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USGS2021

A review of sea lamprey dispersal and population structure in the Great Lakes and the implications for control

Understanding the population structure of invasive sea lamprey ( Petromyzon marinus ) in the Great Lakes basin is essential for an effective control program. We review knowledge of lake connectivity, dispersal during the parasitic stage, and results from phenotypic, demographic, and genetic studies to evaluate how sea lamprey populations are structured. There is no evidence for contemporary movement between Lake Ontario and the Atlantic population, although it appears possible. Dispersal between Lake Ontario and the Finger Lakes is more likely, as is contemporary movement between Lakes Ontario and Erie via the Welland Canal, although neither has been directly observed. Downstream movement from Lake Erie to Lake Ontario via the Niagara River has been reported. Bidirectional movement between Lakes Erie and Huron has been observed, and movement of sea lamprey among the upper Great Lakes (especially between Lakes Huron and Michigan) is relatively common, although complete mixing likely does not occur. The maximum straight-line dispersal distance reported for a tagged sea lamprey was 628 km between the St. Marys River and western Lake Erie. Genetic population studies using a variety of molecular markers generally found weak but significant broad-scale population structure (e.g., between freshwater and anadromous populations, and among Lake Ontario, Lake Erie, and the upper Great Lakes), but finer-scale structure was rarely detected. Nevertheless, some within-basin structure is suggested by regional differences in phenotypic and demographic traits (e.g., sex ratio, body size). Further study will be important because management is most efficiently targeted when the geography of demographically independent populations is well-characterized.

Lake Ontario↗

USGS1996

Recovery of burrowing mayflies (Ephemeroptera: Ephemeridae: Hexagenia ) in western Lake Erie

Burrowing mayflies ( Hexagenia spp.) are native to western Lake Erie and were abundant until the 1950s, when they disappeared due to degraded water and sediment quality. Nymphs were absent from the sediments of most of western Lake Erie after the 1950s, although small, widely disjunct populations apparently persisted near shore. Sediment samples collected in 1993 revealed several small populations near the western and southern shores and beyond the mouths of the Detroit and Maumee rivers. A larger population was found in the southern island area, but nymphs were absent in the middle of the basin. By 1995, nymphs had spread throughout the western half and eastern end of the basin but remained absent from the middle of the basin. These data indicate that Hexagenia began recolonizing nearshore areas before offshore areas. Increasingly large swarms of winged Hexagenia on shore and over the lake between 1992 and 1994 further indicate that mayflies are recolonizing the basin. Factors that have permitted Hexagenia recovery in western Lake Erie probably include improved sediment and water quality attributed to pollution abatement programs implemented after the early 1970s, and perhaps environmental changes in the early 1990s attributed to effects of the exotic zebra mussel ( Dreissena polymorpha ).

Journal of Great Lakes Research↗

USGS2019

Heat flow in the Western Arctic Ocean (Amerasian Basin)

From 1963 to 1973 the U.S. Geological Survey (USGS) measured heat flow at 356 sites in the Amerasian Basin (Western Arctic Ocean) from a drifting ice island (T-3). The resulting measurements, which are unevenly distributed on Alpha-Mendeleev Ridge (AMR) and in Canada and Nautilus basins, greatly expand available heat flow data for the Arctic Ocean. Average T-3 heat flow is ~54.7 ± 11.3 mW m-2, and Nautilus Basin, including Mendeleev Plain, is the only well-surveyed area (~13% of data) with significantly higher average heat flow (63.8 mW m-2). Heat flow and bathymetry are not correlated at a large scale, and turbiditic surficial sediments (Canada and Nautilus basins) have higher heat flow than the sediments that blanket the AMR. Thermal gradients are mostly near-linear, implying that conductive heat transport dominates and that near-seafloor sediments are in thermal equilibrium with overlying bottom waters. Combining the heat flow data with modern seismic imagery suggests that some of the observed heat flow variability may be explained by local changes in sediment thickness or lithology or the presence of basement faults that channel circulating seawater. A thermal model that incorporates thermal conductivity variations along a profile from Canada Basin (thick sediment on mostly oceanic crust) to Alpha Ridge (thin sediment over thick magmatic units associated with the High Arctic Large Igneous Province) predicts heat flow lower than that observed on Alpha Ridge. This, along with other observations, implies that circulating fluids modulate conductive heat flow and contribute to high variability in the T-3 dataset. .

