Distribution, production and role of aquatic macrophytes in a southern Michigan marl lake

A typical marl lake of the Upper Great Lakes region has very few quantitatively important aquatic macrophytes. The macrophytes, however, dominate the total primary production of the lake. Submersed vegetation is extremely sparse on the shallow (less than I m) marl bench that characterizes the littoral of these lakes, and is completely dominated by one. little-known species (Scirpus subterminalis Torr.) between 1 and 7 m. A detailed investigation of the spatial and seasonal distribution of macrophytic species and biomass showed that S. subterminalis strongly dominated the lake (79% of total biomass). S. suhterminalis represented an almost pure stand (to 200 g m^?2 mean annual ash-free dry weight) at all times of the year at intermediate depths of macrophytic growth (1–6 m). Two species of Chara (of eight varieties and forms) were present in significant quantities (12% of total biomass; to 100 g m^?2) but were severely limited to shallow depths (0-S-l m) and protected areas. Several annual submersed angiosperms were present (9% of total biomass), but only two species were quantitatively important. Potamogeton illinoensis Morong. and P. praelongus Wulfen formed brief summer peaks (less than 100 g m^?2) at 3 and 4–6 m, respectively. A striking feature of the seasonal biomass distribution of Scirpus subterminalis was the higher, viable biomass (to 150g m^?2) throughout the winter under ice cover. Cyclic fluctuations of the S. subterminalis populations were discerned at different depths, each with different periodicities. The population at 2 m exhibited a fall peak; that at 4 m had a summer maximum. The lowest overall biomass of S. subterminalis occurred in the 2 m population in June. Chara populations at 0–2 m also exhibited a relatively constant biomass throughout the year. The appearance of Nitella at 7 m in July-October and of Chara at 5 m in September-October was interpreted as an interaction between light, thermal, and carbon stratification. Estimates of macrophytic productivity of perennial (‘evergreen’) species populations whose biomass remains relatively constant throughout the year were made employing several different methods of calculation and turnover factors. All methods resulted in productivity estimates in good agreement with the conservative value of 178 g m^?2 year^?1 for the entire lake. In comparison to the other components (phyto-planktonic, epiphytic and epipelic algae) of the primary production of Lawrence Lake, the aquatic macrophytes constituted a major portion (anuual mean 82·77 g C m^?2 year^?1 or 48·3 %) of the total production of the lake. The low diversity but relatively high quantitative importance of macrophytes in marl lakes is attributed to an adverse dissolved inorganic and organic chemical milieu which inhibits phytoplanktonic production and allows only certain adapted macrophytes to develop strongly. The phenomenon of perennial biomass levels throughout the year is believed to be much more common than previously suspected and has iikely resulted from adaptations of submersed macrophytes to ameliorated conditions of water and temperatures relative to the terrestrial situation in winter.     

Global diversity of aquatic macrophytes in freshwater

Aquatic macrophytes are aquatic photosynthetic organisms, large enough to see with the naked eye, that actively grow permanently or periodically submerged below, floating on, or growing up through the water surface. Aquatic macrophytes are represented in seven plant divisions: Cyanobacteria, Chlorophyta, Rhodophyta, Xanthophyta, Bryophyta, Pteridophyta and Spermatophyta. Species composition and distribution of aquatic macrophytes in the more primitive divisions are less well known than for the vascular macrophytes (Pteridophyta and Spermatophyta), which are represented by 33 orders and 88 families with about 2,614 species in c. 412 genera. These c. 2,614 aquatic species of Pteridophyta and Spermatophyta evolved from land plants and represent only a small fraction (∼1%) of the total number of vascular plants. Our analysis of the numbers and distribution of vascular macrophytes showed that whilst many species have broad ranges, species diversity is highest in the Neotropics, intermediate in the Oriental, Nearctic and Afrotropics, lower in the Palearctic and Australasia, lower again in the Pacific Oceanic Islands, and lowest in the Antarctic region. About 39% of the c. 412 genera containing aquatic vascular macrophytes are endemic to a single biogeographic region, with 61–64% of all aquatic vascular plant species found in the Afrotropics and Neotropics being endemic to those regions. Aquatic macrophytes play an important role in the structure and function of aquatic ecosystems and certain macrophyte species (e.g., rice) are cultivated for human consumption, yet several of the worst invasive weeds in the world are aquatic plants. Many of the threats to fresh waters (e.g., climate change, eutrophication) will result in reduced macrophyte diversity and will, in turn, threaten the faunal diversity of aquatic ecosystems and favour the establishment of exotic species, at the expense of native species. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

