A BASELINE STUDY OF EVAPORATIVE WATER CHEMISTRY AND MICROBIAL MAT DIVERSITY FROM ALKALINE LAKES IN WARNER VALLEY, OREGON

Warner Valley, Oregon is an alluvial system containing numerous geothermal springs and evaporative lakes underlain and hosted by basaltic flows and deposits from Pleistocene Lake Warner. Alkaline, fresh to brackish lakes in the northern end of Warner Valley are well suited to long-term study being located within an Area of Critical Environmental Concern (ACEC) under management of the BLM. ACEC is relatively free of agricultural and anthropogenic activities, but is seasonally perturbed by large numbers of migrating Arctic Swans. Springs typically originate from fractures within the Miocene Steens Mountain Basalt, are bicarbonate dominated, have temperatures ranging from 8.9 to 71.2°C and pH from 6.5 to 8.3. Calcium is the dominant cation during the colder, wetter months whereas Na⁺ becomes significant during the warmer, evaporative months. Warmer springs contain both green and gold algal mats. Water chemistries of the lakes exhibit a strong seasonality and range from moderately to highly alkaline to sulfate-chloride and chloride-sulfate dominated with a range in pH from 8.3 to 10.5. Lakes are relatively dilute in late fall through early spring as much of the water originates from snow melt with a minor geothermal component. Lake waters undergo significant evaporative concentration from late spring through the summer. Within this context, the lakes host a wide variety of chemistries and algal/bacterial mats (purple, green, and gold). In particular, Anderson Lake contains Arsenic ranging from 600 – 700 ppb, is a Na-Cl dominated chemistry with pH=8.6, TDS=4560, and hosts a complex purple-sulfur bacteria population.