Salinity effects on macroinvertebrate assemblages and waterbird food webs in shallow lakes of the Wyoming High Plains

We determined the biomass and community structure of macroinvertebrates (>500 µm) associated with macrophytes, sediments, and unvegetated open water in three oligosaline (0.8 to 8.0 mS cm^–1) and three mesosaline (8.0 to 30.0 mS cm^–1) lakes in the Wyoming High Plains, USA. Total biomass of epiphytic and benthic invertebrates did not change with salinity, but biomass of macroinvertebrate zooplankton in open water was significantly higher in mesosaline lakes. Community composition of invertebrates differed between the two salinity categories: large grazer/detritivores (gastropods and amphipods) were dominant in oligosaline lakes, whereas small planktivores and their insect predators were more prevalent in mesosaline lakes. Both direct physiological effects of salinity, as well as a shift in the form of primary production from macrophytes to phytoplankton, probably explain these changes in community composition. Salinity effects on invertebrate communities appear to be less important to top avian consumers than are costs of osmoregulation.     

Epiphytes of the St. Lucia Estuary and their response to water level and salinity changes during a severe drought

St. Lucia is the largest estuary in South Africa with extensive areas of submerged macrophytes that fluctuate rapidly in response to water level and salinity changes. Epiphytes associated with submerged macrophytes were sampled during a severe drought between November 2004 and October 2005 when very low water level and high, variable salinity characterised the estuary. Potamogeton pectinatus and Ruppia cirrhosa were the dominant submerged macrophytes throughout the estuary, with P. pectinatus occurring at relatively low salinity (∼10 ppt) and R. cirrhosa at higher salinity (9–33 ppt). Zostera capensis, normally the other dominant submerged macrophyte, was conspicuously absent under the prevailing conditions. Epiphytic biomass, estimated as chlorophyll a, varied greatly between sites and over the 12 month sampling period, ranging from 10.9 to 71.7 mg Chl a m⁻² leaf area for P. pectinatus and 16.9–165.0 mg Chl a m⁻² leaf area for R. cirrhosa. Epiphytic biomass was twice as high in the Southern Lake where R. cirrhosa occurred, probably because the dominant epiphytes were macroalgae. An assessment of the diatom species composition of the epiphytic community indicated the dominance of only six species throughout the estuary. Neither epiphytic biomass nor diatom species composition showed strong statistical relationships with the environmental variables measured and it is believed that biological factors may be more important than the physico-chemical environment in determining epiphyte biomass distribution. Because epiphyte biomass is dependent on the presence of host surface area it will only contribute substantially to overall system biomass and productivity when submerged macrophyte area cover is high. In the St. Lucia Estuary this will occur when the water level is high and the upper level of the salinity gradient does not increase above that of seawater.     

Growth dynamics of Potamogeton pectinatus L. in Lake Burullus,Egypt: a modelling approach

In this study, we used a macrophyte model to describe the growth production and the interaction between above‐ and below‐ground organs of Potamogeton pectinatus in Lake Burullus, Egypt. Above‐ and below‐ground biomass of P. pectinatus was sampled on a monthly basis from April to December 2011 at three sites of Lake Burullus. Shoots started to grow in April, reached the maximum biomass in September and then rapidly decreased in October when they moved into the senescence stage. Tubers biomass reduced in August due to the upward translocation to shoots, but sharply increased to the maximum in October by downward translocation from shoots and roots. Potamogeton pectinatus allocated approximately 82.3% of its total biomass to shoots, 15.5% to tubers and 2.2% to roots.     

Bionomics of invertebrates within an extensive Potamogeton pectinatus bed of a California marsh

Fourteen samples of sago pondweed (Potamogeton pectinatus L.) and associated invertebrates were collected every two weeks over a single season of plant growth in a large monospecific pondweed-bed located in Coyote Hills Marsh (Alameda Co., California, USA), using pull-up samplers that collect plants, epiphytic macroinvertebrates, and microcrustaceans throughout the water column. The macro-invertebrate fauna was dominated by insects, primarily chironomids. Semi-aquatic neustonic taxa, including an aphid and a springtail, were common; this is in contrast with most aquatic plant-invertebrate studies, in which neustonic insects are seldom collected because of sampling bias. Over the entire season, P. pectinatus biomass and the densities of four insect taxa (Anopheles spp. mosquitoes, Hydrellia sp. brineflies, Ademon sp. parasitic wasps, and coenagrionid damselflies) were significantly correlated. These correlations resulted from both similar overall phenologies of the plant and each of the insect taxa, and ecological relationships in which P. pectinatus provides either a specialized habitat or food source. macroinvertebrate numbers were highest in mid-summer, when P. pectinatus forms a dense floating canopy; microcrustaceans were more common during plant senescence in early autumn. Individuals of some taxa may be distributed in proportion to plant biomass; this occurred commonly in damselflies, perhaps as a result of territoriality in these nymphs.     

