Using aquatic macrophyte community indices to define the ecological status of European lakes

Defining the overall ecological status of lakes according to the Water Framework Directive (WFD) is to be partially based on the species composition of the aquatic macrophyte community. We tested three assessment methods to define the ecological status of the macrophyte community in response to a eutrophication pressure as reflected by total phosphorus concentrations in lake water. An absolute species richness, a trophic index (TI) and a lake trophic ranking (LTR) method were tested at Europe-wide, regional and national scales as well as by alkalinity category, using data from 1,147 lakes from 12 European states. Total phosphorus data were used to represent the trophic status of individual samples and were plotted against the calculated TI and LTR values. Additionally, the LTR method was tested in some individual lakes with a relatively long time series of monitoring data. The TI correlated well with total P in the Northern European lake types, whereas the relationship in the Central European lake types was less clear. The relationship between total P and light extinction is often very good in the Northern European lake types compared to the Central European lake types. This can be one of the reasons for a better agreement between the indices and eutrophication pressure in the Northern European lake types. The response of individual lakes to changes in the abiotic environment was sometimes represented incorrectly by the indices used, which is a cause of concern for the use of single indices in status assessments in practice.     

Assessment of the ecological status of regulated lakes: stressor-specific metrics from littoral fish assemblages

Although in situ sediment capping is frequently used to reduce internal loading of contaminants and nutrients, post-application assessment rarely includes the potential undesirable short-term effects on plankton species composition. We hypothesised that a modified zeolite (Z2G1) application as a sediment capping agent in Lake Okaro, New Zealand, could cause significant undesirable shifts in species composition of both zooplankton and phytoplankton due to burial of resting stages or interference with feeding for the zooplankton. Alternatively, we predicted that the capping agent might have no effect due to, for example, the coarse grain size of the material (1–3 mm). We used multidimensional scaling (MDS) and analysis of similarity (ANOSIM) to identify any adverse effects of Z2G1 on zooplankton and phytoplankton species composition (i.e. shifts in community structure, including species loss) by comparing the community structure before and after the Z2G1 application. We found no significant differences in species composition before and after the Z2G1 application at the depths investigated (surface and 9 m). However, all of the analyses showed statistically significant differences among seasons, indicating seasonal variations in plankton composition far outweigh those that may have resulted from the Z2G1 application. Coarse particle size, low dose rate and a restricted area where the sediment capping agent was applied were considered to be the factors limiting potential adverse effects on plankton species. Considerations of finer-grained material to increase coverage and efficacy of phosphorus adsorption require assessment for their effects on zooplankton, however, and a direct mode of application into the hypolimnion is recommended to minimise effects on zooplankton and phytoplankton communities.     

An assessment of macrophyte community metrics in the determination of the ecological condition and total phosphorus concentration of Mediterranean ponds

The macrophyte vegetation of 51 ponds situated in the Duero river basin on the Northern Iberian Plateau was studied with the aim of selecting metrics that responded clearly to perturbation and that should be included in a multimetric index for assessing the ecological condition (expression of the quality of the structure and functioning of aquatic ecosystems associated with surface waters) of Mediterranean ponds. Furthermore, the specific response of metrics to the total phosphorus (TP) concentration was also investigated because of agricultural activities, which usually increase the concentration of nutrients in aquatic systems, are one of the principal types of impairment affecting ponds in the Duero basin.A total of 19 metrics representing several aspects of the structure of macrophyte communities (cover, richness, diversity) were selected as potential metrics.The strong overlap which was observed for macrophyte metrics between classes of ecological conditions (bad, poor, moderate, good, best available) and TP concentrations (>600, 600-300, 300-100, 100-50, <50 μg L⁻¹ TP) constitutes a major problem in defining and separating these classes. For this reason, Mann-Whitney U-test and discrimination efficiency were carried out to determine which of the measures best discriminated between slightly impaired sites (ponds in good or best available condition) and perturbed ponds (ponds in moderate, poor or bad condition). Most of the metrics showed significant differences (p < 0.05) between slightly impaired and perturbed ponds. However, only total cover and hydrophyte richness, which had the highest discrimination efficiency (>78%), showed no inter-quartile overlap (25th-75th percentile) between the two ecological classes. For these reasons, both total cover and hydrophyte richness were selected for the implementation of a multimetric index able to discriminate between slightly impaired and degraded Mediterranean flatland ponds.Currently, eutrophication is considered the main pressure on lakes. However, macrophyte metrics were far less sensitive to TP concentration than to ecological condition changes. This shows that other pressures are also of considerable importance. Thus, the definition of the ecological condition of lakes using macrophytes should not be based only on responses to eutrophication pressure, as has been done in some European countries.     

