Introduction

The riparian zone of running water systems is a site of intensive ecological interactions between the aquatic and the terrestrial parts of the stream valley. Wetlands that occur in this zone exchange water with the aquifer and with the main channel during flood events (Figure 1). Riparian wetlands are buffer zones for the water budget of the landscape: they take up excess water from flood events and release it gradually afterwards.

Modern ecological theory recognizes the important role riparian wetlands play for biodiversity and for the energy and matter budgets along the whole range of river courses. The carbon and nutrient budgets are influenced by dissolved and particulate substances from the bordering terrestrial ecosystems, by the autochthonous production from the wetland plants, and by allochthonous organic matter delivered by the floodwater. The proportions between these sources are defined by the hydrological patterns, landscape morphology, and climatic conditions. (see Rivers and Streams: Physical

Figure 1 Inputs, turnover, and exchange of organic matter in the stream channel (left) and a riparian wetland water body (center) at low and high water levels. Black arrows indicate organic matter inputs, white arrows indicate water exchange pathways, spirals indicate nutrient spiralling or downriver transport, and circular arrows indicate sites of organic matter turnover in situ. Curly brace indicates water-level fluctuations during flood events. Modified from Wantzen KM, Yule C, Tockner K, and Junk WJ (2006) Riparian wetlands. In: Dudgeon D (ed.) Tropical Stream Ecology, pp. 199-217. Amsterdam: Elsevier.

Figure 1 Inputs, turnover, and exchange of organic matter in the stream channel (left) and a riparian wetland water body (center) at low and high water levels. Black arrows indicate organic matter inputs, white arrows indicate water exchange pathways, spirals indicate nutrient spiralling or downriver transport, and circular arrows indicate sites of organic matter turnover in situ. Curly brace indicates water-level fluctuations during flood events. Modified from Wantzen KM, Yule C, Tockner K, and Junk WJ (2006) Riparian wetlands. In: Dudgeon D (ed.) Tropical Stream Ecology, pp. 199-217. Amsterdam: Elsevier.

Setting and Adapted Biota and Rivers and Streams: Ecosystem Dynamics and Integrating Paradigms).

The crossover between humid and dry conditions creates habitats for organisms coming from either aquatic or terrestrial ecosystems, and for those biota that are specialized on wetland conditions. As the transversal dimension of streamside wetlands is generally small, their overall importance for landscape ecology, biogeochemistry, and biodiversity is often overlooked. However, the total size of these wetlands can be considerable in areas with dense stream networks. Moreover, the corridor-shaped extension of riparian wetlands makes them perfect pathways for the gene flow between remote populations of aquatic and terrestrial biota. Many ecological services are uniquely provided by riparian wetlands, including erosion control, filtering of nutrients and pesticides from adjacent cropland, mitigation of floods, and recreation, which increases their conservation value in a socioeconomic context.

There is a large array of environmental conditions that vary between the different types of riparian wetlands, especially climatic region and prevailing vegetation type, and landscape morphology and hydrologic patterns. This article deals with the different types of riparian wetlands, their deterministic environmental conditions, prevailing ecological processes, typical biota, and aspects of conservation.

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