Ecosystem development in different types of littoral enclosures

Macrophyte growth was studied in two enclosure types (gauze and polythene) in a homogeneousPotamogeton pectinatus bed in Lake Veluwe (The Netherlands). The gauze was expected to allow for sufficient exchange with the lake to maintain similar seston densities, the polythene was expected to exclude fish activity and most water exchange. Polythene enclosures held higher totalP. pectinatus biomass (ash-free dry weight, AFDW) than the lake, gauze enclosures were intermediate. The enclosures had a higher abundance of other macrophyte species (Chara sp.,Potamogeton pusillus) than the lake. Seston ash content was not but seston AFDW, periphyton ash content and AFDW were lower in polythene than in gauze enclosures. The difference in plant biomass between gauze and polythene may be attributed to a difference in periphyton density and in seston AFDW due to zooplankton grazing (Rotatoria andDaphnia densities were higher in polythene enclosures). Since seston and periphyton AFDW and ash content were similar in lake and gauze enclosures, the intermediate macrophyte biomass in the gauze enclosures may be explained by reduced wave action and mechanical stress. Alternatively, phytoplankton inhibition by allelopathic excretions from the macrophytes may have caused the high macrophyte biomass in the polythene, and an absence of sediment-disturbing fish the intermediate biomass in the gauze enclosures. Creation of sheltered areas may favour macrophyte growth through both mechanisms and we conclude that this can be an important tool in littoral biomanipulation.     

The distribution of submerged aquatic macrophyte biomass in a eutrophic stream,Badfish Creek: the effect of environment

The distribution of biomass of the macrophyte community in Badfish Creek was examined in three sections (A–C) totaling ten kilometers. Biomass samples were taken in a stratified-random manner, with sediment characteristics, depth, current velocity and incident light measured at each site to correlate individual biomass samples with environmental factors. Total community biomass decreased in the downstream section (C), with the biomass ofElodea canadensis decreasing abruptly below section A. The only environmental factors which were correlated with the decrease in macrophyte community biomass, especially that ofPotamogeton pectinatus, in section C was the increase in substrate heterogeneity and sand substrates which lacked surface gravel. The change in substrate was related to channelization. Considering the stream as a whole, the biomass of the dominant species,Potamogeton pectinatus, was correlated with incident light. Other species present wereCeratophyllum demersum andCladophora glomerata. Analysis of riparian vegetation type indicates that tree cover significantly reduced macrophyte biomass by incident light reduction.     

Phosphorus cycling in a dense Potamogeton pectinatus L. Bed

Summary An analysis of phosphorus concentrations and standing stocks in the various components of a dense Potamogeton pectinatus L. community in a brackish lake showed that the amounts of P per unit area varied in the following order: Sediments > Above ground macrophytes > Detritus > Benthic Invertebrates > Below ground macrophyte tissue > Epiphytic algae > Water soluble P > Water borne particulate P. Seasonal changes in the variability of these stocks are described, and shown to be controlled by the annual growth and decomposition pattern of the Potamogeton. The sediments were suggested as the major source of P for the plant biomass. Studies using ³²P tracer showed that of a given input of P to the water, 32% went to large epiphytic algae, 17% to the Potamogeton, 16% to the benthic fauna (mostly filter feeding bivalves), 28% to the sediments (almost all incorporated in the top 1 cm), and the remaining 7% was adsorbed on to, or absorbed by microorganisms associated with detritus. Analysis of ³²P uptake curves indicated that of the P absorbed by the Potamogeton, a significant proportion went to the complex adnate periphyton on the leaf surface. We were unable to separate this fraction. Movement of P in the community was shown to be a closed cycle, and any release of P from decaying macrophytes would be rapidly reabsorbed by epiphytic algae. It is unlikely that phosphorus, once cycling in the macrophyte community, would become transferred to the circulation in the open lake.     