Nutrient and oxygenation conditions in transitional and coastal waters: Proposing metrics for status assessment

In response to the requirements of the Water Framework Directive, a methodology is proposed for assessing the physico-chemical status, specifically nutrient and oxygenation conditions, of the transitional and coastal waters. The method involved several steps: firstly reference conditions were established according to the near-natural reference site criterion and taking into account the main anthropogenic pressures affecting each water body. Secondly, the data were analyzed by bootstrap statistical techniques; the use of percentiles rather than mean values is proposed, in order to minimize the standard sampling error. Finally, the quality ratios for each parameter were calculated taking into account variations in salinity and each status boundary defined as a 50% deviation relative to the next higher class. The final physico-chemical status of each water body was then defined according to the “one out all out” principle. The method was applied to coastal and transitional waters in the central part of the Cantabrian Sea (NW Spain). The results obtained reveal good physico-chemical conditions in most of the water bodies under study, and also indicate strong relationships between the anthropogenic pressures analyzed and the status of each water body.     

Sampling techniques and inter-surveyor variability as sources of uncertainty in Polish macrophyte metric for lake ecological status assessment

According to the Water Framework Directive, the results of the ecological status assessment should be accompanied with estimates of the level of confidence and precision of the determination. The Polish macrophyte-based method for lake assessment (Ecological State Macrophyte Index, ESMI) was tested for its uncertainty. The data from 12 lakes surveyed using four modifications of the sampling procedure, different numbers of transects and by two or three independent surveyors were analysed and the risk of misclassification was estimated. The choice of the sampling technique had no effect on abundance parameters (C _max and %cover), but it affected significantly the taxonomic composition indices (H and J′). It did not influence, however, the final assessment result, since in all the methods used, the ESMI values were comparable and showed no significant differences of means. Although the mean ESMI values were statistically indifferent and gave the same assessment result irrespective of the number of transects surveyed, the lower the number of transects, the higher the SD value and the more uncertain the assessment result. The risk of misclassification of the 12 lakes varied from 0.5% to over 40% depending on the sampling standard deviation value and the proximity of the index observed value to the class boundary.     

Factors affecting light penetration in shallow lakes

Light conditions were studied in six lakes of the Danube Delta for a period of 2 years and were described as a function of 12 independent variables forming a data matrix with more than 1000 sample units. Light extinction was explained in percentage of 64% by phytoplankton, of 11% by detritus, of 7% by zooplankton, of 1.4% by dissolved organic matter and of 0.15 by bacterioplankton. The influence of mineral particles was insignificant. Equations are produced here for the relationship to water turbulence, wind intensity and lake depth. The threshold for full water turbulence was between 7 and 8% for a fluctuation domain of critical winds of 3.2–5.4 m s^-1 and for a depth domain of 1–3 m.     

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 south-western 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.     

Factors influencing hydrocarbon degradation in three freshwater lakes

The mixed microbial flora of 3 lakes in Ohio with differing histories of hydrocarbon pollution was examined in relation to the ability to use hydrocarbons. Weathered kerosene was spiked with naphthalene, pristane, 1,13-tetradecadiene, andn-hexadecane and added to water-sediment mixtures from the 3 lakes, and utilization of the 4 marker hydrocarbons was measured. Each of the marker hydrocarbons was metabolized; naphthalene was the most readily used and pristane was the most resistant. Values for dissolved oxygen suggest that oxygen did not limit hydrocarbon degradation in the water column at any site examined. Nutrient addition studies indicated that nitrogen and phosphorus limited hydrocarbon degradation at all sites examined. Maximum numbers of heterotrophic bacteria were detected when the water temperature was 10°C or higher. The data indicate that temperature limits hydrocarbon degradation in the winter, except at a site which had been impacted by an oil spill and which received chronic inputs of hydrocarbons and nutrients. In samples from that site, all 4 marker hydrocarbons were degraded at 0°C. Results of temperature and nutrient-addition experiments suggest that different seasonal populations of hydrocarbon users are selected at that site, but not at other lake sites.     

