbor of Baltimore, MD, to the mainstem of the northern Chesapeake Bay. Sampling took place at six sites during three sampling intensives (June 1996, February 1997, and July 1997) and at one site every ninth day between March 1997 and March 1998 to measure spatial, daily, and annual variability in the fluxes. The direction and magnitude of the daily fluxes of individual PAHs were strongly influenced by the wind speed and direction, by the air temperature, and by the highly variable PAH concentrations in the gas and dissolved phases. Individual fluxes ranged from 14 200 ng m-2 day-1 net volatilization of fluorene during high winds to 11 400 ng m-2 day-1 net absorption of phenanthrene when prevailing winds blowing from the northwest across the city of Baltimore elevated gaseous PAH concentrations over the water. The largest PAH volatilization fluxes occurred adjacent...

Ecological risk assessment of copper and cadmium in surface waters of Chesapeake Bay watershed

AbstractThis ecological risk assessment was designed to characterize risk of copper and cadmium exposure in the Chesapeake Bay watershed by comparing the probability distributions of environmental exposure concentrations with the probability distributions of species response data determined from laboratory studies. The overlap of these distributions was a measure of risk to aquatic life. Dissolved copper and cadmium exposure data were available from six primary data sources covering 102 stations in 18 basins in the Chesapeake Bay watershed from 1985 through 1996. Highest environmental concentrations of copper (based on 90th percentiles) were reported in the Chesapeake and Delaware (C and D) Canal, Choptank River, Middle River, and Potomac River; the lowest concentrations of copper were reported in the lower and middle mainstem Chesapeake Bay and Nanticoke River. Based on the calculation of 90th percentiles, cadmium concentrations were highest in the C and D Canal, Potomac River, Upper Chesapeake Bay, and West Chesapeake watershed. Lowest environmental concentrations of cadmium were reported in the lower and middle mainstem Chesapeake Bay and Susquehanna River. The ecological effects data used for this risk assessment were derived primarily from acute copper and cadmium laboratory toxicity tests conducted in both fresh water and salt water; chronic data were much more limited. The 10th percentile (concentration protecting 90% of the species) for all species derived from the freshwater acute copper toxicity database was 8.3 μg/L. For acute saltwater copper data, the 10th percentile for all species was 6.3 μg/L copper. The acute 10th percentile for all species in the freshwater cadmium database was 5.1 μg/L cadmium. The acute 10th percentile for all saltwater species was 31.7 μg/L cadmium. Highest potential ecological risk from copper exposures was reported in the C and D Canal area of the northern Chesapeake Bay watershed. Relatively high potential ecological risk from copper exposure was also reported in Middle River. Moderate potential ecological risk from copper exposure was reported in selected locations in the Choptank and Potomac Rivers. Potential ecological risk from copper exposure was either low or data were insufficient to assess ecological risk in the other 14 basins. Potential ecological risk from cadmium exposures was much lower than for copper. Highest potential ecological risk from cadmium exposure was reported in the C and D Canal. Low to moderate potential ecological risk for the most sensitive trophic group (fish) was reported in the Potomac River, upper mainstem bay, West Chesapeake watershed, Choptank River, and Chester River. In the other 12 basins, ecological risk was either judged to be low or insufficient data were available for determining risk.

Diffusive Exchange of Gaseous Polycyclic Aromatic Hydrocarbons and Polychlorinated Biphenyls Across the Air−Water Interface of the Chesapeake Bay

Dissolved and gas-phase concentrations of nine polycyclic aromatic hydrocarbons and 46 polychlorinated biphenyl congeners were measured at eight sites on the Chesapeake Bay at four different times of the year to estimate net diffusive air−water gas exchange rates. Gaseous PAHs are absorbed into the bay's surface waters during the spring, and lighter compounds revolatilize in the late summer and early fall due to seasonal changes in surface water temperature and atmospheric PAH levels. On an annual basis, the atmosphere is a net source of volatile PAHs to the Chesapeake Bay, and gas absorption may be the largest external source of fluorene and phenanthrene, providing up to three times the combined loadings from wet and dry aerosol deposition and from tributaries. Largest PAH absorptive fluxes occurred in the northern Chesapeake when prevailing winds carried PAH-enriched air from the Baltimore-Washington urban area over the bay. In contrast to PAHs, PCBs volatilize from the Chesapeake Bay throughout the year, with the largest fluxes occurring in September and the smallest fluxes in June. However, higher chlorinated (6−8) homologues are absorbed by bay waters during most of the year. Highest PCB volatilization rates were observed in the northern Chesapeake Bay and near the James River in the southern bay, indicating volatilization offsets PCB loading from the bay's tributaries. Volatilization is the dominant removal process for PCBs from the Chesapeake Bay, removing an estimated 400 kg/year. This value is larger than current external PCB loadings, suggesting that release of PCBs from historically contaminated sediments supports volatilization from the bay.

