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Michael H. Bothner

Publications and source records attributed to Michael H. Bothner.

At least 55 records · Page 3Linked to original sources
USGS2000

Time-averaged fluxes of lead and fallout radionuclides to sediments in Florida Bay

Recent, unmixed sediments from mud banks of central Florida Bay were dated using 210 Pb/ 226 Ra, and chronologies were verified by comparing sediment lead temporal records with Pb/Ca ratios in annual layers of coral ( Montastrea annularis ) located on the ocean side of the Florida Keys. Dates of sediment lead peaks (1978±2) accord with prior observations of a 6 year lag between the occurrence of maximum atmospheric lead in 1972 and peak coral lead in 1978. Smaller lags of 1–2 years occur between the maximum atmospheric radionuclide fallout and peaks in sediment temporal records of 137 Cs and Pu. Such lags are consequences of system time averaging (STA) in which atmospherically delivered particle-associated constituents accumulate and mix in a (sedimentary?) reservoir before transferring to permanent sediments and coral. STA model calculations, using time-dependent atmospheric inputs, produced optimized profiles in excellent accord with measured sediment 137 Cs, Pu, lead, and coral lead distributions. Derived residence times of these particle tracers (16±1, 15.7±0.7, 19±3, and 16±2 years, respectively) are comparable despite differences in sampling locations, in accumulating media, and in element loading histories and geochemical properties. For a 16 year weighted mean residence time, STA generates the observed 6 year lead peak lag. Evidently, significant levels of nondegradable, particle-associated contaminants can persist in Florida Bay for many decades following elimination of external inputs. Present results, in combination with STA model analysis of previously reported radionuclide profiles, suggest that decade-scale time averaging may occur widely in recent coastal marine sedimentary environments.

Florida↗
USGS2000

Anthropogenic platinum and palladium in the sediments of Boston Harbor

Anthropogenic activity has increased recent sediment concentrations of Pt and Pd in Boston Harbor by approximately 5 times background concentrations. Surface sediments and downcore profiles were investigated to evaluate Pt and Pd accumulation and behavior in urban coastal sediments. There is no clear correlation between temporal changes in Pt and Pd consumption and sediment concentration. However, Pt/Pb and Pd/Pb ratios suggest that Pt and Pd flux into the Harbor may not be decreasing with cessation of sludge input as rapidly as other metals. This is supported by the large discrepancy between fluxes associated with sludge and effluent release and those calculated from surface sediment concentrations. This evidence supports catalytic converters as a major source of Pd and Pt to Boston Harbor but cannot preclude other sources. Pd does not exhibit signs of post-burial remobilization below the mixed layer in the sediment cores, although near-surface variability in Pd concentrations may indicate a labile Pd component. Pt displays an inverse correlation with Mn above the oxic/suboxic transition, similar to behavior seen in pristine sediments where Pt is thought to be chemically mobile. This study does not support the use of Pd and Pt as tracers of recent contaminated sedimentation. However, the possibility of a labile Pt and Pd in these sediments highlights the need for further study of the biological uptake of these metals.

Environmental Science & Technology↗
USGS2000

Holocene and recent sediment accumulation rates in southern Lake Michigan

Rates of sediment accumulation in Lake Michigan are a key component of its geologic history and provide important data related to societal concerns such as shoreline erosion and the fate of anthropogenic pollutants. Previous attempts to reconstruct Holocene rates of sediment accumulation in Lake Michigan, as well as in the other Laurentian Great Lakes, have been bedeviled by the effect of refractory terrestrial material on radiocarbon ages from total organic carbon samples of lake sediments. AMS radiocarbon ages on small samples of biogenic carbonate (ostracodes and mollusks) in Lake Michigan provide accurate Holocene ages. The present bicarbonate reservoir effect is estimated from shells of mollusks collected live before atmospheric nuclear testing to be 250 yr. From paired samples of biogenic carbonate and terrestrial macrofossils, the past reservoir effect is thought to be less than 500 yr. The radiocarbon ages indicate a distinct decrease in sediment accumulation rates throughout the southern basin of Lake Michigan at about 5 ka, about the time when lake level stabilized at the Nipissing level after rising rapidly for several thousand years. Average rates of sediment accumulation for the historic period (the last 150 yr) can be estimated from radioisotopes ( 210 Pb and 137 Cs), pollen stratigraphy, and changes in sediment properties associated with human activity. Multiple methods are necessary because at any given site, problems arise in the assumptions or applicability of one or more methods. In general, the mass accumulation calculations suggest that sediments were deposited 4 to 11 times faster in the historic period than before human settlement. The character of the sediment did not change in a dramatic way, but sediment magnetic properties suggest shifts in the sources of sediment. The data suggest that some of the changes in sources and (or) character of the sediment occurred just before human settlement and were probably related to climatic changes associated with the Little Ice Age.

