Search

Development of effective methods for assessing the ecological status of lakes based on littoral benthic fauna has been hampered by the lack of quantitative data on the relative impacts of key pressures on the benthic community. We used variance partitioning at 126 sites belonging to 14 natural Mediterranean lakes to analyze the pure and shared effects of eutrophication, morphological alterations, microhabitat type, lake morphometry and geographic position on the littoral macroinvertebrate community. The spatial arrangement of the sampling sites was responsible for 9.1% of the total variance in littoral benthic community composition, lake morphometry accounted for 4.3% of variation, and microhabitat type accounted for 3.9%. Communities appeared to be affected primarily by morphological alterations to lake shorelines, and their impact was 2.5 times as important as that of eutrophication. The structure of littoral benthic communities was governed by processes acting at several spatial scales from region to lake scale. Thus, several pressures and the various spatial scales at which these act should be taken into account when implementing methods of assessing lake ecological condition based on littoral benthic invertebrates. Region-specific methods for subalpine and volcanic lakes might enhance the validity of assessment of results of morphological alterations and improve management of those water resources.

The assessment of the impacts of human morphological alterations on lake ecological condition based on littoral benthic fauna is still in its infancy, especially in the Mediterranean area of Europe. Lake Piediluco is a riverine lake, sited in Central Italy, whose water level is strictly regulated for hydroelectric reasons and hence can be classified as a Heavily Modified Water Body (HMWB) according to the E.U. Water Framework Directive (WDF). Here, we aim at comparing the invertebrate assemblages among sites with a different degree of morphological alterations by identifying potential indicator species and metrics sensitive to morphological alterations, and by comparing the fauna composition collected using two sampling procedures (composite vs habitat-specific samples) with different processing times. Our results show that the invertebrate assemblages of Lake Piediluco differed according to the three types of shoreline alteration (natural, soft- and hard-altered sites) and this was more evident when we analyzed the habitat-specific samples. Several taxa, diversity and metrics based on the number of Ephemeroptera, Trichoptera, Odonata and Mollusca taxa (ETO and ETOM) are found to be sensitive to shoreline alterations and are candidates for inclusion in assessment metrics for WDF compliant monitoring of the ecological status of this lake. While habitat-specific sampling provided a more detailed picture of the assemblages, composite samples provided consistent results and could be used when processing cost is an issue.

The Water Framework Directive is the first international legislation to require European countries to establish comparable ecological assessment schemes for their freshwaters. A key element in harmonising quality classification within and between Europe’s river basins is an “Intercalibration” exercise, stipulated by the WFD, to ensure that the good status boundaries in all of the biological assessment methods correspond to similar levels of anthropogenic pressure. In this article, we provide a comprehensive overview of this international comparison, focusing on the assessment schemes developed for freshwater lakes. Out of 82 lake ecological assessment methods reported for the comparison, 62 were successfully intercalibrated and included in the EC Decision on intercalibration, with a high proportion of phytoplankton (18), macrophyte (17) and benthic fauna (13) assessment methods. All the lake assessment methods are reviewed in this article, including the results of intercalibration. Furthermore, the current gaps and way forward to reach consistent management objectives for European lakes are discussed.

Implementation of the EU Water Framework Directive (WFD) has drawn much attention to hydromorphological alterations of surface waters. The Lake Habitat Survey (LHS) protocol provides a method for characterising and assessing the physical habitats of lakes and reservoirs. Two metrics were developed based on this method: the Lake Habitat Modification Score (LHMS) and the Lake Habitat Quality Assessment (LHQA), as measures of lake modification and habitat value, respectively. However, the use of these metrics to predict measures of ecological quality remains largely untested. Thus, we assessed the relationships between LHS metrics and the littoral macroinvertebrate community in 42 lakes across Europe. A significant relationship was found between littoral macrophyte descriptors and riparian natural land cover variables of the LHQA score and macroinvertebrate community composition in 2 out of 4 European regions. No relationship was found between macroinvertebrate community composition and the LHMS. Some significant correlations were found between selected macroinvertebrate metrics and the LHS scores, but this pattern was not consistent across regions, and no relationship was found with the overall LHMS or LHQA scores. This demonstrates that the LHS metrics do not consistently predict the quality of littoral macroinvertebrate communities across Europe, and a region specific approach may be necessary. However, we could demonstrate a relationship between the site specific LHS variables and the macroinvertebrate community at the site level, and in some cases at the regional level. Therefore, although the LHS metrics do not appear to be a useful for relating habitat quality and pressure to littoral macroinvertebrate communities, selected LHS variables may exhibit stronger relationships with the biota.

Invertebrate communities inhabiting different lake zones are expected to respond differently to natural environmental variation and anthropogenic stressors. We used multivariate statistical methods in order to quantify the effects of eutrophication and morphological pressures on the spatial structure of the invertebrate benthic communities at two depth zones (profundal and sublittoral) in subalpine lakes in Italy, Germany and Austria . In both lake zones, environmental variables related to eutrophication pressures (mid-lake total phosphorus and chlorophyll-a) were significant in structuring the invertebrate community (permutation test: p < 0.01). Three variables relating to morphological pressures (diversity of macrophyte growth forms, sum of pressures in the lake shore, and percentage of natural land cover within a 200 m stretch from the lake shore) were significant (permutation test: p < 0.01) in the sublittoral zone, while in the profundal zone none of the variables included in the analysis related to morphological pressures were significant in structuring the invertebrate community. Variance partitioning analysis showed that profundal communities were mainly affected by eutrophication (8.6 % of total variance; p = 0.005), while in the sublittoral zone eutrophication accounted for only 0.5 % (p = 0.04) of total variance. The effects of morphological pressures could be tracked only in the sublittoral zone, where it accounted for 0.8 % of total variance (p = 0.015). The spatial component was responsible for a large part of the total variance (58.7 % in the profundal, p = 0.005; 44.2 % in the sublittoral zone, p = 0.005) and had interactions with stressor variables in both lake zones. Therefore the analysis of spatial patterns should be included in assessment systems relating invertebrate assemblages to pressures.