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At least 865 records · Page 48Linked to original sources
USGS2022

South Carolina and Landsat

South Carolina, the eighth State admitted to the union, transcends its size with its deep, rich history; striking beauty; vast natural resources; and extensive cultural diversity. Home to part of the Blue Ridge Mountains of the Central Appalachians, the Upstate is graced with more than 100 waterfalls, while the Lowcountry borders the Atlantic Ocean with 187 miles of coastline and 35 barrier islands. Forests cover two-thirds of the State, and forestry and agriculture together, as agribusiness, make up South Carolina’s leading industry. Two historic crops—cotton and tobacco—still rank in the top 10 commodities, though corn and soybeans now rank higher. Poultry, cattle, peanuts, and flowers also make the list. South Carolina’s population totals more than five million. Other residents include a variety of wildlife, bird, reptile, and fish species, including Ursus americanus (black bears), Alligator mississippiensis (American alligators), and Tursiops truncatus (bottlenose dolphins). More than 100 tree species also reside in South Carolina, which pays homage to one with its “The Palmetto State” nickname. South Carolina’s subtropical climate, long coastline, and lower elevations make it highly susceptible to tornado and hurricane activity and coastal flooding. Projected sea-level rise is a growing concern. A view from space can help monitor and manage natural resources on the land and in rivers, marshes, and the coast. Landsat reveals not just what an area looks like now, but also insights from decades ago.

South Carolina↗
USGS2010

Simulation of Runoff and Reservoir Inflow for Use in a Flood-Analysis Model for the Delaware River, Pennsylvania, New Jersey, and New York, 2004-2006

A model was developed to simulate inflow to reservoirs and watershed runoff to streams during three high-flow events between September 2004 and June 2006 for the main-stem subbasin of the Delaware River draining to Trenton, N.J. The model software is a modified version of the U.S. Geological Survey (USGS) Precipitation-Runoff Modeling System (PRMS), a modular, physically based, distributed-parameter modeling system developed to evaluate the impacts of various combinations of precipitation, climate, and land use on surface-water runoff and general basin hydrology. The PRMS model simulates time periods associated with main-stem flooding that occurred in September 2004, April 2005, and June 2006 and uses both daily and hourly time steps. Output from the PRMS model was formatted for use as inflows to a separately documented reservoir and riverrouting model, the HEC-ResSim model, developed by the U.S. Army Corps of Engineers Hydrologic Engineering Center to evaluate flooding. The models were integrated through a graphical user interface. The study area is the 6,780 square-mile watershed of the Delaware River in the states of Pennsylvania, New Jersey, and New York that drains to Trenton, N.J. A geospatial database was created for use with a geographic information system to assist model discretization, determine land-surface characterization, and estimate model parameters. The USGS National Elevation Dataset at 100-meter resolution, a Digital Elevation Model (DEM), was used for model discretization into streams and hydrologic response units. In addition, geospatial processing was used to estimate initial model parameters from the DEM and other data layers, including land use. The model discretization represents the study area using 869 hydrologic response units and 452 stream segments. The model climate data for point stations were obtained from multiple sources. These sources included daily data for 22 National Weather Service (NWS) Cooperative Climate Station network stations, hourly data for 15 stations from the National Climatic Data Center, hourly data for 1 station from the NWS Middle Atlantic River Forecast Center records, and daily and hourly data for 7 stations operated by the New York City Department of Environmental Protection. The NWS Multisensor Precipitation Estimate data set for 2001-2007 was used for computing daily precipitation for the model and for computing hourly precipitation for storm simulation periods. Calibration of the PRMS model included regression and optimization algorithms, as well as manual adjustments of model parameters. The general goal of the calibration procedure was to minimize the difference between discharge measured at USGS streamgages and the corresponding discharge simulated by the model. Daily streamflow data from 35 USGS streamgages were used in model calibration. The streamflow data represent areas draining from 20.2 to 6,780 square miles. The PRMS model simulates reservoir inflow and watershed runoff for use as input into HECResSim for the purpose of evaluating and comparing the effects of different watershed conditions on main-stem flooding in the Delaware River watershed draining to Trenton, N.J. The PRMS model is useful as a planning tool to simulate the effects of land-use changes and different antecedent conditions on local runoff and reservoir inflow and, as input to the HEC-ResSim model, on flood flows in the main stem of the Delaware River.

