Submerged Macrophyte Vegetation Research Articles

Zasolenie strefy hyporeicznej rzeki Moszczenicy w rejonie wysadu solnego Rogóźno

Zasolenie strefy hyporeicznej rzeki Moszczenicy w rejonie wysadu solnego Rogóźno

Water level changes in Lake Constance and their relationship to changes in macrophyte settlement in the outflows of Lake Constance Upper and Lower Lake

Since 2008, water level differences between Upper and Lower Lake Constance have increased after they decreased significantly in the 20th century. Questioning the causes leads to the hypothesis that the significant changes in the submerged macrophyte vegetation due to eutrophication and subsequent oligotrophication have played an essential role over the past decades. To clarify whether macrophyte vegetation is the cause of the changed water levels, the spatial distribution of Swiss pondweed Potamogeton helveticus (syn. Stuckenia helvetica) and the other submerged macrophytes was mapped in 2017. Swiss pondweed, in particular plays a key role as a perennial plant type in flow channels. Shoot densities and lengths of this species were recorded by diving. The investigations were supplemented by hydrodynamic modeling of the effects of macrophyte flow resistance on lake water level relationships.The results show that P. helveticus has indeed increased significantly over the past decade. The species colonizes the bottom of flow channels in the Seerhein up to 6 m deep with up to 1000 shoots per square meter and a length of up to 5 m, whereas in the previous decades it only occurred at the edges of flow channels as small stands with shoot lengths of less than 1 m. In the shallow water zones outside the flow channels, stoneworts in particular have spread in the Seerhein over the past decade. The hydrodynamic modeling supports the hypothesis that aquatic plants are the cause of the changed lake water level conditions and illustrate the related changes in the flow velocity field.

Estimating the change in regional scale distribution of seagrass and macroalgal beds using discrete local distribution data analyzed from aerial images

AbstractThe sensitivity of vegetated habitats to climate change and catastrophic disturbance, as well as their benefits to human beings, motivate efforts to estimate regional changes in distribution. This study examined the regional changes in the distribution of submerged macrophyte vegetation using aerial and satellite images from before and after the 2011 tsunami disturbance along the Pacific coast of northeastern Japan. We conducted an estimation of the change in the distribution of seagrass and macroalgal beds after the tsunami along the whole coastline (1,635 km). This was based on vegetation change in the 13 local areas (each <40 km) spanning 27% of the coastline and included 28% of the macroalgal area and 59% of the seagrass area documented in satellite imagery before the tsunami, using generalized linear modeling (GLM). We found that in the 13 local areas 716.8 and 1,990.3 ha of macroalgal beds and seagrass beds had disappeared, respectively, suggesting that seagrass beds were more impacted by the tsunami than macroalgal beds. Significant predictors in GLM indicated that more seagrass beds disappeared in geographically complex coastal areas, whereas macroalgal beds were only marginally affected in such areas. It was estimated that the total decline in seagrass beds was at least 76% along the whole coastline, whereas macroalgal beds decreased only by about 20%. The magnitude and predictors of losses in these two vegetated habitats were similar to earlier estimates, suggesting that our simplified method with GLM is sufficient to extrapolate monitoring data to a regional scale.

Temperature and salinity effects on submerged aquatic vegetation traits and susceptibility to grazing

