Search

Les riparia – espaces riverains inondables fluviaux et cotiers – ont une longue histoire de crises recurrentes. Leur appropriation par les societes humaines s’accelere dans un monde de plus en plus marque par des bouleversements et des catastrophes. Cet article evoque : 1) la nature patrimoniale de ces espaces, 2) leur insertion dans une histoire de crises recurrentes, 3) leurs potentialites d’adaptation aux crises, 4) leurs potentialites d’attenuation des crises, 5) leur devenir dans un environnement incertain. Les riparia ont toujours ete le theâtre d’evenements hydrologiques plus ou moins extremes. Elles figurent parmi les espaces les plus menaces par le changement climatique en cours et les plus affectes par les questions posees par la surpopulation sous toutes les latitudes et sur tous les continents. Elles sont riches en enseignements pour la fondation d’une ethique des espaces partages dans un monde en crise.

Resume Nous presentons les enjeux de recherche suscites par la directive-cadre europeenne sur l'eau : ils concernent la comprehension de la dynamique des ecosystemes, un approfondissement des connaissances relatives aux eaux souterraines, un important developpement de l'ecotoxicologie et une nouvelle approche de l'economie de l'eau. Pour citer cet article : P.-A. Roche et al., C. R. Geoscience 337 (2005).

At the beginning of the 1970s a study was carried out on over 300 lakes under the direction of OECD. Evidence was found of a relationship between available phosphorus, the type of lake and the biomass of phytoplankton in the lake. The findings gave some credibility to the concept that it might be possible to limit the development of algae by reducing the amounts of available phosphorus. However, experience gained over the next 30 years has given rise to a wide range of uncertainty over the relationship between available phosphorus and the development of phytoplankton in lakes. Against the background of these uncertainties, the prediction of the effects of eutrophication requires a new survey of a very complex process. We initiate such a survey in addressing three issues: 1) the critical load of phosphorus in a lake beyond which algal growth is excessive, 2) the suitability of a lake model to a river situation, 3) the appearance of potentially toxic algal blooms such as those caused by some blue green algae. To address these issues we need to reassess biological models which integrate processes which control the growth and decline of algae with models that reflect the actual characteristics of the species under consideration. It is also necessary to consider the functional diversity of the algae as well as socioeconomical processes in a dynamic view of the management of continental waters.

L'attrait du public pour les ripisylves tient surtout au role epurateur qu'on leur prete en matiere d'amenagement des rivieres. Il est montre dans cet article qu'un usage trop exclusif de la fonction de piegeage des ripisylves peut conduire a negliger leur propriete essentielle, la multifonctionnalite. Cette propriete est consideree en rapport avec la dynamique ecologique des ripisylves et les pratiques d'entretien destinees a stabiliser les berges, a ameliorer la qualite des eaux et a gerer le bois mort. La prise en compte de la variabilite des ripisylves et de leur dimension paysagere apparait comme un prealable indispensable a leur bon usage le long des rivieres.

If we consider riparian areas as landscapes it means that we consider them as entities whose survival depends on ecological as well as on cultural sustainability. Ecological sustainability requires people’s understanding of the role of both diversity and connectivity of riparian areas. Cultural sustainability requires people’s attention and care towards diversity and connectivity. It is argued that interaction between ecological and cultural sustainabilities governs riparian management, and that we still have to promote such an interaction.

Landscape issues are of interest in many disciplines, but they are seldom seen as an opportunity for interdisciplinary or transdisciplinary cooperation. This limits the ability to account for real world complexity. Bridging human and natural sciences intends to foster and coordinate communication about landscape-related issues - within academia and between science and society. The collection of papers in this special issue and the recommendations for future research are selected from the conference Multifunctional landscapes - interdisciplinary approaches to landscape research and aanagement in Roskilde, Denmark, 2000. The contributions all bear evidence of an integrating approach to landscape research, bridging human and natural sciences.

Increasingly complex, global and unexpected environmental issues are likely to occur in the future. At the same time, citizens will become increasingly aware of the effects of these issues. These trends will require new ways of practicing and communicating research. It is crucial for landscape research to address this challenge at the beginning of the new century. Faced with these issues, landscape researchers will have to alternate intra- and interdisciplinary practices of their research, requiring greater skills in communicating among disciplines. They will have to facilitate a wider access to knowledge of landscape analysis by people from southern, particularly tropical, countries. An important aspect of their work will be to participate in the protection of the cultural rights of tribal minorities. They will have to reinforce their partnership with resource managers, their ability to provide more accurate predictions and communication about future landscape scenarios, and, therefore, in answering society’s expectations for expertise. Finally, these challenges, confronting landscape research, will not be addressed successfully without theoretical advances, particularly at the level of nature–culture interactions.

