National Water-Quality Assessment (NAWQA) Program

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Effects of Urbanization on Stream Ecosystems

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Brief Overview

Why study urbanization:
As land areas urbanize, stream ecosystems can be substantially altered. Changes in the landscape as a watershed urbanizes may cause changes in stream hydrology, water quality, physical habitat, and water temperature that are known to have profound effects on aquatic communities of algae, invertebrate and fish. Understanding these interrelationships may contribute to informed decisions that result in practical and effective water-resource management and strategies that protect and restore stream ecosystems.

How this study is unique:
Although there have been many studies conducted on the effects of urbanization on streams, these studies have different designs, limited geographic scope, and measure a limited number of responses. In this study, each study adheres to a nationally consistent design, and measures many response variables using consistent sampling protocols and lab analytical procedures, so that responses to urbanization can be compared locally, regionally, and nationally.

Questions Addressed:
• How do stream ecosystems respond to land-use changes associated with urbanization?
• How do these responses vary across metropolitan areas located in different geographic settings?

• Determine the physical, chemical, and biological responses of stream systems to a gradient of increasing urban intensity.
• Determine the most important landscape features driving hydrologic, chemical, geomorphic, habitat, and ecological responses to urbanization.
• Determine the physical and chemical factors associated with biological responses.
• Compare these responses among metropolitan areas located in different geographic settings (climate, geology, hydrology, biology, water use) across the United States.

Study Design:
For each metropolitan area, locate stream sites in 28-30 basins that have minimal natural variability among them and represent a broad range of urban intensity from low to high. Examine hydrologic, physical habitat, chemical, and biological characteristics of the streams at these sites.

Timing and Locations:
Studies are conducted on a rotational sampling schedule through 2012, including in Birmingham, Alabama; Boston, Massachusetts; and Salt Lake City, Utah, in 2000; Raleigh, North Carolina; Atlanta, Georgia; and Denver, Colorado, in 2003; Dallas-Fort Worth, Texas; Milwaukee-Green Bay, Wisconsin; and Portland, Oregon, in 2004; and Seattle, Washington, in 2007.

What we measure:
• Physical: physical habitat, stream stage, and water temperature.
• Chemical: nutrients, pesticides, organic carbon, suspended sediment, sulfate, chloride, dissolved oxygen, pH, specific conductance in water, and organic contaminants and potential toxicity of extracts of semi-permeable membrane devices (SPMDs - devices that concentrate trace levels of hydrophobic organic contaminants from water).
• Biological: invertebrate, algae, and fish communities, and algal biomass (chlorophyll a, ash-free dry mass).

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