Importance of low-flow and high-flow characteristics to restoration of riparian vegetation along rivers in arid south-western United States

1. Riparian vegetation in dry regions is influenced by low‐flow and high‐flow components of the surface and groundwater flow regimes. The duration of no‐flow periods in the surface stream controls vegetation structure along the low‐flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape heterogeneity and an abundance of pioneer wetland plant species in the floodplain. Vegetation changes on hydrologically altered river reaches are varied, given the great extent of flow regime changes ranging from stream and aquifer dewatering on reaches affected by stream diversion and groundwater pumping to altered timing, frequency, and magnitude of flood flows on reaches downstream of flow‐regulating dams. 3. As stream flows become more intermittent, diversity and cover of herbaceous species along the low‐flow channel decline. As groundwater deepens, diversity of riparian plant species (particularly perennial species) and landscape patches are reduced and species composition in the floodplain shifts from wetland pioneer trees (Populus, Salix) to more drought‐tolerant shrub species including Tamarix (introduced) and Bebbia. 4. On impounded rivers, changes in flood timing can simplify landscape patch structure and shift species composition from mixed forests composed of Populus and Salix, which have narrow regeneration windows, to the more reproductively opportunistic Tamarix. If flows are not diverted, suppression of flooding can result in increased density of riparian vegetation, leading in some cases to very high abundance of Tamarix patches. Coarsening of sediments in river reaches below dams, associated with sediment retention in reservoirs, contributes to reduced cover and richness of herbaceous vegetation by reducing water and nutrient‐holding capacity of soils. 5. These changes have implications for river restoration. They suggest that patch diversity, riparian plant species diversity, and abundance of flood‐dependent wetland tree species such as Populus and Salix can be increased by restoring fluvial dynamics on flood‐suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal. On impounded rivers, restoration of plant species diversity also may hinge on restoration of sediment transport. 6. Determining the causes of vegetation change is critical for determining riparian restoration strategies. Of the many riparian restoration efforts underway in south‐western United States, some focus on re‐establishing hydrogeomorphic processes by restoring appropriate flows of surface water, groundwater and sediment, while many others focus on manipulating vegetation structure by planting trees (e.g. Populus) or removing trees (e.g. Tamarix). The latter approaches, in and of themselves, may not yield desired restoration outcomes if the tree species are indicators, rather than prime causes, of underlying changes in the physical environment.     

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.     

Shoot and leaf demography of Carex curvula ssp. Curvula and Carex curvula ssp. rosae in the Central Alps

Abstract. Populations of Carex curvula ssp. curvula, C. curvula ssp. rosae and their intermediate form were investigated in the Central Alps over a three-year period. The closely related taxa showed a different dominance behaviour in their respective communities. This may be caused by different growth strategies and a different reproduction biology. Therefore, the main aim of the study was to compare the demography of the three taxa. Shoot and leaf turnover, flower and seed production and population half-lives were determined. Differences in growth dynamics were less pronounced between the two species of Carex curvula than between these taxa and their intermediate form which showed the highest shoot turnover, highest number of fertile inflorescences and highest number of seeds per inflorescence. Carex curvula ssp. rosae showed a slightly higher shoot and leaf production but a lower reproduction capacity than Carex curvula ssp. curvula. Recruitment of populations of the three Carex-forms was only by vegetative shoots. Flowering had a striking effect on the shoot dynamics of the species grown in the grassland sites: up to about 70 % of all dead shoots could be identified as dead flowering shoots from the previous year. The different dominance behaviour of the three taxa could not be explained by their demographical features. Interspecific interactions and the occurrence of microniches might affect the growth and reproduction processes of the taxa.     