In this manuscript we investigated the relationshipsbetween the microbiological denitrification process inriver alluvial soils with structures and patterns ofthe floodplain visible at a larger scale. Wehypothesised that both topography and soil grain sizerepresent pertinent environmental factors to forecastdenitrification activity in river floodplain. Thestudy was conducted in 15 alluvial sites along a 30 kmlong stretch of the Garonne River, a seventh-orderstream of the south west of France. Sites wereselected to encompass the widest range possible ofaverage annual flood duration (0.04 to 29 days) andfrequency (return period from 0.6 to 7 years). On anannual basis, we found that average denitrificationrates did not show any significant trend along theflood frequency gradient. Although during the studythe flood frequency and duration was higher than thecalculated average, we did not find any relationshipbetween flood duration and denitrification enzymeactivity. If flood events do not last long enough tomaintain waterlogging conditions conducive to sustaindenitrification activity for long periods, theyindirectly affect the spatial distribution ofdenitrification activity through the sorting out ofsediment deposits. Indeed, we found a significantrelationship between denitrification rates in thefloodplain soils and their texture; highest rates weremeasured in fine textured soils with high silt + claycontent. Below a threshold of 65% of silt and claycontent, the floodplain soils did not present anysignificant denitrification rates. Above thatthreshold denitrification increased linearly. Theseresults demonstrate that alluvial soil texture is alandscape scale factor which has a significant effecton denitrification in floodplains.

The main impacts of riparian vegetation on hydrological processes are briefly reviewed in order to highlight needs and perspectives for research and management goals. This review is based upon three distinct influences of riparian vegetation on hydrological processes: (i) the control of runoff, i.e. the physical impact of living and dead plants on hydraulics, (ii) the impact of plant physiology on water uptake, storage and return to the atmosphere, and (iii) the impact of riparian vegetation functioning on water quality. Riparian vegetation influences runoff through complex hydraulic interactions during baseflows as well as overbank flows. The contribution of fine vegetational structures to landscape hydrological roughness needs to be considered in relation to the spatial complexity (patchiness, vertical stratification, rhizosphere) and temporal variability (phenology, succession) of plant communities. With the exception of some woody species, the uptake, storage and return of water to the atmosphere is poorly known for riparian communities, and therefore the assessment of the regional hydrological importance of the riparian corridor remains difficult to estimate. Although better understood than the above two influences of riparian vegetation on hydrological processes, there are still a number of unresolved issues concerning the role of riparian vegetation in controlling water quality. In particular, little is known about the coupling of microbial and vegetational functions in nutrient cycling and the dynamics of carbon release from coarse and fine plant debris. The influence of vegetation complexity and plant diversity on both qualitative and quantitative aspects of water cycling remains an important area for future research. Fundamental and management issues are identified in relation to the use of riparian vegetation as a model and as a tool.

Riparian zones possess an unusually diverse array of species and environmental processes. The ecological diversity is related to variable flood regimes, geographically unique channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. The resulting dynamic environment supports a variety of life-history strategies, biogeochemical cycles and rates, and organisms adapted to disturbance regimes over broad spatial and temporal scales. Innovations in riparian zone management have been effective in ameliorating many ecological issues related to land use and environmental quality. Riparian zones play essential roles in water and landscape planning, in restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.

This paper focuses on the effect of connectivity on biodiversity by proposing a testable hypothesis of a structural connectivity threshold. Evidence of this threshold is supported by percolation theory and by biological models of extinction. Hypothesizing the existence of this connectivity threshold, a conceptual model linking connectivity and biodiversity is presented. We suggested different measurements of connectivity to test the hypothesis of a structural threshold. The identification of this threshold is considered as a practical means to facilitate biological fluxes and optimize species colonization possibilities in designing a policy of conservation biology at the landscape scale.

(1996). The renewal of floodplain forests along rivers: a landscape perspective. SIL Proceedings, 1922-2010: Vol. 26, No. 1, pp. 35-59.

