Didier Pont

From Natural to Degraded Rivers and Back Again: A Test of Restoration Ecology Theory and Practice

Extensive degradation of ecosystems, combined with the increasing demands placed on the goods and services they provide, is a major driver of biodiversity loss on a global scale. In particular, the severe degradation of large rivers, their catchments, floodplains and lower estuarine reaches has been ongoing for many centuries, and the consequences are evident across Europe. River restoration is a relatively recent tool that has been brought to bear in attempts to reverse the effects of habitat simplification and ecosystem degradation, with a surge of projects undertaken in the 1990s in Europe and elsewhere, mainly North America. Here, we focus on restoration of the physical properties (e.g. substrate composition, bank and bed structure) of river ecosystems to ascertain what has, and what has not, been learned over the last 20 years. First, we focus on three common types of restoration measures—riparian buffer management, instream mesohabitat enhancement and the removal of weirs and small dams—to provide a structured overview of the literature. We distinguish between abiotic effects of restoration (e.g. increasing habitat diversity) and biological recovery (e.g. responses of algae, macrophytes, macroinvertebrates and fishes). We then addressed four major questions: (i) Which organisms show clear recovery after restoration? (ii) Is there evidence for qualitative linkages between restoration and recovery? (iii) What is the timescale of recovery? and (iv) What are the reasons, if restoration fails? Overall, riparian buffer zones reduced fine sediment entry, and nutrient and pesticide inflows, and positive effects on stream organisms were evident. Buffer width and length were key: 5–30 m width and > 1 km length were most effective. The introduction of large woody debris, boulders and gravel were the most commonly used restoration measures, but the potential positive effects of such local habitat enhancement schemes were often likely to be swamped by larger-scale geomorphological and physico-chemical effects. Studies demonstrating long-term biological recovery due to habitat enhancement were notable by their absence. In contrast, weir removal can have clear beneficial effects, although biological recovery might lag behind for several years, as huge amounts of fine sediment may have accumulated upstream of the former barrier. Three Danish restoration schemes are provided as focal case studies to supplement the literature review and largely supported our findings. While the large-scale re-meandering and re-establishment of water levels at River Skjern resulted in significant recovery of riverine biota, habitat enhancement schemes at smaller-scales in other rivers were largely ineffective and failed to show long-term recovery. The general lack of knowledge derived from integrated, well-designed and long-term restoration schemes is striking, and we present a conceptual framework to help address this problem. The framework was applied to the three restoration types included in our study and highlights recurrent cause–effect chains, that is, commonly observed relationships of restoration measures (cause) and their effects on abiotic and biotic conditions (effect). Such conceptual models can provide useful new tools for devising more effective river restoration, and for identifying avenues for future research in restoration ecology in general.

A Predictive Index of Biotic Integrity Model for Aquatic-Vertebrate Assemblages of Western U.S. Streams

Abstract Because of natural environmental and faunal differences and scientific perspectives, numerous indices of biological integrity (IBIs) have been developed at local, state, and regional scales in the USA. These multiple IBIs, plus different criteria for judging impairment, hinder rigorous national and multistate assessments. Many IBI metrics are calibrated for water body size, but none are calibrated explicitly for other equally important natural variables such as air temperature, channel gradient, or geology. We developed a predictive aquatic-vertebrate IBI model using a total of 871 stream sites (including 162 least-disturbed and 163 most-disturbed sites) sampled as part of the U.S. Environmental Protection Agencys Environmental Monitoring and Assessment Program survey of 12 conterminous western U.S. states. The selected IBI metrics (calculated from both fish and aquatic amphibians) were vertebrate species richness, benthic native species richness, assemblage tolerance index, proportion of invert...

The relative influence of catchment, riparian corridor, and reach-scale anthropogenic pressures on fish and macroinvertebrate assemblages in French rivers

This study compares the relative influences of physiography and anthropogenic pressures on river biota at catchment, riparian corridor, and reach scales. Environmental data, catchment and riparian corridor land use, anthropogenic modifications and biological data were compiled for 301 French sites sampled from 2005 to 2008. First, relationships between anthropogenic pressures and fish and macroinvertebrate assemblages were analysed using redundancy analysis. Second, the influences of physiography and the three scales of human pressures on biological assemblages were measured using variance partitioning. Distributions of fish and macroinvertebrate taxa along the pressure gradients agreed with bio-ecological knowledge. At the reach scale, assemblage variability among the 301 French sites was related to the presence of an impoundment and to poor water quality, while at larger scales it was linked to a gradient from forest to agricultural covers. In addition, a large proportion of the explained variability in assemblage composition was related to complex interactions among factors (~40%) and to physiographic variables (~30%). Furthermore, our results highlight that catchment land use better reflects local water quality impairments than hydromorphological degradations. Finally, this study supports the idea that human pressure effects on river communities are linked at several spatial scales and must be considered jointly.