Effects of size and growth rate on vegetative reproduction in Typha

Summary The objective of this study was to separate the effects of plant biomass and growth rate on vegetative reproduction in two species of cat-tail, Typha latifolia and T. angustifolia. Replicate clones of both species were grown under conditions of 100%, 42%, 24%, and 9% full sunlight with harvests at 41, 70, and 91 days after shading. T. angustifolia produced most of its vegetative offspring before the first harvest and increased biomass over the remainder of the experiment by increasing the size of its ramets. In contrast, T. latifolia produced vegetative offspring gradually throughout the experiment adding new ramets only after existing clones were of mature size. As a result of these differences in the cloning process, T. angustifolia showed little correlation between vegetative reproduction and clone size while T. latifolia showed a strong correlation between gegetative reproduction and clone size at the three highest light intensities. Growth rates, average clone size and vegetative reproduction were all reduced by reductions in light intensity for both species. However, no effect of growth rate on the relationship between clone size and vegetative reproduction in T. latifolia could be detected. T. latifolia showed greater survivorship and more biomass production under 9% light than T. angustifolia indicating a greater shade tolerance.     

Comparative impacts of dam water level regimes on herbaceous plant growth strategies in cascade reservoirs and downstream reaches of a major river

1. Flow regulation is a prolific and growing influence on rivers world-wide. Nine cascade hydropower dams were constructed along the 1,150-km Wujiang River in China over the past 30 years, disrupting longitudinal continuity. Water level fluctuations in the associated reservoirs range between daily, weekly, seasonal, and annual, depending on the type of regulation, but the comparative impacts of these regimes on plant growth strategies, or the extent of their downstream influence, is unknown.
2. Competitor, stress-tolerator, and ruderal (CSR) plant strategies were used to assess the impact of reservoir regulation type on the riparian herbaceous plant community based on sampling the inundation zone of nine reservoirs and their downstream river reaches during 2017 and 2018.
3. Our results revealed profound differences in CSR plant strategies of the dominant vegetation with respect to water level regime. While ruderal plants dominated (45%–60% of species), irrespective of regulation type, vegetation in reservoirs exhibited a strong shift from stress-tolerators (e.g., Cynodon dactylon, C-11.9:S-41.5:R-46.5%) to competitors (e.g., Reynoutria japonica, C-77.9:S-0:R-22.0%) with increasing intensity of water level fluctuation, reflecting the shift from annual to daily regulation. The width of the inundation zone was the best overall variable in explaining the CSR strategies of riparian vegetation, both in the reservoir inundation zone (r²-adj = 15.4%) and the downstream river (r²-adj = 7.3%). Retention time significantly explained variation in CSR plant strategies in the reservoir inundation zone (r²-adj = 3.7%, p = 0.002) but not downstream (p > 0.01). There was also a clear scale dependency of CSR plant strategies, with an increase in stress tolerators (average slope = 0.7%/km) and decline of competitor (average slope = −0.3%/km) and ruderal plants (average slope = −0.9%/km) with increasing distance downstream from dams.
4. The growth strategies of the dominant riparian vegetation changed with the magnitude and frequency of water level fluctuations caused by differences in regulation type, and local environmental conditions. Clear scale dependency in the CSR plant strategies was observed with distance from the dam, with ruderals dominating closest to the reservoirs and declining gradually downstream as stress tolerators increased.
5. Our study helps to evaluate the impact of river damming on the functional traits of riparian vegetation and to predict the resilience and restoration potential of riparian vegetation under different forms of human disturbance.

     

Effects of climate‐induced increases in summer drought on riparian plant species: a meta‐analysis

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Effects of river sediment elutriates on Daphnia magna

Laboratory sediment bioassays, both acute and chronic, were conducted on sediment elutriates from the River Eurajoki, SW Finland. The river is under impacts of industrial discharges, community effluents and agricultural run-offs. The water flea Daphnia magna Straus was used as a test organism. None of the elutriates tested were acutely toxic. In a long-term bioassay sediment elutriates had effects on survival, body growth and reproduction. Elutriates prepared from samples of a downstream station were characterized by low survival, small body size, reduced total offspring production, and delayed start of reproduction.     

