Coarse transported organic matter collected from mainstem Big Creek, Middle Fork Salmon River, Idaho, USA (2010-2011).

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).

本研究于2010年12月至2011年3月期间，每月对大溪（Big Creek）主河道中的输运有机质（transported organic matter）开展采样工作。为覆盖昼夜变化（diel variability），每月内均分早、午、晚三个时段进行24小时的输运有机质采集。每月均从河道深槽（thalweg）处采集粗颗粒（粒径>1 mm）输运有机质（CTOM），采集时长为1~4小时。CTOM采集使用直径22.9 cm、网孔1 mm的环形网（hoop net），网体附带流速仪（General Oceanics Inc., Miami, FL, USA）并固定于栅栏柱上。每个采样时段结束后，取下CTOM采样网，并用过滤后的河水冲洗网体。将CTOM分取20~50 mL子样品，经预燃烧（400 ℃下持续30 min）且预称重的玻璃纤维滤膜（孔径0.7 mm）过滤后，立即冷冻保存。剩余CTOM样品经250 mm孔径筛分后转移至塑料容器中，立即冷冻保存，用于后续整体灰分干重（ash-free dry mass, AFDM）的计算。经过滤的CTOM子样品用于测定叶绿素a（chlorophyll-a, chl-a）浓度。本研究参照标准方法（APHA, 1998; Davis等, 2013），对滤膜开展两项分析：其一为叶绿素a（chl-a，藻类色素的表征指标，亦是活体初级生产者的丰度指数），其二为灰分干重（AFDM，活体与衰亡初级生产者的表征指标）。将滤膜置于甲醇中萃取约12小时，随后使用分光光度计测定chl-a浓度，并针对脱镁叶绿素（phaeophytin）进行校正。萃取完成后，将滤膜与含chl-a的甲醇萃取液重新混合，于60 ℃下烘干至少48小时后称重，随后在550 ℃下灰化约4小时。完成chl-a分析后，将CTOM萃取液与滤膜重新混合，并并入剩余的整体AFDM样品中，以计算总AFDM值。利用CTOM的总AFDM值，可计算chl-a与AFDM的比值：将各chl-a测定值除以对应的AFDM值，即可得到chl-a与AFDM的比值，该比值通过对比CTOM中活体自养生物占比（以chl-a表征）与CTOM中活体及衰亡自养生物占比（以AFDM表征），用以指示CTOM的品质。