Best practice for establishing nutrient concentrations to support good ecological status

The EU Member States, Norway and the European Commission in 2000 have jointly developed a common implementation strategy (CIS) for implementing Directive 2000/60/EC, the Water Framework Directive (WFD) to ensure consistent implementation. The focus is on developing a common understanding of the technical and scientific implications of the WFD. One of the objectives is the development of non-legally binding and practical Guidance Documents on various technical issues of the Directive. These are targeted at experts who are directly or indirectly implementing the WFD in river basins. The structure, presentation and terminology are therefore adapted to their needs and formal, legalistic language is avoided wherever possible. In 2009 CIS Guidance on Eutrophication Assessment (Guidance Document No. 23) was published, providing guidance for evaluating the impacts of nutrient enrichment, a major cause of failure to achieve good status under the WFD. However, an apparently wide range of nutrient boundary values to support good ecological status had been established by the Member States. Water Directors requested that the CIS Working Group ECOSTAT investigate this issue, and the subsequent work has been led by the UK (Freshwaters), Germany (Saline waters) and JRC. The aim of the work was to establish the reasons for differences between Member States in the development and application of nutrient boundaries, leading to the production of this guidance on best practice. This work is an addition to, and not a replacement for, the earlier guidance on eutrophication assessment. In developing this guidance, a number of tasks have been undertaken. The range of nitrogen and phosphorus boundary values in use by Member States, and the methods used to derive those values has been reported separately, for both fresh and saline waters. Further work was undertaken to investigate nutrient pressure-biological response relationships in the different surface water categories. This work was then used to inform the development of this guide and the associated statistical toolkit. During the project a series of workshops were held involving nutrient experts nominated by Member States. These experts contributed to the development and testing of the guidance and toolkit, and provided details of alternative methods of boundary setting in use in some Member States. The purpose of this report is to provide technical guidance to enable Member States to establish new, or review existing, boundaries for phosphorus and nitrogen to support good ecological status. This should facilitate the establishment of comparable and consistent boundaries across all Member States. However it is recognised that alternative methods of arriving at boundary values may be valid, and use of this guidance and the associated statistical toolkit is ultimately a decision for the Member State. The responses of biological elements to nutrient availability are complex, and vary between water categories. This guidance is not therefore a substitute for the application of ecological knowledge and understanding at a local level. Furthermore, responses to nutrients may be confounded by the impact of other pressures acting on a water body, and our understanding of how to account for multiple stressors is still developing. The guidance does not specifically address how the nutrient boundaries are used to derive an overall classification, or to drive action to control nutrients, both of which may be relevant to the level at which the boundaries are set.JRC.D.2-Water and Marine Resource

Making waves. Bridging theory and practice towards multiple stressor management in freshwater ecosystems

Embargo until February 26, 2023Despite advances in conceptual understanding, single-stressor abatement approaches remain common in the management of fresh waters, even though they can produce unexpected ecological responses when multiple stressors interact. Here we identify limitations restricting the development of multiple-stressor management strategies and address these, bridging theory and practice, within a novel empirical framework. Those critical limitations include that (i) monitoring schemes fall short of accounting for theory on relationships between multiple-stressor interactions and ecological responses, (ii) current empirical modelling approaches neglect the prevalence and intensity of multiple-stressor interactions, and (iii) mechanisms of stressor interactions are often poorly understood. We offer practical recommendations for the use of empirical models and experiments to predict the effects of freshwater degradation in response to changes in multiple stressors, demonstrating this approach in a case study. Drawing on our framework, we offer practical recommendations to support the development of effective management strategies in three general multiple-stressor scenarios.acceptedVersio

Defining Chlorophyll-a Reference Conditions in European Lakes

The concept of “reference conditions” describes the benchmark against which current conditions are compared when assessing the status of water bodies. In this paper we focus on the establishment of reference conditions for European lakes according to a phytoplankton biomass indicator—the concentration of chlorophyll-a. A mostly spatial approach (selection of existing lakes with no or minor human impact) was used to set the reference conditions for chlorophyll-a values, supplemented by historical data, paleolimnological investigations and modelling. The work resulted in definition of reference conditions and the boundary between “high” and “good” status for 15 main lake types and five ecoregions of Europe: Alpine, Atlantic, Central/Baltic, Mediterranean, and Northern. Additionally, empirical models were developed for estimating site-specific reference chlorophyll-a concentrations from a set of potential predictor variables. The results were recently formulated into the EU legislation, marking the first attempt in international water policy to move from chemical quality standards to ecological quality targets

Quantitative responses of lake phytoplankton to eutrophication in Northern Europe

Based on the currently largest available dataset of phytoplankton in lakes in northern Europe, we quantified the responses of three major phytoplankton classes to eutrophication. Responses were quantified by modelling the proportional biovolumes of a given group along the eutrophication gradient, using generalized additive models. Chlorophyll-a (Chl-a) was chosen as a proxy for eutrophication because all classes showed more consistent responses to Chl-a than to total phosphorus. Chrysophytes often dominate in (ultra-) oligotrophic lakes, and showed a clear decrease along the eutrophication gradient. Pennate diatoms were found to be most abundant at moderate eutrophication level (spring-samples). Cyanobacteria often dominate under eutrophic conditions, especially in clearwater lakes at Chl-a levels >10 μg l−1 (late summer samples). We compare the relationships among types of lakes, based on the lake typology of the northern geographic intercalibration group, and among countries sharing common lake types. Significant differences were found especially between humic and clearwater lakes, and between low- and moderately alkaline lakes, but we could not identify significant differences between shallow and deep lakes. Country-specific differences in response curves were especially pronounced between lakes in Norway and Finland, while Swedish lakes showed an intermediate pattern, indicating that country-specific differences reflect large-scale geographic and climatic differences in the study area

Chlorophyll Reference Conditions for European Lake Types used for Intercalibration of Ecological Status

The Water Framework Directive (WFD), requires European Member States to assess the “ecological status” of surface waters. As part of this, many European countries have developed an ecological quality classification scheme for chlorophyll concentrations as a measure of phytoplankton abundance. The assessment of ecological quality must be based on the degree of divergence of a water body from an appropriate baseline, or ‘reference condition’. It is, therefore, necessary to determine chlorophyll reference conditions for all European lake types. This involves examining how chlorophyll concentrations vary by lake type, in the absence of any nutrient pressures from agriculture or wastewater. For this purpose, a dataset of 540 European lakes considered to be in a relatively undisturbed reference condition has been assembled, including data on chlorophyll concentration, altitude, mean depth, alkalinity, humic content, surface area, and geographical region. Chlorophyll was found to vary with lake type and geographical region, and was found to be naturally highest in low-altitude, very shallow, high alkalinity and humic lake types and naturally lowest in clear, deep, low alkalinity lakes. The results suggest that light and mineral availability are important drivers of chlorophyll concentrations in undisturbed lakes. Descriptive statistics (median and percentiles) of chlorophyll concentrations were calculated from populations of lakes in this reference lake dataset and used to derive lake-type specific reference chlorophyll concentrations. These reference conditions can be applied, through a comparison with observed chlorophyll concentrations at a site, in the assessments of ecological status and provide a consistent baseline to adopt for European countries