To determine whether urban watersheds can act as fractal filters, spectral analysis was applied to 13 years of weekly stream chemistry data for chloride, nitrate and sulfate from eight watersheds in the Baltimore metropolitan area. The analysis was also applied to high-frequency (15- and 30-minute) sensor data for nitrate and specific conductance over periods ranging from several weeks to four years. Spectral analysis of weekly stream chemistry data produced power slopes of 0.60 to 1.2, the same range found for forested watersheds in previous studies. Spectral slopes decreased with increasing watershed percent impervious surface cover, suggesting that the power spectrum is whitened with increasing degree of urbanization. Spectral analysis of high-frequency water quality data spanning a period of four years showed that a break in power slopes occurred near a frequency of 1/week, with a slope of approximately 2 for data at frequencies higher than 1/week regardless of degree of urbanization. The analysis suggests that differing processes dominate the spectra in two discernible frequency domains, with seasonal, annual, and interannual processes dominating the low frequency domain and diurnal and intraweekly processes dominating the high-frequency domain. Such trends cannot be detected solely from analysis of either long-term weekly data or short-term high-frequency data.
|Commitee:||Ghosh, Upal, Kaushal, Sujay, Miller, Andrew J.|
|School:||University of Maryland, Baltimore County|
|Department:||Engineering, Civil and Environmental|
|School Location:||United States -- Maryland|
|Source:||MAI 51/02M(E), Masters Abstracts International|
|Subjects:||Hydrologic sciences, Environmental engineering|
|Keywords:||Spectral analysis, Urban watershed, Water quality sensors|
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