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At least 73 records · Page 4Linked to original sources
USGS2010

Long-term reductions in anthropogenic nutrients link to improvements in Chesapeake Bay habitat

Great effort continues to focus on ecosystem restoration and reduction of nutrient inputs thought to be responsible, in part, for declines in estuary habitats worldwide. The ability of environmental policy to address restoration is limited, in part, by uncertainty in the relationships between costly restoration and benefits. Here, we present results from an 18-y field investigation (1990-2007) of submerged aquatic vegetation (SAV) community dynamics and water quality in the Potomac River, a major tributary of the Chesapeake Bay. River and anthropogenic discharges lower water clarity by introducing nutrients that stimulate phytoplankton and epiphyte growth as well as suspended sediments. Efforts to restore the Chesapeake Bay are often viewed as failing. Overall nutrient reduction and SAV restoration goals have not been met. In the Potomac River, however, reduced in situ nutrients, wastewater-treatment effluent nitrogen, and total suspended solids were significantly correlated to increased SAV abundance and diversity. Species composition and relative abundance also correlated with nutrient and water-quality conditions, indicating declining fitness of exotic species relative to native species during restoration. Our results suggest that environmental policies that reduce anthropogenic nutrient inputs do result in improved habitat quality, with increased diversity and native species abundances. The results also help elucidate why SAV cover has improved only in some areas of the Chesapeake Bay.

Chesapeake Bay↗
USGS2001

Reconstructing the rise of recent coastal anoxia; molybdenum in Chesapeake Bay sediments

Sporadic, direct observations over a 50 yr period inadequately characterize the history of seasonal hypoxia and anoxia in Chesapeake Bay, alarge estuary threatened by eutrophication. Here, we undertake a reconstruction of 20th century oxygen depletion in this estuary using Mo concentrations in 210Pb-dated sediments; Cu concentrations are used to control for anthropogenic influences. Cores from the central channel display mild Mo enrichments above crustal backgrounds (up to 5 ??g/g) and strong Cu enrichments (up to 35 ??g/g). Temporally, Cu enrichment (mostly anthropogenic) began earlier and stabilized in the last two thirds of the 20th century. In contrast, Mo enrichment has grown during the last two thirds of the century. Molybdenum enrichment is mostly hydrogenic, except in a section of the channel that receives additional Mo from erosion of Early Miocene shore deposits. Two geochemical mechanisms promote Mo enrichment: Manganese refluxing concentrates dissolved MoO24- at the sediment-water interface and sulfide substitution into MoO24- produces thiomolybdates, which can be fixed by particles. The Mo enrichment mechanisms operate primarily during periods when bottom waters are anoxic and thiomolybdate formation can occur near the sediment-water interface. This implies a temporal coupling between water-column anoxia and Mo fixation even though fixation occurs only within sediments. The Mo enrichment profiles suggest that Chesapeake Bay has experienced growing O2 depletion since the first half of the 20th century, but especially after 1960. Copyright ?? 2001 Elsevier Science Ltd.

Geochimica et Cosmochimica Acta↗
USGS2011

Continuous resistivity profiling data from the Corsica River Estuary, Maryland

Submarine groundwater discharge (SGD) into Maryland's Corsica River Estuary was investigated as part of a larger study to determine its importance in nutrient delivery to the Chesapeake Bay. The Corsica River Estuary represents a coastal lowland setting typical of much of the eastern bay. An interdisciplinary U.S. Geological Survey (USGS) science team conducted field operations in the lower estuary in April and May 2007. Resource managers are concerned about nutrients that are entering the estuary via SGD that may be contributing to eutrophication, harmful algal blooms, and fish kills. Techniques employed in the study included continuous resistivity profiling (CRP), piezometer sampling of submarine groundwater, and collection of a time series of radon tracer activity in surface water. A CRP system measures electrical resistivity of saturated subestuarine sediments to distinguish those bearing fresh water (high resistivity) from those with saline or brackish pore water (low resistivity). This report describes the collection and processing of CRP data and summarizes the results. Based on a grid of 67.6 kilometers of CRP data, low-salinity (high-resistivity) groundwater extended approximately 50-400 meters offshore from estuary shorelines at depths of 5 to >12 meters below the sediment surface, likely beneath a confining unit. A band of low-resistivity sediment detected along the axis of the estuary indicated the presence of a filled paleochannel containing brackish groundwater. The meandering paleochannel likely incised through the confining unit during periods of lower sea level, allowing the low-salinity groundwater plumes originating from land to mix with brackish subestuarine groundwater along the channel margins and to discharge. A better understanding of the spatial variability and geological controls of submarine groundwater flow beneath the Corsica River Estuary could lead to improved models and mitigation strategies for nutrient over-enrichment in the estuary and in other similar settings.

