HYDROLOGY AND CHANGE IN GOLD LAKE BOG, WILLAMETTE NATIONAL FOREST, OREGON

Gold Lake Bog Research Natural Area is a 656-acre high elevation groundwater-fed fen environment located in the Willamette National Forest in Oregon, and contains the largest known breeding population of the federally threatened Oregon Spotted Frog (Rana pretiosa) west of the cascade crest in Oregon. Willamette National Forest partnered with the Geological Society of America through their GeoCorps™ America internship program to; 1) establish water chemistry, temperature, and water level baseline values 2) quantify encroachment of upland tree species and 3) map sub-environments within the Research Natural Area by dominant species of vegetation and hydrologic characteristics.

In 2014 and 2015, GeoCorps participants installed 7 piezometers with 5 pressure transducers, installed 19 temperature sensors, collected dominant dissolved ion chemistry and tritium count data, collected water quality data, and surveyed surface and groundwater elevations in the fen. Dissolved ion chemistry reveals that the surface water here is incredibly dilute (Average specific conductivity 69.1 uS/cm), in agreement with a study of nearby Waldo lake, and indicates young (< 10 years) spring waters. The dissolved ionic loads and year-round cold (4 to 6 degrees Celsius) temperatures of several pools confirms they are limnocrene springs. The springs are likely essential overwintering sites for Rana pretiosa and a refuge from invasive fish species.

To quantify the encroachment of upland vegetation, 8 photographs from the past 65 years were collected, georeferenced, and the area of low-lying vegetation without tree canopy was mapped through time. A strong decreasing linear trend in open fen area was found, with a linear regression model showing a loss of 1963 square meters per year (R^2 = 0.93). Following previous unpublished work, 9 sub-environments within Gold Lake Bog were identified and described. Using a Topcon auto-laser level and a hand auger, the ground surface and water table elevations were surveyed relative to an arbitrary datum. Distinct variations in water table depth were used to define ecological sub-environments. The collected data serves as a baseline study of Gold Lake Bog hydrology, and demonstrates the ongoing success of GeoCorps in providing useful data for resource managers in the Willamette National Forest.