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.. \. Ict~{f rOvn nl f'lJ e+ ~I. . 1,.TFORNET ,,10NTHL Y ALERT JAN 1986 ':dition 'D0l5 Multiple Regression Analysis for Evaluating Non-Point Source Contributions to Water Quality in the Green River, Wyoming1 tem No. 1..lt1 FHe RETENTION COpy Timothy E. Fannin, Michael Parker, and Timothy J. Maret2 . i.1 Abstract.--The Green-~iver drains 12,000 mi2 of western Wyoming and northern Utah. The basin incorporates a diverse spectrum of geology, topography, soils, and climate. Land use is predominately range and forest, though an increasing number of industries are locating in the southern half of the drainage. We report on the application of a multiple regression model used to associate various riparian and non- riparian basin attributes (geologic substrate, land use, channel slope, etc.) with previous measurements of phosphorus, nitrate, and dissolved solids in the Green River system. We propose possible reasons for such significant water quality/basin attribute associations, and explain some of the advantages and disadvantages of using such a technique to explore those associations in a larRe western watershed. INTRODUCTION The Green River basin of western Wyoming and northern Utah is a Climatologically, topographic- ally, and geologically diverse watershed. Mean o (0 0 temgeratures ran~e from -6 F -21 C) to 86 F (30 C); mean precipitation varies from 11" (28cm) to 41" (104cm), with the latter figure typical for the surrounding mountains. The major vegetative cover in the drainage is range and forest (table 1). e' Table 1.--Land cover by percentage of total basin area in the Green River and Blacks Fork sec- tions (see figure 1) of the Green River Basin. Land cover tYJ)e Alpine Irrigated crops Rock or dunes Wetlands Urban Range Forest Total 2 Area (mi ) Green River section 2 6 1 1 <1 73 16 100 9500 Blacks Fork section o 7 3 1 <1 67 20 100 2920 Ipaper presented at the first North American Riparian Conference. [The University of Arizona, Tucs02' AZ, April 16-18, 1985J. Timothy E. Fannin and Timothy J. Maret are graduate students, and Michael Parker is Associate Professor, in the Department of Zoology and Physi- ~ology, University of Wyoming, Lar~ie, WY. ,.., Thi. p.per 1. b...d upon r....rch conduc~ed under a Brant from the Wyoming Water Research Center, Laramie, WY. Not surprisingly, the area is use~ by man predomin- antely for grazing and forestry. 'Sparsely inhabit- ated, (the population of the study area is only about 52300 people, U.S. Bureau of the Census 1981), other land uses are mining of trona (sodium carbonate) and farming two major areas of irrigated cropland. The basin topographically isoa mixture of ex- tensive flats and rolling hills surrounded on three sides by mountains (fig. 1) Which_have a maximum W.O,",ING lIiAH 'J.",T:' M~"'5 i'j "STAT'"~I " " "Aii.':. ',G t 'laun 1. --Outline map of the study area showing ;-" ., water quality/discharge stations, major stre~ and the Green River and Blacks Fork Sections of the drainage. 201