Maryl↗
USGS2026

Advancing monitoring approaches to enhance tidal Chesapeake Bay habitat assessment for submerged aquatic vegetation, water clarity, chlorophyll a and dissolved oxygen

Water quality monitoring capacity has been declining for the Chesapeake Bay Program (CBP) at a time when information needs are growing, and data gaps exist to address critical decision-support for managers. The CBP Scientific Technical Assessment and Reporting Team is leading a Principal’s Staff Committee requested gap analyses toward understanding support needed to improve water quality monitoring and analysis programming. Advanced technologies and alternative monitoring approaches in the form of satellite-based measurements, Artificial Intelligence/Machine Learning (AI/ML) algorithms for data interpretation, continuous water quality in-situ sensor arrays, and community science efforts offer a growing portfolio of valuable opportunities for expanding data collections and analysis program capacities. However, since 1985, each of these options are examples of growing opportunities to enhance water quality assessments yet has seen limited adoption into elements of Chesapeake Bay water quality monitoring programs. Where new technologies have been adopted (e.g., shallow water continuous water quality monitoring), such temporally rich data streams have supported Bay health insights yet had limited use in regulatory water quality criteria assessment. This Scientific Technical Advisory Committee (STAC) supported workshop provided the ideal forum for engaging our CBP partnership regarding the maturity of new and evolving monitoring and analysis capacities to address program information needs while appreciating limitations with adopting new tools and approaches. Improving natural resources monitoring efficiency and effectiveness will expand the scientific and technical foundations for making robust, strategic choices on decisions for CBP Partnership community-based priorities, policies, and management actions. Workshop findings and recommendations reflect progress in science, technology, and analyses addressing long-standing programmatic limitations in data collection and analysis capacities. State-of-the-science updates highlighted in the workshop span the spectrum of efforts representing improvements, successes, remaining challenges toward operationalizing protocols, and guidance toward research, or adoption and implementation by monitoring programs.

Maryland, Pennsylvania, Virginia↗
USGS2003

U.S. Geological Survey Greater Everglades Science Program: 2002 Biennial Report

Introduction The U.S. Geological Survey (USGS) conducts scientific investigations in south Florida to improve society’s understanding of the environment and assist in the sustainable use, protection, and restoration of the Everglades and other ecosystems within the region. The investigations summarized in this document have been carried out under the Greater Everglades Science Program (previously known as the South Florida Ecosystem Program), which is part of the USGS Place-Based Studies initiative. The USGS Placed-Based Studies initiative is a nationwide program that concentrates on areas with severe environmental problems. Through interdisciplinary investigations the Program provides sound scientific information on which to base informed resource management decisions. Individuals from all the USGS programs (hydrology, geology, biology, mapping) work together with other scientists to cover the diverse scientific disciplines involved in this complex and challenging task. The Greater Everglades Science Program began in 1995 as one of the initial Place-Based Studies programs and serves as a model for similar future collaborative studies. Placed-Based Studies are also being conducted in the San Francisco Bay area, Chesapeake Bay, the Platte River, Greater Yellowstone, Salton Sea, and the Mojave Desert. The South Florida Ecosystem Program is part of a coordinated federal effort, under the South Florida Ecosystem Restoration Task Force. The Task Force was started in 1993, through interagency agreement, to coordinate the efforts of the agencies within six federal departments. In 1996, statutory authority formalized the Task Force and expanded it to include tribal, state, and local governments. The Task Force conducts its activities through the South Florida Ecosystem Working Group and teams, such as the Science Coordination Team. A Science Plan and Integrated Financial Plans are established to focus efforts and prevent duplicative efforts by the agencies.