淡水水生植物化感作用研究进展

水生植物的化感作用对淡水生态系统中水草的可持续管理和湖泊富营养化的生态控制具有非常重要的意义。本文综述了淡水水生植物化感作用的发展历史和研究现状,讨论了水生植物化感作用研究过程中所涉及的实验方法、生物测试方法、化感物质分离方法以及影响水生植物化感研究的环境因素。抑藻圈试验、藻类生长试验和浮萍生长试验是常用的生物测试方法;采用共生培养或单独培养的方法,从种植水中分离、鉴定化感物质,对证实复杂水环境中水生植物化感作用的存在,研究它们化感物质的释放途径和作用机理都具有十分重要的作用。     

Enzymatic isolation of cells from aquatic macrophytes

Cells were isolated by enzymic digestion from a number of aquatic macrophytes and their photosynthetic activities were determined. Eichhornia crassipes (Mart.) Solms, Myriophyllum spicatum L. and M. brasiliense Cambess provided photosynthetically-active cells after digestion with commercial pectinase. Cells from emergent leaves of M. brasiliense were approximately 3 times more active than cells from submersed leaves (56.1 vs. 17.4 μmoles CO₂ mg^?2 Chl h^?1). Cells could be isolated from E. crassipes by grinding as well as by digestion, but the former were less active (3.1 vs. 24.2 μmoles CO₂ mg Chl h^?1). Attempts to isolate cells from Hydrilla verticillata (L.f.) Royle or Potamogeton pectinatus L. were not successful.     

The aquatic macrophytes of Lake Vechten. Species composition,spatial distribution and production

The macrophytic species compositions in Lake Vechten of 1963 and 1979–80 were compared and showed a considerable change. The main vegetation types were mapped in 1973, 1978, 1979 and 1980. All macrophytic communities, i.e. submerged, floating-leaved and emergent vegetation types, declined mainly due to increasing water turbidity, increasing tree-shading and, from 1978 onwards, grazing and trampling by cattle.Production rates, derived from different combinations of measurement and calculation, were compared. The macrophytes contributed only about 7% to the total lake production in 1980.     

Heavy metals in aquatic macrophytes drifting in a large river

Macrophytes drifting throughout the water column in the Detroit River were collected monthly from May to October 1985 to estimate the quantities of heavy metals being transported to Lake Erie by the plants. Most macrophytes (80–92% by weight) drifted at the water surface. Live submersed macrophytes made up the bulk of each sample. The most widely distributed submersed macrophyte in the river, American wildcelery (Vallisneria americana), occurred most frequently in the drift. A total of 151 tonnes (ash-free dry weight) of macrophytes drifted out of the Detroit River from May to October. The drift was greatest (37 tonnes) in May. Concentrations of heavy metals were significantly higher in macrophytes drifting in the river than in those growing elsewhere in unpolluted waters. Annually, a maximum of 2 796 kg (eight heavy metals combined) were transported into Lake Erie by drifting macrophytes. The enrichment of all metals was remarkably high (range: 4 000 × to 161 000 × ) in macrophytes, relative to their concentration in water of the Detroit River. Detroit River macrophytes are thus a source of contaminated food for animals in the river and in Lake Erie.Contribution 734 of the National Fisheries Research Center-Great Lakes, U.S. Fish and Wildlife Service, 1451 Green Road, Ann Arbor, MI 48105.     

Groundwater seepage stimulates the growth of aquatic macrophytes

1. The impact of groundwater seepage on the growth of submerged macrophytes was investigated in experiments on the isoetid Littorella uniflora and the elodeid Myriophyllum alterniflorum both in the laboratory and in the field. Isoetids rely mostly on sediment‐derived CO₂ and nutrients via root uptake, whereas elodeids acquire their inorganic carbon and nutrients from the water column. We thus hypothesised that L. uniflora would respond positively to seeping ground water as it should improve both CO₂ and nutrient supply. 2. Laboratory experiments were conducted by percolating vegetated cores containing natural sediment or technical sand with artificial ground water of high CO₂ concentrations and with either high or low levels of nutrients. Field experiments were conducted in the oligotrophic Lake Hampen, Denmark, with custom‐built seepage‐growth chambers that permitted a near‐natural flow‐through of seeping ground water. Chambers with a solid bottom, and thus no flow‐through of seeping ground water, served as controls in both laboratory and field experiments. In the field, seepage chambers were installed at a site with relatively high seepage fluxes (ground water from forest catchment), at a site with much lower seepage fluxes but with higher nutrient concentrations (ground water from agricultural catchment) and at a reference site with no net discharge or recharge of ground water. 3. Positive growth responses were observed in the field at transects with high groundwater discharge compared to the control chambers with no seepage. No growth response was observed at the reference transect with low or alternating direction of groundwater seepage. The growth rates of L. uniflora in the field were significantly higher in seepage treatments compared to control treatments, and final plant mass was up to 70% higher than that for plants where seepage was excluded. In areas with high groundwater discharge, a strong positive correlation was found between groundwater seepage fluxes, growth rates, and final plant mass for L. uniflora, while there was no such relationship at the reference transect. The growth of M. alterniflorum was also significantly affected by groundwater seepage, but to a lesser degree than L. uniflora. Laboratory experiments generally showed the same trend for both L. uniflora and M. alterniflorum, and the positive influence of seeping ground water was apparently related to increased inorganic carbon supply and, to a lesser degree, improved nutrient availability. 4. Groundwater discharge results in enhanced growth of isoetids and to some extent elodeids inhabiting a groundwater‐fed softwater lake. We propose that the shallow dense vegetation present where most of the discharge takes place acts as a biological filter that retains nutrients that otherwise would end up in the water column and could result in increased algal growth.     

