CARBON DYNAMICS IN EAST LAKE: DIFFUSIVE CO2 ESCAPE

East Lake is one of two volcanic lakes in the Newberry volcano caldera in Oregon (43^o41.21’N, 121^o15.18'W). It has geothermal CO₂ inputs with Hg and H₂S. The Hg is subdivided into the sediment and the fish inhabiting the lake with values of 4 ppm and 3.5 ppm respectively. The active gas input of CO₂ allows for the lake waters to have a pH ranging from 6.5 to 7. Diffusive CO₂ loss occurs due to a higher internal P_CO2 compared to atmospheric P_CO2. Bubble trains have only been observed from bottom to mid-lake levels. Lake waters have ~130 ppm of DIC with slightly higher values at depth. East Diatoms serve as primary producers contributing to CO₂ sequestration as well as biogenic silica supply to the sediment. Sediment cores in East Lake contain 8-12% organic carbon, primarily from the detritus of unicellular primary producers and floating aquatic plants. Biogenic silica analyses based on timed NaOH digestion and spectrophotometry reveal that up to 60% of the lake sediment consists of biogenic silica. XRF analyses of the sediment for trace elements suggest that 20-30 % of the sediment consists of volcanic ash. Photosynthesis and diffusive CO₂ loss balance the geothermal CO₂ input and maintain a d¹³C gradient with depth with highly positive values at the surface (+4‰ to +5‰) and lower values at depth (-.5 ‰). The d¹³C gradient has varied over the years and through the seasons. Hot spring d¹³C (CO₂) values range from -7‰ to -3.5‰. The CO₂ diffusive flux off the lake was measured with a floating accumulation chamber. The data suggest a 30-50 ton CO₂ loss per day from the surface of the lake. This value will be refined given seasonal and day-night variation, as well as spatial distribution variations, which will be improved using sequential Gaussian simulations. The sediment has a bulk dry density of 0.2 g/cm³ and an average sedimentation rate of 2 mm/year. The carbon extraction rate as calculated from the Corg matter in the sediment roughly equals 1.5 tons C/day. Considerations for carbon cycling on a yearly time scale suggest that around 4000 tons C/yr are lost through diffusive CO₂ degassing and that ~160 tons of C are buried per year. The rapid processing and escape of CO₂ gives a short CO₂ lifetime for the lake, with a carbon residence time of ~ 0.5 years.