Open-File Report↗
USGS1997

Forum on Geologic mapping applications in the Washington-Baltimore urban area; proceedings; Reston, Virginia, April 23, 1997

The Forum on Geologic mapping applications in the Washington-Baltimore urban area was convened on April 23, 1997, at Reston, Virginia. The forum was cosponsored by the U.S. Geological Survey and the Maryland Geological Survey, with assistance from the Virginia Division of Mineral Resources. Spatial earth science information in the Washington-Baltimore area provides a scientific framework for environmental assessment, urban planning, and future resource and hazard investigations in this area of the Chesapeake Bay watershed, which has sustained three centuries of urban growth.

Circular↗
USGS2016

Combining citizen science species distribution models and stable isotopes reveals migratory connectivity in the secretive Virginia rail

Stable hydrogen isotope (δD) methods for tracking animal movement are widely used yet often produce low resolution assignments. Incorporating prior knowledge of abundance, distribution or movement patterns can ameliorate this limitation, but data are lacking for most species. We demonstrate how observations reported by citizen scientists can be used to develop robust estimates of species distributions and to constrain δD assignments. We developed a Bayesian framework to refine isotopic estimates of migrant animal origins conditional on species distribution models constructed from citizen scientist observations. To illustrate this approach, we analysed the migratory connectivity of the Virginia rail Rallus limicola , a secretive and declining migratory game bird in North America. Citizen science observations enabled both estimation of sampling bias and construction of bias-corrected species distribution models. Conditioning δD assignments on these species distribution models yielded comparably high-resolution assignments. Most Virginia rails wintering across five Gulf Coast sites spent the previous summer near the Great Lakes, although a considerable minority originated from the Chesapeake Bay watershed or Prairie Pothole region of North Dakota. Conversely, the majority of migrating Virginia rails from a site in the Great Lakes most likely spent the previous winter on the Gulf Coast between Texas and Louisiana. Synthesis and applications . In this analysis, Virginia rail migratory connectivity does not fully correspond to the administrative flyways used to manage migratory birds. This example demonstrates that with the increasing availability of citizen science data to create species distribution models, our framework can produce high-resolution estimates of migratory connectivity for many animals, including cryptic species. Empirical evidence of links between seasonal habitats will help enable effective habitat management, hunting quotas and population monitoring and also highlight critical knowledge gaps.

Journal of Applied Ecology↗
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↗
USGS2019

(U-Th)/He zircon dating of Chesapeake Bay distal impact ejecta from ODP site 1073

Single crystal (U‐Th)/He dating has been undertaken on 21 detrital zircon grains extracted from a core sample from Ocean Drilling Project (ODP) site 1073, which is located ~390 km northeast of the center of the Chesapeake Bay impact structure. Optical and electron imaging in combination with energy dispersive X‐ray microanalysis (EDS) of zircon grains from this late Eocene sediment shows clear evidence of shock metamorphism in some zircon grains, which suggests that these shocked zircon crystals are distal ejecta from the formation of the ~40 km diameter Chesapeake Bay impact structure. (U‐Th/He) dates for zircon crystals from this sediment range from 33.49 ± 0.94 to 305.1 ± 8.6 Ma (2σ), implying crystal‐to‐crystal variability in the degree of impact‐related resetting of (U‐Th)/He systematics and a range of different possible sources. The two youngest zircon grains yield an inverse‐variance weighted mean (U‐Th)/He age of 33.99 ± 0.71 Ma (2σ uncertainties n = 2; mean square weighted deviation = 2.6; probability [ P ] = 11%), which is interpreted to be the (U‐Th)/He age of formation of the Chesapeake Bay impact structure. This age is in agreement with K/Ar, 40 Ar/ 39 Ar, and fission track dates for tektites from the North American strewn field, which have been interpreted as associated with the Chesapeake Bay impact event.

