Papers by Michael Bothner
A New Instrument for Sampling Flocculent Material at the Water/Sediment Interface: RESEARCH-METHOD PAPER
Journal of Sedimentary Research, 1982
Paula J. Quinterno off California. Low oxygen foraminiferal faunas are frequently found in fine-g... more Paula J. Quinterno off California. Low oxygen foraminiferal faunas are frequently found in fine-grained sediments beneath highly productive oceanic waters. An association of species typical of low oxygen environments (<0.5 ml/L of 02) is present in very fine grained sediments of Prince William Sound. It is best developed at Stations 7 and 8, but is also present at Stations 9 and 10 (Fig. ). Abundant diatoms, an indication of high productivity, occur in sediments at these sites. The benthic foraminiferal fauna is dominated by Bolivina pseudobeyrichi, Uvigerina juncea, and Globobulimina spp. Poag ( , 1985) ) found that high abundances of Brizalina (Bolivina) and Uvigerina in the Gulf of Mexico correlated with an oxygen minimum and with* high amounts of organic carbon. A stained specimen of Bolivina pseudobeyrichi is figured on the title page (page 1) of this report. The significance of the low oxygen faunas in the Prince William Sound samples is uncertain, but it should be noted that this fauna is best developed closest to the oil spill (Station 7). Unfortunately, no baseline studies of foraminiferal distribution had been done before the spill; therefore, the composition of previous foraminiferal faunas and any changes since the spill are unknown. Only 4 downcore samples (>2cm) were available for this report, and give only a general idea of what the past faunas were. Rates of sediment accumulation are not known for this area, so we do not know when the various layers were deposited. Furthermore, Corliss (1985) has found some species living (stained) as deep as 15 cm in deep sea cores, so some of the foraminifers in the Prince William Sound samples from the 2-8 cm intervals may have been living at the time of collection, but this cannot be known since stain was only added to samples from the upper 2 cm of the cores. Table compares the abundances of low oxygen taxa in surface samples 7B, 7C, and 9A with abundances at various depths in cores 7C, 9A, and 9B. Surface samples have greater abundances of the 3 low oxygen taxa than do subsurface samples. Two of these genera, Bolivina and Uvigerina have also been correlated with high amounts of organic matter in sediment (Poag, , 1985)). The greater abundance of the low oxygen (and high organic carbon) fauna in the surface samples might be an indication that the oil spill has affected the benthic foraminifers by altering their environment However, the observed fauna! change is slight and is probably the result of natural environmental processes. Although no oil was found in the seafloor sediments, the benthic organisms could be affected by changes in the water column caused by the spill. These changes, however, would not necessarily be detrimental to all species of foraminifers. Bandy, Ingle and Resig (1965a,b) in studies of foraminifers in surface sediments around sewage outfalls off the Los Angeles area found that not all species of foraminifers are adversely affected by pollutants. In fact, the greatest number of living foraminifers were found downcurrent from the outfall. In the Prince William Sound samples, the highest percentages of live foraminifers are found at stations in the vicinity of the spill (Table ). Live specimens of Bolivina pseudobeyrichi make up 17%, 8%, 13%, and 6% of the total benthic foraminiferal faunas at Stations 7 (B and C), 8A, 9A, and 10C, respectively. Live percentages of Uvigerina juncea are 6%, 3%, 11%, 8%, and 11% at Stations 7B, 7C, 8A, 9A, and 10C respectively. Live percentages of Globobulimina spp. make up 8%, 9%, and 4% at stations 7B, 7C, and 10C respectively. It is possible that these species are opportunistic, that is, they are able to tolerate environments that other organisms cannot; therefore, they thrive due to lack of competition. \\ Adercotryma glomerata Ammobaculites spp. Ammodiscus spp. Ammotium cassis Angulogerina angulosa Astacolus Astrononion gallowayi Bolivina decussata B. pseudobeyrichi B. spp. Buccella firigida B. spp. Buliminella tenuata Cassidulina californica C. limbata C. minuta C. tortuosa C. spp. Cibicides lobatulus C. mckannai C. pseudoungeriana C. spp. Cribrostomoides crassimargo C. Jeffreys! C. subglobosus C. spp. Dentalina sp. Discorbis opercularis D. omatissima D. sp. aff. D. praegeri Eggerella advena E. clavatum var.