Patterns of plant species richness and community composition were studied in diverse riparian zones. Eight rivers in south-western France, one river in north-western USA and four rivers in south-eastern Spain were compared. A brief review is presented of factors that have been singled out as controlling diversity along rivers. The proportions of plant group classified according to life-span, morphology, ruderality and location along the rivers were analysed. Both proportions of plant traits and total species richness differed considerably between rivers. Semi-arid rivers were more influenced by local patterns than the other rivers. The patterns exhibited by true riparian species and invading, essentially non-riparian species, showed the importance of the relationships between the river and its close surroundings. The mean proportion of ruderals remained roughly the same in all rivers, suggesting some regulatory mechanisms independent of the general environmental settings. The longitudinal patterns of species richness in riparian plant communities of the oceanic rivers could be related to the intermediate disturbance hypothesis, whereas semi-arid rivers showed very irregular patterns of species richness along their courses, as a consequence of the irregular water availability. Exotic and ruderal species were more sensitive than other groups to the longitudinal zonation of the rivers and to environmental factors influenced by humans. Also, the permanency of superficial water appeared as a major factor in the control of riparian community structure in semi-arid regions.

Invasibility of riparian plant communities was estimated by the percentage of alien species found along the Adour River (Southwest France) and along Lockout Creek, McKenzie River, and Willamette River (Central Cascades, Oregon, U.S.A.). At the patch scale, the invasibilities of riparian plant communities were compared between one exceptionally rich site of the Adour River and patches selected in the Hoh and Dungeness watersheds (Olympic Peninsula, Washington, U.S.A.). Alien species represented 24% of 1396 species for the Adour and 30% of 851 species for the McKenzie. They represented 24% of 148 species for the Hoh drainage and 28% of 200 species for the Dungeness drainage. Similar trends were found along the Adour River and along the McKenzie River for changes in total number of species per site and in percentages of alien species per site. These trends may be related to the intermediate disturbance regimes and to the physical structure of the riparian corridors. Climatic and human factors are also involved in these longitudinal changes. Positive linear relationships were found between the total number of species and the percentage of aliens observed in each site. At the patch scale, most of the sampled communities contained alien species. Although mature vegetative patches appeared to be invasible, young communities contained more alien species than older ones. For entire corridors, a positive linear relationship was found between total species richness and percentage of alien species in each patch type for the richest site of the Adour River. This may be partially explained by landscape features considered in a successional context. We suggest the use of empirical rules, and stress the importance of riparian systems for monitoring the conservation of local and regional species pools are suggested. Se estimo la propension de las comunidades de plantas riberenas a la invasion a partir del porcentaje de especies invasoras encontradas a lo largo del Rio Adaour (Sudoeste de Francia) y a lo largo del arroyo Lookout/Rio McKenzie/Rio Willamette (Cascadas Centrales, Oregon, EUA). A escala de porche una la propension de la comunidad de plantas riberenas a las invasiones fue comparda, entre un sitio excepcionalmente rico en el Rio Adour y parches seleccionados en las cuencas de Hoh y Dungeness (Peninsula Olimpica, Washington, EUA). Las especies invasoras representaron un 24% de las 1396 especies de Adour y un 30% de las 851 especies de McKenzie. Estas tambien representaron un 24% de las 148 especies de la cuenca de Hoh y un 28% de las 200 especies de la cuenca de Dungeness. Tendencias similares fueron encontradas a lo largo del Rio Adour y del McKenzie, para los cambios en el numero total de especies y en el porcentaje de especies invasoras por sitio. Estas tendencias podrian estar relacionadas a los regimenes intermedios de perturbacion y a la estructura fisica de los corredores riberenos. Los factores climaticos y humanos tambien se encuentran involucrados en estos cambios longitudinales. Se encontro una relacion lineal positiva entre el numero total de especies y el porcentaje de especies invasoras observado en cada sitio. A una escala de parche, la mayoria de las muestras de la comunidad contenian especies invasoras. Sin bien, los parches vegetativos maduros parecieron ser propensos a la invasion, las comunidades mas jovenes presentaron mas especies invasoras que las comunidades mas antiguas. En cuanto a los corredores en su totalidad, se encontro una relacion lineal positiva entre la riqueza total de especies y el porcentaje de especies invasoras en cada tipo de parche para el sito mas rico del Rio Adour. Esta relacion puede ser explicada parcialmente por las caracteristicas del paisaje, consideradas dentro de un contexto sucesional. Se sugiere el uso de reglas empiricas y la importancia de los sistemas riberenos para el monitoreo de la conservacion de grupos de especies locales y regionales.

