Ecological classification of lakes: Uncertainty and the influence of year-to-year variability

Regular monitoring of lakes is important to determine their ecological state and development and of key significance when deciding whether action should be taken to improve their quality, for instance by reducing the external loading of nutrients. Imprecise or inadequate knowledge of the ecological state increases the risk of misclassification and of wrong management decisions. Based on Danish lake data, we aimed to determine temporal variations, in particular natural year-to-year differences, and to describe the uncertainty in assessing the ecological state of lakes. We analysed environmental data from ca. 350 Danish lakes (1100 lake years), including three case studies, with long-term data series (up to 24 years), with no significant changes in external nutrient loading. We used summer means of selected water chemical variables, phytoplankton and submerged macrophytes as indicators of ecological state and found considerable variations in all indicators, which could not be ascribed alone to meteorological variation. In shallow lakes, chlorophyll a concentrations exhibited large year-to-year variations, especially at TP ranging between 0.05 and 0.15 mg L⁻¹ where the lakes may shift between a macrophyte- and a phytoplankton-dominated state. For example, chlorophyll a varied by a factor 5–10 between years and was particularly low when submerged macrophyte coverage exceeded 20% compared with lakes without macrophytes. Use of a multimetric index including four phytoplankton indicators reduced the coefficient of variation. Generally, the 95% confidence interval of ecological classification was approximately 50% lower when the assessment of ecological state was based on 4–5 years’ measurements than if based on only one year's measurements. Knowledge and awareness of the uncertainty of indicators used in ecological classification are highly relevant for lake managers and policy makers when defining efficient monitoring and restoration strategies.     

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.     

A fish-based index of estuarine ecological quality incorporating information from both scientific fish survey and experts knowledge

In the Water Framework Directive (European Union) context, a multimetric fish based index is required to assess the ecological status of French estuarine water bodies. A first indicator called ELFI was developed, however similarly to most indicators, the method to combine the core metrics was rather subjective and this indicator does not provide uncertainty assessment. Recently, a Bayesian method to build indicators was developed and appeared relevant to select metrics sensitive to global anthropogenic pressure, to combine them objectively in an index and to provide a measure of uncertainty around the diagnostic. Moreover, the Bayesian framework is especially well adapted to integrate knowledge and information not included in surveys data. In this context, the present study used this Bayesian method to build a multimetric fish based index of ecological quality accounting for experts knowledge. The first step consisted in elaborating a questionnaire to collect assessments from different experts then in building relevant priors to summarize those assessments for each water body. Then, these priors were combined with surveys data in the index to complement the diagnosis of quality. Finally, a comparison between diagnoses using only fish data and using both information sources underlined experts knowledge contribution. Regarding the results, 68% of the diagnosis matched demonstrating that including experts knowledge thanks to the Bayesian framework confirmed or slightly modified the diagnosis provided by survey data but influenced uncertainty around the diagnostic and appeared especially relevant in terms of risk management.     

First steps in the Central-Baltic intercalibration exercise on lake macrophytes: where do we start?

The Water Framework Directive (WFD 2000) defines macrophytes as one of the biological groups required for the ecological assessment of European surface waters. Several indices for macrophyte assessment have been proposed or are currently in use by different European states. As a first step towards performing an intercalibration of these indices a common dataset was developed. This dataset contains abundance data on 789 macrophyte species from 316 different lake sites in ten European countries. Various common species and genera were identified as indicators of reference and impacted conditions within the dataset. Cluster analysis of macrophyte data, supported by non-metric multidimensional scaling, indicated that clusters formed were more reflective of their source country rather than lake type. This might be caused by differences in regional climate, biogeography, monitoring techniques, or a combination of these factors. A total of six national indices were applied to assign quality classes to the lakes. However, this produced results that often differed by one or two quality classes for the same site. We foresee that a more precise intercalibration exercise is necessary, and it should be based on more detailed data considering both seasonality and the latitudinal differences within the area covered.     

