Algal mats were sampled along transects established by the MCM LTER in early to mid-January as in Alger et al. (1997), and mats were identified as either orange, black, green, or red in color. Mats were collected using a brass cork borer (1.7 cm diameter) and placed into Whirlpack® bags containing stream water. In the laboratory, samples were de-watered on pre-combusted Whatman GF/C filters, wrapped in foil, and stored at -20°C. Prior to the year 2000, Chl-a samples were extracted in buffered acetone and analyzed spectrophotometrically using the trichromatic method. After 2000, Chl-a was extracted in buffered acetone and analyzed using a Turner Designs 10-AU field fluorometer. Both methods have been shown to produce comparable Chl-a results (Lorenzen and Jeffrey 1980). For AFDM analysis, samples were dried at 100 °C for 24 h, weighed, burned at 450 °C for 4 h and re-weighed, and then re-wetted and dried to determine mass loss due to hydration of sediments. Both Chl-a and AFDM analyses were performed at Crary Laboratory in McMurdo Station.

Additional notes:

AFDM for 2019-2020 season samples was conducted at CU Boulder in 2022.

Samples collected during the 2020-2021 "Covid year" season were collected by a contractor and sent back to CU Boulder for analysis. Chl-a was analyzed on a UV Vis Spectrophotometer. Samples were kept in refrigeration for two months before Chl-a was analyzed. For AFDM analysis, samples were put directly into drying tins and were not placed on filters.

In the 2022-2023 season, the protocol varied from the the typical protocol, which is to collect a sample of algal mat and dewater it with a combusted and pre-weighed filter. This filter is then a part of the sample when it is dried, combusted, and rewett. Inserting the filter after collection was overlooked and was realized at the rewetting step because the filter aids in rewetting the combusted mat. We made the decision to add the filter at this step in order to continue with the rewetting. We took note of the weight of the filter and subtracted it out as is usually done.