Paper 4: Using diatom life‐forms and ecological guilds to assess organic pollution and trophic level in rivers: a case study of rivers in south‐eastern France.

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Is there a threshold level above which factors affected by human activity explain the variability of diatom assemblages to a greater extent than ecoregions?

In the first study area, corresponding to the high altitude rivers, the pollution level was assessed using the SPI diatom index (Cemagref, 1982). This indicated that in 85% of these rivers water quality was very good, in 11% quality was good, and in 2% it was moderate. No rivers had bad water quality, which meant that the pollution gradient was slight. In the second study area, corresponding to North‐eastern France, the pollution level was also assessed using the SPI. This showed that 5.4% of the rivers had very good water quality, 45.4% good quality, 39.6% moderate quality, 9.5% had bad or very bad quality. The pollution gradient was therefore much steeper than in the high altitude rivers.
Several authors did not find any obvious relationship between diatoms and ecoregions, because the most important gradients were the downstream gradient, the mineral content and pH gradients, and the altitudinal and latitudinal gradients (Pan et al., 2000; Potapova & Charles, 2002a). Others observed a homogenization of diatom communities in ecoregions where pollution was increasing (Leira & Sabater, 2005; Tornes et al., 2007).

Diatoms and ecoregions

In the case of high altitude rivers, the ecoregions of System A most closely matched diatom assemblages: the match was closer than those for source distance, altitude, or pollution, and was equivalent to that for geology. This can be explained by the choice of a particular river type which artificially reduced all the other gradients (altitude, pollution, source distance).
In the case of North‐eastern France, here too the hydro‐ecoregions most closely reflected diatom assemblages. This match was closer than those with river size (assessed by Strahler rank) or pollution (assessed by the SPI). This was also confirmed by a discriminant analysis showing that the most structuring parameters of diatom assemblages were conductivity, pH, and bicarbonate concentration. The variability of these parameters is mainly attributable to the geological substrate, and they are only weakly affected by anthropogenic activity (Agences de l’Eau, 2000). Diatom communities in this area were defined by means of a Twinspan analysis, which showed that the first dichotomy was explained by geological substrate: one community is located on a crystalline substrate, and the other on a sedimentary substrate. Within both of them sub‐communities corresponding to polluted and highly polluted areas were present, and these displayed different diatom species compositions. Geology is therefore the primary factor that determines hydro‐ ecoregions.
Our findings seem to be at odds with those of Pan et al. (2000), Potapova & Charles (2002a), Leira & Sabater (2005) and Tornes et al. (2007). On the contrary, they confirm the results of Soininen (2004, 2007), in Finland and of Rimet et al. (2004) in Luxembourg, who stressed the importance of the ecoregional approach and found that geology, which is a factor that varies at larger spatial scales, had a determining impact on diatom assemblages.

• Conclusions

Communities of unicellular organisms such as diatoms have high dispersal capacities. The invasions of rivers by non‐native diatom species provide a good demonstration of this ability. New‐Zealand lakes provide a good example with Asterionella formosa records in sediments: this species was introduced at the time of the European settlement, salmon eggs being the most likely vector (see review of Spaulding et al., 2010). A long‐term study (Coste & Ector, 2000) of French rivers has identified the arrival of species such as Gomphoneis eriense and Encyonema triangulum. Another example, also in French rivers is provided by a period of five years, during which Achnanthidium druartii spread from a single river site to 40 river sites some of them several being at hundred kilometers apart (Rimet et al., 2010). Since the statement that “Everything is everywhere: but the environment selects” (Beijerinck, 1913), a fierce debate about diatom endemism reigned until recent years. Some authors argued that diatom endemism should be underestimated (e.g. Mann & Droop, 1996) and others were of the opposite opinion and were favorable to Beijerinck’s law (e.g. Finlay et al., 2002). The spatial structure of the diatom assemblages that we observed was generally congruent with Beijerinck’s law. There were clear correspondences between diatom assemblages and ecoregions. In particular it appeared that if the abiotic factors used to define the ecoregions (altitude, geology, climate) were the same, then the diatom compositions found were comparable. Invasions of new species are probably indicative of recent environmental modifications (e.g. water warming) opening new ecological niches that were rapidly filled by non‐native diatom species: the example of Achnanthidium druartii is a good demonstration of this, since within just a few years rivers separated by several hundred kilometers were colonized.
This allowed us to say that in order to improve the effectiveness of ecoregional classifications for diatom assemblages it might be useful to combine some ecoregions that are geographically separated, thus doing away with notions of endemism. These results also reinforce the interest of using an ecoregional approach to developing diatom indices (Grenier et al., 2006; Lavoie et al., 2006).
Despite the findings of Leira & Sabater (2005), Tornes et al. (2007) and Pan et al. (2000), the hypothesis that no relationship between diatoms and ecoregion would be evident for polluted sites was not confirmed in our case. Soininen (2004) also highlights the importance of ecoregions in his study; but he recognized that the location of his polluted sites was biased, and most of them were located within a single ecoregion. In our case, the polluted sites were distributed throughout the study area since diatom communities corresponding to high level of pollutions were found on both crystalline and sedimentary substrates. Nevertheless, land‐use differs from one geological substrate to another: agricultural practices, at least, differ depending on the landscape and geology. We can assume that the composition of diatom assemblages would differ as a result of these different practices that result in different kinds of pollution, even when nutrient and organic matter concentrations are equivalent. This would (once again!) highlight the bioindicative power of diatoms, which would offer fine discrimination between different types of anthropogenic perturbations.

