Macrophyte Community Composition Research Articles

Iron addition as a measure to restore water quality: Implications for macrophyte growth

Eutrophication of shallow lakes in North-West Europe has resulted in cyanobacterial blooms, turbid water, and a decline in submerged macrophytes. Even though external inputs of phosphorus (P) are declining, internal loading of P from the sediment may delay the recovery of these aquatic ecosystems. Iron can be a useful chemical binding agent to combat internal P loading in shallow lakes, but may potentially be harmful for macrophyte growth. We tested whether iron addition as a restoration measure harms the growth of submerged macrophytes. We hypothesized that this depends on the iron dosage and the rooting strategy of the macrophytes. We experimentally tested the effects of Fe (FeCl3) on the submerged macrophytes Potamogeton pectinatus L. and Elodea nuttallii (Planch.) H. St. John. Iron was dosed at a concentration of 20gFem−2 and 40gFem−2 to the surface water or to both the surface water and sediment. E. nuttallii growth was not affected by iron addition, whereas P. pectinatus growth significantly decreased with increasing iron concentrations. Nonetheless, biomass of both species increased in all treatments relative to starting conditions. During the experiment, propagules sprouted from a propagule bank in the sediment including species with a high conservation value and this spontaneous emergence was not influenced by increasing iron concentrations. We conclude that adding iron(III)chloride in dosages of 20–40gm−2 may reduce growth of some macrophyte species, but does not prevent overall macrophyte recovery. It may however affect macrophyte community composition due to differential responses of macrophyte species to iron addition.

Application of a three-tier framework to assess ecological condition of Gulf of Mexico coastal wetlands

A multi-level coastal wetland assessment strategy was applied to wetlands in the northern Gulf of Mexico (GOM) to evaluate the feasibility of this approach for a broad national scale wetland condition assessment (US Environmental Protection Agency's National Wetlands Condition Assessment). Landscape-scale assessment indicators (tier 1) were developed and applied at the sub-watershed (12-digit hydrologic unit code (HUC)) level within the GOM coastal wetland sample frame with scores calculated using land-use maps and geographic information system. Rapid assessment protocols (tier 2), using a combination of data analysis and field work, evaluated metrics associated with landscape context, hydrology, physical structure, and biological structure. Intensive site monitoring (tier 3) included measures of soil chemistry and composition, water column and pore-water chemistry, and dominant macrophyte community composition and tissue chemistry. Relationships within and among assessment levels were evaluated using multivariate analyses with few significant correlations found. More detailed measures of hydrology, soils, and macrophyte species composition from sites across a known condition gradient, in conjunction with validation of standardized rapid assessment method, may be necessary to fully characterize coastal wetlands across the region.

Parameters structuring macrophyte communities in rivers and lakes – results from a case study in North-Central Poland

We analysed macrophyte species composition and abundance, water chemistry and hydromorphological parameters of all major river stretches and lakes in the catchment of the lowland river Wel, Poland. We studied (i) which hydromorphological and physico-chemical factors best explained macrophyte species composition, (ii) if environmental factors structuring macrophyte communities were different between rivers and lakes; and (iii) if macrophyte indices developed to indicate eutrophication correlated with nutrient concentrations. Based on two-way indicator species analysis, correlation analysis and canonical correspondence analysis, we found that river substrate was most important in structuring macrophyte species composition and abundance in rivers, while water quality parameters were most important in lakes; species richness and diversity were correlated with river size and substrate type in rivers, but not in lakes; the relative abundance of macrophyte growth forms was best explained by total organic carbon and Secchi depth in lakes, but it was not correlated with any of the water chemical or hydromorphological parameters in rivers. Irrespective of which factors best explained macrophyte community composition, macrophyte metrics developed to indicate ecological status responded most strongly to total phosphorus concentrations, both in rivers and lakes. We conclude that macrophyte metrics are valuable tools for ecological status assessment also in ecosystems where parameters other than nutrients shape macrophyte community composition.

