Abstract
In August 2010 we collected one 24-hr drift sample from 12 streams (4 of each disturbance class). From June to August 2011, we collected drift samples twice monthly for 15 streams (5 of each disturbance class). In 2012, we collected samples of stream export from unburned and prescribed fire streams in late May and early September. To measure downstream export of organic matter, we placed 250 m mesh drift nets in the thalweg and immediately upstream of its confluence with the main-stem river. For most sample periods, nets were deployed for approximately 24-h during base flow (late July and August). High discharge associated with spring snowmelt, however, precluded continuous 24-hr sampling in May, June, and early July. Therefore, during those months, we sampled 3 times per day (dawn, midday, and dusk). Duration of net deployment ranged from 1 to 180 min. Drift samples were processed monthly for organic matter, sediment, % carbon and nitrogen of organic matter, and invertebrate biomass. Drift samples were processed bimonthly for chlorophyll-a concentrations to capture rapid fluctuations in this metric of organic matter quality. We measured discharge through the nets with a flow meter (+/- 0.01 m/s) (Marsh-McBirney, The Hach Company, Loveland, CO, USA) at the beginning and end of each sample period and at any time the nets were examined for signs of clogging. We calculated the volume of water that traveled through the net during sample periods using averages of water velocities at the beginning and end of each sample period.
After each sampling period, we rinsed the nets with stream water and collected the contents in a 1000-mL graduated cylinder. Subsequently, the samples were subsampled for later analysis of exported organic matter, chl-a, sediment, invertebrate biomass, and C:N of exported organic matter. To measure the amount of chlorophyll-a in stream export >250 m we subsampled material collected in nets during sample periods. We homogenized the sample by agitating the cylinder and filtered a subsample (10 - 25 mL) onto preashed and preweighed glass fiber filters (0.70 ?m, Millipore IRL Ltd, Tullagreen Ireland). We wrapped filters in aluminum foil and stored them on dry ice during transport to the laboratory.
In the laboratory, we analyzed chl-a based on standard methods (Steinman et al. 2007). Briefly, filters from each sampling period and stream were extracted in methanol for ca. 12 hrs, analyzed for chl-a with a spectrophotometer, and corrected for phaeophytin.