Riparian Ecosystem Creation and Restoration:
A Literature Summary
Functions
A fundamental function of rivers, the transport of water and sediments, is influenced by the interaction of geologic, climatic, hydrologic, geomorphic, pedogenic (soil), and biotic processes (Platte et al. 1987b). The magnitude and direction of functional relationships in riparian zones are influenced by hydrology, topography, vegetation, and their interaction (Chapman et al. 1982). A major role of the riparian zone is to dissipate stream energies associated with high flows (Van Haveren and Jackson 1986). This, in turn, permits sediments to deposit and continue development of the alluvial valley floor.
Alluvial riparian zones also function as shallow aquifers that recharge at high flows and drain at low flows (Van Haveren and Jackson 1986). This interaction between surface flows and groundwater storage results in moderated high flows and enhanced or prolonged base flows. The shallow aquifer condition also creates moist soil conditions favorable for riparian plant growth.
Thus, geomorphic and hydrologic characteristics of riparian zones establish the basic components of biological habitat, including saturated soils and instream structural features such as pools, riffles, gravel, and streambanks (Van Haveren and Jackson 1986). Vegetation that thrives in riparian zones, in turn, contributes to geomorphic and hydrologic functioning. Disruption of normal geomorphic or hydrologic function, or the vegetation on which it depends, usually results in impairment to overall riparian resource values.
Vegetation supplies litter that, when covered with sediment during overflow, rapidly decomposes to release nutrients and adds humus to the soil. This process is vital to maintaining productive riparian ecosystems (Anderson et al. 1979). Litter is a key element in the productivity of wetlands and eventually determines the value of a site for animals (Fredrickson and Reid 1986). In seasonal environments, the entire above-ground biomass becomes litter following senescence. Structurally intact above-ground plants, living and dead, are colonized by periphyton that provide food for grazing macroinvertebrates, which in turn provide food sources for a variety of fish and wildlife species.
Ischinger and Schneller-McDonald (1988) analyzed information in the WCR Data Base on the creation and restoration of various freshwater habitats in the western U.S. and found that the function of riparian wetland as valuable wildlife habitat and its contribution to stream fish habitat had been documented. The sediment control, bank stabilization, and flood attenuation functions of riparian wetlands had been documented to some degree. However, the data base contained few articles that quantified functions of natural wetlands in the West or that compared restored or created wetland functions to those of undisturbed sites. Unfortunately, little or no information on the food chain support, water quality, or groundwater recharge/discharge function of wetlands was provided in the data base. This also is true of riparian information for other regions of the U.S. in the data base.
Providing fish and wildlife habitat was the most often stated objective of riparian ecosystem habitat literature in the WCR Data Base. Many of the articles on riparian ecosystem creation/restoration, particularly the more recent ones, include some discussion of wetland functions other than fish and wildlife habitat. However, few attempts have been made to evaluate the hydrologic flow, erosion control, or water quality improvement capabilities of created or restored wetlands.
Previous Section -- Costs of Creation/Restoration
Return to Contents
Next Section -- Fish and Wildlife habitat
