Charles T. Garten

Foliar retention of 15N-nitrate and 15N-ammonium by red maple (Acer rubrum) and white oak (Quercus alba) leaves from simulated rain

Abstract Studies of nitrogen cycling in forests indicate that trees assimilate atmospheric nitrate and ammonium and that differences between atmospheric deposition to the forest canopy and deposition measured in forest throughfall can be attributed to the removal of these ions from rain by tree leaves. Red maple and white oak leaves were exposed to artificial rain solutions (pH 4.1) containing 15N-labeled nitrate (3.5 μg N/ml) or ammonium (2.2 μg N/ml). At two time intervals after exposure (2 hr and 2 days) an exposed leaf and a control (non-exposed) leaf were removed from replicate seedlings. Based on results from 15N analysis, most of the nitrate applied to tree leaves was removed by washing with water; the mean per cent removal (± standard error, N = 4) was 87 ± 1 and 73 ± 4% of the 15NO-N Applied to red maple and white oak leaves, respectively. Relative retention of 15NH4-N by the leaves was greater than that observed for 15NO3-N. In red maple and white oak leaves, 58 ± 9 and 84 ± 7% (mean ± standard error, N = 4), respectively, of the applied ammonium was not removed by washing treatments. Our results show that the foliar uptake of 15NH4+ from simulated rain by deciduous tree leaves is greater than that for 15NO3−. Greater retention of NH4+ than NO3− ions by red maple and white oak leaves from simulated rainfall is consistent with field observations showing a preferential retention of ammonium from rainfall by forest canopies. As nitrogen chemistry and the relative importance of nitrogen compounds in the atmosphere change in response to proposed emission reductions (and possibly climate change), an improved understanding of the fate of airborne nitrogen compounds in forest biogeochemical cycles will be necessary.

Elemental Analysis of Environmental and Biological Samples Using Laser‐Induced Breakdown Spectroscopy and Pulsed Raman Spectroscopy

Abstract Laser‐induced breakdown spectroscopy (LIBS) and a relatively new technique, pulsed Raman spectroscopy (P‐RAMS) are used in this investigation to measure the elemental composition of soils and heterogeneous biological matrices. The LIBS method was used effectively to determine the elemental concentration of carbon and nitrogen in soils, and the presence of metal contaminants in invertebrates. The P‐RAMS method was used in exploratory studies to assess prominent molecular vibration peaks from the same soils analyzed using LIBS. The P‐RAMS spectra for the different soils show a close relationship to the fraction of organic carbon in soils. Our results demonstrate that these techniques greatly facilitate elemental analysis of heterogeneous environmental and biological matrices by reducing sample preparation and analysis times. These techniques can also provide semi‐quantitative results on a regular basis and quantitative results in particular cases.

Behavior of the Long-Lived Synthetic Elements and Their Natural Analogs in Food Chains

Publisher Summary This chapter discusses the behavior of the long-lived synthetic elements and their natural analogs in food chains. Potentially important sources of long-lived radionuclides for uptake into food chains are fallout from nuclear weapons detonations, effluent releases of radionuclides to air and water from nuclear facilities, the resuspension of particulate soil in contaminated areas, accidental spillage, and leakage of radioactive waste from repositories. Deposition onto plant and soil surfaces may occur through irrigation, dry deposition of dust, or wet deposition of snow and rainfall. The potential for entry of long-lived nuclides into food chains from shallow or deep buried nuclear wastes is less well understood as prediction of geologic stability on a millennium scale may be required. Food sources can contribute both biochemically incorporated and surficially deposited material. Contamination of plant and animal surfaces may occur as a result of wind, water, or mechanical resuspension of soil and sediment. Inhalation of aerially resuspended contaminants may also be an important pathway.

A review of parameter values used to assess the transport of plutonium, uranium, and thorium in terrestrial food chains☆☆☆

A general methodology of predicting the food chain transport of atmospherically deposited radionuclides is reviewed with an emphasis on variation in parameter values important for realistic behavioral characterization of environmental releases of plutonium, uranium, and thorium. Parameters important to generic simulations of food chain transport, given a known constant deposition onto vegetation, include: fractional interception of particulates by vegetation, vegetation density, effective half-life of contamination on vegetation, soil-to-plant transfer factors, consumption rates by cattle and man, and transfer of nuclides from forage to meat and from forage to milk. Variation in these parameters, which has been encountered in field studies, is summarized. A partial reduction in the variation of predicted concentrations of actinides in foods can be accomplished by more accurately determining critical parameter values like fractional interception of deposition by vegetation, vegetation biomass, and the effective half-life of contamination on vegetation. Field research describing the site dependency and time dependency of probability density functions for model parameter values is needed to make probabilistic predictions concerning Pu, U, and Th transport in food chains and to reduce the uncertainty associated with model predictions and generic assessments of environmental impact.

Environmental fate and distribution of technetium-99 in a deciduous forest ecosystem

Abstract The aims of the present research are to describe the uptake of 99 Tc by trees intercepting contaminated groundwater from a radioactive waste storage site, to identify the major 99 Tc pools within the woodland ecosystem and to assess the relative mobility of 99 Tc in the existing element cycle. Technetium in the groundwater freely passed through a dialysis membrane with a molecular weight exclusion limit of approximately 3500 amu and 99 Tc in the groundwater chromatographed on Biogel P-2 in a manner similar to pertechnetate anion (TcO 4 − ). Reducing conditions and organic associations at the study site were probably responsible for the relatively large amount (83–92%) of the 99 Tc that was nonextractable from soil by 0·01 m CaCl 2 . More than one-third of the 99 Tc was released from the soil by oxidizing reagents, indicating the presence of chemically reduced forms. The highest average 99 Tc concentrations in vegetation were found in herbaceous plants (18 530 pCi g −1 dry wt). Although 99 Tc was progressively accumulated over the growing season in tree leaves, average concentrations in tree wood and twigs were equal to or greater than concentrations in leaves. Tree wood was the major above-ground pool for 99 Tc because of the high concentrations in wood as well as the large amount of wood relative to other biomass at the site. Technetium was not easily leached from the trees by rainfall and was not readily extractable from forest floor leaf litter by water. The relative importance of return pathways for 99 Tc to the forest floor was leaf fall>stemflow >throughfall, indicating that 99 Tc was conserved by the trees. Snails and millipedes from the leaf litter layer concentrated technetium 20- and 16-fold, respectively, above levels found in the soil. Pertechnetate was rendered less bioavailable after ingestion by a leaf litter macroinvertebrate ( Porcellio sp.) common to the study site.

Integrated Ground-based and Remotely Sensed Data to Support Global Studies of Environmental Change'

Global studies of environmental change require integrated databases of multiple data types that are accurately coordinated in terms of spatial, temporal and thematic properties. Such datasets must be designed and developed jointly by scientific researchers, computer specialists, and policy analysts. The presentation focuses on our approach for organizing data from ground-based research programs so that the data can be linked with remotely sensed data and other map data into integrated databases with spatial, temporal, and thematic characteristics relevant to global studies. The development of an integrated database for Net Primary Productivity is described to illustrate the process.