Algal Species and Biogeochemical Responses To Environmental Change in an Alpine Lake
Abstract
We studied algal species distribution in water samples, a sediment trap, and a 26 cm sediment core from Green Lake 4, an alpine lake in the Colorado Rocky Mountains. Over the past 20 years, nitrogen deposition has increased in Green Lakes Valley and the lake ice-cover has become progressively thinner. In the water column, diatoms accounted for a large portion of the algal biovolume throughout the summer. Above the 9 cm depth in the core (corresponding to about 1940), the organic carbon content and the concentrations of chlorophyll a and fucoxanthin increased, and the fluorescence index changed in a manner indicating increased contribution of microbially-derived fulvic acids to sediment organic matter. Small benthic diatom species, including Fragilaria pinnatta, Fragilaria construens var. venter, and Fragilaria brevistriata, were most abundant above 9-10 cm in the core. Deeper sediments (10-26 cm) were characterized by larger contributions by species of the genus Aulacoseira. Analysis of the complete data set using Principal Components Analysis showed that the first axis explained 78.6 percent of the variation. These results suggest that since about 1940 changes in Green Lake 4 associated with nitrogen enrichment and climatic changes have caused increased growth of the benthic diatom community, greater accumulation of sediment organic matter, and shifts in the dominant diatom species in the water column.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2002
- Bibcode:
- 2002AGUSM.B31C..03M
- Keywords:
-
- 1035 Geochronology;
- 1055 Organic geochemistry