The significance of water inputs to plankton biomass and trophic relationships in a semi-arid freshwater wetland (central Spain)

This study attempts to describe changes in plankton biomass(including bacteria, phytoplankton, ciliates, rotifers, andcrustaceans) in the semi-arid, hypertrophic, freshwater wetland,Las Tablas de Daimiel National Park (central Spain), in relationto water inflow. An inter-annual comparison of 1996 and 1997,with contrasting rainfall, reveals that inflows in the formof flooding act as a bottom-up structuring force on total planktonbiomass. However, the responses of plankton biomass to floodingwere different in strength between the two years, which canbe attributed to shifts in plankton community structure. Crustaceanzooplankton conditioned total plankton biomass in 1996, basedon the relationship between the high individual biomass andcommunity development. Crust-aceans decreased in 1997, whilebacteria, phytoplankton and rotifers increased. The quantitativeincrease of the latter groups resulted in a higher total planktonbiomass in 1997. The key position of crustaceans in the wetlandplankton is also reflected in their capability for exertingsignificant top-down control, which was clearly evident in 1996but weaker in 1997, based on their numerical reduction. Statisticalanalyses provide evidence that the decline of trophic interactionsin 1997 is related to the strength of flooding in that year,thereby highlighting the significance of the disruptive actionof physical disturbance on biotic interactions in the plankton.Flooding and areal inundation were also shown to be significantfor spatial heterogeneity. In 1996, site-specific developmenttook place in the absence of prolonged flooding effects, resultingin high spatial heterogeneity. In 1997, however, remarkablehomogenization of plankton biomass occurred along the majorwater flow path. Thus, wetland landscape heterogeneity dependson inflows which condition areal inundation. This, in turn,influences plankton dynamics.     

The value of plant functional groups in demonstrating and communicating vegetation responses to environmental flows

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红穗苔草对天鹅洲湿地淹水时间变化的形态学响应

以天鹅洲湿地的优势种红穗苔草（Carex argyi）作为研究对象,以淹水持续时间作为水位变化的衡量指标,选取3个淹水持续时间不同的位点,研究了淹水时间长短对红穗苔草形态指标的影响。通过野外原位观测试验发现,红穗苔草的株高及叶片的长、宽对淹水时间的长短反应敏感,而单个分株上的绿叶数对淹水时间的长短不敏感。适度的淹水可以显著增加叶片的长度和株高,长期淹水和相对干旱的环境不利于叶片的伸长和株高的增加。短时间淹水处理株高一直维持较高的水平,并保持相对的稳定。淹水会显著增加叶片的宽度,长时间淹水的处理效果更明显,且维持时间较长。长期淹水会提高红穗苔草地上部生物量的分配比例。尽管不同水位点土壤氮含量有显著差异,但是氮对红穗苔草形态指标并无显著的影响。以上实验结果表明,红穗苔草可以通过调节其叶片的形态及地下和地上部分生物量的分配比例来适应淹水胁迫的不利环境,有利于其在水位波动条件下种群的稳定和维持。     

飞来峡水库蓄水初期营养状态及浮游生物分布特征

于2000年丰水期和枯水期调查分析了新建河流型水库-飞来峡水库在蓄水初期的营养状态及浮游生物特征。结果表明:水库处于营养累积高峰期,已开始回落,但流域上游大量含磷废水使水库中磷含量继续上升,目前属于中营养型。共记录到浮游植物29种(属),以蓝藻门、绿藻门、硅藻门种类较多,其中丰水期以蓝藻和绿藻为主,枯水期是硅藻占优势,除大坝附近外,浮游植物两个季节密度变化不大,为0.39×10⁶cells·L^-1.浮游动物53种(属),其中包括僧帽溞和透明薄皮溞两种嗜寒性种类,丰度为52ind.·L^-1,枯水期高于丰水期,数量以轮虫和无节幼体为多。     

Colonising Strategies and Diapause of Planktonic Rotifers (Monogononta,Rotifera) during Aquatic and Terrestrial Phases in a Floodplain (Lower Oder Valley,Germany)

The floodplains of the River Oder are inundated in winter and spring and are desiccated during summer. The plankton community developing towards the end of winter is dominated by monogonont rotifers. Some species maintain populations on the flooded areas as well as in the remaining permanent waters after flooding. Other species are found during the inundation period only. These species produce drought‐resistant diapause stages, beginning at low population densities between 5 to 36 females L^–1. Experiments showed that 9 out of 10 species, which were observed to produce resting eggs during the aquatic phase, were able to survive the terrestrial phase through dormancy in the desiccated floodplain soils. Other species colonise the temporarily inundated areas from the permanent waters again during each flooding period.     