Journal research U. S. geological survey, 1976
The Journal of Research is published every 2 months by the U.S. Geological Survey. It contains pa... more The Journal of Research is published every 2 months by the U.S. Geological Survey. It contains papers by members of the Geological Survey and their professional colleagues on geologic, hydrologic, topographic, and other scientific and technical subjects.
Circular, 1984
Analysis of sediment standard and replicate sediment samples 9 3. Chemical analyses of sediment-t... more Analysis of sediment standard and replicate sediment samples 9 3. Chemical analyses of sediment-trap samples collected before and after drilling began jg IV
Data Series, 2007
Sedimentary facies, short-lived isotopes 7 Be, 137 Cs, and 210 Pb, and magnetic properties of sed... more 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.
Open-File Report, 1990
This document describes the work elements and progress during the first six months of a Joint Fun... more This document describes the work elements and progress during the first six months of a Joint Funding Agreement (cost share) between the Massachusetts Water Resources Authority (MWRA) and the U. S. Geological Survey for oceanographic work in western Massachusetts Bay. The objective of this study is to develop a predictive capability for the fate and transport of contaminants which are strongly sorbed by suspended and bottom sediments. The present Agreement covers the first two years of a planned five-year monitoring program. This program will be coordinated with the comprehensive research program that is directed by the Massachusetts Bays Management Committee. The major components of this Joint Funding Agreement and the progress to date include: * Continuous measurements of currents and sediment transport in the vicinity of the proposed ocean outfall using instrumented moorings and bottom tripods. The first deployment of moorings took place on December 5, 1989. The moorings will be replaced three times per year during the two-year period of this contract. The long-term continuous measurements are necessary to characterize the transport processes over time as well as during catastrophic events, such as storms. Material in suspension is being collected with new instrumentation, permitting chemical and physical analysis of the sediment transported during storms. * Creation of a digital map of the sea-floor morphology and texture. as interpreted from continuous-coverage sidescan-sonar data calibrated with photographs and sediment analyses at representative locations. The hand drawn interpretive map has been completed in the 20 square nautical mile survey area around the proposed outfall. The digital map has been completed over 5 sq miles. Our preliminary maps have been of value in deciding the precise location of the outfall. * Determination of the rates of sediment accumulation and mixing and the inventories of contaminants in sediments of Massachusetts Bay. Sediment cores have been collected in depositional areas of Mass Bay and the depth profiles of radioisotopes, heavy metals and sediment texture are being determined. This information will be used to characterize the longterm fate of contaminants added to Massachusetts coastal waters from a variety of sources. * Analysis of the exchange of water and particulates between Boston Harbor and Massachusetts Bav using numerical models and field measurements. The development of a high resolution numerical model of the tidal exchange between Boston Harbor and Massachusetts Bay is nearly completed. The new model was successful in predicting a weakly recirculating gyre observed over the Deer Island flats during flood tide. After the current field has been further verified by comparison with moored current observations, particle tracking experiments will be conducted to quantify the exchange between Boston Harbor and Massachusetts Bay induced by these currents. This effort will provide critical basic information on the physical processes influencing the fate of contaminants at the harbor entrance. * Recommendations for any additional field measurements necessary to verify model results.
Open-File Report, 1976
PREFACE The Atlantic Margin Coring Project was planned in consultation with the State Geological ... more PREFACE The Atlantic Margin Coring Project was planned in consultation with the State Geological Surveys of the Atlantic Coastal States and was carried out by a team of more than 40 scientists and technicians of the U.S. Geological Survey and State Geological Surveys who served alternating tours of duty aboard the D/V 6LOMAR CONCEPTION.
