Long-term ecological field surveys from the McMurdo Dry Valleys Long Term Ecological Research program (MCM LTER) have documented the abundance and diversity of microbial mat types across ephemeral glacial meltwater streams in the McMurdo Dry Valleys region of Antarctica. However, field surveys are limited and are incapable of being performed across the entirety of streams within a field season. Therefore, we used remote sensing to examine the distribution of these diverse communities across streams in order to determine whether large scale distribution patterns are similar to those the MCM LTER has already thoroughly studied in situ. As part of our 2018-2019 field campaign, we established two to three 20 x 20 m plots within five different streams (Bowles Creek, McKnight Creek, a relict channel, Canada Stream, and Crescent Stream) in the Fryxell Basin of Taylor Valley. We performed point transect and quadrat field surveys of microbial mat and moss cover within each 20 x 20 m plot. We then used hyperspectral measurements of mat and moss collected in the field, previously archived in “Spectral and biological characteristics of microbial mats and mosses across Fryxell Basin, Taylor Valley, Antarctica (2018-2019),” in linear spectral mixing models to determine mat and moss coverage in the same 20 x 20 m plots within an atmospherically corrected WorldView-2 satellite image from Dec. 12, 2018. We ground truthed our modeled mat and moss abundances with our field survey coverages and determined the limitations of our methods. We then modeled mat and moss coverage across Huey Creek and Von Guerard Stream to apply our methods to streams without ground truthing measurements. Our results demonstrate the spatial distribution of moss and black, orange, red, and green microbial mat across Fryxell Basin streams. Observations of mat and moss coverage at the basin-wide scale are similar to those seen in localized stream areas.
During the 2018-2019 austral summer, field surveys were conducted across 20 x 20 m plots established in several streams across the Fryxell Basin of Taylor Valley, Antarctica. Two plots were established in Bowles Creek, McKnight Creek, and Crescent Stream. Three plots were established in Canada Stream and a relict channel, but only the first and third plot in the relict channel was surveyed because plot 2 was outside the channel. Plots were assigned before the field season based on areas with homogenous NDVI signatures. Field surveys involved point transect and quadrat coverage estimates. Point transect measurements were collected by establishing cardinal (N, E, S, W), and intercardinal (NE, NW, SE, SW) transects across the 20 x 20 m plots. Every 25 cm along all transects, surface types were categorized as “dry” and “exposed” or “inundated” and “black mat, orange mat, red mat, black/orange mat, black/orange/red mat, orange/red mat, moss, cobbles/pebbles, sand, or rock.” Results were then averaged across the 20 x 20 m plots as abundances. For quadrat surveying, 1 x 1 m quadrats were randomly generated in the Esri geographic information system software, ArcGIS, within the 20 x 20 m plots. Ten quadrats per 20 x 20 m plot were established for most stream plots. However, due to field logistics and time constraints, some plots only had 6, 8, or 9 quadrats surveyed. Once in the field, 20 x 20 m general plot overview descriptions were recorded (weather, flow conditions, vegetation coverage, any notable features or changes since previous visit), and then each 1 x 1 m quadrat was surveyed. Observations of mat or moss type (black mat, orange mat, red mat, green mat, sandy orange mat, black/orange mat, black/orange/red mat, black/red mat, orange/red mat, moss, moss with black mat on top, black mat with moss on top, black mat and moss with orange mat on top), coverage, water levels (dry, moist, saturated, inundated), and substrate type were recorded. All coverages were then averaged for each quadrat and applied to the entire 20 x 20 m plot (multiple by two if ten quadrats). Further methodological details can be found in Spectral and biological characteristics of microbial mats and mosses across Fryxell Basin, Taylor Valley, Antarctica (2018-2019).
For our remote sensing techniques, we first atmospherically corrected a WorldView-2 (WV2) image of Fryxell basin taken on Dec. 12, 2018 using the same methods as Salvatore et al. 2021. We then used multispectral data, found in “Spectral and biological characteristics of microbial mats and mosses across Fryxell Basin, Taylor Valley, Antarctica (2018-2019),” as endmember spectra in linear spectral mixing models in the program, Davinci. Model outputs included averaged abundances of mat and moss within each 20 x 20 m plot and the measured and modeled WV2 spectrum of the 20 x 20 m plot. After merging all coverage datasets, averaged abundances of mat and moss within each 20 x 20 m plot were statistically compared with field survey abundances to determine how well our models were fitting measured in situ data (R2, p-value, RMSE, AIC, and reduced chi-squared were calculated from the results). Other modeled results of mat and moss abundances for entire stream channels were outputted as geotiffs, which were then uploaded to the Harris geospatial deep learning software, ENVI, for further analysis. In ENVI, the reassigned WV2 bands displayed the different coverages of moss and each mat type. Using the statistics tool, percent coverages of mat and moss were found for entire stream channels. Percent coverages were converted to areal coverages by dividing the percentages by the total area of the stream channels.
Funding for this work was provided by the National Science Foundation grants #OPP-1758224 and #OPP-1745053 to Mark Salvatore, a Graduate Research Fellowship award to Schuyler Borges, and #OPP-1637708 and #OPP-2224760 to the MCM LTER for assistance with data management.