Paper 1: 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. From rivers of the Alps, the Pyrenees, the Massif‐Central and the Iberic system, diatoms were studied. 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 deviaton 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 characterised 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 factors 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 and Iberic region on crystalline geology, and group IV included weakly polluted streams of the Apls and Pyrenees. Some suggestions for the improvement of the ecoregions adapted to benthic diatoms were given in the conclusion.

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• Introduction

Diatoms are unicellular algae that represent an important part of biodiversity in rivers. Diatom assemblages responses to anthropogenic disturbances have been observed for a long time (e.g. Butcher 1947). Diatoms reproduce and divide rapidly and quickly react to water quality changes (e.g. Round 1991). This prompted water managers to select as one of the tools for assessing a wide range of water quality, alongside macroinvertebrates and fish, benthic diatoms as bioindicators, which investigate environmental quality over longer time period (Stevenson & Pan 1999).
Now, diatom indices are used routinely in different European countries to assess the biological quality of running waters (Prygiel et al. 1999). In 2000, the European Parliament & The Council of the European Union (2000) advised European countries to assess running water quality by using diatoms, as part of the phytobenthos, in addition to phytoplankton, fish, macroinvertebrates and macrophytes. It also calls for applying of the “Ecological Quality Ratio” which uses bioindicators to evaluate stream quality by assessing the difference between the observed site community to a non‐ disturbed reference community belonging to the same stream type in the same ecoregion (Ector et al. 2004). Thereby, reference conditions for each stream type had to be defined. Two different typological systems were proposed in the Water Framework Directive –WFD– (European Parliament & The Council of the European Union 2000). The first is system A, in which ecoregions, based on altitude, geology and sizes of the running water catchment area were fixed. This system has the advantage of being easily applicable to all of Europe and the ecoregions proposed in this typological system are large, spread over several European countries.
In the second system B, the requisite factors (altitude, latitude, longitude, geology and size) were used to define the stream types but optional factors can be added to this system typology.
System B is more complex, as each country is currently developing its own typology based more criteria (e.g. Wimmer et al. 2000, Wasson et al. 2001, Munné & Prat 2005). Therefore, comparisons of stream types between different European countries will require complex intercalibration studies.
So far, the ecoregions proposed in system A have never been tested on a large geographical scale, including several countries. A difference in certain catchments characteristics, such as land use, geology and background nutrient fluxes, is expected. For example in Norwegian rivers, macroalgal growth took place after only a small increase of total phosphorus concentrations from 4 to 12 µg.l‐1 (Lindstroem 1999) whereas in northern French rivers these concentrations are below the classification range; 500 µg.l‐1 is the lowest reference level (Prygiel 1991).

Table of contents :

1. Introduction
a. General framework
b. Bio‐assessment in rivers
c. Diatom biology
d. Diatom diversity: an advantage for bioassessment?
e. Diatom life forms and ecological guilds
f. Geographical distribution of diatom assemblages
g. Diatoms and pesticide contamination
h. Main objectives of the study
• Diatoms and ecoregions
• Taxonomic resolution and alternative metrics in diatom bioassessment
• Diatoms and pesticide contamination
i. References
2. Diatoms and ecoregions
a. Preamble and major results
• Introduction
• Methodology
• Results and Discussion
• Conclusions
• References
b. Paper 1: Benthic diatoms in western European streams with altitudes above 800 m: Characterisation of the main assemblages and correspondence with ecoregions.
• Abstract
• Introduction
• Methods
• Results
• Discussion
• Conclusions
• Acknowledgments
• References
c. Paper 2: Benthic diatom assemblages and their correspondence with ecoregional
classifications: case study of rivers in north‐eastern France.
• Abstract
• Introduction
• Material and methods
• Results
• Discussion
• Acknowledgments
• References
3. Taxonomic resolution and life‐forms in diatom biomonitoring
a. Preamble and major results
• Introduction
• Methodology
• Results and discussion
• Conclusions
• References
b. Paper 3: Biomonitoring river diatoms: implications of taxonomic resolution.
• Abstract
• Introduction
• Methods
• Results
• Discussion
• Conclusions
• Acknowledgments
• References
c. Paper 4: Using diatom life‐forms and ecological guilds to assess organic pollution and trophic level in rivers: a case study of rivers in south‐eastern France.
• Abstract
• Introduction
• Material and Methods
• Results
• Discussion
• Conclusion
• Acknowledgments
• References
4. Diatoms and pesticide contamination
a. Preamble and major results
• Introduction
• Methodology
• Results and discussion
• Conclusions
• References
b. Paper 5: Use of diatom life‐forms and ecological guilds to assess pesticide contamination in rivers: lotic mesocosm approaches.
• Abstract
• Introduction
• Methods
• Results
• Discussion
• Conclusions
• Acknowledgments:
• References
5. Conclusions and perspectives
a. Main conclusions
• Diatoms and ecoregions
• Taxonomic resolution and alternative metrics in diatom bioassessment
• Diatoms and pesticide contamination
b. Future prospects
c. References

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