Journal of Geophysical Research B: Solid Earth↗

USGS2003

Support of total maximum daily load programs using spatially referenced regression models

The spatially referenced regressions on watershed attributes modeling approach, as applied to predictions of total nitrogen flux in three North Carolina river basins, addresses several information needs identified by a National Research Council evaluation of the total maximum daily load program. The model provides reach-level predictions of the probability of exceeding water-quality criteria, and estimates of total nitrogen budgets. Model estimates of point- and diffuse-source contributions and nitrogen loss rates in streams and reservoirs compared moderately well with literature estimates. Maps of reach-level predictions of nutrient inputs and delivery provide an intuitive and spatially detailed summary of the origins and fate of nutrients within a basin.

Journal of Water Resources Planning and Management↗

USGS2018

Size and age of Stonecats in Lake Champlain; Estimating growth at the margin of their range to aid in population management

Little is known about populations of Stonecat Noturus flavus , especially in the northeastern United States, where they are at the edge of their range. In Lake Champlain tributaries, Stonecats are listed as endangered in Vermont but not in New York. Here we describe the growth of Stonecats in two tributaries to Lake Champlain, one in Vermont (LaPlatte River), which was our primary interest, and one in New York (Great Chazy River), with von Bertalanffy growth models fit to lengths at the times of marking and recapture and to observed length and age data. We also compared growth of Stonecats in these waters to results from other locations near the middle of their distribution. Stonecats in the Great Chazy River were larger at ages 1–3, but similar in size for ages 4 and 5, than Stonecats from the LaPlatte River. Stonecats in Lake Champlain tributaries were generally larger at age than those from the middle of their range, except for those from Lake Erie. From our mean length‐at‐age results and previous literature estimates of length at maturity for Stonecats, it appears that Stonecats in Lake Champlain reach maturity by age 3, though future research that directly estimates age at maturity would be more informative. These results will help managers assess the effect of various environmental and human stressors that Stonecats have experienced in the Lake Champlain basin in recent years. Furthermore, our results expand the literature, which lacks information about growth of this species. Finally, our mark–recapture approach to estimating growth of Stonecats can be applied to other species, especially where data are limited because of their status, and in other systems.

New York, Vermont↗

USGS2012

Basin and range crustal and upper mantle structure, northwest to central Nevada

We present an interpretation of the crustal and uppermost mantle structure of the Basin and Range of northwestern Nevada based on seismic refraction/wide‐angle reflection, near‐vertical reflection, and gravity data. In comparison to most previous estimates, we find that the crust is somewhat thicker (32–36 km versus 22–30 km), and the uppermost mantle velocity is somewhat higher (8.0 km/s versus 7.3–7.9 km/s). Along our transects, the crust is thinnest (32 km) in the Carson Sink‐Buena Vista Valley region and increases by 2–4 km to the west and east, respectively. There is considerable complexity throughout the crust where velocities range from of 2.5 km/s at the surface to 7.4 km/s in the lowermost crust. Variations in velocity and structure of the upper crustal layers reveal apparent basement velocity depressions (areas of lower velocities extending up to 10 km in depth) that underlie some surface ranges as well as the basins. The middle crust rises from about 20 km beneath central Nevada to within 12 km of the surface beneath the area of thinnest crust and is characterized by a modest (∼0.1 km/s) change in velocity and low‐velocity gradients. These midcrustal layers mark the onset of high crustal reflectivity and the apparent limiting depth to which Basin and Range faults can be traced in near‐vertical reflection profiles, suggesting that these midcrustal layers represent the transition between the brittle and ductile zones of the crust. The lower crust is more structurally complex, with layers thickening and thinning in a systematic manner with the upper crustal layers; generally, where there are velocity depressions in the upper crust, the lower crust is thickest and shallowest. The geometry of these lower crustal layers (derived from refraction modeling) coincides with changes in the crustal reflectivity, determined from the Consortium of Continental Reflection Profiling reflection data. The lower crustal layer is unusually high in velocity (7.4 km/s) and is likely the layer identified as mantle in some previous studies. We do not identify the 7.4 km/s layer as mantle because (1) there is an underlying layer with a velocity (8.0 km/s) that is more consistent with the worldwide average velocity for the upper mantle, and (2) the 7.4 km/s layer does not correspond to the “reflection” Moho. Gravity modeling and comparison to existing seismic models show a general consensus in many aspects with respect to crustal structure. This new model forms the basis for speculation on some of the processes associated with rifting of the Basin and Range Province. One such process, lithospheric magmatism, is inferred from the strong attenuation of transmitted seismic waves, which occurs at the same interface at which high‐amplitude, bright spot reflections originate. Unlike previous models, the overall structure and velocity of the crust and uppermost mantle of our new model are similar to other regions worldwide which have undergone high degrees of extension.

