European aquatic ecological assessment methods: A critical review of their sensitivity to key pressures

Abstract

The European Union has embarked on a policy which aims to achieve good ecological status in all surface waters (i.e. rivers, lakes, transitional and coastal waters). In theory, ecological status assessment methods should address the effects of all relevant human pressures. In this study, we analyze the degree to which methods European countries use to assess ecological status tackle various pressures affecting European waters. Nutrient pollution is by far the best-covered pressure for all four water categories. Out of total of 423 assessment methods, 370 assess eutrophication and pressure-specific relationships have been demonstrated for 212 of these. “General degradation” is addressed by 238 methods, mostly validated by relationships to combined pressure indices. Other major pressures have received significantly less effort: hydromorphological degradation is assessed by 160 methods and pressure-specific relationships have been demonstrated for just 40 of these. Hydromorphological pressures are addressed (at least by one BQE) only by 25% countries for coastal waters and 70–80% for lakes and transitional waters. Specific diagnostic tools (i.e. single-pressure relationships) for hydromorphology have only been developed by a few countries: only 20% countries have such methods for lakes, coastal and transitional waters and less than half for rivers. Toxic contamination is addressed by 90 methods; however, pressure-specific relationships have been demonstrated for just eight of these. Only two countries have demonstrated pressure-specific acidification methods for rivers, and three for lakes. In summary, methods currently in use mostly address eutrophication and/or general degradation, but there is not much evidence that they reliably pick up the effects of other significant pressures such as hydromorphology or toxic contamination. Therefore, we recommend that countries re-examine: (1) those pressures which affect different water categories in the country; (2) relevant assessment methods to tackle those pressures; (3) whether pressure-response relationships have been developed for each of these.

Benthic Diatoms in River Biomonitoring—Present and Future Perspectives within the Water Framework Directive

“…Phytobenthos seems to overestimate the ecological status, classifying more than 70% of water bodies to good and high status, whereas fish seem to be the strictest BQE and thus the most influential to the ecological status due to the one-out/all-out principle (Figure 2). This observation does not diminish the importance of benthic diatoms as suitable bioindicators, but could be related to many different types of pressures in water bodies [63], such as long-term hydrological and habitat alterations to which other BQEs respond better. However, it could also be attributed to naturally poor habitats, where other BQEs are poorly represented [7].…”

Assessment of the Pressure Level over Lentic Waterbodies through the Estimation of Land Uses in the Catchment and Hydro-Morphological Alterations: The LUPLES Method

“…Sites with high pressure levels where those with poorer values of indicators of bad ecological status (such as chl-a concentration), also showing lower values of indicators of good ecological status (such as the benthic invertebrate EQR), which indicates the clear relationship between the pressures quantified by our method and their associated impacts on the biological communities. The response of the biological indicators to the pressures assessed by the LUPLES method was studied by the BQE, defined in the WFD, which is already intercalibrated and used at the European level [62,63], using the normalized values (EQR) to allow the comparison of the assessed impact, regardless the metric used.…”

“…Macrophytes, however, are also used as indicators of the impacts caused by hydrological and morphological pressures, and their coverage is used as a metric of the ecological status for the BQE "other aquatic flora" [43]. Considering the relevance of the hydro-morphology of the waterbody for the status of macrophyte communities [19], the identification of hydrological and morphological pressures is key for ecological status assessments [63]. This is even more important in Mediterranean waterbodies due to the higher levels of hydrological stress [43].…”

Assessing the Ecological Status of European Rivers and Lakes Using Benthic Invertebrate Communities: A Practical Catalogue of Metrics and Methods

“…A significant challenge for ESC assessment is the combination of multiple stressors, that all exert-in function of their combination and magnitude-distinct roles in different habitats [58,59]. In addition to this challenge, many of the currently used ESCATs lack information on stressor-response relationships, and thus may fail to identify stressors, or accurately rank stressor importance [59,60]. This is particularly true for rapidly applied modules and metrics with a long history of use and impedes designing and implementing best management measures.…”