Estuarine Restoration of Submersed Aquatic Vegetation: The Nursery Bed Effect

The historic decline of submersed aquatic vegetation (SAV) in mesohaline regions of Chesapeake Bay, United States involved a diversity of plant species. The recent modest recovery is mostly, however, associated with a single, prolific but ephemeral species, Ruppia maritima. Two previously abundant and more stable species, Potamogeton perfoliatus and Stuckenia pectinata, have shown virtually no evidence of recovery. Based on previous studies that demonstrated the ability of R. maritima stands to enhance water clarity and nutrient conditions for SAV growth, we hypothesized that these beds would serve as effective “nursery” areas to incite transplant success for other SAV. We conducted experiments in a two‐phase study at small and large spatial scales designed to explore this “nursery effect” as a restoration approach to increase plant species diversity. The first phase was conducted at small spatial scales to test effects of patch density by planting P. perfoliatus and S. pectinata into bare, sparse, and densely vegetated areas within three similar R. maritima beds in a tributary of Chesapeake Bay. Mean seasonal percent survivorship and shoot density were significantly higher in bare patches compared to vegetated patches. In the second phase of the study, P. perfoliatus was transplanted into separate R. maritima beds of different densities to test the effect of bed scale plant density on P. perfoliatus survival and growth. Transplant success of P. perfoliatus was positively correlated with the density of R. maritima among all sites.     

Sensitivity of fitness to macroparameter changes: an analysis of survivorship and individual growth in sea urchin life histories

Summary Feeding relationships between roach and ide from two sites in a mesotrophic lake SE Norway are presented and discussed. When animal food supply was scarce, both fish species increased their consumption of macrophytes; roach sevenfold, and ide threefold. Along a typical littoral vegetation gradient, ide fed among helophytes, while roach fed in the zone outside. This different habitat selection was reflected in the most important plants consumed (ide: Equisetum fluviatile, roach: Characeae), and confirmed by gill net catches. During the vegetative season, roach avoided areas with dense vegetation. In shallow areas beyond the littoral, the most important food plant for both fish species was Potamogeton perfoliatus, which constituted 80% of the total food consumed (dry weight basis) in the roach and 35% in the ide. The diet shift to plants seemed to be strongly influenced by the supply of animal food and the intensity of intra-and interspecific competition.     

Patterns of aquatic weed regrowth following mechanical harvesting in New Zealand hydro-lakes

Mechanical harvesting is used to control submerged aquatic weeds in parts of the hydro-lakes in New Zealand's North Island. Problem species are Egeria densa and Lagarosiphon major (Hydrocharitaceae), and Ceratophyllum demersum. Experiments were conducted in two contrasting hydro-lakes. Lake Aratiatia; clear water (K _o 0.2 m^–1) and a low residence time (< 8 h), and Lake Ohakuri; turbid water (K _o = 0.6) and a longer residence time (> 5 days). Growth rates were measured underwater in harvested and control (unharvested) plots. Regrowth of C. demersum was dependent on the prior establishment of the rooted Hydrocharitaceae. Regrowth of the Hydrocharitaceae was inhibited where significant water movement occurred. Regrowth declined after 3 six-monthly harvests allowing the establishment of low growing native Nitella spp. beds in the smaller clear water lake. In Lake Ohakuri there was a change in species dominance from Ceratophyllum to Elodea canadensis in shallow (1–2 m) water. No change in species dominance was observed in deeper (>2 m) water and native species were not able to re-establish. The recommended cutting frequency for management of surface weed growths was only once per year in Lake Aratiatia, but twice per year in Lake Ohakuri.     

Propagule bank buildup of Chara aspera and its significance for colonization of a shallow lake

Several aspects of the propagule bank dynamics including germination, burial and storage characteristics, and the relationship between the distribution of the propagule bank and cover of an expanding Chara vegetation (dominated by C. asperaDeth. ex Willd.) was studied in the shallow lake Veluwemeer. The density of oospores in the sediment was positively correlated with the number of years that Chara was present at that particular site. After six years of Chara presence, at least 1.7 × 10⁶ oospores m^–2 had accumulated in the sediment. Oospores in sediment were evenly distributed in the 15 cm top layer, which was very similar to the foraging depth of Bewick's Swans (Cygnus columbianus bewickii Yarr). Burial in the sediment may be an important mechanism by which oospores are stored. On the other hand, at shallow areas about 50% of the biomass was consumed enhancing the potential dispersal of oospores by water birds. In a laboratory experiment, 100% of the tested bulbils of C. aspera emerged and thus may be important for short time survival of established vegetation. In contrast, oospore germination varied between 1 and 15% depending on light level and burial depth. The low germination and the high accumulation of oospores suggest that oospores are adapted to long time survival in a dormant state. Charophytes colonized Veluwemeer step by step in the course of about nine years. Not all the sites with suitable light conditions were colonized at the same speed. C. aspera established a dense vegetation only at sites with high oospores densities (> c. 1 × 10⁴ m^–2). The results indicate that the high density of oospores needed for attaining complete vegetation cover may be an important limiting factor during colonization.     