Open-File Report, 1992
The U.S. Geological Survey (USGS) is conducting studies in Boston Harbor, Massachusetts Bay, and ... more The U.S. Geological Survey (USGS) is conducting studies in Boston Harbor, Massachusetts Bay, and Cape Cod Bay designed to define the geologic framework of the region and to understand the transport and accumulation of contaminated sediments. The region is being studied because of environmental problems caused by the introduction of wastes for a long time, because a new ocean outfall (to begin operation in 1995) will change the location for disposal of treated Boston sewage from Boston Harbor into Massachusetts Bay, and because of the need to understand the transport of sediments and associated contaminants in order to address a wide range of management questions. The USGS effort complements and is closely coordinated with the research and monitoring studies supported by the Massachusetts Environmental Trust, the Massachusetts Bays Program, and by the Massachusetts Water Resources Authority. The USGS study includes (1) geologic mapping, (2) circulation studies, (3) long-term current and sediment transport observations, (4) measurements of contaminant inventories and rates of sediment mixing and accumulation, (5) circulation modeling, (6) development of a contaminated sediments data base, and (7) information exchange. A long-term objective of the program is to develop a predictive capability for sediment transport and accumulation. Key results to date: * Areas of sediment erosion and deposition have been mapped within Boston Harbor. Areas of deposition on the seabed are shallow subtidal flats and sheltered depressions where the tidal currents are weak. Contaminants most likely will accumulate in these areas. The shores of the mainland, where waves are relatively large, and harbor islands and the sea bed of constricted channels, where tidal currents are strong, are areas of erosion. Contaminants are not likely to accumulate in these areas of erosion. * Detailed mapping of the western Massachusetts Bay sea floor in the region of the new Boston sewage outfall shows an extremely varied bottom that provides a wide range of biological habitats. Areas of coarse sand, gravel, and boulders lie adjacent to areas of finer sediments. The surveys have identified areas of fine-grained sediments that are likely sites of contaminant accumulations and candidates for long-term monitoring of environmental quality. * Remote sensing mapping techniques are essential to adequately determine the complex spatial variability of the bottom morphology and sediment texture; accurate maps cannot be prepared from analysis of sediment grab samples alone. * The concentrations of heavy metals (lead and silver for example) in fine-grained sediments of Massachusetts Bay near the new outfall site are higher than background concentrations, a condition common in marine areas adjacent to metropolitan centers that have received wastes for a long time. These elevated concentrations may make it difficult to detect changes in contaminant levels that might occur at the new outfall site. To accurately assess future changes caused by the outfall or by other sources, a carefully documented baseline of present contaminant levels is being established. quality made near the new outfall site suggest that away in a consistent direction by a transported by a variety of processes, inflow. One-day particle excursions are located in a region to the west of the * What are the present contaminant levels in the sediments and how will they change? A long-term objective of the program is to develop a predictive capability for sediment transport and accumulation. To address the issues of contaminant transport and accumulation in the Massachusetts bays, the USGS has developed and is carrying out a research and mapping program that consists of seven components. The seven components are: 1. Geologic mapping of sedimentary environments 2. Circulation in Massachusetts and Cape Cod Bays 3. Long-term current and sediment transport observations 4. Contaminant inventories and rates of sediment mixing and accumulation 5. Circulation modeling 6. Contaminated sediments data base 7. Information exchange This report provides a brief summary of the objectives, rationale, fieldwork, results to date, and plans for 1992 for each component.