Variable response of functional macrophyte groups to lake characteristics, land use, and space: implications for bioassessment

We investigated how land use at multiple scales affects functional macrophytes groups and ecological status index in the boreal region. We employed a variance partitioning analysis to quantify the relative role of lake characteristics, multiple-scaled land use (catchment, buffer zones of 100, 300 and 500 m), and space in explaining the composition and richness of functional macrophyte groups (emergent and submerged macrophytes and hydrophytes) and ecological status of macrophytes in 110 Finnish lakes. Partial redundancy analysis (community composition) and partial linear regression (richness and status index) revealed that macrophyte community composition, richness, and status index were mostly explained by the pure effect of lake characteristics, which dominated over space for most macrophyte variables. Land use adjacent to shoreline had a higher effect on emergent macrophytes and status index compared to the land use of the whole catchment. Our findings suggest that emergent macrophytes can indicate changes in water quality and hydro-morphology originated from the close vicinity of the littoral zone. Ecological quality assessment based on emergent macrophytes only is probably not sufficient, but including emergent species in the assessments is recommended, especially in the species-poor boreal region.

Human and natural drivers of changing macrophyte community dynamics over 12 years in a Neotropical riverine floodplain system

ABSTRACTThe Rio Paraná is the world's tenth largest river (discharge in the upper river, studied here, during major flood events exceeds 12 700 m3s‐1). Together with its associated floodplain water bodies, this Neotropical river system supports a freshwater biodiversity of worldwide conservation significance, but one increasingly affected by human pressures, particularly the effects of river impoundment.Multivariate analysis of data from repeated (2000–2002 and 2011) macrophyte–environment surveys of a set of stations within a 230 km stretch of functioning riverine floodplain, downstream of the most recently completed dam on the Upper Paraná, the Porto Primavera Dam, together with published data (from 1999 and 2005–2007), was used to test the hypothesis that human influences might outweigh the importance of natural factors in driving the aquatic vegetation dynamics (macrophyte community composition, alpha‐diversity, and abundance) of this system during the period 1999–2011.The macrophyte communities present showed differences of species composition and abundance that could be strongly related to the scale and duration of the immediately preceding annual flood pulse, as well as local variations in physico‐chemical conditions. For rare Neotropical endemic species, which are a good marker of the conservation status of the system, there was a reasonable degree of stability between the 2000–2002 and 2011 survey periods, with eight of 16 such species being present in both surveys, three present in 2000–2002 only, but an additional five such species found only in 2011.The conclusion is that vegetation changes in the system can be referred both to direct human impacts (river regulation), and to indirect human or natural impacts (floods, alien species invasion byHydrilla verticillata, and local environmental factors). Overall there was evidence that major floods associated with El Niño ‐ Southern Oscillation (ENSO) climatic events had a much greater impact than other drivers, whether natural or anthropogenic.Copyright © 2013 John Wiley & Sons, Ltd.

Macrophytes in shallow lakes: Relationships with water, sediment and watershed characteristics

We examined macrophyte–environment relationships in shallow lakes located within the Prairie Parkland and Laurentian Mixed Forest provinces of Minnesota. Environmental variables included land cover within lake watersheds, and within-lake, water and sediment characteristics. CCA indicated that sediment fraction smaller than 63μm (f<63), open water area, turbidity, and percent woodland and agricultural cover in watersheds were significant environmental variables explaining 36.6% of variation in macrophyte cover. When Province was added to the analysis as a spatial covariate, these environmental variables explained 30.8% of the variation in macrophyte cover. CCA also indicated that pH, f<63, percent woodland cover in watersheds, open water area, emergent vegetation area, and organic matter content were significant environmental variables explaining 43.5% of the variation in macrophyte biomass. When Province was added to the analysis as a spatial covariate, these environmental variables explained 39.1% of the variation in macrophyte biomass. The f<63 was the most important environmental variable explaining variation for both measures of macrophyte abundance (cover and biomass) when Province was added as a spatial covariate to the models. Percent woodland in watersheds, turbidity, open water area, and Ca+Mg explained 34.5% of the variation in macrophyte community composition. Most species showed a negative relationship with turbidity and open water area except for Potamogeton richardsonii, Stuckenia pectinata, and filamentous algae. Our study further demonstrates the extent to which macrophyte abundance and community composition are related to site- and watershed-scale variables including lake morphology, water and sediment characteristics, and percent land cover of adjacent uplands.