Chesapeake Bay↗
USGS2004

Geology of the National Capital Region: Field trip guidebook

The 2004 Joint Northeast-Southeast Section Meeting of the Geological Society of America is the fourth such meeting and the third to be held in or near Washington, D.C. This guidebook and the field trips presented herein are intended to provide meeting participants, as well as other interested readers, a means to understand and enjoy the rich geological and historical legacy of the National Capital Region. The field trips cover all of the major physiographic and geologic provinces of the central Appalachians in the Mid-Atlantic region. Trip 1 outlines the tectonic history of northern Virginia along an east-to-west transect from the Coastal Plain province to the Blue Ridge province, whereas the other field trips each focus on a specific province. From west to east, these excursions investigate the paleoclimate controls on the stratigraphy of the Paleozoic rocks of the Allegheny Plateau and Valley and Ridge province in West Virginia, Pennsylvania, and Maryland (Trip 3); Eocene volcanic rocks that intrude Paleozoic rocks in the westernmost Valley and Ridge province in Virginia and West Virginia (Trip 4); age, petrology, and structure of Mesoproterozoic gneisses and granitoids located in the Blue Ridge province within and near Shenandoah National Park, Virginia (Trip 2); the use of argon data to unravel the complex structural and thermal history of the metamorphic rocks of the eastern Piedmont province in Maryland and Virginia (Trip 5); the use of cosmogenic isotopes to understand the timing of bedrock incision and formation of terraces along the Potomac River in the eastern Piedmont province near Great Falls, Virginia and Maryland (Trip 6); the nature of the boundary between rocks of the Goochland and Chopawamsic terranes in the eastern Piedmont of Virginia (Trip 7); the role of bluffs and fluvial terraces of the Coastal Plain in the Civil War Battle of Fredericksburg, Virginia (Trip 8); and the Tertiary lithology and paleontology of Coastal Plain strata around the Chesapeake Bay of Virginia and Maryland (Trip 9). Some of the field trips present new geochronological research that uses isotopic techniques to unravel Earth history and processes, including U-Pb dating to determine the timing of metamorphism and igneous activity associated with the Mesoproterozoic Grenville orogeny (Trip 2); argon (4DAr/39Ar) analysis to understand the complex Paleozoic history of deformation and metamorphism in the Piedmont (Trip 5); and cosmogenic beryllium-10 data to derive exposure ages of landforms and deposits of the Potomac River valley (Trip 6). Several trips shed insight on significant or enigmatic geologic features of the region. Trip 3 presents evidence for global paleoclimate controls on the Paleozoic stratigraphy of the Appalachian basin, including evidence for Late Devonian glacial deposits. Trip 4 investigates unusual Eocene igneous rocks in the Eastern United States, and Trip 2 visits several local ductile high-strain zones, offering geologists opportunities to consider the importance of such structures relative to the poorly understood Rockfish Valley fault zone in the Blue Ridge province. In the Piedmont province, Trip 7 focuses on a controversial terrane boundary, whereas Trip 5 crosses several lithologic belts with distinct thermotectonic histories that suggest terrane boundaries. Trip 6 sheds new light on the erosional history of a major river gorge cut into crystalline rocks in the Fall Zone. Four trips are recommended for Earth science teachers and are cosponsored by the National Association of Geologic Teachers (NAGT). These trips focus on the tectonic history of northern Virginia (Trip 1), terraces of the Potomac River at Great Falls and cosmogenic isotope analysis to date the terraces and the incision history (Trip 6), and Tertiary lithology and paleontology of the Chesapeake Bay region (Trip 9). Trip 8 takes advantage of the rich Civil War history of this region to look at the role that geology played in the strategies and outcome of the Battle of Fredericksburg. This guidebook is the result of much hard work by many individuals. The editors wish to thank the field trip leaders and authors, the technical reviewers, and Nancy Stamm of ths USGS Geologic Names Committee. We also owe a very special thanks to Linda Gundersen, Chief Scientist, Geologic Discipline, USGS, who provided funding for the guidebook.

Maryland, Virginia, Washington DC↗
USGS2021

Environmental and anthropogenic drivers of contaminants in agricultural watersheds with implications for land management

