On the chemical and physical limnology of Crater Lake, Orego

Active inputs of hydrothermally-enriched fluids at the bottom of Crater Lake, Oregon create small vertical and horizontal heterogeneities in the deep-lake temperature and salt distribution. To characterize the physical properties of Crater Lake, and to constrain the modes and time scales of mixing of heat and salt, I have developed an experimental approach to derive an in situ specific conductance and temperature dependant expression for salinity in Crater Lake.;The heat and salt budgets of the deep lake, which are dominated by subsurface hydrothermal activity, are constrained by a time series of CTD data and by data from a thermistor chain mooring. The net (conductive and convective) heat flow due to hydrothermal activity is $sim$1 W m$sp{-2}$ and the corresponding salt flux is $sim$5 $mu$g $rm msp{-2}{cdot}secsp{-1}.$ The annual vertical exchange of surface water with water from the lake's hypolimnion occurs during early winter and to some extent during late spring. This exchange mixes the hydrothermal heat and salt from the deep lake to the surface.;The eastern portion of the South Basin of Crater Lake is the dominant region of hydrothermal input. Detailed mapping of the near-bottom temperature and salinity distribution in this basin has allowed the development of constraints which identify the possible modes of entry for the enriched fluids into the deep lake.;Small temporal and spatial variations in the distribution of dissolved oxygen in the deep lake yield information on the mixing time-scales, carbon flux, and the relative importance of hydrothermal activity on the oxygen budget. An increase in deep lake oxygen during the winter of 1988-89 indicates that 30-45% of deep lake water was replaced with well-oxygenated surface water. The consumption rate of dissolved oxygen in the deep basin of Crater Lake is $sim$4.4 mmol O$sb2$ m$sp{-2}$ day$sp{-1}.$ This consumption of oxygen is primarily due to the oxidation of organic matter and, to a lesser extent, the oxidation of reduced inorganic species which are introduced to the system via the subsurface hydrothermal springs.