Nevada↗

USGS2016

Fault segmentation: New concepts from the Wasatch Fault Zone, Utah, USA

The question of whether structural segment boundaries along multisegment normal faults such as the Wasatch fault zone (WFZ) act as persistent barriers to rupture is critical to seismic hazard analyses. We synthesized late Holocene paleoseismic data from 20 trench sites along the central WFZ to evaluate earthquake rupture length and fault segmentation. For the youngest (<3 ka) and best-constrained earthquakes, differences in earthquake timing across prominent primary segment boundaries, especially for the most recent earthquakes on the north-central WFZ, are consistent with segment-controlled ruptures. However, broadly constrained earthquake times, dissimilar event times along the segments, the presence of smaller-scale (subsegment) boundaries, and areas of complex faulting permit partial-segment and multisegment (e.g., spillover) ruptures that are shorter (~20–40 km) or longer (~60–100 km) than the primary segment lengths (35–59 km). We report a segmented WFZ model that includes 24 earthquakes since ~7 ka and yields mean estimates of recurrence (1.1–1.3 kyr) and vertical slip rate (1.3–2.0 mm/yr) for the segments. However, additional rupture scenarios that include segment boundary spatial uncertainties, floating earthquakes, and multisegment ruptures are necessary to fully address epistemic uncertainties in rupture length. We compare the central WFZ to paleoseismic and historical surface ruptures in the Basin and Range Province and central Italian Apennines and conclude that displacement profiles have limited value for assessing the persistence of segment boundaries but can aid in interpreting prehistoric spillover ruptures. Our comparison also suggests that the probabilities of shorter and longer ruptures on the WFZ need to be investigated.

Utah↗

USGS1973

Application of the source-area concept of storm runoff to a small Arizona watershed

An attempt to demonstrate the source-area concept of storm runoff by analysis of the rainfall-runoff relation for the watershed of Queen Creek tributary in south-central Arizona was moderately successful. The demonstration was somewhat marred by the necessity to make several simplifying assumptions to eliminate some of the many basin variables of unknown magnitude. The percentage of watershed contributing storm runoff was related to total rainfall received that is, antecedent and storm rainfall on the assumption that the availability of rainfall excess from any subarea was dependent on the saturation, or near saturation, of a permeable upper layer of soil. An average unit hydrograph was used for all computed sizes of the runoff-contributing area.