Environmental and spatial correlates of community composition, richness and status of boreal lake macrophytes

We assessed the relative roles of natural covariates, human disturbance (water quality and catchment land use) together with geography in driving variation in aquatic macrophyte community composition, richness and status among 101 lakes in southern and central Finland. In addition to all species together, we studied different growth forms (i.e. emergent and submerged macrophytes and aquatic bryophytes) separately. Partial redundancy analysis (taxonomic composition) and partial least-squares regression (species richness and status index) were employed to display the share of variability in macrophyte assemblages that was attributable to the environmental factors (both natural and human-affected) and the spatial filters generated through principal coordinates of neighbor matrices (PCNM).Macrophyte community composition, richness and status were explained by natural covariates, together with joint effects of human disturbance variables and space. The contributions of pure fractions of human disturbance and space were mostly modest, albeit variable among macrophyte groups and status indices. Alkalinity, historical distributions, colour, dynamic ratio and lake area were most important natural covariates for macrophytes. Of those variables influenced by human, macrophytes were mostly explained by conductivity, total phosphorus, turbidity and chlorophyll-a.Our results demonstrate, as expected, that macrophytes are dominantly affected by local environmental variables, whereas dispersal-related processes seem not to be important at regional extent. Response of macrophyte growth forms to environment and space, however, varied significantly. Community composition and richness of emergent macrophytes showed congruent response to natural covariates and human disturbance. Aquatic bryophytes, which are rarely studied along lake macrophytes, responded stronger than other growth forms to human disturbance. Contrary to our expectations, ecological indices were not affected by dispersal-related processes, but were mainly explained by natural covariates. This study is the first to investigate spatial patterns in aquatic macrophytes derived bioassessment. Geographical structuring of environmental variables and regional extent negatively affected indices, suggesting that ecological status assessment needs further development.

Environmental clustering of lakes to evaluate performance of a macrophyte index of biotic integrity

Proper classification of sites is critical for the use of biological indices that can distinguish between natural and human-induced variation in biological response. The macrophyte-based index of biotic integrity was developed to assess the condition of Minnesota lakes in relation to anthropogenic stressors, but macrophyte community composition varies naturally across the state. The goal of the study was to identify environmental characteristics that naturally influence macrophyte index response and establish a preliminary lake classification scheme for biological assessment (bioassessment). Using a comprehensive set of environmental variables, we identified similar groups of lakes by clustering using flexible beta classification. Variance partitioning analysis of IBI response indicated that evaluating similar lake clusters could improve the ability of the macrophyte index to identify community change to anthropogenic stressors, although lake groups did not fully account for the natural variation in macrophyte composition. Diagnostic capabilities of the index could be improved when evaluating lakes with similar environmental characteristics, suggesting the index has potential for accurate bioassessment provided comparable groups of lakes are evaluated.

Spatial extent, regional specificity and metacommunity structuring in lake macrophytes

AbstractAimSpatial extent is inherently related to the potential roles of the main mechanisms structuring metacommunities. We examined the effects of varying spatial extent (ecological province, region and subregion) on the environmental and spatial components of variation in lake macrophyte communities. We also studied these effects separately for three macrophyte functional groups.LocationThe US state of Minnesota.MethodsWe examined average and heterogeneity differences in macrophyte community composition and environmental variation among the subregions of Minnesota using canonical analysis of principal coordinates (CAP) and homogeneity of multivariate dispersion (PERMDISP), respectively. We further used partial redundancy analysis (pRDA) to decompose variation in macrophyte community composition between environmental variables and spatial location at each spatial extent and geographical region. Spatial variables were derived using principal coordinates of neighbour matrices (PCNM) analysis.ResultsCAP and PERMDISP analyses showed that the subregions differed both in average community composition and in the heterogeneity of community composition for all macrophyte taxa, for emergent and submerged macrophytes, but not for non‐rooted macrophytes. We did not, however, find significant differences in overall environmental heterogeneity among the subregions. Variation partitioning using pRDAs showed that species sorting is more important than spatial processes for macrophytes, although these patterns were relatively weak. There was, however, much regional specificity, with the environmental and spatial fractions of community composition varying widely at different spatial extents, among different geographical regions and among functional groups. Contrary to our initial expectations, we did not find increasing spatial structuring and decreasing environmental control with increasing spatial extent.Main conclusionsOur findings indicate that, in macrophyte metacommunities, the relative contribution of spatial processes and environmental control varies rather unpredictably with spatial extent and geographical region. Our findings are thus of importance in advancing metacommunity ecology by showing that drawing wide‐ranging conclusions based on a single spatial extent or a single geographical region may be unwise.