Conditions for seedling establishment and probable function of seed in the clonal sedge Carex rugulosa Kük. in riverside marshes

Carex rugulosa Kük. forms large meadows in moist zones along estuarine riversides. These meadows are usually maintained by rhizomatous ramet production (clonal growth), and the appearance of seedlings is uncommon. We studied the conditions required for seedling establishment. In areas in which clonal ramets were dense (906–1050/m²), and the relative light intensity at ground level was low (0.8–3.8%), seed germination was entirely suppressed. In contrast, many seedlings (288–513/m²) were observed in areas in which clonal ramets had been considerably reduced (13–269/m²) by continuous inundation in the previous year. In these areas, the relative light intensity had increased (20.5–79.3%). It was inferred that seeds resisted the prolonged inundation that killed the ramets, and that germination was induced under these open conditions. These results suggest that the main functions of sexual reproduction in C. rugulosa are recovery after severe damage to vegetation using seeds from the seed bank and the dispersal of seeds to areas without dense vegetation. Most seedlings died when the marshy meadow was temporarily inundated by heavy rain. However, transplanted seedlings survived better at artificially elevated sites that were not submerged. This shows that inundation during the seedling stage impedes seedling survival. Therefore, seeds can contribute to recovery after ramet decline or colonization to open area when (i) the rainfall is not heavy to cause seedling submergence or (ii) seeds are dispersed to higher area which is not inundated.     

Root Plasticity of Populus euphratica Seedlings in Response to Different Water Table Depths and Contrasting Sediment Types

Riparian plants in arid regions face a highly variable water environment controlled by hydrological processes. To understand whether riparian plants adapt to such environments through plastic responses, we compared the root traits, biomass allocation and growth of Populus euphratica Oliv. Seedlings grown in lysimeters filled with clay or clay/river sand sediments under inundation and varying water table conditions. We hypothesized that adaptive phenotypic plasticity is likely to develop or be advantageous in seedlings of this species to allow them to adapt desert floodplain environments. Growth was significantly reduced by inundation. However, rather than following relatively fixed trait and allocation patterns, the seedlings displayed adaptive mechanisms involving the development of adventitious roots to enhance plant stability and obtain oxygen, together with a lower proportion of root biomass. At the whole-plant level, at deeper water table depths, seedlings allocated more biomass to the roots, and total root length increased with decreasing water table depths, regardless of the sediment, consistent with optimal partitioning theory. The sediment type had a significant effect on seedling root traits. P. euphratica displayed very different root traits in different sediment types under the same hydrological conditions, showing a greater first-order root number in clay sediment under shallower water table conditions, whereas rooting depth was greater in clay/river sand sediment under deep water table conditions. In clay sediment, seedlings responded to lower water availability via greater root elongation, while the root surface area was increased through increasing the total root length in clay/river sand sediment, suggesting that seedlings facing deeper water tables are not always likely to increase their root surface area to obtain more water. Our results indicate that P. euphratica seedlings are able to adapt to a range of water table conditions through plastic responses in root traits and biomass allocation.     

Seasonal timing of inundation affects riparian plant growth and flowering: implications for riparian vegetation composition

Changes to the timing of peak river flows caused by flow regulation affect riparian vegetation composition, but the mechanisms driving such vegetation changes are not well understood. We investigated experimentally the effects of timing of inundation on riparian plant growth and flowering. We collected 168 sods from 14 sites across five lowland rivers in south-eastern Australia. Plant cover and flowering within the sods were surveyed each season for a year. During this period, sods were inundated for 6 weeks in either early spring or in summer. Terrestrial plant taxa (which included most exotic species) senesced in response to inundation, regardless of its timing. In contrast, native amphibious species (particularly amphibious forbs) responded favourably to inundation in spring, but were unaffected by inundation in summer. Native and exotic emergent macrophytes responded favourably to inundation regardless of timing, and flowered frequently in both the spring- and the summer-inundation treatments. In contrast, many native annuals flowered only in the spring-inundation treatment, while more exotic grasses flowered in the summer-inundation treatment. In temperate climates, inundation in early spring followed by non-flooded conditions is likely to be important for promoting the growth of amphibious forbs and the recruitment and flowering of riparian annuals. Without inundation in spring, many terrestrial exotic weeds may flourish and set seed prior to any subsequent inundation (e.g. in summer). We contend that natural seasonal timing (i.e. winter-early spring) of flow peaks is important for the maintenance of native riverbank vegetation and reducing the extent of terrestrial exotic species within the riparian zone.     