Extending the phytoplankton tool kit for the UK Water Framework Directive: indicators of phytoplankton community structure

The Water Framework Directive (WFD) demands consideration of normative definitions for assessing ecological state of marine waters. For phytoplankton, ‘deviations from the ideal’ need to be considered for species composition and abundance, average biomass and the occurrence of blooms. A combination of phytoplankton metrics has been developed which, when considered in combination, should provide a confident assessment of the ecological state of each water body under assessment. The aim of this study was to evaluate phytoplankton community structure in different coastal and estuarine water bodies within England and Wales, and to contribute evidence towards the development of a community-based phytoplankton indicator. Influences of seasonality on the species assemblage were tested using a long-term data set available from a long-term monitoring site just offshore of Plymouth, UK. There is a substantive seasonal influence to the data, with a maximum of 10–14 common species (out of a potential 20) reoccurring within the same calendar month over a 10-year time span. Comparisons between reference and test water bodies give a range of common species of between 3 and 11 species within water type and season. A statistical and qualitative approach for comparing the most common species occurring between a reference and test site were tested for development of a WFD phytoplankton assessment tool. Overall, the results indicate that there are distinct phytoplankton assemblages over seasons which could form the basis of a community assessment metric. However, differences in boundary conditions are negligible between the different areas. There is evidence that community populations may be ubiquitous across marine water types in England and Wales, and development of generic seasonal lists across typologies could be appropriate in the further development of this tool.     

Neighbourhood-scale urban riparian ecosystem classification

Urban riparian ecosystems are now recognized as essential components in determining the vulnerability of nature and human systems to climate change, but still remains uncertainty concerning how to stratify and classify urban riparian landscapes into units of ecological significance at spatial scales appropriate for management. Ecosystem classification presents a tool that allows for quantifying the social and ecological processes of ecosystems so as to shape them into relatively homogeneous management objectives, and provides the potential of offering decision support to urban planners based on urban ecological principles. The purpose of this study is to explore and develop a framework for urban riparian ecosystem classification. The classification framework integrates 9 ecosystem components and 29 spatially-explicit variables that characterized by the biophysical landscape, built environment and human population. Then this framework is applied at the neighbourhood scale in Huangpu River basin, Shanghai city, China, employing hierarchical cluster analysis. The results of the ecosystem classification show that the riparian ecosystems in the Huangpu River could be grouped into three principal categories and these ecosystems are aligned along a gradient of increasing urbanization. We highlight the conservation and payment for riparian ecosystem services delivered in the upstream of Huangpu River, and revegetation and enhancement of riparian ecosystems in the more urbanized downstream area. We also find that riparian vegetation connectivity and coverage were negatively related to land use mix, built environment density, and economic wealth. In terms of riparian vegetation ecology, neighbourhood scale land use mix and built environment density are more influential than socioeconomic background (such as average family income and immigrant status).     

Performance of a new phytoplankton composition metric along a eutrophication gradient in Nordic lakes

A new phytoplankton metric is presented, which is developed from a large dataset of Norwegian lakes (>2,000 samples from >400 lakes). In contrast to previous metrics, this index is not built on selected ‘indicative’ taxa, but uses all available taxonomic information at genus and species level. Taxa optima with respect to lake trophic status (derived from total phosphorus concentrations) are used to calculate a phytoplankton trophic index (TI) for each sample. Analysis of the TI shows that phytoplankton communities exhibit highly non-linear responses to eutrophication in Norwegian lakes. Reference lakes are characterized by very similar TIs despite having considerable variation in total phosphorus and chlorophyll a concentrations. TI exhibits a non-linear distribution along the eutrophication gradient which separates unimpacted from impacted sites in the study area. We further show that TI exhibits smaller seasonal variations than chlorophyll a, making it a more reliable indicator for lake monitoring. Implications for its applicability within the WFD are discussed.     

