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  • Articles  (16)
  • paleolimnology  (14)
  • Florida  (2)
  • Reduction of NO  (2)
  • Springer  (16)
  • 1
    Electronic Resource
    Electronic Resource
    Reduction of NO by CO on PdO-MoO3/γ-Al2O3 of low molybdena loading (1992)
    Springer
    Catalysis letters 16 (1992), S. 311-321 
    Details
    ISSN: 1572-879X
    Keywords: Reduction of NO ; PdO catalysts ; MoO3 catalysts ; bimetallic catalysts ; PdO-MoO3 ; catalysts ; automotive catalysts ; automotive pollution control ; NO x
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic activity for the reduction of NO by CO of five PdO-MoO3/γ-Al2O3 catalysts is compared in the presence of varying amounts of oxygen at reaction temperatures from 25 to 550 °C. The samples were prepared by different methods and contain about 2% of Mo and 2% Pd. Results are compared with the activities and selectivities of PdO/ γ-A12O3 and PdO-MoO3/γ-Al2O3 containing 2% Pd and 2% Pd + 20% Mo, respectively. All catalysts showed appreciable activity at temperatures between 300 and 550 °C and at stoichiometric ratios,R, of the oxidizing to reducing gases of 0.1 〈R 〈 1.1. The activity of three PdO-MoO3/ γ-A12O3 catalysts with low concentrations of Mo and Pd was found to be significantly higher than the activity of PdO/γ-Al2O3 at 1.1 〈R 〈 1.3 and at temperatures between 300 and 500 °C. The improved activity is ascribed to the interaction of the active metals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764343
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  • 2
    Electronic Resource
    Electronic Resource
    Reduction of NO by H2 on PdO-MoO3/γ-Al2O3 of low molybdena loading (1993)
    Springer
    Catalysis letters 18 (1993), S. 289-297 
    Details
    ISSN: 1572-879X
    Keywords: Reduction of NO ; NO x ; PdO-MoO3 catalysts ; pollution abatement ; automotive catalysts ; mixed metal catalysts ; MoO3 catalysts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic activity and selectivity of three PdO-MoO3/γ-Al2O3 catalysts containing about 2% Pd and 2% Mo were studied for the reduction of NO by h2 in the presence of varying amounts of oxygen at temperatures from 50 to 550 °C. The results are compared with those for PdO/γ-Al2O3, PdO-MoO3/γ-Al2O3 containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. In the absence of oxygen, the conversion of NO to N2 and N2O is higher on the three catalysts than it is on PdO/γ-Al2O3 at 500 and 550 °C. In the presence of oxygen, the yields of N2 and N2O are generally lower on two of the PdO-MoO3/γ-Al2O3 catalysts than on PdO/γ-Al2O3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00769449
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  • 3
    Electronic Resource
    Electronic Resource
    A multi-proxy study of Holocene environmental change in the Maya Lowlands of Peten, Guatemala (1998)
    Springer
    Journal of paleolimnology 19 (1998), S. 139-159 
    Details
    ISSN: 1573-0417
    Keywords: geochemistry ; Guatemala ; Holocene ; lakesediment ; Maya ; magnetic susceptibility ; paleolimnology ; pollen ; stable isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We used multiple variables in a sediment core from Lake Peten-Itza, Peten, Guatemala, to infer Holocene climate change and human influence on the regional environment. Multiple proxies including pollen, stable isotope geochemistry, elemental composition, and magnetic susceptibility in samples from the same core allow differentiation of natural versus anthropogenic environmental changes. Core chronology is based on AMS 14C measurement of terrestrial wood and charcoal and thus avoids the vagaries of hard-water-lake error. During the earliest Holocene, prior to ∼9000 14C yr BP, the coring site was not covered by water and all proxies suggest that climatic conditions were relatively dry. Water covered the coring site by ∼9000 14C yr BP, coinciding with filling of other lakes in Peten and farther north on the Yucatan Peninsula. During the early Holocene (∼9000 to ∼6800 14C yr BP), pollen data suggest moist conditions, but high δ 18O values are indicative of relatively high E/P. This apparent discrepancy may be due to a greater fractional loss of the lake's water budget to evaporation during the early stages of lake filling. Nonetheless, conditions were moist enough to support semi-deciduous lowland forest. Decrease in δ 18O values and associated change in ostracod species at ∼6800 14C yr BP suggest a transition to even moister conditions. Decline in lowland forest taxa beginning ∼5780 14C yr BP may indicate early human disturbance. By ∼2800 14C yr BP, Maya impact on the environment is documented by accelerated forest clearance and associated soil erosion. Multiple proxies indicate forest recovery and soil stabilization beginning ∼1100 to 1000 14C yr BP, following the collapse of Classic Maya civilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007968508262