Disturbance-mediated trophic interactions and plant performance

Disturbances, such as flooding, play important roles in determining community structure. Most studies of disturbances focus on the direct effects and, hence, the indirect effects of disturbances are poorly understood. Within terrestrial riparian areas, annual flooding leads to differences in the arthropod community as compared to non-flooded areas. In turn, these differences are likely to alter the survival, growth, and reproduction of plant species via an indirect effect of flooding (i.e., changes in herbivory patterns). To test for such effects, an experiment was conducted wherein arthropod predators and herbivores were excluded from plots in flooded and non-flooded areas and the impact on a common riparian plant, Mimulus guttatus was examined. In general, the direct effect of flooding on M. guttatus was positive. The indirect effects, however, significantly decreased plant survival for both years of the experiment, regardless of predator presence, because of an increased exposure to grasshoppers, the most abundant herbivore in the non-flooded sites. Leafhoppers, which were more abundant in the flooded sites, had much weaker and varying effects. During 2000, when the leafhopper herbivory was high, arthropod predators did not significantly reduce damage to plants. In 2001, the mean herbivory damage was lower and predators were able to significantly reduce overall leafhopper damage. The effects of predators on leafhoppers, however, did not increase plant survival, final weight, or the reproduction potential and, thus, did not initiate a species-level trophic cascade. Overall, it was the differences in the herbivore community that led to a significant decrease in plant survival. While flooding certainly alters riparian plant survival through direct abiotic effects, it also indirectly affects riparian plants by changing the arthropod community, in particular herbivores, and hence trophic interactions.     

Unnatural flooding alters the functional diversity of riparian vegetation of the Three Gorges Reservoir

1. The response of riparian vegetation to flow regulation has been a research focus for decades. Several studies have shed light on the effects of flow stabilisation on riparian woody species, but other life forms exposed to intensified inundation have been overlooked. Furthermore, studies from a functional perspective are scarce.
2. We evaluated the functional response of riparian vegetation along the shores of the Three Gorges Reservoir on the Yangtze River in China to unnaturally long annual flooding (>7 months) after the first year of filling. We aimed to answer the following: (1) can we derive well-defined flow-response guilds from the riparian zones of the Yangtze River? and (2) which plant traits and guilds are favoured or disfavoured by the unnaturally long flooding environment?
3. Woody and herbaceous species were inventoried in 12 reaches along the shorelines of the Three Gorges Reservoir and another 12 reaches along the free-flowing Yangtze River. We performed a cluster analysis to derive riparian guilds using abundance data (projective coverage) from 40 riparian plant species and 13 responsive traits. Structural composition and functional diversity of the unnaturally and naturally flooded riparian vegetation were compared.
4. Unnaturally long flooding substantially reduced species richness, but it did not change the riparian vegetation cover. This novel flooding reduced functional diversity, mostly owing to the loss of stress-tolerant woody species and competitive perennial herbs. However, competitive annual herbs and flood-tolerant riparian herbs, as the most abundant functional guilds, were favoured even under such long-term hypoxic conditions.
5. These guilds under regulation revealed a high functional resilience to prolonged flooding along the upstream reaches of the Yangtze River. Flooding tolerance and the capacity to synchronise germination and growth with short-exposure periods underlie the plant species changes. Our findings are useful for anticipating the effects of long-lasting inundation on riparian areas triggered by flow regulation or warmer climates. The functional perspective lends confidence that our conclusions can be generalised to other geographical regions despite not sharing the same species pool. Finally, the plant species that showed a high flooding tolerance should be considered for the restoration of riparian areas affected by the Three Gorges Reservoir.

