Forest structure and light regimes following moderate wind storms: implications for multi-cohort management.

Moderate-severity disturbances appear to be common throughout much of North America, but they have received relatively little detailed study compared to catastrophic disturbances and small gap dynamics. In this study, we examined the immediate impact of moderate-intensity wind storms on stand structure, opening sizes, and light regimes in three hemlock-hardwood forests of northeastern Wisconsin. These were compared to three stands managed by single-tree and group selection, the predominant forest management system for northern hardwoods in the region. Wind storms removed an average of 41% of the stand basal area, compared to 27% removed by uneven-aged harvests, but both disturbances removed trees from a wide range of size classes. The removal of nearly half of the large trees by wind in two old-growth stands caused partial retrogression to mature forest structure, which has been hypothesized to be a major disturbance pathway in the region. Wind storms resulted in residual stand conditions that were much more heterogeneous than in managed stands. Gap sizes ranged from less than 10 m2 up to 5000 m2 in wind-disturbed stands, whereas the largest opening observed in managed stands was only 200 m2. Wind-disturbed stands had, on average, double the available solar radiation at the forest floor compared to managed stands. Solar radiation levels were also more heterogeneous in wind-disturbed stands, with six times more variability at small scales (0.1225 ha) and 15 times more variability at the whole-stand level. Modification of uneven-aged management regimes to include occasional harvests of variable intensity and spatial pattern may help avoid the decline in species diversity that tends to occur after many decades of conventional uneven-aged management. At the same time, a multi-cohort system with these properties would retain a high degree of average crown cover, promote structural heterogeneity typical of old-growth forests, and maintain dominance by late-successional species.     

Temporal scales of landscape change following storms on a human-altered coast,New Jersey,USA

Cycles of storm destruction and rebuilding of human facilities are as much a part of a predictable cycle of shoreline change as destruction and re-establishment of landforms and wildlife habitat by natural processes. An evaluation of the human-induced and natural geomorphic responses to three storms in two vulnerable developed areas in New Jersey reveals that storms can have limited effect in re-establishing a natural coastal resource base of lasting significance. Reconstruction of coastal landscapes by human action may be more rapid than natural restoration, decreasing the likelihood for geomorphic features to develop based on natural processes. Reliance on storm processes to create new natural habitat in locations where there is human investment in buildings and support infrastructure is not realistic unless a proactive stance is taken to include naturally-functioning characteristics of the coastal system in reconstruction efforts. By striving to control construction of shorefront buildings to reduce their potential for damage, managers may be taking attention away from the separate but critical issue of ensuring that post-storm reconstruction effort include the potential for replacing loss of natural geomorphic features and wildlife habitat.     

沙尘与大雾天气对京津石空气质量影响

采用北京、天津、石家庄2001-2010年沙尘与大雾天气的统计数据以及城市空气污染指数（API）,分析北京、天津、石家庄3市空气污染指数变化特征及大雾和沙尘天气下北京、天津、石家庄3市空气质量情况,进而得出沙尘大雾天气对京津石空气质量的影响。结果表明：2001-2010年间北京、天津、石家庄3市API总体呈下降趋势,天津、石家庄相对于北京空气质量改善较为明显,且空气质量夏季〉秋季〉春冬季。沙尘天气条件下,北京、天津、石家庄3市API平均值分别为255、179和167,空气质量出现良的比率天津为24%,北京、石家庄为10%左右,出现重污染的比率北京高达50%以上,天津和石家庄均在20%左右;3市沙尘天气高频次均出现在3-5月份,但北京沙尘天气发生次数远大于天津和石家庄。大雾天气条件下,北京、天津、石家庄3市API平均值为185、130和167,空气质量出现优或良的比率：天津〉石家庄〉北京,北京和石家庄出现重污染的比率均接近30%,天津不到10%,所以大雾天气对3市空气质量影响较小,大雾天气频次的变化波动并未对该地区空气质量的年际变化造成显著影响,3市高频次大雾天气集中在10-12月份,对该时段内空气污染呈现加重趋势有一定的贡献。所以沙尘和大雾天气均对北京、天津和石家庄空气质量存在不利影响,其中对北京影响最为严重,对天津影响最轻。整体上沙尘对3市的空气质量影响较大,大雾天气影响较小。     