If not managed properly, modern agricultural practices can alter surface and groundwater quality and drinking water resources resulting in potential negative effects on aquatic and terrestrial ecosystems. Exposure to agriculturally derived contaminant mixtures has the potential to alter habitat quality and negatively affect fish and other aquatic organisms. Implementation of conservation practices focused on improving water quality continues to increase particularly in agricultural landscapes throughout the United States. The goal of this study was to determine the consequences of land management actions on the primary drivers of contaminant mixtures in five agricultural watersheds in the Chesapeake Bay, the largest watershed of the Atlantic Seaboard in North America where fish health issues have been documented for two decades. Surface water was collected and analyzed for 301 organic contaminants to determine the benefits of implemented best management practices (BMPs) designed to reduce nutrients and sediment to streams in also reducing contaminants in surface waters. Of the contaminants measured, herbicides (atrazine, metolachlor), phytoestrogens (formononetin, genistein, equol), cholesterol and total estrogenicity (indicator of estrogenic response) were detected frequently enough to statistically compare to seasonal flow effects, landscape variables and BMP intensity. Contaminant concentrations were often positively correlated with seasonal stream flow, although the magnitude of this effect varied by contaminant across seasons and sites. Land-use and other less utilized landscape variables including biosolids, manure and pesticide application and percent phytoestrogen producing crops were inversely related with site-average contaminant concentrations. Increased BMP intensity was negatively related to contaminant concentrations indicating potential co-benefits of BMPs for contaminant reduction in the studied watersheds. The information gained from this study will help prioritize ecologically relevant contaminant mixtures for monitoring and contributes to understanding the benefits of BMPs on improving surface water quality to better manage living resources in agricultural landscapes inside and outside the Chesapeake Bay watershed.

Delaware, Maryland, New Jersey, New York, Pennsylv↗
USGS2016

Science to support aquatic animal health

Healthy aquatic ecosystems are home to a diversity of plants, invertebrates, fish and wildlife. Aquatic animal populations face unprecedented threats to their health and survival from climate change, water shortages, habitat alteration, invasive species and environmental contaminants. These environmental stressors can directly impact the prevalence and severity of disease in aquatic populations. For example, periodic fish kills in the upper Chesapeake Bay Watershed are associated with many different opportunistic pathogens that proliferate in stressed fish populations. An estimated 80 percent of endangered juvenile Puget Sound steelhead trout die within two weeks of entering the marine environment, and a role for disease in these losses is being investigated. The introduction of viral hemorrhagic septicemia virus (VHSV) into the Great Lakes—a fishery worth an estimated 7 billion dollars annually—resulted in widespread fish die-offs and virus detections in 28 different fish species. Millions of dying sea stars along the west coast of North America have led to investigations into sea star wasting disease. U.S. Geological Survey (USGS) scientists are assisting managers with these issues through ecological investigations of aquatic animal diseases, field surveillance, and research to promote the development of mitigation strategies.

Fact Sheet↗
USGS2019

Long-term annual aerial surveys of submersed aquatic vegetation (SAV) support science, management, and restoration

Aerial surveys of coastal habitats can uniquely inform the science and management of shallow, coastal zones, and when repeated annually, they reveal changes that are otherwise difficult to assess from ground-based surveys. This paper reviews the utility of a long-term (1984-present) annual aerial monitoring program for submersed aquatic vegetation (SAV) in Chesapeake Bay, its tidal tributaries, and nearby Atlantic coastal bays, USA. We present a series of applications that highlight the program’s importance in assessing anthropogenic impacts, gauging water quality status and trends, establishing and evaluating restoration goals, and understanding the impact of commercial fishing practices on benthic habitats. These examples demonstrate how periodically quantifying coverage of this important foundational habitat answers basic research questions locally as well as globally, and provides essential information to resource managers. New technologies are enabling more frequent and accurate aerial surveys at greater spatial resolution and lower cost. These advances will support efforts to extend the applications described here to similar issues in other areas

Chesapeake Bay↗
USGS2022

Comparing Landsat Dynamic Surface Water Extent to alternative methods of measuring inundation in developing waterbird habitats

This study investigates the applicability of the Landsat Dynamic Surface Water Extent (DSWE) science product for waterbird habitat modeling in multiple non-canopied habitat types. We compare surface water distribution estimates derived from DSWE to two site-specific survey methods: visual surveys and digitized aerial imagery. These site-specific surveys were conducted on Poplar Island, a restoration island project in the Chesapeake Bay, USA. Visual surveys were collected bimonthly from 2006 – 2013, and digitized aerial imagery was collected annually from 2006 – 2015. As a restoration island, Poplar Island presents a unique opportunity to analyze DSWE in a rapidly changing site. We structure our analysis based on the procedural development of individual sub-island cells developed from unconsolidated dredge material into fully restored wetlands that have independent hydrologic connection to the surrounding bay. Each development status is analyzed using our three DSWE classifications: Open Water (OW), a conservative estimate; Wetland Inclusive (WI), an aggressive estimate; and Development Dependent (DD), a landcover adaptive estimate. The OW classification consistently underestimates surface water coverage especially in the more complex, fully developed cells. The WI classification is better able to capture the tidal channels in these cells, but marginally overestimates surface water coverage in more sparsely vegetated cells. The DD classification does not significantly improve upon the estimations of the WI classification. Our data indicate that DSWE can be a capable alternative to our site-specific survey methods. However, the product is limited by Landsat’s 30 m spatial resolution, especially in more structurally complex wetlands. A recommended classification method for characterizing waterbird habitats would depend on the goals and targeted scale of analysis, for which DSWE may be a viable option.

