1982-2002; ill., maps; Title covers calendar years 1985-1987; CA 9000-3-0003 Subagreement 12; Includes bibliographic references; Issues lack volume numbering
Executive Summary Independent studies of Crater Lake during the late 1970's and early 19801s suggested that the lake had decreased in transparency and that the species composition and distribution of the phytoplankton had changed relative to results from short-term studies conducted between 1913 and 1969. Careful review found that the transparency and phytoplankton data were inadequate for the bases of any definitive conclusions on whether long term changes had occurred in lake water quality. Nonetheless, in order to build on the existing baseline data the National Park Service initiated a limnological study of Crater Lake in the summer of 1982. That fall, Congress mandated (Public Law 97-250) a 10-year study of the lake to be conducted by the Secretary of the Interior. The goals of the program were to: (1) develop a limnological data base; (2) develop an understanding of lake organization and structure; and (3) establish a long-term monitoring program to examine lake characteristics through time. The studies will investigate the lake for changing conditions and if found, studies to identify the cause(s) will be initiated. Field work, begun in 1982, has been limited to the period between late June-early July to the middle of September owing to sampling difficulties during the rest of the year. The results to date have indicated that the lake is very oligotrophic and that water clarity is high. Secchi disc depth readings are generally in the high 20 to low 30 m range. In 1985, the Secchi reading of 37.1 m was near record levels in early July. Readings during August and September, 1985, were at levels similar to those recorded in 1982 through 1984. It is still too early in the project, however, to determine if lake clarity has declined. With the monitoring program in place, the direction of the program has moved to emphasize the interrelationships among environmental, terrestrial, anthropogenic and aquatic aspects of the ecosystem. A conceptual model has been developed within which specific research objectives have been established. Using the conceptual model, areas needing further study became apparent. These areas include refinement of the lake water budget, initial development of a nutrient budget, defining the amount of sedimentation and documenting interrelationships among the physical, chemical and biological components within the lake. Assessment of changing lake conditions will be addressed from trend analyses on the lake monitoring data, repeating earlier studies of lake color and optical properties, and paleolimnological work to reconstruct the history of the phytoplankton and crustacean zooplankton communities through time from an examination of cores of lake sediment. -2-
Executive Summary Independent studies of Crater Lake during the late 1970's and early 19801s suggested that the lake had decreased in transparency and that the species composition and distribution of the phytoplankton had changed relative to results from short-term studies conducted between 1913 and 1969. Careful review found that the transparency and phytoplankton data were inadequate for the bases of any definitive conclusions on whether long term changes had occurred in lake water quality. Nonetheless, in order to build on the existing baseline data the National Park Service initiated a limnological study of Crater Lake in the summer of 1982. That fall, Congress mandated (Public Law 97-250) a 10-year study of the lake to be conducted by the Secretary of the Interior. The goals of the program were to: (1) develop a limnological data base; (2) develop an understanding of lake organization and structure; and (3) establish a long-term monitoring program to examine lake characteristics through time. The studies will investigate the lake for changing conditions and if found, studies to identify the cause(s) will be initiated. Field work, begun in 1982, has been limited to the period between late June-early July to the middle of September owing to sampling difficulties during the rest of the year. The results to date have indicated that the lake is very oligotrophic and that water clarity is high. Secchi disc depth readings are generally in the high 20 to low 30 m range. In 1985, the Secchi reading of 37.1 m was near record levels in early July. Readings during August and September, 1985, were at levels similar to those recorded in 1982 through 1984. It is still too early in the project, however, to determine if lake clarity has declined. With the monitoring program in place, the direction of the program has moved to emphasize the interrelationships among environmental, terrestrial, anthropogenic and aquatic aspects of the ecosystem. A conceptual model has been developed within which specific research objectives have been established. Using the conceptual model, areas needing further study became apparent. These areas include refinement of the lake water budget, initial development of a nutrient budget, defining the amount of sedimentation and documenting interrelationships among the physical, chemical and biological components within the lake. Assessment of changing lake conditions will be addressed from trend analyses on the lake monitoring data, repeating earlier studies of lake color and optical properties, and paleolimnological work to reconstruct the history of the phytoplankton and crustacean zooplankton communities through time from an examination of cores of lake sediment. -2-