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The European Water Framework Directive (WFD) is one of the most studied environmental legislations and recently turned twenty. The paper deals with a literature search and analysis of 4120 references related to this Directive. After a period of strong increase in article production (2002–2012) WFD scientific productivity is currently still high (~ 260 papers year −1 ), suggesting a persistent interest of the scientific community on this issue. Most research supporting the WFD was on water sciences, but contributions were also from governance and socio-economic disciplines. Studies on biological quality elements and rivers were prominent. The WFD implementation has seen a strong participation of scientists from all EU countries, and partially also from outside-EU nations. To improve the EU water policy and management, the paper suggests a greater interconnection between WFD and other EU Directives and indicates some emerging environmental issues to which the Directive should address.

Coastal and marine management require the evaluation of multiple environmental threats and issues. However, there are gaps in the necessary data and poor access or dissemination of existing data in many countries around the world. This research identifies how remote sensing can contribute to filling these gaps so that environmental agencies, such as the United Nations Environmental Programme, European Environmental Agency, and International Union for Conservation of Nature, can better implement environmental directives in a cost-effective manner. Remote sensing (RS) techniques generally allow for uniform data collection, with common acquisition and reporting methods, across large areas. Furthermore, these datasets are sometimes open-source, mainly when governments finance satellite missions. Some of these data can be used in holistic, coastal and marine environmental management frameworks, such as the DAPSI(W)R(M) framework (Drivers–Activities–Pressures–State changes–Impacts (on Welfare)–Responses (as Measures), an updated version of Drivers–Pressures–State–Impact–Responses. The framework is a useful and holistic problem-structuring framework that can be used to assess the causes, consequences, and responses to change in the marine environment. Six broad classifications of remote data collection technologies are reviewed for their potential contribution to integrated marine management, including Satellite-based Remote Sensing, Aerial Remote Sensing, Unmanned Aerial Vehicles, Unmanned Surface Vehicles, Unmanned Underwater Vehicles, and Static Sensors. A significant outcome of this study is practical inputs into each component of the DAPSI(W)R(M) framework. The RS applications are not expected to be all-inclusive; rather, they provide insight into the current use of the framework as a foundation for developing further holistic resource technologies for management strategies in the future. A significant outcome of this research will deliver practical insights for integrated coastal and marine management and demonstrate the usefulness of RS to support the implementation of environmental goals, descriptors, targets, and policies, such as the Water Framework Directive, Marine Strategy Framework Directive, Ocean Health Index, and United Nations Sustainable Development Goals. Additionally, the opportunities and challenges of these technologies are discussed.

With the implementation of the EU Water Framework Directive (WFD), the member states have to classify the ecological status of surface waters following standardised procedures. It was a matter of some surprise to lake ecologists that zooplankton were not included as a biological quality element (BQE) despite their being considered to be an important and integrated component of the pelagic food web. To the best of our knowledge, the decision of omitting zooplankton is not wise, and it has resulted in the withdrawal of zooplankton from many so-far-solid monitoring programmes. Using examples from particularly Danish, Estonian, and the UK lakes, we show that zooplankton (sampled from the water and the sediment) have a strong indicator value, which cannot be covered by sampling fish and phytoplankton without a very comprehensive and costly effort. When selecting the right metrics, zooplankton are cost-efficient indicators of the trophic state and ecological quality of lakes. Moreover, they are important indicators of the success/failure of measures taken to bring the lakes to at least good ecological status. Therefore, we strongly recommend the EU to include zooplankton as a central BQE in the WFD assessments, and undertake similar regional calibration exercises to obtain relevant and robust metrics also for zooplankton as is being done at present in the cases of fish, phytoplankton, macrophytes and benthic invertebrates.