The role of cladocerans reflecting the trophic status of two large and shallow Estonian lakes

The role of pelagic cladoceran communities is discussed on the basis of a comparative study conducted in two Estonian lakes, the moderately eutrophic Lake Peipsi (N_tot 700, P_tot 40 μg l^?1 as average of ice-free period of 1997–2003) and in a strongly eutrophic Lake Võrtsjärv (N_tot 1600, P_tot 54 μg l^?1). The cladoceran community was found to reflect the differences in the trophic state of these lakes. In L. Peipsi, characteristic species of oligo-mesotrophic and eutrophic waters co-dominated (making up 20% or more of total zooplankton abundance or biomass), whereas in L. Võrtsjärv only species of eutrophic waters occurred. In L. Peipsi, the dominant cladocerans were Bosmina berolinensis and Daphnia galeata, while Chydorus sphaericus was the most abundant cladoceran in L. Võrtsjärv. The cladocerans of L. Peipsi (mean individual wet weight 25 μg) were significantly (threefold) larger than those of L. Võrtsjärv (8 μg). The mean wet biomass of cladocerans was higher and total cladoceran abundance was lower in L. Peipsi compared to L. Võrtsjärv (biomass varied from 0.133 to 1.570 g m^?3; mean value 0.800 g m^?3 in L. Peipsi and from 0.201 to 0.706 g m^?3, mean 0.400 g m^?3 in L. Võrtsjärv; the corresponding data for abundances were: 8,000–43,000 ind. m^?3, mean 30,000 ind. m^?3 for L. Peipsi, 50,000–100,000, mean 52,000 ind. m^?3 for L. Võrtsjärv). Based upon differences in body size, cladocerans were more effective transporters of energy in L. Peipsi than in L. Võrtsjärv. Cladocerans proved to be informative indicators of the trophic status and of the efficiency of the food web in studied lakes.     

Phytoplankton and ecological status of forest lakes in the Omsk Priirtyshye

According to the materials of multiyear studies, the author estimates the ecological status of forest lakes in the Omsk Priirtyshye with respect to the phytoplankton development indicators. The species composition, structure, and floristic similarity degree of the phytoplankton of polytypic forest lakes are described. The author also determines the trophic status and water quality of these lakes. It is found that excessive recreation has a negative impact on the ecological status of the lakes.     

Comparison of two indices based on macrophyte assemblages to assess the ecological status of coastal waters in the transition between the Atlantic and Mediterranean eco-regions

Several indices based on the composition and abundance of aquatic flora have been developed to assess the ecological status of coastal waters along the European coasts in the context of the Water Framework Directive. This directive pointed out the intercalibration of indices based on the same biological element within an eco-region to ensure the consistency and comparability among them. For a better management of coastal areas in the transition zone between two eco-regions, the comparison of indices developed for each eco-region may also be necessary. The aim of this work was to compare two indices based on macrophytes that have been proposed for two different and adjoining eco-regions: the RSL (Reduced Species List) in the Atlantic eco-region and the CARLIT (Cartography of littoral and upper sublittoral communities) in the Mediterranean. These indices were applied in 14 sites in the transition between the Atlantic Ocean and the Mediterranean Sea, where a wide range of anthropogenic pressures can be found, from high (Algeciras Bay) to almost negligible ("El Estrecho" Natural Park). Overall, both indices were sensitive to anthropogenic pressures and suitable to assess the ecological status. The comparison between indices suggested a bias in the assessment of the ecological status between good and high classes due to a different definition of high ecological status class between RSL and CARLIT. In addition, the most important disagreements between indices were found in the most degraded localities. The results showed, however, a high comparability between RSL and CARLIT despite their marked conceptual and methodological differences.     