Open-File Report↗
USGS2016

Potential effects of alterations to the hydrologic system on the distribution of salinity in the Biscayne aquifer in Broward County, Florida

To address concerns about the effects of water-resource management practices and rising sea level on saltwater intrusion, the U.S. Geological Survey in cooperation with the Broward County Environmental Planning and Community Resilience Division, initiated a study to examine causes of saltwater intrusion and predict the effects of future alterations to the hydrologic system on salinity distribution in eastern Broward County, Florida. A three-dimensional, variable-density solute-transport model was calibrated to conditions from 1970 to 2012, the period for which data are most complete and reliable, and was used to simulate historical conditions from 1950 to 2012. These types of models are typically difficult to calibrate by matching to observed groundwater salinities because of spatial variability in aquifer properties that are unknown, and natural and anthropogenic processes that are complex and unknown; therefore, the primary goal was to reproduce major trends and locally generalized distributions of salinity in the Biscayne aquifer. The methods used in this study are relatively new, and results will provide transferable techniques for protecting groundwater resources and maximizing groundwater availability in coastal areas. The model was used to (1) evaluate the sensitivity of the salinity distribution in groundwater to sea-level rise and groundwater pumping, and (2) simulate the potential effects of increases in pumping, variable rates of sea-level rise, movement of a salinity control structure, and use of drainage recharge wells on the future distribution of salinity in the aquifer. Results from the simulation of historical conditions indicate that the model generally represents the observed greater westward extent of elevated salinity in the central part of the intruded area relative to the northern and southernmost parts of the intruded area. Results of sensitivity testing indicate that the extent of elevated salinity is most sensitive to pumping in areas where the source of saltwater is largely offshore, from the Atlantic Ocean, and is most sensitive to sea-level rise in areas where the source of salinity is downward leakage of brackish water from canals. Simulations of future scenarios indicate that increases in pumping near the existing interface may cause the interface to advance and decreases in pumping may cause it to retreat. Climatic effects, such as periods of prolonged drought or high precipitation, may augment or counteract long-term effects of changes in pumping on aquifer salinity at well fields. With increasing rates of sea-level rise, the freshwater-saltwater interface advances progressively inland, and flow-averaged salinities at well fields near the existing interface increase commensurately. Hypothetical southeastward (downstream) re-positioning of the existing G–54 salinity-control structure may prevent the interface from moving northwestward along and near the North New River canal, but beneficial effects are localized. Implementation of freshwater recharge wells in the city of Hallandale Beach may also have only a localized freshening effect in the aquifer and little appreciable effect on the freshwater-saltwater interface or on concentrations of salinity at well fields. Model accuracy and use are limited by uncertainty in the physical properties and boundary conditions of the system, uncertainty in historical and future conditions, and generalizations made in the mathematical relationships used to describe the physical processes of groundwater flow and transport. Because of these limitations, model results should be considered in relative rather than absolute terms. Nonetheless, model results do provide useful information on the relative scale of response of the system to changes in pumping distribution, sea-level rise, and mitigation activities.

Florida↗
USGS2011

Cold-climate slope deposits and landscape modifications of the Mid-Atlantic Coastal Plain, Eastern USA

The effects of Pleistocene cold-climate geomorphology are distributed across the weathered and eroded Mid-Atlantic Coastal Plain uplands from the Wisconsinan terminal moraine south to Tidewater Virginia. Cold-climate deposits and landscape modifications are superimposed on antecedent landscapes of old, weathered Neogene upland gravels and Pleistocene marine terraces that had been built during warm periods and sea-level highstands. In New Jersey, sequences of surficial deposits define a long history of repeating climate change events. To the south across the Delmarva Peninsula and southern Maryland, most antecedent topography has been obscured by Late Pleistocene surficial deposits. These are spatially variable and are collectively described as a cold-climate alloformation. The cold-climate alloformation includes time-transgressive details of climate deterioration from at least marine isotope stage (MIS) 4 through the end of MIS 2. Some deposits and landforms within the alloformation may be as young as the Younger Dryas. Southwards along the trend of the Potomac River, these deposits and their climatic affinities become diffused. In Virginia, a continuum of erosion and surficial deposits appears to be the product of ‘normal’ temperate, climate-forced processes. The cold-climate alloformation and more temperate deposits in Virginia are being partly covered by Holocene alluvium and bay mud.