Seasonal timing of first rain storms affects rare plant population dynamics

A major challenge in forecasting the ecological consequences of climate change is understanding the relative importance of changes to mean conditions vs. changes to discrete climatic events, such as storms, frosts, or droughts. Here we show that the first major storm of the growing season strongly influences the population dynamics of three rare and endangered annual plant species in a coastal California (USA) ecosystem. In a field experiment we used moisture barriers and water addition to manipulate the timing and temperature associated with first major rains of the season. The three focal species showed two- to fivefold variation in per capita population growth rates between the different storm treatments, comparable to variation found in a prior experiment imposing eightfold differences in season-long precipitation. Variation in germination was a major demographic driver of how two of three species responded to the first rains. For one of these species, the timing of the storm was the most critical determinant of its germination, while the other showed enhanced germination with colder storm temperatures. The role of temperature was further supported by laboratory trials showing enhanced germination in cooler treatments. Our work suggests that, because of species-specific cues for demographic transitions such as germination, changes to discrete climate events may be as, if not more, important than changes to season-long variables.     

Hierarchical regulation of nitrogen export from urban catchments: interactions of storms and landscapes.

In urban catchments of arid central Arizona, we investigate how the export of mineral and organic nitrogen (N) in storm runoff is regulated by interactions between local landscape characteristics and broader scale storm features. First, we test whether N export is more a function of (1) processes that affect N concentration in runoff or (2) the propensity of the catchment to convey rainfall as runoff. With data pooled across catchments, the mass of N in export (load) is determined by processes regulating runoff N concentration. There are exceptions when catchments are examined individually, where N load from some catchments is determined by the hydrologic responsiveness of the catchment. Second, we investigate the relationship between N export and catchment features. Loads per catchment area were greater from more impervious catchments, probably because impervious catchments held more N in a mobilizable phase and conveyed more rainfall as overland flow. Loads per area were lower from larger catchments, possibly owing to more N-retention hot spots in larger catchments. Catchments with the greatest N exports were those with commercial land use, and loads decreased as development became less prevalent or as residential replaced industrial land use. Third, we investigated how catchment features moderated direct responses of N export to storms. Export was less correlated with storm features in catchments that were larger, more pervious, and less industrial. Results support an "N build and flush" hypothesis, which purports that there is little biotic processing of N deposited to arid, urban surfaces with little organic matter. The rate and duration of deposition determine the size of the mobile N pool. Any amount of rainfall capable of generating overland flow would entrain nearly all mobilizable N and export it from the catchment. Nonetheless, these results suggest that, even with daunting seasonal and interannual variability in storm conditions, material export can be reduced by managing intrinsic catchment features.     

Storms impact on morphodynamics of human controlled coastal features in western France: the prevailing role of local management practices

On the western coast of France some storms have a dramatic impact while others have almost none. Some sites were insensitive to storms until the 50ies and are, today, retreating. This paper tries to explain why. First we sort out which storms are responsible for retreat and second we search for any change in management practices on the sites. The erosive storms are not always the most powerful ones (high wind speeds or high waves) but the ones which occur during the peak of high spring tides and have long period waves. The sites which retreat are the ones which, during the 20th Century; were maintained and rebuild, for economic reasons after each small storm event. Today they are left to themselves as they have no more economic activities and are turned into “natural areas”. Therefore the sensitivity of these sites to storm is human-induced. Though, they may be even more sensitive if the observed evolution in storminess (namely the increasing frequency of clusters of storms) appears to be a real trend.     