Grazing by a native and an exotic crayfish on aquatic macrophytes

1. We compared grazing by native noble crayfish ( Astacus astacus ) and the exotic signal crayfish ( Pacifastacus leniusculus ) on seedling or well-established macrophytes.
2. In a pool experiment, seedlings of emergent Scirpus lacustris and floating-leaved Potamogeton natans were heavily grazed by adult signal crayfish, whereas established plants of the same species sustained only minor damage.
3. In a preference experiment two submerged macrophytes ( Chara vulgaris and Elodea canadensis ), and both seedlings and established plants of S. lacustris and P. natans , were presented pairwise to signal and noble crayfish. There was no significant difference in preference by the two crayfish species. Chara vulgaris was preferred to all other plants presented, established plants of S. lacustris and P. natans were never preferred, and seedlings of P. natans were preferred to established P. natans .
4. An aquarium experiment was conducted in which the consumption of Chara by signal and noble crayfish was measured in relation to water temperature. Signal crayfish consumed significantly more Chara than noble crayfish, especially at higher temperatures.
5. Our results indicate that the signal crayfish is the more voracious grazer especially at higher temperatures. There may be negative effects on vegetation (emergents and floating-leaved, as well as submerged species) when the signal crayfish is introduced. Chara species are particularly susceptible, since they are preferred by crayfish and the genus includes a large number of rare species. Stocking of crayfish therefore could lead to the decline or removal of submerged species in order of crayfish feeding preferences and could prevent the spread or cause a decline of emergent and floating-leaved vegetation.     

Grazing by a native and an exotic crayfish on aquatic macrophytes

1. We compared grazing by native noble crayfish ( Astacus astacus ) and the exotic signal crayfish ( Pacifastacus leniusculus ) on seedling or well-established macrophytes.
2. In a pool experiment, seedlings of emergent Scirpus lacustris and floating-leaved Potamogeton natans were heavily grazed by adult signal crayfish, whereas established plants of the same species sustained only minor damage.
3. In a preference experiment two submerged macrophytes ( Chara vulgaris and Elodea canadensis ), and both seedlings and established plants of S. lacustris and P. natans , were presented pairwise to signal and noble crayfish. There was no significant difference in preference by the two crayfish species. Chara vulgaris was preferred to all other plants presented, established plants of S. lacustris and P. natans were never preferred, and seedlings of P. natans were preferred to established P. natans .
4. An aquarium experiment was conducted in which the consumption of Chara by signal and noble crayfish was measured in relation to water temperature. Signal crayfish consumed significantly more Chara than noble crayfish, especially at higher temperatures.
5. Our results indicate that the signal crayfish is the more voracious grazer especially at higher temperatures. There may be negative effects on vegetation (emergents and floating-leaved, as well as submerged species) when the signal crayfish is introduced. Chara species are particularly susceptible, since they are preferred by crayfish and the genus includes a large number of rare species. Stocking of crayfish therefore could lead to the decline or removal of submerged species in order of crayfish feeding preferences and could prevent the spread or cause a decline of emergent and floating-leaved vegetation.     

Changes in submersed macrophytes in Chautauqua Lake, 1937–1975

SUMMARY. Changes in macrophyte richness, relative abundances, depth distributions and dominant species from 1937 to 1975 were assessed in Chautauqua, a eutrophic lake. Change was greatest in dominant species, with several formerly abundant native Potamogeton species being replaced by the exotics, Potamogeton crispus and Myriophyllum spicatum . Two extensively practiced management techniques, herbicidal poisoning and mechanized cutting, were considered to be primarily responsible for the observed macrophyte changes.     