Maryland↗
USGS2024

Evaluation and review of best management practices for the reduction of polychlorinated biphenyls to the Chesapeake Bay

Polychlorinated biphenyls (PCBs) continue to impact the environment due to historic and ongoing anthropogenic sources (for example, industrial and agricultural), despite their ban. Contaminated stormwater has been identified as a vector for PCB transport to many estuaries impaired by PCBs. Management of these regulated discharges is typically achieved by best management practices (BMPs). This review focuses on PCB reduction practices and BMPs to assist management decision making and provide information on the current state of the science. Studies have quantitatively demonstrated the efficacy of green infrastructure BMPs and gray infrastructure improvements to reduce PCB loads, and other studies have demonstrated qualitative reductions for other BMP types. This review also highlights the disconnect between PCB load reduction and PCB bioavailability when selecting a remediation strategy. Additionally, the review evaluates modeling approaches to assess PCB load reduction to inform management decisions and suggests why there are still significant barriers to implementation.

Chesapeake Bay watershed↗
USGS2021

Groundwater discharges as a source of phytoestrogens and other agriculturally derived contaminants to streams

Groundwater discharge zones in streams are important habitats for aquatic organisms. The use of discharge zones for thermal refuge and spawning by fish and other biota renders them susceptible to potential focused discharge of groundwater contamination. Currently, there is a paucity of information about discharge zones as a potential exposure pathway of chemicals to stream ecosystems. Using thermal mapping technologies to locate groundwater discharges, shallow groundwater and surface water from three rivers in the Chesapeake Bay Watershed, USA were analyzed for phytoestrogens, pesticides and their degradates, steroid hormones, sterols and bisphenol A. A Bayesian censored regression model was used to compare groundwater and surface water chemical concentrations. The most frequently detected chemicals in both ground and surface water were the phytoestrogens genistein (79%) and formononetin (55%), the herbicides metolachlor (50%) and atrazine (74%), and the sterol cholesterol (88%). There was evidence suggesting groundwater discharge zones could be a unique exposure pathway of chemicals to surface water systems, in our case, metolachlor sulfonic acid (posterior mean concentration = 150 ng/L in groundwater and 4.6 ng/L in surface water). Our study also demonstrated heterogeneity of chemical concentration in groundwater discharge zones within a stream for the phytoestrogen formononetin, the herbicides metolachlor and atrazine, and cholesterol. Results support the hypothesis that discharge zones are an important source of exposure of phytoestrogens and herbicides to aquatic organisms. To manage critical resources within the Chesapeake Bay Watershed, more work is needed to characterize exposure in discharge zones more broadly across time and space.

Delaware, Maryland, New Jersey, New York, Pennsylv↗
USGS2003

Pesticides, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls in transport in two Atlantic coastal plain tributaries and loadings to Chesapeake Bay

Concentrations of current-use pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine (OC) insecticides were determined above the reach of tide in the Chesterville Branch and Nanticoke River on the eastern shore of Chesapeake Bay during base-flow and storm-flow hydrologic regimes to evaluate mass transport to Chesapeake Bay. The two rivers monitored showed relatively high concentrations of atrazine, simazine, alachlor, and metolachlor in comparison to previously investigated western shore tributaries, and reflected the predominant agricultural land use in the eastern shore watersheds. The four current use pesticides showed the greatest seasonal contribution to annual loadings to tidal waters of Chesapeake Bay from the two rivers, and the relative order of annual loadings for the other contaminant classes was PAHs > PCBs > OC insecticides. Annual loadings normalized to the landscape areas of selected Chesapeake Bay watersheds showed correlations to identifiable source areas, with the highest pesticide yields (g/km2/yr) occurring in eastern shore agricultural landscapes, and the highest PAH yields derived from urban regions.

Journal of Environmental Science and Health - Part↗