Diversity of European seagrass indicators: patterns within and across regions

Seagrasses are key components of coastal marine ecosystems and many monitoring programmes worldwide assess seagrass health and apply seagrasses as indicators of environmental status. This study aims at identifying the diversity and characteristics of seagrass indicators in use within and across European ecoregions in order to provide an overview of seagrass monitoring effort in Europe. We identified 49 seagrass indicators used in 42 monitoring programmes and including a total of 51 metrics. The seagrass metrics represented 6 broad categories covering different seagrass organizational levels and spatial scales. The large diversity is particularly striking considering that the pan-European Water Framework Directive sets common demands for the presence and abundance of seagrasses and related disturbance-sensitive species. The diversity of indicators reduces the possibility to provide pan-European overviews of the status of seagrass ecosystems. The diversity can be partially justified by differences in species, differences in habitat conditions and associated communities but also seems to be determined by tradition. Within each European region, we strongly encourage the evaluation of seagrass indicator–pressure responses and quantification of the uncertainty of classification associated to the indicator in order to identify the most effective seagrass indicators for assessing ecological quality of coastal and transitional water bodies.     

An application of canonical correspondence analysis for developing ecological quality assessment metrics for river macrophytes

1. Aquatic macrophyte composition and abundance is required by the European Union's Water Framework Directive for determining ecological status. Five metrics were produced that can be combined to determine the deviation of aquatic macrophytes from reference conditions in Northern Ireland's rivers. 2. Species optima and niche breadths along silt, nitrate, pH, conductivity and dissolved oxygen gradients were generated from aquatic macrophyte and water quality surveys conducted at 273 sites throughout Northern Ireland using Canonical Correspondence Analysis (CCA). Five metric scores based on these environmental gradients were determined at new monitoring sites using the mean optima of the species occurring at the site, weighted by percentage cover and niche breadth of each species. 3. A preliminary reference network of 32 sites of high physico‐chemical and hydromorphological quality, and representative of the range of river types in Northern Ireland, enabled reference metric scores to be produced for each river type. Five unimpacted and twenty impacted sites were used for testing the performance of the metrics. By subtracting reference metric scores from metric scores at a monitoring site measures of ecological impact could be determined along five different impact gradients. Metrics were also combined to give a measure of total ecological change. 4. The metrics system distinguished unimpacted from impacted sites and correctly identified 77% of the known impacts. The metrics distinguished different types of impact, e.g. silt and nitrate. 5. Aquatic macrophyte occurrence and abundance has high natural variability at a site, both temporally and spatially. This method was designed to be sensitive to ecological change whilst reducing noise caused by natural variation.     

A review of dystrophic lake and pool habitat in Europe: An Irish perspective

Freshwater lakes and pools contained within peatlands are unique habitats that support rare and specialised species. Despite this, these ecosystems have been overlooked in conservation and management practices. One of these habitats, ‘3160 Natural dystrophic lakes and ponds’, is protected under the European Union (EU) Habitats Directive with a concerning proportion of these habitats having an “unfavourable-bad” or an “unfavourable-inadequate” conservation status across Europe. Our current understanding of the key physico-chemical and ecological features of this habitat is inadequate which is hindering the implementation of effective conservation measures. This review summarises the current knowledge of this protected lake habitat as defined under the EU Habitats Directive. With a focus on Ireland, we demonstrate how the current monitoring and assessment methods used to characterise and assess the structure and function and conservation status of this habitat, which relies largely on the use of macrophyte community composition and surrogate physico-chemical data collected under the EU Water Framework Directive, is ineffective. We propose the incorporation of further or alternative ecological metrics including, but not limited to, algae and macroinvertebrates which are needed to improve our understanding of the structure and function of this priority lake habitat. In addition, application of such data via ecological metrics would allow for the quantification of biodiversity and species rarity metrics which would aid in identifying sites of conservation importance.     