Changes in the hydrological regime affect the phenomenon of invasion by plant species along riparian systems. The dynamics of exotic (non-native) and native species were examined at five sites that differed in exposure to hydrological disturbance (floods) during three consecutive years (medium, wet and dry years). When considering the disturbance gradient, exotic plants were favoured by direct exposure to floods (main channel) and by high flood frequencies. The response to year to year changes in hydrology was rapid for both native and exotic communities. However, the exotic plants responded more rapidly and were favoured by a dry year. A general framework including human and natural factors involved in invasions by exotic plants along rivers is presented.

Many climate change adaptation efforts aim to address the implications of potential changes in the frequency, intensity, and duration of weather and climate events that affect the risk of extreme impacts on human society. That risk is determined not only by the climate and weather events (the hazards) but also by the exposure and vulnerability to these hazards. Therefore, effective adaptation and disaster risk management strategies and practices also depend on a rigorous understanding of the dimensions of exposure and vulnerability, as well as a proper assessment of changes in those dimensions. This chapter aims to provide that understanding and assessment, by further detailing the determinants of risk as presented in Chapter 1. The first sections of this chapter elucidate the concepts that are needed to define and understand risk, and show that risk originates from a combination of social processes and their interaction with the environment (Sections 2.2 and 2.3), and highlight the role of coping and adaptive capacities (Section 2.4). The following section (2.5) describes the different dimensions of vulnerability and exposure as well as trends therein. Given that exposure and vulnerability are highly context-specific, this section is by definition limited to a general overview (a more quantitative perspective on trends is provided in Chapter 4). A methodological discussion (Section 2.6) of approaches to identify and assess risk provides indications of how the dimensions of exposure and vulnerability can be explored in specific contexts, such as adaptation planning, and the central role of risk perception and risk communication. The chapter concludes with a cross-cutting discussion of risk accumulation and the nature of disasters.

For several years, measures to insure healthy river functions and to protect biodiversity have focused on management at the scale of drainage basins. Indeed, rivers bear witness to the health of their drainage basins, which justifies integrated basin management. However, this vision should not mask two other aspects of the protection of aquatic and riparian biodiversity as well as services provided by rivers. First, although largely depending on the ecological properties of the surrounding terrestrial environment, rivers are ecological systems by themselves, characterized by their linearity: they are organized in connected networks, complex and ever changing, open to the sea. Second, the structure and functions of river networks respond to manipulations of their hydrology, and are particularly vulnerable to climatic variations. Whatever the scale considered, river networks represent “hotlines” for sharing water between ecological and societal systems, as well as for preserving both systems in the face of global change. River hotlines are characterized by spatial as well as temporal legacies: every human impact to a river network may be transmitted far downstream from its point of origin, and may produce effects only after a more or less prolonged latency period. Here, I review some of the current issues of river ecology in light of the linear character of river networks.

The paper discusses how variability of river margins interacts with riparian function at the landscape level, in order to develop inferences about the future of this interaction with respect to potential effects of a global climatic change. A riparian approach to the ecology of river landscapes should be useful in that it offers an opportunity to improve our understanding and management of the effects of environmental change at the ecosystem level.

Riparian corridors possess an unusually diverse array of species and environmental processes. This "ecological" diversity is related to variable flood regimes, geomorphic channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. This dynamic environment results in a variety of life history strategies, and a diversity of biogeochemical cycles and rates, as organisms adapt to disturbance regimes over broad spatio-temporal scales. These facts suggest that effective riparian management could ameliorate many ecological issues related to land use and environmental quality. We contend that riparian corridors should play an essential role in water and landscape planning, in the restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.

SUMMARY 1 A review is presented of types of satellite remote-sensing data currently available, and their recent uses in studies of river systems. 2 Broad-scale assessments of relative water quality may be carried out, although precise indication of water quality requires samples to be taken in situ. 3 In the event of flooding, the extent of inundation may be determined and damage assessed quickly. Some radar data allow measurements of flood water even when obscured by vegetation. 4 Riparian vegetation may be mapped over large areas, although the recognition of specific tree species remains difficult. 5 One of the most basic and widely used applications of remote-sensing data for rivers is that of mapping, both as a single event and over time to follow changes, e.g. channels in a delta. Entire catchments may be mapped, although the efficiency of detection of low-order streams is dependent upon the characteristics of the system used. 6 Remote-sensing data has been widely used in all of the above types of study, but is rarely employed on a long-term basis. Several factors can explain this situation, including, for example, the absence of reliable absolute relationships between spectral data and ecological parameters. 7 A clear definition of observational needs (e.g. spectral bands, ground resolution, acquisition frequency) of stream ecologists, together with the identification of ecological parameters that may be collected relatively easily from space, will improve remote sensing as an ecological tool in many restoration and management situations.

