Photosynthetic control of atmospheric carbonyl sulfide during the growing season.

Climate models incorporate photosynthesis-climate feedbacks, yet we lack robust tools for large-scale assessments of these processes. Recent work suggests that carbonyl sulfide (COS), a trace gas consumed by plants, could provide a valuable constraint on photosynthesis. Here we analyze airborne observations of COS and carbon dioxide concentrations during the growing season over North America with a three-dimensional atmospheric transport model. We successfully modeled the persistent vertical drawdown of atmospheric COS using the quantitative relation between COS and photosynthesis that has been measured in plant chamber experiments. Furthermore, this drawdown is driven by plant uptake rather than other continental and oceanic fluxes in the model. These results provide quantitative evidence that COS gradients in the continental growing season may have broad use as a measurement-based photosynthesis tracer.

A model for the effect of rhizodeposition on the fate of phenanthrene in aged contaminated soil.

Microcosm data were used to develop a deterministic model to describe how rhizodeposition affects the fate of phenanthrene in aged contaminated soil. Microbial mineralization and soil sequestration of 14C-phenanthrene were compared in microcosms amended weekly with phenolic-rich mulberry root extracts versus unamended controls. Mineralization was higher in the amended soils simulating the rhizosphere (57.7 +/- 0.9%) than in controls simulating bulk (unplanted) soils (53.2 +/- 0.7%) after 201 days (p < 0.05). Humin was the main soil sink for the residual 14C-label. Whereas the total 14C-label associated with humin remained constant in biologically active soils (at about 30%), it increased up to 80% after 201 days in sterile controls. The initial phenanthrene extraction with n-butanol (commonly used to assess bioavailability) slightly underestimated the fraction thatwas mineralized (assessed by 14CO2 recovery). Changes in the unextractable fraction (determined by combustion in a biological oxidizer) suggested the presence of two soil sequestration domains: (1) irreversibly bound residue, and (2) an intermediate transition phase that is unextractable by solvents at a given point in time but could become bioavailable due to physicochemical or biological transformations of the binding matrix. The fate of phenanthrene was accurately modeled by considering the transfer of the 14C label between different soil compartments as first-order kinetic processes. Model simulations suggested that the system was approaching a stable end-point after 201 days of simulated rhizoremediation, and corroborated that microorganisms have a significant impact on the fate of phenanthrene in soil.

A methodology to estimate carbon storage and flux in forestland using existing forest and soils databases.

Sequestration of carbon through expansion and management of forestland can assist in reducing greenhouse gas concentrations in the atmosphere. Quantification of the amount of carbon presents an ongoing challenge that calls for new approaches. These new approaches must seek to simplify the science-based accounting of carbon storage and flux, while adhering to general principles of greenhous gas accounting. Quantifying change in carbon storage and carbon flux consists of two steps: developing a baseline of carbon storage, and measuring resulting storage and flux following a change of conditions. A methodology is proposed that accomplishes both steps, applicable to an aggregate-level analysis using the state of Iowa (U.S.A.) as a case study. The method combines existing databases from the U.S. Forest Service (USFS) and U.S. Department of Agriculture (USDA), and merges these with the methods of Birdsey (USDA. 1992. 1995: IPCC, 1997: EIIP, 1999) for partitioning carbon stocks into storage pools. Forested ecosystems in the study area contain approximately 137.3 metric tons organic carbon per hectare, or 114 million metric tons of carbon in aggregate. Of this total, 44.7 million tons are stored in biomass tissue, and 69.2 million tons of carbon are contained in soils. Carbon flux due to forests in the state of Iowa is estimated to be a net annual sequestration (removal from the atmosphere) of 4.3 million metric tons of CO2-equivalent, approximately 5% of the net annual CO2-equivalent emissions from the state (Ney et al.. 1996).

Phytotoxicity of chlorinated aliphatics to hybrid poplar (Populus deltoides x nigra DN34).