Monitoring water quality parameters and their ecological effects in transitional waters is usually performed through in situ sampling programs. These are expensive and time-consuming, and often do not represent the total area of interest. Remote sensing techniques offer enormous advantages by providing cost-effective systematic observations of a large water system. This study evaluates the potential of water quality monitoring using Sentinel-2 observations for the period 2018–2020 for the Sado estuary (Portugal), through an algorithm intercomparison exercise and time-series analysis of different water quality parameters (i.e., colored dissolved organic matter (CDOM), chlorophyll-a (Chl-a), suspended particulate matter (SPM), and turbidity). Results suggest that Sentinel-2 is useful for monitoring these parameters in a highly dynamic system, however, with challenges in retrieving accurate data for some of the variables, such as Chl-a. Spatio-temporal variability results were consistent with historical data, presenting the highest values of CDOM, Chl-a, SPM and turbidity during Spring and Summer. This work is the first study providing annual and seasonal coverage with high spatial resolution (10 m) for the Sado estuary, being a key contribution for the definition of effective monitoring programs. Moreover, the potential of remote sensing methodologies for continuous water quality monitoring in transitional systems under the scope of the European Water Framework Directive is briefly discussed.

Phytoplankton constitutes a diverse array of short-lived organisms which derive their nutrients from the water column of lakes. These features make this community the most direct and earliest indicator of the impacts of changing nutrient conditions on lake ecosystems. It also makes them particularly suitable for measuring the success of restoration measures following reductions in nutrient loads. This paper integrates a large volume of work on a number of measures, or metrics, developed for using phytoplankton to assess the ecological status of European lakes, as required for the Water Framework Directive. It assesses the indicator strength of these metrics, specifically in relation to representing the impacts of eutrophication. It also examines how these measures vary naturally at different locations within a lake, as well as between lakes, and how much variability is associated with different replicate samples, different months within a year and between years. On the basis of this analysis, three of the strongest metrics (chlorophyll-a, phytoplankton trophic index (PTI), and cyanobacterial biovolume) are recommended for use as robust measures for assessing the ecological quality of lakes in relation to nutrient-enrichment pressures and a minimum recommended sampling frequency is provided for these three metrics.

The Baltic Sea is suffering from eutrophication caused by nutrient discharges from land to sea, and these loads might change in a changing climate. We show that the impact from climate change by mid-century is probably less than the direct impact of changing socioeconomic factors such as land use, agricultural practices, atmospheric deposition, and wastewater emissions. We compare results from dynamic modelling of nutrient loads to the Baltic Sea under projections of climate change and scenarios for shared socioeconomic pathways. Average nutrient loads are projected to increase by 8% and 14% for nitrogen and phosphorus, respectively, in response to climate change scenarios. In contrast, changes in the socioeconomic drivers can lead to a decrease of 13% and 6% or an increase of 11% and 9% in nitrogen and phosphorus loads, respectively, depending on the pathway. This indicates that policy decisions still play a major role in climate adaptation and in managing eutrophication in the Baltic Sea region.

One of the main challenges in river management is the setting of nutrient thresholds that support good ecological status, which is the main objective to achieve for the European member states. This is a complex process, which needs an accurate analysis of the data collected so far for the ecological classification of rivers belonging to different typologies. We analysed the data of the multiannual monitoring concerning diatoms and nutrients in the upper Po River (NW Italy) with the aim of exploring the response of diatom community in terms of species composition, ecological guilds and indices. We considered data of 390 samples, of which 2/3 belonging to the “Central macrotype” (i.e. lowland stretches) and 1/3 to “Alpine siliceous”. We performed a Principal Coordinate Analysis to detect community patterns with respect to water chemical classification and macrotypes highlighting species and ecological guilds characteristic of samples along a water quality gradient. We then performed a partial RDA to focus on the role of environmental and spatial factors in shaping the diatom community in each of the two macrotypes. Finally, we investigated the concordance between the Italian normative indices ICMi (for diatoms) and LIMECO (a chemical index of water quality). We found significant differences in the diatom communities of the two macrotypes and in their response to water quality and to spatial factors. Communities resulted as much more uniform in sites with a low water quality, with characteristic species such as Navicula gregaria, Nitzschia palea and Sellaphora nigri. On the other hands, moderately disturbed sites (in terms of trophic level) were characterised by the highest guild diversity. The RDA confirmed the importance of spatial factors in shaping the diatom assemblages, especially in Alpine streams where the physical barriers may condition species dispersion. The comparison between the two normative indices highlights that the correspondence in the classification is achieved in the 57% (Alpine macrotype) and 43% (Central macrotype) of samples. According to our findings, we suggest the revision of the ICMi, both class boundaries and reference value. In addition, we recommend to lower LIMECO threshold for total phosphorus: indeed, several studies have shown significant changes in the diatom community composition starting from very low values (below the current LIMECO threshold, i.e. 50 µgL-1). Moreover, the extension of our study to the whole Po River basin will complete our knowledge of species not yet included in the diatom indices and of the community response to nutrient levels also in other macrotypes.

