Establishing a baseline and tracking changes in water quality & chemistry prior to large-scale mining activities in a desert watershed
Brian T. Thompson
Department of Hydrology and Atmospheric Sciences
The University of Arizona, Tucson, AZ
It is important to establish a baseline of water quality in a watershed prior to the establishment of mining operations to better assess future impacts. This can be accomplished by collecting storm water and baseflow samples along potentially-affected creeks and ephemeral washes. Cienega Creek Natural Preserve is a protected riparian corridor in Pima County, Arizona, that is a reservoir of biodiversity and endangered aquatic species. A large porphyry copper mine is in the final stages of being permitted and would be established on a ridgeline above one of the major ephemeral tributaries of Cienega Creek. Previous research reported increasing levels of suspended and dissolved metals during storm flow events and in base flow starting in 2022 as land began to be cleared for the development of mining activities. My research builds on this recent work to see if trace metals concentrations continue to increase with further land disturbance in headwaters of the catchment. Basic water chemistry (e.g. pH, alkalinity), as well as cations, anions, and dissolved metals were collected and analyzed from base flow and storm event samples. Initial results indicate that some total and dissolved metal concentrations (particularly zinc and copper) in both storm flow and base flow continue to show an upward trajectory. Increased metals in streamflow could have negative implications for aquatic life in Cienega Creek.