Geological Society Special Publication↗
USGS1978

Accuracy and consistency comparisons of land use and land cover maps made from high-altitude photographs and Landsat multispectral imagery

Accuracy analyses for land use and land cover maps of the 74712-km 2 Central Atlantic Regional Ecological Test Site were performed for a 1-percent sample of the area. Researchers compared Level II land use and land cover maps produced at three scales, 1:24000, 1:100000, and 1:250000 from high-altitude photographs, with point data obtained in the field. The same procedures were employed to determine the accuracy of the Level I land use and land cover produced at 1:250 000 scale from high-altitude photographs and color composite Landsat imagery. The accuracy of the Level II maps was 85 percent at 1:24 000, 77 percent at 1:100 000, and 73 percent at 1:250 000. The accuracy of the Level I 1:250000 maps produced from high-altitude photographs was 77 percent and for those produced from Landsat multispectral imagery was 70 percent. The accuracy of the Level I land use maps produced using Landsat imagery is approximately that of the Level I land use maps produced from high-altitude photography with the exception of urban and built-up land. No built-up land was identified from Landsat imagery in the non-urban areas.

Journal of Research of the U.S. Geological Survey↗
USGS2016

Submarine glacial landforms on the Bay of Fundy–northern Gulf of Maine continental shelf

The Bay of Fundy–northern Gulf of Maine region surrounds the southern part of Nova Scotia, encompassing, from west to east, the Bay of Fundy, Grand Manan Basin, German Bank, Browns Bank, Northeast Channel and northeastern Georges Bank (Fig. 1a, b). During the last glacial maximum ( c. 24–20 14 C ka BP), the SE margin of the Laurentide Ice Sheet (LIS) occupied the study area, the rest of the Gulf of Maine and the continental Scotian Shelf off Atlantic Canada (see Dyke et al. 2002 , fig. 1; Shaw et al. 2006 , fig. 8; Hundert & Piper 2008 , fig. 16). Early mapping of the glaciated region on the Scotian Shelf using side-scan sonar imagery and seismic-reflection profiles revealed topographic features interpreted to be recessional moraines indicative of retreat of the LIS ( King et al. 1972 ; King 1996 ). Subsequently, multibeam sonar seafloor mapping of local-scale glacial landforms on the inner Scotian Shelf off Halifax, Nova Scotia (Fig. 1b) provided further information on the dynamics of the advance and retreat of the ice sheet ( Loncarevic et al. 1994 ). Interpretation of seismic-reflection profiles across Georges Bank revealed that the surficial sediment is a veneer of glacial debris transported to Georges Bank by the LIS during the late Pleistocene from continental areas to the north ( Shepard et al. 1934 ; Knott & Hoskins 1968 ; Schlee 1973 ; Twichell et al. 1987 ; Fader et al. 1988 ). Recent high-resolution multibeam sonar surveys of German Bank and the Bay of Fundy mapped a complex of ice-advance and ice-retreat features attributed to the activity of the LIS ( Todd et al. 2007 ; Todd & Shaw 2012 ).

Geological Society, London, Memoirs↗
USGS1985

Saprolite formation beneath Coastal Plain sediments near Washington, D.C.

Crystalline rocks buried beneath Atlantic Coastal Plain sediments in the Washington, D.C., area commonly have weathering profiles that resemble exposed saprolite of the Piedmont. Cuts along the Washington Metropolitan Area Transit Authority (WMATA) route in northern Virginia show a bedrock weathering profile beneath Cretaceous and younger sediments. Three lines of evidence indicate that this buried weathering profile (saprolite) has formed in the subsurface and is post-Miocene in age: The thickness of the profile, ranging from 2 to 15 m, is thinner beneath clays and thicker beneath sands, apparently a function of the permeability of the overlying material. The buried profile shows no evidence of soil formation at its upper surface and, therefore, no evidence of ever having been sub-aerially exposed. Consolidation tests on the cohesive clayey silts in the samples of the weathering profile indicate mechanical equilibrium with the present overburden, whereas consolidation tests on superjacent Cretaceous clays indicate over-consolidation resulting from a thicker pre-upper Miocene overburden. The post-Miocene age for the subsurface saprolite profile shows that not all saprolite beneath Cretaceous sediment is pre-Cretaceous in age. These observations have important implications for the interpretation of age of the exposed Piedmont saprolite.

Washington, D.C.↗
USGS2020

Molecular indicators of methane metabolisms at cold seeps along the United States Atlantic margin

