Trace element variations in ancient cave speleothems are often interpreted as indicators of changes in paleo-rainfall and hydrologic conditions. However, these records are difficult to interpret ...without an understanding of the physicochemical controls on stalagmite chemistry plus site-specific calibration of changes in net rainfall to variations in dripwater and speleothem chemistry. In this study we examine geochemical relationships between net rainfall (Precipitation minus Evapotranspiration; P−ET), drip rates, drip water chemistry, and contemporaneous calcite chemistry to test the hypothesis that speleothem Mg/Ca and Sr/Ca records are proxies for rainfall amount.
HRC is contained within four low-magnesium limestone units capped sporadically by a remnant dolomitic limestone. Aqueous concentrations of magnesium (post evapotranspiration) decrease with increasing vertical travel distance between the soil zone and the point of in-cave drip emergence (Drip Path Length – DPL) as dissolved high-Mg solutions sourced from the dolomitic caprock are diluted with dissolved low-Mg limestone waters sourced from the host limestone. Dripwater Mg/Ca and Sr/Ca ratios covary and provide diagnostic indicators of the two dominant mechanisms controlling dripwater chemistry: (1) mixing of post-evaporative solutions derived from two geochemical endmembers (dissolution of dolomite and limestone); and (2) evolution of hydrochemistry away from dissolved bedrock compositions due to Prior Calcite Precipitation (PCP) above the drip sites. By resolving the linear mixing relationships for drip water Mg/Ca and Sr/Ca sources and the distribution coefficients for trace element transfer in the PCP dripwater-to-calcite precipitation reactions and applying these principles to our time series, we find that the extent of PCP production within the karst is directly controlled by the balance between Precipitation (P) and Evapotranspiration (ET): higher net rainfall (P−ET>1: wet conditions) reduces PCP, and lower net rainfall with increased evapotranspiration (P−ET<1) increases PCP.
Farmed calcite X/Ca ratios faithfully track hydrologically-influenced seasonal variations in dripwater chemistry for X=Mg, Sr, and Na. However, the relationship between changes in net rainfall and changes in Mg/Ca and Sr/Ca ratios in modern calcite is unique at each site and differs significantly at closely-spaced drip/stalagmite locations. This suggests that in situ modern hydrochemical calibrations should be performed atop individual speleothems prior to harvesting for paleoclimate investigations, and that such calibrations may not reflect past conditions as drip paths change. We apply this understanding to published dripwater data and speleothem time series from other caves. A major implication is that in order to interpret stalagmite Sr/Ca and Mg/Ca ratios as ‘wet vs. dry’ proxies, speleothem Sr/Ca and Mg/Ca variations must be coherent and in-phase over all time periods (i.e., Sr/Mg ratios must be constant). These criteria will help to distinguish ‘rainfall amount’ versus ‘rainfall source’ in speleothem δ18O records.
Soil contamination in urban environment by trace metals is of public concerns. For better risk assessment, it is important to determine their background concentrations in urban soils. For this study, ...we determined the background concentrations of 9 trace metals including As, Ba, Cd, Co, Cu, Ni, Pb, Se, and Zn in 214 urban soils in Florida from two large cities (Orlando and Tampa) and 4 small cities (Clay County, Ocala, Pensacola and West Palm Beach). The objectives were to determine: 1) total concentrations of trace metals in urban soils in cities of different size; 2) compare background concentrations to Florida Soil Cleanup Target Levels (FSCTLs); and 3) determine their distribution and variability in urban soils via multivariate statistical analysis. Elemental concentrations in urban soils were variable, with Pb being the highest in 5 cities (165–552 mg kg−1) and Zn being the highest concentration in Tampa (1,000 mg kg−1). Besides, the As and Pb concentrations in some soils exceeded the FSCTL for residential sites at 2.1 mg kg−1 As and 400 mg kg−1 Pb. Among the cities, Clay County and Orlando had the lowest concentrations for most elements, with Cd, Co, and As being the lowest while Ba, Pb and Zn being the highest. Among all values, geometric means were the lowest while 95th percentile was the highest for all metals. Most 95th percentile values were 2–3 folds higher than the GM data, with Pb presenting the greatest difference, being 4 times greater than GM value (58.9 vs. 13.6 mg kg−1). Still they were lower than FSCTL, with As exceeding FSCTL for residential sites at 2.1 mg kg−1. In addition, the linear discriminate analysis showed distinct separation among the cities: Ocala (Ba & Ni) and Pensacola (As & Pb) were distinctly different from each other and from other cities with higher metal concentrations. The large variations among elemental concentrations showed the importance to establish proper background concentrations of trace metals in urban soils.