沙尘暴对暴露儿童健康效应的研究

为了研究沙尘暴对儿童可能造成的急性危害,以沙尘暴源区——甘肃省武威市的某2所小学3～5年级的1040名学生(年龄8～14岁)为研究对象,在2004年和2005年的3～5月沙尘暴频发期间进行健康状况问卷调查,共调查4场沙尘暴事件,所调查的症状有咳嗽、咯痰、气短、肺部喘鸣、胸部憋闷、咽干口苦、眼睛干涩、流泪、流涕、打喷嚏、心情压抑等11种常见的症状.结果表明,沙尘暴发生当天(滞后0d)儿童各种所查症状发生的相对危险度(RR)均有不同程度地升高,沙尘暴过后(滞后1～5d),儿童各种症状的RR逐渐降低,沙尘暴过后4d(滞后4d),几乎所有症状均恢复正常.暴露儿童在沙尘暴发生当天,除肺部喘鸣和胸部憋闷发生的RR升高不显著外(p>0.05),其他所查症状发生的RR均有显著性升高(p<0.05,p<0.01,p<0.001).沙尘暴过后虽然各种症状RR均有所下降,但下降速度不同:在滞后1～2d,气短、眼睛干涩、流泪和心情压抑等4种症状RR仍显著高于沙尘暴前,直到滞后3d才恢复到正常水平;而咳嗽、咯痰、咽干口苦和打喷嚏等4种症状RR在滞后4d才恢复正常;流涕症状RR在滞后5d才基本恢复正常.不同年度和不同时期的沙尘暴事件对儿童健康症状的影响有所不同.从以上结果可以看出:沙尘暴对儿童的健康既有当日急性效应又有一定的短期滞后效应.     

Floodplain Rehabilitation as a Hedge against Hydroclimatic Uncertainty in a Migration Corridor of Threatened Steelhead

A strategy for recovering endangered species during climate change is to restore ecosystem processes that moderate effects of climate shifts. In mid‐latitudes, storm patterns may shift their intensity, duration, and frequency. These shifts threaten flooding in human communities and reduce migration windows (conditions suitable for migration after a storm) for fish. Rehabilitation of historic floodplains can in principle reduce these threats via transient storage of storm water, but no one has quantified the benefit of floodplain rehabilitation for migrating fish, a widespread biota with conservation and economic value. We used simple models to quantify migration opportunity for a threatened migratory fish, steelhead (Oncorhynchus mykiss), in an episodic rain‐fed river system, the Pajaro River in central California. We combined flow models, bioenergetic models, and existing climate projections to estimate the sensitivity of migration windows to altered storm patterns under alternate scenarios of floodplain rehabilitation. Generally, migration opportunities were insensitive to warming, weakly sensitive to duration or intensity of storms, and proportionately sensitive to frequency of storms. The rehabilitation strategy expanded migration windows by 16–28% regardless of climate outcomes. Warmer conditions raised the energy cost of migrating, but not enough to matter biologically. Novel findings were that fewer storms appeared to pose a bigger threat to migrating steelhead than warmer or smaller storms and that floodplain rehabilitation lessened the risk from fewer or smaller storms across all plausible hydroclimatic outcomes. It follows that statistical downscaling methods may mischaracterize risk, depending on how they resolve overall precipitation shifts into changes of storm frequency as opposed to storm size. Moreover, anticipating effects of climate shifts that are irreducibly uncertain (here, rainfall) may be more important than anticipating effects of relatively predictable changes such as warming. This highlights a need to credibly identify strategies of ecosystem rehabilitation that are robust to uncertainty. Rehabilitación de Planicies Inundables como Cerco contra la Incertidumbre Hidroclimática en un Corredor Migratorio de Oncorhynchus mykiss, Especie Amenazada     

Aerodynamics of ancient egyptian Obelisks and their structural response to Boundary Layer wind

Environmental Fluid Mechanics - Ancient Egyptian obelisks have been carved thousands of years ago and survived many earthquakes and wind storms. This study examines the aerodynamic characteristics...     

九龙江流域典型汇水区地表径流氮磷流失特征分析

选取九龙江流域5个典型汇水区,通过流域主要雨季天然降雨径流过程监测,对所获得的氮磷营养盐的监测数据进行归纳与分析,着重探讨了暴雨事件下径流氮磷流失及其形态的变化规律。结果表明:暴雨事件下农业汇水区地表径流氮输出以水溶态为主,磷以泥沙结合态为主,天然林地为主的汇水区则相反,前者以泥沙结合态为主,后者以水溶态为主;5个汇水区暴雨事件中总氮最高浓度值为日常采样浓度值的2.9～11.3倍,暴雨事件中总磷最高浓度值为日常采样浓度值的2.9～20.5倍;氮磷输出量均值的差异反映氮磷输出量大小受土壤质地、施肥量、土壤氮磷含量、土壤保水保肥性能等因素的综合影响。整个径流过程中水量和氮磷浓度随时间变化幅度较大,且2者变化呈大体相同的趋势。氮磷及其各形态的浓度多数在相同时间内达到峰值。泥沙结合态氮、水溶态磷变化幅度较小,水溶态氮和泥沙结合态磷浓度变化幅度较大。统计各汇水区雨量不同的降雨事件下氮磷流失负荷表明,特大暴雨对汇水区氮磷负荷的贡献非常显著。     

