Variation of cytosine methylation in response to water availability in two contrasting growth types of an amphibious plant Alternanthera philoxeroides

We used methylation-sensitive amplified polymorphisms (MSAP) to examine the alterations of cytosine methylation in two contrasting growth types of an amphibious plant Alternanthera philoxeroides in response to change of water availability. Using 34 pairs of selective primer combinations, we amplified 1026 and 1128 clear and reproducible bands in root and leaf of A. philoxeroides, respectively. When the aquatic types of plants were transplanted into drought culture, we found a decrease in the overall DNA methylation. When the terrestrial types of plants were transferred into flood culture, we detected a higher frequency of methylation than demethylation events. Alterations of DNA methylation were more evident in root than in leaf in response to change of water availability. When the confounding effects of variable environmental factors were removed, differences of cytosine methylation profiles were observed between two growth types of plants under common growth conditions.     

New challenges in the management of the Brazilian Pantanal and catchment area

The Pantanal wetland is a vast seasonally inundated area of extraordinary landscape and biological diversity and complexity. It is located in the upper portion of the Paraguay River basin in central South America. During the rainy season, increased stream discharge from the surrounding basin produces an annual flood pulse through the Pantanal. Increasing human impact, such as dam construction, deforestation, agricultural related activities, and the Hidrovia project in the Parana-Paraguay waterway, threaten the ecological stability of the Pantanal area. As a result, there is an urgent need to introduce new management practices in the Pantanal Basin. In this paper we present a concept for managing the Pantanal catchment based on the integration of ecological knowledge, institutional organization, and involvement of different stakeholders. We propose approaches for an integrated management of the Pantanal and its catchment based on improving data bases and the empowerment of the stakeholder groups. The latter depends on increasing the level of education and access to information, as well as implementing procedures to improve public involvement and enforcement of environmental regulations.This revised version was published online in March 2005 with corrections to the issue cover date.     

Habitat heterogeneity and disturbance influence patterns of community temporal variability in a small temperate stream

Both habitat heterogeneity and disturbance can profoundly influence ecological systems at many levels of biological and ecological organization. However, the joint influences of heterogeneity and disturbance on temporal variability in communities have received little attention despite the intense homogenizing influence of human activity. I performed a field manipulation of substrate heterogeneity in a small New England stream, and measured changes in benthic macroinvertebrate communities for 100 days—a period that included both a severe drought and a flood. Generally, community variability decreased with increasing substrate heterogeneity. However, within sampling intervals, this relationship tended to fluctuate through time, apparently tracking changes in hydrology. At the beginning of the experiment, community temporal variability clearly decreased along a gradient of increasing substrate heterogeneity—a result consistent with an observational study performed the previous year. During the subsequent weeks, droughts and flooding created exceptionally high variability in both hydrology and benthic macroinvertebrate community structure resulting in the disappearance of this relationship. However, during the last weeks of the experiment when hydrologic conditions were relatively more stable, the negatively sloped relationship between community temporal variability and habitat heterogeneity reemerged and mimicked relationships observed both early in the experiment and in the previous year’s study. High habitat heterogeneity may promote temporal stability through several mechanisms including stabilization of resources and increased refugia from minor disturbances or predation. However, the results of this experiment suggest that severe disturbance events can create large-scale environmental variability that effectively swamps the influence of habitat heterogeneity, illustrating that a thorough understanding of community temporal variability in natural systems will necessarily consider sources of environmental variability at multiple spatial and temporal scales. Handling editor: L. M. Bini     

Flooded flatheads: evidence of increased growth in Mississippi River <Emphasis Type="Italic">Pylodictis olivaris</Emphasis> (Pisces: Ictaluridae) following the Great Midwest Flood of 1993

Both the Mississippi and Missouri rivers experienced major flooding in the spring and summer of 1993, inundating much of their floodplains for long periods, and allowing fish access to vast but previously inaccessible benthic foraging areas. In response to the latter, we hypothesized that flathead catfish (Pylodictis olivaris) would exhibit altered post-flooding growth as compared to like-aged fish whose lives were flood-free. To test this hypothesis, we obtained the left pectoral fin spines from hoop-netted Mississippi River flathead catfish collected in the vicinity of Crystal City, Missouri, USA, and conducted an individual-based back-calculated growth comparison of individuals captured pre-flood (1991) and post-flood (1996). For like-aged cohorts, our back-calculated length-at-age data clearly show that the post-flooding growth in 1996-collected fish was superior to that of the 1991-collected fish that had experienced less exceptional flow regimes. This outcome suggests that increased forage or/and foraging opportunities can be a consequence of flooding, and that flathead catfish are able to capitalize on this. The natural flooding regime of big rivers may thus be an important contributor to the growth and success of certain fish species; consequently, modifying the river’s natural hydrograph and channel morphology may be detrimental. Handling editor: J. A. Cambray An erratum to this article is available at .     