A lipid biomarker study was undertaken to determine the microbial composition and variability in authigenic carbonates and associated soft bottom habitats from the Norfolk and the Baltimore Canyon seep fields along the US mid-Atlantic margin. Results from this study capture a distinct molecular signal from methane oxidizing archaea, including archaeol (I), sn-2-hydroxyarchaeol, pentamethylicosane (PMI), and crocetane. These consortia of methane-oxidizing Archaea have been identified as carrying out anaerobic oxidation of methane (AOM), thereby favoring the precipitation of methane derived authigneic carbonates. The carbon isotope (δ13C) values of AOM-related lipids were strongly depleted in 13C, (i.e., archaeol: -91.64 ‰, sn-2-hydroxyarchaeol: -129.18 ‰, pentamethylicosane (PMI); -131.36 ‰, and crocetane: -70.94 ‰), confirming the dominance of methane as the dominant carbon source for the Archaea during AOM fractionation. The presence of terminally branched fatty acids such as the antesio- and iso-C15:0 components, diagnostic of sulfate-reducing bacteria (SRB), and their depleted δ13C signature (-107.6 ‰), supports syntrophy of SRB with methane-oxidizing archaea. While lipid biomarker profiles of authigenic carbonates biomarker are similar to those found in the seep sediment, suggesting a similar microbial assemblage within the seep-microbiome, a range in lipid composition, distribution, and isotopic signature between seep sites and matrix type suggests AOM is performed by multiple archaeal sources, instead of a single archaeal species.

Atlantic margin↗
USGS2024

Methane seeps on the U.S. Atlantic margin: An updated inventory and interpretative framework

Since the discovery of >570 methane flares on the northern U.S. Atlantic margin between Cape Hatteras and Georges Bank in the last decade, the acquisition of thousands of kilometers of additional water column imaging data has provided greater coverage at water depths between the outer continental shelf and the lower continental slope. The additional high-resolution data reveal >1400 gas flares, but the removal of probable duplicates from the combined database of new flares and those recognized in 2014 yields ∼1139 unique sites. Most of these sites occur in clusters of 5 or more seeps, leaving about 275 unique locations (including 47 clusters) for seepage along the margin. As a function of depth, seep distribution is heavily skewed toward the upper continental slope at water depths shallower than 400 m on the southern New England margin and ∼ 550 m in the Mid-Atlantic Bight, with additional seeps clustered at ∼1100 m and just deeper than ∼1400 m in both sectors. Despite little ongoing tectonic deformation or active faulting on this passive margin, a variety of processes driven from below the seafloor (e.g., migration of fluids along faults or through permeable strata, seepage above diapirs or other pre-existing structures) and from above (e.g., erosion, sapping, unroofing) contribute to the development of seeps in different settings along the margin. In addition, the prevalence of seeps on promontories overlooking shelf-breaking canyons may be directly related to the three-dimensional nature of the hydrate stability zone in these locations. As a function of depth, the parts of the slope at the contemporary landward limit of gas hydrate stability are devoid of seeps, and the upper slope zones with the most concentrated seepage were not within the gas hydrate stability zone even during the Last Glacial Maximum. Thus, if the large number of upper slope seeps is at least partially sourced in gas hydrate degradation, the gas emitted at these seeps must have migrated there from greater depths on the continental slope.

Marine Geology↗
USGS1981

Tertiary carbonate-dissolution cycles on the Sierra Leone Rise, eastern equatorial Atlantic Ocean

Most of the Tertiary section on Sierra Leone Rise off northwest Africa consists of chalk, marl, and limestone that show cyclic alterations of clay-rich and clay-poor beds about 20–60 cm thick. On the basis of biostratigraphic accumulation rates, the cycles in Oligocene and Miocene chalk have periods which average about 44,000 years, and those in Eocene siliceous limestone have periods of 4000–27,000 years. Several sections were sampled in detail to further define the cycles in terms of content of CaCO 3 , clay minerals, and relative abundances of calcareous nannofossils. Extending information gained by analyses of Pleistocene cores from the continental margin of northwest Africa to the Tertiary cycles on Sierra Leone Rise, both dilution by noncarbonate material and dissolution of CaCO 3 could have contributed to the observed relative variations in clay and CaCO 3 . However, dissolution of CaCO 3 as the main cause of the carbonate-clay cycles on the Sierra Leone Rise, rather than dilution by clay, is suggested by the large amount of change (several thousand percent) in terrigenous influx required to produce the observed variations in amount of clay and by the marked increase in abundance of dissolution-resistant discoasters relative to more easily dissolved coccoliths in low-carbonate parts of cycles. The main cause of dissolution of CaCO 3 was shoaling of the carbonate compensation depth (CCD) during the early Neogene and climatically induced fluctuations in the thickness of Antarctic Bottom Water.