L’écologie du paysage étudie les interactions entre l’organisation de l’espace et les processus écologiques. Elle s’intéresse aux causes et aux conséquences de l’hétérogénéité de l’espace, en combinant les concepts et méthodes de la géographie et de l’écologie. Sa démarche s’inscrit dans le cadre d’une approche intégrée des paysages. Après avoir exposé les principes de base, cet article précise ici comment l’écologie du paysage aborde l’organisation de l’espace et, sur l’exemple de la fragmentation des habitats, comment elle relie cette organisation aux processus qui caractérisent les dynamiques des populations et des communautés. Ces analyses conduisent s’interroger sur les conditions d’une science pour l’action et, en conclusion, sur la place de l’écologie parmi les disciplines du paysage. Landscape ecology studies the interactions between spatial patterning and ecological processes. It focuses on the causes and consequences of spatial heterogeneity, combining concepts and methods of geography and ecology. It comes within the framework of a landscape integrated approach. In this paper, we summarize some basic principles and focus on habitat fragmentation to illustrate how landscape ecology addresses spatial organization and the processes that characterize population and community dynamics. This analysis leads us to examine what are the conditions of a science for action and to conclude on the position of ecology among the disciplines devoted to the study of landscapes.

1. Denitrification in floodplain soils is one of the main biological processes emitting and reducing nitrous oxide, a greenhouse gas, and the main process responsible for the buffering capacity of riparian zones against diffuse nitrate pollution. 2. The aim of this study was to measure denitrification rates under a wide range of current climatic conditions and hydrological regimes in Europe (from latitude 64°N to latitude 42°N and from longitude 2°W to longitude 25°E), in order to determine the response patterns of this microbial process under different climatic and hydrological conditions, and to identify denitrification proxies robust enough to be used at the European scale. 3. Denitrification activity was significant in all the floodplain soils studied whatever the latitude. However, we found an increase in rates of an order of magnitude from high to mid latitudes. Maximum rates (above 30 g N m?2 month?1) were measured in the maritime conditions of the Trent floodplain. These rates are similar to mineralisation rates measured in alluvial soils and of the same order of magnitude as the amount of N stored in herbaceous plants in alluvial soils. 4. We used Multivariate Adaptative Regression Splines to relate the response variable denitrification with five relevant predictors, namely soil moisture, temperature, silt plus clay, nitrate content and herbaceous plant biomass. 5. Soil moisture, temperature, and nitrate were the three main control variables of microbial denitrification in alluvial soils in decreasing order of importance. 6. The model developed for denitrification with interaction effects outperformed a pure additive model. Soil moisture was involved in all interactions, emphasising its importance in predicting denitrification. 7. These results are discussed in the context of scenarios for future change in European hydrological regimes.

This chapter examines the major avenues and ecological consequences of human-mediated change, status and trends associated with major changes, ecological principles associated with responses to changes in flow regimes, and the environmental consequences of significant changes expected to occur due to changes in climate and land use. Anthropogenic disturbance is a human-mediated event or activity virtually unknown in natural systems in terms of type, frequency, intensity, duration, spatial extent, or predictability. In contrast to natural perturbations, anthropogenic stress is not a revitalizing agent but a debilitating one. Multiple anthropogenic stresses added to a natural disturbance regime can proliferate or reduce the number of successional pathways in riparian vegetation, often truncating subsequent processes, and depending on the type of alteration, may increase the presence of terrestrial species in the riparian zone. Flow regulation affects the ecological integrity of riparia by disrupting sediment transport as well as by reducing flood peaks, flooding frequency, and channel-forming flows. Riparian zones undergo a stabilization process, which undermines the natural processes, facilitates invasion by upland and exotic species, and alters the standing stocks and fluxes of energy and nutrients in the reconfigured system. Projected changes in climate and land use place additional pressures on already stressed riparian ecosystems. Although riparia are generally viewed as resilient and able to maintain healthy and self-sustaining conditions, rapid climatic and terrain changes may impose new environmental regimes that may exceed the limits of resilience. Significant changes in temperature, precipitation, nutrients, and invasive plants are also reflected in riparian characteristics.