Managed flooding can augment the benefits of natural flooding for native wetland vegetation

Managed flooding is increasingly being used to maintain and restore the ecological values of floodplain wetlands. However, evidence for its effectiveness is sometimes inconsistent and water available for environmental purposes often limited. We experimentally inundated a floodplain wetland (or “billabong”) in late spring by pumping water from its adjacent creek, aiming to promote the native wetland flora and suppress terrestrial exotics. Vegetation was surveyed before (spring) and after (late summer) the managed flood in the experimental billabong and in three control billabongs. Floodplain water levels were continuously monitored. Wet conditions caused two of the control billabongs to also flood, but to a lesser extent than the experimental billabong. We therefore assessed vegetation changes relative to flooding duration. With increasing flooding duration, the cover of wetland vegetation (amphibious and aquatic species) increased and the cover of terrestrial and exotic vegetation decreased, with these effects largest in the deliberately flooded billabong. Flooding durations greater than 20 days generally resulted in increased cover of wetland plants and restricted the growth of terrestrial plants. Reinstatement of more appropriate flooding regimes can thus promote native wetland plants, while suppressing terrestrial exotic species. Our study also provides evidence for the use of modest water allocations to augment the benefits of natural flooding in the maintenance and restoration of native wetland plant communities.     

Provenance,genotype, and flooding influence growth and resource acquisition characteristics in a clonal,riparian shrub

Premise

Riparian plants can exhibit intraspecific phenotypic variability across the landscape related to temperature and flooding gradients. Phenotypes that vary across a climate gradient are often partly genetically determined and may differ in their response to inundation. Changes to inundation patterns across a climate gradient could thus result in site-specific inundation responses. Phenotypic variability is more often studied in riparian trees, yet riparian shrubs are key elements of riparian systems and may differ from trees in phenotypic variability and environmental responses.

Methods

We tested whether individuals of a clonal, riparian shrub, Pluchea sericea, collected from provenances spanning a temperature gradient differed in their phenotypes and responses to inundation and to what degree any differences were related to genotype. Plants were subjected to different inundation depths and a subset genotyped. Variables related to growth and resource acquisition were measured and analyzed using hierarchical, multivariate Bayesian linear regressions.

Results

Individuals from different provenances differed in their phenotypes, but not in their response to inundation. Phenotypes were not related to provenance temperature but were partially governed by genotype. Growth was more strongly influenced by inundation, while resource acquisition was more strongly controlled by genotype.

Conclusions

Growth and resource acquisition responses in a clonal, riparian shrub are affected by changes to inundation and plant demographics in unique ways. Shrubs appear to differ from trees in their responses to environmental change. Understanding environmental effects on shrubs separately from those of trees will be a key part of evaluating impacts of environmental change on riparian ecosystems.     

Response of floodplain grassland plant communities to altered water regimes

Floodplain grasslands are often composed of a mosaic of plant communities controlled by hydrological regime. This article examines the sensitivity of floodplain grassland plant communities to water regime using reciprocal transplantation of an inundation grassland and a flood-meadow within an English floodplain. Experimental treatments comprised control, transplanted and lifted plots; the last treatment, in order to elucidate any disturbance effects of transplantation. Plant community response was analysed using species abundance and their ecological traits. Results from both communities showed substantial annual variations related to hydrology, including significant species changes, but generally, vegetation seemed to be responding to drier conditions following a major flood event. This ‘drying’ trend was characterised by increased species diversity, a greater abundance of competitive species and fewer typical wetland plants. Transplanted community composition increasingly resembled receptor sites and transplant effects were most pronounced the first year after treatment for both vegetation types. Differential responses to water regime were detected for the two plant communities. The inundation grassland community was particularly dynamic with a composition that rapidly reflected drying conditions following the major flood, but transplantation into a drier flood-meadow site prompted little additional change. The flood-meadow community appeared more resistant to post-inundation drying, but was sensitive to increased wetness caused by transplantation into inundation grassland, which significantly reduced six species while none were significantly favoured. The effects of disturbance caused by lifting the transplants were limited in both communities, although five species showed significant annual fluctuations. The study shows that small alterations in water regime can prompt rapid vegetation changes and significant plant species responses in floodplain grasslands, with effects probably magnified through competitive interactions. The dynamic properties of floodplain vegetation demonstrated by this study suggest that its classification, management and monitoring are challenging and ideally should be based on long-term studies.     

