Biodiversity of floodplain river ecosystems: ecotones and connectivity1

Abstract

A high level of spatio‐temporal heterogeneity makes riverine floodplains among the most species‐rich environments known. Fluvial dynamics from flooding play a major role in maintaining a diversity of lentic, lotic and semi‐aquatic habitat types, each represented by a diversity of successional stages. Ecotones (transition zones between adjacent patches) and connectivity (the strength of interactions across ecotones) are structural and functional elements that result from and contribute to the spatio‐temporal dynamics of riverine ecosystems. In floodplain rivers, ecotones and their adjoining patches are arrayed in hierarchical series across a range of scales. At a coarse scale of resolution, fringing floodplains are themselves complex ecotones between river channels and uplands. At finer scales, patches of various types and sizes form habitat and microhabitat diversity patterns. A broad spatio‐temporal perspective, including patterns and processes across scales, is needed in order to gain insight into riverine biodiversity. We propose a hierarchical framework for examining diversity patterns in floodplain rivers. Various river management schemes disrupt the interactions that structure ecotones and alter the connectivity across transition zones. Such disruptions occur both within and between hierarchical levels, invariably leading to reductions in biodiversity. Species richness data from the connected and disconnected floodplains of the Austrian Danube illustrate this clearly. In much of the world, species‐rich riverine/floodplain environments exist only as isolated fragments across the landscape. In many large rivers, these islands of biodiversity are endangered ecosystems. The fluvial dynamics that formed them have been severely altered. Without ecologically sound restoration of disturbance regimes and connectivity, these remnants of biodiversity will proceed on unidirectional trajectories toward senescence, without rejuvenation. Principles of ecosystem management are necessary to sustain biodiversity in fragmented riverine floodplains. Copyright © 1999 John Wiley & Sons, Ltd.

Cladocera fauna composition in a river-lagoon system of the upper Paraná River floodplain, with a new record for Brazil

“…River floodplains are non-equilibrium systems whose ecological integrity depends upon a certain level of disturbance (Ward et al, 1999). These environments, strongly influenced by water level fluctuations, are heterogeneous landscapes with high biological diversity.…”

Stream restoration and environmental river mechanics

“…Reduced peak flows and incision of the channel bed result in detachment from the floodplain and reduced later migration rates. Changes in the magnitude, frequency and timing of peak flows affect the diversity of habitat features, which in turn affects the biodiversity and sustainability of the ecosystems (Poff et al, 1997;Ward and Stanford, 1995;Ward et al, 1999;Power et al, 1996). Generally, successful restoration strategies downstream of dams should include: restoration of peak flows to reconnect channel and floodplain habitats, stabilization of baseflows, and restoration of seasonal temperature pattern (Stanford et al, 1996).…”

Alterations of riverine ecosystems adversely affect bird assemblages

“…The alteration of flow regimes is the most serious threat to the environment and populations of riverine ecosystems (Naiman et al, 1995;Sparks, 1995;Ward et al, 1999). Humans have expended great effort to regulate watercourses to improve their value for transportation, water supply, flood control, agriculture and power generation.…”