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•Background concentrations of 9 trace elements in 214 urban soils were determined.•Arithmetic and geometric mean, 95th percentile and upper confidence level were calculated.•Regardless city size, human activities had similar impacts on elemental concentrations.•As, Ba, Cr and Pb levels exceeded Florida Soil Cleanup Target Levels for residential sites.•Among all values, GM was the lowest while 95th percentile was the highest.
Large concentration variations showed the importance to establish proper background concentrations of trace metals in urban soils.
Many of Florida’s large springs have seen an order of magnitude increase in nitrate concentration since the mid-twentieth century, which has contributed to the proliferation of nuisance algae and ...alteration of spring ecosystems. Cost-effective strategies to limit nitrate inputs require identification of contributing land areas within springs (springsheds) where surficial nitrogen sources are most likely to be transported to the underlying aquifer. To address spatial variability in vulnerability to nitrogen loading, spatial models specific to nitrate were developed for the Silver Springs springshed (Florida, USA). Random forest classification models were trained using an extensive (1554 wells) groundwater nitrate dataset assembled from public water system and agency monitoring data. Spatial layers representing soil hydrology, subsurface geology, recharge potential, and nitrogen sources were used as predictor variables. Random forest models produced out-of-bag error estimates of 21% or less, and variable importance plots indicated that a subset of subsurface geological predictors was the most important contributors to overall model accuracy. Although predictors representing land use and nitrogen sources contributed less to overall model accuracy, they were still important in the final spatial discrimination of the most vulnerable areas. Random forest model accuracy was further improved by kriging of model residuals, and kriged residuals were added to model estimates to produce final prediction maps. The models developed are well suited for a management decision framework for environmental restoration, as it informs the manager with maps of probabilistic information. Recognizing the potential for legacy nitrate impacts, we recommend the current models be adopted as a part of a tiered approach to restoration projects that first prioritizes critical areas using the models presented herein and subsequently uses site-specific information to verify local impacts.
•Novel in situ measurements of groundwater fluxes in rock matrix and conduit zones.•Simple analytical solutions to identify flow contribution from conduit vs matrix.•Tested in Silver Springs, one of ...the largest springs in the world.•Conduits were a small fraction of the aquifer cross-sectional area.•Conduits contributed between 75 and 96% of the total groundwater flow.
Groundwater flow discharging to springs from carbonate aquifers is governed by the interaction of slow matrix flow and fast fracture/conduit flow, which creates highly complex flow and transport conditions. An important unknown is the relative contribution of matrix and conduit flow to the total discharge. This study experimentally investigated groundwater fluxes in the Floridan aquifer within the springshed of Silver Springs, FL, one of the largest freshwater springs in the world with mean discharge of approximately 20 m3/s. Using in situ passive flux meters (PFMs, n = 48 at 16 wells) and a new karstic borehole dilution (KBHD, n = 21 at 7 wells) technique we measured groundwater fluxes in rock matrix and non-matrix (conduit and fracture) zones of 0.06 ± 0.003 m/day and 3.05 ± 1.8 m/day (mean ± standard error). These data, combined with previously conducted tracer tests (n = 12 at 3 sites), were coupled with simple analytical and numerical solutions to identify the proportion of the aquifer that contributes most significantly to water flow to the spring with three different modeling scenarios: single domain, dual domain including matrix and non-matrix zones, and triple domain including matrix, fracture, and conduit zones. The analytical and numerical models coupled with the in situ measured fluxes for the dual and triple domain scenarios showed good agreement with measured head profiles (Nash-Sutcliffe E > 0.90), when compared to the homogeneous porous domain scenario (E = −1.84). Conduit and fracture zones were estimated to represent between 2% and 22% of the aquifer cross-sectional area (at radial distance of 3 km from the spring outlet), yet these zones contributed between 75 and 96% of the total groundwater flow. The results of this study offer field-measured hydrogeologic data that can be used for active resource management in springsheds, and the simple modeling approach presented here may be applicable to other springsheds with fairly simple geometry to estimate the relative contributions of fast and slow water flow and solute transport pathways to the spring outlet.
