In order to test hypotheses about groundwater flow under and into Chesapeake Bay, geophysical surveys were conducted by U.S. Geological Survey (USGS) scientists on Chesapeake Bay and the Potomac River Estuary in September 2006. Chesapeake Bay resource managers are concerned about nutrients that are entering the estuary via submarine groundwater discharge, which are contributing to eutrophication. The USGS has performed many related studies in recent years to provide managers with information necessary to make informed decisions about this issue. The research carried out as part of the study described here was designed to help refine nutrient budgets for Chesapeake Bay by characterizing submarine groundwater flow and discharge of groundwater beneath part of the mainstem and a major tributary, the Potomac River Estuary.

In order to test hypotheses about groundwater flow under and into Chesapeake Bay, geophysical surveys were conducted by U.S. Geological Survey (USGS) scientists on Chesapeake Bay and the Potomac River Estuary in September 2006. Chesapeake Bay resource managers are concerned about nutrients that are entering the estuary via submarine groundwater discharge, which are contributing to eutrophication. The USGS has performed many related studies in recent years to provide managers with information necessary to make informed decisions about this issue. The research carried out as part of the study described here was designed to help refine nutrient budgets for Chesapeake Bay by characterizing submarine groundwater flow and discharge of groundwater beneath part of the mainstem and a major tributary, the Potomac River Estuary.

In order to test hypotheses about groundwater flow under and into Chesapeake Bay, geophysical surveys were conducted by U.S. Geological Survey (USGS) scientists on Chesapeake Bay and the Potomac River Estuary in September 2006. Chesapeake Bay resource managers are concerned about nutrients that are entering the estuary via submarine groundwater discharge, which are contributing to eutrophication. The USGS has performed many related studies in recent years to provide managers with information necessary to make informed decisions about this issue. The research carried out as part of the study described here was designed to help refine nutrient budgets for Chesapeake Bay by characterizing submarine groundwater flow and discharge of groundwater beneath part of the mainstem and a major tributary, the Potomac River Estuary.

In order to test hypotheses about groundwater flow under and into Chesapeake Bay, geophysical surveys were conducted by U.S. Geological Survey (USGS) scientists on Chesapeake Bay and the Potomac River Estuary in September 2006. Chesapeake Bay resource managers are concerned about nutrients that are entering the estuary via submarine groundwater discharge, which are contributing to eutrophication. The USGS has performed many related studies in recent years to provide managers with information necessary to make informed decisions about this issue. The research carried out as part of the study described here was designed to help refine nutrient budgets for Chesapeake Bay by characterizing submarine groundwater flow and discharge of groundwater beneath part of the mainstem and a major tributary, the Potomac River Estuary.

In order to test hypotheses about groundwater flow under and into Chesapeake Bay, geophysical surveys were conducted by U.S. Geological Survey (USGS) scientists on Chesapeake Bay and the Potomac River Estuary in September 2006. Chesapeake Bay resource managers are concerned about nutrients that are entering the estuary via submarine groundwater discharge, which are contributing to eutrophication. The USGS has performed many related studies in recent years to provide managers with information necessary to make informed decisions about this issue. The research carried out as part of the study described here was designed to help refine nutrient budgets for Chesapeake Bay by characterizing submarine groundwater flow and discharge of groundwater beneath part of the mainstem and a major tributary, the Potomac River Estuary.

In order to test hypotheses about groundwater flow under and into Chesapeake Bay, geophysical surveys were conducted by U.S. Geological Survey (USGS) scientists on Chesapeake Bay and the Potomac River Estuary in September 2006. Chesapeake Bay resource managers are concerned about nutrients that are entering the estuary via submarine groundwater discharge, which are contributing to eutrophication. The USGS has performed many related studies in recent years to provide managers with information necessary to make informed decisions about this issue. The research carried out as part of the study described here was designed to help refine nutrient budgets for Chesapeake Bay by characterizing submarine groundwater flow and discharge of groundwater beneath part of the mainstem and a major tributary, the Potomac River Estuary.

A geophysical survey to delineate the fresh-saline groundwater interface and associated sub-bottom sedimentary structures beneath Indian River Bay, Delaware, was carried out in April 2010. This included surveying at higher spatial resolution in the vicinity of a study site at Holts Landing, where intensive onshore and offshore studies were subsequently completed. The total length of continuous resistivity profiling (CRP) survey lines was 145 kilometers (km), with 36 km of chirp seismic lines surveyed around the perimeter of the bay. Medium-resolution CRP surveying was performed using a 50-meter streamer in a bay-wide grid. Results of the surveying and data inversion showed the presence of many buried paleochannels beneath Indian River Bay that generally extended perpendicular from the shoreline in areas of modern tributaries, tidal creeks, and marshes. An especially wide and deep paleochannel system was imaged in the southeastern part of the bay near White Creek. Many paleochannels also had high-resistivity anomalies corresponding to low-salinity groundwater plumes associated with them, likely due to the presence of fine-grained estuarine mud and peats in the channel fills that act as submarine confining units. Where present, these units allow plumes of low-salinity groundwater that was recharged onshore to move beyond the shoreline, creating a complex fresh-saline groundwater interface in the subsurface. The properties of this interface are important considerations in construction of accurate coastal groundwater flow models. These models are required to help predict how nutrient-rich groundwater, recharged in agricultural watersheds such as this one, makes its way into coastal bays and impacts surface water quality and estuarine ecosystems. For more information on the survey conducted for this project, see https://cmgds.marine.usgs.gov/fan_info.php?fan=2010-006-FA.

