Kohler, Tyler J听1听;听McKnight, Diane M听2
1听INSTAAR, University of Colorado
2听INSTAAR, University of Colorado
In the McMurdo Dry Valleys, perennial cyanobacterial mats have adapted to undependable streamflow by persisting in a desiccated state during winter, but resume photosynthesizing with rehydration in summer months. Flow years are variable, and dry periods are common both within and among seasons. Previous investigators have hypothesized that different mat types may respond differently to this intermittency in stream flow. However, the short growing seasons and complex diel and seasonal hydrology of the dry valley streams make modeling mat responses to flow complex, and a dataset with a sufficient temporal and spatial breadth to test these interactions has previously not been available. To understand the seasonal hydrologic controls on the biomass of different algal mats across Antarctic Dry Valley streams, we extracted 20 years of microbial mat biomass data from the McMurdo LTER database, which includes the chlorophyll-a and ash-free dry mass of four different mat types (black, orange, green and red) along 16 stream transects in the Taylor Valley from 1994-2013. We compared these variables with hydrologic indices (total annual discharge, harshness, zero flow days) calculated from corresponding stream gauges. We observed that microbial mats collectively decreased during the middle of the 20-year flow period coinciding with a 鈥渇lood鈥� year. However, when separated by low- and high-biomass streams patterns diverged. Low coverage streams decreased in biomass before the high flow year, coinciding with several low flow seasons. High coverage streams maintained biomass during low flow years, but lost biomass as a result of the flood. Furthermore, the degree of correlation between hydrologic variables and biomass differed by mat type, which reflects the alternative strategies employed by different communities to persist in a highly ephemeral environment. These results show that hydrology, geomorphology, and mat type are collectively important for predicting mat biomass. Additionally, this work may shed light on how these communities, as well as those in other polar and arid regions, may respond to changes in flow or geomorphology in the future.