Chromium ions phytoaccumulation by three floating aquatic macrophytes from a nutrient medium

In the present work, the trivalent and hexavalent chromium phytoaccumulation by three living free floating aquatic macrophytes Salvinia auriculata, Pistia stratiotes, and Eicchornia crassipes was investigated in greenhouse. These plants were grown in hydroponic solutions supplied with non-toxic Cr³⁺ and Cr⁶⁺ chromium concentrations, performing six collections of nutrient media and plants in time from a batch system. The total chromium concentrations into Cr-doped hydroponic media and dry roots and aerial parts were assayed, by using the Synchrotron radiation X-ray fluorescence technique. The aquatic plant-based chromium removal data were described by using a nonstructural kinetic model, obtaining different bioaccumulation rate, ranging from 0.015 to 0.837 l mg⁻¹ d⁻¹. The Cr³⁺ removal efficiency was about 90%, 50%, and 90% for the E. crassipes, P. stratiotes, and S. auriculata, respectively; while it was rather different for Cr⁶⁺ one, with values about 50%, 70%, and 90% for the E. crassipes, P. stratiotes, and S. auriculata.     

Successional patterns of aquatic macrophytes in Jebba Lake, Nigeria

Macrophyte succession in Jebba Lake, Nigeria, was observed through the first four years after impoundment. Two distinct serai phases, a floating fern phase and a draw-down flora phase could be recognized. The floristic composition of the macrophyte vegetation was also investigated to check earlier predictions (Obot & Mbagwu, 1986) on the probable structure of the macrophyte flora. The failure of obligate floating macrophytes such as Pistia, Azolla and Salvinia to establish in the lake as predicted is discussed. However, rooted emergent macrophytes were observed to be more successful than would be expected from the predictions.     

Flow-resistance adaptations of rigid-stemmed aquatic macrophytes in simulated water channels

This study investigated the development of interspecific adaptations of flow-resistance mechanisms to higher flow rates in rigid-stemmed Hygrophila salicifolia (Vahl) Nees (willow leaf Hygrophila sp.) plants placed in simulated water channels. The results indicate that adaptations to higher flow rates include a reduction in: growth rate, average fresh weight, average dry weight, and average diameter; but an increase in the number of parallel shoots. These effects combine to create a streamlined profile, reduce plant damage, and increase propagation through adventitious budding. Higher flow rates also reduced the ratio of average plant height to average root length in rigid-stemmed Hygrophila sp. The increased root length, strengthening of plant anchors, and reduction of uprooting seen at higher flow rates are likely to increase slope stability and reduce riverbank topsoil runoff. Moreover, rigid-stemmed aquatic macrophytes develop different adaptations than flexible-stemmed water plants (e.g., water celery); for these plants, higher flow velocities trigger an increase in the average density of vascular bundles and a reduction of the average root length, which results in uprooting and movement to different locations. These results suggest that different aquatic macrophytes play different roles in water channels. Our methods and findings can inform further investigations into the roles played by different aquatic macrophytes in ecological engineering and help to identify optimal planting materials or precursors for riverbanks.     

Solid state fermentation of aquatic macrophytes for crude protein extraction

Aquatic macrophytes such as Elodea nuttalli, Vallisneria natans, Alterranthera philoxerides that are widely distributed in water environments of Lake Taihu basin were used as substrate of solid state fermentation to produce crude protein extraction. The effects of single-strain fermentation and mixed strains fermentation of aquatic macrophytes on the production of crude protein extraction and cellulase activity are analyzed, respectively. The experimental results showed that the crude protein content of products with mixed strains fermentation is higher than that with single-strain fermentation. The crude protein content of V. natans fermented by Aspergillus niger and Candida utilis is the highest among the aquatic macrophytes examined in this study. V. natans is used as the substrate to be fermented by C. utilis and A. niger; their ratio is 1:1 at 28 ± 1 °C for 72 h. The crude protein of fermented V. natans is as high as 49.54%, with 128.82% of its increase rate. The cellulose activity reaches a maximum of 4.21 μ/ml at 84 h of fementation of V. natans. Thus, the solid state fermentation of aquatic macrophytes to produce crude protein extraction is promising, which make aquatic macrophytes a potential resource and thus is beneficial to the long-term ecological restoration of eutrophic lakes.     

