Description of Study Objectives

The three primary objectives of the EUSE study are as follows:

• Determine the hydrologic, geomorphic, chemical, habitat, and biological characteristics of streams that respond to land-use changes associated with urbanization in specific environmental settings and among a range of environmental settings.

• Determine the most important landscape features associated with or related to hydrologic, chemical, geomorphic, habitat, and ecological responses to urbanization.

• Determine the physical and chemical characteristics associated with biological responses and compare these characteristics across environmental settings.

In 1999 a series of investigations were initiated in the NAWQA Program to examine differences in biological, chemical, and physical characteristics of streams across a gradient of urban-development intensity. Approximately 30 relatively small watersheds (typically ranging in area from 50 to 250 square kilometers [km²]) were studied in each of the nine study areas across the United States; a total of 265 watersheds were studied (table 1, 108 KB). These study watersheds correspond to a gradient of urbanization. Urban characteristics, such as land use and density of housing and infrastructure, as well as a composite measure of urban intensity (McMahon and Cuffney, 2000; Tate and others, 2005) range from relatively low intensity to relative high intensity within the study watersheds. Within each of the nine study areas, differences in variability of natural features, such as topography and soil characteristics, were minimized to enhance the likelihood of detecting any effects of urbanization in instream response.

Urbanization, represented by urban land-cover, infrastructure, socioeconomic conditions, and other development characteristics, affects stream ecosystems by a number of intervening processes (fig. 2). The EUSE study was designed to collect information about the processes associated with this complex system and address the objectives described above.

Figure 2. Conceptual framework for studying the effects of urbanization on stream ecosystems, 1999–2004.