Strength and uncertainty of phytoplankton metrics for assessing eutrophication impacts in lakes

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

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

Performance de l'Indice Phytoplancton Lacustre (IPLAC) : un indice phytoplancton multimétrique pour évaluer l'état écologique des plans d'eau en France

International audienceA new phytoplankton-based index was designed to respond to the Water Framework Directive (WFD) requirements concerning the assessment of lake ecological status. The 'Indice Phytoplancton Lacustre' (IPLAC) is a multimetric index, taking into account biomass, abundance and species composition of communities. The first metric is based on the total phytoplankton biomass (MBA), the second on the abundance and taxonomic composition (MCS) of 165 indicator taxa. The IPLAC was developed on 2 independent databases, one for the calibration and the second for the validation of the metrics. The calibration dataset was composed of 255 'lake-years' from 214 distinct lakes sampled between 2005 and 2012. The validation dataset included 173 lake-years in order to confirm the response of the index to the trophic gradient and anthropogenic pressure. The results show that the IPLAC correctly highlights chemical pressure (eutrophication). Especially high Pearson correlations are shown with total phosphorus (r = -0.71, p-valu

Recherches en écologie végétale appliquées au lacs du littoral aquitain

National audiencePrésentation des activités de recherche de l'équipe CARMA d'Irstea (EABX) en écologie végétale appliquées aux lacs du littoral aquitain. L'écologie des végétaux aquatiques et le fonctionnement des lacs aquitains, les communautés algales, l'échantillonnage passif du phosphore et les communautés de macrophytes aquatiques seront présentés

Des applications informatiques pour faciliter l'acquisition des données Macrophytes dans les réseaux de surveillance des masses d'eau continentales

International audienceLes macrophytes ont été reconnus élément de qualité biologique mais, pour exploiter au mieux les informations qu'ils fournissent, il convient de mettre en place des outils performants. Quels choix techniques ont été retenus pour rendre ces données les plus pertinentes possibles

Les écosystèmes lacustres, dynamique naturelle au long cours et interactions avec les activités humaines

National audiencePrésentation de quelques éléments d'analyse de l'évolution des plans d'eau du littoral aquitain vis-à-vis du changement climatiqu

Local distribution of macrophytes and consequences for sampling methods in large rivers

During the years 2003 and 2004, the distribution of macrophytes was studied at eight sites in two large rivers in the southwest of France (the Dordogne and Garonne). Using a pinpoint method, we obtained 7,083 observations and recorded physical parameters such as depth, distance from bank, water velocity, and substrate type. By using logistic regressions, we showed that a combination of these factors significantly influences the distribution of macrophytes. This enabled us to highlight transversal distribution patterns. Helophyte spermatophytes, free-floating taxa, and most of the nonanchored algae were characteristic of the shallow areas located near the banks. The deepest areas were characterized by a reduced number of species with a majority of submerged spermatophytes which are resistant to high velocity, anchored algae, and bryophytes. These results can be used to implement the Macrophyte Biological Index for Rivers (IBMR) for large rivers

Un système opérationnel de surveillance et d'alerte des proliférations de cyanobactéries : application aux plans d'eau landais

International audienceThe large lakes of the Landes have bathing areas regularly monitored for public health by the environmental services of the community of municipalities of the great lakes (CCGL) and the community of municipalities of Mimizan (CCM). Regulation impose biological monitoring, and especially for cyanobacteria, as they are potentially toxic to humans (due to cyanotoxins production). Nevertheless, analyses are carried out in laboratory and generate a delay of response of at least 36 hours damaging to sanitary safety and leading to important costs. The work carried out between Irstea Bordeaux and the communities of municipalities proposed to reduce the delay of response and to limit the costs by modifying the monitoring and alert decision tree with the use of a fluorimetric field probe. The adapted decision tree is based on thresholds of cyanobacteria quantities expressed in chlorophyll-a equivalent, instead of the number of counted cells usually practiced. It provides at least the same safety level and is, sometimes, more precautionary. This work enables managers to implement a monitoring and alert protocol for cyanobacteria based on the use of the fluorimetric probe during summers.Les grands plans d'eau landais accueillent des zones de baignade, surveillées régulièrement pour des raisons de santé publique par les services chargés de l'environnement de la communauté de communes des grands lacs (CCGL) et de la communauté de communes de Mimizan (CCM). La règlementation y impose une surveillance biologique, comportant le suivi des cyanobactéries productrices éventuelles de cyanotoxines toxiques pour l'homme. Néanmoins, les analyses sont réalisées en laboratoire et comportent un délai de réponse d'au moins 36 heures, dommageable à la sécurité sanitaire et entraînant des couts financiers élevés. Le travail mené conjointement par Irstea Bordeaux et les communautés de communes permet de proposer une réduction du temps de réponse et une limitation des couts, en modifiant l'arbre décisionnel règlementaire de surveillance et d'alerte grâce à l'usage d'une sonde fluorimétrique de terrain. L'arbre décisionnel a été réadapté et validé avec des seuils de quantité de cyanobactéries exprimés en équivalent de chlorophylle-a, au lieu du dénombrement de cellules habituellement pratiqué. Il assure à minima le même niveau de sécurité sanitaire et s'avère, dans certains cas, plus protecteur que le protocole règlementaire. Ces résultats permettent aux gestionnaires la mise en ½uvre d'un protocole de surveillance et d'alerte des cyanobactéries basé sur l'utilisation d'une sonde fluorimétrique au cours des saisons estivales

Avantages et limites de l'intercalibration de méthodes d'évaluation phytoplanctoniques basée sur l'expérience des réservoirs du GIG méditerranéen

International audienceThe status of European legislation regarding inland water quality after the enactment of the Water Framework Directive (WFD) originated scientific effort to develop reliable methods, primarily based on biological parameters. An important aspect of the process was to ensure that quality assessment was comparable between the different Member States. The Intercalibration process (IC), required in the WFD ensures the unbiased application of the norm. The presented results were developed in the context of the 2nd IC phase. An overview of the reservoir type definition of the Lake Mediterranean Geographical Intercalibration Group, where four types were considered divided by both alkalinity and climate, together with the results for selection of Maximum Ecological Potential sites (MEP) are presented. MEP reservoirs were selected based on pressure and biological variables. Three phytoplankton-based assessment methods were intercalibrated using data from Mediterranean countries. The Mediterranean Assessment System for Reservoirs Phytoplankton (Spain), the New Mediterranean Assessment System for Reservoirs Phytoplankton (Portugal and Cyprus) and the New Italian Method (Italy) were applied. These three methods were compared through option 3 of the Intercalibration Guide. The similarity of the assessments was quantified, and the Good/Moderate (GM) boundaries assessed. All three methods stood as comparable at the GM boundary except for the MASRP in siliceous wet reservoirs, which was slightly stricter. Finally, the main taxonomic groups represented in the phytoplankton community at MEP conditions were identified, as well as their main changes with an increasing trophic status. MEP sites are dominated by chrysophytes in siliceous wet reservoirs and by the diatoms Cyclotella and Achnanthes in calcareous ones. Cyanobacteria take over the community in both calcareous and siliceous wet reservoirs as eutrophication increases. In summary, the relevance and reliability of the quality assessment methods compared were confirmed both from an ecological perspective and a health risk management point of view