The McMurdo Dry Valleys (MDV) is a polar desert on the western coast of the Ross Sea in Antarctica. Here, numerous glacial meltwater streams flow for about two months each summer. In contrast, ephemeral wetlands and their associated streams become active only during warm summers with high solar radiation when sub-surface flows are generated from snowfields. One such wetland, the Wormherder Creek wetland in Taylor Valley, harbors much greater biodiversity of soil fauna compared to adjacent perennially dry soils. To further understand the structure and function of these wetland ecosystems, we investigated the hydrology and hydroecology of the Wormherder Creek wetland during a warm, sunny summer. To determine hydrologic flowpaths, we injected a conservative tracer (LiCl and NaBr) for a 2-hr period into an inflow stream originating from a spring above the wetland.
Results/Conclusions
The tracer was only observed at the stream sites in the first 100 m below the injection site and was not detected in the two streams that flow through the main wetland. Eight hours after the first arrival of the tracer at the upper stream sites, a second greater pulse of tracer occurred. The interstitial water at these sites reached high concentrations that were maintained during the post-injection period. The tracer was non-detectable in the interstitial water in the main wetland. These results indicate that the main wetland is connected to a large reservoir which receives drainage from an upper reservoir associated with the spring and an additional source of meltwater. Major ion concentrations were uniform in the two streams and the shallow subsurface throughout the wetland. The abundant microbial mats in the streams had high autotrophic index values, ranging from 9-38 µg Chla/mg AFDM, indicative of an actively photosynthesizing mat community. The diatom communities in the mats were relatively uniform compared to those in mats from Dry Valley streams with regular flow. Four endemic and one widespread diatom taxa of the genus Luticola accounted for an average of 86% of the community. These results indicate that intermingling of flowpaths and the long-term storage capacity in the wetland results in uniform interstitial and stream water quality, which, in turn, may explain the relatively high productivity of the microbial mats and the minimal spatial variation of the diatom community. These wetland characteristics may have provided a distinct niche to which some of endemic Luticola taxa became adapted, contributing to the biodiversity of the diatom meta-community in the MDV.