沉水植物重建对富营养水体氮磷营养水平的影响

利用富营养浅水湖泊(武汉东湖)中所建立的大型实验围隔系统,研究了沉水植物对水体N、P营养水平的影响．结果表明,沉水植物重建后N、P营养水平显著降低．在研究期间,水生植物围隔总N和总P水平均显著低于对照围隔和大湖水体,而且水生植物围隔的总P含量一般维持在0．1mg·L^-1左右。季节性波动远低于对照围隔和大湖水体．水生植物围隔水体中氨态氮和亚硝态氮含量较低．而硝态氮含量与对照围隔和和大湖水体差别不大．由此可见。恢复以沉水植物为主的水生植被,可以有效地降低N、P营养循环速度,控制浮游植物过度增长,是重建富营养湖泊生态系统的重要措施．     

Leaf litter breakdown budgets in streams of various trophic status: effects of dissolved inorganic nutrients on microorganisms and invertebrates

1. We investigated the effect of trophic status on the organic matter budget in freshwater ecosystems. During leaf litter breakdown, the relative contribution of the functional groups and the quantity/quality of organic matter available to higher trophic levels are expected to be modified by the anthropogenic release of nutrients. 2. Carbon budgets were established during the breakdown of alder leaves enclosed in coarse mesh bags and submerged in six streams: two oligotrophic, one mesotrophic, two eutrophic and one hypertrophic streams. Nitrate concentrations were 4.5–6.7 mg L⁻¹ and the trophic status of each stream was defined by the soluble reactive phosphorus concentration ranging from 3.4 (oligotrophic) to 89 μg L⁻¹ (hypertrophic). An ammonium gradient paralleled the phosphate gradient with mean concentrations ranging from 1.4 to 560 μg L⁻¹ NH₄‐N. The corresponding unionised ammonia concentrations ranged from 0.08 to 19 μg L⁻¹ NH₃‐N over the six streams. 3. The dominant shredder taxa were different in the oligo‐, meso‐ and eutrophic streams. No shredders were observed in the hypertrophic stream. These changes may be accounted for by the gradual increase in the concentration of ammonia over the six streams. The shredder biomass dramatically decreased in eu‐ and hypertrophic streams compared with oligo‐ and mesotrophic. 4. Fungal biomass increased threefold from the most oligotrophic to the less eutrophic stream and decreased in the most eutrophic and the hypertrophic. Bacterial biomass increased twofold from the most oligotrophic to the hypertrophic stream. Along the trophic gradient, the microbial CO₂ production followed that of microbial biomass whereas the microbial fine particulate organic matter and net dissolved organic carbon (DOC) did not consistently vary. These results indicate that the microorganisms utilised the substrate and the DOC differently in streams of various trophic statuses. 5. In streams receiving various anthropogenic inputs, the relative contribution of the functional groups to leaf mass loss varied extensively as a result of stimulation and the deleterious effects of dissolved inorganic compounds. The quality/quantity of the organic matter produced by microorganisms slightly varied, as they use DOC from stream water instead of the substrate they decompose in streams of higher trophic status.     

Historical changes in species composition and richness accompanying perturbation and eutrophication of Danish lowland streams over 100 years

1. European lowland streams have experienced increased perturbation and eutrophication during the past 100 years. We use archive information from 27 Danish stream sites around 1896 and new data from 208 stream sites in 1996 to evaluate the accompanying changes in stream vegetation. Among the stream sites, 13 were both studied in 1896 and 1996. 2. The species richness of submerged plants has declined profoundly over the 100-year period, particularly among the large group of Potamogeton species. This is evident both from the direct comparison of the 13 stream reaches included in both studies, and from the general comparison of all stream reaches included in the two studies. 3. The Potamogeton vegetation has become less diverse, and is now dominated by species resistant to frequent disturbance through a high dispersal capacity. Potamogeton species, adapted to eutrophic conditions, have also increased relative to species more typical of oligotrophic conditions over this period. The dominant submerged species in the contemporary stream vegetation generally show a high capacity for dispersal and regrowth of detached shoots. 4. The decline of species richness in Danish streams can be partly explained by a decline in the species richness in lakes in the stream system. The rich vegetation observed downstream of lakes in the past has mostly disappeared due to loss of the vegetation in the now eutrophic lakes and increasing turbidity downstream. 5. The overall decline in richness, and the directional change in dominance patterns among stream species, can thus be explained by the loss of suitable habitats and the strong anthropogenic impacts, which have driven several European aquatic species close to extinction.     