Marine Geology↗
USGS2021

Simulated effects of sea-level rise on the shallow, fresh groundwater system of Assateague Island, Maryland and Virginia

The U.S. Geological Survey, in cooperation with the National Park Service, developed a three-dimensional groundwater-flow model for Assateague Island in eastern Maryland and Virginia to assess the effects of sea-level rise on the groundwater system. Sea-level rise is expected to increase the altitude of the water table in barrier island aquifer systems, possibly leading to adverse effects to ecosystems on the barrier islands. The potential effects of sea-level rise were evaluated by simulating groundwater conditions under sea-level-rise scenarios of 20 centimeters (cm), 40 cm, and 60 cm. Results show that as sea level rises, low-lying areas of the island originally represented as receiving freshwater recharge in the baseline scenario are inundated by saltwater. This change from freshwater recharge to saltwater decreases the overall amount of freshwater recharging the system. As the water table rises in response to the higher sea levels, freshwater flow out of the system changes, with more freshwater leaving as submarine groundwater discharge and less freshwater leaving as seeps and evapotranspiration. At the current land-surface altitude, as much as 50 percent of the island may be inundated with a 60-cm rise in sea level, and the low-lying marshes may change from freshwater to saltwater. Groundwater levels at 32 wells were monitored for as long as 12 months between October 2014 and September 2015 on Assateague Island. Results from objective classification analysis of 14 shallow monitoring wells show two dominant processes affecting groundwater levels in two different settings on the island. On the western side of the island, between the primary dune and the inland bays, water levels clearly respond to precipitation events. This side of the island is more protected from ocean tides and typically is more vegetated than the eastern side. On the eastern side of the island, between the Atlantic Ocean and the primary dune, water levels clearly respond to tidal events. Specific conductance was measured at four wells, two on the western part of the island and two on the eastern part of the island. Specific conductance values in the two wells west of the primary dune show episodic decreases, coinciding with precipitation events. Specific conductance values in the two wells on the eastern side of the primary dune show episodic increases, coinciding with high-tide events. These high frequency monitoring data are intended to aid in designing a monitoring network that can document both short-term and long-term hydrologic processes on Assateague Island National Seashore. This study uses a modeling approach consistent with models developed for Gateway National Recreation Area, Sandy Hook Unit (New Jersey) and Fire Island National Seashore (New York). Combined, these models are meant to improve the regional capabilities for predicting climate-change effects on barrier islands and provide resource managers with a common set of tools for adaptation and mitigation of potentially adverse effects of sea-level rise.

Maryland, Virginia↗
USGS2003

Ground-water flow and saline water in the shallow aquifer system of the southern watersheds of Virginia Beach, Virginia

Population and tourism continues to grow in Virginia Beach, Virginia, but the supply of freshwater is limited. A pipeline from Lake Gaston supplies water for northern Virginia Beach, but ground water is widely used to water lawns in the north, and most southern areas of the city rely solely on ground water. Water from depths greater than 60 meters generally is too saline to drink. Concentrations of chloride, iron, and manganese exceed drinking-water standards in some areas. The U.S. Geological Survey, in cooperation with the city of Virginia Beach, Department of Public Utilities, investigated the shallow aquifer system of the southern watersheds to determine the distribution of fresh ground water, its potential uses, and its susceptibility to contamination. Aquifers and confining units of the southern watersheds were delineated and chloride concentrations in the aquifers and confining units were contoured. A ground-water-flow and solute-transport model of the shallow aquifer system reached steady state with regard to measured chloride concentrations after 31,550 years of freshwater recharge. Model simulations indicate that if freshwater is found in permeable sediments of the Yorktown-Eastover aquifer, such a well field could supply freshwater, possibly for decades, but eventually the water would become more saline. The rate of saline-water intrusion toward the well field would depend on the rate of pumping, aquifer properties, and on the proximity of the well field to saline water sources. The steady-state, ground-water-flow model also was used to simulate drawdowns around two hypothetical well fields and drawdowns around two hypothetical open-pit mines. The chloride concentrations simulated in the model did not approximate the measured concentrations for some wells, indicating sites where local hydrogeologic units or unit properties do not conform to the simple hydrogeology of the model. The Columbia aquifer, the Yorktown confining unit, and the Yorktown-Eastover aquifer compose the hydrogeologic units of the shallow aquifer system of Virginia Beach. The Columbia and Yorktown-Eastover aquifers are poorly confined throughout most of the southern watersheds of Virginia Beach. The freshwater-to-saline-water distribution probably is in a dynamic equilibrium throughout most of the shallow aquifer system. Freshwater flows continually down and away from the center of the higher altitudes to mix with saline water from the tidal rivers, bays, salt marshes, and the Atlantic Ocean. Fresh ground water from the Columbia aquifer also leaks down through the Yorktown confining unit into the upper half of the Yorktown-Eastover aquifer and flows within the Yorktown-Eastover above saline water in the lower half of the aquifer. Ground-water recharge is minimal in much of the southern watersheds because the land surface generally is low and flat.