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  • 4
    Electronic Resource
    Electronic Resource
    A simple, inexpensive piston corer for collecting undisturbed sediment/water interface profiles (1992)
    Springer
    Journal of paleolimnology 7 (1992), S. 157-161 
    Details
    ISSN: 1573-0417
    Keywords: coring device ; paleolimnology ; sediments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196870
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  • 5
    Electronic Resource
    Electronic Resource
    Recent sedimentary histories of shallow lakes in the guatemalan savannas (1990)
    Springer
    Journal of paleolimnology 4 (1990), S. 239-252 
    Details
    ISSN: 1573-0417
    Keywords: Guatemala ; paleolimnology ; pollen ; 210Pb ; savannas ; sediment geochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Shallow basins in the savannas of Peten, Guatemala filled with water after 305±55 BP (calibrated age+1430–1660 AD). Aguadas Chimaj and Chilonche possess dilute waters and iron-rich, clayey sediments that are poor in Ca and Mg, reflecting the highly weathered nature of riparian soils. Low 210Pb flux rates to Chimaj (0.085 pCi cm-2 yr-1) and Chilonche (0.134 pCi cm-2 yr-1) are attributed to low 222Rn emission rates from the nearby Caribbean Sea. Mean sediment accumulation rates in Chimaj and Chilonche for the past 150 years are 0.015 g cm-2 yr-1 and 0.047 g cm-2 yr-1 respectively. Forest expansion after 305 BP is documented in pollen profiles from the small aguadas and larger Lake Oquevix. Regional reforestation postdates the 9th century Classic Maya collapse and coincides with indigenous depopulation that was a consequence of European intrusion that began in the early 1500s. The timing of forest regrowth indicates the importance of historical anthropogenic factors in controlling Peten's vegetation. Nevertheless, other sedimentological lines of evidence (e.g. lithology, algal remains and charcoal particles) suggest that changing climate and/or local hydrology may have played a role in the reforestation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239697
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  • 6
    Electronic Resource
    Electronic Resource
    A sedimentary record of human disturbance from Lake Miragoane, Haiti (1988)
    Springer
    Journal of paleolimnology 1 (1988), S. 85-97 
    Details
    ISSN: 1573-0417
    Keywords: land-water interactions ; limnology ; paleolimnology ; 210Pb ; sediment geochemistry ; West Indies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Lake Miragoane, Haiti is one of the largest, natural freshwater lakes in the Caribbean (A=7.06 km2, zmax=41.0 m, conductivity = 350 μS cm−1). Lake waters are dominated by calcium and bicarbonate ions. The lake was thermally stratified, and oxygen profiles were clinograde during summer visits in 1983 and 1985. A 72-cm mud-water interface core was taken near the center of the lake and dated with 210Pb. The local 210Pb fallout rate is low (0.09 pCi cm−2 yr−1), about 20% of the global average. Bulk sedimentation rates ranged from 0.008 to 0.030 g cm−2 yr−1 during the past 130 years (0–8 cm depth). Sediment geochemistry and pollen have been analyzed in the topmost 58 cm of the section. Tentative ages were assigned to the core by extrapolation of 210Pb dates. According to this preliminary chronology, the bottom part of the core (58–30 cm) records pre-Columbian sedimentation (1000–500 B.P.) and contains pollen evidence of intact, dry and mesic forest. Pre-Columbian deposits are rich in organic matter (x = 30%) and relatively poor in carbonates (x = 15% as CO2). The top 30 cm of the core preserve the record since European contact (500 B.P. to present). Pollen data reveal two episodes of deforestation following European arrival. Consequent soil erosion is documented by a decrease in organic matter content (x = 15%) and an increase in carbonates (x = 27% as CO2). Surficial sediments reflect the widespread deforestation and soil loss that characterize the watershed today.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196066