Confronting coastal morphodynamics with counter-erosion engineering: the emblematic case of Wissant Bay,Dover Strait

Wissant Bay is a picturesque and highly frequented French coastal resort comprising beaches, dunes, marshes, and bold capes facing the Dover Strait. Situated at the southern approaches to the North Sea, the 8 km-long bay has, arguably, the most rapidly eroding shoreline in metropolitan France. Retreat has largely affected much of the bay shoreline west of Wissant town, with parts of this sector having lost up to 250 m in the last 50 years, whereas a much smaller sector east of the town is a zone of accretion. Various dune, beach and nearshore morphodynamic studies conducted over the last decade have identified chronic sand bleeding from the western sector and longshore transport to the east, within a framework of what appears to be an ongoing shoreline rotation process within a dominant longshore sediment transport cell between the headland of Cape Gris Nez to the west and the bold chalk cliffs of Cape Blanc Nez to the east. Retreat of the narrowing beach-dune barrier poses a threat in the coming years, as there is a likelihood of it being breached by storms. The seawall protecting Wissant town has also been repeatedly damaged since 2000 due to the chronic sand deficit. These changes involve interactions between a nearshore sand bank, a complex macrotidal beach comprising multiple subtidal to intertidal bars and troughs subject to strong longshore sand transport especially during storms, and aeolian dunes. The nearshore bank acts as a dissipater of incident storm wave energy and as a sand source for the multi-barred beaches and dunes, and has been strongly impacted by past massive aggregate extraction. The bank is, in turn, part of a larger system of mobile banks reworked by storms and tidal currents within the framework of a sand circulation system between the eastern English Channel and the southern North Sea. The aim of this work is to confront knowledge acquired on the morphodynamics of the bay with an engineering plan proposed to counter erosion and reestablish shoreline stability. The plan is based essentially on the creation of an ‘equilibrium’ beach profile, capable of withstanding storms, comprising an enlarged upper beach berm, and constructed through beach nourishment from a nearshore source located 20 km east of Wissant Bay. The plan has not been implemented because of cost. Even if it were to be implemented, its efficiency seems very doubtful because the beach profile simulations on which it is based neglect the complex multi-barred morphology and the overwhelming dominant longshore transport over bars during storms. The plan is also geared towards resolving a local problem of erosion that is embedded in the larger and rather complex spatiotemporal morphodynamics and sediment transport mechanisms evoked above. Wissant Bay is emblematic of the problems of erosion facing many communes in France, and elsewhere. The fight against shoreline erosion generally starts with the commonly insurmountable hurdle of fund-raising for costly engineering proposals that are not always based on a clear grasp of the embedded scales of change affecting the coast.     

Reconstruction of an interrupted primary beach plain succession using a Geographical Information System

This study reports on a primary succession on a beach plain on the Dutch Wadden island of Schiermonnikoog. Vegetation succession started in 1959 when a sand dike was constructed to prevent structural erosion of the area by storm floods. Since then the sandy beach behind the dike has been protected from the direct influence of the North Sea. Heavy storms in 1972, however, created a large gap in the dike which has remained open since. Occasional storm floods during winter penetrate deeply into the area and salt water can cover parts of the beach plain for several months. This had a pronounced impact on the vegetation. Vegetation maps for six different years and data from a permanent plot have been used to reconstruct vegetation succession over a 42-yr period. Certain parts of the area seem to have changed little, while others have developed a grassland or scrub cover. The heavy storms and associated processes such as sand blowing, intensive flooding and increased salinity have created a disturbance/stress gradient of progressive and regressive succession across the beach plain. In certain places the vegetation cover has repeatedly been destroyed and succession re-initiated. It is concluded that the different stages of succession and associated diversity of plant species only can persist through the maintenance of the natural dynamics of the area.     