Water-Resources Investigations Report↗
USGS1981

Rates and possible causes of neotectonic vertical crustal movements of the emerged southeastern United States Atlantic coastal plain

Emerged Pliocene and Pleistocene shorelines and associated marine deposits were used to determine the magnitude and rate of vertical crustal movement during the past 3 m.y. in the United States Atlantic Coastal Plain of South and North Carolina. On the basis of a new regional ostracode assemblage zonation, planktic biostratigraphic data, and radiometric data, emerged marine deposits were determined to be primarily interglacial and can tentatively be correlated with hemispheric warm intervals in evidence from deep-sea data. The paleontologic evidence indicates a primary glacio-eustatic component to the local sea-level record and a secondary tectonic component. Net vertical uplift rates averaging 1 to 3 cm/1,000 yr, but perhaps as high as 5 to 10 cm/1,000 yr, are in evidence for the emerged Coastal Plain. Although details of the timing of regional rheological events remain obscure, the trend of net uplift contrasts with general subsidence rates of about 2 to 4 cm/1,000 yr since the Cretaceous in submerged parts of the continental margin near subsiding sedimentary troughs. Hydro-isostatic crustal response to multiple deglaciation events may have periodically uplifted the coast, but long-term lithospheric flexural upwarping in response to sediment loading offshore is a more plausible mechanism to explain the present positions of shorelines above present mean sea level. A eustatic sea-level model is proposed for interglacial high stands of the past 3.0 m.y.

Geological Society of America Bulletin↗
USGS1974

Preliminary model for extrusion and rifting at the axis of the Mid-Atlantic Ridge, 36°48′ North

The inner rift valley of the Mid-Atlantic Ridge at 36°48′ N. is 1.5 to 3 km wide and 100 to 400 m deep. It is symmetrical in profile with a discontinuous medial ridge 100 to 240 m high and 800 to 1,300 m wide along its axis. The medial ridge is replaced every 1 to 3 km with a central trough 200 to 600 m wide. The medial ridge is apparently built by eruptions of pillow basalt recurring at intervals of roughly 14,000 years at a given point. Between eruptions (and possibly during them), the ridge splits and divides along its axis and subsides, which produces the central trough. As the trough widens and deepens, it eventually taps magma in a shallow reservoir, initiating a new eruption that rebuilds the medial ridge. Outward spreading of the inward-dipping shingled halves of the former medial ridge produces a layer of pillowed basalts about 400 m thick (oceanic layer 2A), in which resides the bulk of the remanant magnetization of the ocean floor. This layer overlies a layer of intrusive rock (layer 2B) composed of a dike complex that feeds eruptions building the medial ridge as well as the outward moving, solidified shells of a shallow magma chamber.

Geology↗
USGS2014

Nitrate fate and transport through current and former depressional wetlands in an agricultural landscape, Choptank Watershed, Maryland, United States

Understanding local groundwater hydrology and geochemistry is critical for evaluating the effectiveness of wetlands at mitigating agricultural impacts on surface waters. The effectiveness of depressional wetlands at mitigating nitrate (NO 3 ) transport from fertilized row crops, through groundwater, to local streams was examined in the watershed of the upper Choptank River, a tributary of Chesapeake Bay on the Atlantic Coastal Plain. Hydrologic, geochemical, and water quality data were collected from January of 2008 through December of 2009 from surface waters and networks of piezometers installed in and around current or former depressional wetlands of three major types along a gradient of anthropogenic alteration: (1) natural wetlands with native vegetation (i.e., forested); (2) prior-converted croplands, which are former wetlands located in cultivated fields; and (3) hydrologically restored wetlands, including one wetland restoration and one shallow water management area. These data were collected to estimate the orientation of groundwater flow paths and likely interactions of groundwater containing NO 3 from agricultural sources with reducing conditions associated with wetlands of different types. Natural wetlands were found to have longer periods of soil saturation and reducing conditions conducive to denitrification compared to the other wetland types studied. Because natural wetlands are typically located in groundwater recharge areas along watershed divides, nitrogen (N) from nearby agriculture was not intercepted. However, these wetlands likely improve water quality in adjacent streams via dilution. Soil and geochemical conditions conducive to denitrification were also present in restored wetlands and prior-converted croplands, and substantial losses of agricultural NO 3 were observed in groundwater flowing through these wetland sediments. However, delivery of NO 3 from agricultural areas through groundwater to these wetlands resulting in opportunities for denitrification were limited, particularly where reducing conditions did not extend throughout the entire thickness of the surficial aquifer allowing NO 3 to pass conservatively beneath a wetland along deeper groundwater flow paths. The complexity of N fate and transport associated with depressional wetlands complicates the understanding of their importance to water quality in adjacent streams. Although depressional wetlands often contribute low NO 3 water to local streams, their effectiveness as landscape sinks, for N from adjacent agriculture varies with natural conditions, such as the thickness of the aquifer and the extent of reducing conditions. Measurement of such natural geologic, hydrologic, and geochemical conditions are therefore fundamental to understanding N mitigation in individual wetlands.

