A conceptual framework for assessing impacts of roads on aquatic biota

Roads are pervasive features of modern landscapes and have major impacts on air, land, and water quality. The United States has >6.2 million km of public roads used by >200 million vehicles (National Research Council [NRC]1997). Road corridors (road plus maintained parallel strips) cover 1% of the United States (NRC 1997) but their direct environmental impacts extend to 20% of the land surface (Forman 2000). Ecological effects extend 100 to 1,000 m (average of 300 m) on each side of four-lane roads (Forman and Deblinger 2000). These effects, which stem from both construction and use, vary considerably in type and degree among regions and among particular roads (Forman and Alexander 1998; Trombulak and Frissell 2000). Roads strongly affect the composition and operation of surrounding ecosystems. Natural habitats such as forests, wetlands, and streams are commonly disfigured, fragmented, or contaminated because of roads (Forman and Deblinger 2000; Trombulak and Frissell 2000; Paul and Meyer 2001). Effects on biotic populations and communities can be dramatic and extensive. Major direct effects on wild animals include modified behavior, impaired movement, and mortality from collisions with vehicles (Trombulak and Frissell 2000). Forman and Deblinger (2000) estimated that effects on large mammals, birds, and amphibians typically extended to 300 m on both sides of a four-lane highway in Massachusetts. In addition, key ecological processes, including the transport of water and sediment and the dispersal of organisms, are modified by roads (Forman and Deblinger 2000; Trombulak and Frissell 2000). Despite the increasing prominence of roads across most landscapes, their impacts on aquatic biota are not well documented. Intuitively, effects on water quality (e.g., via toxic spills and runoff), habitat quality (via sediment loading and channel modification), and habitat connectivity (via barriers to movement) may often be severe. Roads may constrain fish distribution and abundance or impair ecosystem health. Many road crossings over streams constrain movements by small fishes (Warren and Pardew 1998). Such movements are essential for individuals to complete their life cycles and for metapopulations to remain viable (Schlosser and Angermeier 1995). To the extent that roads contribute to fine-sediment loading in waterways, they are serious threats to aquatic biota (Waters 1995; Wood and Armitage 1997). Roads are known to endanger 94 species across many taxa in the United States (Czech et al. 2000) and probably contribute to local extirpation and regional endangerment of many fishes. Managers of fishes and fisheries should be keenly interested in the environmental impacts of roads, especially proposed roads. Assessing environmental impacts of human activities on public resources is an iterative collaboration among the public, resource managers, and scientists. Roles of the public include articulating the impacts of concern (e.g., through legislation) and hold-