Sediment dynamics and the role of flash floods in sediment export from medium-sized catchments: a case study from the semi-arid tropical highlands in northern Ethiopia

Purpose  

The Ethiopian highlands are a fragile environment characterized by steep slopes, intense rainfall, a sparse vegetation cover, and the occurrence of flash floods. Although important efforts have been made to mitigate the ongoing soil erosion and land degradation problems, the sediment dynamics at medium-sized catchment scale (100–10,000 km²) are not fully understood. Therefore, this study aims to provide a better understanding of sediment export processes and the importance of flash flood events in semi-arid tropical catchments.     

Major Changes in Fusarium spp. in Wheat in the Netherlands

The re-emergence of fusarium head blight throughout the world and especially in Western Europe prompted a survey of the situation in the Netherlands. To allow for a high throughput screening of large numbers of samples, a diagnostic PCR method was developed to detect the most common species of Fusarium occurring on wheat. Seven primer pairs were tested for their ability to identify isolates of Fusarium avenaceum, F. culmorum, F. graminearum, F. poae, F. proliferatum and Microdochium nivale var. majus and M. nivale var. nivale. Each primer pair only generated a PCR product with the corresponding Fusarium species and all PCR fragments had different molecular sizes. This allowed the generation of these amplicons using a mixture of all seven primer pairs. The robustness of this multiplex PCR encouraged us to screen a large series of isolates collected in 2000 and 2001. In both years 40 fields were sampled leading to a collection of 209 isolates from 2000 and 145 isolates from 2001. The results of the multiplex PCR demonstrated that F. graminearum was the most abundant species in the Fusarium complex on wheat in both years. This is in sharp contrast to reports from the 1980s and early 1990s, which found F. culmorum as the predominant species. Primers derived from the tri7 and tri13 genes, which are implicated in the acetylation and oxygenation of the C-4 atom of the backbone of the trichothecene molecule, were used to discriminate between deoxynivalenol and nivalenol (NIV) producers. The populations of F. culmorum and F. graminearum both showed a slight increase in NIV-producers in 2001.     

Temporospatial and kinetic characteristics of sheep walking on a pressure sensing walkway

The walking gait of sheep was analyzed in terms of temporospatial and kinetic parameters and weight distribution among the 4 limbs. Eighteen mature female Suffolk-mix sheep walked comfortably with a halter-guide over a 1.5-m pressure sensing walkway. Six valid trials were acquired for each sheep without any previous selection or habituation. Stance phases of the forelimb and hind limb were 66.3% and 68.9%, respectively, of total gait cycle, and limb velocity was 1.06 m/s in both forelimbs and hind limbs while walking. The mean peak vertical force (PVF) and vertical impulse (VI) as percentage of body weight in the forelimbs were 52.5% and 19.9%, respectively, and those of the hind limbs were 38.5% and 14.9%, respectively. More body weight was loaded on the forelimbs than the hind limbs, at 59% and 41% of body weight, respectively. The walking gait of sheep measured with the pressure sensing (PS) walkway was similar to that reported in dogs and horses. The PS walkway enabled collection of temporospatial and kinetic data, and simplified the process of data collection.     

Effects of Environmental Stress on Forest Crown Condition in Europe. Part III: Estimation of Critical Deposition and Concentration Levels and Their Exceedances

The stress by air pollution at the systematicPan-European 16 × 16 km² forest (crown) condition monitoring network, is discussed by comparingsite-specific estimates of critical and presentconcentration and deposition levels for S and Ncompounds and ozone. Results indicate that theexceedance of critical levels, related to directabove-ground impacts, decrease going from O₃ >SO₂ > N compounds. Critical N loads related toeffects on the forest understorey are exceeded atapproximately 25% of the plots, located mainly inWestern and Central Europe. Critical N loads relatedto effects on trees are hardly ever exceeded, but mostlikely, this is an under estimate. Critical aciddeposition levels are exceeded at approximately 30%of the plots with a low base saturation, where acidinputs may release toxic Al. This is especially thecase in Central and Eastern Europe, where presentloads are high and in boreal forest in SouthernScandinavia where critical loads are low. Although theuncertainties in the calculated exceedances is large,the spatial pattern, which is most important for acorrelative study, seems reliable, implying that thecritical load concept is suitable for regional risk assessments.     