Relationship between freshwater gastropods and plant communities reflecting various trophic levels

Plant communities were examined in ponds in Brittany (north-west France) and then classified into six types reflecting different trophic levels: oligotrophic, oligodystrophic, mesotrophic, meso-dystrophic, meso-eutrophic an eutrophic. In 45 of these ponds, aquatic snails were sampled in order to determine the relationship between the gastropod species richness and the water trophic levels as indicated by plant community types. The second aim of this study was to determine whether some gastropod species were characteristic of a particular trophic level. The number of plant communities in the ponds was also taken into consideration.A trophic gradient was found along the F1 axis on the principal plane of the correspondence analyses. The species richnesses low or zero and especially the lymneid, Lymnaea glabra were close to the oligo-dystrophic and oligotrophic communities. In contrast, the highest numbers of snail species (5 and above) were found in the most eutrophic ponds where Hippeutis complanatus, Planorbis planorbis, Lymnaea stagnalis and Planorbarius corneus were particularly common. The latter species inhabited the ponds including on average the greatest number of macrophyte communities but no significant differences were found between snail species. The ponds which contained the greatest numbers of plant communities included the richest gastropod communities (7 and more) but also the poorest ones (0 or 1 species). Relationships between freshwater snails, macrophytes and trophic levels are discussed.Laboratoire de Zoologie et d'Ecophysiologie     

Aquatic vegetation and trophic condition of Cape Cod (Massachusetts,U.S.A.) kettle ponds

The species composition and relative abundance of aquatic macrophytes was evaluated in five Cape Cod, Massachusetts, freshwater kettle ponds, representing a range of trophic conditions from oligotrophic to eutrophic. At each pond, aquatic vegetation and environmental variables (slope, water depth, sediment bulk density, sediment grain size, sediment organic content and porewater inorganic nutrients) were measured along five transects extending perpendicular to the shoreline from the upland border into the pond. Based on a variety of multivariate methods, including Detrended Correspondence Analysis (DCA), an indirect gradient analysis technique, and Canonical Correspondence Analysis (CCA), a direct gradient approach, it was determined that the eutrophic Herring Pond was dominated by floating aquatic vegetation (Brasenia schreberi, Nymphoides cordata, Nymphaea odorata), and the algal stonewort, Nitella. Partial CCA suggested that high porewater PO₄-P concentrations and fine-grained sediments strongly influenced the vegetation of this eutrophic pond. In contrast, vegetation of the oligotrophic Duck Pond was sparse, contained no floating aquatics, and was dominated by emergent plants. Low porewater nutrients, low sediment organic content, high water clarity and low pH (4.8) best defined the environmental characteristics of this oligotrophic pond. Gull Pond, with inorganic nitrogen-enriched sediments, also exhibited a flora quite different from the oligotrophic Duck Pond. The species composition and relative abundance of aquatic macrophytes provide good indicators of the trophic status of freshwater ponds and should be incorporated into long-term monitoring programs aimed at detecting responses to anthropogenically-derived nutrient loading.     

