This study was conducted in the Talladega 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, a tributary to the Coosa River (within the larger Mobile-Tombigbee basin). The watershed contains 0.92 km^2 of mixed coniferous and deciduous forest in the Piedmont Upland physiographic province. Located near Anniston, AL, the watershed spans an elevation range from 340 to 480 m above sea level. 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 1400 mm/yr.
These samples were collected in support of the Talladega flow manipulation experiment, part of Approach 4 of the Aquatic Intermittency effects on Microbiomes in Streams (AIMS) Project. Briefly, a before-after-control-impact (BACI) experimental design was followed to assess the impacts of flow reduction and flow recovery on microbial communities and ecosystem processes. A small plywood dam and plastic drainage pipes were used to divert flow from an 85-m section of the stream. This resulted in two study reaches: 1, an impacted reach downstream of the dam, where flow is reduced when the dam is activated but recovers when the dam is deactivated, and 2, an un-impacted reference reach upstream of the dam where flow is not impacted by the damming. Within each reach, five transects (spaced ~15-m apart) were sampled at six time points, including before flow reduction (t1), during a 1-month-long flow reduction (t2, t3), and after flow recovery (t4-t6).
This dataset pertains specifically to ash-free dry mass (AFDM), a measurement of organic matter content. Four stream substrate types were collected for AFDM (surface water, rock surfaces, leaf litter, and sediment) following the AIMS Microbial Field Sampling SOP (Zeglin and Busch, 2024). Dry masses and ashed masses were measured and used to calculate the proportion of AFDM (AFDM g / DM g) for each sample type. For water, 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). Some samples were not collected due to time constraints in the field, and are flagged as not collected. In 33 out of 60 water samples, organic matter content was too low for AFDM to be detected, and so while AFDM is listed as zero for these samples, they are also flagged as being below the detection limited. AFDM was consistently detectable in other substrates.

References:
Zeglin, L., M. Busch (2024). AIMS SOP - Microbial Field Sampling, HydroShare, http://www.hydroshare.org/resource/4b071711215341118330c22f18b5d20d