Elaboration d’une méthodologie d’évaluation de la qualité écologique des petits plans d’eau

Development of a biological method to assess the Swiss pond ecological quality

Contexte de la recherche, objectifs du projet

The ecological assessment of the aquatic environment is in the focus of current concerns aiming at the monitoring of the ecological quality of surface waters. Standardized methods for ecological assessment exist concerning running waters (e.g.: biotic indices, physico-chemical measurements) and lakes (e.g.: indices "Oligochaetes", measurement of Phosphorus concentrations), but they do not apply in the specific context of small standing water bodies (cf Binderheim-Bankay 1998, Williams et al. 1998).The biological methods existing for running waters or for lakes are based upon the indications given by taxa (taken separately or grouped), such as: diatoms, macrophytes, invertebrates identified at various taxonomic levels and used individually (Oligochaeta, Chironomidae), or in combination (EPT taxa), fish. Recent approaches use "multi-metric" indices (cf Karr & Chu, 1999), and offer new prospects for the monitoring. They allow comparisons between the investigated sites and reference sites. This approach was chosen by Pond Action (2000) for the development of an original method for the assessment of small standing water bodies; however this method still remains restricted to Great Britain (Biggs, comm. pers. 2000).

The recent work carried out on 146 small standing water bodies in Switzerland or sampled during this work (Antoine, 2002 ; Auderset-Joye et al., 2002; Castella-Müller, 2004; ; Hafner, 2006; ; Hinden, 2004 ; Indermuehle et al., in prep.; Oertli and al., 2000, 2003; Ott, unpublished; Rimann, 2001) provides a database to identify and test metrics to be integrated into an ecological assessment method. Among the metrics, it could be included richness, taxonomic, intolerance to human degradation, conservation values, or biological/ecological traits metrics. Relating the metric to the state of degradation of the ponds (reflected through 7 parameters based on plant communities, land use, and the trophic state), it would be possible to develop a specific method to assess pond ecological quality. The index in elaboration will be particularly attractive for managers, especially for its replicated sampling design, its facility of use in routine biomonitoring, and the reduced cost of field and laboratory analyses.

Main steps or objectives:

1. To identify the needs of the "end-users" (federal and cantonal administrations).
2. To inventorise all potentially usable metrics (literature search, analysis of the available database, external contacts).
3. According to the metrics selected, to bridge the gaps in the database by sampling of selected ponds (field and laboratory work).
4. To rank the documented water bodies from our database according to their degree of degradation (measurable by parameters based on plant communities, land use, and the trophic state).
5. To develop a standardized method for the evaluation of the ecological quality (stage to be carried out in close cooperation with the "end-users" (cantonal and federal administrations).
6. To test the selected metrics on an external dataset (Switzerland and France).

Mots-Clés

Ecological quality, water quality, multi-metric index, macrophytes, macroinvertebrates, biomonitoring, small waterbodies, ponds, Swiss legal basis, European Water Framework Directive, human degradations.

Financement

• LEBA, Université de Genève
• Bourse Augustin Lombard de la « Société de physique et d’histoire naturelle de Genève » (SPHN)
• Office cantonal de l’environnement et de l’énergie du canton de Lucerne
• Services d’hydrobiologie des cantons de Genève et Vaud
• « Centre d’analyse minérale des Sciences de la Terre », Université de Lausanne
• Département de limnologie de l’Institut fédéral suisse des sciences et technologies de l’eau (EAWAG) de Dübendorf
• Office fédéral de l’environnement (OFEV), Berne

Synthèse des principaux résultats

Macroinvertébrés (thèse N. Menetrey).

Titre de la recherche: Development of a biological method to assess the Swiss pond ecological quality.

A) Abstract of: Menetrey, N.*, B. Oertli, and J. B. Lachavanne. 2011. 

The CIEPT: A macroinvertebrate-based multimetric index for assessing the ecological quality of Swiss lowland ponds.

Ecological Indicators 11: 590–600:

