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Michael H. Bothner

Publications and source records attributed to Michael H. Bothner.

At least 37 records · Page 2Linked to original sources
USGS2007

Insights on geochemical cycling of U, Re and Mo from seasonal sampling in Boston Harbor, Massachusetts, USA

This study examined the removal of U, Mo, and Re from seawater by sedimentary processes at a shallow-water site with near-saturation bottom water O 2 levels (240–380 μmol O 2 /L), very high organic matter oxidation rates (annually averaged rate is 880 μmol C/cm 2 /y), and shallow oxygen penetration depths (4 mm or less throughout the year). Under these conditions, U, Mo, and Re were removed rapidly to asymptotic pore water concentrations of 2.2–3.3 nmol/kg (U), 7–13 nmol/kg (Mo), and 11–14 pmol/kg (Re). The depth order in which the three metals were removed, determined by fitting a diffusion-reaction model to measured profiles, was Re < U < Mo. Model fits also suggest that the Mo profiles clearly showed the presence of a near-interface layer in which Mo was added to pore waters by remineralization of a solid phase. The importance of this solid phase source of pore water Mo increased from January to October as the organic matter oxidation rate increased, bottom water O 2 decreased, and the O 2 penetration depth decreased. Experiments with in situ benthic flux chambers generally showed fluxes of U and Mo into the sediments. However, when the overlying water O 2 concentration in the chambers was allowed to drop to very low levels, Mn and Fe were released to the overlying water along with the simultaneous release of Mo and U. These experiments suggest that remineralization of Mn and/or Fe oxides may be a source of Mo and perhaps U to pore waters, and may complicate the accumulation of U and Mo in bioturbated sediments with high organic matter oxidation rates and shallow O 2 penetration depths. Benthic chamber experiments including the nonreactive solute tracer, Br − , indicated that sediment irrigation was very important to solute exchange at the study site. The enhancement of sediment–seawater exchange due to irrigation was determined for the nonreactive tracer (Br − ), TCO 2 , NH 4 + "> NH 4 + , U and Mo. The comparisons between these solutes showed that reactions within and around the burrows were very important for modulating the Mo flux, but less important for U. The effect of these reactions on Mo exchange was highly variable, enhancing Mo (and, to a lesser extent, U) uptake at times of relatively modest irrigation, but inhibiting exchange when irrigation rates were faster. These results reinforce the observation that Mo can be released to and removed from pore waters via sedimentary reactions. The removal rate of U and Mo from seawater by sedimentary reactions was found to agree with the rate of accumulation of authigenic U and Mo in the solid phase. The fluxes of U and Mo determined by in situ benthic flux chamber measurements were the largest that have been measured to date. These results confirm that removal of redox-sensitive metals from continental margin sediments underlying oxic bottom water is important, and suggest that continental margin sediments play a key role in the marine budgets of these metals.

Geochimica et Cosmochimica Acta↗
USGS2007

Sedimentary properties of shallow marine cores collected in June and September 2006, Hanalei Bay, Kaua'i, Hawai'i

Sedimentary facies, short-lived isotopes 7 Be, 137 Cs, and 210 Pb, and magnetic properties of sediment cores in Hanalei Bay, Kaua‘i, Hawai‘i, were used to assess sediment sources and patterns of deposition associated with seasonal flooding of the Hanalei River. Sediment cores were collected from the seafloor in June and September of 2006 to supplement similar data collected during the summer of 2005. The youngest and thickest terrigenous sediment was observed on the east side of the bay: near the Hanalei River mouth and in a bathymetric depression, known locally as the Black Hole, that acts as a temporary sediment sink. Deposits from floods that occurred between February and April 2006 left flood deposits in the eastern bay that, by June of 2006, were on the order of 10 cm thick. A flood occurred on August 7, 2006, that was smaller than floods that occurred the previous winter but was a substantial discharge event for the summer season. Deposits from the winter 2006 floods continued to dominate the sedimentary record in the eastern bay through early fall, even after the addition of newer sediment during the August 7 flood; this is consistent with the much higher sediment input of the winter floods compared with the August 7 flood. Broad variations in magnetic grain size and relative magnetite-hematite abundance in several sediment cores indicate many sources of upland terrigenous sediment. As a group, recent flood deposits show much less variation in these properties compared with older deposits, implying either that the 2006 winter–spring flood sediment originated from one or more distinct upland settings, or that substantial mixing of sediment from multiple sources occurred during transport. Sediment is most readily remobilized and advected out of the bay during winter, when oceanic conditions are energetic. In summer, wave and current measurements made concurrently with this study showed weak currents and little wave energy, indicating that sediment delivered during summer floods most likely remains in the bay until winter storms can remove it. Increased turbidity and sedimentation on corals resulting from floods of the Hanalei River could affect the sustainability of coral reefs and their many associated species. This possibility is of particular concern during summer months when wave energy is low and sediment is not readily remobilized and transported out of the bay. The timing (seasonality) and magnitude of sediment input to the coastal ocean relative to seasonal variations in wave and current energy could have significant ecological consequences for coral-reef communities in the Hawaiian Islands.

