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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5101–D

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Table 9. Spearman’s rank correlation coefficients (rho values) between diatom algal metrics and the urban intensity index and select environmental variables, Willamette River basin and surrounding area, Oregon and Washington.

[See appendix A for definitions of environmental variables. Average concentrations were used for TN, NO₂+NO₃, total phosphorus, soluble reactive phosphorus, specific conductance, SO₄, and DOC. Correlation coefficients were considered strong when absolute value ≥ 0.66 (bolded and shaded) and moderate when 0.66 > rho ≥ 0.50 (bolded). Nutrient, nitrogen, and oxygen taxa: van Dam and others (1994). High nutrient indicating (eutrophic) taxa require high nutrient levels. Nitrogen heterotrophs–taxa may use organic nutrient forms. High organic taxa-α-meso/polysaprobous–taxa indicative of depressed dissolved oxygen levels (10–70 percent) and elevated biological oxygen demand (4–22 mg/L). Brackish water–taxa tolerate elevated levels of dissolved ions. Low oxygen–taxa tolerant of low dissolved oxygen levels. High oxygen–taxa require high dissolved oxygen levels. Pollution, Bahls (1993): tolerant–taxa generally tolerant of nutrient and organic enrichment; sensitive–taxa generally sensitive to nutrient and organic enrichment. Silt index: calculated by Sprouffske and others, 2006. Sum of motile Navicula and Nitzschia diatom taxa. Abbreviations: mg/L, milligram per liter; nd, no data]

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