Submerged macrophyte vegetation provides valuable ecosystem services, but climate- and management-driven changes may alter plant traits in unexpected and interactive ways. Further, such changes in plant traits may influence herbivore response, with feedback to bed characteristics. We manipulated temperature (20, 25, 30 °C) and salinity (0, 6, 12) in mesocosms to simulate current and predicted scenarios for the San Francisco Bay area. We measured traits of Stuckenia pectinata (sago pondweed) and subsequent effects on invertebrate (amphipod, Ampithoe valida) grazing. Counter to predictions, higher temperatures tended to have positive effects on plant traits (leaf area, aboveground biomass, nitrogen [N], phosphorus [P], protein, and total phenolic content). Also, unexpectedly, the highest salinity treatment had few negative effects except when temperature was coolest; i.e., 20 °C and a salinity of 12 led to decreased carbon [C], N, P, protein, phenolic concentrations, and aboveground biomass. Conversely, the highest salinity (12) at the highest temperature (30 °C) produced the highest leaf N and P, and plants from this treatment suffered most from herbivory. Consumption rates significantly increased with lower leaf fiber and higher total leaf N and protein content; i.e., plants with more nutritious leaves and less structural defense were consumed most. Climate change is expected to increase both salinity and temperature, but manipulation of freshwater supply could lead to decreased salinity. The range of responses in S. pectinata traits and invertebrate grazing shown by our results imply that the specific combination and magnitude of human influences will differentially shape these submerged macrophyte beds and their functions.

Phyto- and zooplankton dynamics in two ICOLLs from Southern Portugal

Foz do Almargem and Salgados are two small, intermittently closed and open lakes and lagoons (ICOLLs) located in the Portuguese southern coast, both remaining isolated from the sea throughout great part of the year. Based on environmental and biotic parameters, the first lagoon was classified as mesotrophic, with a greater marine influence, while the second one was classified as hypereutrophic. The plankton relations and seasonal variation were examined in both lagoons aiming at understanding the biological patterns here present and relating them with the environmental conditions, as well as inferring possible top-down or bottom-up control in the communities, determining also in which alternative trophic state they are: a clean water lagoon, with submerged macrophyte vegetation; or a turbid water lagoon, with only phytoplankton as primary producer.The plankton community greatly differs in the two lagoons. Salgados lagoon presented extremely high concentrations of phytoplankton, which form blooms throughout the year, mostly composed by potential harmful organisms. This lagoon also had very high densities of zooplankton. Phytoplankton and zooplankton density was always lower in Foz do Almargem. Rotifera, Ostracoda and Cladocera dominated the Zooplankton community in Salgados. In Foz do Almargem, Rotifera also dominates, together with other groups, such as annelids, crustaceans and mollusks larvae, which denotes a stronger marine influence. In both lagoons, organisms with body size inferior to 100 μm mainly composed the zooplankton. In Salgados lagoon, excess nutrient load induced a high density of phytoplankton, which is utilized by a high density of zooplankton, following a bottom-up control model. The lagoon clearly showed a permanent turbid-water alternative state due to excess nutrients. On Foz do Almargem, the frequent openings of the inlet throughout the wet season caused strong physical disturbance, which prevented the development of a stable planktonic community.

Mass development of monospecific submerged macrophyte vegetation after the restoration of shallow lakes: Roles of light, sediment nutrient levels, and propagule density

After restoration, eutrophicated shallow freshwaters may show mass development of only one or two submerged macrophyte species, lowering biodiversity and hampering recreation. It is unclear which environmental factors govern this high percentage of the volume inhabited (PVI22PVI: The percent of the water volume inhabited by submerged macrophytes.) by submerged macrophytes, and whether the development of a more diverse, low canopy vegetation is likely to occur if dominant species decline in abundance.We hypothesized that (1) adequate light and high sediment nutrient availability leads to massive development of submerged macrophytes, and (2) that macrophyte species richness is low at high PVI, but that this is not caused by a lack of viable propagules of non-dominant species (especially charophytes).To test these hypotheses, fifteen shallow waters in the Netherlands were studied with respect to submerged vegetation (including propagules), water, and sediment characteristics.The probability of high submerged macrophyte PVI is highest in shallow waters where light availability in the water layer and phosphorus availability in the sediment are abundant. These conditions typically occur upon restoration of eutrophic waterbodies by reducing water nutrient loading or applying biomanipulation. Other factors, as top-down control, can additionally influence realised PVI. Viable propagules of species other than the dominant ones, including charophytes, were found in most of the sediments, indicating that once the dominant species declines, there is local potential for a diverse submerged vegetation to develop. Results can be used to predict when mass development occurs and to tackle the factors causing mass development.