Arizona↗

USGS1995

Lake trout rehabilitation in Lake Huron

Efforts to restore lake trout ( Salvelinus namaycush ) in Lake Huron after their collapse in the 1940s were underway in the early 1970s with completion of the first round oflampricide applications in tributary streams and the stocking of several genotypes. We assess results of rehabilitation and establish a historical basis for comparison by quantifying the catch of spawning lake trout from Michigan waters in 1929-1932. Sixty-eight percent of this catch occurred in northern waters (MH-1) and most of the rest (15%) was from remote reefs in the middle of the main basin. Sea lampreys ( Petromyzon mari-nus ) increased in the early 1980s in the main basin and depressed spawning populations of lake trout. This increase was especially severe in northern waters and appeared to be associated with untreated populations in the St. Marys River. Excessive commercial fishing stemming from unresolved treaty rights also contributed to loss of spawning fish in northern Michigan waters. Seneca-strain lake trout did not appear to be attacked by sea lampreys until they reached a size > 532 mm. At sizes > 632 mm, Seneca trout were 40-fold more abundant than the Marquette strain in matched-planting experiments. Natural reproduction past the fry stage has occurred in Thunder Bay and South Bay, but prospects for self-sustaining populations of lake trout in the main basin are poor because sea lampreys are too abundant, only one side of the basin is stocked, and stocking is deferred to allow commercial gillnetting in areas where most of the spawning occurred historically. Backcross lake trout, a lake trout x splake ( S. fontinalis x S. namaycush ) hybrid, did not reproduce in Georgian Bay, but this genotype is being replaced with pure-strain lake trout, whose early performance appears promising.

Journal of Great Lakes Research↗

USGS2002

Concordant paleolatitudes for Neoproterozoic ophiolitic rocks of the Trinity Complex, Klamath Mountains, California

New paleomagnetic results from the eastern Klamath Mountains of northern California show that Neoproterozoic rocks of the Trinity ophiolitic complex and overlying Middle Devonian volcanic rocks are latitudinally concordant with cratonal North America. Combining paleomagnetic data with regional geologic and faunal evidence suggests that the Trinity Complex and related terranes of the eastern Klamath plate were linked in some fashion to the North American craton throughout that time, but that distance between them may have varied considerably. A possible model that is consistent with our paleomagnetic results and the geologic evidence is that the Trinity Complex formed and migrated parallel to paleolatitude in the basin between Laurasia and Australia–East Antarctica as the Rodinian supercontinent began to break up. It then continued to move parallel to paleolatitude at least through Middle Devonian time. Although the eastern Klamath plate served as a nucleus against which more western components of the Klamath Mountains province amalgamated, the Klamath superterrane was not accreted to North America until Early Cretaceous time.

California↗

USGS2004

Upper crustal structure of southwestern British Columbia from the 1998 Seismic Hazards Investigation in Puget Sound

This paper applies nonlinear three-dimensional travel time tomography to refraction data recorded during the 1998 Seismic Hazards Investigation in Puget Sound (SHIPS) to derive the first large-scale, high-resolution upper crustal velocity model for southwestern British Columbia. A minimum structure P wave velocity model is constructed using 175,000 first arrival travel times picked from data recorded by 58 temporary onshore stations. The model details forearc crustal structures related to terrane accretion and subsequent basin formation to a depth of about 10 km. The Metchosin igneous complex (correlative with the Eocene Crescent-Siletz Terrane in Washington) is imaged as a laterally extensive WNW trending high-velocity anomaly underlying southernmost Vancouver Island and much of the Strait of Juan du Fuca. Northeast of the Strait of Georgia, the southwesterly dip of the contact between the Wrangellia terrane rocks of Vancouver Island and the Coast Plutonic Complex suggests Wrangellia rocks are down-faulted against the plutonic complex. At the southwestern end of the Strait of Juan de Fuca, the 50 km long WNW trending Clallam basin has a maximum thickness of 5-6 km. Near the eastern end of the Strait of Juan de Fuca, Port Townsend basin has an inferred thickness of approximately 4-5 km. The southern end of the 9 km thick Georgia basin is bounded by a high-velocity basement ridge. Beneath the Strait of Georgia, clusters of well-located earthquakes have a prominent NW trend and coincide spatially with rapid lateral velocity changes. Clusters of microearthquakes there are associated with the intersection of several east trending structural highs within this NW trend. Copyright 2004 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

USGS1996

Gravity field over the Sea of Galilee: Evidence for a composite basin along a transform fault

