Über die Phasenprobe und die nächsten Abkömmlinge des Chlorophylls

The Science of Nature -     

Survey methods for assessing land cover map accuracy

The increasing availability of digital photographic materials has fueled efforts by agencies and organizations to generate land cover maps for states, regions, and the United States as a whole. Regardless of the information sources and classification methods used, land cover maps are subject to numerous sources of error. In order to understand the quality of the information contained in these maps, it is desirable to generate statistically valid estimates of accuracy rates describing misclassification errors. We explored a full sample survey framework for creating accuracy assessment study designs that balance statistical and operational considerations in relation to study objectives for a regional assessment of GAP land cover maps. We focused not only on appropriate sample designs and estimation approaches, but on aspects of the data collection process, such as gaining cooperation of land owners and using pixel clusters as an observation unit. The approach was tested in a pilot study to assess the accuracy of Iowa GAP land cover maps. A stratified two-stage cluster sampling design addressed sample size requirements for land covers and the need for geographic spread while minimizing operational effort. Recruitment methods used for private land owners yielded high response rates, minimizing a source of nonresponse error. Collecting data for a 9-pixel cluster centered on the sampled pixel was simple to implement, and provided better information on rarer vegetation classes as well as substantial gains in precision relative to observing data at a single-pixel.     

Temporal variability in trace metal solubility in a paddy soil not reflected in uptake by rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Alternating flooding and drainage conditions have a strong influence on redox chemistry and the solubility of trace metals in paddy soils. However, current knowledge of how the effects of water management on trace metal solubility are linked to trace metal uptake by rice plants over time is still limited. Here, a field-contaminated paddy soil was subjected to two flooding and drainage cycles in a pot experiment with two rice plant cultivars, exhibiting either high or low Cd accumulation characteristics. Flooding led to a strong vertical gradient in the redox potential (Eh). The pH and Mn, Fe, and dissolved organic carbon concentrations increased with decreasing Eh and vice versa. During flooding, trace metal solubility decreased markedly, probably due to sulfide mineral precipitation. Despite its low solubility, the Cd content in rice grains exceeded the food quality standards for both cultivars. Trace metal contents in different rice plant tissues (roots, stem, and leaves) increased at a constant rate during the first flooding and drainage cycle but decreased after reaching a maximum during the second cycle. As such, the high temporal variability in trace metal solubility was not reflected in trace metal uptake by rice plants over time. This might be due to the presence of aerobic conditions and a consequent higher trace metal solubility near the root surface, even during flooding. Trace metal solubility in the rhizosphere should be considered when linking water management to trace metal uptake by rice over time.     

Toxicology of C1–C3 chlorinated hydrocarbons

Mutagenicity and carcinogenicity of C₁1bC₃ chlorinated hydrocarbons and the underlying mechanisms are described and discussed in the light of recent results.     

An evaluation of adaptation options for climate change impacts on agriculture in Kazakhstan

Agriculture in Kazakhstan is sensitive to climate, and wheat yields could be reduced up to 70% under climate change. With the transition from a socialist economy to a free market economy, decisions are being made now that will affect Kazakhstan's ability to cope with climate change. A team of Kazakh and American researchers examined the cost-effectiveness and barriers to implementations of adaptation options for climate change. Twelve adaptation options that increase flexibility to respond to climate change were identified using a screening matrix. Four options, forecasting pest outbreaks, developing regional centers for preserving genetic diversity of seeds, supporting a transition to a free market, and reducing soil erosion through the use of changed farming practices, were examined. The Adaptation Decision Matrix (ADM) was then applied to estimate benefits using expert judgment (using an arbitrary numerical scale, not monetary values) and benefits estimates were compared to costs to determine cost-effectiveness. The ADM uses subjective measures of how well adaptation options meet policy objectives. Controlling soil erosion was estimated to have the highest benefits, but the high costs of implementation appears to make it relatively cost-ineffective. Supporting a transition to a free market was ranked as the most cost-effective measure, with regional centers second. However, use of different scales to quantify benefits or different weights can result in regional centers being more cost-effective than the transition to a free market. Regional centers was also judged to have fewer barriers to implementation than a transition to a free market. These results will be incorporated in Kazakhstan's National Action Plan. The ADM and other tools are relatively easy to apply, but are quite subjective and difficult to evaluate. The tools can be quite useful by decision makers to analyze advantages and disadvantages between different adaptation options, but should be supplemented with additional, particularly quantitative analysis.