ECOLOGICAL RISK ASSESSMENT OF COPPER AND CADMIUM IN SURFACE WATERS OF CHESAPEAKE BAY WATERSHED

This ecological risk assessment was designed to characterize risk of copper and cadmium exposure in the Chesapeake Bay watershed by comparing the probability distributions of environmental exposure concentrations with the probability distributions of species response data determined from laboratory studies. The overlap of these distributions was a measure of risk to aquatic life. Dissolved copper and cadmium exposure data were available from six primary data sources covering 102 stations in 18 basins in the Chesapeake Bay watershed from 1985 through 1996. Highest environmental concentrations of copper (based on 90th percentiles) were reported in the Chesapeake and Delaware (C and D) Canal, Choptank River, Middle River, and Potomac River; the lowest concentrations of copper were reported in the lower and middle mainstem Chesapeake Bay and Nanticoke River. Based on the calculation of 90th percentiles, cadmium concentrations were highest in the C and D Canal, Potomac River, Upper Chesapeake Bay, and West Chesapeake watershed. Lowest environmental concentrations of cadmium were reported in the lower and middle mainstem Chesapeake Bay and Susquehanna River. The ecological effects data used for this risk assessment were derived primarily from acute copper and cadmium laboratory toxicity tests conducted in both fresh water and salt water; chronic data were much more limited. The 10th percentile (concentration protecting 90% of the species) for all species derived from the freshwater acute copper toxicity database was 8.3 μg/L. For acute saltwater copper data, the 10th percentile for all species was 6.3 μg/L copper. The acute 10th percentile for all species in the freshwater cadmium database was 5.1 μg/L cadmium. The acute 10th percentile for all saltwater species was 31.7 μg/L cadmium. Highest potential ecological risk from copper exposures was reported in the C and D Canal area of the northern Chesapeake Bay watershed. Relatively high potential ecological risk from copper exposure was also reported in Middle River. Moderate potential ecological risk from copper exposure was reported in selected locations in the Choptank and Potomac Rivers. Potential ecological risk from copper exposure was either low or data were insufficient to assess ecological risk in the other 14 basins. Potential ecological risk from cadmium exposures was much lower than for copper. Highest potential ecological risk from cadmium exposure was reported in the C and D Canal. Low to moderate potential ecological risk for the most sensitive trophic group (fish) was reported in the Potomac River, upper mainstem bay, West Chesapeake watershed, Choptank River, and Chester River. In the other 12 basins, ecological risk was either judged to be low or insufficient data were available for determining risk.

The impact of impulsive noise on bald eagles at Aberdeen Proving Ground, Maryland.

The U.S. Army Aberdeen Proving Ground supports one of the largest bald eagle concentrations on the Northern Chesapeake Bay (Buehler et al., 1987). The testing of large caliber weapons and detonation of large explosive charges at U.S. Army Aberdeen Proving Ground is creating significant noise and producing concerns on the potential effects on bald eagles. The population using Aberdeen consists of approximately 15 nesting pairs and up to 100 wintering or nonbreeding residents. Systematic observations on potential influence of noise on bald eagles were made from November 1993 through December 1995. We detected no response in a high percentage of nesting and roosting eagles exposed to numerous types of noise at varying levels of intensity.

Perch Trees and Shoreline Development as Predictors of Bald Eagle Distribution on Chesapeake Bay

We studied the influence of shoreline perch trees and human development on bald eagle (Haliaeetus leucocephalus) distribution on the northern Chesapeake Bay. Bald eagle distributions may be determined by available suitable shoreline perch areas. Models based on human development and shoreline habitat variables may alleviate problems associated with classifying bald eagle habitat by identifying characteristics predictive of eagle presence. We observed 2,962 eagles during 36 shoreline surveys and relocated 110 radiomarked eagles 1,350 times during 1985-92. We counted 5,928 suitable (height ≥ 6.1 m, diam at breast height [dbh] ≥ 20.0 cm, and shoreline accessibility ≥ 30°) perch trees in 229, 250- x 50-m segments along shoreline during 1990-91. Shoreline segments used by eagles had more suitable perch trees (x = 30.3 vs. 22.0; P < 0.001) and a larger percentage of forest cover (x = 54.9 vs. 39.4; P < 0.001) than unused segments. Suitable trees on segments with eagle use were closer to water than suitable trees on segments without eagle use (x = 8.4 vs. 17.0 m; P = 0.009). Most segments classified as marsh (66.7%) were unused. Marsh segments had fewer suitable perch trees, less forest cover, and a greater mean distance from water to the nearest suitable perch tree than did other land types (P < 0.001). Developed segments had fewer suitable perch trees, less forest cover, and a shorter distance from water to the nearest suitable perch tree than undeveloped forested segments (P ≤ 0.01). Logistic regression models based on various measures of perch tree abundance and shoreline development correctly predicted eagle use for 65.9-71.0% of segments

Chesapeake bay atmospheric deposition study, year 1: Sources and dry deposition of selected elements in aerosol particles