The impact of eutrophication on aquaticmacrophyte diversity in weakly mineralized streams in the Northern Vosges mountains(NE France)

The relationships between water chemistry and aquatic macrophyte species were studied in an attempt to evaluate the impact of eutrophication on aquatic macrophyte diversity in weakly mineralized streams in the Northern Vosges mountains (NE France). The macrophyte specific richness and abundance increased along an upstream to downstream zonation, which was characterized by an increase in mineralization and nutrient levels. A comparison of aquatic macrophyte diversity of two streams has shown the impact of human-induced perturbations (fish-farms, domestic sewage) in such weakly mineralized and poorly buffered waters. Disturbed sites with very high nutrient loading were characterized by a low vascular plant richness and by the presence of filamentous algae. In order to preserve the floristic diversity of weakly mineralized streams, water quality should be improved, the riverbanks restored and discharges reduced.     

Relations between trophic state indicators and plant biomass in Florida lakes

We collected quantitative data on macrophyte abundance and water quality in 319 mostly shallow, polymictic, Florida lakes to look for relationships between trophic state indicators and the biomasses of plankton algae, periphyton, and macrophytes. The lakes ranged from oligotrophic to hypereutrophic with total algal chlorophylls ranging from 1 to 241 mg m^–3. There were strong positive correlations between planktonic chlorophylls and total phosphorus and total nitrogen, but there were weak inverse relationships between the densities of periphyton and the trophic state indicators total phosphorus, total nitrogen and algal chlorophyll and a positive relationship with Secchi depth. There was no predictable relationship between the abundance of emergent, floating-leaved, and submersed aquatic vegetation and the trophic state indicators. It was only at the highest levels of nutrient concentrations that submersed macrophytes were predictably absent and the lakes were algal dominated. Below these levels, macrophyte abundance could be high or low. The phosphorus–chlorophyll and phosphorus–Secchi depth relationships were not influenced by the amounts of aquatic vegetation present indicating that the role of macrophytes in clearing lakes may be primarily to reduce nutrient concentrations for a given level of loading. Rather than nutrient concentrations controlling macrophyte abundance, it seems that macrophytes acted to modify nutrient concentrations.     

Synergistic effects of water temperature and dissolved nutrients on litter decomposition and associated fungi

In woodland streams, the decomposition of allochthonous organic matter constitutes a fundamental ecosystem process, where aquatic hyphomycetes play a pivotal role. It is therefore greatly affected by water temperature and nutrient concentrations. The individual effects of these factors on the decomposition of litter have been studied previously. However, in the climate warming scenario predicted for this century, water temperature and nutrient concentrations are expected to increase simultaneously, and their combined effects on litter decomposition and associated biological activity remains unevaluated. In this study, we addressed the individual and combined effects of water temperature (three levels) and nutrient concentrations (two levels) on the decomposition of alder leaves and associated aquatic hyphomycetes in microcosms. Decomposition rates across treatments varied between 0.0041 day^?1 at 5 °C and low nutrient level and 0.0100 day^?1 at 15 °C and high nutrient level. The stimulation of biological variables at high nutrients and temperatures indicates that nutrient enrichment of streams might have a higher stimulatory effect on fungal performance and decomposition rates under a warming scenario than at present. The stimulation of fungal biomass and sporulation with increasing temperature at both nutrient levels shows that increases in water temperature might enhance fungal growth and reproduction in both oligotrophic and eutrophic streams. The stimulation of fungal respiration and litter decomposition with increasing temperature at high nutrients indicates that stimulation of carbon mineralization will probably occur at eutrophied streams, while oligotrophic conditions seem to be ‘protected’ from warming. All biological variables were stimulated when both factors increased, as a result of synergistic interactions between factors. Increased water temperature and nutrient level also affected the structure of aquatic hyphomycete assemblages. It is plausible that if water quality of presently eutrophied streams is improved, the potential stimulatory effects of future increases in water temperature on aquatic biota and processes might be mitigated.     