The Relationships Between Environmental Factors and the Submerged Potametea Associations in Lakes of North-eastern Poland

A comparative analysis of submerged Potametea communities in lakes of north-eastern Poland was conducted with respect to 16 water chemistry and 14 substrate parameters. The analysis of 187 relevés based on TWINSPAN clustering showed the existence of 8 aquatic vegetation types. Each of them is characterized by a strong dominance of one of the following macrophytes: Potamogeton lucens, P. perfoliatus, Myriophyllum spicatum, M. verticillatum, Elodea canadensis, Ceratophyllum demersum, Ranunculus circinatus and Hydrilla verticillata. The above vegetation types correspond to the plant associations distinguished using the Braun-Blanquet method (Potametum lucentis, Potametum perfoliati, Myriophylletum spicati etc.) It was demonstrated that among properties of water analysed, COD-KMnO₄, SO₄²⁻, pH, Na⁺, K⁺, Ca²⁺, total hardness, total Fe, Cl⁻ and colour appear to be most important in differentiating the habitats of the communities studied. In the case of substrates the properties which best differentiated the habitats compared were hydration, organic matter content, total N, PO₄³⁻, K⁺, dissolved SiO₂, SO₄²⁻, Cl⁻ and pH. Most of the aquatic plant communities investigated are distinct with respect to their phytocoenotic structure and ecology and could be good indicators of various types of habitats in lake ecosystems.     

Contrasting effects of habitat structure on the recruitment and mortality of an epibiotic macroalga

Field surveys over 2 years in contiguous beds of the seagrassesZostera capricorni andPosidonia australis showed that the green algaCodium duthieae was consistently more abundant inZ. capricorni than inP. australis. In 1 year, mature plants were also more abundant at the boundary between the seagrass beds than in either bed. Field experiments and programmes of sampling were used to investigate three potential explanations for the unusual distribution of this alga: (1) that the availability of substrata suitable for attachment of the alga differed between the two seagrass beds; (2) that mortality of matureC. duthieae differed between the seagrass beds; and/or (3) that the intensity of recruitment was different in the two seagrass beds.C. duthieae plants were exclusively epibionts of the bivalveAnadara trapezia. Detailed sampling showed that the abundance ofA. trapezia was similar in both seagrass beds and that the distribution of bivalves suitable as substrata forC. duthieae plants was not obviously related to proximity to the boundary between the beds. Two experiments investigated the survival ofC. duthieae plants in each bed. In the first, matureC. duthieae plants transplanted into theP. australis bed suffered similar rates of mortality to plants which were disturbed and moved within theZ. capricorni bed or which were left undisturbed in theZ. capricorni bed. Fewer of the host bivalves were recovered from theZ. capricorni bed, however, indicating that the mechanism of mortality differed between the beds, hosts being more frequently dislodged in theZ. capricorni bed. Removal of the leaves of the seagrasses had consistently greater effects on near-bottom current velocities in theZ. capricorni bed than in theP. australis bed and significantly increased mortality ofC. duthieae in theZ. capricorni bed. Survival of plants was greater in plots of artificial leaves ofP. australis placed in theZ. capricorni bed than in plots of the naturalZ. capricorni leaves or plots where the natural leaves were removed. Most mortality in theZ. capricorni bed was due to dislodgement of the alga and its bivalve substratum. Corresponding manipulations of leaves in theP. australis bed had consistently smaller effects on survivorship of both the alga and its host. Patterns in the recruitment of the alga most clearly reflected the distribution of adults.C. duthieae recruits were 5 times more abundant in theZ. capricorni bed and at the boundary between the two beds than in theP. australis bed. The results demonstrate how habitat structure, provided by the canopy of leaves of the two species of seagrass, can have contrasting effects on the recruitment and mortality of a macroalga. In the case ofC. duthieae, it appears that the differential pattern of recruitment is the primary determinant of the distribution of adult plants.     