Restoring macrophyte diversity in shallow temperate lakes: biotic versus abiotic constraints

Although many lake restoration projects have led to decreased nutrient loads and increased water transparency, the establishment or expansion of macrophytes does not immediately follow the improved abiotic conditions and it is often unclear whether vegetation with high macrophyte diversity will return. We provide an overview of the potential bottlenecks for restoration of submerged macrophyte vegetation with a high biodiversity and focus on the biotic factors, including the availability of propagules, herbivory, plant competition and the role of remnant populations. We found that the potential for restoration in many lakes is large when clear water conditions are met, even though the macrophyte community composition of the early 1900s, the start of human-induced large-scale eutrophication in Northwestern Europe, could not be restored. However, emerging charophytes and species rich vegetation are often lost due to competition with eutrophic species. Disturbances such as herbivory can limit dominance by eutrophic species and improve macrophyte diversity. We conclude that it is imperative to study the role of propagule availability more closely as well as the biotic interactions including herbivory and plant competition. After abiotic conditions are met, these will further determine macrophyte diversity and define what exactly can be restored and what not.

Delivery and deposition of organic matter in surface sediments of Lagoa do Caçó (Brazil)

Elemental and isotopic compositions of organic matter in surficial sediments from five transects across Lagoa do Caco (Brazil) were analyzed to identify the depth-related processes that affect the production and deposition of sedimentary organic matter in this shallow tropical lake. Each of four transverse transects began at a margin dominated by aquatic macrophytes (Eleocharis), crossed the central deep part of the lake, and terminated in the opposite, macrophyte-dominated margin. In each transect, TOC concentrations, C/N ratios, and δ13C values decreased between 0 and 4 m, whereas δ15N values increased. The variables remained stable in sediment from 4 m water depth to the center of the lake at 10 m. The depth-related patterns reflect differences in both the delivery and the deposition of organic matter in the lake. Organic matter is produced in abundance in the marginal area by emersed and submerged macrophyte vegetation that diminishes with depth and disappears at 4 meters. After the disappearance of macrophytes, organic matter is produced at low rates principally by open-lake phytoplankton. Drawdown of dissolved oxygen is high in the lake margins, but it is low in the oligotrophic open waters of the lake. Preservation of organic matter is consequently better in sediments of the lake margins than in deep waters. The depth-related pattern of organic matter delivery and deposition in the sediments of Lagoa do Caco, in which water levels are sensitive to groundwater fluctuations, shows that the elemental and isotopic compositions of sediment organic matter can provide a record of changes in the paleohydrology of this and other similar shallow lake systems.

Competition between isoetids and invading elodeids at different concentrations of aquatic carbon dioxide

Summary1. The growth of submerged macrophytes in softwater lakes is often assumed to be carbon limited. Isoetid species are well adapted to grow at low carbon availability and therefore commonly dominate the submerged macrophyte vegetation in softwater lakes. In many such lakes, however, large‐scale invasions of fast‐growing elodeid species, replacing the isoetid vegetation, have been observed.2. In a laboratory experiment, we tested how rising aquatic carbon availability, in interaction with different densities of the isoetid Littorella uniflora, affected the growth (and thereby the potential invasion success) of the elodeid Myriophyllum alterniflorum. For this purpose, the growth of M. alterniflorum was determined at a combination of three concentrations of dissolved CO2 (15, 90, 200 μmol L−1) and three densities of L. uniflora (0, 553, 1775 plants m−2).3. At an ambient CO2 of 15 μmol L−1, M. alterniflorum could not sustain itself, whereas at raised CO2 concentrations, growth became positive and increased with higher CO2 availability.4. The presence of L. uniflora, independent of its density, reduced the growth of M. alterniflorum by 50%. Whether this is related to nutrient availability or other factors is not clear.5. Despite the growth reduction of M. alterniflorum by L. uniflora, at CO2 ≥90 μmol L−1, L. uniflora was still overgrown by M. alterniflorum. This may imply that, in field situations, M. alterniflorum can invade softwater systems with relatively high CO2 availability, even in the presence of dense stands of L. uniflora.