The abundance of phytophilous invertebrates on different species of submerged macrophytes*

SUMMARY. 1. We tested Krecker's model (1939) which states that the abundance of invertebrates per unit macrophyte biomass varies with plant species and is higher on plants with finely dissected leaves than on plants with broad leaves. The abundance of invertebrates was measured in thirteen lacustrine macrophyte beds in southern Québec, Canada. The model was tested for the total abundance of invertebrates and for the abundances of Chironomidae, Cladocera, Cyclopoida, Gastropoda, Hydracarina, Ostracoda and Trichoptera. 2. More epiphytic invertebrates were found on the dissected Myriophyllum spp. than on the broad-leaved Potamogeton amplifolius Tuckerm, P. robbinsii Oakes and Vallisneria americana Michx. (P<0.01). More invertebrates were also found on P. amplifolius than on P. robbinsii or V. americana (P<0.01). The total abundance of invertebrates was not systematically related to the degree of plant dissection. 3. The abundances of Chironomidae, Cladocera, Cyclopoida, Gastropoda, Hydracarina, Ostracoda and Trichoptera varied on different plant species (P<0.01). Contrary to Krecker's hypothesis, however, macrophytes with finely dissected leaves (Ceratophyllum demersum and Myriophyllum spp.) did not in general support more invertebrates per unit plant biomass than plants with large leaves (Potamogeton amplifolius, P. robbinsii and Vallisneria americana).     

Macrophyte communities and their impact on benthic fluxes of oxygen, sulphide and nutrients in shallow eutrophic environments

The impact of macrophyte communities on benthic fluxes has been analyzed in three shallow coastal environments: Etang du Prévost (Mediterranean coast of France), characterized by the large floating macro-alga Ulva rigida; Certes fishponds (Bassin d'Arcachon), covered by Ruppia cirrhosa; and the inner intertidal mud-flat in the Arcachon Bay (French Atlantic coast), which has extensive Zostera noltii meadows. In these bodies of water, primary production is dependent primarily on the dominant seagrasses and macroalgae that are also responsible for the large quantity of organic matter deposited on the sediment surface. In 1993 and 1994, fluxes of oxygen, sulphide and nutrients were measured in early and late summer, which were selected in order to represent the production and decomposition phases of the dominant macrophytes. Experimental work was undertaken to measure: (1) standing crop of dominant macroalgae and rooted phanerogams and the elemental and macromolecular composition of plant biomass; (2) benthic fluxes of oxygen, sulphide, nitrogen and phosphorus using incubation of multiple dark and light benthic chambers; (3) water-sediment profiles of free-sulphide in sediment cores with rooted phanerogams (Ruppia) as well as with floating Seaweeds (Ulva).At the selected sampling sites, in addition to external (tides) and/or internal (sediment reactivity) factors, we observed differences in benthic fluxes which were clearly related to growth patterns and structure of the macrophyte communities. The Z. noltii meadows were stable and characterized by slow growth and almost constant biomass. In the more sheltered sampling station in the Certes fishponds, R. cirrhosa beds showed a summer decrease due to extensive epiphyte growth. During the decomposition phase, significant fluxes of free-sulphide occurred inside the dark benthic chambers, probably due to the metabolism of the epiphytic layer. In the Etang du Prévost, U. rigida achieved high biomass levels, even though the macroalgal beds exhibited a patchy distribution due to wind action and the hydrodynamics of the lagoon. In the decomposition phase, which was coincident with the annual dystrophic crisis the rapid decomposition of Ulva led to high fluxes of free sulphide.The shift from the production to decomposition phase resulted in substantial changes in nutrient recycling only in the macro-algal-dominated system. During the growth period dissolved inorganic nitrogen and phosphorus were kept at low levels due to macrophyte uptake. In contrast during the decomposition phase when the macroalgal biomass was mineralised, nitrogen and phosphorus were rapidly recycled. The same processes did not occur in the Certes fishponds probably because of the greater internal buffering capacity linked either to plant morphology/physiology or to the properties of the sediment.     

