Determination of critical soil water content and matric potential for wind erosion

Purpose  

Soil strength and thus stability concerning wind erosion are controlled by the soil water content. The concept of soil critical water content (Θ_crit.) for deflation was extended to include matric potential (Ψ_crit.) as well. The focus of this paper is to quantify the Θ_crit. and Ψ_crit. as the upper boundary for wind erosion or as the lower boundary for soil strength, to model the Ψ_crit. at the immediate soil surface (0–0.2 cm) and to evaluate the effect of soil moisture upon erosion as a function of time and sampling height.     

Multiple catenanes derived from calix[4]arenes

A multicatenane is described in which two belts consisting of four annelated rings attached to the wide rims of two calix[4]arenes are interwoven in such a way that each ring of one belt penetrates two adjacent rings of the other belt and vice versa. The key step of the synthesis of this [8]catenane is the exclusive formation of preorganized heterodimers between a multimacrocyclic tetraurea calix[4]arene and an "open-chain" tetraurea calix[4]arene containing eight omega-alkenyl groups. When a tetraurea calix[4]arene containing four alkenyl groups is used, a bis-[3]catenane is formed analogously.     

Iron(III) photo-induced degradation of isoproturon: correlation between degradation and toxicity

The degradation of isoproturon photoinduced by Fe(III) was investigated under both artificial and solar light. The monomeric species Fe(OH)2+ present under the experimental conditions ([Fe(III)] = 3 x 10(-4) M) is the main Fe(III) species responsible for the degradation of isoproturon. The process involves the attack on the pollutant by OH radicals generated by irradiation of Fe(OH)2+. The major primary photoproducts were identified; they accumulate in the solution medium before being degraded. The toxicity of the solution to marine bacterium Vibrio fisheri (Beijerinck) Lehmann & Neumann was monitored during the degradation process. It increased in the early stages of the reaction and, among the photoproducts, the N-formyl derivative appeared to be the major product responsible for the increase in toxicity.     

The ModCom modular simulation system

Simulation models of agro-ecological systems are typically written in a manner that precludes reusability of parts of the model without a significant amount of familiarity with and rewriting of existing code. Similarly, replacing a part of a model with a functionally equivalent part from another model is typically difficult. The objective of this study was to develop a method to enable the assembly of simulation models from previously and independently developed component models. Recent advances in software engineering have enabled the development of software applications from smaller parts (called components) on the basis of an abstract decomposition of the relevant domain (called a framework). Based on a requirements analysis of existing simulation models we developed the ModCom simulation framework. ModCom provides a set of interface specifications that describe components in a simulation. ModCom also provides implementations of the core simulation services. The framework interfaces use well-defined binary standards and allows developers to implement the interfaces using a broad range of computer languages. Using this framework, simulation models can be assembled by connecting component models in much the same way that Lego blocks are put together to assemble a house. ModCom thus allows modelers to create models and modeling tools that are easily exchanged (in binary form or source code) with colleagues across the hall or across the globe.     

Degradation of Diuron Photoinduced by Iron(III) in Aqueous Solution

The degradation of diuron photoinduced by iron(III) in aqueous solution has been investigated with different iron(III) species (monomeric species Fe(OH)²⁺, dimeric species Fe₂(OH)₂⁴⁺ and water-soluble oligomeric species) under monochromatic excitation at 365 nm and under sunlight. The rate of degradation depends on the concentration in Fe(OH)²⁺, the most reactive species in terms of ^•OH radical formation. The major photoproduct is 3-(3,4-dichlorophenyl)-1-formyl-1-methylurea which represents more than 60% of diuron disappearance. The mechanism only involves the attack by ^•OH radicals arising from iron(III) excited species. The half-lives of diuron when submitted to such a process in the environment were estimated to be 1–2 h and a few days according to the concentration of Fe(OH)²⁺ (respectively 70% and <10% of total iron(III) concentration).     

Anticipating floodplain trajectories: a comparison of two alternative futures approaches

Scenario-based investigations explore alternative future courses of action in a widening array of situations. Anticipating landscape patterns and the values behind them are recurring needs in such investigations. While it is accepted that how scenario assumptions are framed and who frames them matters, the sensitivity of resulting trajectories to contrasting scenario framing and modeling processes is rarely tested. Using comparable scenarios we contrast landscape change trajectories produced from two distinct approaches to modeling scenario assumptions: the first uses lay citizen groups and deterministic land allocation modeling, the second uses experts from biophysical and social sciences and agent-based modeling. Scenarios are defined and mapped for the year 2050 in western Oregon’s Willamette River Basin along a gradient of conservation oriented to development-oriented assumptions using first citizen-based and then expert-based approaches. The landscape variability and trajectories for the citizen-based Conservation 2050 and Development 2050 scenarios are then characterized and compared with those of the expert-based Conservation 2050 and Development 2050 scenarios. Results distinguish areas where trajectories always vary regardless of approach or scenario from those that never vary. Policy influence on trajectory is illustrated using agent-based model results where land conversion serves purposes of wealth production and ecosystem function. Results depict areas with strong coupling between policy and trajectory as those places experiencing the same pattern of change over time regardless of scenario. Results also indicate that the greater the variability of a given scenario’s trajectories, the more successful the scenario is at avoiding scarcity of wealth and ecosystem function.     

Exceedance of critical loads of nitrogen and sulphur and its relation to forest conditions

The calculation of critical loads and their exceedance is one method to describe the vulnerability of forests to environmental stress caused by anthropogenic impact. Exceedance of critical loads for acidifying inputs and nitrogen was compared to different indicators of the soil and forest conditions in the German part of the extensive forest monitoring (ICP Forests/EU Level I), including more than 1,800 plots. In addition, an empirical relationship between the C/N ratio of the forest floor humus layer (C/N _Humus) and the estimated nitrogen output for ten plots of the intensive monitoring (ICP Forests/EU Level II) was established in order to estimate the potential nitrogen output on Level I plots dominated by Norway spruce. Regarding all tree species assessed, the exceedance of critical loads for nitrogen and sulphur is negatively correlated with pH and base saturation up to 30 cm soil depth. The sulphur deposition and the exceedance of critical loads are highly correlated with the sulphur content of leaves and needles, whereas the respective relations for nitrogen were lower. The crown condition was weakly positively related to the sulphur content in tree leaves and needles. For Norway spruce sites, high exceedance of critical loads for nitrogen and nitrogen deposition corresponded well with low C/N _Humus. In regions with high nitrogen load and low C/N ratios in the humus layer, the calculated nitrogen output was high. The results support the concept of critical thresholds in that way that their exceedance can impair forest ecosystem functions like nitrogen retention.     

Isolation and X-ray crystal structure of a new isoquinoline-N-oxide alkaloid from Calycotome villosa subsp. intermedia

A new isoquinoline-N-oxide alkaloid was extracted from the alkaloid fraction of a methanol extract of the seeds of Calycotome villosa subsp. intermedia. Its structure was established as 1-hydroxymethyl-6,7-dimethoxyisoquinoline-N-oxide (1) by spectroscopic techniques and X-ray diffraction analysis.