Flood drift and propagule bank of aquatic macrophytes in a riverine wetland

Abstract. Drift of aquatic macrophyte propagules was investigated in a wetland along the River Rhône, during the first flood after the growing season (i.e. in the winter of 1995–1996). Input and output drift were studied at the beginning, around the top, and at the end of the river overflow in the upper reach of a cut-off channel. The soil propagule bank was sampled along the study area before and after the flood. The amount and composition of viable propagule drift and bank were determined, analysed and compared. Drift densities and richness were on average higher at the outlet of the channel than at the inlet (respectively: 23.2 vs 13.1 viable propagules/100 m³ of water and 8.7 vs 2.6 taxa per sample). Immigrating taxa were mostly in the form of helophyte seeds, whereas numerous resident hydrophyte species left the disturbed area rather as vegetative propagules. Temporal variability in propagule bank structure was weak, and mean bank densities did not change before and after the flood (respectively: 33 047 ± 10 510 vs 35 653 ± 15 070 viable propagules/m² of ground, including Chara). However, the density of Elodea canadensis significantly increased after the flood while that of Eleocharis acicularis decreased. This contrast suggests that flood responses vary among species. Despite a broad overlap in the taxa (18 out of 25 were common both to drift and bank collections), no significant relationship occurred in composition or structural changes between flood drift and propagule bank. Flood acted as a means of distribution of existing propagules and also as a provider of new vegetative dispersal units.     

Alkali and alkaline earth metals in decomposing macrophytes in a wetland system

The background concentration of selected alkali and alkaline earth metals (sodium, potassium, calcium and magnesium) in some macrophytes was explored in the wetland system of Keoladeo National Park, Bharatpur, India. Changes in the concentration of these elements in the course of macrophyte decomposition were also studied. The species selected were Paspalum distichum, Paspalidium punctatum, Cyperus alopecuroides, Pseudoraphis spinescens, Ipomoea aquatica, Neptunia oleracea and Hydrilla verticillata, which dominate the aquatic vegetation of the Park. Litterbag decomposition experiments were carried out with nylon bags of two different mesh sizes (0.14 and 0.375 mm) in the laboratory and in the field. Among the macrophytes, Hydrilla was the fastest decaying species with the lowest half-life (12.65 days) and Paspalidium the slowest with the highest half-life (385.08 days). Overall, the grasses had low decay rate and high half-life. Background concentration of Na, K, Ca and Mg varied among the plant species. During decomposition and towards the end of the experiment, Na, K and Ca gradually declined whereas Mg increased. The variation was significant (ANOVA, P <0.05) among metals and macrophytes. Na showed no correlation with the weight loss of decomposing macrophytes in the field or in the laboratory tanks. In the field, the K concentration, in contrast with the observations in the tanks, was negatively correlated with the biomass and positively correlated with Ca content. Ca concentration in the biomass was negatively correlated with the weight of the remaining biomass, while Mg was positively correlated with the biomass in the litterbags.     

Alkali and alkaline earth metals in decomposing macrophytes in a wetland system

The foraging habitat selections of brown-eared pheasant (Crossoptilon mantchuricum) and the common pheasant (Phasianus colchicus) were studied in Huanglongshan Nature Reserve Shaanxi, China. Foraging habitat characteristics were measured on the basis of expected differences between species at 183 sites from November to December 2006 and January 2007. The results showed that both species selected foraging habitats with altitude (<1200 m), conifer forest, half sunny and half shady slope, sunny slope, density of trees (<5 individuals/100 m²), cover of shrub (>50%), visibility class (<10%) and distance to water source (<300 m). However, the brown-eared pheasant selected habitats with cover of trees (30–50%), middle or lower slope location, distance to edge of woods (<300 m) and human disturbance (<500 m), and the selection on density of shrub was not observed, compared to the selections on cover of trees (<30%), lower slope location, distance to edge of woods (<500 m) and human disturbance (<300 m), and density of shrub (>500 individuals/100 m²) for common pheasant. We also found that the common pheasant avoid predators by concealment whereas brown-eared pheasant evade predations by running away strategy.     