Tributyltin pollution biomonitoring under the Water Framework Directive: Proposal of a multi-species tool to assess the ecological quality status of EU water bodies

The Water Framework Directive (WFD) is a key legislative action developed by the European Union in order to protect aquatic ecosystems. One of the concerning pollutants, listed in this directive as a priority hazardous substance, is tributyltin (TBT), a biocide largely used in antifouling paints and identified as a causative agent of imposex/intersex in gastropods. In order to integrate TBT pollution monitoring within this legislative framework, a practical exercise is here proposed to assess the evolution of surface water ecological status in Ria de Aveiro (NW Portugal). Three bioindicators – the caenogastropods Nucella lapillus, Nassarius reticulatus and Littorina littorea – were used under the general WFD benthic invertebrate quality element, and the vas deferens sequence index (VDSI) and the intersex index (ISI) were selected as biomarkers for the purpose of assessing the condition of this quality element regarding the impact of TBT pollution. Levels of VDSI in N. lapillus and N. reticulatus, and ISI in L. littorea, were surveyed in 2013 and compared with previous data available for the same species and study area in 1998 and 2005, providing a time lapse for a period of 15 years. VDSI and ISI values were converted into Ecological Quality Ratios (EQR) and EQR boundaries were set for each species in order to define the five ecological status classes (High, Good, Moderate, Poor and Bad). We propose N. lapillus as key bioindicator, however the combined use of further species is very useful to cover a wider study area. Based on the proposed method, it is concluded that the ecological status of the surface waters surveyed in Ria de Aveiro, concerning the impact of TBT pollution on the above benthic invertebrate taxa, improved considerably since 1998 and achieved a Good Ecological Status in 2013, thus meeting the WFD environmental objectives for this priority hazardous substance even before 2015.     

Classifying aquatic macrophytes as indicators of eutrophication in European lakes

Aquatic macrophytes are one of the biological quality elements in the Water Framework Directive (WFD) for which status assessments must be defined. We tested two methods to classify macrophyte species and their response to eutrophication pressure: one based on percentiles of occurrence along a phosphorous gradient and another based on trophic ranking of species using Canonical Correspondence Analyses in the ranking procedure. The methods were tested at Europe-wide, regional and national scale as well as by alkalinity category, using 1,147 lakes from 12 European states. The grouping of species as sensitive, tolerant or indifferent to eutrophication was evaluated for some taxa, such as the sensitive Chara spp. and the large isoetids, by analysing the (non-linear) response curve along a phosphorous gradient. These thresholds revealed in these response curves can be used to set boundaries among different ecological status classes. In total 48 taxa out of 114 taxa were classified identically regardless of dataset or classification method. These taxa can be considered the most consistent and reliable indicators of sensitivity or tolerance to eutrophication at European scale. Although the general response of well known indicator species seems to hold, there are many species that were evaluated differently according to the database selection and classification methods. This hampers a Europe-wide comparison of classified species lists as used for the status assessment within the WFD implementation process.     

A workflow to integrate ecological monitoring data from different sources

Programs and initiatives aiming to protect biodiversity and ecosystems have increased over the last decades in response to their decline. Most of these are based on monitoring data to quantitatively describe trends in biodiversity and ecosystems. The estimation of such trends, at large scales, requires the integration of numerous data from multiple monitoring sites. However, due to the high heterogeneity of data formats and the resulting lack of interoperability, the data integration remains sparsely used and synthetic analyses are often limited to a restricted part of the data available.Here we propose a workflow, comprising four main steps, from data gathering to quality control, to better integrate ecological monitoring data and to create a synthetic dataset that will make it possible to analyse larger sets of monitoring data, including unpublished data.The workflow was designed and applied in the production of the Status of Coral Reefs of the World: 2020 report, where more than two hundred individual datasets were integrated to assess the status and trends of hard coral cover at the global scale. The workflow was applied to two case studies and associated R codes, based on the experience acquired during the production of this report.The proposed workflow allows for the integration of datasets with different levels of taxonomic and spatial precision, with a high degree of reproducibility. It provides a conceptual and technical framework for the integration of ecological monitoring data, allowing for the estimation of temporal trends in biodiversity and ecosystems or to test ecological hypotheses at larger scales.     