Hawai'i↗
USGS2006

Quantity, composition, and source of sediment collected in sediment traps along the fringing coral reef off Molokai, Hawaii

Sediment traps were used to evaluate the frequency, cause, and relative intensity of sediment mobility/resuspension along the fringing coral reef off southern Molokai (February 2000–May 2002). Two storms with high rainfall, floods, and exceptionally high waves resulted in sediment collection rates > 1000 times higher than during non-storm periods, primarily because of sediment resuspension by waves. Based on quantity and composition of trapped sediment, floods recharged the reef flat with land-derived sediment, but had a low potential for burying coral on the fore reef when accompanied by high waves. The trapped sediments have low concentrations of anthropogenic metals. The magnetic properties of trapped sediment may provide information about the sources of land-derived sediment reaching the fore reef. The high trapping rate and low sediment cover indicate that coral surfaces on the fore reef are exposed to transient resuspended sediment, and that the traps do not measure net sediment accumulation on the reef surface.

Hawaii↗
USGS2006

Coastal circulation and sediment dynamics in Hanalei Bay, Kaua'i, Hawaii: Part II: Tracking recent fluvial sedimentation: Isotope stratigraphy obtained in Summer 2005

Delivery and dispersal of fluvial sediment in Hanalei Bay, Kaua’i, Hawaii, have important implications for the health of local coral reefs. The reef community in Hanalei Bay represents a relatively healthy ecosystem. However, the reefs are periodically stressed by storm waves, and increases in sediment and dissolved substances from the Hanalei River have the potential to cause additional stress. Increased turbidity and sedimentation on corals during Hanalei River floods that occur in seasons of low wave energy, when sediment would not be readily remobilized and advected out of the bay, could affect the health and sustainability of coral reefs and the many associated species. Measurements of short-lived isotopes 7 Be and 137 Cs in sediment cores have been used to trace the thickness and distribution of terrestrial sediment in Hanalei Bay, in order to assess spatial and temporal patterns of sediment deposition and remobilization relative to coral-reef locations. A third isotope, 210 Pb, derived primarily from seawater, provides additional information about recent sedimentary history. Isotope profiles and observations of sedimentary facies from cores collected at multiple locations in June 2005, and again in August 2005, indicate the presence of recent fluvial sediment and organic debris in the east part of the bay near the mouth of the Hanalei River. Away from the immediate vicinity of the river mouth, sediment in the uppermost 1 m below the sea floor had not retained a significant quantity of fluvial sediment within the eight months prior to either sampling effort. During the study interval in summer 2005 the Hanalei River had no major floods and there was relatively little sediment input to the bay. Sediment away from the river mouth was dominated by carbonate sand, although some terrestrial sediment was present in sub-sea-floor horizons. Sedimentary facies and isotope inventories throughout the bay showed substantial spatial heterogeneity. Sediment cores will be collected again at the same sites discussed here during early and late summer 2006. If possible, additional sites will be sampled in the Black Hole depocenter near the river mouth. Major floods in winter and spring 2006 are expected to leave a significant new sediment signal in the bay that should be detected in summer 2006.