湿地草本植物枯落物分解的影响因素

草本植物是湿地的主要植被类型之一,其枯落物是湿地有机物质的重要组成部分。本文概述了影响湿地草本植物枯落物分解的主要因素及研究进展,主要包括枯落物自身质量、生物因素、环境因素和人类活动与全球变化等。认为,枯落物质量是本质要素,生物是分解的主导因素,环境等外部因素起到重要作用。讨论了该领域有待深入研究的方向,指出要深入湿地枯落物分解机理的研究,加强多尺度、大环境梯度和多种影响因素的综合研究,加强全球变化对湿地枯落物分解的影响研究,增强实验方法研究等。     

湿地植物供碳功能与优化

尾水湿地氮的反硝化去除往往受限于碳缺乏。综述了湿地植物供碳促反硝化的主要途径与影响因素,构建了华东地区典型冷、暖季型湿地植物供碳的一般性季节动态模式,以期为发挥湿地植物稳定高效供碳功能、缓解尾水湿地碳缺乏问题提供解决思路。湿地植物的主要供碳途径包括根系分泌、地下有机质分解和地上有机质分解(淋溶)等,湿地植物的供碳动态是物种和环境因子综合影响的结果,存在极大的时空异质性。湿地植物具有很强的供碳促反硝化潜力,地上最大生物量为5 kg/m~2的芦苇全年脱氮潜力可高达0.57 kg N/m~2。在构建的湿地植物生物质积累量和供碳量的一般性模式中,冷、暖季型湿地植物无论是生物质积累量(总生物量)和还是供碳量(分解部分+根系分泌物)均存在显著的季节性差异,以及季节间的互补特征。因此,冷、暖季型湿地植物间进行合理的配置,是发挥湿地植物供碳功能且避免生物质分解引起二次污染的可行性措施。今后在湿地植物供碳定量化研究方法、多种供碳途径的定量化监测、供碳功能调控策略,以及稳定高效供碳促反硝化人工湿地构建等方向需做进一步研究。     

Spatial genetic analysis of two polyploid macrophytes reveals high connectivity in a modified wetland

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Laboratory study of heavy metal phytoremediation by three wetland macrophytes

Detention ponds and constructed wetlands have proven to be effective in reducing peak stormwater runoff volume and flow, and recent interest has extended to utilizing them to improve stormwater runoff quality. A review of stormwater runoff studies indicated that lead, zinc, copper, cadmium, phosphorus, and chloride are contaminants of primary concern. In laboratory settings, the uptake of contaminants by three wetland plant species, Glyceria grandis, Scirpus validus, and Spartina pectinata, was examined and removal rates from nutrient solutions inflow and nonflow reactors were measured. The removal rates varied by plant species and target contaminant, and no one species was the best accumulator of all six contaminants. Belowground tissues of all three species accumulated higher concentrations of the four heavy metals and aboveground tissues accumulated higher concentrations of phosphorus and chloride. Plants grown in flow reactors showed significantly higher accumulation rates than those grown in nonflow reactors. Also, plants grown hydroponically accumulated higher concentrations of the six target contaminants than those grown in sand reactors. However, those grown in sand had a much greater increase of biomass and removed a greater mass of the six target contaminants. Removal rates measured in these experiments can be used to design detention ponds to maximize stormwater remediation.     

Temporal trends and effects of diversity on occurrence of exotic macrophytes in a large reservoir

Two exotic invasive macrophyte species (the emergent Urochloa subquadripara - tenner-grass - and the submersed Hydrilla verticillata - hydrilla) were investigated in a large sub-tropical reservoir. We analyzed their occurrences over an extended period and tested the hypothesis that macrophyte richness decreases their invasibility. The alternative hypothesis that the occurrence of these exotics is affected by fetch and underwater radiation (important determinants of macrophyte assemblage composition in this reservoir) was also tested. Incidence data (presence/absence) was obtained over 9.5 years at 235 stations. Logistic regression was applied to test whether the likelihood of occurrence of these two species was affected by macrophyte richness, fetch or underwater radiation. Tenner-grass was recorded at a high frequency and quickly recovered from disturbances caused by water drawdown. In contrast, H. verticillata was first recorded in 3 sites in January 2007, but it spread quickly, reaching 30.5% of the sites 19 months later. The main channel of the Paraná River was the main source of propagules for this species. The likelihood of occurrence of tenner-grass was positively affected by macrophyte richness but negatively affected by fetch. Thus, wave disturbance is probably more important than diversity in preventing invasion by this species. Hydrilla, by contrast, was negatively affected by macrophyte richness and positively affected by fetch and underwater radiation. Although this result might indicate that macrophyte diversity prevents hydrilla invasion, this is probably not true because hydrilla colonized deeper sites where few species of plant exist. Resistance to disturbances caused by water drawdown (tenner-grass) and waves (hydrilla) as well as persistency of tenner-grass and fast spread of hydrilla make these exotic species a cause for concern because of their potential impacts on water uses and maintenance of diversity.     