Macroinvertebrate and diatom communities as indicators for the biological assessment of river Picentino (Campania,Italy)

Pollution of rivers is an increasing problem that affects biological diversity and structure of natural ecosystem. The present study reported the results of the preliminary analysis of diatom and macroinvertebrate communities of river Picentino (Italy, Campania) in respect of the WFD/60/2000/EC. Because of the sensitive to a variety of environmental factors the two categories of organism are used as excellent indicators of changes taking place in water ecosystems, especially eutrophication. Sampling of benthic diatoms and macroinvertebrates has been carried out in five stations along the river during April–May 2014 in order to apply the ICMi and the STAR_ICMi and assess river quality. The data showed a diversification in diatomic and macroinvertebrate communities in relation to environmental stresses and level of pollution, with the disappearance of species higher sensitive to eutrophication and organic load in the upper course of the river. River water quality was found to deteriorate from the upperstream to the downstream because of the increasing of human impact and the intensive agriculture activity along the river.We conclude that the monitoring of diatomic and macroinvertebrate communities could give detailed information about the ecological status of rivers. However it is necessary to increase the achieved data by monitoring other biological communities in order to define adequated strategies to save and preserve the rivers habitat.     

Assessing eutrophication in the Portuguese continental Exclusive Economic Zone within the European Marine Strategy Framework Directive

This study reports the state and causes of eutrophication in the Portuguese continental Exclusive Economic Zone (EEZ), during a 14-year period (1995–2008), following the European Marine Strategy Framework Directive (MSFD) and using the trophic index TRIX for an integrated evaluation of indicators of eutrophication, and identifies areas where monitoring is needed to improve the eutrophication assessment. A non-continuous dataset for the 8 indicators specified by the MSFD for eutrophication assessment was used, including published and grey data. Eutrophication indicators were validated and thresholds reviewed, considering regional differences. The diatom:flagellate ratio was found a poor indicator of eutrophication as shifts in the diatom:flagellate ratio naturally occur associated with alternating water column turbulence and upwelling, and stratification, and therefore, could not be associated with anthropogenic nutrient enrichment effects. Assessment areas were, as a whole, classified as non-problem areas concerning eutrophication. Although nutrient enrichment was observed in coastal waters, related to river plume influence, nutrient enrichment direct and indirect effects were generally not detectable, possibly due to water column dispersion and mixing processes. Only occasionally, mild eutrophication was found in specific areas under the influence of major river (Douro, Vouga and Guadiana) plumes, associated with high nutrient and phytoplankton biomass levels and seagrass decline, which indicates the need for directed monitoring on eutrophication in those areas.     

An ecological quality status assessment procedure for soft-sediment benthic habitats: Weighing alternative approaches

An assessment procedure for determining the ecological quality status of soft-sediment benthic habitats requires the following aspects: (1) habitat assignation of the samples (habitat approach), (2) reference or target conditions for the benthic parameters (reference approach), and (3) the selection of indicator tools to assess the relative quality status (indicator approach). For all these aspects, different approaches exist, and the indicator selection and reference approaches are largely documented. The aspect of the habitat approach is sometimes neglected, but is essential in determining the reference conditions per habitat type. Benthic habitats differ in structure and function, and as such will show wide variations in statistics or measures between habitats. A major problem, mainly in coastal soft-bottom systems, is to track the deviation lines within data of the different benthic habitat types. This study shows that both a classical community analysis and the use of habitat suitability maps seem to be appropriate tools, but further fine-tuning is necessary. For the second assessment step, an objective assessment of reference conditions is a challenge in areas lacking pristine or minimally disturbed sites, and areas of which historic data are not available. This can be remedied by using a dataset of the area with a good spatial and temporal coverage of the benthic data, thereby avoiding data originating from highly impacted areas. For the third aspect in the assessment procedure, we recommend the use of different indicators with different properties (parameters, algorithms) since it indicates their weaknesses and strengths in the local region.In general, this study showed us that it is valuable to test different existing approaches for EcoQ assessment in a local area, revealing strengths, weaknesses and shortcomings within the assessment regarding data, habitat identification, monitoring strategy, reference settings and indicator use. All these aspects need to be taken into account within an ecological quality status assessment of an area in order to improve its confidence.     