The Sea of Galilee (Lake Kinneret) is located at the northern portion of the Kinneret-Bet Shean basin, in the northern Dead Sea transform. Three hundred kilometers of continuous marine gravity data were collected in the lake and integrated with land gravity data to a distance of more than 20 km around the lake. Analyses of the gravity data resulted in a free-air anomaly map, a variable density Bouguer anomaly map, and a horizontal first derivative map of the Bouguer anomaly. These maps, together with gravity models of profiles across the lake and the area south of it, were used to infer the geometry of the basins in this region and the main faults of the transform system. The Sea of Galilee can be divided into two units. The southern half is a pull-apart that extends to the Kinarot Valley, south of the lake, whereas the northern half was formed by rotational opening and transverse normal faults. The deepest part of the basinal area is located well south of the deepest bathymetric depression. This implies that the northeastern part of the lake, where the bathymetry is the deepest, is a young feature that is actively subsiding now. The pull-apart basin is almost symmetrical in the southern part of the lake and in the Kinarot Valley south of the lake. This suggests that the basin here is bounded by strike-slip faults on both sides. The eastern boundary fault extends to the northern part of the lake, while the western fault does not cross the northern part. The main factor controlling the structural complexity of this area is the interaction of the Dead Sea transform with a subperpendicular fault system and rotated blocks.

Sea of Galilee↗

USGS1975

Stratigraphy, conodont dating, and paleotectonic interpretation of the type Milligen Formation (Devonian), Wood River area, Idaho

The Milligen Formation at and near its type locality in the Wood River area is considerably older than and unrelated to rocks of Early Mississippian age called Milligen Formation in the Lost River Range and other ranges of east-central Idaho. Conodont faunas were found in limestones of a thin upper member of the sparsely fossiliferous marine Milligen Formation in its principal reference section at Milligen Gulch, at Fisher Canyon, and near Bellevue, Idaho. The faunas include indigenous conodonts here assigned to the early Late Devonian (early Frasnian) Lower and Middle Polygnathus asymmetricus Zones, and reworked conodonts derived from several Middle and Early Devonian conodont zones. An underlying much thicker argillite member of the Milligen contains fewer limestones, but a thin encrinite interbed near the middle of the member yielded early Middle Devonian (Eifelian) conodonts. This lower member probably represents most of Middle and Early Devonian time. Although its base is nowhere exposed in the Wood River area, the Milligen is inferred to have been deposited on the Silurian Trail Creek Formation, which crops out just to the east in the Pioneer Mountains. The age of the Milligen is therefore wholly Devonian and the highest fossiliferous beds are no younger than early Late Devonian. Reworked Middle and Early Devonian conodonts in limestone turbidites of the upper member of the Milligen Formation are identical to conodonts found in shelf (miogeosynclinal) carbonate rocks farther east. A postulated eastern source for the turbidites is supported by new data on the distribution, thickness, and tectonic facies of Devonian rocks that suggest the presence of a Late Devonian ridge on the continental shelf east of the Milligen depositional area. The Milligen Formation was intensely folded and was emergent during most of the Mississippian time when it formed part of the Antler Highlands, which shed flysch sediments eastward into the Copper basin. The Wood River Formation of Pennsylvanian and Permian age was then deposited over a subdued topography on the Milligen Formation. The Hailey Conglomerate Member at the base of the Wood River filled many irregularities in the surface. This depositional contact later was largely destroyed and the contact between the Milligen and Wood River is now a regional thrust fault at most places.