A system-dynamic model on the competitive growth between Potamogeton malaianus Miq. and Spirogyra sp.

A system-dynamic model has been built to evaluate the competition between submerged macrophytes Potamogeton malaianus Miq. (PM) and filamentous green algae Spirogyra sp. (SP). The data background is based on a spring–summer and an autumn–winter experiment carried out in artificial field ponds. The experiments had the aim to acquire a knowledge base necessary to a successful restoration of submerged macrophyte vegetation in Lake Taihu, China by use of P. malaianus Miq. The model mainly focuses on variations in water volume; biomass dynamics of P. malaianus Miq., Spirogyra sp. and zoobenthos; nutrients cycling between water column, P. malaianus Miq., Spirogyra sp., zoobenthos, detritus and sediment. Sixteen state variables are included in the model: biomass of P. malaianus Miq., Spirogyra sp. and zoobenthos; nitrogen in sediments, detritus, in P. malaianus Miq., in Spirogyra sp. and zoobenthos; total dissolved nitrogen; phosphorus in sediments, detritus, in P. malaianus Miq., in Spirogyra sp. and in zoobenthos; total dissolved phosphorus, and water volume of the experiment pond. The calibration and validation of the model show a good accordance with the results of the spring–summer experiment and the autumn–winter experiment. Model outputs show that higher temperature, shading effect and improper nutrients would result in a decrease in biomass of P. malaianus Miq. The most crucial factor having a negative effect on the growth of P. malaianus Miq. is Spirogyra sp., which entangles the stems and leaves of P. malaianus Miq. In order to successfully restore the vegetation of P. malaianus Miq., Spirogyra sp. should be suppressed in the early phase.

Effects of mooring management on submerged vegetation, sediments and macro-invertebrates in Lake Constance, Germany

Mooring areas are a common form of berthing in many of Germany’s inland waters for the growing number of sporting boats. A circular swinging zone around the anchor zone is formed, in which the submerged macrophyte vegetation is destroyed to a large extent, and the sediment surface is eroded. We investigated the effects of two types of buoy (conventional and so-called hook-buoys) in comparison with undisturbed reference sites nearby. The aim of the study was to identify possible harmful consequences of mooring sites to lake littoral habitats in Lake Constance-Untersee, and to provide information to managers to aid them in the formulation of mooring management plans with the least ecological impact. The study focused on submerged vegetation, surface sediments and macro-invertebrate colonisation. In the swinging circle of conventional buoys (87 m2) we observed a significant sediment matter erosion of 0.9 tonnes and a reduction of organic matter amount by 4.5% of the undisturbed reference. The vegetation free area increased by 122%, and the phytomass (mainly Chara div. spp.) was reduced by 14.6% per berth. The psammophilous macro-invertebrate numbers were not significantly affected (−3%) in contrast to the phytophilous taxa which were reduced by 12.7% per berth. The mayfly larvae were the most negatively affected taxon. Oligochaetes profited from the clearing of the sediment surface in the swinging circles. The ecological effects of the hook-buoys were more minor, mainly due to the smaller swinging circle (6 m2). We concluded that the detrimental effects of mooring can be significantly reduced by mooring systems, e. g. the hook-buoy system as it was used in this study, which reduce the area disturbed and cleared by the anchor chain. We argue that these results can be generalised to mooring areas with soft bottom and dense macrophyte vegetation in Lake Constance and other large lakes.