Hierarchical toolbox: Ensuring scientific accuracy of citizen science for tropical coastal ecosystems

Increased human population growth threatens the ecological functioning and goods and services provided by tropical coastal ecosystems. However, a lack of scientific baselines and resources hamper efforts to develop and monitor ecological indicators of environmental change. Citizen science can provide a cost and time effective solution, but needs considerable context specific development to ensure it provides valid information of the quality level required for acceptance by the scientific community. We reviewed the use of sampling methods for shore crabs as an example of an abundant tropical coastal organism with high citizen science suitability and ecological indicator capacity. We propose a hierarchical toolbox based on the distinction between rapid methods, allowing fast, noninvasive sampling by independent citizens, and medium speed methods allowing detailed but more invasive sampling requiring trained citizens working in close interaction with professionals. The hierarchical structure enables full use of the large scale data collection ability of citizen scientists at lower levels, while ensuring validation of errors at higher levels. Additionally, at each level, bias reduction and data validation measures can be employed. We conclude that citizen science methodologies can provide accurate large scale data to develop the ecological baselines urgently needed to monitor and manage environmental change in many tropical coastal ecosystems. We discuss a stepwise implementation of the toolbox leading to accuracy metadata which can be independently reviewed as an ultimate accuracy assessment and data integration mechanism among multiple projects.     

Validation of diatoms as proxies for phytobenthos when assessing ecological status in lakes

Research to develop tools to assess the ecological status of phytobenthos, as required in Annex V of the European Union Water Framework Directive, has focussed largely on diatoms. Diatoms are often the most abundant and diverse group of algae within the phytobenthos and have been used widely for other monitoring purposes. However, there is little empirical justification for the use of diatoms as proxies for the wider phytobenthos. In this paper, we re-examine an existing dataset compiled largely from littoral samples from standing waters in the English Lake District and compared transfer functions for total phosphorus, dissolved inorganic carbon, conductivity and calcium concentration generated from diatoms and non-diatoms separately and together. The results show that transfer functions generated from diatoms alone are as powerful as transfer functions generated from diatoms and non-diatoms combined, while transfer functions generated from non-diatoms alone are less effective. These results provide support for the use of diatoms as proxies for phytobenthos when ecological status is being assessed. Handling editor: J. Saros     

Site-specific chlorophyll reference conditions for lakes in Northern and Western Europe

The Water Framework Directive (WFD) requires EU Member States to assess the “ecological status” of surface waters. As a component of ecological status, many European countries are developing a classification scheme for chlorophyll concentrations as a measure of phytoplankton biomass. The chlorophyll classification must be based on the degree of divergence of a water body from an appropriate baseline or ‘reference condition’. This article describes the development of a series of regression models for predicting reference chlorophyll concentrations on a site-specific basis. For model development, a large dataset of European lakes considered to be in reference condition, 466 lakes in total, was assembled. Data were included from 12 European countries, but lakes from Northern and Western Europe dominated and made up 92% of all reference lakes. Data have been collated on chlorophyll concentration, altitude, mean depth, alkalinity, humic type, surface area and geographical region. Regression models were developed for estimating site-specific reference chlorophyll concentrations from significant predictor ‘typology’ variables. Reference chlorophyll concentrations were found to vary along a number of environmental gradients. Concentrations increased with colour and alkalinity and decreased with lake depth and altitude. Forward selection was used to identify independent explanatory variables in regression models for predicting site-specific reference chlorophyll concentrations. Depth was selected as an explanatory variable in all models. Alkalinity was included in models for low colour and humic lakes and altitude was included in models for low colour and very humic lakes. Uncertainty in the models was quite high and arises from errors in the data used to develop the models (including natural temporal and spatial variability in data) and also from additional explanatory variables not considered in the models, particularly nutrient concentrations, retention time and grazing. Despite these uncertainties, site-specific reference conditions are still recommended in preference to type-specific reference conditions, as they use the individual characteristics of a site known to influence phytoplankton biomass, rather than adopt standards set to generally represent a large population of lakes of a particular type. For this reason, site-specific reference conditions should result in reduced error in ecological status classifications, particularly for lakes close to typology boundaries.