A comparative study of the use of inorganic carbon resources by Chara aspera and Potamogeton pectinatus

We studied the potential role of dissolved inorganic carbon (DIC) in determining vegetation dominance of Potamogeton pectinatus L. and Chara aspera Deth. ex Willd. by monitoring the seasonal dynamics of DIC in a shallow lake and comparing the use of DIC of the two species. The HCO₃⁻-concentration in summer dropped from 2.5 to <0.5 mM with seasonally increasing Chara biomass, whereas outside the vegetation concentrations remained at 2.5 mM. Inside Potamogeton spp. vegetation DIC decreased from 2.5 to ca. 0.75 mM HCO₃⁻. A growth experiment showed ash-free biomass for P. pectinatus was nearly two times as high as for C. aspera at 3 mM HCO₃⁻, but almost two times lower at 0.5 mM than at 3.0. In a separate experiment, P. pectinatus precultured at a relatively low HCO₃⁻-level had a lower net photosynthetic rate (P_max, 0.1 mmol O₂ g⁻¹ DW h⁻¹) than C. aspera (P_max, 0.1 mmol O₂ g⁻¹ DW h⁻¹) over the range of HCO₃⁻-concentrations tested (P_max, 0.14 mmol O₂ g⁻¹ DW h⁻¹). In response to CO₂ no significant differences between the compensation points (P. pectinatus, 28 mM; C. aspera 66 mM), were observed, but the photosynthetic rate increased faster than for C. aspera than for P. pectinatus. Under field conditions, the use of CO₂ is not important since inside vegetation CO₂-concentrations were below 10 μM, and thus, not available for photosynthesis of either species during the main part of the growth season. It is suggested that C. aspera may be a better competitor for HCO₃⁻ than P. pectinatus in conditions with a low HCO₃⁻ supply. As HCO₃⁻ is a strong limiting factor for growth inside the vegetation and probably the only carbon source available, the superior ability of C. aspera to use HCO₃⁻ may be an important factor explaining its present dominance in Veluwemeer.     

Protocols for Use of Potamogeton perfoliatus and Ruppia maritima Seeds in Large‐Scale Restoration

Restoration of submerged aquatic vegetation from seed has been hampered by a lack of information on the appropriate conditions for collecting, processing, and storing seeds prior to dispersal. Seeds must be processed and stored under conditions that maintain seed viability, meet dormancy requirements, and prevent premature germination. This study examined the effects of collection date, processing technique, aeration, storage and induction temperature and salinity, and storage period on seed germination of two mesohaline aquatic species, Potamogeton perfoliatus and Ruppia maritima. Collection date and processing technique were significant factors affecting seed yield from donor populations. Seeds of both species remained viable and germinated best when stored at 4°C, and then exposed to freshwater induction conditions. However, their responses to other factors differed. Aeration during storage was necessary in order to maintain viability of P. perfoliatus seeds, whereas it was unnecessary for R. maritima seeds. Storage in freshwater at 4°C prevented germination of P. perfoliatus seeds, while high salinity during cold storage was necessary to minimize premature germination of R. maritima. Mean germination time of P. perfoliatus was dependent on storage salinity; in contrast, mean germination time of R. maritima seeds was dependent on induction salinity. These differences indicate that the methods required to produce large quantities of underwater plant seed amenable to large‐scale restoration efforts must be tailored to the specific requirements of individual species and must consider the range of processes from initial harvest through seed testing prior to field establishment.     

Swan foraging shapes spatial distribution of two submerged plants,favouring the preferred prey species

Compared to terrestrial environments, grazing intensity on belowground plant parts may be particularly strong in aquatic environments, which may have great effects on plant-community structure. We observed that the submerged macrophyte, Potamogeton pectinatus, which mainly reproduces with tubers, often grows at intermediate water depth and that P. perfoliatus, which mainly reproduces with rhizomes and turions, grows in either shallow or deep water. One mechanism behind this distributional pattern may be that swans prefer to feed on P. pectinatus tubers at intermediate water depths. We hypothesised that when swans feed on tubers in the sediment, P. perfoliatus rhizomes and turions may be damaged by the uprooting, whereas the small round tubers of P. pectinatus that escaped herbivory may be more tolerant to this bioturbation. In spring 2000, we transplanted P. perfoliatus rhizomes into a P. pectinatus stand and followed growth in plots protected and unprotected, respectively, from bird foraging. Although swan foraging reduced tuber biomass in unprotected plots, leading to lower P. pectinatus density in spring 2001, this species grew well both in protected and unprotected plots later that summer. In contrast, swan grazing had a dramatic negative effect on P. perfoliatus that persisted throughout the summer of 2001, with close to no plants in the unprotected plots and high densities in the protected plots. Our results demonstrate that herbivorous waterbirds may play a crucial role in the distribution and prevalence of specific plant species. Furthermore, since their grazing benefitted their preferred food source, the interaction between swans and P. pectinatus may be classified as ecologically mutualistic.     