Michigan↗
USGS1998

Erosion, weathering, and sedimentation

This chapter explains how a variety of nuclides have been applied to catchments throughout the world. One of the most exciting new approaches for quantifying the rate at which catchments erode is the measurement of in situ produced cosmogenic nuclides. The commonly applied nuclides for erosion rate measurements are 3 He, 10 Be, 26 A1, and 36 C1. Use of such nuclides was restricted to determining denudation rates of exposed bedrock outcrops. It appears that samples have generally been collected from outcrops standing above the surrounding landscape. These protrusions of bedrock may erode more slowly because they shed water rapidly, thus reducing the efficacy of chemical weathering. Geomorphologists have used sediment deposits or suspended particle loads in rivers to evaluate erosive processes in catchments. Linking this approach to fluxes of anthropogenic radionuclides such as 137 Cs or natural 210 Pb opens up a new avenue for understanding processes such as particle formation via weathering, soil formation, denudation, transport, and sedimentation. There are some factors that must be considered when attempting to use Sr isotopes to identify solute sources or quantify mineral weathering rates or processes at the catchment scale. First, 87 Sr/ 86 Sr observed in streamflow probably does not reflect current weathering in the catchment but rather a partial integration of the weathering history and the evolution of the cation exchange pool. Second, Sr release must be distinguished from mineral dissolution as a bulk mass transfer process in cases where Sr may be preferentially lost from the mineral relative to more tightly bound cations. Third, an understanding of the emplacement history of catchment soil substrates, for example, moraine vs. alluvium; residuum vs. colluvium; fractured vs. massive bedrock, may be critical to confirming the weathering reactions inferred from the Sr isotopes.

Book chapter↗
USGS1998

Chemical gradients in sediment cores from an EPA reference site off the Farallon Islands - Assessing chemical indicators of dredged material disposal in the deep sea

Heavy metal and organic contaminants have been determined in undisturbed sediment cores from the US Environmental Protection Agency reference site for dredged material on the continental slope off San Francisco. As expected, the concentrations are significantly lower than toxic effects guidelines, but concentrations of PCBs, PAHs, Hg, Pb, and Clostridium perfringens (a bacterium spore found in sewage) were nearly two or more times greater in the surface sediments than in intervals deeper in the cores. These observations indicate the usefulness of measuring concentration gradients in sediments at the San Francisco deep ocean disposal site (SF-DODS) where a thin (0.5 cm thick) layer of dredged material has been observed beyond the boundary. This thin layer has not been chemically characterized by the common practice of homogenizing over the top 10 cm. An estimated 300 million cubic yards of dredged material from San Francisco Bay are expected to be discharged at the SF-DODS site during the next 50 years. Detailed depth analysis of sediment cores would add significant new information about the fate and effects of dredged material in the deep sea.

Marine Pollution Bulletin↗
USGS1998

Metal concentrations in surface sediments of Boston Harbor: Changes with time

The concentrations of metals in surface sediments of Boston Harbor have decreased during the period 1977–1993. This conclusion is supported by analysis of: (1) surface sediments collected at monitoring stations in the outer harbor between 1977 and 1993; (2) metal concentration profiles in sediment cores from depositional areas of the harbor; and (3) historical data from a contaminated-sediment database, which includes information on metal and organic contaminants and sediment texture. The background and matrix-corrected concentrations of lead (Pb) measured in the surficial layer (0–2 cm) of cores decreased by an average of 46%±12% among four locations in the outer harbor during the 16 y period. Chromium (Cr), copper (Cu), mercury (Hg), silver (Ag), and zinc (Zn) exhibited similar trends. Results from our sediment sampling are supported by historical data that were compiled from diverse sources into a regional sediment database. This sediment database contains approximately 3000 samples; of these, about 460 samples were collected and analyzed for Cu, Hg, or Zn and many other sediment parameters in Boston Harbor surface sediments between 1971–1993. The database indicates that the concentrations of these three metals also decreased with time in Boston’s Inner Harbor. The decreases in metal concentrations that are observed in more recent years parallel a general decrease in the flux of metals to the harbor, implemented by: (1) ending the sewage sludge discharge to the Harbor in December, 1991; (2) greater source reduction (e.g. recovery of silver from photographic processing) and closing or moving of industries; (3) improvements in wastewater handling and sewage treatment; and (4) diminishing use of lead in gasoline beginning about 1973. Despite the general decrease in metal concentrations in Boston Harbor surface sediments, the concentrations of Ag and Hg measured at some outer harbor stations in 1993 were still at, or above, the level associated with frequent adverse effects to marine organisms (guidelines are: Ag 3.7 μ g g −1 , Hg 1.17 μ g g −1 , from Long et al., 1995 ). Concentrations of the other metals listed were in the range considered to occasionally induce adverse biological effects.

