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The summer of 1993 will be remembered as the time when record amounts of rain flooded the Mississippi and its tributary rivers, causing one of the decade's worst natural disasters. Accounts from the hard-hit Des Moines area exemplify what many foodservice operators and their staff did to help their customers and neighbors struck by the disaster.
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Seedlings of Taxodium distichum L., Quercus lyrata Walt. and Q. falcata var. pagodaefolia Ell. were grown for 22 days in a rhizotron system providing two soil redox potential regimes, +170 mV (low Eh) and +560 mV (high Eh). Leaf chlorophyll concentration and gas exchange, root alcohol dehydrogenase (ADH) activity, root and leaf ethylene production, and growth and biomass partitioning were measured. In response to the low Eh soil treatment, stomatal conductance was reduced in Q. falcata and Q. lyrata but not in T. distichum, whereas net photosynthesis was reduced significantly in all species; however, net photosynthesis in T. distichum began to recover within 2 weeks of treatment initiation. Within each treatment, mean stomatal conductance and net photosynthesis were significantly greater in T. distichum than in the oak species. Leaf chlorophyll concentration was not affected by the soil treatments. All species showed significant reductions in root and leaf dry weights in response to the low Eh soil condition. The low Eh soil treatment resulted in increased root ADH activity and ethylene production in T. distichum, but had no effect on root ADH activity and ethylene production in the oak species.
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To investigate the effect of flooding disturbance on the net primary productivity of Songnen steppe, a comparatively thorough study was conducted on Sanjiadian State-owned Rangeland in Da'an city, Jilin Province, which was partly flooded in 1998. The study site was located in the south Songnen plain of Northeastern China, dominated by Leymus chinensis grassland. An extensively mild slope with flooding gradients (from un-flooded to heavily flooded) was taken as the study site. Two flooded transects coded FL and FH which was respectively subjected to 3 and 9 months of flooding were designed, and an un-flooded one coded CK at a relatively higher elevation was set as a control. Before flooding occurred in 1998, the slope had an almost uniform soil and L. chinensis dominated vegetation. Each transect was 0.2 hm2 (100 m x 20 m) in size, and the two flooded transects were almost paralleled each other, with the longer sides of them perpendicular to the retrieving direction of floodwater. In each transect twenty 1 m2 sized quadrats were randomly chosen to survey the community structure and the aboveground biomass. Comparative analyses were made on the dynamics of soil water, soil N and P, and species composition of grassland communities that occurred in responses to flooding disturbance. The results showed that the lightly and heavily flooded transects had a significantly larger aboveground biomass than the control, with the increase of 89.54% and 113.45%, respectively. The heavily flooded transect had a slightly but insignificantly larger aboveground biomass than the lightly flooded one, indicating that on flooded sites, water was not the limiting factor of the aboveground biomass. The acute changes of soil water caused by flooding led to the changes of soil nutrients and species assemblages, which would impact community biomass. Just as the case for aboveground biomass, the soil water contents of the two flooded transects were significantly larger than that of control, which was the direct effect of flooding disturbance. The contents of soil available N and P on the flooded transects were higher than that on the control, as resulted by the increase of soil water. The species composition had an obvious difference between flooded transects and control, and the major change on the flooded transects was the decrease of Xeric and Mesoxeric plants and the increase of Hygric and Hygro-mesic plants, compared to the control. It's deduced from the results that the mechanisms that the flooding disturbance influenced the net primary productivity were: 1) Flooding disturbance firstly changed soil water content, the leading limiting factor of grassland productivity, especially in dry years, and thus, lessened the limitation of aridity on grassland productivity. 2) Flooding induced increase of soil water content led to the drastic increases of nutrient availability, and thereby, eliminated the restriction of pre-flood nutrient scarcity on grassland productivity. 3) Still due to the afterward effects of flooding disturbance, the species composition of the community transformed from relatively shorter plant species assemblage towards taller and bigger plant species assemblage that were more productive.