Open-File Report, 1987
This study is part of a multidisciplinary program conducted on the continental slope and rise off... more This study is part of a multidisciplinary program conducted on the continental slope and rise off the North, Middle, and South Atlantic states to characterize the biology, chemistry, and geology of the sea floor. The specific objectives are to measure and evaluate the extent of environmental changes which relate to exploratory drilling activities. In this report we use trace-metal concentrations to assess both the depositional pattern and fate of discharged drilling mud. Sediment samples collected during six cruises to the continental slope and rise off the Mid-Atlantic states have been analyzed for 12 metals [aluminum (Al), barium (Ba), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni), vanadium (V), and zinc (Zn)]. We found that Ba was the only metal that showed an increase as a result of drilling, and the magnitude of the Ba increase was small «32%). In one core collected during Cruise 3 at Station 1, adjacent to the drilling site in Block 372, the Ba concentration in the surface sediment was 13 percent higher than measured deeper in the core. Concentrations of Ba in one of the three replicate surface sediments from Cruise 6, Station 1, were 20 percent higher than concentrations in deeper sediments. Neither samples from other replicate box cores from Cruise 3 or from Cruise 6, Station 1, nor replicate sub-cores from the same box core, show the same increase, indicating a patchy distribution of drilling-related Ba. There is no consistent trend of increasing Ba concentration in blended surface sediment from Station 1, Cruises 1 to 6. The average concentrations of Ba at Station 1 are similar to concentrations at stations away from drilling rigs and in sediments having similar grain size. At stations 13 and 14, located within 1.4 km of the drilling in Block 93, no significant changes in the average Ba concentration of bottom sediments were measured between predrilling and postdrilling samples. The barium increases are probably not harmful to benthic organisms on the basis of the low enrichments, the patchy distribution, and the low toxicity of BaSOA (based on its use in medicine). The strongest Ba signal from drilling mud was measured in sediments collected in sediment traps positioned in the upper 850 m of the water column at a mooring located 2.4 km southwest of the drilling rig in Block 372. Discrete particles of barite were identified in the sample using a scanning electron microscope equipped with an energy dispersive X-ray detector. The larger particles have dimensions of 60 x 90 vim. Their transport from the drilling rig to the sediment trap mooring is predictable given a calculated settling velocity and the measured currents. For samples collected from the study area during Cruise 1, the distribution of metals in surface sediments appears to vary with the changes in the concentrations of fine sediment and organic carbon. The concentrations of the metals analyzed in these sediments are the same or lower than they are in average shales from around the world, and are characteristic of uncontaminated sediments. The highest concentration (555 ppm) of Ba measured in sediments at Station 1 is less than the concentration in average shales (580 ppm). Pb concentrations are consistently higher in the upper 5-10 cm of sediment than in deeper sections of sediment cores, but the average values in surface sediments do not exceed those measured in average shales. Pb enrichment in surface sediments has been observed at other locations off the U.S. East Coast and is thought to be related to the onshore burning of gasoline containing Pb additives. The inventories of anthropogenic lead in the sediments of this study area are higher than are predicted from long-term atmospheric fluxes. This suggests enhanced deposition of lead in these sediments. Oxidizing; air-acetylene Butyl acetateflame W.I.
Open-File Report, 2001
To assess the environmental impact of the Massachusetts Bay outfall for Boston's treated sewage e... more To assess the environmental impact of the Massachusetts Bay outfall for Boston's treated sewage effluent, grain size and characteristics of aggregates in bottom sediments have been measured during a comprehensive monitoring program. Both a sandy and a muddy bottom location within 2.5 km of the outfall have been sampled three times per year since 1990. These samples have provided about 11 years of pre-discharge baseline data used to evaluate natural variability. The sandy location (station #2) showed a very consistent textural trend over the monitoring period. Mean textural percentages were slightly over 97% sand, 1.5% silt, and 0.9% clay. The withinstation variability of the sand was less than 2%. No seasonal differences in grain size were observed. There was very little change in the grain size distribution at this site following unusually large storms in October 1991 and December 1992. However, the concentration of aggregates, measured separately from the texture, decreased from about 1.5% to 0.5% after the December 1992 storm perhaps because of its longer duration. The aggregates at this station were composed primarily of quartz, with small concentrations of fecal pellets, worm tubes, and amorphous organic material all bound in an elastic mucus-like matrix. The majority of the fecal pellets were larger than 0.25 mm, consistent with the size produced from an assemblage of benthic polychaetes, isopods, and amphipods. The muddy location ( station #3) contained 50-90% silt plus clay. No seasonal textural trends were evident, but clay concentrations increased 35% following the severe storm in December, 1992. Increases in clay concentration were also detected during February and May of 2001.These dates mark the 4th and 7th months after the September 2000 start of the new outfall. The ongoing monitoring study will compare these most recent and any future textural changes with chemical analyses of the sediments. The comparison will help to determine if a clear linkage can be made between the operation of the outfall and any changes observed in the sediments. The organic mineral aggregates at station #3 peaked (54%) in concentration during the early fall of 1993. Except for this peak, values were typically between 5% and 15% during the 11 year monitoring period. There were no seasonal trends. Speculation suggests that the peak in aggregate concentration may have been caused by larger populations of benthic organisms, which developed following the influx of fine-grained organic-matter-rich sediment after the unusual storm of December 1992. High concentrations of aggregates are restricted to the upper 2 cm based on profiles in sediment cores up to 50 cm long and suggests that this form of sediment encapsulation is fragile in the sedimentary record.