Aquatic faunal responses to an induced regime shift in the phosphorus‐impacted Everglades

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Regulation of submersed macrophyte biomass in a temperate lowland river: Interactions between shading by bank vegetation, epiphyton and water turbidity

Growth of aquatic vegetation is often controlled by light supply, which is potentially decreased by bank vegetation, water turbidity and epiphytic biofilm. To understand the relative importance of these shading factors and the interactions between them we analysed the seasonal course of macrophyte biomass, shading by bank vegetation, turbidity of the water column and epiphytic light absorption in shaded and sunny sections of a temperate eutrophic lowland river. At a shaded site, bank vegetation decreased the light supply by 79%, 0.5 m water column by 45% and 2-week-old epiphyton by 28% during the vegetation period. Growth of submersed macrophytes, but not of epiphyton, was light-limited in the shaded sections. We found a saturation-type correlation between light supply and macrophyte biomass. Therefore, the additional light absorption of the water column or epiphyton only shortened the period of optimum light supply at the sunny site, but was crucial for macrophyte development at the shaded site. Light absorption of phytoplankton was most important in spring and that of epiphyton in late summer. Submersed macrophytes effectively retained particles and thus improved light supply of downstream stands, but this positive feedback effect was only relevant for shaded sections in summer.     

The role of emergent vegetation in structuring aquatic insect communities in peatland drainage ditches

Availability of macrophyte habitat is recognized as an important driver of aquatic insect communities in peatland drainage ditches; however, eutrophication can lead to the decline of submerged vegetation. While emergent vegetation is able to persist in eutrophicated ditches, vegetation removal, carried out during ditch maintenance, can reduce the availability of this habitat. In this study, we applied the landscape filtering approach to determine whether the absence of emergent vegetation is a habitat filter which structures aquatic insect communities in peatland drainage ditches under different trophic conditions. To this end, a field study was carried out in one mesotrophic (Naardermeer) and one eutrophic (Wormer and Jisperveld) peatland in the province of North Holland, The Netherlands. We assigned life history strategies to insect species and applied linear mixed models and redundancy analyses to taxonomic and functional aquatic insect community data. Our results indicate that while differences between peatlands primarily determine the species pool within each wetland, emergent vegetation acted as a secondary filter by structuring functional community composition within ditches. The eutrophic peatland was dominated by insects adapted to abiotic extremes, while species with good dispersal abilities were strongly related to emergent vegetation cover. This study demonstrates the applicability of life history strategies to provide insight into the filtering of species due to availability of emergent macrophyte habitat. To ensure greater diversity of insect communities in ditch habitats, it is recommended that some vegetation be spared during maintenance to leave patches from which insect recolonization can occur.     

Primary producers in a Pampean stream: temporal variation and structuring role

Low current velocities, high nutrient levels, the lack of riparian forest vegetation, and the development of dense and rich macrophyte communities characterize Pampean streams. The objective of this study was to describe the main physical, chemical, and biological characteristics of a headwater Pampean stream as well as to analyze the role of macrophytes and phytobenthos. The study was conducted in a stream considered to be not much disturbed by human activities. Samples of water and organisms (macrophytes, benthic algae and invertebrates) were taken monthly for 14 months in two sampling stations, in fast flow and slow flow sites. Macrophyte biomass and diversity increased in spring and summer, and they decreased in autumn, when the plant community was greatly affected by an important flood. Phytobenthos biomass was lower in late summer, possibly due to the establishment of a dense cover of the floating macrophyte Lemna gibba L. Density of amphipods and gastropods greatly increases in spring and summer, jointly with the macrophyte development. Analysis of correlation showed that current velocity is the most important factor influencing macrophyte biomass and phytobenthos structure, while depth, nutrients, and herbivores are linked factors. Pampean streams could be considered systems dynamically fragile, because habitat heterogeneity is generated by aquatic vegetation, a substratum that varies along time.     

Are diatom-based biotic indices developed in eutrophic,organically enriched waters reliable monitoring metrics in clean waters?

The application of diatom indices developed for organically enriched and eutrophic waters in oligotrophic and relatively pristine streams in the Eastern Highlands of Zimbabwe was investigated based on data collected in May–August 2007. Better suitability of diatom indices in investigating the quality of eutrophic, organically enriched waters compared to oligotrophic waters is demonstrated. More robust data sets on taxonomy and autecology of a great number of diatom species are required to make the indices more powerful tools in monitoring water quality and ecological integrity of streams in the region.     

