Observations of Greenhouse Gases and Nitrate Concentrations in a Maine River and Fringing Wetland

Abstract In the Sheepscot River, ME, we measured percent saturations of dissolved methane (CH4) and carbon dioxide (CO2) and concentrations of nitrate (NO3-) four times in the main stem and once in the West Branch. River water was super-saturated with CH4 at all sites throughout the study, and measurements were generally higher at lower-gradient sites (1000–5000% saturation) than higher-gradient sites (generally <1000%). Percent saturations of CO2 in the main stem varied in both time and space and were under-saturated at some sites. CO2 percent saturations and NO3- concentrations in the more-developed West Branch were significantly higher than the main stem, likely because of the position of mainstem sites downstream of Sheepscot Pond where primary production and degassing could occur. We also measured CH4 and CO2 fluxes from wetland soil adjacent to the main stem, which averaged 710 (± 59) µmolCH4/m2/h and -51 (± 6.4) mmolCO2/m2/h. Our findings suggest that rivers and fringing wetlands in the formerly gl...