Cumulative consumption of the lake macrophyte Elodea by abundant generalist invertebrate herbivores

Previous investigations have shown that macrophyte biomass can be substantially reduced by invertebrate herbivores but have not provided evidence for the links between the magnitude of the observed damage and the densities of herbivores. The results of this study support the hypothesis that the abundant occurrence of the epiphytic generalist herbivores may result in their cumulative consumption which, in turn, can be regarded as the mechanism responsible for often observed relatively high level of herbivory on freshwater macrophytes. The percentage of Elodea sp. biomass consumed by invertebrates was estimated for six European lakes, based on analysis of gut contents, daily rations and the density of epiphytic herbivores. Although the daily ration of these invertebrates when feeding upon Elodea averaged only 14.6% of their dry mass, their biomass was relatively high (from 0.163 to 1.161 g DW per 100 g DW plant). The estimated percentage of Elodea biomass consumed during one summer month by epiphytic invertebrates ranged from 0.5 to 5.9%. These values, after extrapolating to the whole growing season would mean that the biomass of Elodea lost to herbivory was between about 2 and 23%, an estimate which are within the range of consumption reported by other authors.     

Seasonal dynamics of macrophytes and phytoplankton in shallow lakes: a eutrophication‐driven pathway from plants to plankton?

1. Seasonal relationships between macrophyte and phytoplankton populations may alter considerably as lakes undergo eutrophication. Understanding of these changes may be key to the interpretation of ecological processes operating over longer (decadal‐centennial) timescales. 2. We explore the seasonal dynamics of macrophytes (measured twice in June and August) and phytoplankton (measured monthly May–September) populations in 39 shallow lakes (29 in the U.K. and 10 in Denmark) covering broad gradients for nutrients and plant abundance. 3. Three site groups were identified based on macrophyte seasonality; 16 lakes where macrophyte abundance was perennially low and the water generally turbid (‘turbid lakes’); 7 where macrophyte abundance was high in June but low in August (‘crashing’ lakes); and 12 where macrophyte abundance was high in both June and August (‘stable’ lakes). The seasonal behaviour of the crashing and turbid lakes was extremely similar with a consistent increase in nutrient concentrations and chlorophyll‐a over May–September. By contrast in the stable lakes, seasonal changes were dampened with chlorophyll‐a consistently low (<10–15 μg L^?1) over the entire summer. The crashing lakes were dominated by one or a combination of Potamogeton pusillus, Potamogeton pectinatus and Zannichellia palustris, whereas Ceratophyllum demersum and Chara spp. were more abundant in the stable lakes. 4. A long‐term loss of macrophyte species diversity has occurred in many shallow lakes affected by eutrophication. One common pathway is from a species‐rich plant community with charophytes to a species‐poor community dominated by P. pusillus, P. pectinatus and Z. palustris. Such compositional changes may often be accompanied by a substantial reduction in the seasonal duration of plant dominance and a greater tendency for incursions by phytoplankton. We hypothesise a slow‐enacting (10–100 s years) feedback loop in nutrient‐enriched shallow lakes whereby increases in algal abundance are associated with losses of macrophyte species and hence different plant seasonal strategies. In turn such changes may favour increased phytoplankton production thus placing further pressure on remaining macrophytes. This study blurs the distinction between so‐called turbid phytoplankton‐dominated and clear plant‐dominated shallow lakes and suggests that plant loss from them may be a gradual process.     

Nine polymorphic microsatellite loci for the fennel Pondweed Potamogeton pectinatus L.

Fennel (= Sago) pondweed (Potamogeton pectinatus L.) is a submersed macrophyte of nearly cosmopolitan distribution. The plant is of worldwide ecological importance as structuring component of shallow lakes, and as food for waterfowl. We developed nine polymorphic microsatellite primers for the population genetic analysis of P. pectinatus. The loci were identified using a GA/CT‐enriched genomic library using subtractive hybridization with magnetic particles. All nine loci were highly polymorphic with 6–9 alleles and heterozygosities ranging from 0.23 to 0.80 in a subset of N = 40 genotypes from five locations.     

Community structures of ammonia‐oxidising archaea and bacteria in high‐altitude lakes on the Tibetan Plateau

1. Community structures of planktonic ammonia‐oxidising archaea (AOA) and bacteria (AOB) were investigated for five high‐altitude Tibetan lakes, which could be classified as freshwater, oligosaline or mesosaline, to develop a general view of the AOA and AOB in lakes on the Tibetan Plateau. 2. Based on PCR screening of the ammonia monooxygenase α‐subunit (amoA) gene, AOA were present in 14 out of 17 samples, whereas AOB were detected in only four samples. Phylogenetic analyses indicated that the AOB communities were dominated by a unique monophylogenetic lineage within Nitrosomonas, which may represent a novel cluster of AOB. AOA, on the other hand, were distinct among lakes with different salinities. 3. Multivariate statistical analyses indicated a heterogeneous distribution of the AOA communities among lakes largely caused by lake salinity, whereas the uniform chemical properties within lakes and their geographical isolation may favour relatively homogeneous AOA communities within lakes. 4. Our results suggest a wide occurrence of AOA in Tibetan lakes and provide the first evidence of salinity‐related differentiation of AOA community composition as well as potential geographical isolation of AOA in inland aquatic environments.     