A geophysical survey to delineate the fresh-saline groundwater interface and associated sub-bottom sedimentary structures beneath Indian River Bay, Delaware, was carried out in April 2010. This included surveying at higher spatial resolution in the vicinity of a study site at Holts Landing, where intensive onshore and offshore studies were subsequently completed. The total length of continuous resistivity profiling (CRP) survey lines was 145 kilometers (km), with 36 km of chirp seismic lines surveyed around the perimeter of the bay. Medium-resolution CRP surveying was performed using a 50-meter streamer in a bay-wide grid. Results of the surveying and data inversion showed the presence of many buried paleochannels beneath Indian River Bay that generally extended perpendicular from the shoreline in areas of modern tributaries, tidal creeks, and marshes. An especially wide and deep paleochannel system was imaged in the southeastern part of the bay near White Creek. Many paleochannels also had high-resistivity anomalies corresponding to low-salinity groundwater plumes associated with them, likely due to the presence of fine-grained estuarine mud and peats in the channel fills that act as submarine confining units. Where present, these units allow plumes of low-salinity groundwater that was recharged onshore to move beyond the shoreline, creating a complex fresh-saline groundwater interface in the subsurface. The properties of this interface are important considerations in construction of accurate coastal groundwater flow models. These models are required to help predict how nutrient-rich groundwater, recharged in agricultural watersheds such as this one, makes its way into coastal bays and impacts surface water quality and estuarine ecosystems. For more information on the survey conducted for this project, see https://cmgds.marine.usgs.gov/fan_info.php?fan=2010-006-FA.

Apalachicola Bay and St. George Sound contain the largest oyster fishery in Florida, and the growth and distribution of the numerous oyster reefs here are the combined product of modern estuarine conditions and the late Holocene evolution of the bay. A suite of geophysical data and cores were collected during a cooperative study by the U.S. Geological Survey, the National Oceanic and Atmospheric Administration Coastal Services Center, and the Apalachicola National Estuarine Research Reserve to refine the geology of the bay floor as well as the bay's Holocene stratigraphy. Sidescan-sonar imagery, bathymetry, high-resolution seismic profiles, and cores show that oyster reefs occupy the crests of sandy shoals that range from 1 to 7 kilometers in length, while most of the remainder of the bay floor is covered by mud. The sandy shoals are the surficial expression of broader sand deposits associated with deltas that advanced southward into the bay between 6,400 and 4,400 years before present. The seismic and core data indicate that the extent of oyster reefs was greatest between 2,400 and 1,200 years before present and has decreased since then due to the continued input of mud to the bay by the Apalachicola River. The association of oyster reefs with the middle to late Holocene sandy delta deposits indicates that the present distribution of oyster beds is controlled in part by the geologic evolution of the estuary. For more information on the surveys involved in this project, see http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2005-001-FA and http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2006-001-FA.

Apalachicola Bay and St. George Sound contain the largest oyster fishery in Florida, and the growth and distribution of the numerous oyster reefs here are the combined product of modern estuarine conditions and the late Holocene evolution of the bay. A suite of geophysical data and cores were collected during a cooperative study by the U.S. Geological Survey, the National Oceanic and Atmospheric Administration Coastal Services Center, and the Apalachicola National Estuarine Research Reserve to refine the geology of the bay floor as well as the bay's Holocene stratigraphy. Sidescan-sonar imagery, bathymetry, high-resolution seismic profiles, and cores show that oyster reefs occupy the crests of sandy shoals that range from 1 to 7 kilometers in length, while most of the remainder of the bay floor is covered by mud. The sandy shoals are the surficial expression of broader sand deposits associated with deltas that advanced southward into the bay between 6,400 and 4,400 years before present. The seismic and core data indicate that the extent of oyster reefs was greatest between 2,400 and 1,200 years before present and has decreased since then due to the continued input of mud to the bay by the Apalachicola River. The association of oyster reefs with the middle to late Holocene sandy delta deposits indicates that the present distribution of oyster beds is controlled in part by the geologic evolution of the estuary. For more information on the surveys involved in this project, see http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2005-001-FA and http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2006-001-FA.