Hawaii↗
USGS2004

Wave- and tidally-driven flow and sediment flux across a fringing coral reef: Southern Molokai, Hawaii

The fringing coral reef off the south coast of Molokai, Hawaii is currently being studied as part of a US Geological Survey (USGS) multi-disciplinary project that focuses on geologic and oceanographic processes that affect coral reef systems. For this investigation, four instrument packages were deployed across the fringing coral reef during the summer of 2001 to understand the processes governing fine-grained terrestrial sediment suspension on the shallow reef flat (h=1m) and its advection across the reef crest and onto the deeper fore reef. The time-series measurements suggest the following conceptual model of water and fine-grained sediment transport across the reef: Relatively cool, clear water flows up onto the reef flat during flooding tides. At high tide, more deep-water wave energy is able to propagate onto the reef flat and larger Trade wind-driven waves can develop on the reef flat, thereby increasing sediment suspension. Trade wind-driven surface currents and wave breaking at the reef crest cause setup of water on the reef flat, further increasing the water depth and enhancing the development of depth-limited waves and sediment suspension. As the tide ebbs, the water and associated suspended sediment on the reef flat drains off the reef flat and is advected offshore and to the west by Trade wind- and tidally- driven currents. Observations on the fore reef show relatively high turbidity throughout the water column during the ebb tide. It therefore appears that high suspended sediment concentrations on the deeper fore reef, where active coral growth is at a maximum, are dynamically linked to processes on the muddy, shallow reef flat.

Hawaii↗
USGS2004

Bioturbation depths, rates and processes in Massachusetts Bay sediments inferred from modeling of 210Pb and 239 + 240Pu profiles

Profiles of 210 Pb and 239 + <240 Pu from sediment cores collected throughout Massachusetts Bay (water depths of 36-192 m) are interpreted with the aid of a numerical sediment-mixing model to infer bioturbation depths, rates and processes. The nuclide data suggest extensive bioturbation to depths of 25-35 cm. Roughly half the cores have 210 Pb and 239 + 240 Pu profiles that decrease monotonically from the surface and are consistent with biodiffusive mixing. Bioturbation rates are reasonably well constrained by these profiles and vary from ~0.7 to ~40 cm 2 yr -1 . As a result of this extensive reworking, however, sediment ages cannot be accurately determined from these radionuclides and only upper limits on sedimentation rates (of ~0.3 cm yr -1 ) can be inferred. The other half of the radionuclide profiles are characterized by subsurface maxima in each nuclide, which cannot be reproduced by biodiffusive mixing models. A numerical model is used to demonstrate that mixing caused by organisms that feed at the sediment surface and defecate below the surface can cause the subsurface maxima, as suggested by previous work. The deep penetration depths of excess 210 Pb and 239 + 240 Pu suggest either that the organisms release material over a range of >15 cm depth or that biodiffusive mixing mediated by other organisms is occurring at depth. Additional constraints from surficial sediment 234 Th data suggest that in this half of the cores, the vast majority of the present-day flux of recent, nuclide-bearing material to these core sites is transported over a timescale of a month or more to a depth of a few centimeters below the sediment surface. As a consequence of the complex mixing processes, surface sediments include material spanning a range of ages and will not accurately record recent changes in contaminant deposition.

Massachusetts↗
USGS2004

Long-Term Oceanographic Observations in Western Massachusetts Bay Offshore of Boston, Massachusetts: Data Report for 1989-2002

This data report presents long-term oceanographic observations made in western Massachusetts Bay at two locations: (1) 42 deg 22.6' N., 70 deg 47.0' W. (Site A, 33 m water depth) from December 1989 through December 2002 (figure 1), and (2) 42 deg 9.8' N., 70 deg 38.4' W. (Site B, 21 m water depth) from October 1997 through December 2002. Site A is approximately 1 km south of the new ocean outfall that began discharging treated sewage effluent from the Boston metropolitan area into Massachusetts Bay on September 6, 2000. These long-term oceanographic observations have been collected by the U.S. Geological Survey (USGS) in partnership with the Massachusetts Water Resources Authority (MWRA) and with logistical support from the U.S. Coast Guard (USCG - http://www.uscg.mil). This report presents time series data through December 2002, updating a similar report that presented data through December 2000 (Butman and others, 2002). In addition, the Statistics and Mean Flow sections include some new plots and tables and the format of the report has been streamlined by combining yearly figures into single .pdfs. Figure 1 (PDF format) The long-term measurements are planned to continue at least through 2005. The long-term oceanographic observations at Sites A and B are part of a USGS study designed to understand the transport and long-term fate of sediments and associated contaminants in the Massachusetts bays. (See http://woodshole.er.usgs.gov/project-pages/bostonharbor/ and Butman and Bothner, 1997.) The long-term observations document seasonal and inter-annual changes in currents, hydrography, and suspended-matter concentration in western Massachusetts Bay, and the importance of infrequent catastrophic events, such as major storms or hurricanes, in sediment resuspension and transport. They also provide observations for testing numerical models of circulation. This data report presents a description of the field program and instrumentation, an overview of the data through summary plots and statistics, and the data in NetCDF and ASCII format for the period December 1989 through December 2002 for Site A and October 1997 through December 2002 for Site B. The objective of this report is to make the data available in digital form and to provide summary plots and statistics to facilitate browsing of the long-term data set.