AQUATIC MACROPHYTE COMMUNITIES OF THE WILDERNESS LAKES: COMMUNITY STRUCTURE AND ASSOCIATED ENVIRONMENTAL CONDITIONS

SUMMARY

The structure and summer biomass (g m^?2 dry mass) of the principal aquatic macrophyte communities of the Wilderness Lakes were measured. Both emergent and submerged communities were included in the study. Productivity estimates were made by multiplying biomass by production/biomass ratios for each species. Salinity gradients in the system are described and details of the different sediment types associated with the macrophytes are given. There was considerable variation in production rates between the different water bodies often coinciding with a salinity gradient. However, rapid, natural changes in the communities are described which also influence production rates in a given water body. Production rates (g dry mass m^?2 a^?1) were of the order: Typha latifolia > Phragmites australis > Scirpus littoralis > Potamogeton pectinatus > Chara qlobularis > Ruppia cirrhosa. The significance of the macrophyte rates is discussed in relation to Wilderness Lakes area as a whole.     

Effects of the exotic macrophyte, para grass (Urochloa mutica), on benthic and epiphytic macroinvertebrates of a tropical floodplain

1. We examined the effect of the exotic macrophyte, para grass (Urochloa mutica), on benthic and epiphytic macroinvertebrates of a tropical floodplain in northern Australia. Macroinvertebrates were sampled from four grass communities: (1) para grass, (2) hymenachne (Hymenachne acutigluma), a native perennial; (3) rice (Oryza meridionalis), a native annual, and (4) areas where para grass had been sprayed with herbicide. 2. Macroinvertebrate richness, abundance and community similarity showed very few differences among the grass communities, particularly in the epiphytic habitat. Benthic invertebrates showed some differences among grasses, with lower richness and abundance and different community structure associated with hymenachne. Herbicide control of para grass had no apparent effect on benthic invertebrates but reduced the abundance of epiphytic invertebrates in the short term. 3. The results of this study indicate that para grass has very little impact on macroinvertebrate communities, despite the changes to macrophyte communities. This is probably because para grass has similar physical structure to the native grasses and because none of these grasses contribute directly to aquatic food webs. Control of para grass using herbicide has little impact on aquatic invertebrates. This suggests that predicting the impact of weed invasion in wetlands requires an understanding of both the functional properties of macrophytes and the habitat preferences of the macroinvertebrates.     

Metal content in higher aquatic plants in a small siberian water reservoir

The dynamics of metal content in higher aquatic plants (macrophytes) in a small Bugach water reservoir in 1998–2006 was studied. A comparative estimation of the metal content in six macrophyte species (Typha latifolia L., Typha angustifolia L., Polygonium amphibium L., Potamogeton perfoliatus L., Potamogeton pectinatus L., Phragmites australis (Cav) Trin. Ex Steud.) showed that their metal concentrations do not generally exceed those known from the literature. Cluster analysis showed that the macrophyte species under study form two ecological groups with respect to the metal content, i.e., submerged plants (hydrophytes) and emergent aquatic plants (heliophytes).     

Mechanisms regulating abundance of submerged vegetation in shallow eutrophic lakes

Shallow eutrophic lakes tend to be either in a turbid state dominated by phytoplankton or in a clear-water state dominated by submerged macrovegetation. Recent studies suggest that the low water turbidity in the clear-water state is maintained through direct and indirect effects of the submerged vegetation. This study examined what mechanisms may cause a recession of the submerged vegetation in the clear-water state, and thereby a switch to the turbid state. The spatial distribution of submerged vegetation biomass was investigated in two shallow eutrophic lakes in the clear-water state in southern Sweden. Biomass of submerged vegetation was positively correlated with water depth and wave exposure, which also were mutually correlated, suggesting that mechanisms hampering submerged vegetation were strongest at shallow and/or sheltered locations. The growth of Myriophyllum spicatum, planted in the same substrate and at the same water depth, was compared between sheltered and wave exposed sites in two lakes. After 6 weeks the plants were significantly smaller at the sheltered sites, where periphyton production was about 5 times higher than at the exposed sites. Exclosure experiments were conducted to evaluate the effects of waterfowl grazing on macrophyte biomass. Potamogeton pectinatus growth was decreased by grazing, whereas M. spicatum was not affected. The effects were greater at a sheltered than at a wave-exposed site, and also negatively related to distance from the reed belt. These results suggest that competition from epiphytes and waterfowl grazing hamper the development of submerged vegetation at sheltered and/or shallow locations. An increased strength of these mechanisms may cause a recession of submerged vegetation in shallow eutrophic lakes in the clear-water state and thereby a switch to the turbid state. Received: 24 June 1996 / Accepted: 8 September 1996     