Processes influencing the transport and fate of contaminated sediments in the coastal ocean: Boston Harbor and Massachusetts Bay
Circular, 2007
Open-File Report, 2010
During the period August 14-23, 2002, the discharge of total suspended solids (TSS) from the Mass... more During the period August 14-23, 2002, the discharge of total suspended solids (TSS) from the Massachusetts Water Resources Authority sewage-treatment plant ranged from 32 to 132 milligrams per liter, causing the monthly average discharge to exceed the limit specified in the National Pollution Discharge Elimination System permit. Time-series monitoring data collected by the U.S. Geological Survey in western Massachusetts Bay were examined to evaluate changes in environmental conditions during and after this exceedance event. The rate of sediment trapping and the concentrations of near-bottom suspended sediment measured near the outfall in western Massachusetts Bay increased during this period. Because similar increases in sediment-trapping rate were observed in the summers of 2003 and 2004, however, the increase in 2002 cannot be definitively attributed to the increased TSS discharge. Concentrations of copper and silver in trapped sediment collected 10 and 20 days following the 2002 TSS event were elevated compared to those in pre-event samples. Maximum concentrations were less than 50 percent of toxicity guidelines. Photographs of surficial bottom sediments obtained before and after the TSS event do not show sediment accumulation on the sea floor. Concentrations of silver, Clostridium perfringens, and clay in surficial bottom sediments sampled 10 weeks after the discharge event at a depositional site 3 kilometers west of the outfall were unchanged from those in samples obtained before the event. Simulation of the TSS event by using a coupled hydrodynamic-wave-sediment-transport model could enhance understanding of these observations and of the effects of the exceedance on the local marine environment.
Marine Pollution Bulletin, 2006
Sediment traps were used to evaluate the frequency, cause, and relative intensity of sediment mob... more 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.
Marine Geology, 2009
Oceanographic measurements and sediment samples were collected during the summer of 2006 as part ... more Oceanographic measurements and sediment samples were collected during the summer of 2006 as part of a multi-year study of coastal circulation and the fate of terrigenous sediment on coral reefs in Hanalei Bay, Kauai. The goal of this study was to better understand sediment dynamics in a coral reef-lined embayment where winds, ocean surface waves, and river floods are important processes. During a summer period that was marked by two wave events and one river flood, we documented significant differences in sediment trap collection rates and the composition, grain size, and magnitude of sediment transported in the bay. Sediment trap collection rates were well correlated with combined wave-current near-bed shear stresses during the non-flood periods but were not correlated during the flood. The flood's delivery of fine-grained sediment to the bay initially caused high turbidity and sediment collection rates off the river mouth but the plume dispersed relatively quickly. Over the next month, the flood deposit was reworked by mild waves and currents and the fine-grained terrestrial sediment was advected around the bay and collected in sediment traps away from the river mouth, long after the turbid surface plume was gone. The reworked flood deposits, due to their longer duration of influence and proximity to the seabed, appear to pose a greater long-term impact to benthic coral reef communities than the flood plumes themselves. The results presented here display how spatial and temporal differences in hydrodynamic processes, which result from variations in reef morphology and orientation, cause substantial variations in the deposition, residence time, resuspension, and advection of both reef-derived and fluvial sediment over relatively short spatial scales in a coral reef embayment.
A new instrument for sampling flocculent material at the water/sediment interface
Journal of Sedimentary Research, 1982
Geochimica et Cosmochimica Acta, 2007
This study examined the removal of U, Mo, and Re from seawater by sedimentary processes at a shal... more 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 870 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 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.