Lethal Punishment Vandiver, Margaret
2005, 20051222, 2005-12-22
eBook
Why did some offenses in the South end in mob lynchings while similar crimes led to legal executions? Why did still other cases have nonlethal outcomes? In this well-researched and timely book, ...Margaret Vandiver explores the complex relationship between these two forms of lethal punishment, challenging the assumption that executions consistently grew out of-and replaced-lynchings.
Vandiver begins by examining the incidence of these practices in three culturally and geographically distinct southern regions. In rural northwest Tennessee, lynchings outnumbered legal executions by eleven to one and many African Americans were lynched for racial caste offenses rather than for actual crimes. In contrast, in Shelby County, which included the growing city of Memphis, more men were legally executed than lynched. Marion County, Florida, demonstrated a firmly entrenched tradition of lynching for sexual assault that ended in the early 1930s with three legal death sentences in quick succession.
With a critical eye to issues of location, circumstance, history, and race, Vandiver considers the ways that legal and extralegal processes imitated, influenced, and differed from each other. A series of case studies demonstrates a parallel between mock trials that were held by lynch mobs and legal trials that were rushed through the courts and followed by quick executions.
Tying her research to contemporary debates over the death penalty, Vandiver argues that modern death sentences, like lynchings of the past, continue to be influenced by factors of race and place, and sentencing is comparably erratic.
Stable oxygen (δ18O) and carbon (δ13C) isotope values from fossil tooth enamel can be used to better understand mammalian responses to changing climates and impacts of increasing evaporative ...conditions on the diets of Pleistocene taxa. Previous work demonstrated dietary modification in response to interglacial warming; however, it is difficult to know if these changes resulted from changing climates, alterations of their habitat, or both. Here, we further investigate the influences of increasing evaporative conditions and changing vegetation on diets using oxygen and carbon isotopes from medium- to large-bodied herbivores from Pleistocene sites in Florida (Haile 8A, Tri-Britton, Leisey Shell Pit 1A, Inglis 1A). Bulk and serial stable isotope values indicate that Tri-Britton was the warmest and driest site with forests and C4 grasslands, and may have been able to support closely related taxa (e.g. multiple peccaries and camelids). In contrast to Tri-Briton and Leisey Shell Pit 1A, Haile 8A was the wettest site and may have represented a transitional climate. The diets of Hemiauchenia, Platygonus, and Mylohyus changed from browsing (Inglis 1A, Haile 8A) to mixed feeding (Leisey Shell Pit 1A, Tri-Britton), potentially in response to warmer temperatures and/or more arid environments. Mammut, Odocoileus, and Palaeolama maintained primarily C3 diets at all sites; however, δ13C values were greatest at Leisey Shell Pit 1A and Tri-Britton. Tapirus and Equus also had significantly greater δ13C values at Tri-Britton as compared to other sites, further suggesting more evaporative conditions. With higher temperatures and/or increased aridity, dietary generalists modified their diets more than specialists, often including a greater proportion of C4 vegetation than during cooler and/or wetter periods. Collectively, these data suggest that increased evaporative conditions during the Pleistocene may have contributed to a broader range of diets in generalist herbivores when compared to dietary specialists.
•Stable carbon and oxygen isotopes of Pleistocene mammals in Florida were analyzed.•δ18O and aridity index values can be used to reconstruct paleoclimates in Florida.•More arid conditions likely supported more open habitats with C4 vegetation.•Sites with diverse habitats may have allowed for the presence of confamilies.•Dietary modification is only documented in dietary generalists.
