The reversible process concept applied to the environmental management of large river systems

Abstract

The wetland ecosystems occurring within alluvial floodplains change rapidly. Within the ecological successions, the life span of pioneer and transient stages may be measured in several years or decades depending on the respective influences of allogenic (water dynamics, erosion, and deposition) and autogenic developmental processes (population dynamics, eutrophication, and terrestrialization). This article emphasizes the mechanisms that are responsible for the ecosystem changes and their importance to environmental management. Two case studies exemplify reversible and irreversible successional processes in reference to different spatial and temporal scales. On the scale of the former channels, the standing-water ecosystems with low homeostasis may recover their previous status after human action on the allogenic processes. On the scale of a whole reach of the floodplain, erosion and deposition appear as reversible processes that regenerate the ecological successions. The concepts of stability and reversibility are discussed in relation to different spatiotemporal referential frameworks and different levels of integration. The reversible process concept is also considered with reference to the energy inputs into the involved subsystems. To estimate the probability of ecosystem regeneration or the cost of restoration, a concept of "degrees of reversibility" is proposed.Within large river systems, the environmental management of alluvial floodplains raises some particular problems related to the rapid changes of wetlands on a decennial time scale. The lifetime of the involved ecosystems spans only some years or decades, a temporal-spatial phenomenon pertinent to the concepts of stability and instability. Therefore, how can we use concepts elaborated within theoretical ecology or other sciences to provide assistance to decision makers?Many authors have studied stability and the assimilative capacity with regard to the living communities (Webster and others 1983), but few have addressed the biotope as well. Since whole ecosystems (that is, biocoenose plus biotope) are involved in environmental management, we focus here on ecosystem changes and the mechanisms responsible for these changes. We therefore address two principle questions: Which of these processes allow the system to return to a previous developmental stage? And within

Assessment of the effects of cyclic floodplain rejuvenation on flood levels and biodiversity along the Rhine River

“…Cyclic Floodplain Rejuvenation may be a feasible strategy in rivers where geomorphic dynamics has diminished and flood safety is a concern, in the USA (USACE, 2000;Bolton and Shellberg, 2001), as well as in Europe (Buijse et al, 2002). In highly regulated rivers it is impossible to return the ecosystem to its pristine state (Amoros et al, 1987). Moreover, it may even prove difficult to reintroduce geomorphological dynamics that are strong enough to restore habitat heterogeneity.…”

Floodplains of a regulated southern alpine river (Brenno, Switzerland): ecological assessment and conservation options

“…The spectrum from allogenic to autogenic processes includes both fast rejuvenation processes caused by intense fluvial morphodynamics and slow terrestrialization processes by eutrophication and internal accumulation of fine matter (Amoros et al, 1987a). In general, human-induced reductions in fluvial dynamics impede rejuvenation and promote terrestrialization processes (Ward and Stanford, 1995).…”

“…The rarity of active floodplains in Europe (Brown et al, 1997) renders this an urgent task. The assessment of stability and reversibility of ecological succession in a floodplain indicates the recovery potential (Amoros et al, 1987a). The degree of reversibility depends on the role that autogenic and allogenic development processes play in different functional habitats and the way in which human influences have transformed these roles.…”

Importance of floodplain waters for the conservation of chironomid (Diptera) biodiversity in a 6thorder section of the Garonne river (France)

“…In Europe, in the first half of the XX th century, planning of rivers with the aim of commercial navigation and hydro-elec tric production involved the separation of the main channel from its alluvial plain (Walker 1985, Ward & Stanford 1986. The result was an alteration of the floodplain waters, which progressively filled in and di sappeared (Amoros et al 1987, Finlayson & Moser 1991, Ward & Stanford 1995b. However, the length of time that this takes allows the conservation of these zones within the large river systems and enables the study of their functioning, as for example, on the River Danube (Heiler et al 1994, Tockner & Bretschko 1996, the Rhine and the Meuse rivers in the Netherlands (Van den Brink & Van den Velde 1991) or on the French Haut-Rhóne (Amo ros 1991, Castella et al 1991, Cellot et al 1994).…”