A submodel for anaerobic mud-water exchange of phosphate

A submodel for anaerobic mud-water exchange of phosphate is obtained from experiments in the laboratory. Phosphorus in the sediment can be divided into exchangeable and non-exchangeable phosphorus. The exchangeable phosphorus is decomposed in accordance with a first-order reaction. The phosphorus moves, after the decomposition process, from the interstitial water to the water phase, in accordance with a diffusion expression. The yearly increase of the sediment was determined by means of the lead concentration as a function of the depth.     

Do female roe deer in good condition produce more sons than daughters

In polygynous roe deer Capreolus capreolus, males are only slightly heavier than females and the overall sex ratio at birth is close to unity. We studied offspring sex ratio and litter size (range 1–4, n = 74) of culled females, in utero, which provided an opportunity to examine responses of sex ratio to maternal condition. Male embryos were heavier than their sisters, and male fawns (9 months old) heavier than female fawns, suggesting a higher growth rate in males. There was no evidence for differential mortality between the sexes from birth to 9 months old. Heavier adult females produced larger embryos than lighter, or primiparous females. The overall sex ratio of embryos did not differ from unity, but adult does had more male embryos (55%) than primiparous does (32%), and the proportion of male embryos in a litter increased with the mother's body mass. Litter size also tended to increase with maternal age and body mass. We argue that this pattern reflects adaptive variation in offspring sex ratio.     

Extended prediction models for crashes at roundabouts

This paper builds upon the results of previously developed crash prediction models for roundabouts. The originally investigated sample was extended from 90 to 148 roundabouts. Poisson and gamma modelling techniques were used, the latter ones since underdispersion in the crash data was observed. Separate models were fit for crashes with six different types of road users: bicyclists, motorcyclists, passenger and heavy four-wheel vehicles, moped riders and pedestrians. A further distinction was made between single-vehicle and multiple-vehicle crashes.The results show that the overall number of crashes is more or less proportional to the number of motorized vehicles. The mean number of single-vehicle crashes per passing vehicle is lower on busier roundabouts. Confirmation is found for the existence of a ‘safety-in-numbers’ effect for different types of road users. Three-leg roundabouts tend to perform worse than roundabouts with four or more legs. More crashes seem to occur at roundabouts with bypasses for traffic in some direction. Larger central islands correlate with more single-vehicle crashes. Moped riders and motorcyclists are strongly overrepresented in both single-vehicle and multiple-vehicle crashes whereas bicyclists are clearly overrepresented in multiple-vehicle crashes. Roundabouts with cycle paths perform better than roundabouts with other types of cycle facilities, particularly in comparison with roundabouts with cycle lanes close to the roadway.     

Preface

Water, Air, &; Soil Pollution: Focus -     

Land pressure and customary tenure: Cropland allocations in Swaziland

This paper examines the effects of growing land pressure on the distribution and quality of cropland allocations on customary tenured land (CTL) in Swaziland. Within the wider Sub‐Saharan context, the reform of indigenous tenure systems is now generally seen as a process of adaptation rather than replacement. The legal recognition of (existing and future) user rights is considered a practical way forward. This essentially rights‐based approach may divert attention from technical inadequacies indigenous systems may have, particularly under conditions of increasing land pressure. The case of CTL substantiates such shortcomings. CTL has seen a marked growth in population and land allocations since Independence. This had led to concerns on the land distribution efficiency in view of the improved agricultural production required to sustain the increasing number of rural households. By analysing historical changes in the number, size and quality of cropland allocations in selected rural communities, this paper demonstrates the occurrence of a high degree of inconsistency in cropland distribution at the community level, as well as inefficient land distribution at higher levels of scale. These shortcomings threaten the sustainability of the local agricultural production systems, and will need to be addressed in any meaningful reform process.