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  • 7
    Electronic Resource
    Electronic Resource
    Low-background gamma counting: applications for210Pb dating of sediments (1994)
    Springer
    Journal of paleolimnology 10 (1994), S. 115-128 
    Details
    ISSN: 1573-0417
    Keywords: radiometric ; chronology ; 210Pb ; 226Ra ; 137Cs ; Lake ; paleolimnology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Sediment cores from three lakes were dated with210Pb using a constant rate of supply (CRS) model. We used low-background gamma counting to measure naturally occurring levels of210Pb,226Ra, and137Cs in sediment samples because sample preparation is simple and non-destructive,226Ra activity provides a direct measure of supported210Pb activity for each sample analyzed, and137Cs activity may provide an independent age marker for the 1962–1963 peak in atmospheric fallout of this radionuclide. In one core supported210Pb activity was estimated equally well from226Ra activity of each sampling interval or from the mean total210Pb activity of constant activity samples at depth. Supported210Pb activity was constant with depth in this core. In a short freeze core, determining226Ra activity of every sample proved advantageous in estimating supported210Pb activity because supported210Pb activity could be estimated from210Pb measurements only at the deepest sampling interval. Supported210Pb activity estimated from226Ra activity also yielded more precise estimates of highly variable sedimentation rates. In the third core226Ra activity exceeded210Pb activity at the top of the core and varied 20 fold with depth. This high input of226Ra in disequilibrium with210Pb is attributed to recent erosion of radium-bearing materials in the drainage basin. These data invalidate the assumption that supported210Pb activity is constant in sediment cores and can be estimated from the mean total210Pb activity at depths where210Pb activity is constant. We recommend using gamma counting or another independent assay of226Ra to validate the assumption of constant supported210Pb activity in sediment cores if there is reason to expect that226Ra activity varies with depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00682508
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  • 8
    Electronic Resource
    Electronic Resource
    A multi-proxy trophic state reconstruction for shallow Orange Lake, Florida, USA: possible influence of macrophytes on limnetic nutrient concentrations (1999)
    Springer
    Journal of paleolimnology 21 (1999), S. 215-233 
    Details
    ISSN: 1573-0417
    Keywords: Florida ; geochemistry ; 210Pb dating ; macrophytes ; nutrients ; paleolimnology ; sediments ; shallow lakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We retrieved four sediment cores from shallow, eutrophic, macrophyte-dominated Orange Lake (A = 51.4 km2, zmax 〈5 m, zmean 〈 2 m), north-central Florida, USA. The 210Pb-dated profiles were used to evaluate spatial and temporal patterns of bulk sediment and nutrient accumulation in the limnetic zone and to infer historical changes in lake trophic state. Bulk density, organic matter, total carbon, total nitrogen, total phosphorus and non-apatite inorganic phosphorus (NAIP) concentrations displayed stratigraphic similarities among three of four cores, as did accumulation rates of bulk sediment, organic matter and nutrients. Accumulation rates were slower at the fourth site. Nutrients showed generally increasing rates of accumulation since the turn of the century. Percentages of periphytic diatom taxa increased progressively in the cores after ~ 1930. Diatom-inferred limnetic total P trends were similar among profiles. Eutrophic conditions were inferred for the period prior to the turn of the century. The lake was hypereutrophic in the early decades of the 1900s, but inferred limnetic total P values declined after ~ 1930. Declining inferred limnetic total P trends for the last 60--70 years were accompanied by concomitant increases in accumulation rates of total P and NAIP on the lake bottom. Several lines of evidence suggest that after ~ 1930, phosphorus entering Orange Lake was increasingly utilized by submersed macrophytes. Paleolimnological records from Orange Lake highlight the importance of using multiple sediment variables to infer past trophic state and suggest that aquatic macrophytes can play a role in regulating water-column nutrient concentrations in shallow, warm-temperate lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008079500375