Maryl↗
USGS2000

Functional groups and elemental analyses of cuticular morphotypes of Cordaites principalis (Germar) Geinitz, Carboniferous Maritimes Basin, Canada

Well-preserved cuticles were isolated from Cordaites principalis (Germar) Geinitz leaf compressions, i.e., foliage from extinct gymnosperm trees Coniferophyta: Order Cordaitales. The specimens were collected from the Sydney. Stellarton and Bay St. George subbasins of the once extensive Carboniferous Maritimes Basin of Atlantic Canada. Fourier transformation of infrared spectra (FTIR) and elemental analyses indicate that the ca. 300-306-million-year-old fossil cuticles share many of the functional groups observed in modern cuticles. The similarities of the functional groups in each of the three cuticular morphotypes studied support the inclusion into a single cordaite-leaf taxon, i.e., C. principalis (Germar), confirming previous morphological investigations. Vitrinite reflectance measurements on coal seams in close proximity to the fossil-bearing sediments reveal that the Bay St. George sample site has the lowest thermal maturity, whereas the sites in Sydney and Stellarton are more mature. IR absorption and elemental analyses of the cordaite compressions corroborate this trend, which suggests that the coalified mesophyll in the leaves follows a maturation path similar to that of vitrinite. Comparison of functional groups of the cordaite cuticles with those from certain pteridosperms previously studied from the Sydney Subbasin shows that in the cordaite cuticles highly conjugated C-O (1632 cm-1) bands dominate over carbonyl stretch that characterizes the pteridosperm cuticles. The differences demonstrate the potential of chemotaxonomy as a valuable tool to assist distinguishing between Carboniferous plant-fossil groups. Published by Elsevier Science B.V.

International Journal of Coal Geology↗
USGS2013

Nutrient and sediment concentrations, yields, and loads in impaired streams and rivers in the Taunton River Basin, Massachusetts, 1997-2008

Rapid development, population growth, and the changes in land and water use accompanying development are placing increasing stress on water resources in the Taunton River Basin. An assessment by the Massachusetts Department of Environmental Protection determined that a number of tributary streams to the Taunton River are impaired for a variety of beneficial uses because of nutrient enrichment. Most of the impaired reaches are in the Matfield River drainage area in the vicinity of the City of Brockton. In addition to impairments of stream reaches in the basin, discharge of nutrient-rich water from the Taunton River contributes to eutrophication of Mount Hope and Narragansett Bays. To assess water quality and loading in the impaired tributary stream reaches in the basin, the U.S. Geological Survey, in cooperation with the Massachusetts Department of Environmental Protection compiled existing water-quality data from previous studies for the period 1997-2006, developed and calibrated a Hydrological Simulation Program-FORTRAN (HSPF) precipitation-runoff model to simulate streamflow in areas of the basin that contain the impaired reaches for the same time period, and collected additional streamflow and water-quality data from sites on the Matfield and Taunton Rivers in 2008. A majority of the waterquality samples used in the study were collected between 1999 and 2006. Overall, the concentration, yield, and load data presented in this report represent water-quality conditions in the basin for the period 1997-2008. Water-quality data from 52 unique sites were used in the study. Most of the samples from previous studies were collected between June and September under dry weather conditions. Simulated or measured daily mean streamflow and water-quality data were used to estimate constituent yields and loads in the impaired tributary stream reaches and the main stem of the Taunton River and to develop yield-duration plots for reaches with sufficient water-quality data. Total phosphorus concentrations in the impaired-reach areas ranged from 0.0046 to 0.91 milligrams per liter (mg/L) in individual samples (number of samples (n)=331), with a median of 0.090 mg/L; total nitrogen concentrations ranged from 0.34 to 14 mg/L in individual samples (n=139), with a median of 1.35 mg/L; and total suspended solids concentrations ranged from 2/d) for total phosphorus and 100 lb/mi 2 /d for total nitrogen in these reaches. In most of the impaired reaches not affected by the Brockton Advanced Water Reclamation Facility outfall, yields were lower than in reaches downstream from the outfall, and the difference between measured and threshold yields was fairly uniform over a wide range of flows, suggesting that multiple processes contribute to nonpoint loading in these reaches. The Northeast and Mid-Atlantic SPAtially-Referenced Regression On Watershed (SPARROW) models for total phosphorus and total nitrogen also were used to estimate annual nutrient loads in the impaired tributary stream reaches and main stem of the Taunton River and predict the distribution of these loads among point and diffuse sources in reach drainage areas. SPARROW is a regional, statistical model that relates nutrient loads in streams to upstream sources and land-use characteristics and can be used to make predictions for streams that do not have nutrient-load data. The model predicts mean annual loads based on longterm streamflow and water-quality data and nutrient source conditions for the year 2002. Predicted mean annual nutrient loads from the SPARROW models were consistent with the measured yield and load data from sampling sites in the basin. For conditions in 2002, the Brockton Advanced Water Reclamation Facility outfall accounted for over 75 percent of the total nitrogen load and over 93 percent of the total phosphorus load in the Salisbury Plain and Matfield Rivers downstream from the outfall. Municipal point sources also accounted for most of the load in the main stem of the Taunton River. Multiple municipal wastewater discharges in the basin accounted for about 76 and 46 percent of the delivered loads of total phosphorus and total nitrogen, respectively, to Mount Hope Bay. For similarly sized watersheds, total delivered loads were lower in watersheds without point sources compared to those with point sources, and sources associated with developed land accounted for most of the delivered phosphorus and nitrogen loads to the impaired reaches. The concentration, yield, and load data evaluated in this study may not be representative of current (2012) point-source loading in the basin; in particular, most of the water-quality data used in the study (1999-2006) were collected prior to completion of upgrades to the Brockton Advanced Water Reclamation Facility that reduced total phosphorus and nitrogen concentrations in treated effluent. Effluent concentration data indicate that, for a given flow rate, effluent loads of total phosphorus and total nitrogen declined by about 80 and 30 percent, respectively, between the late 1990s and 2008 in response to plant upgrades. Consequently, current (2012) water-quality conditions in the impaired reaches downstream from the facility likely have improved compared to conditions described in the report.

