A PRELIMINARY ASSESSMENT OF THE EFFECTS OF ELEVATION AND ASPECT ON DEPOSITION OF AIRBORNE POLLUTION IN AN ALPINE CRITICAL ZONE: SAN JUAN MOUNTAINS, COLORADO, USA

The critical zone, as defined by the National Science Foundation in 2007, is the area that extends from the top of the canopy to the bottom of the aquifer. This zone can be treated as an ecosystem, spatially ranging from tropical locations to high alpine and arctic locations. A scenic and mineral-rich critical zone occurs in the San Juan Mtns. Alpine critical zones occur as systems and are impacted by various components including, inputs, storages, pathways, and outputs. All of these components facilitate what enters, leaves, remains, and the routes of travel through the system. How mass or energy enter, leave or remain is regulated by various types of thresholds. Airborne pollutants enter the critical zone system, and, unfortunately, can negatively affect on not only the immediate, but surrounding biological and anthropogenic communities. Previous studies in Europe and the eastern US, suggest, for site-specific locations, that elevation and aspect may play a significant role in patterns of deposition. Thus, one can ask: what is the threshold-role of elevation and aspect on volumes and spatial patterns of deposition of pollutants in the San Juan Mountains? The research objective is to establish ranges and degree windows for elevation and aspect, respectively. Preliminary deposition data and water-quality data were collected for Aluminum, Iron, Manganese, Nitrate, Phosphate, and Sulfate; temperature, dissolved oxygen, pH, and specific conductance were also collected for the water samples. Dry deposition samples were collected using 1.5 um filter paper which was deployed for five days; wet deposition was collected using plastic rain gauges. Water quality samples were collected in-stream adjacent to the deposition sample sites. Samples were collected at four uniform elevations along four streams between two aspects for a total of sixteen sample sites. Differences in concentrations of the measured pollutants at different elevations and aspects suggest a first approximation of the effects of aspect and elevation on pollution deposition. Refining the elevation zones and spatial aspects most affected by airborne pollution will facilitate a better understanding of the impact on this system. These findings will also be useful for the management, prevention, and remediation of pollutant effects to the San Juan ecosystem.