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Ecological Responses of Streams to Urbanization: A US Geological Survey Review

Explore the impact of urbanization on biological, physical, and chemical responses in streams across the US, with insights on monitoring, planning, and mitigation strategies. Discover the correlation between urban intensity and biological degradation, chemical trends, and hydrologic changes.

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Ecological Responses of Streams to Urbanization: A US Geological Survey Review

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  1. North Carolina Water Science Center Ecological responses of streams to urbanization: A review of results from the U.S. Geological Survey's urban streams studies Thomas F. Cuffney North Carolina Water Science Center Raleigh, North Carolina

  2. National Water-Quality Assessment (NAWQA) Program 11 Urban Stream Studies Seattle Portland Milwaukee-Green Bay Boston Salt Lake City Denver Sacramento Raleigh Birmingham Atlanta Dallas-Ft. Worth

  3. Raleigh Urban Study Area Piedmont

  4. Objectives: • Define biological, physical, and chemical responses to urbanization across conterminous US. • Identify the primary environmental factors associated with these responses. • Compare how responses and driving factors change across the US. -- What measures best depict urban effects (monitoring)? – What factors can be changed to mitigate urban effects (planning and remediation)? – Can urban effects be managed using national criteria or are regional or local criteria required (management and legislation)?

  5. Representing urban intensity: urban intensity index (UII) Index based on land-cover, population, infrastructure and socioeconomic factors correlated with changes in population density

  6. Urban variables positively correlated with population density

  7. Urban variables negatively correlated with population density

  8. Urban intensity index (UII) Raleigh Example: Census variables: 2000 population density Household density National Land-cover Data: % of basin in developed lands % of stream buffers in developed lands Infrastructure: road density

  9. % Impervious and Urban Intensity index (UII) -- Atlanta

  10. Urban intensity (UII) at 10% impervious surface 0.92 0.95 0.88 0.92 0.95 0.78 0.95 0.83 0.88

  11. Biological responses to urbanization Fish, Invertebrates, and Algae

  12. Expected response Good Biological condition (≈ 10 % impervious surface) Poor Urban intensity (UII)

  13. Typical response (Inverts Atlanta) 10% impervious surface 40% of total change Invertebrate response

  14. Boston Fish: Exhaustion Fish response Urban intensity (UII)

  15. Invertebrates responses to urbanization (Y = a + b*UII) across US

  16. Invertebrates responses to urbanization (Y = a + b*UII) across US

  17. Land cover at “background” sites: UII < 20 Forest + shrublands Agriculture Agriculture + grasslands Irrigation? Grazing? % Basin area WEST CENTRAL EAST

  18. Summary of biological responses to urbanization (UII) • Significant relation between urban intensity and biological degradation. • Invertebrates are the strongest and most consistent indicators. • Algae and fish responses are more variable. • Relations were strongest when urbanization involved conversion of forest or shrub lands. • Relations were weakest when urbanization involved conversion of agricultural or grass lands. • Little evidence for resistance to urbanization (no initial threshold).

  19. Changes in water chemistry associated with urbanization and biological responses

  20. Chemical trends with urbanization • Conductivity • Pesticides: • Number detected • Total concentration • Pesticide index • Nutrients: Chemistry Invertebrates

  21. Chemical trends with urbanization (continued) • Polycyclic aromatic hydrocarbons (PAH): • Number detected • Total concentration • Very few instances where human or aquatic life standards were exceeded. • Relations with urbanization were also affected by presence of agriculture and grasslands (Central: Dallas, Denver, Milwaukee). Chemistry Invertebrates

  22. Hydrologic changes associated with urbanization and biological responses

  23. Key Findings from Urban Studies • Degrades biological communities: • Invertebrates are “best” biological indicator. • No level of urbanization without an effect. • Increases chemical contamination: • Number and conc. of pesticides. • Number and conc. of PAH’s. • Modifies hydrology • Increases flashiness. • Decreases duration of peak flows in many urban areas, but not all.

  24. Key Findings (continued) • Factors associated with urban degradation that may be useful for mitigation: • Decrease effects of road density in basin. • Decrease effects housing density in basin. • Restore forest and shrub lands (basins and buffers). • Restore connection between precipitation, ground water, and surface water (restore normal hydrology). • Responses vary geographically: • East = West in biological (invertebrate) responses. • = Central (agriculture + grasslands). • Extent of “background” degradation affects how biology and chemistry respond to urbanization. • Regional approaches to management and legislation may be required. /

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