Idaho↗

USGS1977

Analysis of the recharge potential of storm-water basins on Long Island, New York

Many of the more than 2,200 storm-water basins on Long Island, N.Y., are potential sites for infiltration of large volumes of reclaimed water (highly treated domestic and industrial sewage). By use of a finite-difference method of calculation, changes in basin storage during idealized high-intensity storms were determined for the North Massapequa basin, a typical basin on Long Island. Calculations for a 100- year storm, in which a runoff coefficient of 20 percent was used but in which infiltration rate, storm intensity, storm duration, and return period were varied, indicate that this test basin would not overflow even if the infiltration rate declined from its present 1.5 feet per hour (0.46 meter per hour) to about 0.03 ft/h (0.009 m/h). The large reserve capacity of the test basin and similar basins on Long Island demonstrates the feasibility of using storm-water basins for infiltration of a supplemental water supply (supplemental recharge). If reclaimed water were ponded to a depth of 4 ft (1.2 m) in the test basin and if water application were alternated for equal periods between the test basin and a nearby basin with similar characteristics, the volume of infiltration would be slightly more than two million gallons per day (0.09 cubic meters per second) at an infiltration rate of 1.5 ft/h (0.46 m/h). With supplemental recharge, 60 percent of available storage capacity would be used during a 10-yr storm, and 80 percent would be used during a 100-yr storm, using a runoff coefficient of 20 percent.

New York↗

USGS2012

Use of ASTER and MODIS thermal infrared data to quantify heat flow and hydrothermal change at Yellowstone National Park

The overarching aim of this study was to use satellite thermal infrared (TIR) remote sensing to monitor geothermal activity within the Yellowstone geothermal area to meet the missions of both the U.S. Geological Survey and the Yellowstone National Park Geology Program. Specific goals were to: 1) address the challenges of monitoring the surface thermal characteristics of the > 10,000 spatially and temporally dynamic thermal features in the Park (including hot springs, pools, geysers, fumaroles, and mud pots) that are spread out over ~ 5000 km 2 , by using satellite TIR remote sensing tools (e.g., ASTER and MODIS), 2) to estimate the radiant geothermal heat flux (GHF) for Yellowstone's thermal areas, and 3) to identify normal, background thermal changes so that significant, abnormal changes can be recognized, should they ever occur (e.g., changes related to tectonic, hydrothermal, impending volcanic processes, or human activities, such as nearby geothermal development). ASTER TIR data (90-m pixels) were used to estimate the radiant GHF from all of Yellowstone's thermal features and update maps of thermal areas. MODIS TIR data (1-km pixels) were used to record background thermal radiance variations from March 2000 through December 2010 and establish thermal change detection limits. A lower limit for the radiant GHF estimated from ASTER TIR temperature data was established at ~ 2.0 GW, which is ~ 30–45% of the heat flux estimated through geochemical thermometry. Also, about 5 km 2 of thermal areas was added to the geodatabase of mapped thermal areas. A decade-long time-series of MODIS TIR radiance data was dominated by seasonal cycles. A background subtraction technique was used in an attempt to isolate variations due to geothermal changes. Several statistically significant perturbations were noted in the time-series from Norris Geyser Basin, however many of these did not correspond to documented thermal disturbances. This study provides concrete examples of the strengths and limitations of current satellite TIR monitoring of geothermal areas, highlighting some specific areas that can be improved. This work provides a framework for future satellite-based thermal monitoring at Yellowstone and other volcanic and geothermal systems.

Idaho, Montana, Oregon, Wyoming↗

USGS2010

Testing statistical self-similarity in the topology of river networks

Recent work has demonstrated that the topological properties of real river networks deviate significantly from predictions of Shreve's random model. At the same time the property of mean self-similarity postulated by Tokunaga's model is well supported by data. Recently, a new class of network model called random self-similar networks (RSN) that combines self-similarity and randomness has been introduced to replicate important topological features observed in real river networks. We investigate if the hypothesis of statistical self-similarity in the RSN model is supported by data on a set of 30 basins located across the continental United States that encompass a wide range of hydroclimatic variability. We demonstrate that the generators of the RSN model obey a geometric distribution, and self-similarity holds in a statistical sense in 26 of these 30 basins. The parameters describing the distribution of interior and exterior generators are tested to be statistically different and the difference is shown to produce the well-known Hack's law. The inter-basin variability of RSN parameters is found to be statistically significant. We also test generator dependence on two climatic indices, mean annual precipitation and radiative index of dryness. Some indication of climatic influence on the generators is detected, but this influence is not statistically significant with the sample size available. Finally, two key applications of the RSN model to hydrology and geomorphology are briefly discussed.