Centennial‐scale changes to the aquatic vegetation structure of a shallow eutrophic lake and implications for restoration

1. We investigate long‐term (>200 years) changes to the composition and spatial structure of macrophyte communities in a shallow, eutrophic lake (Barton Broad, eastern England) and consider the implications for lake restoration. 2. Historical macrophyte data were assembled from a variety of sources: existing plant databases, museum herbaria, journal articles, old photographs and eyewitness accounts. Additionally, two types of sediment core sample were analysed for plant macro‐remains and pollen; bulk basal samples from multiple core sites analysed to provide information on ‘pre‐disturbance’ macrophyte communities and two whole cores analysed to determine historical change. 3. Prior to the late 1800s, macrophyte communities were diverse and included a multilayered mosaic of short‐stature submerged taxa and taller submerged and floating‐leaved species. With the progression of eutrophication after around 1900, the former community was displaced by the latter. Diversity was maintained, however, since an encroaching Schoenoplectus–nymphaeid swamp generated extensive patches of low‐energy habitat affording refugia for several macrophytes otherwise unable to withstand the hydraulic forces associated with open water conditions. When this swamp vegetation disappeared in the 1950s, many of the ‘dependent’ aquatic macrophytes also declined leaving behind a sparse, species‐poor community (as today) resilient to both eutrophication and turbulent open waters. 4. The combination of historical and palaeolimnological data sources offers considerable benefits for reconstructing past changes to the aquatic vegetation of lakes and for setting restoration goals. In this respect, our study suggests that successful restoration might often be better judged by reinstatement of the characteristic structure of plant communities than the fine detail of species lists; when nutrients are low and the structure is right, the right species will follow.     

Macrophytes as indicators of stream condition in the wet tropics region,Northern Queensland,Australia

This study investigates the use of aquatic macrophytes as indicators of stream condition in catchments with varied land use and levels of riparian disturbance in the Wet Tropics region of North Queensland (Australia), a region of global significance in terms of faunal and floral diversity. In a paired catchment design spatial variations in macrophyte assemblage structure were characterised using multivariate and univariate techniques. Seven metrics were trialled: total macrophyte cover, species richness, % alien taxa, % native taxa, % submerged taxa, % emergent taxa and % Poaceae. Forty-four macrophyte taxa were recorded from the study area. Poaceae, Cyperaceae and mosses were the most frequently recorded taxa. Upper catchment areas in all tributaries surveyed were dominated by mosses and Cladopus queenslandicus (Domin) C.D.K. Cook (Podestemaceae). This assemblage occurred in areas with intact riparian canopy cover and good overall riparian condition. Macrophyte assemblages in lower catchment areas were distributed along gradients of riparian disturbance. Simultaneous autoregression model coefficients indicated that riparian condition had a negative influence on macrophyte cover, species richness and the proportions of alien taxa, emergent taxa and Poaceae present at sites in the Wet Tropics. Macrophyte metrics were not strongly influenced by the types of land use or water quality. These findings suggest that a riparian condition assessment would provide an adequate first assessment of the state of aquatic macrophyte assemblages in Wet Tropics streams.     

城市湖泊富营养化成因和特征*

城市湖泊的功能主要体现在旅游、如愿、洪涝调蓄排水、调节气候以及改善城市生态环境等方面。根据湖泊所处地理位置和湖泊水质退化现象,阐述了城市湖泊水体从贫营养到富营养转变的主要原因;从水质的理化指标、底质污染物含量和水生态系统等方面初步时论了城市型浅水湖泊富营养化的特征。同非城市湖泊相比:大部分城市湖泊的水体透明度下降,污染严重的湖泊还会出现水体发黑或出现水华;水质和底质的氮磷及其它污染物含量较高,水生态系统急剧退化,水生植物以浮游植物为主,藻类大量繁殖,高等水生植物不断消亡。根据综合营养度指数对我国主要城市湖泊进行分级评价的结果表明,我国城市湖泊均达到了富营养化或严重富营养化程度。     