Nutrient resorption in wetland macrophytes: comparison across several regions of different nutrient status

This study explored patterns of nutrient resorption in wetland macrophytes to test the prediction that plants from regions with a strong nutrient limitation will show higher resorption of the limiting nutrient. Nitrogen and phosphorus resorption was assessed in macrophytes from marshes of different nutrient status in tropical and temperate regions, and expressed as resorption efficiency (NRE, PRE) and proficiency (NRP, PRP). Macrophytes were grouped into three categories: Typha, graminoids and broadleaved plants. Nitrogen was less limiting than P, consequently N availability varied less than P availability, NRP and NRE were lower, and N resorption was mostly incomplete. NRP was determined more by growth form than by local conditions. The large range of soil P concentrations allowed an exploration of relationships between P availability and resorption along a wide gradient. P-limited macrophytes (N : P > 16) had significantly higher PRP and PRE. Resorption proficiency was found to be a more sensitive indicator of changes in nutrient availability than resorption efficiency. The results confirmed that resorption in wetland macrophytes depends on nutrient availability, and is higher at nutrient-limited sites. A particularly strong relationship was found between resorption indicators and P limitation expressed either as live tissue N : P or soil P.     

Effect of reservoir drawdown on biomass of three species of aquatic macrophytes in a large sub-tropical reservoir (Itaipu, Brazil)

The biomass and maximum depth of colonization (Z _max) of Egeria najas Planchon (submerged), and the biomass and area covered by a stand of Eichhornia crassipes (Mart.) Solms and Salvinia herzogii Raddi (floating species) were assessed to measure the effects of a 5 m drawdown in water level of the Itaipu Reservoir (Brazil–Paraguay), which lasted about 3 months. The frequency of occurrence of the two first species, and of Salvinia spp was also assessed in the main arms of the reservoir. A conspicuous decrease of E. najas biomass was observed and this attribute did not reach the previous values even 10 months after the water level had returned to normal. Rapid growth of free-floating species (surface t _doub = 2.9 and 3.2 days for total biomass of S. herzogii and E. crassipes, respectively, and 2.3 days for surface area covered by both species) was recorded immediately after the water level returned to normal. This fast growth was related to phosphorus increases in water. A clear succession was observed over a period of 103 days, during which S. herzogii was slowly substituted by E. crassipes. The effects of water level drawdown were also observed on E. najas frequency, given that this species occurred in 38% of the stands investigated before the water drawdown, but in only 9 and 6% of stands following 1 and 10 months of water level recovery, respectively. Water drawdown did not affect the frequency of occurrence of the floating species, which remained approximately constant, and lower than 15% in several of the reservoir arms investigated.     

