PubMed · 10154206
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
A Wolf. Documenting disaster response.. https://pubmed.ncbi.nlm.nih.gov/10154206/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
We review the "critical point" concept for large earthquakes and enlarge it in the framework of so-called "finite-time singularities." The singular behavior associated with accelerated seismic release is shown to result from a positive feedback of the seismic activity on its release rate. The most important mechanisms for such positive feedback are presented. We solve analytically a simple model of geometrical positive feedback in which the stress shadow cast by the last large earthquake is progressively fragmented by the increasing tectonic stress.
Concentrations of total mercury (T-Hg) were determined in sediments and riparian (bankside) soils from the River Yare, Norfolk, UK to assess the current extent of contamination arising from a historical point source discharge. The results demonstrate that the spatial distribution pattern in surficial sediments and soils follows that of a distinct pollution plume with an initial increase 2-3 km downstream from the point source discharge at Whitlingham Sewage Treatment Works (STW) outfall. Average T-Hg concentrations in the surficial sediments ranged from 0.1 to 8.13 mg kg(-1); bankside soil concentrations ranged from 0.1 to 2.63 mg kg(-1). There has been a decline in downstream background sediment concentrations of Hg over time. This is likely to be the result of burial by fresh relatively uncontaminated sediments and possibly in the lower reach as a consequence of the influence of the freshwater-saline interface occurring near Cantley. Channel morphology was also shown to be an important factor in determining the large variations of Hg concentrations between sample points within transects. The predominant source of Hg to the soils appears to be due to dredging and the deposition of sediments during flooding.
The response of mature forest stands to a reduction in water availability has received little attention. In particular, the extent to which a short-term reduction in gas exchange can be alleviated in the long-term by acclimation processes is not well understood. We studied the impact of a severe reduction in water availability on the water relations and growth of 35-year-old Pinus laricio Poiret. trees in a replicated experiment. Sapwood and needle increments, soil and tree water status, stand transpiration, xylem embolism and plant hydraulic architecture were monitored over a 3-year period in control and drought-treated plots. Needle length was reduced in drought-treated trees by 30, 19 and 29%, and sapwood increments by 50, 27 and 24% over the 3 years. Drought did not result in tree mortality or in extensive xylem embolism or foliage dieback. On the contrary, a conservative water-use strategy was observed, because minimum leaf water potentials did not differ between treatments or over the season. Plant hydraulic resistance was also unaffected by restricted water availability. Stand transpiration was strongly reduced by drought treatment over the summer, but not during the winter, despite significant differences in leaf area between control and drought-treated trees, implying higher transpiration rates per unit leaf area in the droughted plants. This suggests that water transport capacity, rather than the amount of leaf area, controlled stand transpiration, which is at variance with expectations based on experiments with seedlings and short-term experiments with mature trees.