Mycena auricoma,a new species ofMycena sectionRadiatae from Japan,andMycena spinosissima,a new record in Japan

Two lignicolous species ofMycena (Agaricales, Basidiomycetes) are described and illustrated from eastern, Japan:Mycena auricoma sp. nov., forming ephemeral coprinoid basidiomata and belonging to sectionRadiatae, was found on a dead fallen twig ofQuercus serrata. It appears to close to a Malaysian species,“Trogia” crinipelliformis. Mycena spinosissima in sectionSacchariferae, new to Japan, was collected from dead bark ofAphananthe aspera, a dead fallen inflorescence ofCryptomeria japonica, and a dead fallen twig ofQuercus serrata.     

Seasonal changes in abundance and shifts in dominance of life history stages of the carrageenophyte Sarcothalia crispata (Rhodophyta, Gigartinales) in south central Chile

The population dynamics of the carrageenophyte Sarcothalia crispatais described from subtidal beds at two localities in south-central Chile. Seasonal fluctuations in total density and biomass were not evident. Frondswere identified to phase by the presence of reproductive structures and theresorcinol reaction. The monthly changes in abundance of each kind offrond were determined. Permanent gametophytic or sporophyticdominance was not evident: the more exposed site showed a seasonal shiftfrom sporophytic dominance in summer to gametophytic dominance inwinter, whereas the more protected site showed an interannual shift fromgametophytic to sporophytic dominance. The differences between localitiesand years suggest a very local population dynamics with large contributionof self-seeding to the maintenance of the S. crispata beds.     

Nothobartsia,a new genus ofScrophulariaceae from southwest Europe

Recent systematic studies ofBartsia andOdontites showed the necessity to exclude the closely related perennial speciesBartsia aspera (Portugal and northern Morocco) andBartsia spicata (Central Pyrenees) from the genusBartsia as a segregate genus namedNothobartsia. Morphologically this new genus combines characteristic features ofBartsia and ofOdontites. Its autonomous systematic position is supported by the cladistic analysis, showing thatNothobartsia represents a relatively primitive genus standing close to the common ancestral root ofBartsia, Euphrasia, andOdontites.     

Long-term change in water transparency before and after the loss of eelgrass beds in an estuarine lagoon,Lake Nakaumi,Japan

Long-term changes in Secchi disk transparency in Lake Nakaumi, Japan, from 1932 to the present, which includes the periods before and after the loss of eelgrass (Zostera marina L.) beds, were compiled from previous reports. During the first (July 1932–February 1934) and the second (January 1949–November 1950) periods, the mean transparency was greater than 3 m at all observed stations. Data during the third period (July 1954–March 1956) are only available for the station at the center of the lake. The mean transparency during the third period was significantly lower than that of the second period but higher than the mean during the fourth period. This observation suggests that the decrease of transparency occurred during the third period. Because the decline of eelgrass beds in Lake Nakaumi occurred in the mid-1950s, the decrease of transparency most likely resulted from the shift in primary producers from submerged macrophytes to phytoplankton. Although the maximum transparency sometimes exceeded 3 m, mean transparencies during the fourth period (May 1975–December 2003) were less than 2 m at all stations, significantly lower than those during the first and second periods. The shift in the chief primary producer, from benthic macrophytes to phytoplankton, caused a subsequent shift in secondary producers. The opportunistic filter-feeding bivalve Musculista senhousia, regarded as a biofouling species of local fisheries, increased in Lake Nakaumi. The long-term monitoring data of transparency suggested that restoration of submerged aquatic vegetation may be indispensable for the remediation of the lake environment in this shallow eutrophic lagoon.     