广西澄江喀斯特湿地沉水植物碳、氮、磷化学计量特征

沉水植物是水生生态系统中重要的初级生产者。当前有关沉水植物生态化学计量特征的研究主要集中在非喀斯特区,而在喀斯特区的相关研究较为缺乏。因此,以广西澄江喀斯特典型湿地中的7种沉水植物为研究对象,分析沉水植物地上部分及底泥的碳（C）、氮（N）、磷（P）化学计量特征。结果显示,（1）7种沉水植物地上部分总碳、总氮和总磷平均含量最大值均出现在小茨藻（Najas minor）分别为（325.4±5.01） g/kg、（33.07±1.59） g/kg和（3.79±0.16） g/kg;C ： N、C ： P、N ： P平均值分别为10.14±0.18、96.23±3.56和9.47±0.32,C ： N最大值（11.89±0.54）出现在苦草（Vallisneria natans）,C ： P和N ： P最大值（113.27±18.14和11.13±1.63）均出现在穗花狐尾藻（Myriophyllum spicatum）。（2）底泥有机碳、总氮、总磷、碱解氮和速效磷含量平均值分别为（15.05±0.56） g/kg、（2.06±0.08） g/kg、（0.58±0.01） g/kg、（162.53±9.16） mg/kg和（21.73±0.86） mg/kg,有机碳、总氮、总磷、碱解氮和速效磷的平均含量最大值均出现在小茨藻（N.minor）分别为（18.54±1.04） g/kg、（2.55±0.25） g/kg、（0.66±0.03） g/kg、（214.82±32.05） mg/kg和（26.37±3.31） mg/kg;底泥的C ： N、C ： P和N ： P平均值分别是7.33±0.14、25.7±0.72和3.53±0.09,C ： N、C ： P和N ： P最大值分别出现在金鱼藻（Ceratophyllum demersum）（7.45±0.32）、小茨藻（N. minor）（28.29±1.29）和黑藻（Hydrilla verticillata）（3.89±0.25）。（3）沉水植物的地上部分总碳与底泥的有机碳和总氮均呈显著负相关性;沉水植物的地上部分总氮与底泥有机碳、碱解氮、C ： P均呈显著正相关性;沉水植物地上部分C ： N、C ： P均与底泥有机碳、总氮、总磷、碱解氮、C ： P、N ： P呈显著负相关,表明不同喀斯特湿地沉水植物和底泥之间的养分耦联性不同。本研究为喀斯特湿地生态系统生态化学计量学研究提供理论依据。     

Pressurised aeration in wetland macrophytes: Some theoretical aspects of humidity-induced convection and thermal transpiration

The pressurised gas-flows, humidity-induced convection (HIC) and thermal transpiration (TT), which are important for aeration and for greenhouse gas emissions in some wetland macrophytes, are described and discussed. Results obtained from simple mathematical modelling of the processes are presented to illustrate some of their more relevant features. It is emphasised that both processes require the presence of a micro-porous partition having a significantly greater resistance to pressure flow than to diffusion. In particular it is shown that whilst the potential to pressurise by these processes is inversely related to the pore diameters of the partition, the maximum gas flows are generated where pore diameters range from 0.1 to 0.2 μm. Where partitions are a surface feature (e.g. emergent macrophytes) a dominant role for HIC is predicted; where partitions are an embedded feature (e.g. water-lilies) it is deduced that HIC will still play a significant role, but the contribution of TT could be greater.     

Effects of invasive wetland macrophytes on habitat selection and movement by freshwater turtles

Biological Invasions - Invasive species can significantly impact native wildlife by structurally altering habitats and access to resources. Understanding how native species respond to habitat...     

Strong top-down effects of omnivorous fish and macroinvertebrates on periphytic algae and macrophytes in a tropical reservoir

Aquatic Ecology - Top-chain predators play a fundamental role in the functioning of shallow reservoirs. Studies to elucidate the cascade effects produced by fish on macroinvertebrates and...     

Influence of freshwater macrophytes on the littoral ecosystem structure and function of a young Colorado reservoir

The presence of rooted macrophytes, mostly the milfoil Myriophyllum sibiricum, was manipulated in enclosures in the littoral zone of a Colorado reservoir. The presence of macrophytes significantly increased the abundance of major invertebrate taxa by 70–1725% and increased the emission of methane 127%. The increase in abundance of most invertebrates was probably due to the habitat and surfaces provided by milfoil as stable isotope analyses indicated that milfoil was an insignificant carbon source for all of the invertebrate taxa, except for the milfoil midge Cricotopus myriophylli. Cricotopus is known to specialize on milfoil (other members of the genus specialize on Hydrilla or are generalists), had an isotopic signature that indicated a diet of milfoil, and was about 15 times more abundant when milfoil was present than when it was absent. Milfoil had no detectable effect on the total particulate phosphorus (TPP), soluble reactive phosphorus (SRP), total dissolved phosphorus (TDP), dissolved organic phosphorus (DOP), and Chl a of water within the enclosures. However, enclosures containing milfoil had higher concentrations of SRP in the pore water of surface sediments than enclosures that had milfoil removed. SRP in pore water dropped below 2 μg/L at >2 cm sediment depth and DOP increased progressively from nearly zero at the surface to about 150 μg/L at 15 cm depth, regardless of vegetation. Thus, milfoil had significant effects on many, but not all, measures of littoral ecosystem structure and function that were monitored.     