Response of three arid zone floodplain plant species to inundation

For species to persist on floodplains and in temporary wetlands in arid climates, where large and unpredictable water level fluctuations are common, at least one life history stage must be able to survive inundation. We investigated the survival and performance (RGR, total biomass and above-to-belowground biomass (A:B)) of three common and often coexisting arid zone floodplain species: Xanthium strumarium, Cyperus gymnocaulos and Ludwigia peploides. Observations suggested the species had different responses to inundation, which was tested in a controlled pond experiment. Plants were held at three elevations (+ 10 cm, ? 20 and ? 70 cm) and subjected to three hydrological regimes (static 90 cm, 1 and 5 cm day^?1 inundation) for 16 weeks. Xanthium strumarium died when completely inundated for longer than 4 weeks but when partially flooded survived, showed lower growth rates, increased A:B and produced adventitious roots. C. gymnocaulos showed reduced growth rates when partially flooded and senesced to rhizomes when completely inundated for longer than 4 weeks, which re-sprouted after inundation pressure was removed. L. peploides responded positively to flooding with increased A:B and the production of adventitious roots. The species exhibited three contrasting responses to inundation, which do not necessarily fit neatly within existing water regime functional classification frameworks.     

Zooplankton abundance and evidence for its reduction by macrophyte mats in two Orinoco floodplain lakes

Zooplankton populations were sampled over one annual cycle intwo floodplain lakes of the Orinoco River, Venezuela, in anattempt to establish the relationship between abundance patternsand the hydrology and morphometry of the lakes. One of the lakes(Tineo) is relatively large with a gently sloping basin; theother one (Aguilera) is smaller and channel-shaped. The hydraulicresidence time of Lake Aguilera during inundation by the riveris shorter (<1 day) than the minimum generation times ofcrustacean (4–12 days) and rotiferan (2.5 days) zooplankton.For Lake Tineo, residence time during inundation (7 days) islonger than generation times for all taxa except copepods. AlthoughLake Aguilera receives water from Lake Tineo during inundation,zooplankton densities were greatly reduced during passage througha large bed of the floating aquatic grass Paspalum repens locatednear the outlet of Lake Tineo. This retention was not size-selectiveand affected phytoplankton as well as zooplankton. In the Orinocofloodplain zooplankton densities are affected not only by hydraulicresidence times but also by passage of water between lakes,which exposes populations to large losses within macrophytebeds. Retention of plankton by floating macrophyte beds is potentiallyimportant to the trophic ecology of tropical floodplain lakesbecause it results in the concentration of planktonic productionin epiphytic and benthic habitats, where it can readily supportfood webs consisting of macroinvertebrates and fishes. Exportof plankton from floodplain waterbodies to the river is alsoreduced by this mechanism. ¹Present address: Department of Biological Sciences, Universityof California, Santa Barbara, CA 93106, USA     

本地和外来草本物种对水分条件时间异质性的可塑响应

极端气候导致的干旱和水淹事件频发，影响了外来植物和本地植物的生长。为了解外来种和本地种植物对干旱和水淹事件发生顺序的响应，探讨草本植物适应水分时间异质性的策略，该文以美国蒙大拿州西部4种本地植物和4种外来植物为研究对象，将所有植物分别进行持续湿润(对照，CK)、水淹-干旱(I-D)和干旱-水淹(D-I)处理，并观测一系列形态和生物量特征的变化。结果表明：(1)与CK相比，D-I和I-D处理均显著降低了外来种的总生物量(P<0.05)。(2)D-I显著降低了本地种早期总生物量、后期地下生物量和根冠比，但显著提高了其后期的相对生长(P<0.05)。(3)D-I处理显著降低了所有植物的地下-地上生物量关系的异速指数，外来种异速指数显著高于本地种(P<0.05)。综上认为，极端事件(水淹和干旱)的发生顺序能改变外来植物和本地植物的生物量分配，早期干旱比后期干旱更容易减少植物生物量的积累，但能促进本地种后期的生长；本地种在环境胁迫下不被降低的总生物量表现说明维持表型稳定的能力较强；D-I处理下本地种和外来种地上和地下生物量关系的分配方式不同。     