Restoration management of abandoned chalk grassland in the Netherlands

After abandonment of chalk grassland in the Netherlands, Brachypodium pinnatum had become very dominant and this resulted in a dramatic decrease of plant diversity. Restoration of these abandoned sites is important, because of its former high diversity with many nationally endangered species. To restore the chalk grassland vegetation, the impact of the introduction of different experimental cutting regimes was investigated during three years. The thick litter layer and the dominance of Brachypodium was strongly reduced after introduction of all cutting regimes. In all cutting treatments forb phytomass increased considerably, especially in the twice-a-year cutting vegetation, where the forb phytomass became as high as that of Brachypodium. Phanerogamic species diversity was stimulated in all cutting regimes. Especially the number of short-lived forbs. with a persistent seed bank, increased markedly in the twice-a-year cutting treatment. It is concluded that cutting the vegetation twice is adequate to reduce the negative effects of the thick litter layer and the abundant growth of Brachypodium. It creates an appropriate starting point for more detinite management, whether mowing or grazing. However, the restoration of a more complete species assortment strongly depends on the re-invasion possibilities of these species.     

Production and ecology of eelgrass (Zostera marinal L.) in the Grevelingen estuary,the Netherlands,before and after the closure

The Grevelingen estuary was cut off from the North Sea and from the influences of the river Rhine by a dam in 1971, and became a stagnant salt-water lake. Production and ecology ofZostera marina L. were studied in 1968 and in 1973–1975, both through standing stock estimations, biomass increases in permanent quadrats, and correlation of distribution patterns with ecological factors. After the closure of the estuary the intertidal eelgrass population extended downwards to 5 m below lake level, probably owing to the increased transparency of the water; the area occupied, and the density of the eelgrass beds increased strongly. Eelgrass annual overground production, based on doubled maximum standing crop values in July–August, was estimated at 50 g C/m² in 1968, 121 g C/m² in 1973 and 91 g C/m² in 1975 inZostera beds, and 4 g C/m² in 1968, 18 g C/m² in 1973 and 23 g C/m² in 1975 for the entire Grevelingen area. A minimum estimate of net production inZostera beds at a depth of 0.50–0.75 m, based on short term changes in biomass in 2 permanent quadrats in 1974 and 1975, was 40.5 g C/m²/yr for overground parts and 12.7 g C/m²/yr for underground parts. Horizontal distribution of celgrass is not primarily limited by grainsize distribution, but more by exposure to wave action and currents. On account of irradiance reduction light is a limiting factor in the vertical distribution of the eelgrass population in Lake Grevelingen. Communication no. 146 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherlands.     

Range expansion of the greater white-toothed shrewCrocidura russula in Switzerland results in local extinction of the bicoloured white-toothed shrewC. leucodon

The distribution limits ofCrocidura russula (Hermann, 1780) andC. leucodon (Hermann, 1780) were investigated during an interval of 25 years in the bottom of the Rhone valley above Lake Geneva, Switzerland (total data set: 105 spatio-temporal occurrences, 1137 shrews). In 1975, the contact zone between the two species was situated in the region of Martigny. In 1999/2000, new sampling revealed three results: (1) The contact zone showed an upward shift of about 25 km. (2) In the expanded range ofC. russula, the resident species has totally disappeared (confirmed by owl pellets analysis). (3) This demonstrates a dominance ofC. russula overC. leucodon. Three hypotheses which may explain the range expansion ofC. russula were evaluated: (1) habitat modification favouring linear dispersal due to the construction of a highway; (2) temporal event favoured by climate fluctuations, or (3) ongoing postglacial colonisation of Europe. Hypothesis 1 was rejected, because the progression of the shrews anticipated the construction. Hypothesis 3 received only weak support because range limits ofC. russula in the region of Nice have been stable for thousands of years. Therefore hypothesis 2, admitting that ongoing climate change has facilitated range expansion, is the most probable.     

Carbon,phosphorus and nitrogen budgets of the littoral Equisetum belt in an oligotrophic lake

Stores and flows of carbon, phosphorus and nitrogen in a littoral Equisetum stand were studied in 1978–1980 in the oligotrophic, mesohumic lake Pääjärvi, southern Finland. The major carbon and nutrient stores were sediment and Equisetum. The seasonal cycle of the macrophyte vegetation had a profound influence on the whole littoral ecosystem. In spring, when only dead remains of Equisetum were present above ground, there were few differences in nutrient, chlorophyll a and zooplankton concentrations between the littoral and the open lake; phytoplankton and epiphytes were the major producers.In early June, when new shoots of Equisetum reached the water surface, water exchange between the littoral and the open lake started to diminish, and the characteristic features of a closed macrophyte zone gradually developed: by August the P, Chl a and zooplankton concentrations in the littoral were 5–10 times those in the open lake. From late June until autumn Equisetum was overwhelmingly dominant both in biomass and in production.The measured total primary production and respiration values indicated a high rate of internal cycling of carbon and nutrients. The daily P requirements of plant growth exceeded the total P stored in the water by a factor of 2–4, and also exceeded the release of nutrients in excretion. High N:P ratios in the water (total 10–64, inorganic 18–171) suggested that P was probably always the limiting nutrient.The P content of the annual production of Equisetum in Pääjärvi was 2.3% of the mean annual P load, and 5.3% of the mean total P storage in the water volume of the lake.     