Vegetation and flow regime in lowland streams

1. The hydrological regime is important to the distribution of benthic organisms in streams. The objective of this study was to identify relationships between hydrological variables, describing the flow regime, and macrophyte cover, species richness, diversity and community composition in Danish lowland streams.
2. We quantified macrophyte vegetation in 44 Danish streams during summer by cover, species richness and diversity. Flow regime was characterized by 18 non-intercorrelated variables describing magnitude, frequency and duration of low and high flow events, timing or predictability of flow and general flow variability.
3. We found support in the stepwise multiple regressions analysis for our expectation that macrophyte cover is lowest in streams with high flow variability and highest in streams with long duration of low flow and low flow variability. We found support for the intermediate disturbance hypothesis as there were significant quadratic relationships between species richness and diversity as functions of disturbance frequency. There was poor discrimination in a detrended correspondence analysis (DCA) analysis of macrophyte community composition between four twinspan groups separating streams with different hydrological properties. Moreover, we did not find any relationship between the presence of disturbance-tolerant species and hydrological disturbance, suggesting that plant community composition developed independently of stream hydrology.     

Macrophytes from some high Andean lakes of Ecuador and their low potential as bioindicators of eutrophication

The occurrence of macrophyte in three high Andean lakes of Ecuador, Lago San Pablo, Laguna La Mica and Lago Cuicocha was recorded in 5-9 transects per lake. The first two lakes are eutrophic, the third is an extremely oligotrophic caldera lake. The dominant species in eutrophic lakes are Ceratophyllum demersum, Myriophyllum quitense, Polamogeton illinoensis, P. striatus and Elodea matthewsii. In the oligotrophic lake P. pectinatus, P. illinoensis, and the Characeae Chara rusbyana, Ch. globularis and Nitella acuminata occur. The maximum depth of the macrophyte's presence can be used as an indicator of the trophic state, ranging from about 5 m in Mica to 35 m in Cuicocha. The bioindication value of the macrophyte species in these high Andean lakes is low, because few species occur and because some of them are not specific to environmental conditions.     

西太湖水生植物时空变化

水生植物在浅水湖泊生态系统中具有十分重要的作用。根据中国科学院太湖湖泊生态系统研究站1989年以来的常规监测资料,将西太湖（除东太湖以外的湖区）划分为9个区,采用点截法（point intercept method）,于2002～2005年对各区水生植物的种类、生物量和空间分布情况进行了6次调查。结果表明：西太湖现有水生植物16种,分属于11科12属;水生植物总面积约10220hm^2,其中沉水植物分布面积约占64．58％;挺水植物约占0．29％;漂浮植物约占38．16％。各个种之间生物量差异显著,马来眼子菜、荇菜、芦苇的生物量在所有水生植物中居前3位。多样性分析表明,水生植物种类4a来未发生明显变化,但种类和生物量季节性差异较大。水生植物呈环状分布在距湖岸5km以内的水域和部分岛屿周围,东岸和南岸为水生植物的主要集中分布区域,分布区连续性好,且水草种类齐全。挺水植物种类单一,仅有芦苇（Phragmites communis）一种,分布区域多限于水深小于1．6m的湖岸;沉水植物共有8种,为水生植物的主要组成部分,马来眼子菜（Potamogeton malaianus）的分布频度最高,在西山岛周围水域逐年扩张,成为该区域的先锋种;漂浮植物3种,主要以荇菜（Nymphoides peltata）为主,在七都水域有逐渐扩张的趋势。马来眼子菜、芦苇、荇菜表现出对水环境较强的适应能力,目前为西太湖的3个优势种。20世纪50年代以来,西太湖水生植物种类减少了50种,其中水质下降是导致水生植物种类不断减少甚至消失的一个重要原因。围网养殖和不合理的捕捞方式也对局部水域的植物造成极大的破坏。水生植物生存环境日益严峻,种群单一化趋势日益明显。