The role of palaeolimnology in assessing eutrophication and its impact on lakes

Eutrophication is perhaps the most pervasive form of pollution. Here we first review its effects on lake ecosystems based largely on modern ecological investigation. The longer time scale afforded by palaeolimnological investigation has seen an increase in the number of the publications since 1990 with a disproportionate increase in citations demonstrating the increasing use and usefulness of palaeolimnology to help understand lakes ecosystems and their response to eutrophication. We summarise briefly the history and origins of palaeolimnological investigation into eutrophication and its impacts in lakes. Then we review quantitative and qualitative palaeolimnological methods for tracking change in nutrient concentrations, algal community and abundance, macrophyte community composition and abundance and zooplanktivorous fish density. The usefulness of stable isotope analysis on sediment organic matter to track eutrophication is assessed and alternative methods discussed. A current challenge is to determine the effects of recent climate change on lake ecosystems. The impacts of climate change and eutrophication on the ecology of lakes have many similarities making it difficult to disentangle the impact of one from the other, in particular where the eutrophication impacts are greatest. We review a number of recent palaeolimnological studies, in particular those integrating long term monitoring data, which have gone some way to identifying when nutrients or climate may be having the greatest impact. Finally, we discuss possible future directions for the discipline, such as the greater integration of studies of evolutionary change using molecular techniques.

The impact of environmental factors on the distribution pattern of aquatic macrophytes in a middle-sized Mediterranean stream

We studied the aquatic macrophyte assemblage structure along a Mediterranean lotic ecosystem from the upper reaches to the most downstream areas. We examined how environmental characteristics affect the composition and abundance of macrophyte communities spatially and temporally. Field survey data were collected from the Acheron river catchment, between 2005 and 2007. The identification of plant assemblages and the hierarchical structure of each group of species were analyzed using hierarchical classification (Bray–Curtis) and Indicator Species Analysis (ISA). The relationships between macrophyte community composition and water quality were examined using Redundancy Analysis (RDA) while the temporal variability was assessed using Canonical Variate Analysis (CVA). A total of 81 aquatic macrophyte taxa were recorded and Bray–Curtis classification identified 6 different vegetation groups. ISA results produced bryophyte and pteridophyte indicator species for the fast flowing sites near river springs while lower parts were dominated by Phragmites australis, Potamogeton pectinatus and macroalgae species. In the mid-river sections 4 different vegetation groups were identified: (i) Scirpus holoschoenus–Polygonum salicifolium–Plantago major occupied fast flowing waters and riffle habitat, (ii) Arundo donax–Scirpus lacustris–Fontinalis antipyretica located at urban sites, (iii) Brachythecium rutabulum–Pellia endiviifolia–Equisetum telmateia located at shaded sites with low nutrient concentration; and (iv) hydrophytes and helophytes which were found to be dominant in Acherons river tributaries and were associated with slower flowing water, low water clarity and high nitrate and ammonia nitrogen concentrations.Life form analysis indicated that mosses and liverworts (bryophytes) dominate the upper part of the river basin while emergent plants (helophytes) were abundant both in upper and middle reaches. Monte Carlo permutation testing revealed that NO3–N, NH4–N, pH, conductivity, water temperature, mean water velocity are strongly correlated with aquatic macrophyte distribution. Canonical Variates Analysis (CVA) and Canonical Correspondence Analysis (CCA's) showed a strong seasonal signal with nitrogen nutrients (nitrite, nitrate, and ammonium), dissolved oxygen, pH and water temperature all significant discriminating variables. Nitrogen appeared to be the most important nutrient since it was found to be significant as nitrate, nitrite and ammonium forms in all seasons.

