Crater Lake Limnological Studies Final Report
Special Short-Term Studies
Several studies should be included in the long-term program in addition to the routine sampling conducted to examine the hypotheses described above. These special studies are as follows:
Nutrient Budget and Particle Flux. Biological activity around the edges of the lake certainly affects the nutrient budget of the whole lake. This effect should be evident specifically in the nitrogen budget. This hypothesis is supported by several observations. The highest fluxes of lithogenic and biogenic components occur during late spring, and this flux is probably controlled by solar radiation, the degree of thermal stratification, and nutrients introduced into the euphotic zone from deep lake mixing and snow melt runoff. Recent studies indicate that nutrient recycling is closely related to primary productivity. However, there is an inbalance in the internal nitrogen budget of the lake (see Particle Flux Measurements section). This discrepancy may reflect “edge effects” from the lake margins. Additional studies are needed to evaluate the source of this discrepancy.
Nutrient bioassays. Some assemblages of phytoplankton are probably nutrient limited. Nutrient-limitation experiments with phytoplankton should be conducted to assess which nutrients limit primary production in the lake. Such studies would also help to refine the nutrient budget of the lake.
Nutrient regeneration by zooplankton. Nutrient regeneration by zooplankton probably has a significant effect on primary productivity and the concentration of deep-water chlorophyll. Experiments should be conducted that examine this regeneration by experimental manipulation of nutrients and densities of natural zooplankton assemblages.
Nearshore plants and animals. Biological components of the nearshore zone of the lake probably play important roles in the structure and function of the lake, but little is known about the distribution and abundance of these components. In the nearshore zone of the lake, the identity, distribution, and abundance of macrophytes, attached algae, and benthic macro-invertebrates, and the distribution and abundance of introduced crayfish should be described. Permanent sites should be established and sampled at yearly intervals to assess changes in distribution and abundance through time, especially in relation to changes in climate and the surface elevation of the lake.
Deep-water Moss. Preliminary studies of a deep-water moss (Drepanocladus aduncus)in Crater Lake indicate that this moss probably has an important impact on lake productivity and nutrient dynamics. In addition, the moss provides a suitable surface for a diverse assemblage of epiphytal algae which may have significant effects on benthic primary productivity and nutrient availability in certain areas of the lake. The distribution, productivity, and nutrient uptake of this moss should be studied in the field and laboratory.
Zooplankton. Copepods and chydorid crustacean zooplankton, which may only inhabit the littoral zone of the lake, may be important members of the zooplankton community of the lake. A survey of the zooplankton populations in the littoral zone is recommended.
Boat and automobile petroleum wastes. Petroleum wastes from boat traffic on the lake and automobile traffic around the lake may pollute the lake. Studies of the effects of automobile and boat engine exhausts, gasoline, and oil on the lake are recommended. These studies should include an assessment of contributions via runoff from roads and parking lots on the caldera rim.
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