Multi-level assessment of ecological coastal restoration in South Texas

Adaptive management can be a very useful tool for assessing and improving coastal ecological engineering restoration projects. A shoreline restoration project using ecological engineering approaches to mitigate coastal erosion was developed and implemented in 2003 at Loyola Beach, Baffin Bay, TX. The project incorporated riprap, fiber matting, geotextile, and vegetation as an alternative to conventional hard structures for erosion control. As part of the restoration expansion, a detailed evaluation of the previous project was completed at several levels, including the landscape, geotechnical design, environmental and ecological considerations, and social and economic factors. The findings indicated that the vegetation and its underlying geotechnical integrity have played an important role in erosion mitigation. Overall the project was successful in the protection of the shoreline and was shown to be more ecologically beneficial than other hard structures. Based on the preliminary success of the initial project, the restoration techniques were adapted for another beach extension to the west. The assessment did reveal some weaknesses in the original project design including the need for more substantial toe protection and periodic maintenance requirements. Based on these assessments, some additional new methods for the restoration extension were proposed and implemented. The broader applicability of this restoration approach outside the local region has been presented through several outreach activities and delivered to coastal planners and land owners throughout the Texas Coastal Bend and Northern Mexico.     

Uncertainty in ecological status assessments of lakes and rivers using diatoms

The EU’s Water Framework Directive requires all surface water bodies to be classified according to their ecological status. As biological communities show both spatial and temporal heterogeneity, expressions of ecological status will, inevitably, have an element of uncertainty associated with them. A consequence of this environmental heterogeneity is that there is a risk that status inferred from one or more samples is different to the true status of that water body. In order to quantify the scale of temporal uncertainty associated with benthic diatoms, replicate samples were collected from sites across the ecological status gradient in lakes and rivers in the UK. Variability (expressed as standard deviation of temporal replicate samples from a single site) could be described using a polynomial function and this was then used to calculate the risk of placing a water body in the wrong ecological status class. This risk varied depending on the distance from the class boundaries and the number of replicates. Based on these data, we recommend that ecological status is determined from a number of samples collected from a site over a period of time.     

Production of some oligochaete species in large Estonian lakes

The production of Potamothrix hammoniensis, Lamprodrilus isoporus, and Uncinais uncinata was estimated in the eutrophic lakes Peipsi-Pihkva and Vôrtsjärv. Growth characteristics of these species are briefly described. Calculated production values were 6–32 (P. hammoniensis), 19–79 (L. isoporus), and 1–4 kJ m² (U. uncinata), respectively. The annual P/B ratios for the same species were, 0.8–1.7, 2.5–4.8, and 4.4–5.4, respectively.     

Ecological status assessment of European lakes: a comparison of metrics for phytoplankton, macrophytes, benthic invertebrates and fish

Data on phytoplankton, macrophytes, benthic invertebrates and fish from more than 2000 lakes in 22 European countries were used to develop and test metrics for assessing the ecological status of European lakes as required by the Water Framework Directive. The strongest and most sensitive of the 11 metrics responding to eutrophication pressure were phytoplankton chlorophyll a, a taxonomic composition trophic index and a functional traits index, the macrophyte intercalibration taxonomic composition metric and a Nordic lake fish index. Intermediate response was found for a cyanobacterial bloom intensity index (Cyano), the Ellenberg macrophyte index and a multimetric index for benthic invertebrates. The latter also responded to hydromorphological pressure. The metrics provide information on primary and secondary impacts of eutrophication in the pelagic and the littoral zone of lakes. Several of these metrics were used as common metrics in the intercalibration of national assessment systems or have been incorporated directly into the national systems. New biological metrics have been developed to assess hydromorphological pressures, based on aquatic macrophyte responses to water level fluctuations, and on macroinvertebrate responses to morphological modifications of lake shorelines. These metrics thus enable the quantification of biological impacts of hydromorphological pressures in lakes.     