Physical circulation and spatial exchange dynamics in a shallow floodplain wetland

This paper examines the spatial patterns of water exchange based on water temperature variation between littoral and pelagic zones and compares the patterns in a series of shallow lakes at different water levels. Exchange patterns were assessed by developing isotherms along the transects and estimating the surface energy budget using the vertical temperature profi le and time-series measurements. Our results indicate the presence of density-driven fl ow induced by the differential temperature gradient between littoral areas, which are dominated by either fl oating-leaved or submerged vegetation, and the open pelagic region. Persistent stratifi cation was noted in the narrower lakes, which was thought to be due to the presence of dense submerged vegetation that attenuate wind-driven turbulence. In addition, variation of thermal stratifi cation and mixing dynamics between these lakes at different water levels has corresponding effects on the biological and chemical regimes. The circulation contributes to increased transport of the phosphate that could favour submerged species and subsequently induce shifts of macrophyte community composition. The results of this study have implications for the rehabilitation and management of lake ecosystems.

Aquatic macrophytes as indicators of water quality in subtropical shallow lakes, Southern Brazil

AIMS: We evaluated the potential of aquatic macrophyte communities as bioindicators in six small shallow lakes. METHODS: The sampling was conducted monthly for one year, during which all macrophytes were surveyed, and the water temperature, dissolved oxygen, pH, conductivity, total alkalinity, chlorophyll-a, suspended matter, total nitrogen (Nt) and total phosphorus (Pt) were measured. RESULTS: In total, forty-three species were recorded, and there were significant differences in the species richness and limnological conditions among the lakes studied. A canonical correspondence analysis showed that the concentration of nutrients (Nt and Pt), chlorophyll-a, suspended matter, dissolved oxygen and pH were the most important predictors of the distribution of macrophytes. Some emergents were related to the high concentration of nutrients, chlorophyll-a, and suspended matter. Moreover, the most submersed species were associated with environments with low nutrient concentrations and the lowest values chlorophyll-a and suspended matter. In addition, some species submerged and floating were related to low values pH, alkalinity and dissolved oxygen. Limnological differences between lakes may be cited as the main causes of the observed heterogeneous distribution of macrophytes. CONCLUSIONS: These results indicate the importance of limnological characteristics of the different environments in the macrophyte community composition and the potential role of this community as a bioindicator in shallow lakes in southern Brazil.

Do effects of landscape factors on coastal pond macrophyte communities depend on species traits?

We investigated the richness and composition of aquatic macrophyte communities of non-fragmented ponds in a matrix of coastal dunes in Southern Brazil. We tested three hypotheses on natural wetlands: (1) area, diversity of habitats and hydroperiod increase the total macrophyte richness; (2) isolation among ponds decreases the total macrophyte richness; and (3) the influence of environmental factors on macrophyte richness and composition change among macrophyte groups with different degrees of tolerance to hydrological variation. Our results showed that area was not a determining factor for macrophyte richness in coastal dune ponds. Diversity of habitats positively influenced total macrophyte richness, both hydrophyte and emergent species. Total richness of macrophytes declined with the increase in distance from source areas. However, this pattern varied among the study macrophyte groups with different degree of tolerance to hydrological variations. Whereas richness of hydrophyte and emergent species richness were related with isolation, the richness of amphibious species was not. Species composition was determined by the combination of the following environmental factors: isolation, diversity of habitats and hydroperiod. The current process of fragmentation taking place in Southern Brazil will increase the isolation among wetlands, and will influence the aquatic macrophyte species. The isolation effects may be most severe for hydrophytes.

Response of macrophyte communities and status metrics to natural gradients and land use in boreal lakes