Massachusetts↗
USGS1997

Chemical and textural characteristics of sediments at an EPA reference site for dredged material on the continental slope SW of the Farallon Islands

A U.S. Environmental Protection Agency (EPA) reference site for dredged material has been established on the Continental Slope off San Francisco in water depths of 800-1500 m. This site, 35 km southwest of the Farallon Islands, serves as a reference for sediment testing in support of dredging and disposal at the San Francisco Deep Ocean Disposal Site (SF-DODS). An estimated 300 million cubic yards of dredged material from San Francisco Bay are expected to be discharged at this site during the next 50 years. Information from the reference site provides an additional baseline for monitoring environmental changes at the SF-DODS. This study provides sediment data on a suite of heavy metals and organic compounds which make up the EPA list of "chemicals of concern" because of their potential toxicity to marine organisms.

California↗
USGS1996

Osmium isotopes and silver as tracers of anthropogenic metals in sediments from Massachusetts and Cape Cod bays

High concentrations of osmium (Os) and silver (Ag) and low 187Os/186Os ratios in Boston sewage make these elements sensitive tracers of the influence of sewage on marine sediments in Massachusetts and Cape Cod bays. Pristine marine sediments have Ag concentrations more than 200 times lower than sewage sludge, Os concentrations 10-40 times lower, and 187Os/186Os ratios six times higher. Surface sediments from both Massachusetts and Cape Cod bays exhibit both high Ag concentrations and low 187Os/186Os ratios indicating the influence of sewage particles on marine sediments in this region extends some 70 km from the point of sewage release. In detail, the distribution of Os and Ag do not support a model of simple physical mixing of sewage particles with normal marine sediments. Deviations from the mixing model may be the result of fractionation of Os and Ag in the marine environment, and [or] independent temporal variations in the Os and Ag content of the waste stream. The results of this investigation suggest that osmium isotopes may be widely applicable as tracers of the influence of sewage on sediments in estuarine environments and that subtle variations in the isotopic composition of Os in the waste stream may help constrain the sources of Os and other metals delivered to the environment.

Cape Cod Bay, Massachusetts Bay↗
USGS1996

Linear alkylbenzenes as tracers of sewage-sludge-derived inputs of organic matter, PCBs, and PAHs to sediments at the 106-mile deep water disposal site

Linear alkylbenzenes (LABs) are sensitive source-specific tracers of sewage inputs to the marine environment. Because they are highly particle reactive and nonspecifically sorbed to organic matter, LABs are potential tracers of the transport of both sludge-derived organic matter and other low solubility hydrophobic contaminants (e.g., PCBs and PAHs); sediment trap studies at the 106-Mile Site have shown LABs to be valuable in testing models of sludge deposition to the sea floor. In this study we report on the distributions of LABs, PCBs, PAHs, and Ag in surface sediments collected within a month of the complete cessation of dumping (July, 1992) in the vicinity of the dump site. Total LAB concentrations were lower than those measured by Takada and coworkers in samples from nearby sites collected in 1989. LABs from both studies appear to be significantly depleted (6 to 25-fold) in surface sediments relative to excess Ag (another sludge tracer) when compared to sewage sludge and sediment trap compositions. Comparison of LAB sediment inventories to model predictions of sludge particle fluxes supports the contention that LABs have been lost from the bed. The use of LABs to examine the short-or long-term fate of sludge derived materials in deep-sea sediments should be questioned. The causes of this LAB depletion are unclear at this point, and we discuss several hypotheses. The concentrations of total PCBs and PAHs are both correlated with sludge tracers, suggesting that there may be a measurable contribution of sludge-derived inputs on top of other nonpoint sources of these contaminant classes. This possibility is consistent with the composition of these contaminants determined in recent and historical analyses of sewage sludge.

