|High Lakes Project||Glacier Bay||Argentina||New Zealand||Colorado Rockies|
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.
Glacier Bay, Alaska
Deglaciation over the past 250 or so years has left behind lakes of different ages in the landscape surrounding Glacier Bay, Alaska. Earlier studies by Dan Engstrom, Sheri Fritz, and Olaf Olson demonstrated that dissolved organic carbon (DOC) concentrations increased with lake age. Since DOC is the primary variable regulating the penetration of UV radiation into less productive glacial lakes, we hypothesized that changes in UV along this deglaciation chronosequence might play a role in regulating zooplankton community structure. Olaf and a crew of undergraduate students carried out surveys of the UV penetration and zooplankton communities in lakes of different ages as well as experimental work manipulating UV and zooplankton species. The observed patterns of distribution and abundance of zooplankton as well as the results of the experimental work were consistent with the hypothesis that UV influences zooplankton community structure and succession during early lake ontogeny. The strong dependency of UVR transparency on terrestrially-derived DOC suggests a linkage between development of terrestrial plant communities within the watershed, changes in lake hydrology, and the early succession of zooplankton communities following deglaciation.
Diagrammatic representation of the UV exposure and low temperature constraints placed on zooplankton at different depths in lakes of different ages (see figure). The attenuation of 320 nm UVR down to the 1% UV attenuation depth is indicated by shading of the lake basin, while the depth of the thermocline is indicated by a horizontal line. The presence of the zooplankton species in the lakes is shown diagrammatically where filled organisms represent established populations (> l/L), and unfilled organisms represent sparse populations (< 1/L). All three lakes have thermal gradients that offer a demographic advantage to zooplankton that reside in the surface waters. In the oldest lake, where all five zooplankton species have established populations, potentially damaging UV radiation is attenuated rapidly, providing a potential refuge from both of these physical constraints in the warm surface waters. In lakes of intermediate age, where only 3-4 zooplankton species exist, they will be faced with either high UV exposure in the warm surface waters, or lower temperatures in the deeper, low-UV strata. In the youngest lake, where only two species exist in very low numbers, UV exposure may occur throughout the water column.
Southern Andes of Argentina
Some of the clearest lakes in the world are located in Patagonia in the Southern Andes of Argentina and Chile. The high elevation of some of these lakes as well as their proximity to the areas of high ozone depletion in Antarctica suggest that these lakes may experience some of the highest exposures to damaging solar UV radiation in the world. As part of a survey of 65 glacial lake sites in the northern and southern hemispheres, we trekked to the Bariloche region of Argentina to sample these clear lakes. Our goal was to develop an empirical model to determine the most important predictor of UV penetration in glacial lakes of low to moderate productivity. The results of our survey and the modeling efforts of Don Morris demonstrated that dissolved organic carbon concentration can account for over 90% of the variation in UV attenuation in these lakes. When these data are plotted as UV attenuation depths versus DOC concentration, a striking relationship becomes apparent wherein at low DOC concentrations (< 100 uM), there is a rapid increase in the depth to which potentially damaging UV penetrates (see figure and Williamson et al. 1996).
Research in New Zealand has been carried out in collaboration with Carolyn Burns at the University of Otago in Dunedin, New Zealand, an international expert on zooplankton and lakes. The focus of this work has been on the presence of UV photoprotective compounds (mycosporine amino acids and carotenoids) in zooplankton in lakes that varied in their UV transparency. Bright red pigmented copepods often dominate in these high UV alpine lakes when they lack visual predators. Studies of cladocerans and copepods from lakes around the world have demonstrated that while copepods often have high levels of a class of photoprotective compounds, the mycosporine like amino acids (MAAs), cladocerans have very low levels (Persaud et al. 2007).
To date our work in the Colorado Rockies consists of a single scouting trip to look for populations of large pigmented zooplankton such as Hesperodiaptomus shoshone and Daphnia middendorfiana as well as to do some UV profiling in another set of alpine lakes. As is true in alpine lakes around the world, we found that even the most remote alpine lakes that we sampled had been stocked with fish and lacked these large pigmented zooplankton species. We did, however, find H. shoshone in Green Lake 4 (which was accidentally stocked with fish just prior to our visit!) and in a small pool next to the trail to the Green Lakes, and added a few more lakes to our alpine UV and zooplankton database.