This paper discusses whether flood hazard in the UK is increasing and considers issues of flood risk management. Urban development is known to increase fluvial flood frequency, hence design measures are routinely implemented to minimize the impact. Studies suggest that historical effects, while potentially large at small scale, are not significant for large river basins. Storm water flooding within the urban environment is an area where flood hazard is inadequately defined; new methods are needed to assess and manage flood risk. Development on flood plains has led to major capital expenditure on flood protection, but government is attempting to strengthen the planning role of the environmental regulator to prevent this. Rural land use management has intensified significantly over the past 30 years, leading to concerns that flood risk has increased, at least at local scale; the implications for catchment-scale flooding are unclear. New research is addressing this issue, and more broadly, the role of land management in reducing flood risk. Climate change impacts on flooding and current guidelines for UK practice are reviewed. Large uncertainties remain, not least for the occurrence of extreme precipitation, but precautionary guidance is in place. Finally, current levels of flood protection are discussed. Reassessment of flood hazard has led to targets for increased flood protection, but despite important developments to communicate flood risk to the public, much remains to be done to increase public awareness of flood hazard.
The objective of this experiment was to study changes of antioxidants and antioxidative enzymes in the flooding-stressed sweet potato leaf, as affected by paclobutrazol (PBZ) treatment at 24 h prior to flooding. Sweet potato 'Taoyuan 2' were treated with 0 and 0.5 mg/plant of PBZ, afterwards subjected to non-flooding and flooding-stress conditions for 0, 1, 3, and 5 d, followed by a 2 d drainage period. The study was conducted as a factorial experiment in completely randomized blocks with three replications maintained within a screen house. Plants with various antioxidative systems responded differently to flooding stress according to the duration of the flooding period and subsequent drainage period. The increased levels of antioxidants and antioxidative enzymes observed on different days of flooding afforded the sweet potato leaf with improved flooding tolerance. Glutathione reductase activity in the leaf was significantly enhanced over 5 d continuous flooding followed by a drainage period, in comparison with non-flooding conditions. Under non-flooding conditions, antioxidative system of leaf was regulated and elevated by PBZ pre-treatment. PBZ treatment may enable sweet potato 'Taoyuan 2' to maintain the balance between the formation and the detoxification of activated oxygen species. Our results also show that under flooding-stress conditions, the level of 'Taoyuan 2' antioxidative system is linked to PBZ treatment. Pre-treating with PBZ may increase levels of various components of antioxidative systems after exposure to different durations of flooding and drainage, thus inducing flooding tolerance. PBZ exhibited the important function of enhancing the restoration of leaf oxidative damage under flooding stress after the pre-application of 0.5 mg/plant. These findings may have greater significance for farming in frequently flooded areas.
This paper presents a review of changes in flood risk estimation on Scottish rivers resulting from re-analysis of flood records or from the application of new methods. The review arises at a time when flood damages have received recent prominence through the occurrence of a number of extreme floods in Scotland, and when the possible impacts of climate change on flood risk are receiving considerable attention. An analysis of the nine longest available peaks-over-threshold (POT) flood series for Scottish rivers reveals that, for thresholds yielding two events per year on average, annual POT frequencies on western rivers have increased in the 1980s/1990s to maximum recorded values, while in the east, values were highest in the 1950s/1960s. These results support the results of flood modelling work based on rainfall and temperature records from the 1870s, which indicate that, in western catchments, annual POT frequencies in the 1980s/1990s are unprecedented. No general trends in flood magnitude series were found, but an unexpected cluster of extreme floods is identified as having occurred since 1988, resulting in eight of Scotland's 16 largest gauged rivers producing their maximum recorded flows since then. These shifts are related to recent increases in the dominance of westerly airflows, share similarities with the results of climate change modelling, and collectively point to increases in flood risk in many parts of Scotland. The paper also reviews advances in flood risk estimation arising from the publication of the UK Flood Estimation Handbook, developments in the collection and use of historic flood estimation and the production of maps of 100-year flood areal extent. Finally the challenges in flood risk estimation posed by climate change are examined, particularly in relation to the assumption of stationarity.
Effects of short-term (32 days) flooding on photosynthesis, stomatal conductance, relative growth rate and tissue starch concentrations of flood-intolerant Quercus alba L. (white oak), bottomland Quercus nigra L. (water oak), bottomland Fraxinus pennsylvanica Marshall. (green ash) and flood-tolerant Nyssa aquatica L. (water tupelo) seedlings were studied under controlled conditions. Net photosynthetic rates of flooded N. aquatica seedlings were reduced by 25% throughout the 32-day flooding period. Net photosynthetic rates of flooded Q. alba seedlings fell rapidly to 25% of those of the control seedlings by Day 4 of the flooding treatment and to 5% by Day 16. In F. pennsylvanica and Q. nigra, net photosynthetic rates were reduced to 50% of control values by Day 8 but remained at approximately 30 and 23%, respectively, of control values by Day 32. Leaves of flooded Q. alba seedlings accumulated approximately twice as much starch as leaves of non-flooded control plants, whereas root starch concentrations decreased to 67% of those of control plants by the end of the 32-day flooding treatment. In contrast, flooding caused only a small increase in leaf starch concentrations of N. aquatica plants, but it increased root starch concentrations to 119% of those of the control plants by the end of the experiment. The co-occurring bottomland species, Fraxinus pennsylvanica and Q. nigra, differed from each other in their patterns of stomatal conductance and root starch concentrations. We conclude that the maintenance of low leaf starch concentrations, and high pre-flood root tissue starch concentrations are important characteristics allowing flood-tolerant species to survive in flooded soils.