Floodplain ecosystem dynamics under extreme dry and wet phases in semi‐arid Australia

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漓江水陆交错带植物叶性状对水淹胁迫的响应及经济谱分析

以漓江水陆交错带为研究区,分两个条带分别量测了适生植物的5个叶性状指标:最大净光合速率(A_(max))、比叶重(LMA)、单位质量叶片全氮含量(N_(mass))、单位质量叶片全磷含量(P_(mass))、单位质量叶片全钾含量(K_(mass))。研究重度淹没带与微度淹没带不同功能型植物叶性状间的差异,分析并讨论重度淹没带叶性状间的关系与全球尺度是否存在差异,探究重度淹没带植物对水淹生境的生理响应机制。结果如下:(1)重度淹没带植物叶片的A_(mass)、N_(mass)、P_(mass)显著高于微度淹没带。(2)乔木、灌木叶片的LMA均显著高于草本植物,而A_(mass)、PPUE均显著低于草本植物。(3)重度淹没带草本叶性状指标的N_(mass)、P_(mass)、PNUE均显著高于微度微度淹没带,而乔木、灌木的叶性状在两个条带的差异则不显著。(4)重度淹没带植物叶性状关系与全球尺度基本一致,其植物叶片具有低LMA,高A_(mass)、Nmas s、P_(mass)。分析可知,重度淹没带植物在出露期提高叶片光合效率及相关营养水平可能是其适应水淹胁迫特殊生境的关键策略之一;不同功能型植物对同一环境的适应能力存在一定的差异,草本对于水淹环境的响应更为积极,适应能力更好;重度淹没带也存在叶经济谱,其植物在经济谱中属于"快速投资-收益"型物种。     

Biogeochemistry and effects of copper,manganese and zinc added to enclosures in Island Billabong,Magela Creek,northern Australia

Three large plastic enclosures (5 m diam, volume 40 m³) were used to study the effects of copper, manganese and zinc, on the phytoplankton community in Island billabong, a floodplain billabong (waterhole) situated in the Magela Creek in tropical northern Australia. Copper was added to one enclosure, and manganese and zinc to another, to give initial concentrations around ten times the normal wet season values. The enclosures and the billabong were monitored over a ten week period towards the end of the dry season, with the enclosures allowed to stabilise for four weeks before the metals were added.The control enclosure adequately simulated the temperature and pH changes in the billabong. The trends in conductivity, dissolved oxygen and major ion concentrations were similar in the enclosure and the billabong, with the minor differences observed attributed to either epiphytic growth on the enclosure walls (influenced dissolved oxygen, pH and bicarbonate concentration) or ingress of sulphate-rich groundwater into the billabong (influenced sulphate concentration and conductivity). Major differences in both the composition of species and the size of the phytoplankton populations were observed between the three enclosures and between the control enclosure and the billabong. This variability reflects the great natural variability in the phytoplankton communities in tropical lentic systems, and means that enclosures are unlikely to adequately simulate the biological communities in the billabongs.The control enclosure appeared to simulate quite well the longer term changes in total concentration and speciation of the three metals (copper, manganese & zinc) in the billabong. The mean concentrations of copper and zinc were similar in the two systems, although the mean concentration of manganese in the billabong was almost double that in the enclosure, possibly due to ingress of manganese-enriched groundwater. Particulate forms dominated the speciation of copper and manganese. There was considerable short term variation in both total metal concentration and speciation in both the enclosure and the billabong. This variability appears to be a feature of these small tropical waterbodies.The added heavy metals were found to have minimal detrimental effect on the phytoplankton community in each metal-loaded enclosure. The high natural variability in the phytoplankton community in these tropical systems will make it difficult to separate natural changes from those caused by low level contamination from mining operations should this occur.All three metals were rapidly removed from the water column, so that by the end of the six week period, only ca. 5% of each added metal remained in the water column. Association with the particulate matter (phytoplankton, abiotic particulate matter and MnO_x in enclosure 2) followed by sedimentation was the major removal pathway. Epiphytes growing on the enclosure walls appeared to have a minor influence (<10% of the total amount of metal added) on the removal of the added metals. For copper, uptake by phytoplankton followed by sedimentation was the major (65%) removal process. Manganese and zinc, added together, were found to influence each other. The major manganese removal process (60%) was rapid (ca. 3 days) involving bacterial oxidation and sedimentation of the MnO_x formed. This material appeared to have little influence on the behaviour of zinc, possibly because other particulate matter competed more effectively for the zinc. A further 30% of the added manganese was removed via initial adsorption to other particulate matter, possibly phytoplankton. Approximately one third of this adsorbed manganese (10% of the total added) appeared to undergo delayed oxidation some 8 days after the initial additions, and the heavier particles settled out more rapidly. This path was responsible for removing the major amount (ca. 60%) of the added zinc. We hypothesis that the sorbed zinc inhibited the bacterial oxidation of the manganese. A further 25% of the zinc was removed in association with a burst of phytoplankton activity. The occurrence of bursts in the phytoplankton activity, when populations can increase very substantially and then decrease again, all within the space of a day, appears to be an important mechanism for removing copper and zinc from the water column in these tropical water bodies     