     

Can environmental flows moderate riparian invasions? The influence of seedling morphology and density on scour losses in experimental floods

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Effects of sediment deposition on the seaweed Sargassum on a fringing coral reef

 Coral reef degradation may involve shifts from coral to algal dominance and may be caused in part by increased sediment loads. Inshore fringing reef flats in the central Great Barrier Reef region are often subjected to periods of high sedimentation and are often dominated by macroalgae such as Sargassum. Experiments reported here examine the impacts of sediments on the recruitment, growth, survival, degeneration and vegetative regeneration of Sargassum microphyllum on a fringing coral reef flat in the central Great Barrier Reef. Comparison of three levels of sediment deposition (experimental addition, control (ambient condition) and experimental removal) showed that increased amounts of sediment significantly decreased rates of recruitment, growth, survival and vegetative regeneration, but not degeneration of S. microphyllum. In addition, the regenerative ability of S. microphyllum thalli with short, persistent erect branches (untreated) was compared with that of thalli experimentally cut back to the holdfast. This experimental damage significantly reduced regeneration. Accepted: 6 October 1997     

Dynamics of Nutrient Contents (Phosphorus,Nitrogen) in Water,Sediment and Plants After Restoration of Connectivity in Side‐Channels of the River Rhine

During the last century, canalization of the Rhine river led to disconnection of side‐arms, over‐sedimentation of these channels, loss of the fluvial dynamics, and aquatic vegetation change or disappearance. Recent restoration projects aim to reconnect disconnected arms to the main channel. The objective of this study was to assess the nutrient dynamics in restored channels during the vegetation colonization process. In spring, summer, and autumn 2009, the phosphorus and nitrogen contents were measured in water, sediment, and plants, sampled in six channels, two reference sites and four restored ones at different dates. Aquatic vegetation was monitored during the same period. Sites were mesotrophic related to the water nutrient concentrations. However, vegetation communities indicated a eutrophic level, as they were dominated by species like Elodea nuttallii, Myriophyllum spicatum, and Potamogeton perfoliatus. Sites were discriminated by P content and mineral nitrogen in the sediment. We showed an effect of species and season on the plant nutrient content, but there was no relationship between plant nutrient content and nutrients in water and sediment. A negative correlation between mean N plant content and the cover of each species was found. Vegetation characteristics (species richness and cover) and bioavailable phosphorus in the sediment were also correlated. In the restored side‐arms of the river Rhine, phosphorus‐rich sediment seems to be important in the recolonization dynamics, as it was linked to higher species richness, whereas nitrogen played a role in the colonization patterns as a growth limiting factor.     

Relative contributions of sexual and asexual regeneration strategies in Populus nigra and Salix alba during the first years of establishment on a braided gravel bed river

Populus nigra L. var betulifolia and Salix alba L. var alba are early successional riparian tree species threatened throughout Continental Europe by significant changes to the natural physical processes governing their natural habitat – geomorphologically active floodplains. River management activities have dramatically altered natural patterns of river flow and rates of sediment delivery along rivers, with possible consequences for the balance between sexual and asexual regeneration strategies in these species. Conservation strategies will benefit from a greater understanding of the ways in which dynamic physical processes on the floodplain influence sexual and asexual recruitment. This paper describes a field survey investigating the relative abundance and spatial distributions of P. nigra and S. alba sexual and asexual recruits during the first years of establishment along a braided gravel bed river. Sexual and asexual recruits were identified by excavation along transects in a wet and a dry field season and distributional differences were described in terms of elevation on the floodplain, local sediment type and exposure to floodwaters. Regeneration was overwhelmingly from seed in the first 2–3 years following recruitment, but poor survival rates among sexual recruits saw a shift in the relative abundance of regeneration strategies over time. In relating hydrological data to recruitment, unseasonal flood disturbances had a negative effect on recruitment from seed and a positive effect on vegetative regeneration. Seedlings were associated with fine sediment deposits and were restricted primarily to low elevations on the flood plain, while asexual recruits had a wider spatial distribution. Certain microsite types were unique to either regeneration strategy.     