Journal of Geophysical Research F: Earth Surface↗

USGS2016

Determining the spatial variability of wetland soil bulk density, organic matter, and the conversion factor between organic matter and organic carbon across coastal Louisiana, U.S.A.

Soil bulk density (BD), soil organic matter (SOM) content, and a conversion factor between SOM and soil organic carbon (SOC) are often used in estimating SOC sequestration and storage. Spatial variability in BD, SOM, and the SOM–SOC conversion factor affects the ability to accurately estimate SOC sequestration, storage, and the benefits ( e.g., land building area and vertical accretion) associated with wetland restoration efforts, such as marsh creation and sediment diversions. There are, however, only a few studies that have examined large-scale spatial variability in BD, SOM, and SOM–SOC conversion factors in coastal wetlands. In this study, soil cores, distributed across the entire coastal Louisiana (approximately 14,667 km 2 ) were used to examine the regional-scale spatial variability in BD, SOM, and the SOM–SOC conversion factor. Soil cores for BD and SOM analyses were collected during 2006–09 from 331 spatially well-distributed sites in the Coastwide Reference Monitoring System network. Soil cores for the SOM–SOC conversion factor analysis were collected from 15 sites across coastal Louisiana during 2006–07. Results of a split-plot analysis of variance with incomplete block design indicated that BD and SOM varied significantly at a landscape level, defined by both hydrologic basins and vegetation types. Vertically, BD and SOM varied significantly among different vegetation types. The SOM–SOC conversion factor also varied significantly at the landscape level. This study provides critical information for the assessment of the role of coastal wetlands in large regional carbon budgets and the estimation of carbon credits from coastal restoration.

Louisiana↗

USGS1995

Seafloor environments within the Boston Harbor- Massachusetts Bay sedimentary system: A regional synthesis

Modern seafloor sedimentary environments within the glaciated, topographically complex Boston Harbor and Massachusetts Bay area have been interpreted and mapped from an extensive collection of sidescan sonar records and supplemental marine geologic data. Three categories of environments are present that reflect the dominant long-term processes of erosion or nondeposition, deposition, and sediment reworking. (1) Environments of erosion or nondeposition comprise exposures of bedrock, glacial drift, coarse lag deposits, and possibly coastal plain rocks that contain sediments (where present) ranging from boulder fields to gravelly sands and occur in areas of relatively strong currents. (2) Environments of deposition contain fine-grained sediments ranging from muddy sands to muds that have accumulated in areas of predominantly weak bottom currents. (3) Environments of sediment reworking contain patches with textures ranging from sandy gravels to muds that have been produced by a combination of erosion and deposition in areas with variable bottom currents. The distribution of sedimentary environments across the Boston Harbor-Massachusetts Bay area is extremely patchy. Locally, this patchiness is due either to modifications of bottom-current strength (caused by the irregular topography and differences in water depth) or to small-scale changes in the supply of fine-grained sediments. Regional patchiness, however, reflects differences in geologic and oceanographic conditions among the estuarine, inner shelf, and basinal parts of the sedimentary system. The estuarine part of the system (Boston Harbor) is a depositional trap for fine-grained sediments because it is protected from large waves, has generally weak and variable tidal currents, and receives a large supply of fine grained detritus from natural and anthropogenic sources. The inner shelf, on the other hand, is largely an area of erosion or nondeposition due to sediment removal and redistribution during past sea-level changes, to sediment resuspension and winnowing by modern waves and currents, and to an inadequate supply of fine-grained sediments. The basinal part of the system (Stellwagen Basin) is mainly a tranquil depositional environment in which fine-grained sediments from several potential sources settle through the water column and accumulate under weak bottom currents. This study indicates areas within the Boston Harbor-Massachusetts Bay sedimentary system where fine-grained sediments and associated contaminants are likely to be either moved or deposited. It also provides a guide to the locations and variability of benthic habitats.

Massachusetts Bay↗