Changing patterns of water distribution under the influence of land reforms and simultaneous WUA establishment

In 2005 the Uzbek government accelerated the dissolution process of collective farms through full-scale land reform. As the central production unit, the collective enterprise was supplanted by a private, family-based enterprise. Simultaneously Water Users Associations (WUAs) were established that operate and maintain the irrigation and drainage infrastructure of the former collective farms. Though these land-cum-water reforms could in principle initiate enormous changes, there is still a strong continuity due to the state-regulated agricultural system. Although officially only cotton and wheat production are still subject to a state order system, the whole agricultural production is still under strict state control. This paper builds on research conducted during the spring and summer of 2005 and 2006 in the oasis of Khorezm, Uzbekistan. Through field walks in combination with semi- and non-structured interviews, two cases of water management at former collective farm (FCF) level were distinguished: one at the onset of reform and one two years after full-scale reforms. The former shows the strong interlinkage at FCF level between the control of agricultural production and water management. However, the second case shows that even in the post-reform context, where the co-ordination of production and the control of cropping areas are formally no longer arranged at this level, these functions are informally reproduced through the new institutions. The WUA forms a crucial link between privatised producers and a state preoccupied with control.     

AFLP analysis of genetic diversity in leafy kale (<Emphasis Type="Italic">Brassica oleracea</Emphasis> L. convar. <Emphasis Type="Italic">acephala</Emphasis> (DC.) Alef.) landraces,cultivars and wild populations in Europe

AFLP markers were used to characterize diversity and asses the genetic structure among 17 accessions of kale landraces, cultivars and wild populations from Europe. The range of average gene diversity in accessions was 0.11–0.27. Several landraces showed higher levels of diversity than the wild populations and one cultivar had the lowest diversity measures. The landraces that were most genetically diverse were from areas where kales are known to be extensively grown, suggesting in situ conservation in these areas as a supplement to storage of seeds in gene banks. An analysis of molecular variance (AMOVA) showed that 62% of the total variation was found within accessions. For most accessions, genetic distance was not related to geographic distance. Similarities among accessions were probably not caused by recent gene flow since they were widely separated geographically; more likely the relationship among them is due to seed dispersal through human interactions. Our results indicate that a kale population found in a natural habitat in Denmark was probably not truly wild but most likely an escape from a cultivated Danish kale that had subsequently become naturalized.     

Variation in Pathogenicity Among South African Isolates of Phytophthora cinnamomi

Phytophthora cinnamomi isolates from South Africa were evaluated for differences in growth rate in vitro and levels of pathogenicity towards Eucalyptus smithii in the field. Inoculations were conducted in the field in summer and winter in two subsequent years at two locations in South Africa using 59 P. cinnamomi isolates. The isolates differed significantly in growth rate in vitro, as well as in levels of pathogenicity to E. smithii in the field. Growth rate in vitro was significantly influenced by interactions with culture age, geographic origin and genetic background as determined using isozymes. Levels of pathogenicity in the field were influenced by season of inoculation and average minimum temperatures at trial sites. The host from which P. cinnamomi isolates were originally obtained did not significantly affect levels of pathogenicity in the field. Culture age had a significant negative effect on growth rate in vitro and pathogenicity in the field. Significant differences in levels of pathogenicity could be found for different multilocus isozyme genotypes. Geographic origin and mating type of P. cinnamomi isolates had no significant effect on levels of pathogenicity in the field. A positive correlation was found between growth rate in vitro and levels of pathogenicity in the field. Levels of variation for pathogenicity within A1 mating type isolates were significantly lower than for A2 mating type isolates. Results of this study provide valuable information on selection of P. cinnamomi isolates for future resistance/tolerance screening assays of Eucalyptus germplasm in South Africa.