|Lake Tahoe||Canadian Rocky Mountains||U.S. Rocky Mountains||IGERT||High Lakes Project|
UV Transparency in Lake Tahoe
In 2006 we began monitoring UV transparency of Lake Tahoe, the largest subalpine lake in the U.S. While we have studied a variety of highly transparent systems around the world, Lake Tahoe is an interesting addition because of its size and depth (2nd deepest lake in U.S.). Recent work is focusing on the effects of climate teleconnections and wildfire on incident and underwater UV in Tahoe and nearby lakes, especially as related to the Rim Fire - the 2013 wildfire that was the third largest in California's history. Although overall Lake Tahoe is known for its highly transparent waters, transparency ranges from very high to very low around the periphery of the lake depending on the site. With the help of TERC researchers stationed at Lake Tahoe, we have been collecting monthly UV and temperature data since 2006 at two sites, Charles Goldman's Index Site and a mid-lake site. These routine measurements enable us to look at seasonal changes in transparency in this unique system as well as long-term changes resulting from human disturbance. In an effort to learn more about how the zooplankton community protects itself from this high UV environment, cultures of Leptodiaptomus tyrrelli are being maintained at Miami University for experimental use.
Invasion Ecology of Warmwater Fish in Lake Tahoe
Changes in UV transparency and warming trends in the surface waters of Lake Tahoe may be altering the susceptibility of this lake to invasion by warmwater fish species. Water transparency to visible light in Lake Tahoe has declined substantially since the 1960's and climate change is driving warming of the surface waters. This creates a potential refuge for invasive warmwater fish. There are no long-term records of changes in UV transparency in Lake Tahoe, but our data from the past few years demonstrate much stronger gradients in UV than in visible transparency along inshore-offshore, along-shore, as well as seasonal gradients. Warmwater fish have invaded many of the areas of the lake where lower transparency related to influx of DOM or nutrients have created a refuge from damaging UV radiation. In collaboration with researchers at University of Nevada-Reno, the Tahoe Environmental Research Center (TERC), and Jim Oris (also at Miami University), we investigated the effects of transparency on invasive species such as bluegill sunfish and largemouth bass.
Canadian Rocky Mountain Lakes
Climate Change and Zooplankton Species Shifts in the Canadian Rockies
In the Canadian Rockies we are working in collaboration with Janet Fischer and Mark Olson from Franklin and Marshall College on fishless lakes where the lack of visual predators provides an excellent system for exploring the effects of UV radiation on the vertical distribution and invasion potential of zooplankton with climate change. Both visual predators and UV may cause downward avoidance migrations of zooplankton during the day, so the lack of visual predators permits us to focus on UV effects. Variation in visual predation and UV exposure can lead to strong differences in the size, pigmentation, and species distribution of zooplankton (right). We are also collaborating with Rolf Vinebrooke from the University of Alberta, who is continuing some of the pioneering work of David Schindler in the Canadian Rockies. Rapid climate change and reductions in snow pack have been observed in the Canadian Rockies in recent years. Our collaborating group is exploring what impact these changes have on the large, highly pigmented crustaceans that are present in the highest elevation alpine lakes. One of the central concerns is that warming temperatures will allow the elevation of the treeline to increase, reducing the UV transparency of lakes due to increasing chromophoric dissolved organic matter (CDOM) concentrations, permitting the invasion of low elevation zooplankton species and endangering the more unique large, pigmented alpine zooplankton that have historically inhabited the lakes.
United States Rocky Mountain Lakes
Since 2001 we have been working in the Rocky Mountains of Montana and Wyoming in collaboration with Jasmine Saros at University of Maine to examine the interactive effects of two global change stressors: nitrogen deposition and climate change on a series of alpine and subalpine lakes. Such high elevation lakes are notoriously nutrient limited by N availability as well as P. Paleolimnological records indicate that there have been rapid changes in diatom community structure in these lakes in recent years. Our research is exploring the role of ecosystem subsidies in the form of N deposition and climate-mediated changes in dissolved organic matter (DOM) in regulating transparency to ultraviolet (UV) and photosynthetically active radiation (PAR). Nitrogen deposition and changes in transparency influence the vertical structure of the ecosystem by modifying the distribution of phytoplankton (deep chlorophyll maximum) and zooplankton grazers. We also are interested in the role of trophic forcing by zooplankton grazers versus abiotic forcing (temperature, UV and PAR transparency) in regulating the recently observed changes in diatom community structure.
In addition, routine data are collected each year to grow the UV and zooplankton databases for 8 core lakes in the Beartooth Mountains: Glacier, Emerald, Beauty, Kersey, Fossil, Island, Beartooth and Heart. These core lakes include both alpine and subalpine lakes, allowing our lab to ask questions about DOC source and quality in these two environments, factors that may be altered by climate change. In addition, large and small scale experiments have been carried out in these lakes to investigate the effects of photobleaching on DOC and zooplankton migration. In this system, we have also explored the usefulness of deuterium, a stable hydrogen isotope, in determining whether the source of organic material in alpine and subalpine lakes was terrestrially derived or produced within the lake.
Undergraduates have received funds from the Undergraduate Summer Scholar (USS) program through Miami University as well as the Research Experience for Undergraduates (REU) program through the National Science Foundation to conduct independent research projects at these Rocky Mountain field sites. Graduate students can use these lakes as part of a larger data set from lakes around the world, or focus their efforts on specific questions related to this region.
IGERT: Environmental Aquatic Resource Sensing (2009-2013)
The National Science Foundation's IGERT (Integrated Graduate Education and Research Traineeship) program offered an interdisciplinary approach to train the scientists and engineers of tomorrow. In collaboration with Kent State University, the Global Change Limnology Laboratory IGERT focused on Environmental Aquatic Resource Sensing (EARS). Threats to aquatic systems are diverse and understanding these changes and their effects requires new tactics and technologies. To address these concerns, there is increasing use of automated sensors to collect environmental data creating an urgent need for training of a new cohort of environmental scientists. The EARS IGERT merged the use of advanced sensors and cyberinfrastructure with traditional aquatic environmental science disciplines to develop science professionals equipped for positions in academia, the government or the private sector. Students in the Global Change Limnology lab had the opportunity to become involved through sensor design and development, creation of sensor networks, and management/analysis of the resulting large, complex data sets as outlined in the other Current Research sections on the Global Change Limnology website.
High Lakes Project
The High Lakes Project, in cooperation with NASA and NASA scientists, aims to understand the unique aquatic environments and ecology of high elevation (4,000 - 6,000 m) lakes in the altiplano region of Chile and Bolivia in South America. The highest elevation volcanic lakes in the world are located in this region and their elevation, climate, and isolation make them some of the least understood lakes on Earth and excellent potential analogs for Martian lakes that existed 4.5 billion years ago. Further, this region is projected to experience rapid change due to global climate change. The lakes of the altiplano receive some of the highest incident UV of any place on Earth. We explored the physical environment in these lakes and their ecology with a focus on the underwater UV environment and the organisms that have adapted to the extremely high UV to better characterize these unique ecosystems and the biota within them. The zooplankton communities of many of these lakes are dominated by bright red zooplankton that contain high levels of photoprotective compounds that permit them to exist in these high UV environments. Flamingos feed on these copepods and derive their own color from these photoprotective pigments in their prey.