Land-cover change (urbanisation, deforestation, and cultivation) results in increased flood frequency and severity. Mechanisms include reduced infiltration capacity, lower soil porosity, loss of vegetation, and forest clearing, meaning lower evapotranspiration. Major research challenges lie in quantification of effects in terms of flood characteristics under various conditions, ascertaining the combined effects of gradual changes over long time periods, and developing model tools suitable for land-use management. Large floods during the 1990s gave a new focus on these problems. Reference is made to the Norwegian HYDRA research programme on human impacts on floods and flood damage. The paper concludes that land-use change effects on floods are most pronounced at small scale and for frequent flood magnitudes. Model simulations of effects of land-use change can now be used to reduce flood risk. Modern flood management strategies have abandoned the position that dams and dikes are the only answers to mitigating flood disasters. Today, the strategic approach is more often: do not keep the water away from the people, keep people away from the water. Flood management strategies should include flood warnings, efficient communication, risk awareness, civil protection and flood preparedness routines, effective land-use policies, flood risk mapping, ... as well as structural measures.
To investigate the effects of flooding disturbance on the interspecific relationships among grassland plant species, a comparatively thorough study was conducted on Sanjiadian National Rangeland in the territory of Da'an city, Jilin Province, which was partly flooded in 1998. The study site was located in the south of Songnen plain, Northeastern China, dominated by Leymus chinensis grassland. Along the flooding gradients (from un-flooded to heavily flooded) formed on an extensive mild slope taken as the test site, four flooded transects coded T1, T2, T3 and T4 respectively, but subjected to the flood of different durations were designed, and also an un-flooded one coded T0 was set as a control at relatively higher elevation. Before flooding occurred in 1998, the slope had almost uniform soil and L. chinensis dominated vegetation. Contingency table was used to calculate the interspecific association indice, while Spearman rank correlation coefficient was adopted to analyze the interspecific covariance. The results showed that flooding disturbance had little effect on the association type for most species pairs, but had some effect on the rank coefficients of inter-specific co-variation. Different species pairs varied greatly in their responses to the flooding disturbance, suggesting that the inter-specific co-varying relations were not only dependent on environmental perturbation or disturbance factors, but also on (probably to a larger extent) the biological & ecological properties of the species that comprised the species pairs. The interspecific association types that could be determined between Potentilla paradoxa and all the other plant species were always positive, and little affected by flooding disturbance. As a main companion species, P. paradoxa had a broad ecological breadth, and weak selectivity for habitat. Contrarily, the interspecific association types that could be determined between Phragmites australis and others plant species (in addition to Scirpus planiculmis) were always negative, probably due to the biological properties of the plant. P. australis was a kind of clonal plant with long rhizomes, and enlarge its population through vegetative propagation by rhizomes. When in good water conditions, P. australis had a powerful competitive ability, thereby, imposed competitive or exclusive effects on the other plant species, thus formed the negative correlations between the plant and the other, which could be little affected by flooding disturbance. Interspecific covariance was not only influenced by environmental or disturbance factors, but also dependent on the different responses to the changing environments during the disturbances between the component species that comprised the species pairs. The two plant species that had similar and dissimilar water demands would tended to be positive and negative covariance respectively, if water conditions changed towards an extreme. Interspecific covariance based on the numerical properties of the communities were much more sensitive to the external disturbance than the interspecific associations calculated only based on the binary data of "presence or absence of species".