Data Series↗
USGS2004

Time-series photographs of the sea floor in western Massachusetts Bay: June 1997 to June 1998

This report presents time-series photographs of the sea floor obtained from an instrumented tripod deployed at Site A in western Massachusetts Bay (42° 22.6' N., 70? 47.0' W., 30 m water depth, from June 1997 through June 1998. Site A is approximately 1 km south of an ocean outfall that began discharging treated sewage effluent from the Boston metropolitan area into Massachusetts Bay in September 2000. Time-series photographs and oceanographic observations were initiated at Site A in December 1989 and are anticipated to continue to September 2005. This is the first in a series of reports planned to summarize and distribute these images in digital form. The objective of these reports is to enable easy and rapid viewing of the photographs and to provide a medium-resolution digital archive. The images, obtained every 4 hours, are presented as a movie (in .avi format, which may be viewed using an image viewer such as QuickTime or Windows Media Player) and as individual images (.tif format). The images provide time-series observations of changes of the sea floor and near-bottom water properties.

Massachusetts↗
USGS2004

Time-series photographs of the sea floor in western Massachusetts Bay: June 1998 to May 1999

This report presents time-series photographs of the sea floor obtained from an instrumented tripod deployed at Site A in western Massachusetts Bay (42° 22.6' N., 70? 47.0' W., 30 m water depth, figure 1) from June 1998 through May 1999. Site A is approximately 1 km south of an ocean outfall that began discharging treated sewage effluent from the Boston metropolitan area into Massachusetts Bay in September 2000. Time-series photographs and oceanographic observations were initiated at Site A in December 1989 and are anticipated to continue to September 2005. This one of a series of reports that present these images in digital form. The objective of these reports is to enable easy and rapid viewing of the photographs and to provide a medium-resolution digital archive. The images, obtained every 4 hours, are presented as a movie (in .avi format, which may be viewed using an image viewer such as QuickTime or Windows Media Player) and as individual images (.tif format). The images provide time-series observations of changes of the sea floor and near-bottom water properties. The photographs obtained at Site A are part of a long-term study to understand the transport and long-term fate of sediments and associated contaminants in the Massachusetts bays. (See the Web site Boston Sewage Outfall: The Fate of Sediments and Contaminants in Massachusetts Bay, http://woodshole.er.usgs.gov/project-pages/bostonharbor/ .) This long-term study is carried out by the U.S. Geological Survey ( USGS ) in partnership with the Massachusetts Water Resources Authority ( MWRA )( http://www.mwra.state.ma.us/ ) and the U.S. Coast Guard ( USCG ) ( http://www.uscg.mil ). Long-term oceanographic observations at Site A were obtained to document seasonal and inter-annual changes in currents, hydrography, and suspended-matter concentration, and the importance of infrequent catastrophic events, such as major storms or hurricanes, in sediment resuspension and transport. (See Butman and others (2002) for a description of the oceanographic measurements at Site A and Butman and Bothner (1997) for discussion of sediment transport in Massachusetts Bay.)

Data Series↗
USGS2004

Time-series photographs of the sea floor in western Massachusetts Bay: May 1999 to September 1999; May 2000 to September 2000; and October 2001 to February 2002

This report presents time-series photographs of the sea floor obtained from an instrumented tripod deployed at Site A in western Massachusetts Bay (42° 22.6' N., 70° 47.0' W., 30 m water depth) from May 1999 to September 1999; May 2000 to September 2000; and October 2001 to February 2002. Site A is approximately 1 km south of an ocean outfall that began discharging treated sewage effluent from the Boston metropolitan area into Massachusetts Bay in September 2000. Time-series photographs and oceanographic observations were initiated at Site A in December 1989 and are anticipated to continue to September 2005. This one of a series of reports that present these images in digital form. The objective of these reports is to enable easy and rapid viewing of the photographs and to provide a medium-resolution digital archive. The images, obtained every 4 hours, are presented as a movie (in .avi format, which may be viewed using an image viewer such as QuickTime or Windows Media Player) and as individual images (.tif format). The images provide time-series observations of changes of the sea floor and near-bottom water properties.