Abstract Week-long aerosol particulate samples collected over a 57-week period at two shoreline sites along the northern Chesapeake Bay were analysed for up to 44 elements, including l4 elements of interest to Bay water quality (i.e. Al, As, Cr, Fe, Mn, S, Se, V and Zn, by nuclear ; and Cd, Cu, Ni and Pb by atomic spectroscopy techniques) to examine their temporal and spatial variations in Bay air, sources, and estimate dry deposition fluxes to the Bay surface. The concentrations of non-crustal elements V, Se, Cr and Zn were elevated in winter months, whereas elements with substantial crustal residence, AI, Fe and Mn, were elevated during periods in spring and summer. Despite substantial differences in weekly concentrations, annual average concentrations determined for the two sites were quite similar, differing by ⩽ 23% for all elements except Al, 35%. Chemical mass balance calculations made with 11 generic sources suggest that incinerators were important sources of Cr, Cd, Sb and Zn in Bay air; oil combustion, V; regional sulfate, S; local coal combustion, Se; steel, As; and soil, AI, Fe and Mn, with small amounts from wood combustion, regional sulfate, steel and coal combustion. Lead and Cd concentrations were well correlated and peaked in fall, suggesting another important source for these elements. Estimated dry deposition fluxes were comparable to wet fluxes for all elements.

New sedimentation, resuspension, and burial

A model is derived for the probability of burial of a sediment particle as a function of time after initial deposition, in an environment where bottom sediment resuspension exceeds the amount of new sediment deposited in the interval between resuspension episodes. Under steady state conditions, the probability of burial is predicted to exponentially approach 1.0 over time. The characteristic burial time scale Tb is a simple function of the ratio of resuspension to sedimentation N and the time between resuspension episodes Tr. Tb has a secondary dependence on the fraction of Tr during which bottom sediments are in suspension, but this dependence becomes negligible for large N. Allowing for erosion of previously buried sediments under nonsteady state conditions causes the probability of burial to vary about the exponential curve. Moderate departures from steady state do not seriously affect the validity of the results, but large departures from steady state cause large fluctuations in probability of burial and some departure from the exponential trend. Nevertheless, Tb and the exponential burial probability model that it represents should be useful indicators under most conditions. Example calculations of Tb are carried out with resuspension and sedimentation data from northern Chesapeake Bay. These estimates of Tb range between a minimum of 7 d in the midbay channel in summer to a maximum of 30 d in the turbidity maximum channel.

Butyltin and copper monitoring in a Northern Chesapeake Bay marina and river system in 1989: An assessment of tributyltin legislation

This study was designed to: (1) evaluate dibutyltin (DBT) and tributyltin (TBT) bi-weekly in the water column for four months during the peak boating season (June-September, 1989) at seven stations in the Back Creek and Severn River area of Maryland waters of Chesapeake Bay; (2) compare butyltin values from the 1989 study with values obtained from a similar butyltin monitoring study conducted in 1988 (after Maryland TBT legislation) and 1986 (before Maryland TBT legislation); (3) determine the extent of TBT paint use in the Back Creek area by surveying boat owners; (4) determine dissolved copper concentrations from three of the seven stations bi-weekly during the four-month study; and (5) compare dissolved copper concentrations at these stations with previous copper data collected in 1988.Mean four-month DBT concentrations ranged from 10 to 73 ng/L at the seven stations. Highest DBT concentrations occurred at Station 1 in a marina; lowest concentrations occurred at Station 7 in the Severn River. Mean four-month TBT concentrations ranged from 177 ng/L at Station 1 (marina) to 21 ng/L at Station 7 (Severn River). Maximum TBT concentrations of 361 and 570 ng/L occurred at marina SDtations 1 and 3, respectively. Temporal trends in both DBT and TBT (station mean concentrations by date) showed that peak concentrations occurred during the early part of the boating season followed by reductions in late summer and early fall. Spike concentrations of both DBT (117 and 62 ng/L) and TBT (308 and 366 ng/L) were reported on two sampling dates near a boat maintenance facility in Back Creek.There was a significant reduction in DBT concentrations from 1986 to 1989 when date was treated as a fixed effect. However, TBT concentrations were not significantly reduced between 1986 and 1989 when mean concentrations of TBT were averaged across stations and dates for each year. A significant reduction was reported at Station 1 (marina station) when each station was examined for differences between years. TBT was also reported to significantly decrease (p=0.0442) at Station 7 between 1988 and 1989. A boat owner survey in the study area showed that 6% of the recreational boats that were surveyed were painted with TBT paint in 1989. This was a significant decrease in TBT paint use from the previous year when 31% of recreational boat owners surveyed used TBT paints.An evaluation of dissolved copper concentrations at three stations in the study area in 1989 showed that mean concentrations from bi-weekly sampling for four months was 10 μg/L at Station 1, 7.8 μg/L at Station 4 and 2.7 μg/L at Station 7. Copper concentrations decreased with distance away from the Back Creek marinas. Copper concentrations at all three stations were significantly lower in 1989 than in 1988.