Chapter 1: Overview and Background
The degradation and simplification of aquatic systems from anthropogenic activities has led to large efforts throughout the world to restore aquatic habitats for economic, cultural, and environmental reasons (NRC 1992). Nowhere is this more evident than in temperate streams, rivers, and estuaries of North America, where hundreds of millions of dollars are invested annually in restoring or improving habitat to increase both resident and anadromous fish populations. For example, between 2000 and 2003, the U.S. government distributed more than $170 million to the states of Washington, Oregon, California, and Alaska, to fund restoration of salmon habitat under the Pacific Coastal Salmon Recovery Fund (Joe Scordino, National Marine Fisheries Service, Seattle, personal communication). Millions more are invested by other federal, state, provincial, and local programs throughout Canada and the United States to restore aquatic ecosystems for salmonids and other coolwater biota.
These restoration efforts are largely in response to impacts on watersheds and estuaries that occurred following European settlement of North America. Forest practices have negatively impacted many streams by increasing fine and coarse sediment, altering stream hydrology, disrupting delivery of woody and organic debris, and simplifying habitat (Salo and Cundy 1987; Meehan 1991; Murphy 1995). Improving the navigation of rivers and estuaries through dredging and snagging (removal of wood), still widely practiced today, has greatly simplified many rivers (Sedell and Froggatt 1984; Collins et al. 2003). Agricultural activities have had detrimental effects on estuaries, floodplains, wetlands, and low-gradient tributaries through dredging, draining, filling, pollution, and channelization of waterways (NRC 1992). Irrigation and the overappropriation of water rights, particularly in arid regions, has led to reduced stream flows, which can lead to higher water temperatures, changes in hydrology, reduced total wetted habitat, reduced ability to transport sediment, and other deleterious effects (Orth 1987; Hill et al. 1991). Mining and other extraction industries have had many negative effects on streams, from direct alteration and removal of substrates to pollution and release of toxic substances (Nelson et al. 1991). Residential development, industrialization, and urbanization have lead to a suite of problems for aquatic habitats, including filling and channelization, changes in hydrology from increased impervious surface area, pollutants from point and nonpoint sources, elimination of riparian zones, and simplification of habitat (Booth 1990; Booth et al. 2002; Conrad 2003). All these factors have contributed to the degradation and simplification of aquatic habitats across entire ecosystems and are the basis for the development of numerous rehabilitation techniques and comprehensive restoration efforts underway.