Loïc Tudesque

Benthic diatoms in Western European streams with altitudes above 800 m: characterisation of the main assemblages and correspondence with ecoregions

High altitude rivers in European mountains show a large diversity of benthic diatom assemblages. Diatoms were studied from rivers of the Alps, the Pyrenees, the Massif-Central and the Iberic system. The study area spread across four countries, Italy, France, Switzerland and Spain. Since 2000, the European Water Framework Directive (WFD) has required the assessment of stream quality using bioindicators and any deviation from reference conditions measured. References for each river type and for each bioindicator, such as diatoms, are in the process of being defined. System A is a typological system proposed by the WFD, in which ecoregions spread over several countries were defined. The first aim of this study was to assess the importance of these ecoregions for diatoms compared to other environmental factors. To reduce the heterogeneity of the diatom assemblages due to the river continuum and also pollution, only the rivers higher than 800 meters were selected. These rivers include a majority of sites that are only slightly polluted, or not at all. In total 261 sampling sites were considered from four ecoregions: the Iberic region, the Pyrenees, the Alps and the Western Highlands. The sampling sites were characterized by differences in geology, distance from the source and altitudes. Statistical analysis showed that geographic ecoregions of system A and geology were the most important environmental descriptors for diatoms. Distance from the source and altitude were less important and pollution was the least important parameter. The second aim was to describe and to typify the main diatom assemblages of these European mountains. Eight clusters gathered into four main groups were identified. Group I was mainly recorded in the Alps and the Pyrenees; group II had in common its close proximity to the source; group III was often found in the Western Highlands on crystalline geology, and group IV was present in all ecoregions and included weakly polluted streams. Some suggestions for the improvement of the ecoregions based on benthic diatoms were given in the conclusion.

Small-scale gold mining erodes fish assemblage structure in small neotropical streams

The current gold rush experienced by the Guiana shield is profoundly disturbing freshwater ecosystems. Indeed, streams act as receptors for the water that drains gold mining sites and that contain a high load of sediment and toxicants. We here investigated how gold mining activities affect the structure of fish assemblages in small forest streams in French Guiana. We selected six streams subjected to different types of gold mining impact (reference, former gold mining and currently exploited sites) to measure the impact of gold mining on downstream fish assemblages, but also to determine the resilience of fish assemblages after stopping mining activities. Although overall descriptors of the assemblage such as species richness and fish biomass were not sensitive to gold mining, the fish taxonomic composition was strongly influenced. Furthermore, we showed that the functional structure of fish assemblages was significantly affected by the mining activities favouring smaller and ubiquitous fish at the expense of bigger and habitat specialist species. Even in areas where mining activities had stopped for some time, site resilience was incomplete.

Are diatom diversity indices reliable monitoring metrics

A biological survey was carried out in 640 stations spread over the Loire-Bretagne National Network (France) between 1996 and 2000. Epilithic diatom inventories were obtained following standard methods. A total of 934 diatom taxa were identified. Common diversity indices (species richness, Shannon’s diversity, equitability, dominance, etc.) were calculated and compared against abiotic factors verify their reliability as biomonitoring metrics. Sampling stations were classified according to their trophic status (TP concentration). Several theoretical predictions about the relationship between community structural parameters and limnological variables were tested. In general, diversity indices exhibited poor linear correlations with environmental factors indicating ecological status. No clear patterns were found concerning species accumulation curves, occurrence-abundance, frequency-abundance and frequency distribution of diatom taxa between different trophic levels, although assemblages from stations with lower TP levels were characterized by relatively high dominances of certain taxa, mainly Achnanthidium minutissimum. In the light of these findings, the use of diatom diversity indices in biological quality surveillance protocols in continental waters is discouraged. Results are compared and discussed with similar studies.

A large-scale stream benthic diatom database

A relational database linking benthic diatom records, taxonomic nomenclature including synonyms, and corresponding environmental data has been built in MS Access. It allowed flexible and long-term use of a relatively important amount of data (∼3000 records) gathered in the framework of the EC-funded PAEQANN project, gathering precise and documented information both about benthic diatoms and quantitative or semi-quantitative environmental data. Such a database has been shown to be a useful tool for the definition of benthic diatom typology at a multi-regional scale, the prediction of the impact of environmental characteristics on the structure of diatom communities, and additionally for a new insight on the auto-ecology of some taxa. This database could serve as a template for further work on diatoms and, after some implementation, on other freshwater communities. It could also be the basis for wider typology of stream diatoms, extended to other regions.

Modeling the impact of landscape types on the distribution of stream fish species

Modifications of the landscape adjoining streams perturb their local habitat and their biological diversity, but little quantitative information is available on land cover classes that influence the fish species individually. Data collected from 191 sites in the Adour–Garonne Basin (France) were analyzed to assess the effects of land cover on the distribution of fish species. A multimodel approach was carried out to predict fish species using land cover classes and to define the most important classes applying a hierarchical filtering based on artificial neural network method and sensitivity analysis. Firstly, using three single-class models, a selection of the land cover subclasses contributing the most was carried out for each fish species and each class. Secondly, multiclass models were built with all the previously selected subclasses to predict each species (n-selected subclass model). Finally, the percentages of contribution for artificial, agricultural, and forest areas obtained for the different m...

Modeling the stream water nitrate dynamics in a 60,000-km2 European catchment, the Garonne, southwest France.

The spatial and temporal dynamics in the stream water NO(3)-N concentrations in a major European river-system, the Garonne (62,700 km(2)), are described and related to variations in climate, land management, and effluent point-sources using multivariate statistics. Building on this, the Hydrologiska Byråns Vattenbalansavdelning (HBV) rainfall-runoff model and the Integrated Catchment Model of Nitrogen (INCA-N) are applied to simulate the observed flow and N dynamics. This is done to help us to understand which factors and processes control the flow and N dynamics in different climate zones and to assess the relative inputs from diffuse and point sources across the catchment. This is the first application of the linked HBV and INCA-N models to a major European river system commensurate with the largest basins to be managed under the Water Framework Directive. The simulations suggest that in the lowlands, seasonal patterns in the stream water NO(3)-N concentrations emerge and are dominated by diffuse agricultural inputs, with an estimated 75% of the river load in the lowlands derived from arable farming. The results confirm earlier European catchment studies. Namely, current semi-distributed catchment-scale dynamic models, which integrate variations in land cover, climate, and a simple representation of the terrestrial and in-stream N cycle, are able to simulate seasonal NO(3)-N patterns at large spatial (>300 km(2)) and temporal (> or = monthly) scales using available national datasets.

Three new species of Delicata (Bacillariophyceae – Cymbellales) from New Caledonia and further observations on Delicata nepouiana Krammer and D. neocaledonica Krammer

A recent survey of epilithic diatoms in the running waters of the main island of New Caledonia led to the discovery of three new species of Delicata, Delicata pouemboutensis sp. nov., Delicata gobiniana sp. nov. and Delicata karembeui sp. nov. Delicata pouemboutensis is characterized by a strongly convex dorsal side and a low length/breath ratio (3.2–5.0). Delicata gobiniana has an acicular, almost naviculoid outline, with a high length/breath ratio (7.1–8.7). Delicata karembeui has an unusual stria structure for the genus and a valve face with shallow depressions along the dorsal and ventral sides of the valve. Delicata karembeui can be distinguished from other cymbelloid genera by a combination of features including outline, size, raphe course and stria structure. Delicata neocaledonica Krammer and Delicata nepouiana Krammer, so far only described with light microscopy, were also examined and additional scanning electron microscope observations are included.