Density separation of clay minerals

Illite, chlorite, montmorillonite and kaolinite, as well as natural marine sediments and mixtures of the standards were subjected to density separation by centrifugation in a linear heavy-liquid gradient. The density layers yielded by centrifugation were recovered and analyzed by X-ray diffraction. Separates were not monomineralic but rather were polymineralic usually with minerals of invarient density, such as quartz, in more than one layer. This incomplete separation is attributed to insufficient centrifugation time. The X-ray character of minerals of variable density changes in such a way as to suggest increased crystallinity with depth in the density gradient. Although several samples were known to contain montmorillonite, none of the density layers showed X-ray evidence of this material. The anomalous behavior of montmorillonite is attributed to its imbibing of the polar organic chemicals used as surfactants into its expandable crystal structure to produce an extremely large basal spacing. This problem can be overcome in some cases by heating the clay to 110°C for 8 hours, but in other cases this had little or no effect in collapsing the expanded structure. Even though the project was not a total success, the method holds promise, providing the duration and intensity of the centrifugation is increased and complete purging of polar organic molecules from expandable layered clays can be accomplished

Benthic Foraminifera from the NECOP Study Area Impacted by the Mississippi River Plume and Seasonal Hypoxia

Benthic foraminifera influenced by the Mississippi River plume and seasonal hypoxia were assessed from Louisiana inner-continental shelf sediment samples. Surface foraminifera assemblages were representative of in-situ populations as established by staining techniques. Community diversity and richness/evenness analyses indicate three regimes: high stress (sediment dominated), intermediate stress (hypoxia dominated), and low stress (low sediment accumulation/high oxygen). Epistominella vitrea and Buliminella morgani are useful tracers of rapid sediment accumulation rate and hypoxia. A bottom-water productivity signal west of the Mississippi River plume is indicated by benthic and planktic foraminifera abundance peaks. Surface benthic foraminifera trends are utilized to interpret changes in historical community structure from hypoxic-area sediments deposited since the turn of the century. The hypoxia-tolerant species Buliminella morgani increases markedly upcore, while hypoxia intolerant species decrease or disappear. Diversity and dominance trends temporally correspond to a dramatic increase in U.S. fertilizer application. The results of this study have application to paleoenvironmental research spanning longer geologic timescales. The documented relationships between population structure and stressors in river-dominated marine systems may provide a useful analog for recognition of these conditions in the fossil record

Benthic foraminifera from the NECOP study area impacted by the Mississippi River plume and seasonal hypoxia

Benthic foraminifera influenced by the Mississippi River plume and seasonal hypoxia were assessed from Louisiana inner-continental shelf sediment samples. Surface foraminifera assemblages were representative of in-situ populations as established by staining techniques. Community diversity and richness/evenness analyses indicate three regimes: high stress (sediment dominated), intermediate stress (hypoxia dominated), and low stress (low sediment accumulation/high oxygen). Epistominella vitrea and Buliminella morgani are useful tracers of rapid sediment accumulation rate and hypoxia. A bottom-water productivity signal west of the Mississippi River plume is indicated by benthic and planktic foraminifera abundance peaks. Surface benthic foraminifera trends are utilized to interpret changes in historical community structure from hypoxic-area sediments deposited since the turn of the century. The hypoxia-tolerant species Buliminella morgani increases markedly upcore, while hypoxia intolerant species decrease or disappear. Diversity and dominance trends temporally correspond to a dramatic increase in U.S. fertilizer application. The results of this study have application to paleoenvironmental research spanning longer geologic timescales. The documented relationships between population structure and stressors in river-dominated marine systems may provide a useful analog for recognition of these conditions in the fossil record

A Century of Environmental Variability in Oyster Bay Using Ostracode Ecological and Isotopic Data as Paleoenvironmental Tools

