CASE STUDIES OF AGRICULTURAL WATER CONSERVATION1

Farmers from four irrigation districts in Texas and California were questioned about water conservation practices they are now using, those they plan to adopt, and potential incentives that government might offer to induce still further water conservation on their part. While responses differed somewhat from place to place and among individual farmers, the general results were: a) farmers reported that “water conservation” is not new to them, it is something they practice regularly; b) recent innovations such as laser controlled land leveling devices have permitted some substantial water use reductions in recent years; and c) even greater incentive mechanisms that government could provide and that farmers would accept as useful incentives, such as long term low interest loans for water saving equipment, would probably not be able to reduce water use in agriculture much further than 15 percent below current levels. It is recommended nonetheless that Federal agencies and local water districts and individuals should nonetheless pursue water conservation training and education programs, demonstrations of conjunctive use and water banking opportunities for water saving, and increased loan programs for installation of water saving equipment.     

An ecological perspective on nanomaterial impacts in the environment

Growing concerns over the potential for unintended, adverse consequences of engineered nanoparticles (ENPs) in the environment have generated new research initiatives focused on understanding the ecological effects of ENPs. Almost nothing is currently known about the fate and transport of ENPs in environmental waters, soils, and sediments or about the biological impacts of ENPs in natural environments, and the bulk of modern nanotoxicogical research is focused on highly controlled laboratory studies with single species in simple media. In this paper, we provide an ecological perspective on the current state of knowledge regarding the likely environmental impacts of nanomaterials and propose a strategy for making rapid progress in new research in ecological nanoscience.     

Expanding Carbon Stocks in Existing Forests – A Methodological Approach for Cost Appraisal at the Enterprise Level

The study presents a comprehensive methodology for the appraisal of C-stock expansion in existing forests as a forest management activity according to Art. 3.4 of the Kyoto Protocol. It allows for producer costs of carbon sequestration in forest enterprises to be derived. The methodology is based on a non-linear programming approach considering economic optimisation as well as ecological, social and sustainability needs through constraints and risk integration. While introducing further constraints on carbon stocks, the carbon stored in forest biomass was increased in periodic increments. However, while extending the carbon stocks, the ecological and social constraints as well as sustainability requirements are not to be violated. Costs were derived for every additional Mg (Megagrams) of C per ha sequestered in comparison to a baseline management. Two basic cases were considered: First, a permanent carbon sequestration was assumed. Secondly, a temporary storage of additional carbon over 10 years was supposed. The potential willingness of buyers of carbon certificates to pay for temporary carbon sequestration was derived by a financial consideration. We assumed that, for a buyer, the value of a temporary carbon sequestration certificate would be equivalent to the return on the savings because an investment in technical measures on reduction of carbon emissions can be postponed.     

The potential inhalation hazard posed by dioxin-contaminated soil

Conservative models were used to estimate the airborne concentrations of 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) vapor and particulates originating from soil containing 100 ppb TCDD. The upper-bound estimates were 3.25 pg/m³ of airborne TCDD vapor on-site and 0.51 pg/m³ for TCDD vapor 100 meters downwind. The TCDD air concentration on-site due to suspended particulate is estimated to be 1.4 pg/m³, based on a TSP level of 0.07 mg/m³. Assuming 70 years of continuous exposure to these concentrations, the upper-bound cancer risks determined from the Jury model were estimated to be 9.4 × 10⁻⁶ to 1.1 × 10⁻⁴ and 1.5 × 10⁻⁶ to 1.7 × 10⁻⁵ for inhalation of on- and off-site vapor, respectively, and 4.1 × 10⁻⁶ to 4.6 × 10⁻⁵ for dust inhalation. Since few sites have average soil concentrations as high as 100 ppb TCDD, this worst-case analysis indicates that inhalation will rarely, if ever, be a significant route of exposure to TCDD-contaminated soil. Experimental results support this claim and point to much lower risk estimates (8.4 × 10⁻⁹ to 9.9 × 10⁻⁸), suggesting that the parameters used in the Jury model are likely to overestimate the actual airborne levels of TCDD at contaminated sites.     

Evaluation of environmental impacts from municipal solid waste management in the municipality of Aarhus, Denmark (EASEWASTE).

A new computer based life cycle assessment model (EASEWASTE) was used to evaluate a municipal solid waste system with the purpose of identifying environmental benefits and disadvantages by anaerobic digestion of source-separated household waste and incineration. The most important processes that were included in the study are optical sorting and pre-treatment, anaerobic digestion with heat and power recovery, incineration with heat and power recovery, use of digested biomass on arable soils and finally, an estimated surplus consumption of plastic in order to achieve a higher quality and quantity of organic waste to the biogas plant. Results showed that there were no significant differences in most of the assessed environmental impacts for the two scenarios. However, the use of digested biomass may cause a potential toxicity impact on human health due to the heavy metal content of the organic waste. A sensitivity analysis showed that the results are sensitive to the energy recovery efficiencies, to the extra plastic consumption for waste bags and to the content of heavy metals in the waste. A model such as EASEWASTE is very suitable for evaluating the overall environmental consequences of different waste management strategies and technologies, and can be used for most waste material fractions existing in household waste.