The ability of macrophytes to indicate pressures in rivers was assessed by comparing metrics for nitrate (NO3), ammonia (NH4), soluble reactive phosphorus (SRP), dissolved oxygen saturation (DO), pH (PH) and siltation (SUBS) with direct estimates of the pressures at 810 sites in the Republic of Ireland, supplemented with General Linear Models (GLMs). The bivariate and rank correlation coefficients using the full data range and the first and fourth quartiles of the river pressures varied between 0.22 and − 0.39 for NO3 and DO; they were smaller or not significant for the other four metrics. The GLMs provided evidence for an independent association between NO3 and the nitrate concentration and SUBS and ammonia, indicating some specificity for these metrics. Discriminating sites in the first and fourth quartiles produced Type II errors between 37 (PH) and 69% (NH4), with a mean of 50. As the pressure-impact relationships are not precise enough (low correlation coefficients) that evidence from a single macrophyte metric is reliable, combining the metric with evidence from other biological groups at one site or from three or more sites may be the most useful approach.

The diversity and distribution of polychaetes in the coastal area and the EEZ of the Republic of Cyprus is presented based on both the literature records and new data acquired in a wide range of environmental monitoring programmes and research projects. A total of 585 polychaete species belonging to 49 families were reported in Cyprus waters; among them, 205 species (34%) were recorded based on the literature only, 149 (26%) were new records based on our own data, and a total of 231 spp. (40%) were recorded from both the literature and new data. A total of 51 polychaete species were identified as non-indigenous; among them, 32 were confirmed as alien species, 4 were considered cryptogenic, and 15 were considered questionable as there were doubts about their identity. The Indo-Pacific Schistomeringos loveni was reported for the first time in the Mediterranean Sea, while four species already reported in the literature, namely, Bispira melanostigma, Fimbriosthenelais longipinnis Leonnates aylaoberi, and Rhodopsis pusilla, were added to the list of non-indigenous polychaetes in the Mediterranean Sea. The current work highlights the importance of implementing environmental monitoring programmes and carrying out research surveys targeting benthic macrofauna assemblages.

A small standing-water ecosystem (SWE) is a shallow (<20 m) lentic water body with a surface of a few hectares (≤10 ha). Compared to larger counterparts, they exhibit wider ecotones, sometimes even equaling their whole surface, which maximizes structural heterogeneity, supporting exceptionally high biodiversity, metabolic rates, and functionality. Surprisingly, no binding regulations support global strategies for SWE conservation. This work consists of a literature review performed for the period 2004–2018 to assess the ecological and conservation value of SWEs and the contribution of the Water Framework Directive (WFD) in promoting their conservation. Outcomes from this work open new perspectives on SWEs, which emerge as valuable ecosystems, and confirm their pivotal contribution to watershed biodiversity, resilience, and functionality. Results also suggest clear narrative trends and large knowledge gaps across geographical areas, biological components, and target issues. Additionally, we note that SWEs are under-represented in the frame of WFD implementation, stressing their marginality into assessing procedures. All of this calls for further studies, especially outside Europe and with a global, multi-taxon perspective. These should be devoted to quantitatively assess the roles of SWEs in maintaining global water ecosystem quality, biodiversity, and services, and to prioritize management actions for their conservation.