Hydrologic processes influence diatom community composition in Dry Valley streams

Abstract

Our paper describes the ecological controls on algal-mat diatom communities in the dynamic stream ecosystems of the McMurdo Dry Valleys in Antarctica. Dry Valley diatom communities are relatively diverse, and nearly ½ of the taxa found in these mats are considered endemic. Diatom community composition was examined in 5 streams in Taylor Valley during a 15-y cooling period that included a discrete flood event. Two hydrologic variables, total annual discharge and historical variation in discharge, gave the most parsimonious model of among-stream and interannual variation in diatom communities. Algal-mat biomass and chlorophyll a concentrations decreased after the flood, which occurred during the 2001/2002 summer season. Most algal-mat diatom communities recovered quickly after the flood. However, Green Creek, a relatively high-flow stream with low historical variation in discharge, appears to have experienced a persistent diatom community shift toward increased relative abundance of small, generalist species. Diatom relative biovolume, a proxy for the size of diatoms within a sample, was negatively correlated with stream flow, such that higher-discharge streams contained greater relative abundances of smaller diatoms than lower-flow streams. Therefore, diatom size may play a role in determining the distribution of a species in these streams and may be useful for monitoring environmental changes. Our study demonstrates the importance of understanding factors affecting ecosystem resilience, especially in polar regions, which are experiencing rapid climate changes.

Responses of epibenthic algal assemblages to water abstraction in Hong Kong streams

“…We then calculated the between-reach differences of those indicator taxa and metrics, and related them to between-reach differences in flow (i.e., the focus was on the magnitude of relative difference, not the absolute values). Particular attention was paid to differences in current velocity and discharge given that they are both known to influence algal assemblages Stanish et al, 2011;Villeneuve et al, 2011). Differences in percentage data between reaches were calculated by simple subtraction (upstream minus downstream), while ratio data were calculated from the percentage difference (difference between reaches divided by upstream value).…”

Extreme streams: flow intermittency as a control on diatom communities in meltwater streams in the McMurdo Dry Valleys, Antarctica1This article is derived from a special session entitled “A New Hydrology: Inflow Effects on Ecosystem Form and Functioning” that took place at the February 2011 ASLO Aquatic Sciences conference in San Juan, Puerto Rico.

“…The abundance and productivity of phytoplankton in the ice-covered lakes also decreased during this time period (Doran et al 2002). This cooler period was interrupted by infrequent warm summers with higher flows, which scoured the streambeds (Stanish et al 2011) and affected soil and lake ecosystems (Foreman et al 2004; Barrett et al 2008). Recent climatic studies suggest that the cooling trend is related to the increased ozone hole depletion over the Antarctic continent (Solomon et al 2005).…”

“…Canada Stream, Green Creek, and Bowles Creek drain from the Canada Glacier, and while they exhibited large differences in total annual stream flow (Table 1), all three streams received flow during every season on record (Table 2). Discharge is not continuously monitored on Bowles Creek; however, stream flow in Bowles Creek is correlated with stream flow in Green Creek (Alger et al 1997), and flow was determined based on the relationship of manual discharge measurements between both streams as outlined by Stanish et al (2011).…”

“…Microbial mat transects located on each stream were sampled as part of the MCMLTER monitoring program (Alger et al 1997). All data included in this study were obtained after an intense flood year in 2001-2002, which scoured the streambed and altered some microbial mat diatom communities (Stanish et al 2011). To limit the effect of habitat heterogeneity on microbial mats, only orange-colored mats from within the thalweg of the stream channel were used.…”

“…In a recent study examining changes in diatom communities in the Taylor Valley over two decades, total and interannual variation in stream flow substantially influenced spatial and temporal variation in diatom community composition (Stanish et al 2011). However, the study was conducted on productive streams that showed relatively little variation in flow intermittency.…”