This study aimed to resolve the taxonomy of cassid gastropods from the upper Eocene Ocala Limestone based on specimens collected from Florida Museum of Natural History locality AL004. In 1890, Dall ...described a specimen from this formation, collected in a nearby county as Phalium globosum (subfamily Phaliinae). However, further collection of cassids from AL004 suggested the presence of more than one morphologically distinct taxon. Eocene cassids are particularly interesting because that is presumably the time when cassids experienced rapid diversification, which has implications for the evolutionary history of echinoid-cassid predator-prey interactions. Based on 75 specimens from AL004, it appears that the specimens interpreted as belonging to two or more morphologically distinct taxa are more likely members of a single species with extreme morphological variability, redescribed here as Semicassis globosum. Results of morphometric analyses using nine qualitatively defined cassid morphotaxa (subfamily Phaliinae) suggest that S. globosum is characterised by high intraspecific variability in shell morphology that may reflect high ecophenotypic variability or elevated intraspecific genetic variability. This study highlights the challenges associated with delineating species status using low numbers of specimens, as a dearth of diagnostic material may lead to taxonomic "over-splitting," thereby resulting in an inflated estimate of biodiversity.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
•The Upper Floridan aquifer terrain can be modeled using karst dissolution chemistry.•The model is able to predict the age of the conduit based on initial conditions.•Karst model can represent ...observed head profiles more accurately than one-dimensional groundwater leakage model.
The Floridan aquifer consists of a high presence of karst features that make the landscape prone to sinkholes. Karst conduits can conduct high amounts of water and affect processes such as groundwater transport. A karst conduit evolution model based on dissolution chemistry is applied to the Silver Springs springshed in Ocala, Florida. The model is able to reproduce the observed potentiometric head profiles more accurately than the one-dimensional groundwater flow model for confined aquifer with leaky conditions. In addition, based on the initial fracture geometry and dissolution chemistry, the model predicts the age of the conduits from the analyzed head profiles to be approximately 9–60 Myrs old. The understanding of the karst conduit geometric evolution and mapping can improve conduit age prediction as well as better characterize conduit flow patterns and subsequent groundwater processes.
Shallow-water carbonate deposits are well-known from the Eocene of the US Gulf Coast and Caribbean. These deposits frequently contain abundant larger benthic foraminifera (LBF). However, whilst ...integrated stratigraphic studies have helped to refine the timing of LBF overturning events within the Tethys and Indo-Pacific regions with respect to global bio- and chemo-stratigraphic records, little recent work has been carried out in the Americas. The American LBF assemblages are distinctly different from those of Europe and the Indo-Pacific. It is therefore essential that the American bio-province is included in studies of LBF evolution, biodiversity and climate events to understand these processes on a global scale. Here we present the LBF ranges from two previously unpublished sections spanning 35 and 29 m of the upper Eocene Ocala limestone, as the early stages of a larger project addressing the taxonomy and biostratigraphy of the LBF of Florida. The study indicates that the lower member of the Ocala limestone may be Bartonian rather than Priabonian in age, with implications for the biostratigraphy of the region. In addition, the study highlights the need for multiple sites to assess the LBF assemblages and fully constrain ranges across Florida and the US Gulf and suggests potential LBF events for future integrated stratigraphic study.
•Flow and transport in evolving carbonate aquifer.•Enlargement of sub-surface fractures and pores by chemical dissolution.•Application to field site.
The removal of material in soluble rocks by ...physical and chemical dissolution is an important process enhancing the secondary porosity of soluble rocks. Depending on the history of the soluble rock, dissolution can occur either along fractures and bedding partings of the rock in the case of a telogenetic origin, or within the interconnected pore space in the case of eogenetic origin. In soluble rocks characterised by both fractures and pore space, dissolution in both flow compartments is possible.
We investigate the dissolution of calcite both along fractures and within the pore space of a limestone rock by numerical modelling. The limestone rock is treated as fractured, porous aquifer, in which the hydraulic conductivity increases with time both for the fractures and the pore spaces.
We show that enlargement of pore space by dissolution will accelerate the development of a classical fracture-dominated telogenetic karst aquifer, breakthrough occurs faster. In the case of a pore-controlled aquifer as in eogenetic rocks, enlargement of pores results in a front of enlarged pore spaces migrating into the karst aquifer, with more homogeneous enlargement around this dissolution front, and later breakthrough.
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