Macrophyte-based bioindication in rivers – A comparative evaluation of the reference index (RI) and the trophic index of macrophytes (TIM)

Submerged macrophyte vegetation has been mapped in four calcareous groundwater-fed streams in Bavaria (southern Germany) in order to compare and assess two different methods of river bioindication. The first one, the trophic index of macrophytes (TIM), is a tool to assess the trophic status of running waters. In contrast, the reference index (RI) is an ecological index which evaluates the difference between a reference community and the actual submerged vegetation, depending on the river type, as required by the Water Framework Directive. Water nutrient concentrations were measured once at selected sites in all water courses. The TIM reflects water phosphorus concentrations, accounting also for nutrients enrichment in the sediment, and is not influenced by shading, depth, substrate and flow velocity of the water course. The TIM is very sensitive to small variations in P concentration when the P level is low, while the index tends to a maximum as soluble reactive phosphorus (SRP) and total phosphorus (Ptot) exceed a certain value. The RI indicates river ecological status which is not only influenced by trophic status but by every factor leading to a deviation of the actual macrophyte community from the reference community. In the investigated rivers the RI indicated reduced flow velocity caused by milldams and shading by riparian vegetation, in addition to trophic status. In rivers that are at the boundary between two different river types, classification of river type can play a crucial role for river status assessment. Incorrect classification of river type can lead to both, a “too good” and “too bad” assessment.

Submerged macrophyte vegetation and the European Water Framework Directive: assessment of status and trends in shallow, alkaline lakes in the Netherlands

The submerged macrophyte vegetation of lakes created after enclosing former estuaries, situated in the central and southwestern part of the Netherlands, has been monitored annually from 1992 onwards. Between 1992 and 2004, pronounced changes in overall cover and species composition of the submerged vegetation have occurred, resulting from changes of water quality and morphology in the lakes. In most cases vegetation cover and species diversity increased or remained stable, with the exception of two lakes in the southwest part of the country. Abundance and species composition were assessed according to the requirements of the EU Water Framework Directive, using the assessment procedure proposed to assess macrophytes in natural water bodies in the Netherlands. The assessment procedure included calculation of the ‘ecological quality ratio’ (EQR) for each of eleven water bodies in each of 13 years, based on transect monitoring data. The EQR indicating Good Ecological Status for Macrophytes was achieved in only three of the lakes. The consequences of hydromorphological modifications, and measures necessary to achieve the desired condition are discussed. Nutrient concentrations should be reduced further, while additional management measures are necessary to improve conditions for macrophytes.

The importance of drawdown and sediment removal for the restoration of the eutrophied shallow Lake Kraenepoel (Belgium)

Lake Kraenepoel (Belgium) is a shallow lake (22 ha), divided in two basins since 1957 by a shallow dike. The lake was used for fish farming until World War II and was drawn down about every 5 years to harvest fish. Despite its dense historical carp population, it had clear water and a rich Littorelletea vegetation. During the course of the 20th century, the lake became eutrophic and the Littorelletea vegetation degraded. The northern basin, which was still drawn down about every decade after 1957, retained its clear water and had a dense submerged macrophyte vegetation. The southern basin, which was never drawn down after 1957 and which received direct surface water inputs, had become a turbid shallow lake with phytoplankton blooms in summer. In 2000, efforts were taken to restore the lake: the entire lake was drawn down, the fish community was biomanipulated, nutrient-rich surface water inputs were diverted from the southern basin and sediments were removed (only in the northern basin). Fish biomanipulation and sediment removal were successful in the northern basin, as nutrient levels declined and the Littorelletea vegetation recovered. In the southern basin, sediment analyses indicated that drawdown resulted in sediments with a lower water and organic matter content and water column turbidity decreased after the drawdown. But pH in the southern basin declined to <4, probably because sulphides in the sediment were oxidized during drawdown and sediment desiccation. In contrast, desiccated sediments were removed from the northern basin and pH did not decline below 6 after restoration. In spite of the still high dissolved nutrient concentrations, phytoplankton biomass declined significantly in the southern basin, probably due to acidification. However, no Littorelletea species colonised the lake bottom in the southern basin. Thus, lake drawdown may be a useful management technique to promote clear water conditions in shallow lakes. However, acidification due to sulphide oxidation may be an undesirable outcome and should be considered in drawdown and sediment desiccation manipulations.

