Abstract. Streams and rivers are significant sources of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4), and watershed management can alter greenhouse gas (GHG) emissions from streams. GHG emissions from streams in agricultural watersheds have been investigated in numerous studies, but less is known about streams draining urban watersheds. We hypothesized that urban infrastructure significantly influences GHG dynamics along the urban watershed continuum, extending from engineered headwater flowpaths to larger streams. GHG concentrations and emissions were measured across streams draining a gradient of stormwater and sanitary infrastructure including: (1) complete stream burial, (2) in-line stormwater wetlands, (3) riparian/floodplain preservation, and (4) septic systems. Infrastructure categories significantly influenced drivers of GHG dynamics including carbon to nitrogen stoichiometry, dissolved oxygen, total dissolved nitrogen (TDN), and water temperature. These variables explained much of the statistical variation in nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) saturation in stream water (r2 = 0.78, 0.78, 0.50 respectively). N2O saturation ratios in urban streams were among the highest reported for flowing waters, ranging from 1.1–47 across all sites and dates. The highest N2O saturation ratios were measured in streams draining nonpoint N sources from septic systems and were strongly correlated with TDN. CO2 was highly correlated with N2O across all sites and dates (r2 = 0.84), and CO2 saturation ratio ranged from 1.1–73. CH4 was always super-saturated with saturation values ranging from 3.0 to 2157. Differences in stormwater and sewer infrastructure influenced water quality, with significant implications for enhancing or minimizing stream CO2, CH4, and N2O emissions.
Influence urban infrastructure on water quality and greenhouse gas dynamics in streams