Estimating biogeochemical and biotic interactions between a stream channel and a created riparian wetland: A medium-scale physical model

Straightened channels and altered and drained adjacent riparian wetlands have adversely impacted streams and rivers throughout the US Midwest. This research investigated the biological connection and water quality of a 0.07 ha diversion wetland and adjacent stream at the Olentangy River Wetland Research Park in central Ohio. Before the flowthrough conditions were established, we demonstrated with mark and recapture techniques that the wetland already was a biorefuge for fish under extreme conditions; two species (Centrarchidae) captured in the stream before a total drawdown of the stream were found in the wetland a year later. In addition, water at the bottom remained at around 4 °C over the winter likely due to groundwater input, which possibly provided a warmer shelter for fish. Stream water quality of the lower section, downstream of the wetland outlet, generally improved with hydrologic pulsing in spring after flow-through reconnection due to the trapping of nutrients in the wetland. Mean removal per flood pulse for nitrate-nitrite, total nitrogen (TN), soluble reactive phosphorus (SRP), total phosphorus (TP) were 1.81 g-N m⁻² per pulse, 1.02 g-N m⁻² per pulse, 0.014 g-P m⁻² per pulse, and 0.004 g-P m⁻² per pulse, respectively. The wetland exported 2.8 g-C m⁻² per pulse of organic carbon. A greater attenuation of NO₃⁻ and TP occurred in the marshy outlet channel section of the wetland than the open water section. The diversion wetland successfully removed nitrate and phosphorus during storm pulses in spring. Similar designs should be applied to other locations to examine their function under different climatic and hydrological conditions.     

The role of density-dependent individual growth in the persistence of freshwater salmonid populations

Theoretical and empirical models of populations dynamics have paid little attention to the implications of density-dependent individual growth on the persistence and regulation of small freshwater salmonid populations. We have therefore designed a study aimed at testing our hypothesis that density-dependent individual growth is a process that enhances population recovery and reduces extinction risk in salmonid populations in a variable environment subject to disturbance events. This hypothesis was tested in two newly introduced marble trout (Salmo marmoratus) populations living in Slovenian streams (Zakojska and Gorska) subject to severe autumn floods. We developed a discrete-time stochastic individual-based model of population dynamics for each population with demographic parameters and compensatory responses tightly calibrated on data from individually tagged marble trout. The occurrence of severe flood events causing population collapses was explicitly accounted for in the model. We used the model in a population viability analysis setting to estimate the quasi-extinction risk and demographic indexes of the two marble trout populations when individual growth was density-dependent. We ran a set of simulations in which the effect of floods on population abundance was explicitly accounted for and another set of simulations in which flood events were not included in the model. These simulation results were compared with those of scenarios in which individual growth was modelled with density-independent Von Bertalanffy growth curves. Our results show how density-dependent individual growth may confer remarkable resilience to marble trout populations in case of major flood events. The resilience to flood events shown by the simulation results can be explained by the increase in size-dependent fecundity as a consequence of the drop in population size after a severe flood, which allows the population to quickly recover to the pre-event conditions. Our results suggest that density-dependent individual growth plays a potentially powerful role in the persistence of freshwater salmonids living in streams subject to recurrent yet unpredictable flood events. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

河流沿线土地利用对策的研究

河流沿线土地是与河流、湖泊的生态学过程紧密相连,直接受洪水影响的沿河（湖）土地带,本文以生态学原理为指导,结合中国森林生态网络工程体系建设理论,对河流沿线土地安全和土地利用的原则、指导思想、理论依据及对策等问题进行了探讨,河流沿线土地安全包括土地的生态效闪安全、经济效益安全与社会效益安全3个方面,土地利用策略的原则是要确保三者的统一,找到三者的最佳结合部,土地利用的指导思想是要把治理与开发紧密结合起来,通过各种措施加强土地的安全建设,实行以增加林木比重为主的近自然的利用和管理对策,根据河流特征的地域分异来确定不同河流,不同河段的利用模式,并基于洪水干扰的风险等级和河流沿线土地的空间分异规律,诊为在河流沿线的纵向上,分别中下游不同河实施人为干扰程度不同的管理对策;横向上按照土地分异性和洪水安全性,分别弹性利用带、脆弱利用带和稳定利用带3条不同土地带采取不同的利用对策。     

Relationships between vegetation patterns and hydroperiod on the Roanoke River floodplain,North Carolina

This study quantified relationships between forest composition and flooding gradients on the Roanoke River floodplain, North Carolina. Because flooding is highly variable in time and space, the research was designed to determine the specific hydrological parameters that control woody species abundance on the landscape scale. I specifically tested the importance of spring vs. yearly flood duration, as well as flood duration during hydrologically wet vs. dry years. Field vegetation samples of woody species composition were integrated with spatial data from a Landsat Thematic Mapper (TM) classification and a flood simulation model derived in part from synthetic aperture radar (SAR) imagery. Flood simulations were output and summarized for the periods 1912–1950 (before dams were constructed on the river) and 1965–1996 (after all of the dams were completed). Tenth percentile (dry), median, and 90th percentile (wet) hydroperiod (flood duration) regimes were generated for the spring and year, both pre- and post-dam. Detrended correspondence analysis (DCA) was used to ordinate the plot data, and correlation/regression between ordination axis scores and the flood variables were used to explore the relationships between flooding and species composition. Nineteenth percentile hydroperiod (i.e., wet conditions) correlated most strongly with DCA axis 1 (r>0.9), indicating that inundation during extremely wet years strongly controls species composition on the floodplain. The results were used to quantitatively determine the niche width for both species and mapped vegetation classes in terms of number of days flooded annually and during the spring growth period. The results suggest that spring hydroperiod is an important mechanism that may drive competitive sorting along the flooding gradient, especially during the early years of succession (i.e., pre-dam, which represents the period during which most of the forests sampled were established), and that annual hydroperiod affects the relative dominance of species as the forests mature.