ill.; Report title; Includes appendices: Crater Lake Liminological Studies 1984 and 1985; "Robert E. Benton, Superintendent CLRA." - T.p.; Includes bibliographical references.
2 I. Executive Summary A limnological and monitoring program was initiated at Crater Lake National Park in 1982 in response to a noted 25% reduction in lake water clarity as measured by secchi disk readings between 1937 and 1979. A limnologist was hired as the principal investigator to direct the program and provide quality control. A scientific peer review committee was organized to provide a multidisciplinary critique of program methods and direction. Boats, field equipment, and laboratory apparatus were purchased, and one permanent and two seasonal biological technicians were retained to collect water samples. Results of the monitoring thus far indicate that clarity reduction is due to an increase in phytoplankton. Preliminary analysis indicates that Crater Lake water is low in nitrates, which may be a limiting factor for the phytoplankton population. An increase in nitrates could promote the growth of phytoplankton which, in turn, could reduce the water clarity. Data collected to date are not adequate to determine if the reduction in clarity is a natural phenomenon or man caused. Also winter sampling has been restricted due to difficult logistics, so the data is from summer only and may present a biased perspective. One possible source of nitrates entering the lake may be several springs which flow into the lake from the caldera walls. The water from these springs has been found to have high levels of nitrogen when compared with other springs in the area and the lake water. These springs are located directly below the Rim Village visitor use and development area, and the nitrate concentrations may have some relationship to this development. Program direction for the next two years is to continue the baseline monitoring program, identify special research projects on the lake dynamics, and initiate tracer studies on the springs.
2 I. Executive Summary A limnological and monitoring program was initiated at Crater Lake National Park in 1982 in response to a noted 25% reduction in lake water clarity as measured by secchi disk readings between 1937 and 1979. A limnologist was hired as the principal investigator to direct the program and provide quality control. A scientific peer review committee was organized to provide a multidisciplinary critique of program methods and direction. Boats, field equipment, and laboratory apparatus were purchased, and one permanent and two seasonal biological technicians were retained to collect water samples. Results of the monitoring thus far indicate that clarity reduction is due to an increase in phytoplankton. Preliminary analysis indicates that Crater Lake water is low in nitrates, which may be a limiting factor for the phytoplankton population. An increase in nitrates could promote the growth of phytoplankton which, in turn, could reduce the water clarity. Data collected to date are not adequate to determine if the reduction in clarity is a natural phenomenon or man caused. Also winter sampling has been restricted due to difficult logistics, so the data is from summer only and may present a biased perspective. One possible source of nitrates entering the lake may be several springs which flow into the lake from the caldera walls. The water from these springs has been found to have high levels of nitrogen when compared with other springs in the area and the lake water. These springs are located directly below the Rim Village visitor use and development area, and the nitrate concentrations may have some relationship to this development. Program direction for the next two years is to continue the baseline monitoring program, identify special research projects on the lake dynamics, and initiate tracer studies on the springs.