Endopolyploidization patterns in non-generative antheridial cells in mono- and dioeciousChara spp. (Characeae) with different DNA C-values

Cytophotometric measurements of nuclear DNA contents and morphometric analyses in the antheridia of five species ofChara indicate that the level of endopolyploidy plays an important role in determining the maximum sizes that shield cells, manubria, and capitular cells attain at the final stage of spermiogenesis. Dioecious species with low DNA C-values—C. aspera andC. tomentosa—display higher values of endopolyploidy: their male sex organs are larger and the quantities of spermatozoids per antheridium are greater than those estimated for monoecious species—C. vulgaris, C. fragilis, andC. contraria. Two types of nucleotypic effects were found to synchronize developmental traits in germ line cells and non-generative component parts within the antheridia; both are discussed in relation to the biological productivity of male sex organs in mono- and dioecious species ofChara.     

Process of invasiveness among exotic tunicates in Prince Edward Island, Canada

Over the past decade, four exotic tunicates (Styela clava, Ciona intestinalis, Botrylloides violaceus and Botryllus schlosseri) have been reported in the Brudenell estuary in Prince Edward Island (PEI), Canada. Styela clava was the first exotic tunicate to arrive in 1997, rapidly establishing, spreading, invading, and eventually becoming a nuisance in several estuaries of PEI. In the Brudenell estuary, S. clava remained the only exotic nuisance tunicate until 2003. In the fall of 2004, the vase tunicate C. intestinalis, was reported in low abundance, followed by the two colonial species, B. schlosseri and B. violaceus, reported in the spring of 2005. The abundance of C. intestinalis rapidly increased post-introduction, eventually replacing S. clava as the foremost nuisance species on mussel farms in the estuary. To date, C. intestinalis continues to colonize this estuary at epidemic proportions, resulting in the continuing drop of S. clava abundance. The current abundance of C. intestinalis is estimated at 5 cm⁻², which is similar to S. clava abundance at its height in 2003. The 2006 abundance of S. clava is estimated to have fallen to near 0 cm⁻². The dominance of C. intestinalis as a fouling organism on mussel farms is considered a serious threat to this aquaculture industry, mainly due to its unmanageable weight. The process of the detection, establishment, invasiveness, and eventual rise to nuisance level of exotic tunicates in the Brudenell River is presented.     

Effects of Cu,Pb and Zn on two Potamogeton species grown under field conditions

Two common macrophyte species, Potamogeton perfoliatus L. and Potamogeton pectinatus L. were grown for 12 weeks at shallow depths in sediments contaminated with 1250 or 2500 g Pb or Cu and/or Zn (gDW sediment)^-1. Control experiments were run at background levels of 4, 13, and 38 g Pb, Cu and Zn (gDW sediment)^-1, respectively. Effects of heavy metals on biomass production and metal uptake and distribution in plants are presented in relation to total amount and plant-available fraction of metals in the sediment.All three studied metals gave reduced biomass production, and the toxicity of the metals decreased in the order Zn>Cu>Pb. The root/shoot biomass ratio increased for P. pectinatus, but decreased for P. perfoliatus with metal treatment. The content of any single metal was higher in shoots than in roots of plants grown on sediments not contaminated with that specific metal, but addition of that metal increased the proportion in roots. The uptake by plants of any of the heavy metals increased with increased metal addition. The magnitude of the plant-available fraction of metals of untreated sediment was Zn>Cu>Pb, and increased in contaminated sediments. Addition of Cu decreased both the plant-available fraction and the total concentration of Zn in the sediment, while increased the uptake of Zn by the plants. The opposite was found for Cu when Zn was added. P. pectinatus accumulated about twice as much Cu as P. perfoliatus. On the other hand, the concentration of Pb was higher in P. perfoliatus than in P. pectinatus, and was negligible in P. pectinatus when cultivated in untreated sediments.