*Corresponding author: nathalie.menetrey(at)gmail.com

• Since ponds are limnologically different from rivers and lakes, and as there is a lack of specific methods to assess their ecological quality, we developed a method to assist managers in routine biomonitoring of ponds. For this work, a total of 36 lowland permanent ponds was selected from an existing dataset of 134 Swiss ponds that were classified along a gradient from reference to degraded sites. Site degradation was characterized by seven variables indicative of pond ecological condition: (i) one descriptor of plant communities (macrophyte species richness); (ii) one descriptor of trophic state (total phosphorus and total nitrogen (PN)), and (iii) five anthropogenic stressors linked to land use (percentage of semi-natural areas within a 50-m radius of the site, connectivity with other wetlands within 1 km, percentage of agricultural activities and pastures in the pond catchment, and dominant land use in terms of surface area).
• A total of 55 potential macroinvertebrate and amphibian metrics were tested to assess their relationship to site degradation. The metrics were based on taxonomic richness (total and selected macroinvertebrate groups), intolerance of degradation, conservation values, and biological/ecological traits. The selection of the metrics to be integrated into the index followed a stepwise procedure. To be selected, a metric had to fulfil four criteria. It must have: 1) a significant relationship with at least one of the seven indicators of pond ecological condition; 2) the ability to discriminate between reference and degraded sites; 3) a Relative Scope of Impairment inferior to 1 (low inherent variability of a metric); 4) no redundancy with other metrics used in the index. To produce the index, 18 combinations of selected metrics were tested.
• The final index (CIEPT) was built using three metrics: genera richness of Coleoptera (C), macroinvertebrate family richness (I), and Ephemeroptera, Plecoptera and Trichoptera (EPT) family richness. The CIEPT responded significantly to pond ecological condition and was tested successfully with an external dataset to confirm suitability. The CIEPT Index could be a useful and relatively low cost tool to assist site managers in assessing the ecological quality of ponds.

B) Abstract of: Menetrey, N., B. Oertli, M. Sartori, A. Wagner & J. B. Lachavanne. 2008. Eutrophication: are mayflies (Ephemeroptera) good bioindicators for ponds? Hydrobiologia 597: 125-135:

• Ephemeroptera larvae are recognized worldwide for their sensitivity to oxygen depletion in running waters, and are therefore commonly used as bioindicators in many monitoring programs. Mayflies inhabiting lentic waters, like lakes and ponds, have in contrary been poorly prospected in biomonitoring. For this purpose, a better understanding of their distribution in lentic habitats and of the relations of species presence with environmental conditions are needed.
• Within this framework, 104 ponds were sampled in Switzerland. The Ephemeroptera are found to be an insect order particularly well represented in the ponds studied here (93 % of the lowland ponds). Nevertheless, in terms of diversity, they are relatively poorly represented (mean species number = 1.9). Two species dominated: Cloeon dipterum (Baetidae) and Caenis horaria (Caenidae). The investigations contributed to the updating of the geographical distribution of the species in Switzerland, as many of the observations appear to be from new localities.
• The trophic state of ponds appears here to be important for Ephemeroptera communities. Firstly, there is a negative relationship between total phosphorus concentrations and species richness. Secondly, the presence of Caenis horaria or Cloeon dipterum is dependent on the trophic state. Caenis horaria is most closely associated with low levels of total phosphorus concentrations, while Cloeon dipterum appears to be less sensitive, and is most frequently found in hypertrophic conditions. A probable consequence of these relations, is that Baetidae are always present when Caenidae are also present. Contrastingly, Baetidae is observed as the only mayflies family present in several ponds.

C) Abstract of: Menetrey, N., L. Sager, B. Oertli, J.-B. Lachavanne (2005). Looking for metrics to assess the trophic state of ponds. Macroinvertebrates and amphibians. Aquatic Conservation: Marine and Freshwater Ecosystems 15: 653-664:

• Ponds are particularly rich habitats and play an essential role in the conservation of aquatic biodiversity. Therefore it is necessary to develop a specific method for evaluating their biological integrity, and particularly their water quality. Metrics have been proven to be efficient for studies on running waters. Such an approach would be particularly useful for ponds and thus needs to be tested.
• Eight metrics based on the richness of invertebrates and amphibians and 73 others derived from the biological/ecological trait categories linked to Coleoptera, Odonata and Gastropoda were tested for their potential as indicators of the trophic state of 94 ponds in Switzerland. The relationships between these metrics and the state of water eutrophication were explored.
• Four metrics based on richness responded to excessive nutrient levels in the colline vegetation belt. These were: aquatic Coleoptera species richness; the pooled species richness of aquatic Coleoptera, aquatic Gastropoda, adult Odonata and Amphibians (COGA); the family-level richness of macroinvertebrates and the family-level richness of the combined Megaloptera and Odonata groups (MO). On the other hand, at altitudes above 800m (i.e. montane-subalpine and alpine vegetation belts), two to four other metrics were identified as pond water quality indicators.
• Furthermore, many trait categories were sensitive to excessive nutrient levels. In the colline belt, 13 out of the 33 metrics derived from the biological/ecological traits responded to an increase of the trophic state (i.e. at least one metric for each of the three invertebrate groups tested). However, the patterns of the relationships are unclear and further investigations are required to identify and select the relevant metrics for an assessment of the water quality.
• In conclusion, for the future assessment of pond quality, four metrics derived from richness could be taken into consideration. Nevertheless, further investigations are required to identify the biological/ecological traits that could be combined with these richness metrics.

Plantes aquatiques (thèse L. Sager).

Titre de la recherche: Elaboration d’une méthodologie d’évaluation de la qualité écologique des petits plans d’eau basée sur la végétation