Data Series↗
USGS2004

An operation manual for a time-series, storm-activated suspended sediment sampler deployed in the coastal ocean: function, maintenance, and testing procedures

This manual describes the operation and testing procedures for two models of a multi-port suspended sediment sampler that are moored in the coastal ocean and that collect samples on a programmable time schedule that can be interrupted to collect during a storm. The ability to sense and collect samples before, during, and after the height of a storm is a unique feature of these instruments because it provides samples during conditions when it is difficult or impossible to sample from a surface ship. The sensors used to trigger storm sampling are a transmissometer or a pressure sensor. The purpose of such samples is to assess composition and concentration of sediment resuspended from the seafloor during storms and subsequently transported within the coastal system. Both light transmission and the standard deviation of pressure from surface waves correlate with the passage of major storms. The instruments successfully identified the onset of storms and collected samples before, during, and after the storm maximum as programmed. The accuracy of determining suspended matter concentrations collected by the sediment sampler has not been fully evaluated. Preliminary laboratory tests using a suspension of muddy sediment collected in a near-bottom sediment trap yielded excellent results. However in laboratory tests with different sediment types, the suspended matter concentrations determined with these samplers became less accurate with increasing average grain size. Future calibration work is necessary and should be conducted in a facility that ideally has a water depth of at least 30 feet to prevent cavitation of the pump that draws sea water through the filters. The test facility should also have the capability for adding suspended matter of known composition and concentration to a fixed volume of seawater that is well mixed.

Open-File Report↗
USGS2002

Transport of sludge-derived organic pollutants to deep-sea sediments at deep water dump site 106

Linear alkylbenzenes (LABs), coprostanol and epi-coprostanol, were detected in sediment trap and bottom sediment samples at the Deep Water Dump Site 106 located 185 km off the coast of New Jersey, in water depths from 2400 to 2900 m. These findings clearly indicate that organic pollutants derived from dumped sludge are transported through the water column and have accumulated on the deep-sea floor. No significant difference in LABs isomeric composition was observed among sludge and samples, indicating little environmental biodegradation of these compounds. LABs and coprostanol have penetrated down to a depth of 6 cm in sediment, indicating the mixing of these compounds by biological and physical processes. Also, in artificially resuspended surface sediments, high concentrations of LABs and coprostanols were detected, implying that sewage-derived organic pollutants initially deposited on the deep-sea floor can be further dispersed by resuspension and transport processes. Small but significant amounts of coprostanol were detected in the sediment from a control site at which no LABs were detected. The coprostanol is probably derived from feces of marine mammals and sea birds and/or from microbial or geochemical transformations of cholesterol. Polcyclic aromatic hydrocarbons (PAHs) in sediment trap samples from the dump site were largely from the sewage sludge and had a mixed petroleum and pyrogenic composition. In contrast, PAHs in sediments in the dump site were mainly pyrogenic; contributed either from sewage sludge or from atmospheric transport to the overlying waters. & 1994 American Chemical Society.

Environmental Science & Technology↗
USGS2002

The effect of the new Massachusetts Bay sewage outfall on the concentrations of metals and bacterial spores in nearby bottom and suspended sediments

Since the new outfall for Boston's treated sewage effluent began operation on September 6, 2000, no change has been observed in concentrations of silver or Clostridium perfringens spores (an ecologically benign tracer of sewage), in bottom sediments at a site 2.5 km west of the outfall. In suspended sediment samples collected with a time-series sediment trap located 1.3 km south of the outfall, silver and C. perfringens spores increased by 38% and 103%, respectively, in post-outfall samples while chromium, copper, and zinc showed no change. All metal concentrations in sediments are <50% of warning levels established by the Massachusetts Water Resources Authority. An 11-year data set of bottom sediment characteristics collected three times per year prior to outfall startup provides perspective for the interpretation of post-outfall data. A greater than twofold increase in concentrations of sewage tracers (silver and C. perfringens) was observed in muddy sediments following the exceptional storm of December 11-16, 1992 that presumably moved contaminated inshore sediment offshore. ?? 2002 Elsevier Science Ltd. All rights reserved.

Boston Harbor↗