HISTORICAL CHANGES IN SPRING DISCHARGE IN THE WHITE MESA CULTURAL AND CONSERVATION AREA, MANTI-LA SAL NATIONAL FOREST, SOUTHEASTERN UTAH

Although there are considerable anecdotal data that springs have been disappearing in southwestern forests, there has been remarkably little systematic documentation of historical changes in spring discharge, especially compared to the hundreds of studies of historical changes in discharge of forest streams. In 2013 an agreement was reached among the Ute Mountain Ute Tribe, the Grand Canyon Trust, and the U.S. Forest Service to create the White Mesa Cultural and Conservation Area (WMCCA) on 28,000 acres of the Manti-La Sal National Forest, which was part of the historic homeland of the Ute Mountain Ute Tribe in southeastern Utah. According to the agreement, the WMCCA will not be grazed until 2022. The WMCCA had not previously been grazed since 2001 and is currently the only non-grazed portion of the Manti-La Sal National Forest, so that it is the only portion of the 1.2 million-acre national forest where hydrologic changes in the absence of anthropogenic impact can be studied. The objective of this study is to assess the present status of springs and groundwater flow paths in the WMCCA for comparison with historic maps and databases and as a baseline for comparison with future measurements. Water samples were collected from 20 springs emerging from sandstones of the Triassic Ankareh, Chinle, Dinwoody, Moenkopi, Thaynes and Woodside Formations. Water temperature (8.1-21.8 °C), pH (7.11-10.63), electrical conductivity (149-970 µS/cm), and oxidation-reduction potential (134.1-224.7 mV) were measured on-site. Discharges measured from the 10 flowing springs ranged from 0.011-0.792 L/s. The PerkinElmer Optima 8000 ICP-OES is being used to analyze water samples for Ag, As, Au, Bi, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Th, Ti, U, and Zn. In order to assess groundwater sources and pathways, water samples from all springs are being measured for the stable isotopes of hydrogen and oxygen. In order to assess the residence time of groundwater, water samples from two springs are being analyzed for concentrations of the anthropogenic gases CFC and SF₆. Preliminary measurements indicate that the groundwater in the spring with the greatest discharge has a residence time of 35 years. Further results will be reported at the meeting.