OBJECTIVE: To study the immediate and long-term effects of disasters caused by floods on residents health status. METHODS: Stratified sampling by ranks of flood disaster occurred in 1996 and 1998, flood disaster areas and control areas were carried out. A retrospective study was also carried out to study all diseases involved during 1996 - 1999. RESULTS: The incident rates of acute infectious disease in flooding areas in 1996 and 1998 were both higher than those of non-flooding areas (863.181/100 000 and 736.591/100 000, respectively). But there was no different between the incident rate of the first years in flooding areas and that of non-flooding areas. The prevalence rates of 8 kinds of chronic diseases related to circulatory system, nervous system, digestive system, injury and poisonous diseases in flooding areas were also higher than that in the non-flooding areas. The highest incidence rates of most diseases were in the mountainous flooding areas, followed by areas collapsed by flooding, and the lowest were seen in soakedareas by floods. The incidence rates of intestinal infectious diseases and respiratory infectious diseases were lower in areas where prevention and control measures were weak. CONCLUSION: Flood could lead to the increase of incidence rates both on acute infectious diseases and non-infectious diseases. Interventions on non-infectious diseases should also be enforced to stop the epidemics when preventing and controlling acute infectious disease.
The potential life loss caused by floods has not been studied before. We carried out a retrospective cohort study in flood areas in Hunan, China in 1999. The standard mortality rate (SMR) and years of potential life lost (YPLL) were used to quantify the burden of flood on health. The SMRs of injury/poisoning and malignant neoplasm were higher in the river flood (151.36 x 10(-5), 127.30 x 10(-5)) and drainage problems (143.74 x 10(-5), 105.87 x 10(-5)) groups than those in the no-flood group (113.40 x 10(-5), 74.81 x 10(-5)). The standard rates of YPLL (SYPLL per thousand) in the river flood (89.56 per thousand) and drainage problems (71.30 per thousand) groups were significantly higher than those in the no-flood group (65.74 per thousand, P<0.05). The SYPLL was significantly higher in males than in females. The percentages of attributable risk (PARs) of SMRs and PARs of SYPLLs resulting from flood were 12.26 and 26.60% in the river flood group and 10.56 and 7.80% in the drainage problems group. We conclude that floods increase the affected residents' SYPLL, and that the river flood had stronger effects than the drainage problems floods.
Black spruce (Picea mariana (Mill.) BSP) and tamarack (Larix laricina (Du Roi) K. Koch) are the predominant tree species in the boreal peatlands of Alberta, Canada, where low nutrient availability, low soil temperature and a high water table limit their growth. Effects of flooding for 28 days on morphological and physiological responses were investigated in greenhouse-grown black spruce and tamarack seedlings in a growth chamber. Flooding reduced root hydraulic conductance, net assimilation rate and stomatal conductance, and increased water-use efficiency (WUE) and needle electrolyte leakage in both species. Although flooded black spruce seedlings maintained higher net assimilation rates and stomatal conductance than flooded tamarack seedlings, flooded tamarack seedlings were able to maintain higher root hydraulic conductance than flooded black spruce seedlings. Needles of flooded black spruce developed tip necrosis and electrolyte leakage after 14 days of flooding, and these symptoms were subsequently more prominent than in needles of flooded tamarack seedlings. Flooded tamarack seedlings exhibited no visible injury symptoms and developed hypertrophied lenticels at their stem base. Application of exogenous ethylene resulted in a significant reduction in net assimilation, stomatal conductance and root respiration, whereas root hydraulic conductivity increased in both species. Thus, although flooded black spruce seedlings maintained a higher stomatal conductance and net assimilation rate than tamarack seedlings, black spruce did not cope with the deleterious effects of prolonged soil flooding and exogenous ethylene as well as tamarack.
Cold-hardened winter wheat (Triticum aestivum L. cv. Fredrick) and winter barley (Hordeum vulgare L. cv. Dover) were exposed to total flooding at 2 C. Dover seedlings were damaged more quickly than Fredrick, and after 3 weeks of flooding the survival of Dover was reduced to 10% and Fredrick to about 50%. Tissue moisture was slightly greater in Dover than Fredrick throughout the 4-week flooding period. Carbon dioxide and ethanol accumulated throughout the 4-week flooding period in both cultivars. Lactic acid increased rapidly during the 1st week of flooding, and remained relatively constant during the remainder of the flooding period. Oxygen consumption of seedling shoot tissue after exposure to flooding declined abruptly after only 1 day of flooding, but recovered somewhat during the subsequent 2 weeks. The effect of flooding was more pronounced on the ultrastructure of Dover than Fredrick. Although proliferation of endoplasmic reticulum was observed in the early stages of flooding in both cultivars, the occurrence of distinct parallel arrays and concentric whorls of membranes was prevalent in the flooded barley. Severe ultrastructural damage to a large proportion of apical cells in both cultivars was observed after 2 to 3 weeks of flooding.