Biodiversity of testate amoebae (Arcellinida and Euglyphida) in different habitats of a lake in the Upper Paraná River floodplain

This study aimed to investigate the testate amoebae (Arcellinida and Eugliphida) species diversity in plankton, macrophytes and aquatic sediment samples from a shallow lake of the Upper Paraná River floodplain. Samples were carried out from April 2007 to March 2008. We recorded 89 taxa, belonging to 10 families. Eighty-two taxa were found in the aquatic sediment, 71 in the macrophytes and 53 in the plankton. Highest values of alpha diversity were observed in the aquatic sediment. Although the plankton had the highest number of accidental species, accessory and constant species were also observed in this habitat. Most of the species classified as constant for the plankton belonged to the genus Arcella. Most of the constant species in the macrophytes and aquatic sediment belonged to the genus Difflugia. This study supports the idea that the presence of these protists in the plankton should not be attributed only to stochastic processes because (i) the species diversity recorded in this habitat was remarkably high in relation to the total biodiversity of the lake, and (ii) we also recorded frequent and constant species in the plankton.     

Utilizing a historical database to refine ground cover vegetation as indicators of wetland hydrology

Indicator species provide an easy and quick method of evaluating ecosystems. The species comprising the most useful indicators of wetlands should be distributed across a range of water depths and inundation durations, while each species is representative of a specific condition. Hydrophytic vegetation is commonly used to determine the existence and type of wetland; however, such indicator systems often depend on assigning species qualitatively to discrete categories based on assumptions about their distribution along a gradient of conditions. The current study proposes a wetland indicator system based on the quantitative responses of individual vegetation species to a gradient of water depths and periods of inundation. A long-term database was utilized to determine species responses to hydrological alterations in a series of wetlands. The hydrophytic plant species investigated (n = 29) displayed relatively narrow ranges of mean hydrologic values and were distributed linearly along multiple hydrologic gradients (hydroperiod, average water depth, and maximum water depth) ranging from Amphicarpum muhlenbergianum which was observed at the shallowest water depths and shortest hydroperiod to Pontederia cordata and Ludwigia repens which were characteristic of wetlands with the deepest water and longest hydroperiod. The species distribution and means along the hydrologic gradients tested indicates they are prime candidates for inclusion in a quantitative or continuum indicator system. The historical database utilized for this study provided valuable information for numerous species common to the Tampa Bay region for which little or no ecological information was previously available. The methodology utilized in this paper provides a cost and time effective method for obtaining the vast amounts of information required to refine plant indicator systems using a large number of species.     

Report of a large fish kill resulting from natural acid water conditions in Australia

A large natural fish kill which resulted in the deaths of a total of more than 3400 fish comprising eight different species occurred in a freshwater billabong (lagoon or small permanent waterbody) on the Magela Creek in the subtropical Northern Territory of Australia in January, 1980. The fish deaths were assessed to be the result of a combination of natural acid water runoff into the billabong and resultant elevated aquatic biotoxic aluminium levels. Details of water quality changes which occurred during the event and analytical data for the fish killed are provided, together with some explanation of the sequences of occurrence of the fish kill.     

