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Box 1. Varimax-rotated environmental factors for 31 sites in the upper Rio Grande drainage of New Mexico. Variable Factor 1 Factor 2 Factor 3 Factor 4 Factor 5 Factor 6 Alkalinity 0.85040 0.36683 -0.00391 0.21518 0.05734 0.19357 Ammonia 0.09892 -0.11185 0.11320 -0.14243 0.04580 0.75629 Bicarbonate 0.84804 0.37410 -0.00018 0.20776 0.05795 0.19466 Calcium 0.806S1 0.09680 0.09734 -0.00870 -0.11721 -0.30985 .Chloride 0.10262 0.9S623 0.00416 .•0:01468 10:02465 " 0:04762 Embeddedness 0.06590 -0.02726 0.26940 0.79469 0.17357 -0.07892 Growing Season Length 0.73071 0.40537 -0.05243 0.24037 0.34078 -0.00160 Hardness 0.93223 0.04635 0.27557 0.12226 -0.03698 -0.00169 In-Stream Vegetation 0.20603 0.13042 0.07987 0.80607 -0.17535 -0.01679 Kjeldahl Nitrogen 0.10137 -0.05777 0.15316 -0.10528 0.67039 0.39961 Land Use Designation 0.19491 -0.11671 -0.82315 0.01711 -0.00460 -0.24612 Magnesium 0.78615 -0.10677 0.46646 0.16139 -0.11792 -0.07710 Elevation -0.81446 -0.24652 0.04515 -0.12477 -0.28562 -0.13670 Nitrate/Nitrite 0.26685 -0.27446 0.37913 -0.23388 0.10403 -0.61581 Potassium 0.20740 0.93222 -0.00760 0.11828 0.06890 -0.01340 Sodium 0.48128 0.84040 0.08408 -0.03056 0.02652 -0.09654 Substrate Composition 0.25396 -0.29507 0.12757 -0.06772 -0.72472 0.09060 Sulfate 0.69700 -0.01647 0.16408 -0.37218 -0.13649 -0.26542 Total Dissolved Residue 0.77394 0.53275 0.06788 -0.06316 -0.02551 -0.04394 Total Phosphate 0.34466 -0.05454 0.61817 0.33144 -0.07241 -0.11261 Total Suspended Solids 0.49097 -0.00058 0.77127 0.26862 0.07772 -0.18428 Watershed Area 0.44774 -0.14931 -0.01310 0.02408 0.60074 -0.35551 Eigenvalue 6.94910 3.53119 2.58278 1.91668 1.67959 1.63921 t Variance Explained 31.6 16.1 11.7 8.7 7.6 7.5 environmental factors obtained for the upper Rio Grande drainage. Six multivariate environmental factors account for 83.2% of the variance (Box 1) among sites in the upper Rio Grande drainage. Factor 1 represents elevation and chemical and physical attributes that vary inversely with elevation. In decreasing order of magnitude of coefficients, the most important chemical and physical variables that vary inversely with elevation are hardness, alkalinity, bicarbonate, calcium, total dissolved residue, growing season length, and sulfate. This factor explains about 32% of the multivariate variance. The second factor (Box 1) is indicative of chloride, potassium, and sodium content of the water and it explains about 16% of the variance. Factor 3 is a contrast between the categorical variable "land use designation" and total phosphorus and total suspended solids. This factor describes about 12% of the variance. Factor 4 represents embeddedness and in-strum vegetation and describes about 9% of the sample variance. The fft factor, which explains about 8% of the variance, contrasts substrate composition with Kjeldahl nitrogen and watershed area. Factor 6 (about 7% of the variance) contrasts ammonia with nitrate/nitrite. I,tD 9