This dataset quantifies ash-free dry mass (AFDM) in water, epilithon, leaf litter, and sediment samples collected from non-perennial streams as part of the NSF-funded project AIMS (Aquatic Intermittency Effects on Microbiomes in Streams), including Approach 2 ('seasonal sampling') and Approach 3 (spatially intense synoptic sampling) for three non-perennial stream systems in Alabama, starting in January 2022 and ending in February 2024. All samples were collected following the AIMS Microbial Field Sampling SOP (Zeglin and Busch, 2024). Filters for water and epilithon AFDM quantification were dried at 55 ºC for at least 48 h, weighed, combusted at 500 ºC for 2 h, and reweighed. For leaf litter and sediment AFDM, samples were dried at 70 °C for 48 h, after which they were reweighed to obtain dry mass. These dried subsamples were then combusted at 500 °C for 2 hours and reweighed. Then, for each substrate, AFDM was calculated as the difference between dry and ashed mass for each subsample. We then report AFDM as a proportion of total DM is given for each substrate. AFDM was also calculated in terms of concentration in water (AFDM mg / mL), and for rock surfaces AFDM was estimated in terms of rock area sampled (mg/ cm^2).

Talladega Site Description:
Talladega (stream code=TAL) research watershed (outlet location: 33.76219799, -85.59550775) in the Talladega National Forest (Cleburne County, AL, USA). The watershed drains a non-perennial unnamed tributary of Pendergrass Creek, and contains 0.92 km^2 of mixed coniferous and deciduous forest in the Piedmont Upland physiographic section. Located near Anniston, AL, the watershed spans an elevation range from 345 to 456 m above sea level and is a tributary to the Coosa River (within the larger Mobile-Tombigbee basin). The region has a humid subtropical climate, with mean daily January and July air temperatures of 5.3°C and 25.3°C respectively, and mean annual precipitation of 1,400 mm/yr.

Paint Rock Site Description:
Paint Rock (stream code=PRF) research watershed (outlet location: 34.96861724, -86.16501705) on privately owned property in Jackson County (AL, USA). The watershed drains a non-perennial unnamed tributary to Burks Creek, and contains 2.97 km^2 of deciduous forest in the Cumberland Plateau physiographic section. Located near Estillfork, AL, the watershed spans an elevation range from 211 to 550 m above sea level, and is a tributary to the Paint Rock River (within the larger Tennessee basin). The region has a humid subtropical climate, with mean daily January and July air temperatures of 4.4°C and 25.4°C respectively, and mean annual precipitation of 1,390 mm/yr.

Shambley Creek Site Description:
Shambley Creek (stream code=WHR) research watershed (outlet location: 32.98410915, -88.01334337) was on privately owned property in Greene County (AL, USA). The watershed drains a non-perennial unnamed tributary to Shambley Creek, and contains 0.70 km^2 of coniferous forest managed for silviculture in the East Gulf Coastal Plain physiographic section. Located near Eutaw, AL, the watershed spans an elevation range from 63 to 94 m above sea level, and is a tributary to the Sipsey River (within the larger Mobile-Tombigbee basin). The region has a humid subtropical climate, with mean daily January and July air temperatures of 7.3°C and 27.4°C respectively, and mean annual precipitation of 1,350 mm/yr.