Comparison between the fish communities of lakes, reservoirs and rivers : can natural systems help define the ecological potential of reservoirs?

Abstract.The European Water Framework Directive (WFD) aims at improving the ecological status of continental waters, including man-made water bodies. Thereby it raises the question of the reference conditions for reservoirs. A number of limnologists consider reservoirs as intermediate systems between lakes and rivers. Hence, the aim of this study is to contribute to the implementation of the WFD by comparing the fish communities across these three types of ecosystems. This was achieved using fish sampling data from 21 natural lakes, 50 reservoirs and 549 river stations. The lists of occurring species are very similar between lakes and reservoirs, and appear as a subset of the species occurring in rivers. Lakes and reservoirs are also very similar in terms of common and rare species. Conversely, the comparison of community structures (summarised by correspondence analysis axes) supports the hypothesis of an intermediate position of reservoirs between lake and river systems. This latter result could reflect the effect of large-scale processes undergone by freshwater ecosystems whatever their type and the non-independence of water bodies within their catchments, particularly when considering the communities of highly mobile organisms like fishes. Although the major conservation concerns are about natural systems, artificial ones should also be considered in monitoring and assessment programs in order to allow efficient catchment-scale management policies.

Do Iberian and European fish faunas exhibit convergent functional structure along environmental gradients

Abstract We tested whether the functional structures of Mediterranean and temperate western European fish communities responded similarly along environmental gradients. The species pools of the 2 regions were quite different, with few species common to both regions. Each species was assigned to 1 trait for each of 6 guilds considered. We aggregated occurrences or densities of the species sharing the same traits and then computed 26 metrics describing the functional structure of fish assemblages. For each metric, we fitted and then compared 3 nested models. The 1st model related the metric to environmental variables without taking into account the region. Therefore, the response was assumed to be the same between regions. The 2nd model related the metric to the environmental variables with the region as an additive parameter. Therefore, the response was assumed to be similar between regions but with a constant deviation between them. The 3rd model took into account all interactions between the environmental variables and region. Therefore, the response to the environmental gradient was assumed to be different in the 2 regions. For the 17 metrics finally tested, 11 metrics responded similarly to environmental gradients but generally showed a constant deviation between the 2 regions, and responses of 6 metrics differed between the regions. Our results highlight the roles played by biogeographical factors and the environment on current community structure in 2 neighboring but ecologically distinct regions.

Typology of historical sources and the reconstruction of long‐term historical changes of riverine fish: a case study of the Austrian Danube and northern Russian rivers

Historical data are widely used in river ecology to define reference conditions or to investigate the evolution of aquatic systems. Most studies rely on printed documents from the 19th century, thus missing pre-industrial states and human impacts. This article discusses historical sources that can be used to reconstruct the development of riverine fish communities from the Late Middle Ages until the mid-20th century. Based on the studies of the Austrian Danube and northern Russian rivers, we propose a classification scheme of printed and archival sources and describe their fish ecological contents. Five types of sources were identified using the origin of sources as the first criterion: (i) early scientific surveys, (ii) fishery sources, (iii) fish trading sources, (iv) fish consumption sources and (v) cultural representations of fish. Except for early scientific surveys, all these sources were produced within economic and administrative contexts. They did not aim to report about historical fish communities, but do contain information about commercial fish and their exploitation. All historical data need further analysis for a fish ecological interpretation. Three case studies from the investigated Austrian and Russian rivers demonstrate the use of different source types and underline the necessity for a combination of different sources and a methodology combining different disciplinary approaches. Using a large variety of historical sources to reconstruct the development of past fish ecological conditions can support future river management by going beyond the usual approach of static historical reference conditions.

