Enhanced stream greenhouse gas emissions at night and during flood events

Measurements of water parameters of dissolved oxygen (DO), pH, temperature, salinity, water depth, and electrical conductivity (EC) as well as gas samples of carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and radon (²²²Rn) were collected through time series apparatus, hourly over 1471 hours and 140 discrete samples of dissolved organic carbon (DOC), Nitrate (NO₃-), and Ammonium (NH₄+) were collected exclusively at one site in the headwaters of the stream. A calibrated Hydrolab sonde (Unidata, MS5) measured and logged water temperature (±0.02°C), DO (±0.2 mg/L), EC (±0.02 uS cm @°C), pH (±0.02), and salinity (±0.02) at 10 minute intervals and a ultrasonic doppler (Unidata, Starflow) measured water depth in 15 minute intervals. CO₂, CH₄, N₂O, and²²²Rn samples were collected through a shower head gas equilibration exchanger. The gas exchanger units (Durridge Company) were set up to receive 3 L/min of stream water. The greenhouse gases of CO₂, CH₄ and N₂O were sampled continuously by pumping the equilibrated headspace air from shower head gas equilibration device via a one-way valve to a calibrated cavity ringdown spectroscopy gas analyser (Picarro, G2308, ) with precision of < 3.5 ppb. ²²²Rn was measured from the shower head exchanger through a closed air loop to a calibrated Rad7 analyser (Durridge Company, RAD7) (²²²Rn half-life = 3.84 days) and measured at 10 min time steps. Nutrient samples (including duplicates) were collected with a sample-rinsed 60 mL polyethylene syringe. Discrete samples for dissolved organic carbon (DOC) analysis were filtered using pre-combusted 0.7 µm GF/F filters (Whatman), into 40 mL borosilicate vials (USP Type I). Samples for nitrogen were immediately filtered using Satourious ™ 0.45μm cellulose acetate syringe filters into 10 mL polyethylene sample tubes. All samples were kept in a cold icebox, away from light, for less than 5 hours and then frozen until laboratory analysis. Nutrient analysis of DOC was performed with the 40 mL borosilicate vials (USP Type I) first treated with 30 µL of H₃PO₄ before analysis using an Aurora 1030W TOC Analyser (Thermo Fisher Scientific, ConFLo IV). Nutrient analysis of ammonium (NH₄+) and nitrate (NO₃-) was performed on the 10 mL polyethylene sample tubes colourimetrically using a Lachat Flow Injection Analyser.