Natural and anthropogenic forcing of aquatic macrophyte development in a shallow Danish lake during the last 7000 years

AbstractAim To investigate the long‐term changes in aquatic vegetation in a lowland, shallow lake, and to assess the relationship between aquatic vegetation and natural and anthropogenic catchment changes.Location Gundsømagle Sø, Zealand, Denmark: a shallow (mean depth 1.2 m), hypereutrophic lake (mean annual total phosphorus (TP) c. 700 μg TP L−1) located in a predominantly agricultural catchment (88% cultivated land). The lake is presently devoid of macrophytes.Methods One hundred and forty‐seven contiguous samples from a sediment core (taken in 2000) were analysed for macrofossil remains together with loss‐on‐ignition and dry weight. From an earlier sediment core (taken in 1992), 67 samples were analysed for pollen and the two cores were correlated using the ignition residue profiles. Core chronology was determined by 210Pb and 137Cs dating of the recent lake sediments, while older sediments were dated by pollen‐stratigraphical correlation, as 14C dating proved problematical. Aquatic macrofossil abundance was used to reconstruct past changes in the lake's plant community and water‐level. The contemporary catchment land‐use change was inferred from sedimentary pollen data, and soil erosion to the lake was deduced from the minerogenic content of the lake sediments.Results The macrofossil record covers the last 7000 years, but aquatic plant remains were scarce prior to c. 1300 bc. After this date the abundance of submerged and emergent macrophyte remains increased dramatically, paralleled by an increase in sediment minerogenic matter and non‐arboreal pollen (NAP). Aquatic plant remains were abundant for more than 3000 years until the mid 1900s. Macrofossils of Linum usitatissimum (L.) (flax) and high pollen percentages of ‘Cannabis type’ (hemp) were recorded in periods between c. 1150 bc and 1800 ad.Main conclusions Our study suggests that, between c. 5000 bc and 1300 bc, the submerged plant community was confined to the littoral zone. From 1300 bc onwards, the submerged macrophyte vegetation expanded rapidly across the lake bed, presumably as a response to lake shallowing caused by a combination of climatic‐induced water‐level lowering and enhanced erosional infilling of the lake basin due to intensified anthropogenic activities in the catchment. The lake was meso‐eutrophic and had an extensive and diverse aquatic flora for more than 3000 years, until the middle of the twentieth century. In periods between c. 1150 bc and 1800 ad, the lake experienced direct anthropogenic impact from retting of fibre plants (Linum and Cannabis). Over the last 200 years, erosional infilling of the lake basin increased drastically, probably as a result of agricultural intensification. In the twentieth century, the lake was strongly affected by nutrient enrichment from both point sources (sewage from built‐up areas) and diffuse agricultural run‐off which led to hypertrophic conditions and the collapse of the submerged vegetation c. 1950–60. The concept of ‘naturalness’ and the implications for lake conservation are discussed.

Application of constructed wetlands for wastewater treatment in Hungary

This paper presents a brief survey of the Hungarian constructed wetland types that have been established for wastewater treatment in the last thirty years, and gives an analysis of the design and performance of those reed ponds that have been constructed for the polishing of petrochemical wastewaters. Natural treatment processes are in great demand because they are protective of the environment and have low operation costs and satisfactory purification efficiency. Three major types of treatment wetlands are utilized in Hungary: free water surface system, subsurface flow system, and artificial floating meadow system. Since the 1970s, the petrochemical industry has utilized sewage treatment systems consisting of ponds of emergent and/or submerged macrophyte vegetation that operate as free water surface systems. In the wastewater treatment system of Nyirbogdány, the average COD removal efficiency is around 60%, while the reed-submerged weeds pond has an efficiency of 25%. In the reed pond of the TIFO post-treatment pond system, the total phosphorus removal averaged 40% for several years, while the nitrogen removal efficiency has not exceeded 35%. For both constructed wetlands, the nutrient stabilising and heavy metal accumulating role of the aquatic plant-periphyton complex has been quantified, and the biological water quality has been found to be typical of any other natural water bodies.