Trade-offs among growth, clonal, and sexual reproduction in an invasive plant Spartina alterniflora responding to inundation and clonal integration

The purpose of this article was to study the trade-offs among vegetative growth, clonal, and sexual reproduction in an aquatic invasive weed Spartina alterniflora that experienced different inundation depths and clonal integration. Here, the rhizome connections between mother and daughter ramets were either severed or left intact. Subsequently, these clones were flooded with water levels of 0, 9, and 18 cm above the soil surface. Severing rhizomes decreased growth and clonal reproduction of daughter ramets, and increased those of mother ramets grown in shallow and deep water. The daughter ramets disconnected from mother ramets did not flower, while sexual reproduction of mother ramets was not affected by severing. Clonal integration only benefited the total rhizome length, rhizome biomass, and number of rhizomes of the whole clones in non-inundation conditions. Furthermore, growth and clonal reproduction of mother, daughter ramets, and the whole clone decreased with inundation depth, whereas sexual reproduction of mother ramets and the whole clones increased. We concluded that the trade-offs among growth, clonal, and sexual reproduction of S. alterniflora would be affected by inundation depth, but not by clonal integration.     

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.     

鄱阳湖洲滩湿地植物生长和营养繁殖对水淹时长的响应

水淹时长是影响湿地植物分布的重要因素。在水情不断变化的背景下,鄱阳湖洲滩湿地植物种群和群落的变化规律还不清楚。为了探究淹水时长对鄱阳湖洲滩3种优势植物生长和繁殖的影响,并预测在水文发生剧烈变化后,3种优势植物分布的趋势,采用控制实验模拟了不同水淹时长(0、60、90、120、150 d和180 d)下鄱阳湖湿地3种优势植物(灰化薹草(Carex cinerascens)、南荻(Miscanthus lutarioriparius)和虉草(Phalaris arundinacea))的生长和繁殖情况。研究结果表明:1)南荻在水淹超过120 d后,存活率开始降低,水淹到达180 d完全死亡。而灰化薹草和虉草在淹水180 d后仍全部存活。表明南荻耐淹水的能力弱于其他两种植物。2)水淹显著降低灰化薹草的总生物量,并且总生物量随水淹时长的增加而逐渐降低。而短时间(小于150 d)的水淹没有对虉草总生物量产生显著影响。3)退水初期,灰化薹草的恢复生长趋向于地上部分,而虉草表现为地下和地下部分同步生长。该研究结果可以为预测水文情势变化下鄱阳湖湿地植物种群和群落的动态变化提供依据。     

The influence of leaf litter on zooplankton in floodplain wetlands: changes resulting from river regulation

1. The loss of input of leaf litter through clearing of riparian vegetation may result in significant changes to aquatic ecosystems. River red gums (Eucalyptus camaldulensis) surrounding floodplain wetlands in the Murray–Darling Basin, Australia, contribute large quantities of leaf litter, but the quality of this resource may change depending on the timing of inundation. 2. We used experimental mesocosms to test the hypotheses that zooplankton would have a greater abundance with an input of leaf litter and that fewer zooplankton would emerge from egg banks in cleared than forested wetlands. The experiment was carried out in summer/autumn and in spring to test a third hypothesis that zooplankton would respond to changes in the timing of wetland inundation as a result of river regulation. 3. In summer/autumn, leaf litter reduced zooplankton abundance by 89% at the beginning of the experiment through its influence on water quality. Only a few taxa (Polyarthra spp., Colurella spp. and the cladoceran Family Moinidae) responded positively to leaf litter when water quality improved later in the experiment, indicating a switch in the role of leaf litter from a non‐trophic to a trophic pathway. 4. In spring, microcrustaceans emerged in smaller numbers from sediment sourced from cleared compared to forested wetlands, reflecting different communities in these two wetland types and/or disturbances to the sediment that interfere with emergence. 5. Although leaf litter appears not to be an important resource for zooplankton in floodplain wetlands, riparian clearing may have lasting effects on future emerging zooplankton communities. Additionally, river regulation may have considerable impacts on the influence of leaf litter on zooplankton, which has implications for the management of floodplain river systems.