Isaac R. Kaplan

Bio: Isaac R. Kaplan is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Kerogen & Organic matter. The author has an hindex of 66, co-authored 181 publications receiving 16889 citations. Previous affiliations of Isaac R. Kaplan include Chevron Corporation & University of California, Berkeley.

The Origin and Distribution of Methane in Marine Sediments

Abstract: Methane has been detected in several cores of rapidly deposited (> 50 m/my) deep sea sediments. Other gases, such as carbon dioxide and ethane, are commonly present but only in minor and trace amounts, respectively. The methane originates predominantly from bacterial reduction of CO2, as indicated by complimentary changes with depth in the amount and isotopic composition of redox-linked pore water constituents: sulfate-bicarbonate and bicarbonate-methane.

Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite.

Abstract: Extraterrestrial abiotic amino acids and hydrocarbons in type II carbonaceous chondrite at Murchison, Australia

Motor exhaust emissions as a primary source for dicarboxylic acids in Los Angeles ambient air

Abstract: Low molecular weight dicarboxylic acids (C/sub 2/-C/sub 10/) were analyzed in Los Angeles air and auto exhaust, as well as greenhouse air, soil, dust, and bog sediment samples, as dibutyl esters by gas chromatography and gas chromatography-mass spectrometry with fused silica capillary columns. In the Los Angeles ambient atmosphere, 19 dicarboxylic acids in the range C/sub 2/-C/sub 10/ were identified, including straight-chain, branched-chain, cis- and transunsaturated, and aromatic acids. Oxalic acid is the dominant species, followed by succinic, malonic, maleic, glutaric, adipic, and phthalic acids. Total concentration of C/sub 2/-C/sub 10/ diacids detected in the ambient atmosphere ranged from 5.5 to 21.2 nmol/m/sup 3/ (average 12.2 +/- 6.1 nmol/m/sub 3/). By contrast, gasoline and diesel exhaust samples, collected under idling conditions, showed that distributions of the diacids are similar to those of air samples, but their concentrations are 28 (gasoline) and 144 (diesel) times higher than the average concentration of atmospheric diacids. These results indicate that engine exhaust is an important source of diaids in the urban atmosphere. 13 references, 3 figures. 1 table.

Correlation of carbon and nitrogen stable isotope ratios in sedimentary organic matter 1

Abstract: Samples of organic matter separated from nearshore sediments of the Northeast Pacific are characterized by a linear correlation between ‘3C:‘2C versus 15N:14N. This correlation appears to represent the mixing of marine and terrestrial “end members” of refractory organic matter. Exceptions to the linear plot include organic matter from riverbeds draining agricultural areas, eutrophic lakes or lagoons with large algal populations, and some other exotic environments.

Sequential extraction procedure for the speciation of particulate trace metals

Abstract: An analytical procedure involving sequential chemicai extractions has been developed for the partitioning of particulate trace metals (Cd, Co, Cu, Ni, Pb, Zn, Fe, and Mn) into five fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter, and residual. Experimental results obtained on replicate samples of fluvial bottom sediments demonstrate that the relative standard deviation of the sequential extraction procedure Is generally better than =10%. The accuracy, evaluated by comparing total trace metal concentrations with the sum of the five Individual fractions, proved to be satisfactory. Complementary measurements were performed on the Individual leachates, and on the residual sediments following each extraction, to evaluate the selectivity of the various reagents toward specific geochemical phases. An application of the proposed method to river sediments is described, and the resulting trace metal speciation is discussed.

Study and Interpretation of the Chemical Characteristics of Natural Water

Abstract: The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from human activities. Broad interrelationships among these processes and their effects can be discerned by application of principles of chemical thermodynamics. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibrium, including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the Earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural freshwater. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. Taken together and in application with the further influence of the general circulation of all water in the hydrologic cycle, the chemical principles and environmental factors form a basis for the developing science of natural-water chemistry. Fundamental data used in the determination of water quality are obtained by the chemical analysis of water samples in the laboratory or onsite sensing of chemical properties in the field. Sampling is complicated by changes in the composition of moving water and by the effects of particulate suspended material. Some constituents are unstable and require onsite determination or sample preservation. Most of the constituents determined are reported in gravimetric units, usually milligrams per liter or milliequivalents

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Stable isotopes in ecosystem studies

Abstract: The use of stable isotopes to solve biogeochemical problems in ecosystem analysis is increasing rapidly because stable isotope data can contribute both source-sink (tracer) and process information: The elements C, N, S, H, and all have more than one isotope, and isotopic compositions of natural materials can be measured with great precision with a mass spectrometer. Isotopic compositions change in predictable ways as elements cycle through the biosphere. These changes have been exploited by geochemists to understand the global elemental cycles. Ecologists have not until quite recently employed these techniques. The reasons for this are, first, that most ecologists do not have the background in chemistry and geochemistry to be fully aware of the possibilities for exploiting the natural variations in stable isotopic compositions, and second, that stable isotope ratio measurements require equipment not normally available to ecologists. This is unfortunate because some of the more intractable problems in ecology can be profitably addressed using stable isotope measurements. Stable isotopes are ideally suited to increase our understanding of element cycles in ecosystems. This review is written for ecologists who would like to learn more about how stable isotope analyses have been and can be used in ecosystem studies. We begin with an explanation of isotope terminology and fractionation, then summarize isotopic distributions in the C, N, and S biogeochemical cycles, and conclude with five case studies that show how stable isotope measurements can provide crucial information for ecosystem analysis. We restrict this review to studies of natural variations in C, N, and S isotopic abundances, cxcluding from consideration ~5N enrichment studies and hydrogen and oxygen isotope studies. Our focus on C, N, and S derives in part from our

Metal pollution in the aquatic environment

Abstract: Aquatic chemistry is becoming both a rewarding and substantial area of inquiry and is drawing many prominent scientists to its fold. Its literature has changed from a compilation of compositional tables to studies of the chemical reactions occurring within the aquatic environments. But more than this is the recognition that human society in part is determining the nature of aquatic systems. Since rivers deliver to the world ocean most of its dissolved and particulate components, the interactions of these two sets of waters determine the vitality of our coastal waters. This significant vol ume provides not only an introduction to the dynamics of aquatic chem istries but also identifies those materials that jeopardize the resources of both the marine and fluvial domains. Its very title provides its emphasis but clearly not its breadth in considering natural processes. The book will be of great value to those environmental scientists who are dedicated to keeping the resources of the hydrosphere renewable. As the size of the world population becomes larger in the near future and as the uses of materials and energy show parallel increases, the rivers and oceans must be considered as a resource to accept some of the wastes of society. The ability of these waters and the sediments below them to accommodate wastes must be assessed continually. The key questions relate to the capacities of aqueous systems to carry one or more pollutants."