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Scientific Investigations Report 2006–5101–D

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]

Environmental variables Diatom metric
High indicating taxa   Oxygen indicating taxa   Pollution Silt
index
Nutrient
(eutrophic)
Organic
enrichment
Organic
nitrogen
Low High Tolerant
taxa
Sensitive
taxa
Urban intensity index (UII) 0.46 0.52 0.38 0.33 -0.46 0.36 -0.45 0.40
Total nitrogen (TN) .37 .47 .62 .44 -.27 .71 -.62 .50
Nitrite+nitrate (NO2+NO3) .28 .24 .41 .18 -.15 .63 -.47 .44
Total phosphorus (TP) .55 .64 .69 .62 -.57 .67 -.68 .70
Soluble reactive phosphorus (SRP) .65 .44 .57 .42 -.62 .59 -.51 .62
Nutrient index .52 .54 .65 .52 -.44 .70 -.63 nd
Specific conductance .67 .52 .51 .48 -.74 .50 -.50 .63
Summertime dissolved oxygen (DO) -.20 -.45 -.27 -.47 .28 -.36 .46 -.39
Summertime minimum water temperature .41 .53 .51 .51 -.39 .51 -.61 .52
Sulfate (SO4) .53 .45 .49 .35 -.52 .53 -.44 .60
Dissolved organic carbon (DOC) .25 .70 .56 .69 .50 -.61 .58
Chlorophyll-a .11 .44 .69 .40 -.08 .62 -.56 .54
Ash-free dry mass (AFDM) .29 .63 .73 .63 -.31 .66 -.69 .69

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