Journal of Marine Environmental Engineering↗
USGS1996

Contaminants in the Gulf of Maine-What's here and should we worry?

The Gulf of Maine is a dynamic environment that has highly variable bottom type and localized depositional and transport processes. It is used and impacted by the people around it who hope to use the marine system for many purposes such as fishing, recreation, housing, sewage and dumped disposal, shipping, recreation, and preservation. In order to identify "pollution", which is defined as detrimental effects in the ecosystem that are attributable to human activity, the spatial and temporal distribution of contaminants in Gulf of Maine sediments are established using data that have been compiled into a Contaminated-Sediment Database for the Gulf of Maine. The potential for high contaminant levels in the sediments to induce toxic effects in the Gulf ecosystem is then assessed. In the Gulf of Maine, we have large urban centers that adversely affect the marine ecosystem well offshore through a variety of human activities. We are also in the fortunate position of still having many relatively pristine marine areas. It is unlikely that we will reach an endpoint of "zero toxic effects" in the ecosystem; however, much of the information needed to move closer to the shared goal of managing a sustainable ecosystem in the Gulf of Maine is currently available. Future success will rely on continued efforts to 1) identify rate-limiting physical and biological processes, 2) provide appropriate data synthesis and 3) involve the public.

Maine, Massachusetts, New Hampshire↗
USGS1994

Indicators of sewage contamination in sediments beneath a deep-ocean dump site off New York

The world's largest discharge of municipal sewage sludge to surface waters of the deep sea has caused measurable changes in the concentration of sludge indicators in sea-floor sediments, in a spatial pattern which agrees with the predictions of a recent sludge deposition model. Silver, linear alkylbenzenes, coprostanol, and spores of the bacterium Clostridium perfringens, in bottom sediments and in near-bottom suspended sediment, provide evidence for rapid settling of a portion of discharged solids, accumulation on the sea floor, and biological mixing beneath the water sediment interface. Biological effects include an increase in 1989 of two species of benthic polychaete worm not abundant at the dump site before sludge dumping began in 1986. These changes in benthic ecology are attributed to the increased deposition of utilizable food in the form of sludge-derived organic matter.

New Jersey, New York↗
USGS1994

Submerged and eroded drumlins off northeastern Massachusetts

Streamlined, oval-shaped, oriented topographic highs in Massachusetts Bay are identified as the erosional remnants of drumlins. The topographic highs correlate with outlines of lag gravel deposits on the sea floor and both the highs and lag gravel seafloor footprint have a distinct east-southeast long axis trend. This trend is similar to the preferred orientation of the long axes of drumlins in the Boston Basin and indicates the flow direction of the late Wisconsinan Laurentide Ice Sheet. Modification of the drumlins occurred during two passages of the shoreline, the first during the late Wisconsinan regression when the drumlins were only slightly eroded. The second passage of the shoreline occurred during the marine transgression, when erosion, in the form of cliff-face retreat, removed the upper part of the drumlins.

Massachusetts↗
USGS1994

210Pb balance and implications for particle transport on the continental shelf, U.S. Middle Atlantic Bight

Supply of 210 Pb to the continental shelf off the northeastern United States is dominated by the deposition from the atmosphere, the rate of which is reliably known from previously published work. Excess 210 Pb inventories in the shelf sediments show accumulations that are nearly in balance with the supply, even in areas of relict sands where it is believed that no net accumulation of sediment presently occurs. The 210 Pb distributions in shelf and slope water indicate that the two-way fluid exchange at the shelf-slope front and the net transport in the alongshore flow make comparatively small contributions to the shelf 210 Pb budget. The near balance between supply and decay of 210 Pb on the shelf implies a limit to the particle export flux. It is concluded that the export of particulate organic carbon does not exceed 60 g m −2 y −1 (∼25% of primary production) and is probably lower. The hypothesis is advanced that fine particulate matter introduced to the continental shelf is detained in its transit of the shelf because of bioturbational trapping in the sediment due to benthic animals. Distributions of 210 Pb in suspended particulate matter and in the fine fraction of shelf sediments suggest that the average fine particle must undergo several cycles of deposition-bioturbation-resuspension-redeposition and requires a number of decades for its transit and ultimate export from the shelf. Thus, only the most refractory organic matter is likely to be exported.

Middle Atlantic Bight↗