Abstract
 A Practical Method for Calculating Lake Volume Over Time: Using GPS to measure water availability in small lakes inhabited by the Mountain yellow-legged frog (Rana muscosa) in Kings Canyon National Park, California Track: Ecology and Conservation Author(s): Igor Lacan, Krishna Feldman, Kathleen Matthews To determine changes in water availability for the imperiled mountain yellow-legged frog (MYLF, Rana muscosa), we used resource-grade GPS and ArcGIS with 3D Analyst to estimate lake volume, water surface area and perimeter as lake levels decreased during the summer. Water availability is crucial to MYLF because tadpoles require multiple years before metamorphosing into adults, and breeding is now often restricted to small, shallow fishless lakes that sometimes dry during the summer. To track intra- and inter-annual changes in volume we developed a method that did not require permanent depth markers or survey-grade GPS equipment to collect highly accurate altitude data. We constructed 3D lake bottom topography (bathymetry) in 3D Analyst of lakes at the beginning of summer (maximum water volume) by systematically recording horizontal GPS points on the lake bottom while simultaneously measuring the water depth at each point with a tape measure. Lake perimeters were mapped with GPS multiple times as the lakes receded during the summer, and their water surface areas (SA) were calculated. Because each surface area value is presumed to occur at a unique lake depth, we determined the volume for each perimeter mapped by adjusting the "height of plane" in 3D Analyst until the reported "2D area" matched our calculated water surface area (SA). The difference in volume estimated for one lake using this method and the volume calculated using a depth marker ranged from 0% to 12%. This technique is a practical method for measuring volume changes in small lakes where permanent markers can not be established. Igor Lacan USDA Forest Service PSW - Sierra Nevada Research Center c/o UC Berkeley - Dept of ESPM 137 Mulford Hall # 3114 Berkeley , CA 94720-3114 US Phone: 510 684 4323 E-mail: ilacan@nature.berkeley.edu Krishna Feldman USDA Forest Service - PSW Sierra Nevada Research Center PO Box 245 Berkeley , CA 94701 US Phone: 510 559 6461 E-mail: kfeldman@fs.fed.us Kathleen Matthews USDA Forest Service - PSW Sierra Nevada Research Center PO Box 245 Berkeley , CA 94701 US Phone: 510 559 6454 E-mail: kmatthews@fs.fed.us |
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