GIS AND MORPHOMETRIC ANALYSES OF HYDROLOGIC BASINS FOR INVESTIGATING VARIABLES INFLUENCING GEOLOGIC SOURCES OF METALS ALONG THE SAN JUAN RIVER THROUGH NAVAJO NATION

The San Juan River and its tributaries are a vital water source to the southwestern U.S. Water quality analyses indicate that some metals exceed EPA thresholds throughout the San Juan basin. Constituents of concern (As, Pb, Al, U, and Se) to the San Juan River through Navajo Nation are the focus of a collaborative study with Navajo Nation EPA. Anthropogenic sources of metals could be from legacy mining, petrochemical extraction, coal power plants, municipal waste, and urban and agricultural runoff. Elevated metal concentrations also occur in lithologies sourced from Precambrian to Paleogene igneous terrain in upper elevation headwaters and in Paleozoic to Quaternary sedimentary strata and alluvium further downstream. GIS analysis characterized variables involving terrain, hydrology, and geology that may control lithologic sources of metals. Analysis was performed at the 8-digit HUC scale and using 30-m resolution, Shuttle Radar Topography Mission digital terrain data. Hydrologic networks were delineated, and morphometric parameters determined (e.g., stream order, stream length, basin area, drainage density, relief ratio) to investigate parameters important in effecting water quality. Rock and sediment data from the U.S.G.S. National Geochemical database provided information on geochemical background sources of metals. Geologic unit areas were calculated and intersected with the hydrologic network to test correlations between upstream geology, morphometric parameters, and water quality at basin outlets. Geologic units known to be potential metal sources are locally prevalent. Where specific geologic units are widespread and morphometric parameters are favorable for enhanced weathering, predictions of water quality at basin outlets may be possible.