McCutchan, Jr., James H听1听;听Lewis, Jr., William M听2听;听Blankenship, Ariann L听3听;听Oppold, Mary听4
1听University of Colorado
2听University of Colorado
3听University of Colorado
4听University of Colorado
Little Gaynor Lake is a small endorheic basin between Niwot and Longmont, Colorado. The lake supports high rates of phytoplankton production and, at times, also the production of hydrogen sulfide. Since June 2007, we have recorded hourly changes in water temperature at multiple depths near the middle of the lake. We also have sampled the lake bi-weekly for physical, chemical, and biological parameters, including profiles of temperature, specific conductance, dissolved oxygen, pH, and irradiance, analyses of solute concentrations, and analyses of chlorophyll-a and phytoplankton species composition. Since our sampling began, anoxia developed and hydrogen sulfide accumulated in the water column during periods of thermal stratification, which occurred under ice cover and for brief periods during summer. Shallow lakes are generally more productive than deep lakes and nutrient concentrations were high throughout the study, but Little Gaynor Lake supports chlorophyll concentrations that are among the highest recorded for any lake. Total Chlorophyll a in the water column approached 2000 mg/m2, which is well beyond the theoretical limit dictated by self shading. These exceptional chlorophyll values can be explained, however, by high concentrations of dissolved organic matter in Little Gaynor Lake and the potential for heterotrophic growth in Anabaenopsis elenkinii, the dominant component of the phytoplankton community.