The algae in the lake are diverse in species but sparse in abundance. Over 150 species have been detected and algal abundance has varied considerably through the years (Figure 3). In summer, when the lake is thermally stratified, different algae species live in different layers of the water column down to a depth of about 200 meters (Figure 4). Because of the extreme clarity of the lake, the maximum amount of photosynthesis is able to occur at 40-80 meters. Phytoplankton that are adapted to very low light levels can produce a chlorophyll maximum at 120-140 meters (Figure 5).
Two species of fish inhabit Crater Lake. Both were stocked into this naturally-fishless lake. These include kokanee salmon (landlocked sockeye salmon) and rainbow trout. The latter inhabit the nearshore area of the lake and feed on large-bodied terrestrial insects that fall onto the lake surface, aquatic invertebrates living on the bottom of the lake, and kokanee salmon. Kokanee feed on small-bodied terrestrial insects and bottom fauna, and crustacean zooplankton. Kokanee live in the open waters of the lake to a depth of about 150 meters and, to a lesser extent, along the shoreline of the lake. Fish may have altered the species composition of the lake and have assumed the role of top predator over zooplankton. This may have had cascading effects throughout the food web.The animal plankton (zooplankton) in Crater Lake include nine rotifer species (microscopic multicellular animals 0.20-1.52 millimeters in length) and two crustacean species (0.45-3.12 millimeters in length). The abundance of zooplankton varies greatly through time (Figure 6). Some species are present every year, whereas others occur infrequently. During summer when the lake is thermally stratified, different species live in different portions of the water column down to a depth of about 200 meters.
WHY CONTINUE TO STUDY CRATER LAKE?
Crater lake is a world-class laboratory for studying lakes because of its pristine condition. Because it is preserved in a national park it is expected that there will be minimal future onsite impacts from human activities. The lake provides scientists and park managers with a gauge for assessing changing environmental conditions external to the Park. Long-term monitoring of Crater Lake has been used to develop a baseline of information about the natural dynamics and complexity of the lake. This baseline will serve as a reference when studying the impacts of global climate change and human activities, such as agriculture and urban growth, on other lakes. Scientists working with the U.S. Geological Survey, the National Park Service, and Oregon State University have systematically studied Crater Lake for the last two decades. Long-term monitoring of this lake is a priority of Crater Lake National Park and will continue far into the future.
The long-term lake program involves studying many components of Crater Lake. Currently, the relationships between many of these model components are being investigated using mathematical models. Based on this research, new studies will be undertaken to refine our understanding of how these components interact. Once the models are completed, researchers will have a better understanding of how the lake “works” and how the lake may respond to future environmental changes.
THIS DOCUMENT WAS CREATED IN COLLABORATION WITH OREGON STATE UNIVERSITY AND CRATER LAKE NATIONAL PARK.