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  • 9
    Electronic Resource
    Electronic Resource
    Highly variable sediment distribution in shallow, wind-stressed lakes: a case for sediment-mapping surveys in paleolimnological studies (1996)
    Springer
    Journal of paleolimnology 15 (1996), S. 207-221 
    Details
    ISSN: 1573-0417
    Keywords: sediments ; paleolimnology ; sediment distribution ; sediment mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We examine sediment distribution patterns in seven Florida lakes and discuss implications for paleolimnological studies of shallow, subtropical lakes. The study lakes are highly productive and should exhibit thick organic sediment deposits, but organic sediments are often grossly lacking because basins are shallow, and frequent mixing, lack of stratification, and warm temperatures lead to breakdown of organic material. Organic sediment distribution patterns are highly variable. We observe three types of distribution patterns. When organic sediments are abundant, there may be (1) uniform sediment distribution. In lakes lacking organic sediments, there are (2) distribution to deeper areas if present, or (3) distribution to peripheral areas and embayments when deep waters are absent. We advocate the use of systematic mapping surveys to locate optimal coring sites for paleolimnological studies of shallow, wind-stressed lakes. Because numerous factors affect diagenesis and sediment redistribution, sediment abundance and location are not predictable. Sediment chronologies may be discontinuous and disturbed even in accumulation zones. The extent to which sedimentary records are discontinuous or disturbed is not quantifiable in any practical manner. 210Pb and 137Cs radioisotopic profiles provide qualitative evidence of the degree of stratigraphic disturbance. Total excess 210Pb inventories show that sediments are focused into depositional zones when sediment distribution is uneven. Excess 210Pb inventories are not informative about the completeness of sedimentary profiles unless small inventories suggest discontinuous sedimentation or erosional events. We present examples of disturbed and undisturbed profiles, and discuss how we use radioisotopic and geochemical evidence, and multiple cores to assess stratigraphic continuity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00213041
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  • 10
    Electronic Resource
    Electronic Resource
    Paleolimnological evaluation of historical trophic state conditions in hypereutrophic Lake Thonotosassa, Florida, USA (1996)
    Springer
    Hydrobiologia 331 (1996), S. 143-152 
    Details
    ISSN: 1573-5117
    Keywords: diatoms ; lake management ; paleolimnology ; sediments ; trophic state ; water quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We used paleolimnological methods to evaluate historical water quality in Lake Thonotosassa, Hillsborough County, Florida, USA. Sediment mapping shows that organic deposits are unevenly distributed in the lake. Two short (〈130 cm) sediment cores from the depositional zone were analyzed for radioisotopes (210Pb, 226Ra, and 137Cs), bulk density, organic matter concentration, nutrients (C,N,P), and diatoms. 210Pb results indicate that the profiles represent 〉 100 years of sediment accumulation. There is an abrupt change in sediment composition at about the turn of the century (∼80 cm depth), above which bulk density decreases and concentrations of organic matter, total C, total N, total P, and 226Ra activity increase. Diatom-based reconstructions of historical water-column trophic conditions indicate progressive nutrient enrichment in the lake during the past ∼100 years. Stratigraphic changes in diatom assemblages suggest that anthropogenic nutrient loading converted Lake Thonotosassa from a naturally eutrophic system to a hypereutrophic waterbody after ∼1900. Given the edaphic setting of Lake Thonotosassa, efforts to mitigate recent anthropogenic impacts will, at best, yield the eutrophic conditions that characterized the lake prior to human disturbance. This study illustrates the importance of paleolimnological data for targeting realistic water quality conditions when lake restoration is contemplated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00025415
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