Nutrient and Sediment Loading in Streams of the Lake Atitlán Watershed

Authors: Tracy Allen*, SUNY-Oneonta, Devin Castendyk, Golder Associates, Lakewood, Colorado, Alejandra Aguilar, University of San Carlos, Guatemala, Hugo Villavicencio, University of Alaska, Anchorage
Topics: Water Resources and Hydrology, Geography Education, Environmental Science
Keywords: Streams, water quality, land use, study abroad, experiential learning
Session Type: Poster
Day: 4/11/2018
Start / End Time: 3:20 PM / 5:00 PM
Room: Napoleon Foyer/Common St. Corridor, Sheraton, 3rd Floor
Presentation File: No File Uploaded

Lake Atitlán is located in the southwestern highlands of Guatemala. It is situated inside of a collapsed caldera, surrounded by an escarpment and flanked by three volcanoes. While its setting is dramatic, the water quality of the Lake has been in steady decline. Nutrient loading has led to unprecedented outbreaks of cyanobacteria in 2009 and 2015, and water renowned for its clarity has been clouded. Until recently, the large volume of water in the Lake, 130 km2 surface area by 328 meters maximum depth, diluted contaminants. Because Lake Atitlán is endorheic, three short, high-gradient streams deliver pollutants which accumulate and have no surface outflow. Each summer over the past four years, students in a faculty-led, study-abroad, field course sampled the upper, middle, and lower reaches of the San Francisco, Quiscab, and Catarata streams for nitrogen, phosphorous, and turbidity. All measures of these pollutants far exceed acceptable stream water quality standards. Maximum nitrate and phosphate concentrations reach 11.98 mg/L and 2.09 mg/L, respectively. The major sources of nutrients are human waste and fertilizers, and easily erodible volcanic ash is the primary supplier of sediments. Flash floods, poor land use practices, steep hydraulic gradient, and in-stream gravel mining exacerbate loading. This presentation will discuss spatial and temporal trends in stream water quality, as well as the effect of this experience on student participants.

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