Stable isotopic analysis (δ 18O and δ13C) and characterization of the ostracode community structure were carried out from a high-resolution sediment-core recovered from Oyster Bay in the west of the Everglades National Park. Because of its location, between the Shark River Slough (SRS) and the Gulf of Mexico, the Oyster Bay core locality experiences extreme salinity fluctuations due to the interaction of freshwater run-off, precipitation, and marine water inputs. Ostracode population dynamics and isotopic variability over the 20th century are linked to natural and anthropogenic forces that affect the South Florida coastal ecosystem on interannual to decadal time scales. Three ostracode assemblages can be recognized within the 100-year sediment-core record: the first extending from the turn of the century to about 1950; the second, from the early 1950s to the late 1970s; and the third to core recovery in 1995. An abrupt decrease in ostracode abundance, species diversity, and shifts in species dominance occur in the mid-1980s and reflect episodes of environmental stress. Markedly enriched δ 18O values from the ostracode Peratocytheridea setipunctata and the benthic foraminifer Ammonia parkinsonia typica at this time are concurrent with a major regional drought in South Florida, as well as with documented algal blooms and major die-off of sea grasses in Florida Bay. In addition, the timing of these events is contemporaneous to the onset of the South Florida Water Management District (SFWMD) Rainfall Plan and the closing of the Buttonwood canal. Higher ostracode abundance and species richness occurs between the late- 1950s and late- 1970s. Stable isotopic data and ostracode assemblage characteristics suggest a period of relative environmental stability and possibly improved water circulation in Whitewater Bay and Oyster Bay. Fluctuations in community structure during this time are more systematic and appear to be temporally correlated to rainfall variability patterns. Water management policies at this time are also discemable from the microfaunal and isotopic record, particularly the Congressionally mandated Monthly Minimum Allocation Plan of water supply to SRS. Before 1950, hurricane events and their effects are the major cause for immediate modifications within the ostracode community, though our data show that ostracode populations are capable of rapid recovery. Over the complete record of the last century, the effects of water management practices can be assessed from information embedded in the ostracode record. Nevertheless, the effects of natural climatic variability in Oyster Bay appear to outweigh the impact of anthropogenic forces

Time-Based Correlation of Biogenic, Lithogenic and Authigenic Sediment Components with Anthropogenic Inputs in the Gulf of Mexico NECOP Study Area

Hypotheses related to variability in seasonal hypoxic conditions, coastal nutrient enhancement, and off-shelf transport of carbon on the Louisiana continental shelf were tested by characterization of biogenic, lithogenic, and authigenic components from two shelf and one Mississippi Canyon sediment cores. The authigenic-phase glauconite occurs above detection limits only in the core from the hypoxic area. A major increase in glauconite concentration was coincident with the onset (≈1940) of the increased use of commercial fertilizers in the United States. In the same hypoxic-area core, benthic foraminifera species diversity decreases upcore from approximately the turn of the century to the present in a manner concurrent with glauconite and fertilizer increases. A subset of opportunistic benthic foraminifera species, known to become more prominent in stressed environments (i.e., hypoxic), increased upcore from ∼52% of the total population at core bottom to ≈90% at core top. These benthic foraminifera population and diversity changes were not apparent in a “control” core outside the area of documented hypoxia. Seaward of the shelf, in the Mississippi Canyon, coincident increases in sediment accumulation rate, percentages of coarse fraction and of organic carbon at core top indicate increased offshelf transport of carbon and other components. Quartz percentages indicate that episodic down-canyon transport has been active to core bottom (prior to the mid 1800s)

Historical Salinity Effects on Microfauna in the Lower Everglades and Florida Bay

as well as documentation of salinity related ostracod valve morphological change are studied. Attention is focused on those species capable of withstanding the greatest salinity fluctuations. Core and surface microfaunal populations at Oyster Bay, Jimmy Key, and First National Bank are compared and contrasted. These three sites comprise distinct environmental regimes with well-documented salinity records. Oyster Bay has experienced the greatest salinity variability of the three sites as well as freshest overall conditions over the last 100 years. At the Jimmy Key site, in the center of the Bay, has experienced higher average salinity with less variability over this period. Taphonomic microfaunal studies routinely utilize population characteristics as a tool for paleoenvironmental reconstruction. This study extends population work to include species and individual-specific characteristics, which may record salinity variability. In addition to the field and core collections we are culturing ostracods to examine isotopic and morphological relationships under controlled conditions. This multi-faceted approach extends our population characterization work to include documentation of physiological response of individuals within the microfaunal populations to documented changes in salinity. This data will extend the use of microfauna as indicators of modern and paleosalinity change

Linkages between the South Florida Peninsula and Coastal Zone: Assessment-Based History of Natural and Anthropogenic Influences

Providing a synthesis of basic and applied research, The Everglades, Florida Bay, and Coral Reefs of the Florida Keys: An Ecosystem Sourcebook takes an encyclopedic look at how to study and manage ecosystems connected by surface and subsurface water movements. The book examines the South Florida hydroscape, a series of ecosystems linked by hydrology in a region of intense human development and profound modifications to the natural environment.The book presents scientific studies in the South Florida Hydroscape, discusses policy and management by government and nonprofit groups, and explores how the whole watershed approach must be used to successfully protect coral reefs. The contributions range from the traditional to the controversial, questioning current management schemes and summarizing the results of state-of-the-art research. Billions of dollars, countless man-hours, and innumerable resources have been spent studying the various South Florida ecosystems and how they are linked. The Everglades, Florida Bay, and Coral Reefs of the Florida Keys: An Ecosystem Sourcebook shows you how the principles learned in this region can be applied to other tropical and subtropical hydroscapes.https://nsuworks.nova.edu/occ_facbooks/1062/thumbnail.jp