Classifying aquatic macrophytes as indicators of eutrophication in European lakes

Aquatic macrophytes are one of the biological quality elements in the Water Framework Directive (WFD) for which status assessments must be defined. We tested two methods to classify macrophyte species and their response to eutrophication pressure: one based on percentiles of occurrence along a phosphorous gradient and another based on trophic ranking of species using Canonical Correspondence Analyses in the ranking procedure. The methods were tested at Europe-wide, regional and national scale as well as by alkalinity category, using 1,147 lakes from 12 European states. The grouping of species as sensitive, tolerant or indifferent to eutrophication was evaluated for some taxa, such as the sensitive Chara spp. and the large isoetids, by analysing the (non-linear) response curve along a phosphorous gradient. These thresholds revealed in these response curves can be used to set boundaries among different ecological status classes. In total 48 taxa out of 114 taxa were classified identically regardless of dataset or classification method. These taxa can be considered the most consistent and reliable indicators of sensitivity or tolerance to eutrophication at European scale. Although the general response of well known indicator species seems to hold, there are many species that were evaluated differently according to the database selection and classification methods. This hampers a Europe-wide comparison of classified species lists as used for the status assessment within the WFD implementation process.     

Decomposition dynamics of aquatic macrophytes in the lower Atchafalaya, a large floodplain river

Decomposition of aquatic macrophytes can considerably influence carbon cycling and energy flow in shallow freshwater aquatic ecosystems. The Atchafalaya River Basin (ARB) is a large floodplain river in southern Louisiana that experiences a seasonal floodpulse and is spatially composed of a mosaic of turbid riverine and stagnant backwater areas. During two seasons, winter and fall of 1995, we examined decomposition of four common aquatic macrophytes in the ARB: water hyacinth (Eichhornia crassipes), arrowhead (Sagittaria platyphylla), coontail (Ceratophyllum demersum) and hydrilla (Hydrilla verticillata). To determine decay rates, we used litter bags of two mesh sizes (5 mm and 0.25 mm) and analyzed data with a single exponential decay model. Analysis of decay rates established several trends for aquatic macrophyte decomposition in the ARB. First, macrophytes decayed faster in fall than winter due to the effect of increased temperature. Second, macroinvertebrates were the primary decomposers of macrophytes in riverine sites and microbes were the primary decomposers in backwater areas. These trends may have been related to decomposer-habitat interactions, with well-oxygenated riverine sites more hospitable to invertebrates and backwater areas more favorable to microbes because of high organic inputs and reduced flow. Decay rates for macrophytes, ranked from slowest to fastest, were E. crassipes<S. platyphylla<C. demersum<H. verticillata. Slower decomposition of E. crassipes was probably a result of microbial inhibition by the waxy-cutin outer layer and low nutritional value. The accelerated decomposition of C. demersum and H. verticillata was most likely a function of the large surface area of the highly dissected leaves. Macroinvertebrate numbers were twice as high in riverine sites compared to backwater sites. In the winter, amphipods Gammarus spp. and Hyallela azteca composed a large percentage of the total density on detritus. In the fall, Caenis sp. was prevalent in the backwater habitat and dipterans were abundant in the riverine site. We investigated the microbial component involved in the decomposition of E. crassipes and S. platyphylla and found that the highest microbial respiration rates occurred early in the winter at the backwater site. Bacterial density in the winter on E. crassipes and S. platyphylla averaged 1.4×10⁶ cm^-2 after two days and decreased to 2.0×10⁵ cm^-2 after 28 d. Our results emphasized the importance of the microbial community in the decomposition of macrophytes in the ARB, especially in backwater habitats and in the early stages of decay.     

Distribution of submersed aquatic macrophytes in the tidal Potomac River

Results of a 3-year survey (1978–1980) and review of historic trends have shown a major decline in the number of species and the distribution of submersed aquatic macrophytes in the tidal Potomac River since the early 1900's. The freshwater tidal river is essentially devoid of plants and only very sparse populations remain in the mesohaline section of the estuary. Present plant populations are largely confined to the transition-zone region where salinity instability at the fresh-to-brackish water interface is believed to reduce biotic stress on submersed vegetation. Many factors may be implicated in the loss of vegetation over major regions of the tidal Potomac River; however, long-term conditions of excessive nutrients appear to be primarily responsible for the present distribution.     

Seasonal variations in photosynthetic irradiance response curves of macrophytes from a Mediterranean coastal lagoon

The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O₂ g⁻¹ dw h⁻¹ and 9.1 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O₂ g⁻¹ dw h⁻¹ and 2.6 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹ respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R_d (ranging 6.7–794 μmol O₂ g⁻¹ dw h⁻¹, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).