|IGERT||Beartooths||Lake Tahoe||Canadian Rockies||Bolivia/Chile||Poconos|
Research in Alpine and Subalpine Lakes
Alpine lakes are of particular interest in the ecology of climate change and UV radiation because incident UV increases with elevation (about 24% more 300 nm UV-B per 1000 m elevation). The sparse terrestrial vegetation and steep watersheds at these elevations also often lead to low concentrations of UV-absorbing, chromophoric dissolved organic matter (CDOM) in the water. Many alpine lakes are shallow and clear. In addition, while UV increases with increasing elevation, temperature decreases such that alpine lakes with low CDOM are subjected to higher UV levels at lower temperatures. While increases in cloud cover at high elevations may reduce total UV exposure in some cases, periods of clear skies between clouds may lead to sharp peaks in UV exposure that are less predictable for organisms in alpine lakes. Because UV damage is largely temperature independent, but molecular repair of damaged DNA often is temperature dependent, high UV:temperature ratios such as those found in alpine lakes are likely to increase UV stress levels. Zooplankton at high elevations are often large and brightly colored in the absence of visually feeding fish, but small and more transparent in lakes with fish. This reflects an important trade-off between photoprotection from UV damage and increased susceptibility to visual predation due to photoprotective pigments. Such indirect food web effects may be as important as the direct effects of UV damage, especially in alpine lakes. Alpine lakes are also experiencing more severe climate change than lower elevation lakes. Combined with their low nutrients, short growing season and high levels of incident UV, alpine lakes are strong sentinels for understanding the impacts of climate change and UV on lakes.
IGERT: Environmental Aquatic Resource Sensing
The National Science Foundation's IGERT (Integrated Graduate Education and Research Traineeship) program offers an interdisciplinary approach to train the scientists and engineers of tomorrow. In collaboration with Kent State University, the Williamson Laboratory IGERT focuses 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 joins business, materials science, 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 Williamson lab have the opportunity to become involved through sensor design and development, creation of sensor networks, and management/analysis of the resulting large, complex data sets. Interested graduate and undergraduate students should check out our Student Opportunities for more information.
Since 2001 we have been working in the Beartooth 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: 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. We also are exploring the usefulness of deuterium, a stable hydrogen isotope, in determining whether the source of organic material in alpine and subalpine lakes is terrestrially derived or produced within the lake.
Undergraduate and graduate students are a key component of the Beartooth research team each year. 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 Beartooth Mountain field sites. Undergraduates also are a key component of the data analysis conducted back in the lab during the academic year. 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.
UV Transparency in Lake Tahoe
In 2006 we began monitoring UV transparency of Lake Tahoe, the largest subalpine lake in the US. 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 US). In addition, 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, 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 Diaptomus tyrrelli are being maintained at Miami University for experimental uses and analysis of photoprotective compounds.
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, alongshore, 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 are investigating the effects of transparency on invasive species such as bluegill sunfish and largemouth bass.
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.
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 are exploring the physical environment in these lakes and the ecology of these lakes 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 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.
For over 20 years, we have collected data from two lakes, Giles and Lacawac, in eastern Pennsylvania. During this time, the lab has compiled a large data set, including information about
- zooplankton community composition,
- zooplankton vertical distribution,
- UV, temperature, and dissolved oxygen depth profiles,
- phytoplankton community composition, and
- the quantity and quality of dissolved organic carbon (DOC).
Lake Giles and Lake Lacawac are the home of the UV Lakes project. From 2002-2009, 10 researchers from eight institutions worked to investigate the interactive effects of UV and temperature on pelagic food webs.
Lake Giles (above, left) is a transparent, low DOC lake. In contrast, Lake Lacawac (above, right), which is part of the Lacawac Field Station, is characterized by higher DOC. Because DOC is one of the main factors controlling UV transparency, these striking differences provide a unique opportunity to investigate the effects of UV on the aquatic community. Nearby Lake Waynewood, a more productive lake very similar in size to Lacawac, completes an interesting set of lakes that vary in their trophic status from oligotrophic Lake Giles to mesotrophic/dystrophic Lake Lacawac, to more eutrophic Waynewood. Numerous experiments have been conducted at these sites by collaborating researchers, as well as graduate and undergraduate students through the years.
Our collaborative research in these two study lakes has shown that UV drives the vertical migration of some zooplankton species in transparent lakes and that the tolerance of an organism to UV is not necessarily related to size. Yellow perch spawn their egg masses at deeper depths in the more transparent Lake Giles. Experiments have shown that if they spawned at shallower depths their eggs would perish due to the high UV levels. Dramatic changes in UV transparency have been observed in Lake Giles during the summer, but not in the spring when these perch spawn. UV used to penetrate to depths of over 15 m in July, but now the 1% attenuation (of 320nm UV surface irradiance) depths are closer to 2-4 m. This decrease in transparency in Lake Giles may be due to lake recovery from acid deposition related to the Clean Air Act Amendments. Research continues in these lakes, and with the development of the Lacawac Field Station and new collaborations, exciting opportunities are anticipated.