Effects of a series of chlorinated ethenes and ethanes on hybrid poplar (Populus deltoides x nigra DN34) were assessed in laboratory experiments. Poplar cuttings were grown in sealed reactors with hydroponic solutions and were exposed to a chlorinated solvent for a period of two weeks. Exposure concentrations ranged from 0 to 0.4 mM for perchloroethylene to 0 to 8.4 mM for 1,1-dichloroethane. Effects were assessed by gravimetrically monitoring transpiration and measuring change in cutting mass. The zero-growth concentrations of the chemicals tested were 0.3 mM perchloroethylene, 0.9 mM trichloroethylene, 0.9 mM 1,1,2,2-tetrachloroethane, 2.0 mM 1,1,1-trichloroethane, 2.3 mM 1,1,2-trichloroethane, 4.8 mM trans-dichloroethylene, 5.6 mM 1,1-dichloroethylene, 6.0 mM cis-dichloroethylene, and 10.7 mM 1,1-dichloroethane. Adverse effects were found to increase with increasing number of chlorine atoms within a homologous series of ethenes or ethanes. Ethenes were more toxic than similarly chlorinated ethanes.

Phytoremediation of MTBE from a groundwater plume.

The feasibility of phytoremediation to both remediate and hydraulically contain a methyl tert-butyl ether (MTBE)-contaminated groundwater plume was investigated in a three-phase study that included the following elements: (i) a laboratory bioreactor study that examined the fate and transport of 14C-radiolabeled MTBE in hybrid poplar trees, (ii) a novel approach for a mathematical modeling study that investigated the influence of deep-rooted trees on unsaturated and saturated groundwater flow, and (iii) a field study at a Houston site with MTBE-contaminated groundwater where hybrid poplar trees were planted. In the laboratory study, the predominant fate pathway was uptake and evapotranspiration of [14C]-MTBE from leaves and stems of poplar cuttings rooted in hydroponic solution. The modeling study demonstrates that phytohydraulic containment of MTBE in groundwater by deep-rooted trees can be achieved. The field study demonstrated significant groundwater uptake of groundwater by deep-rooted trees via direct measurement in the first three seasons. The use of vegetation may provide a cost-effective in-situ alternative for containment and remediation of MTBE-contaminated groundwater plumes.

Advances in phytoremediation.

Phytoremediation is the use of plants to remedy contaminated soils, sediments, and/or groundwater. Sorption and uptake are governed by physicochemical properties of the compounds, and moderately hydrophobic chemicals (logarithm octanol--water coefficients = 1.0--3.5) are most likely to be bioavailable to rooted, vascular plants. Some hydrophilic compounds, such as methyl-tert-butylether and 1,4-dioxane, may also be taken up by plants via hydrogen bonding with transpiration water. Organic chemicals that pass through membranes and are translocated to stem and leaf tissues may be converted (e.g., oxidized by cytochrome P450s), conjugated by glutathione or amino acids, and compartmentalized in plant tissues as bound residue. The relationship between metabolism of organic xenobiotics and toxicity to plant tissues is not well understood. A series of chlorinated ethenes is more toxic to hybrid poplar trees (Populus deltoides x nigra, DN-34) than are the corresponding chlorinated ethanes. Toxicity correlates best with the number of chlorine atoms in each homologous series. Transgenic plants have been engineered to rapidly detoxify and transform such xenobiotic chemicals. These could be used in phytoremediation applications if issues of cost and public acceptability are overcome.

Biodegradation of 1,4-dioxane in planted and unplanted soil: effect of bioaugmentation with Amycolata sp. CB1190.