Factors influencing the temporal coherence of five lakes in the English Lake District

1. The lakes in the Windermere catchment are all deep, glacial lakes but they differ in size, shape and general productivity. Here, we examine the extent to which year‐to‐year variations in the physical, chemical and biological characteristics of these lakes varied synchronously over a 30–40‐year period. 2. Coherence was estimated by correlating time‐series of the spring, summer, autumn and winter characteristics of five lakes: Esthwaite Water, Blelham Tarn, Grasmere and the North and South Basins of Windermere. Three physical, four chemical and two biological time‐series were analysed and related to year‐to‐year variations in a number of key driving variables. 3. The highest levels of coherence were recorded for the physical and chemical variables where the average coherence was 0.81. The average coherence for the biological variables was 0.11 and there were a number of significant negative relationships. The average coherence between all possible lake pairs was 0.59 and average values ranged from 0.50 to 0.74. A graphical analysis of these results demonstrated that the coherence between individual lake pairs was influenced by the relative size of the basins as well as their trophic status. 4. A series of examples is presented to demonstrate how a small number of driving variables influenced the observed levels of coherence. These range from a simple example where the winter temperature of the lakes was correlated with the climatic index known as the North Atlantic Oscillation, to a more complex example where the summer abundance of zooplankton was correlated with wind‐mixing. 5. The implications of these findings are discussed and a conceptual model developed to illustrate the principal factors influencing temporal coherence in lake systems. The model suggests that our ability to detect temporal coherence depends on the relative magnitude of three factors: (a) the amplitude of the year‐to‐year variations; (b) the spatial heterogeneity of the driving variables and (c) the error terms associated with any particular measurement.     

Factors influencing the variability of pigments in the surface sediments of mountain lakes

1. Surface sediment biofilm samples from 82 Pyrenean lakes were analysed for marker pigment composition using high performance liquid chromatography (HPLC). 2. Variability in the pigment composition among lakes was investigated by multivariate statistical analyses using a large data set of factors describing lake chemical, physical, morphological and catchment characteristics. 3. Due to the widely varying light penetration in the lakes, the most significant gradient of pigment composition extended from a benthic to a planktonic signal. The most important pigments in the gradient were alloxanthin (cryptophytes marker pigment, planktonic signal) and diatoxanthin (diatoms marker pigment, benthic signal). The molar ratio between these two marker pigments was positively correlated with lake depth. 4. Chlorophyll‐a preservation was found to be positively related to light penetration and the development of an autothrophic biofilm on the surface sediment and negatively related to decreasing pH and the percentage of alpine meadows in the lake catchments. 5. Zooplankton marker pigments in the surface sediment, including grazing by‐products (e.g. phaeophorbides) and carotenoids (astaxanthin, canthaxanthin, echinenone) incorporated into their tissues, were correlated with the areal abundance of zooplankton. 6. Marker pigments for photosynthetic bacteria, BChl‐e and okenone, were found mainly in relatively shallow lakes with large catchments that are forested, probably because of their higher loading of allochthonous organic matter. 7. The evaluation of a preservation index (Chl‐a expressed as a percentage of a‐phorbins) and the alloxanthin/diatoxanthin ratios throughout the sediment record of mountain lakes can provide evidence of historical changes in the relative importance of planktonic versus benthic primary production and might ultimately be interpreted in terms of climatic or environmental changes.     

Factors influencing nitrogen processing in lakes: an experimental approach

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Factors governing nutrient status of mountain lakes in the Tatra Mountains

1. Nutrient and chlorophyll a levels, and bacterial numbers of 84 glacial lakes in the Tatra Mountains (Slovakia and Poland, Central Europe) were determined to assess the impact of catchment vegetation and water acidity on lake trophic status. 2. Catchment vegetation was the crucial factor governing nutrient content of lakes. 3. Concentrations of organic carbon, organic nitrogen, and chlorophyll a, and bacterial numbers were tightly correlated with total phosphorus (TP) content. Their levels were the highest in forest lakes, then decreased in alpine lakes with decreasing amount of catchment vegetation and soil cover, and were the lowest in lakes situated in bare rocks. 4. The above pattern was further modified by lake water acidity. Concentrations of TP, organic carbon, and chlorophyll a were lower in alpine lakes with pH between 5 and 6 than in more or less acid alpine lakes. Zooplankton was absent in all alpine lakes with pH between 5 and 6. 5. Nitrate concentrations followed an inverse trend to TP; lowest values were in forest lakes, then increased with decreasing amount of catchment soils and vegetation. Within the lakes of the same type of catchment vegetation, nitrate concentrations were negatively correlated to TP. N‐saturation of catchment areas and lake primary production were dominant processes controlling nitrate levels in lakes and nitrate contribution to lake acidification.