Estuarine, Coastal and Shelf Science, 2009
Geochemical tracers, including Ba, Co, Th, 7 Be, 137 Cs and 210 Pb, and magnetic properties were ... more Geochemical tracers, including Ba, Co, Th, 7 Be, 137 Cs and 210 Pb, and magnetic properties were used to characterize terrestrial runoff collected in nearshore time-series sediment traps in Hanalei Bay, Kauai, during flood and dry conditions in summer 2006, and to fingerprint possible runoff sources in the lower watershed. In combination, the tracers indicate that runoff during a flood in August could have come from cultivated taro fields bordering the lower reach of the river. Land-based runoff associated with summer floods may have a greater impact on coral reef communities in Hanalei Bay than in winter because sediment persists for several months. During dry periods, sediment carried by the Hanalei River appears to have been mobilized primarily by undercutting of low 7 Be, low 137 Cs riverbanks composed of soil weathered from tholeiitic basalt with low Ba and Co concentrations. Following a moderate rainfall event in September, high 7 Be sediment carried by the Hanalei River was probably mobilized by overland flow in the upper watershed. Ba-desorption in low-salinity coastal water limited its use to a qualitative runoff tracer in nearshore sediment. 210 Pb had limited usefulness as a terrestrial tracer in the nearshore due to a large dissolved oceanic source and scavenging onto resuspended bottom sediment. 210 Pbscavenging does, however, illustrate the role resuspension could play in the accumulation of particlereactive contaminants in nearshore sediment. Co and 137 Cs were not affected by desorption or geochemical scavenging and showed the greatest potential as quantitative sediment provenance indicators in material collected in nearshore sediment traps.
Environmental Science & Technology, 2007
The release of particulate-phase trace metals due to sediment resuspension has been investigated ... more The release of particulate-phase trace metals due to sediment resuspension has been investigated by combining erosion chamber experiments that apply a range of shear stresses typically encountered in coastal environments with a shear stress record simulated by a hydrodynamic model. Two sites with contrasting sediment chemistry were investigated. Sediment particles enriched in silver, copper, and lead, 4-50 times greater than the bulk surfacesediment content, were the first particles to be eroded. As the shear-stress level was increased in the chamber, the total mass eroded increased, butthe enrichment of these trace metals fell, approaching the bulk-sediment content. From the temporal distribution of shear stress generated by the hydrodynamic model for a site in Boston Harbor, resuspension fluxes were estimated. The erosion threshold of this site is exceeded during spring tides, releasing the particles enriched in trace metals into the water colum•n. Due to the higher trace metal content and the regularity of resuspension, low-energy resuspension events (up to a shear stress of 0.2 N/m 2 ) contribute up to 60% of the resuspension metal flux in an average year. The estimated annual quantity of copper and lead resuspended into the water column is higher than estimates of the total riverine flux for these metals. These results indicate that sediment resuspension is a very important mechanism for releasing metals into the water column and provide new insight into the chemical and physical processes controlling the longterm fate of trace metals in contaminated sediments.
Coral Reefs, 2010
Sediment traps are commonly used as standard tools for monitoring ''sedimentation'' in coral reef... more Sediment traps are commonly used as standard tools for monitoring ''sedimentation'' in coral reef environments. In much of the literature where sediment traps were used to measure the effects of ''sedimentation'' on corals, it is clear from deployment descriptions and interpretations of the resulting data that information derived from sediment traps has frequently been misinterpreted or misapplied. Despite their widespread use in this setting, sediment traps do not provide quantitative information about ''sedimentation'' on coral surfaces. Traps can provide useful information about the relative magnitude of sediment dynamics if trap deployment standards are used. This conclusion is based first on a brief review of the state of knowledge of sediment trap dynamics, which has primarily focused on traps deployed high above the seabed in relatively deep water, followed by our understanding of near-bed sediment dynamics in shallow-water environments that characterize coral reefs. This overview is followed by the first synthesis of near-bed sediment trap data collected with concurrent hydrodynamic information in coral reef environments. This collective information is utilized to develop nine protocols for using sediment traps in coral reef environments, which focus on trap parameters that researchers can control such as trap height (H), trap mouth diameter (D), the height of the trap mouth above the substrate (z o ), and the spacing between traps. The hydrodynamic behavior of sediment traps and the limitations of data derived from these traps should be forefront when interpreting sediment trap data to infer sediment transport processes in coral reef environments.
Continental Shelf Research, 2004
The fringing coral reef off the south coast of Molokai, Hawaii is currently being studied as part... more 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 ¼ 1 m) 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.
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Papers by Michael Bothner