粤北天井山国家森林公园三种林木在2008年特大冰雪灾害后的恢复

自2008年5月至2009年8月（共480 d）,对遭受2008年特大冰雪灾害的广东省北部天井山国家森林公园中受灾点（海拔700 m）和未受灾点（海拔550 m）的3种植物：樟树（Cinnamomum camphora）、荷木（Schima superba）和罗浮栲（CastanopsisFagaceae）进行对比实验。选择生理指标为：光系统II最大光化学量子效率（Fv/Fm）、比叶面积（SLA）、叶干物质重（LDMC）、单位叶面积氮含量（Na）、单位叶面积多酚含量（Phena）。研究结果显示：3受灾种Fv/Fm均无下降;受灾罗浮栲、荷木的其他各指标在300 d后已恢复至正常水平,而受灾樟树的各生理指标在300 d后仍显著低于正常（p〈0.1）;受灾樟树的生长模式由快速生长型改变为积累营养型。研究表明：（1）雪灾损伤对光系统II没有累积效果;（2）雪灾造成的冠层改变对中下林层的营养物质分配有影响;（3）作为人工栽培种的樟树,较自然生长种需要更长的灾后恢复期。     

The influence of disturbance events on survival and dispersal rates of Florida box turtles.

Disturbances have the potential to cause long-term effects to ecosystem structure and function, and they may affect individual species in different ways. Long-lived vertebrates such as turtles may be at risk from such events, inasmuch as their life histories preclude rapid recovery should extensive mortality occur. We applied capture-mark-recapture models to assess disturbance effects on a population of Florida box turtles (Terrapene carolina bauri) on Egmont Key, Florida, USA. Near the midpoint of the study, a series of physical disturbances affected the island, from salt water overwash associated with several tropical storms to extensive removal of nonindigenous vegetation. These disturbances allowed us to examine demographic responses of the turtle population and to determine if they affected dispersal throughout the island. Adult survival rates did not vary significantly either between sexes or among years of the study. Survival rates did not vary significantly between juvenile and adult turtles, or among years of the study. Furthermore, neither adult nor juvenile survival rates differed significantly between pre- and post-disturbance. However, dispersal rates varied significantly among the four major study sites, and dispersal rates were higher during the pre-disturbance sampling periods compared to post-disturbance. Our results suggest few long-term effects on the demography of the turtle population. Florida box turtles responded to tropical storms and vegetation control by moving to favorable habitats minimally affected by the disturbances and remaining there. As long as turtles and perhaps other long-lived vertebrates can disperse to non-disturbed habitat, and high levels of mortality do not occur in a population, a long life span may allow them to wait out the impact of disturbance with potentially little effect on long-term population processes.     

渭河阶地全新世成壤环境演变的高分辨率研究

对秦岭北麓渭河阶地全新世土壤剖面进行的高分辨率分析研究，揭示了该地区全新世土壤剖面的黄土-古土壤序列，是由于季风气候变化引起的以风尘堆积占优势的成黄土期和以生物风化作用占优势的成壤期相互更迭造成的。马兰黄土堆积所代表的晚更新世，气候冷干，当地为半荒漠环境；全新世初期是气候转暖转湿的过渡时期；全新世中期(85003100 a B．P．)发育的古土壤S0成壤作用最为强烈，为褐色土类型，分析研究表明其中既有淋溶淀积作用，又有粘化作用发生；各项分析指标也都表明S0反映了全新世中期的温暖湿润气候；在该土壤层形成初期，就有属于老官台文化(7500～7000 a B．P)时期的人在当地从事耕作活动。此后，新石器时代中晚期也有人类开发利用当地的土地资源。全新世晚期从3100 a B．P开始，西北季风增强，气候恶化，但当地降水量的减少似乎滞后于降温，所以先周和西周时代在沣河西岸建立都城的时期，当地土壤湿度似乎较大，而之后则显著干旱化。     

Site-specific and integrated adaptation to climate change in the coastal mangrove zone of Soc Trang Province, Viet Nam