We studied the relations of aquatic macrophyte communities, ecological quality metrics and water quality to lake characteristics and to land use defined at multiple spatial scales (three lake marginal zones (LMZs) of contrasting width and the whole topographic catchment) in 110 boreal lakes in Finland using ordination and generalised additive modelling. Variation in macrophyte community composition of our lakes was related to water quality, land use, latitude and lake morphology. Relationships of macrophyte status metrics – the proportion of type-specific species (TT50), Percent Model Affinity (PMA) and Trophic Index (TI) – to land use were scale dependent. The proportion of agricultural and urban land use adjacent to the lake shoreline (LMZs of 300m and 500m) had a more significant effect on the metrics compared to land use at the catchment scale. The scale-related pattern in the effect of land use was not congruent among metrics and the metrics also showed different indications of deterioration. Lower sensitivity to the measured disturbance of the pressure sensitive metric TI compared to the other metrics (TT50 and PMA) based on general type-specific species composition was presumably due to a lack of helophytes in the species pool used, and due to invariable indicator values across lake types. Moreover, TI varied more with hydromorphology related natural gradients than TT50 and PMA. This could be due to lack of habitat for eutrophication sensitive submerged indicator species in shallow lakes. Our study demonstrates that choosing the most influential catchment scale for the evaluation and mitigation of anthropogenic impacts on lacustrine biota, may be significant in conserving and restoring the ecological quality of freshwaters, as required by, e.g., the European Water Framework Directive.

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.

Effects of grass carp introduction on macrophyte communities in a shallow lake

Abstract In 2002, 2005 and 2007 vegetation and physicochemical properties of pelagial water were investigated in a shallow mid-forest lake. In 2002, the highest phytocoenotic diversity was recorded; charophytes and vascular submerged macrophytes formed their own extensive communities. After stocking with grass carp (Ctenopharyngodon idella Val.) in 2002, reduction of water transparency, as well as changes in qualitative and quantitative composition of macrophyte communities were observed. Submerged vegetation declined during subsequent growing seasons. Charophyte meadows vanished first. The introduction of grass carp appeared to be a potential trigger for the rapid changes observed in the vegetation.

The relative role of environmental, spatial, and land-use patterns in explaining aquatic macrophyte community composition

Quantifying the relative role of environmental and spatial factors to understand patterns in community composition is a fundamental goal of community ecology. We applied a tested and repeatable point-intercept sampling method to aquatic macrophyte assemblages in 225 Wisconsin lakes to understand the ability of environmental, land-use, and spatial patterns to explain aquatic plant distribution and abundance. Using a variation partitioning framework in conjunction with Moran eigenvector maps we found that environmental, land-use, and spatial patterns explained 31% of total adjusted variation in aquatic macrophyte assemblages across the landscape. Environmental factors were the most important (contributing 34% of the total explained variation), but all sources of variation were statistically significant. Community composition varied from north to south along a gradient of alkalinity and from disturbed to undisturbed lakes, diverging according to whether disturbance was urban or agricultural. The large amount of shared variation among predictor variables suggests causal relationships are complex and emphasizes the importance of considering space and land-use in addition to environmental factors when characterizing macrophyte assemblages. This work is the first to examine the joint and unique effects of environment, land-use, and spatial patterns on aquatic plant communities.

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

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

Detecting changes in ecosystem quality following long-term restoration efforts in Cootes Paradise Marsh

Cootes Paradise Marsh is a large urban wetland of western Lake Ontario that has undergone major restoration as part of the Hamilton Harbour Remedial Action Plan. A key component of the restoration plan is exclusion of common carp ( Cyprinus carpio) via construction of the Cootes Paradise Fishway that became operational in 1997. Here, we evaluate the response of the marsh community to carp exclusion using three approaches. First of all we analyze changes in water quality parameters and the community composition of zooplankton, macrophytes and fish. Secondly, we use ecological indices based on water quality, zooplankton, macrophytes and fish communities to track changes in quality. Lastly, we evaluate changes in the wetland quality of Cootes Paradise over the past decade in comparison with two other coastal wetlands of the Laurentian Great Lakes for which long-term data exist (Matchedash Bay of Lake Huron and Long Point Marsh of Lake Erie). Our results show that there has been variable improvement in wetland quality at Cootes Paradise, but compared to the two other wetlands, it is still the most degraded in all aspects studied. The overall trend towards moderately better water quality conditions in Cootes Paradise over the past decade is not directly reflected in the zooplankton, macrophyte and fish communities. We believe that high nutrient levels and high turbidity are preventing the progression to a clear-water macrophyte dominated system. This is one of few long-term studies that tracks the progress of restoration in a degraded marsh. It underscores the difficulty in trying to restore a ‘novel ecosystem’ to its original biotic and abiotic characteristics.