1,4-Dioxane is one of the most recalcitrant and toxic contaminants in the subsurface. This study investigated the potential to enhance dioxane biodegradation in both planted and unplanted soil, by adding the dioxane-degrading actinomycete, Amycolata sp. CB1190. Dioxane was not removed within 120 days in sterile controls or in viable microcosms not amended with CB 1190. Poplar root extract (40 mg/L as COD) stimulated dioxane degradation in bioaugmented soil, and 100 mg/L dioxane were removed within 45 days. Other co-substrates that enhanced dioxane degradation by CB1190 include tetrahydrofuran (THF) and 1-butanol, while glucose and soil extract did not affect dioxane degradation. The stimulatory effect of THF was partly due to enhanced enzyme induction, while that of root extract and 1-butanol was attributed to additional growth of CB1190. In another experiment with dioxane added at 10 mg/kg-soil. reactors planted with hybrid poplar trees removed (by evapotranspiration and biodegradation in the root zone) more dioxane within 26 days than unplanted reactors, regardless of whether CB1190 was added. Nevertheless, CB1190 enhanced mineralization of [14C]-dioxane in all experiments. This enhancement was more pronounced in unplanted soil because plant uptake reduced the availability of dioxane for microbial degradation. These results suggest that bioaugmented phytoremediation is an attractive alternative to remove dioxane from shallow contaminated sites.

Evaluation of different approaches for modeling effects of acid rain on soils in China.

Acid deposition is an environmental problem of increasing concern in China. Acidic soils are common in the southern part of the country and soil acidification caused by acid deposition is expected to occur. Here we test and apply two different approaches for modeling effects of acid deposition and compare results with observed data from sites throughout southern China. The dynamic model MAGIC indicates that, during the last few decades, soil acidification rates have increased considerably due to acid deposition. This acidification will continue if sulfur deposition is not reduced, and if reduced more rapidly than base cation deposition. With the Steady State Mass Balance model (SSMB), and assuming that a molar ratio of Ca2+/Al3+ < 1 in soil water is harmful to vegetation, we estimate a slight probability for exceedance of the critical load for present deposition rates. Results from both modeling approaches show a strong dependence with deposition of base cations as well as sulfur. Hence, according to the models, changes in emission control of alkaline particulate matter prior to sulfur dioxide will be detrimental to the environment. Model calculations are, however, uncertain, particularly because available data on base cation deposition fluxes are scarce, and that model formulation of aluminum chemistry does not fully reproduce observations. An effort should be made to improve our present knowledge regarding deposition fluxes. Improvements to the model are suggested. Our work indicates that the critical loads presented in the regional acid deposition assessment model RAINS-Asia are too stringent. We find weaknesses in the SSMB approach, developed for northern European conditions, when applying it to Chinese conditions. We suggest an improved effort to revise the risk parameters for use in critical load estimates in China.

Peer reviewed: what course for carbon trading?

Although still without a legislative mandate, a marketplace for carbon trading is beginning to develop.

Peer reviewed: East central europe: an environment in transition.

Major changes in the governments and economies of this highly polluted region are improving air and water quality.

Test Medium for the Growth of Nitrosomonas europaea.

A mineral medium for studying the growth of Nitrosomonas europaea was developed and examined. The medium was defined in terms of chemical speciation by using chemical equilibrium computer models. The medium significantly increased the metabolic activity of the organisms compared with previously developed media, yielding a specific growth rate as high as 3.0 day (generation time, 5.5 h). The specific growth rate was enhanced by increasing the inoculum and was linearly correlated with the inoculum-to-total-culture volume ratio on a semilog scale. A reproducible growth rate for N. europaea was obtained with this medium under controlled experimental conditions.

Fate and transport of dieldrin in coralville reservoir: residues in fish and water following a pesticide ban.

A model for the fate and transport of pesticide has been calibrated with field data from 1968 to 1978. The results have aided in a management decision to lift a commercial fishing ban in Coralville Reservoir, eastern Iowa. Dieldrin residues in fish, sediment, and water are all declining at about 15 percent per year. Approximately 50 percent of the pesticide load is exported from the reservoir in the outflow, 40 percent undergoes sedimentation, and 10 percent enters the fish.