Microbial mat nutrient storage in the McMurdo Dry Valleys, Antarctica

Microbial mats from Antarctic Dry Valley streams are important nutrient and carbon subsidies to Dry Valley lakes and soils, either transported by wind or flow. Different mat types are taxonomically distinct and are found in different habitats within the streambed. Because of these differences, different mat types may store and assimilate nutrients differentially. In addition, stream water chemistry differs as a function of the glacier it drains as well as its position along a geochemical gradient that makes element abundance variable from the Ross Sea coast to the inland Taylor Glacier. Quantifying these fluxes is an important step in understanding the ecological connectivity between streams and other habitat types in the Dry Valleys, especially under a changing climate, and is important for comparing with other mats at similar latitudes. Collectively we ask:

1. Do different mat types take up and store elements differentially
2. Does geographic location explain variation in elemental/isotopic composition within mat types
3. Are these potential differences also expressed in the seston/drift that is exported to the closed basin lakes?

Our preliminary results show that both elemental and isotopic compositions of different mat types are variable. Black mats consistently exhibit the highest C:N, C:P, and N:P ratios, while orange mats are consistently lower in C:P and N:P. Green mats have lower d13C signatures and orange have greater, while black and red are intermediate. All are variable in d15N with the exception of black mats, which are close to the atmospheric standard and may indicate fixation. Through the valley, both the elemental and isotopic compositions of mats and drift are variable, though specific trends differ by mat type and the analyte. These data suggest that future modeling of current and future nutrient fluxes should incorporate contributions of mat type and coverage, as these could be significant players in valley-wide biogeochemical cycles.