Gresswell, pers. comm. ) . Given the high concentrations of 

 nutrients in hydro thermal solutions and the evidence for the 

 relatively widespread occurrence of hydrothermal vents, 

 geothermally heated and reacted ground water inputs may prove to 

 have a significant impact on the chemistry and limnology of the 

 lake. 



An indication of possible hydrothermal fluxes into the lake 

 may be seen in the high excess radon-222 concentrations measured 

 in bottom waters of a small hole in the outer portion of Mary 

 Bay. Radon-222 was measured in the water column in both Mary Bay 

 and in the deep basin off Stevenson Island (Fig. 6). In a 98 

 meter deep water column near Stevenson Island measured Rn-222 

 concentrations ranged from 0.06 dpm/1 at the surface (close to 

 the supported Rn-222 concentration of ~0.03 dpm/1) to 18 dpm/L 

 one to two meters above the bottom. In the Mary Bay Rn-222 

 concentrations as high as 70 to 110 dpm/1 were measured in the 

 hypolimnion of a small steep sided hole which dropped off quickly 

 from less than 20 meters to nearly 40. The bottom in this area 

 was complex with steep and variable topography. The hypolimnetic 

 water here was also warm, ~12.5° C. 



The source of this high excess Rn-222 is unknown. Water 

 samples taken from the surface of a shallow thermal pond 

 (temperature = 35° C) less than a 100 meters onshore in Mary Bay 

 yielded extremely high Rn-222 concentrations of 1400-1800 dpm/1. 

 More detailed Rn-222 profiles and an estimate of diffusive 

 emanation from sediments, as well as measurements of the 

 possible sources, hydrothermal fluids and fumarole gases, may 

 allow future estimates of hydrothermal/geothermal inputs. 



Biota Associated with Thermal Activity in the Lake 



Microbial communities 



The microbial communities associated with these thermal 

 features are diverse. Samples collected from mats, vent waters 

 and glass slides incubated over fumaroles and vents were inocu- 

 lated into a variety of enrichment media. A summary of the 

 results of those enrichments, to date, are shown in Table 2. In 

 addition, samples were tested for growth at high temperature 

 (70° C). Of the 13 samples incubated, 6 yielded growth of 

 thermo-philic colonies. The thermophilic bacteria of the 

 terrestrial hot springs have been extensively studied (see Brock 

 1978, for review) and are one of the unique features of the 

 thermal systems in Yellowstone. The enrichments have produced a 

 diverse group of heterotrophic and autotrophic (both 

 lithotrophic and phototrophic ) microorganisms. A Thiothrix - 

 type sulfide oxidizing bacteria was very common in fumaroles and 

 produced many large filamentous colonies which frequently 

 covered entire plants. A positive enrichment for Beggiatoa was 

 also obtained. Mats of purple sulfur bacteria, Chromatium and 



93 



