David Schlezinger | University of Massachusetts, Dartmouth (original) (raw)
Address: North Dartmouth, Massachusetts, United States
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Royal Netherlands Institute for Sea Research
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Papers by David Schlezinger
Chemical Geology, 2000
Chemical stratification occurs in the water columns and sediments of many aquatic habitats result... more Chemical stratification occurs in the water columns and sediments of many aquatic habitats resulting in vertical chemical and redox gradients. Various types of microorganisms are often associated with specific depths and chemical parameters in these situations. For example, magnetite-producing magnetotactic bacteria are known to form horizontal "plates" of cells at the oxic/anoxic transition zone (OATZ) of such environments. Here, we report the presence of populations of diverse magnetic protists in a seasonally chemically stratified, coastal salt pond. The protistan types included several biflagellates, a dinoflagellate, and a ciliate that were each associated with specific depths and thus, specific chemical, microbiological and redox conditions in the water column. Most cells contained crystals of magnetite usually arranged in chains similar to the magnetosomes in the magnetotactic bacteria. The origin of the particles is unknown. There was no evidence of the presence of endosymbiotic magnetotactic bacteria within the protists nor were the protists observed to be engulfing magnetotactic bacteria despite the fact that high numbers of the latter were present at the same depths as the protists. However, this does not exclude ingestion of magnetotactic bacteria as a source of the magnetic particles while others may biomineralize magnetite. Because protists play an important role in the availability of iron for phytoplankton in marine waters by ingesting and reducing colloidal iron particles, the protists described here could playa significant role in iron cycling in chemically stratified anoxic basins, either through endogenous production of magnetic iron oxide and/or iron sulfide particles, or by ingestion of magnetotactic bacteria and the subsequent reduction and dissolution of iron oxide and/or sulfide particles in their magnetosomes.
Journal of Archaeological Science, 2000
Human occupation enriches soils with phosphorus, which may provide a useful chemical tracer for s... more Human occupation enriches soils with phosphorus, which may provide a useful chemical tracer for site delineation in archaeological studies. In the present study, fine scale soil profiles of inorganic, particulate organic and total phosphorus through a prehistoric Indian site and nearby control site in Cape Cod, MA, indicated a greater predictive value of particulate organic P over inorganic P and total P in determining the vertical boundaries of an anthrosol. The value of inorganic P and total P as occupation tracers was confounded by vertical migration of inorganic P species. Inorganic P mobility was found to result from diagenesis and other post-depositional alterations, including the effects of recent sea water flooding on soil concentrations of dominant exchangeable cations. Parallel measurements of organic carbon and total nitrogen confirmed organic enrichment within the anthrosol. Evaluations of elemental ratios distinguished the anthrosol from the unimpacted soil locations by a 50% higher average C:P ratio and a two-fold higher average C:N ratio of its residual organic fraction which declined exponentially with depth. Combining C, N and organic P data yielded a robust tracer for distinguishing anthropogenic organic matter enrichment from naturally occurring deposition through all soil levels examined at this prehistoric site. Profiles of organic matter C:OP and C:N ratios indicated that C enrichment occurred well below the stratigraphically defined anthrosol boundary indicating site habitation prior to the anthrosol deposition. This contention of earlier site usage was supported by comparison of depth profiles of C:OP ratios with lithic debitage density profiles. Significant correlations between C:OP ratios and lithic debitage density suggested that C enrichment relative to OP may be a useful indicator of habitation and may yield insight into intra-site variation in the intensity of land use.
Chemical Geology, 2000
Chemical stratification occurs in the water columns and sediments of many aquatic habitats result... more Chemical stratification occurs in the water columns and sediments of many aquatic habitats resulting in vertical chemical and redox gradients. Various types of microorganisms are often associated with specific depths and chemical parameters in these situations. For example, magnetite-producing magnetotactic bacteria are known to form horizontal "plates" of cells at the oxic/anoxic transition zone (OATZ) of such environments. Here, we report the presence of populations of diverse magnetic protists in a seasonally chemically stratified, coastal salt pond. The protistan types included several biflagellates, a dinoflagellate, and a ciliate that were each associated with specific depths and thus, specific chemical, microbiological and redox conditions in the water column. Most cells contained crystals of magnetite usually arranged in chains similar to the magnetosomes in the magnetotactic bacteria. The origin of the particles is unknown. There was no evidence of the presence of endosymbiotic magnetotactic bacteria within the protists nor were the protists observed to be engulfing magnetotactic bacteria despite the fact that high numbers of the latter were present at the same depths as the protists. However, this does not exclude ingestion of magnetotactic bacteria as a source of the magnetic particles while others may biomineralize magnetite. Because protists play an important role in the availability of iron for phytoplankton in marine waters by ingesting and reducing colloidal iron particles, the protists described here could playa significant role in iron cycling in chemically stratified anoxic basins, either through endogenous production of magnetic iron oxide and/or iron sulfide particles, or by ingestion of magnetotactic bacteria and the subsequent reduction and dissolution of iron oxide and/or sulfide particles in their magnetosomes.
Journal of Archaeological Science, 2000
Human occupation enriches soils with phosphorus, which may provide a useful chemical tracer for s... more Human occupation enriches soils with phosphorus, which may provide a useful chemical tracer for site delineation in archaeological studies. In the present study, fine scale soil profiles of inorganic, particulate organic and total phosphorus through a prehistoric Indian site and nearby control site in Cape Cod, MA, indicated a greater predictive value of particulate organic P over inorganic P and total P in determining the vertical boundaries of an anthrosol. The value of inorganic P and total P as occupation tracers was confounded by vertical migration of inorganic P species. Inorganic P mobility was found to result from diagenesis and other post-depositional alterations, including the effects of recent sea water flooding on soil concentrations of dominant exchangeable cations. Parallel measurements of organic carbon and total nitrogen confirmed organic enrichment within the anthrosol. Evaluations of elemental ratios distinguished the anthrosol from the unimpacted soil locations by a 50% higher average C:P ratio and a two-fold higher average C:N ratio of its residual organic fraction which declined exponentially with depth. Combining C, N and organic P data yielded a robust tracer for distinguishing anthropogenic organic matter enrichment from naturally occurring deposition through all soil levels examined at this prehistoric site. Profiles of organic matter C:OP and C:N ratios indicated that C enrichment occurred well below the stratigraphically defined anthrosol boundary indicating site habitation prior to the anthrosol deposition. This contention of earlier site usage was supported by comparison of depth profiles of C:OP ratios with lithic debitage density profiles. Significant correlations between C:OP ratios and lithic debitage density suggested that C enrichment relative to OP may be a useful indicator of habitation and may yield insight into intra-site variation in the intensity of land use.