Application of constructed wetlands for wastewater treatment in Hungary

This paper presents a brief survey of the Hungarian constructed wetland types that have been established for wastewater treatment in the last thirty years, and gives an analysis of the design and performance of those reed ponds that have been constructed for the polishing of petrochemical wastewaters. Natural treatment processes are in great demand because they are protective of the environment and have low operation costs and satisfactory purification efficiency. Three major types of treatment wetlands are utilized in Hungary: free water surface system, subsurface flow system, and artificial floating meadow system. Since the 1970s, the petrochemical industry has utilized sewage treatment systems consisting of ponds of emergent and/or submerged macrophyte vegetation that operate as free water surface systems. In the wastewater treatment system of Nyirbogdány. the average COD removal efficiency is around 60%, while the reed-submerged weeds pond has an efficiency of 25%. In the reed pond of the TIFO post-treatment pond system, the total phosphorus removal averaged 40% for several years. while the nitrogen removal efficiency has not exceeded 35%. For both constructed wetlands, the nutrient stabilising and heavy metal accumulating role of the aquatic plant-periphyton complex has been quantified, and the biological water quality has been found to be typical of any other natural water bodies.

94Z/00020 The impact of desiccation of a freshwater marsh (Garcines Nord, Camargue, France) on sediment-water-vegetation interactions. Part 2: the submerged macrophyte vegetation : C. Van Wijck & C.-J. De Groot, Hydrobiologia, 252(1), 1993, pp 95–103

94Z/00020 The impact of desiccation of a freshwater marsh (Garcines Nord, Camargue, France) on sediment-water-vegetation interactions. Part 2: the submerged macrophyte vegetation : C. Van Wijck & C.-J. De Groot, Hydrobiologia, 252(1), 1993, pp 95–103

Further long-term changes in the submerged macrophyte vegetation of the eutrophic Lake Mikolajskie (North Poland)

On the basis of quantitative sampling of submerged vegetation, repeated in Lake Mikolajskie a further 10 years after the last survey, and compared with 1980, 1971 and 1963, continuing changes are reported. There was a further decrease of the depth range and thus of the colonized area. The frequency and percentage contribution of some formerly abundant species diminished, as the submerged vegetation continued to change to a Myriophyllum-Potamogeton assemblage.

Perspectives for submerged macrophytes in shallow lake restoration projects in The Netherlands

Some well-documented studies on restoring eutrophic lake systems in The Netherlands by fish stock management have been evaluated with the emphasis on the role of macrophytes. Furthermore, the factors determining the light climate for submerged macrophytes in a large shallow eutrophic lake (Lake Veluwe) have been assessed and the potential success of biomanipulation in large scale projects is discussed. Today relatively little attention has been paid to macrophyte management although the importance of macrophytes in lake restoration has been recognized regularly. The biomanipulation strategy was successful in small scale projects. In a large scale project, however, wind-induced resuspension may largely determine the underwater light climate through attenuation by the water column and periphytic layer. Therefore, restoration of relatively large waterbodies by fish stock management only is expected not to lead to any noteworthy improvement of the light climate for submerged macrophytes. Additional measures aimed at reducing wind-induced resuspension of sediment particles and reestablishing of the macrophyte stands are required for successful biomanipulation strategies. Water quality managers should pay more attention to macrophyte stands in biomanipulation projects because macrophytes enhance a more stable and diverse ecosystem. Restoration objectives and the methods of their achievement must be carefully planned since an abundant submerged macrophyte vegetation may have undesirable effects as well.