几种湿地植物净化生活污水COD、总氮效果比较

以无植被、基质为河砂的潜流型人工湿地为对照,研究了石菖蒲、灯心草和蝴蝶花3种类型植被、基质均为河砂的潜流型人工湿地净化生活污水COD、总氮的效果．结果表明,在污水COD浓度小于200mg·L^-1、总氮浓度小于30mg·L^-1的低浓度范围里,无植被的人工湿地和有植被的人工湿地对污水中COD、总氮均有很好的去除效果,两者差异不大,其COD去除率均达90％以上,总氮的去除率达80％以上．随着污水中COD和总氮浓度的增加,无植被人工湿地和有植被人工湿地去除COD和总氮的效果均有不同程度下降,两者差异明显,有植被的人工湿地能维持较高的COD、总氮的去除效果,无植被的人工湿地COD和总氮去除效果下降很快,植被在人工湿地系统去除污水COD和总氮过程中起着重要的作用．在整个试验阶段,石菖蒲植被人工湿地COD和总氮平均净化效率分别为80．46％和77．77％、灯心草人工湿地分别为75．53％和71．17％、蝴蝶花人工湿地分别为70．50％和66．38％,无植被人工湿地分别为61．39％和55．81％．同无植被人工湿地COD和总氮净化效果相比,石菖蒲植被人工湿地净化效果最好;其次为灯心草植被人工湿地,再次为蝴蝶花植被人工湿地．不同类型植被的人工湿地净化污水中COD和总氮的效果与其生物量关系密切,这与植被系统吸收同化有机物质和总氮数量、根际微生物分解有机物质和硝化-反硝化作用有关。     

Habitat preferences of four chironomid species associated with aquatic macrophytes in an irrigation reservoir

Habitat preferences of four chironomid species associated with aquatic macrophytes were studied during the vegetation season from April to October at an irrigation reservoir located in Nagoya, Japan.The two smaller sized species,Corynoneura cuspis Tokunaga andPentapedilum tigrinum Hashimoto, were found to be abundant in two floating-leaved plants,Nymphoides indica O. Kuntze andTrapa japonica Flerov. Phytophages,C. cuspis larvae were observed freely moving on the surfaces of leaves and stems within both of these floating-leaved plant communities. Although found within both plant communities,P. tigrinum larvae, as facultative leaf miners, were more concentrated on the surfaces and within the leaves ofN. indica, which have a thin epidermis and thick mesophyll layer.The two larger sized species,Glyptotendipes viridis (Macquart) andPentapedilum sordens (van der Wulp), were found to be living principally within the stems ofN. indica and the petioles ofT. japonica. These parts of the plants, with thin epidermis and many lacunae in the parenchyma, are favorable for miners.     

The use of macrophytes in bioremediation

The development of reedbed technology for bioremediation is reviewed. The future development, potential and implementation of these systems are considered in detail together with the cost effectiveness and ease of maintenance.     

The invertebrate fauna of four macrophytes in a lotic system

SUMMARY. 1. Invertebrates associated with four species of aquatic plants and on the adjacent substrate were investigated in a riffle/run section of a hard-water stream.
2. Invertebrates were more numerous on stones than on any species of plant (> 17,000m⁻² versus 1000–4000 m⁻²). Gatherers were more abundant on Ranunculus longirostris , where proportionally more fine detritus was trapped in the leaf bundles than on other plants. Scrapers were most numerous on Charu vulgaris , where attached diatoms were also most prevalent.
3. Invertebrate community structure on three plant speeies was quite different from that on stones. This was not the case for Potamogeton amplifolius which appeared to be used by the organisms as a mere extension of the substrate.