Reproductive strategies may explain plant tolerance to inundation: A mesocosm experiment using six marsh species

We investigated the impact of inundation duration on sexual and asexual reproduction strategies in six hygrophilic angiosperm species (2 annuals - Ranunculus sardous and Ranunculus ophioglossifolius, 2 rhizomatous - Juncus articulatus and Eleocharis palustris, and 2 stoloniferous species - Glyceria fluitans and Agrostis stolonifera). Plant growth during three inundation durations (natural, +3 weeks, +6 weeks) was assessed in 20 mesocosms. Biomass and reproductive traits were measured at the onset of flowering and at seed set.The six species maintained or increased their total mass in response to increased inundation period, suggesting a good tolerance to inundation stress. No changes were recorded in flowering time for the five species that flowered. The two annual species increased the number of flowers and mass allocated to sexual reproduction with increased duration of inundation, promoting extensive seed production. The response was species-specific in perennial species with an either a positive or a negative Gaussian curve of both traits in response to the increased duration of inundation. The duration of inundation affected ramet production in all perennial species except A. stolonifera, promoting ramet production in two out of the three species. In all species except E. palustris, the length and number of stolons or rhizomes were maintained, suggesting the importance of these connections in the resistance of perennial plants to flooding stress. These species occurring in repeatedly inundated habitats thus appeared to be tolerant to long inundations thanks to both sexual reproduction and vegetative propagation.     

三峡工程中的生物多样性保护

三峡工程导致长江水文情势改变,水库淹没和移民搬迁,成为影响生物多样性的直接的,主要的因素,本文根据最新调查和研究成果,评述了三峡工程对生物多样性的影响,介绍了正在采取的措施及其效果。水库淹没和移民搬迁是影响陆生生物的主要因素。三峡库区有144个植物群系,6388种高等植物,3418种昆虫,500种陆生脊椎动物,其中36个植物群系受到部分或全部淹没影响,4种地方特有植物的野生种群遭到淹没（1种全淹,3种部分淹没）。水文情势改变是影响水生生物的主要因素,长江水系共有鱼类350种,浮游动植物,底栖动物,水生植物等1085种。其中三峡工程对部分珍稀大型水生动物,40余种特有鱼类和“四大家鱼”的影响值得重视,我们将通过建立长期的生物监测站,设立保护区和保护点,采用人工繁殖放流等措施保护生物多样性,减少三峡工程对生物多样性的不利影响,避免因三峡工程而造成物种丧失。     

Morphologische und ökologische Grundlagen der Vorlandsicherung durchPuccinellia maritima (Gramineae)

Investigations on the influence of daylength, light intensity, inundation and accretion tolerance on the morphological and ecological characteristics ofPuccinellia maritima in connection with the role of increasing salinity and temperature (results of former investigations) lead to a deeper understanding of the role this species plays in land reclamation and preservation of coastal areas. The results obtained indicate that the species exhibits a temperature — related seasonal dimorphism with short-stem growth at daylengths up to about 12 h light/day (vernal and autumnal types, caespitose growth) and a long-stem growth at daylength of about 16 h and more light/day (aestival type, stoloniferous growth). Increasing salinity (above 10‰ S) and inundation with artificial sea water (25‰ S) reduce stem and leave development. Accretion of long-stems with sand +3% peat-mixture up to 30 cm yields in 5‰ S further development of runners under long-day conditions and longation of short-stems (up to 10 cm) up to the new soil-surface level. Three shortstem types and two long-stem types can be distinguished. These results explain the natural responses of the species, the forming of the Puccinellietum maritimae within the allogene succession and its role in land preservation. The species is a facultative halophyte which occupies, due to competition from other species, the lower part of its inundation amplitude, utilising its high-salt tolerance. Its aestival long-stem and its autumnal/vernal short-stem production increases the sedimentation rate of soil particles during inundation; the following accretion leads to an elongation of short-stems up to the new soil level, and to an increased production of adventitious roots; the latter results in soil fixation.