Abstract
We sampled transported organic matter in Big Creek mainstem monthly from December 2010 to March 2011. During each month, transported organic matter was collected during 3 time periods (morning, mid-day, and night) for a 24 h period to encompass diel variability. Each month, coarse (>1 mm) transported organic matter (CTOM) was collected from the thalweg for 1 - 4 h. CTOM was collected with a hoop net (22.9 cm diameter, 1-mm mesh) with attached flowmeter (General Oceanics Inc., Miami, FL, USA) connected to a fencepost. At the end of each sampling period, the CTOM nets were removed and rinsed with filtered river water. CTOM was sub-sampled (20 - 50 mL), filtered onto pre-combusted (400 C for 30 min) and pre-weighed glass-fiber filters (0.7 mm), and frozen immediately. The remaining volume of CTOM and was sieved (250 mm), transferred to plastic containers, and frozen immediately for later calculation of bulk AFDM.
CTOM filtered sub-samples were used to quantify chl-a concentrations. Based on standard methods (APHA, 1998, Davis et al. 2013), filters were analyzed for chlorophyll-a (chl-a, measure of algal pigments and index of living primary producers) and ash-free dry mass (AFDM, measure of living and senesced primary producers). Filters were extracted in methanol for c. 12 h, analyzed for chl-a with a spectrophotometer and corrected for phaeophytin. After extraction, the filters and methanol extract containing the chl-a component were recombined, dried at 60 C for at least 48 h, weighed and ashed at 550 C for c. 4 h. After chl-a analysis, the CTOM extract and filter were recombined and added to the remaining bulk AFDM for the calculated total AFDM. The total AFDM values of CTOM were used to calculate the ratio of chl-a to AFDM. The chl-a values were divided by the corresponding AFDM values to generate the ratio of chl-a to AFDM, an indicator of CTOM quality by contrasting the portion of living autotrophs of CTOM (chl-a) to the portion of living and senesced autotrophs of CTOM (AFDM).