Kohler, Tyler J听1听;听Stanish, Lee F听2听;听Esposito, Rhea M.听3听;听Simmons, Breana听4;听McKnight, Diane M听5
1听University of Colorado
2听University of Colorado
3听University of Louisiana at Lafayette
4听Colorado State University
5听University of Colorado
In Antarctic Dry Valley streams, the availability of liquid water is a limiting resource for life. Resident diatom communities living within perennial cyanobacterial mats have adapted to undependable flow regimes by persisting for long periods in a desiccated state until flow resumes (Esposito et al. 2006). To understand species and ecological responses of stream ecosystems to renewed flow, water was experimentally redirected into a 2 km tributary of Harnish Creek after remaining dry for nearly two decades. Regenerated microbial mats were sampled along longitudinal transects as part of the McMurdo LTER over subsequent field seasons beginning in 1995. Mats were actively growing within 10 days of rewetting, and contained a diversity of diatom taxa, primarily species of the genera听Hanstschia听补苍诲听Luticola.听Many of these diatoms are endemic to the region, suggesting species radiation and strong controls on community composition by environmental factors. The objective of our study was to characterize changes in diatom community composition since the initial rewetting of the abandoned channel with samples from the 2007-08 (low flow) and 2008-09 (high flow) field seasons. We observed that two widespread听Hantschia听species and one endemic species of听Luticola听had become dominant throughout most of the tributary, whereas at the site with the greatest chlorophyll-a content, a different endemic听Luticola听species was dominant. Overall, most variation in community composition was among sites rather than between the low and high flow summers. Additionally, we investigated whether these changes correspond to standing stocks of benthic biomass as measured by chlorophyll-a and AFDM, as well as dissolved nutrient concentrations and physical characteristics. We used a multivariate approach to test for differences in diatom community composition, as well as for correlation with biomass, nutrients, and physical parameters. This research contributes to our understanding of mechanisms mediating diatom community dynamics and associated ecological feedbacks following the rehydration of Antarctic Dry Valley stream ecosystems, as well as how these ecosystems will respond to climate warming in the future.
McKnight, D.M., Tate C.M., Andrews E.D., Niyogi D.K., Cozzetto K., Welch K., Lyons W.B., and Capone D.G., 2007, Reactivation of a cryptobiotic stream ecosystem in the McMurdo Dry Valleys, Antarctica: A long-term geomorphological experiment: Geomorphology, v. 89, p. 186-204.