Submerged vegetation development in two shallow, eutrophic lakes

Submerged macrophyte vegetation in two shallow lakes in the Netherlands, Lake Veluwemeer and Lake Wolderwijd, has been affected by eutrophication in the late 1960's and 1970's. Recent changes in the vegetation occurred in the period following lake restoration measures. Between 1987 and 1993, the dominance of Potamogeton pectinatus decreased, while Charophyte meadows expanded over the same time interval. The pattern of change of the dominant macrophyte species might result from changes in the underwater light climate. Seasonally persistent clear water patches associated with the Chara meadows have been observed in the last few years. The interaction between submerged macrophyte vegetation succession and water transparency in the lakes is discussed.     

Differences in tolerance of pondweeds and charophytes to vertebrate herbivores in a shallow Baltic estuary

It has been suggested that herbivorous waterfowl may be important in shaping aquatic plant communities in shallow wetlands. As such, a shift from canopy forming pondweeds to bottom-dwelling charophytes in a formerly turbid pondweed dominated lake has been partly attributed to waterfowl herbivory. Here we study the separate and combined effects of both belowground herbivory in spring by whooper swans and Bewick ‘s swans, and grazing in summer by waterfowl and fish on the community composition in a shallow Baltic estuary during one year. The macrophyte community was dominated by charophytes (mainly Chara aspera) with Potamogeton pectinatus and Najas marina present as subdominants. Other species were rare. Both spring and summer herbivory had no effect on total plant biomass. However, P. pectinatus was more abundant in plots that were closed to spring and summer herbivores. N. marina was more abundant in grazed plots, whereas Chara spp. biomass remained unaffected. Probably belowground propagules of both C. aspera and P. pectinatus were consumed by swans but since C. aspera bulbils were numerous it may have compensated for the losses. P. pectinatus may not have fully recovered from foraging on tubers and aboveground biomass. Our results are in line with other studies in Chara dominated lakes, which found no effect of grazing on summer aboveground Chara biomass, whereas several studies report strong effects of herbivory in lakes dominated by P. pectinatus.     

Submerged macrophytes as indicators of the ecological quality of lakes

1. We analysed submerged macrophyte communities from 300 Danish lakes to determine the efficacy of different species, maximum colonisation depth (C_max) of plants as well as coverage and plant volume inhabited (PVI) as indicators of eutrophication. 2. Most species occurred at a wide range of phosphorus and chlorophyll a (Chla) concentrations, but some species of isoetids (Lobelia, Isoëtes) and Potamogeton (Potamogeton gramineus, Potamogeton alpinus and Potamogeton filiformis) were mainly found at low nutrient concentrations and hence may be considered as indicators of nutrient poor conditions. However, species typically found in nutrient‐rich conditions, such as Elodea canadensis and Potamogeton pectinatus, were also found at total phosphorus (TP) <0.02 mg P L^?1 and Chla <5 μg L^?1 and therefore cannot be considered as reliable indicators of eutrophic conditions. 3. Submerged macrophyte coverage, PVI and the C_max were negatively correlated with TP and Chla. However, variability among lakes was high and no clear thresholds were observed. At TP between 0.03 and 0.07 mg P L^?1 plant coverage in shallow lakes ranged from nearly 0 to 100%, whilst at concentrations between 0.10 and 0.20 mg P L^?1 only 29% of the lakes had coverage >10%. C_max was found to be a useful indicator only in deep lakes with unvegetated areas in the deeper part, whereas the use of coverage was restricted to shallow lakes or shallow areas of deep lakes. 4. Overall, submerged macrophytes responded clearly to eutrophication, but the metrics investigated here showed no well‐defined thresholds. We developed a simple index based on species richness, presence of indicator species, coverage and C_max, which might be used to track major changes in macrophyte communities and for lake classification.