The dynamic coastline of Soc Trang Province in the Mekong Delta of Viet Nam is in most parts protected from erosion, storms and flooding by a narrow belt of mangroves. However, the unsustainable use of natural resources and development in the coastal zone is threatening the protection function of this forest belt. This situation is exacerbated by the impacts of climate change, particularly by the increased intensity and frequency of storms, floods and by rising sea levels. Based on analysis of past experience of mangrove planting and historical changes in mangrove cover, an integrated and site-specific approach to adaptation to climate change has been put in place, which comprises mangrove planting and rehabilitation with emphasis on resilience to climate change, and participatory involvement of local communities in effective mangrove management and protection through co-management. To address uncertainties associated with the impacts of climate change, testing of new mangrove planting techniques has started. This includes mimicking successful natural regeneration for small-scale planting in sites with high wave energy and transformation of existing even-aged plantations into more diverse forests—both in terms of structure and species composition. The pre-requisite for mangrove rehabilitation in erosion sites has successfully been put in place: breakwaters made from bamboo have reduced erosion and stimulated sedimentation. The design and construction of the wave-breaking structures, which was based on a numerical model which simulates hydrodynamics and shoreline development, ensures that downdrift erosion can be avoided as far as possible. A comprehensive monitoring program has been established and initial results provide evidence for the effectiveness of the bamboo breakwaters. Early experience shows that co-management is an effective way of maintaining and enhancing the protection function of the mangrove forest belt and at the same time providing livelihood for local communities. Payment for ecosystem services contributes to sustainability of co-management as well as livelihood improvement.     

Determination of set-back lines on eroding coasts. Example of the beaches of the Gulf of Lions (French Mediterranean Coast)

The study presented here describes a method for defining set-back lines along eroding coasts. The method (a mathematical model) combines the long-term shoreline retreat trend with short-term shoreline erosion (during storms). Simulations are carried out for 2030 and compared with the beach width to determine whether the shoreline is likely to shift onshore. The mathematical model is applied to the Frontignan and Carnon beaches (south of France). Both sites possess hard engineering coastal structures and downdrift erosion on the natural beaches. The set-back lines indicate that beaches with groynes are generally wide enough to resist shoreline retreat, while the downdrift “natural” beaches are not. We discuss the possible utilisation of set-back line estimations.     

High-frequency observations of early-stage larval abundance: do storms trigger synchronous larval release in <Emphasis Type="Italic">Semibalanus balanoides</Emphasis>?

The acorn barnacle, Semibalanus balanoides, is thought to release larvae in response to phytoplankton blooms, but there is evidence that another, unidentified cue for release may exist. We conducted high-frequency sampling in Little Harbor, Massachusetts, USA, to determine whether early-stage larval abundance was related to several environmental variables, and to characterize vertical distributions of the larvae. Larval concentrations peaked at 2.52 and 1.02 individuals l⁻¹ during two storms. Larvae were more abundant near the surface than near the bottom. We suggest the hypothesis that turbid conditions and upward-swimming behavior may protect newly-released larvae from predation and cannibalism. Future studies should test this hypothesis with barnacles and other invertebrates.     

Nested numerical scheme in a polar coordinate shallow water model for the coast of Bangladesh

This study is concerned with the development of storm surge model to predict water level accurately due to surge associated with a cyclone along the coast of Bangladesh. Considering the funnel shape of the Bay of Bengal, coastal bending and the existence of off-shore islands, a vertically integrated model in cylindrical polar coordinate system is developed using nested numerical scheme. A fine mesh scheme capable of incorporating coastal bending and offshore islands properly in the numerical scheme is nested into a coarse mesh scheme covering up to 15° N latitude of the Bay of Bengal. The developed model is used to estimate water levels at different coastal and island stations associated with a few storms that hit the coast of Bangladesh. The computed surge levels compared well with observed ones and predicted surge levels investigated with different approaches.     

Technical aid for hydraulics research in developing nations

Many water-related problems are shared by most of the developing countries and the industrialized nations could be in position of offering aid in such problems. Water scarcity and access to safe water, water pollution, severe storms and floods, droughts, waterborne diseases and landslides and mud floods are the most commonly shared problems among developing nations. These problems were discussed in a workshop organized as part of the Fifth International Symposium on Environmental Hydraulics in 2008. The discussion included identification of actors both in the developing and developed nations (vgr. local and national governments, NGOs, universities, foundations and private and public research institutions), aid modalities such as education, technology transfer, technology development and direct investment as well as restrictions and barriers in the form of political and legal issues, economic limitations, cultural differences and geographic distances. Recommendations about how developed nations could help developing countries are issued.