Massachusetts↗
USGS2017

Rare earth mineral potential in the southeastern U.S. Coastal Plain from integrated geophysical, geochemical, and geological approaches

We combined geophysical, geochemical, mineralogical, and geological data to evaluate the regional presence of rare earth element (REE)−bearing minerals in heavy mineral sand deposits of the southeastern U.S. Coastal Plain. We also analyzed regional differences in these data to determine probable sedimentary provenance. Analyses of heavy mineral separates covering the region show strong correlations between thorium, monazite, and xenotime, suggesting that radiometric equivalent thorium (eTh) can be used as a geophysical proxy for those REE-bearing minerals. Airborne radiometric data collected during the National Uranium Resource Evaluation (NURE) program cover the southeastern United States with line spacing varying from ∼2 to 10 km. These data show eTh highs over Cretaceous and Tertiary Coastal Plain sediments from the Cape Fear arch in North Carolina to eastern Alabama; these highs decrease with distance from the Piedmont. Quaternary sediments along the modern coasts show weaker eTh anomalies, except near coast-parallel ridges from South Carolina to northern Florida. Prominent eTh anomalies are also observed over large riverbeds and their floodplains, even north of the Cape Fear arch where surrounding areas are relatively low. These variations were verified using ground geophysical measurements and sample analyses, indicating that radiometric methods are a useful exploration tool at varying scales. Further analyses of heavy mineral separates showed regional differences, not only in concentrations of monazite, but also of rutile and staurolite, and in magnetic susceptibility. The combined properties suggest the presence of subregions where heavy mineral sediments are primarily sourced from high-grade metamorphic, low-grade metamorphic, or igneous terrains, or where they represent a mixing of these sources. Comparisons between interpreted sources of heavy mineral sands near the Fall Line and igneous and metamorphic Piedmont and Blue Ridge units showed a strong correspondence with rocks closest to the Fall Line and poor correspondence with rocks farther inland. This strongly suggests that the primary source of those heavy minerals, especially monazite, is the rocks that formed the rocky coast that was present during opening of the Atlantic Ocean, which in turn indicates the importance of coastal processes in forming heavy mineral sand concentrations. Furthermore, narrow radiometric eTh and K anomalies are associated with major rivers, indicating limited spatial influence of fluvial processes. Later coastal plain sediment deposition appears to have involved reworking of sediments, providing an “inheritance” of the rocky coast composition that persists for some distance from the Fall Line. However, this inheritance is reduced with distance, and sediments within ∼100 km of the coast in Georgia and Florida exhibit properties indicative of mixing from multiple sources.

GSA Bulletin↗