The effects of selective fish predation on the horizontal distribution of pelagic Cladocera in a southern French reservoir

A four-year study showed a clear seasonal succession of species within the cladoceran community of the large, oligotrophic Sainte-Croix reservoir (S.E. France). Diaphanosoma brachyurum and Ceriodaphnia pulchella were strictly limited to the warm stratified period (July to October), whereas Bosmina longirostris and Bosmina coregoni were dominant during spring and autumn. Daphnia longispina was the only species to occur throughout the year with higher densities in spring.In spring and late autumn, the discharge of the inflowing river Verdon was high and the abundance of all species showed a gradient over the whole lake with lower densities close to the inflow. During the stratified period, water inflow was very low and species showed different patterns. Densities of the small form Ceriodaphnia pulchella were similar all along the long axis of the lake, whereas Daphnia densities were significantly higher near the dam. The distribution pattern of Diaphanosoma, an intermediate-sized species, showed similar trends to that of Daphnia. The only planktivorous fish in the pelagic zone, the bleak (Alburnus alburnus), fed mostly on large-bodied species (> 1.0 mm) and was more abundant close to the inflow current. A comparison between the length frequency distributions of cladocera upstream and downstream provided a clear demonstration of the effects of size-selective predation on prey populations. Finally, the interactions between spatial heterogeneity and long-term development of the zooplankton community and the indirect effects of predation are discussed.

Global warming and potential shift in reference conditions: the case of functional fish-based metrics

The reference condition approach, advocated by the Water Framework Directive, is the basis of most currently used multimetric indices using functional traits of fish species. The ecological status of streams is assessed by measuring the deviation of the observed trait values from the theoretical values of reference conditions in the absence of anthropogenic disturbances. While reference conditions serve as baselines for ecological assessment, they vary with natural environmental conditions. Therefore, global warming appears to be a major threat to the use of current indices for diagnosing future stream conditions, as climate change is projected to modify assemblage composition, suggesting that the functional structure of fish assemblages will also be affected. The main objectives of this study are to assess the potential effect of climate change on the trait composition of fish assemblages and the consequences for the establishment of reference conditions. The results highlight the relation between environmental, especially climatic, conditions and functional traits and project the effects of climate change on trait composition. Traits based on species intolerance are expected to be most negatively affected by the projected climatic shift. The consequences for the development of multimetric indices based on fish functional traits are discussed.

Sensitivity analysis of environmental changes associated with riverscape evolutions following sediment reintroduction: geomatic approach on the Drôme River network, France

The present paper aims to put into practice a conceptual framework for gravel-bed river sustainable management previously proposed by Pont et al. [(2009) Conceptual framework and interdisciplinary approach for the sustainable management of gravel-bed rivers: the case of the Drôme River basin (SE France). Aquatic Sciences, 71 (3), 356–370] for the Drôme River Basin (France). It tests the capacity of the functional sector concept (Petts, G.E. and Amoros, C., 1996. Fluvial hydrosystems. Springer) when used to assess the risks of environmental changes. The application of this concept is illustrated by examples focusing on the potential impacts of sediment replenishment on functional sector diversity used as a proxy of habitat diversity, and on trout distribution at a network scale. We used remote sensing and Geographic Information System (GIS) methods to produce original data. A cluster analysis performed on the components of a principal component analysis established a functional sector typology based on channel planform parameters. We calculated an index of present and 1948 functional sector diversity for the entire channel network to highlight past evolutions. A sensitivity analysis was then performed to predict changes in functional sector diversity resulting from defined options of sediment reintroduction through planned forest removal. A similar procedure was developed to evaluate likely changes in brown trout distribution resulting from the impacts of the actions on canopy cover and summer water temperature. The methodological procedure is described, as well as the different assumptions made to move from a theoretical framework to a more practical one. Two examples are used as pilots to evaluate the value of a sensitivity analysis approach based on functional sector types (FSTs) to test management actions aimed at improving aquatic ecology. Limitations and potential improvements are then discussed.

Effects of temperature on biological and biochemical indicators of the life‐history strategy of bullhead Cottus gobio

The biological and biochemical effects of temperature on life-history strategy of female bullhead Cottus gobio were investigated. Fish from two populations (Bez Basin, south-east France) experiencing contrasted thermal environments (i.e. more or less stable) were reared during 4 months at three distinct temperatures (7, 9 or 12 degrees C). Both somatic (soma fresh mass and muscle triglyceride content) and reproductive (gonad fresh mass, fecundity, mean diameter of eggs and gonad triglyceride content) indicators were examined. Mixed models indicated that an increasing temperature had significant negative effects on all life-history indicators except for soma fresh mass. Differences in life-history strategy with regard to muscle and gonad triglyceride contents, however, suggest that populations experiencing more variable thermal environments may be better adapted than others to cope with an increasing temperature. These findings may have important implications for C. gobio populations, within the context of climate warming.