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The purpose of our approach was to take into account the nested spatial scales driving stream functioning in the description of pressures/ecological status links by analysing the results of a hierarchical model. The development of this model has allowed us to answer the following questions: Does the consideration of the indirect links between anthropogenic pressures and stream ecological status modify the hierarchy of pressure types impacting benthic invertebrates? Do the different nested scales play different roles in the anthropogenic pressures/ecological status relationship? Does this model lead to better understanding of the specific role of hydromorphology in the evaluation of stream ecological status? To achieve that goal, we used the Partial Least Square (PLS) path modelling method to develop a structural model linking variables describing (i) land use and hydromorphological alterations at the watershed scale, (ii) hydromorphological alterations at the reach scale, (iii) nutrients-organic matter contamination levels at the site scale, and (iv) substrate characteristics at the sampling site scale, to explain variation in values of a macroinvertebrate-based multimetric index: the French I 2 M 2 . We have highlighted the importance of land use effects exerted on both hydromorphological and chemical characteristics of streams observed at finer scales and their subsequent indirect impact on stream ecological status. Hydromorphological alterations have an effect on the substrate mosaic structure and on the concentrations of nutrients and organic matter at site scale. This result implies that stream hydromorphology can have a major indirect effect on macroinvertebrate assemblages and that the hierarchy of impacts of anthropogenic pressures on stream ecological status generally described in the literature - often determining strategic restoration priorities - has to be re-examined. Finally, the effects of nutrients and organic matter on macroinvertebrate assemblages are lower than expected when all the indirect effects of land use and hydromorphological alterations are taken into account. [ABSTRACT FROM AUTHOR]

We built a corpus of models capable of explaining the variability of the biological indices used in the French surveillance monitoring network and also predict the ecological status of non-monitored water bodies. Benthic macroinvertebrates, diatoms and fish indices have been used to determine the ecological status of 1100 sites of the monitoring network distributed homogeneously over national territory. The pressures taken into account to explain and predict ecological status cover three spatial scales: catchment, reach, site. The set of predictive data cover three types of pressure: land use pressure, hydromorphological pressure and physico-chemical pressure measured at catchment, reach and site scale, respectively. We showed that the parameters characterising the load of nutrients and organic matter had a predominant effect on the three biological compartments, and that land use variables played an integrating role of the different pressures acting on rivers and explained a major part of their degradation. On the contrary, we also showed that it was more difficult to characterise the role of the hydromorphological descriptors measured at the intermediate scale of the reach due to the difficulty of characterising the links between scales. The three predictive models developed demonstrated good performances to evaluate biological condition and are of great interest for managers as it permits using a set of pressure data to successively predict the status of water bodies for which biological monitoring data are unavailable. [ABSTRACT FROM AUTHOR]

Recent progress in very high spatial resolution imagery ( VHSRI) has increased the availability of fine-scale land cover data over extensive areas. This new spatial information might improve our understanding of how land cover affects stream ecosystems., Land cover information was investigated in whole catchments and riparian areas in Normandy ( France) and related to stream macroinvertebrates at 155 sites. The first model was based on the land cover data obtained via moderate spatial resolution imagery ( MSRI) at the catchment scale. The second and the third models were additionally based on riparian land cover data both locally (at the site) and upstream. The riparian land cover data were derived from the MSRI for the second and from the VHSRI for the third model., Riparian vegetation (at a distance from the channel of 5-100 m) was poorly detected by MSRI when compared to VHSRI. The model based on higher resolution data at the riparian scale (i) ensured that relationships identified at the riparian corridor scale were independent from those at whole catchment scale, (ii) identified the influence of riparian vegetation on the aquatic environment as being most pronounced when using data from a 20-m wide strip (i.e. 20 m on each bank for a total of 40 m) and (iii) disentangled the effects of roads from other urban infrastructure., This study confirms the advantages of using very high resolution data in landscape approaches to the study of aquatic ecosystems. It provides accurate spatial information at the riparian scale that improves interpretation of the influence of land cover on the ecological condition of streams and allows identification of relevant features for management. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to demonstrate the interest of High Spatial Resolution Imagery (HSRI) and the limits of coarse land cover data such as CORINE Land Cover (CLC), for the accurate characterization of land cover structure along river corridors and of its functional links with freshwater ecological status on a large scale. For this purpose, we compared several spatial indicators built from two land cover maps of the Herault River corridor (southern France): one derived from the CLC database, the other derived from HSRI. The HSRI-derived map was obtained using a supervised object-based classification of multi-source remotely-sensed images (SPOT 5 XS-10m and aerial photography-0.5m) and presents an overall accuracy of 70%. The comparison between the two sets of spatial indicators highlights that the HSRI-derived map allows more accuracy in the quantification of land cover pressures near the stream: the spatial structure of the river landscape is finely resolved and the main attributes of riparian vegetation can be quantified in a reliable way. The next challenge will consist in developing an operational methodology using HSRI for large-scale mapping of river corridor land cover, for spatial indicator computation and for the development of related pressure/impact models, in order to improve the prediction of stream ecological status. [Copyright &y& Elsevier]