Effects of Salinity on Denitrification and Greenhouse Gas Production from Laboratory-incubated Tidal Forest Soils

Abstract

We measured ambient and potential denitrification in tidal freshwater floodplain forest (tidal forests) soils along the Altamaha, Ogeechee, and Satilla Rivers in southeast Georgia to characterize nitrogen removal from these understudied systems. Further, we measured the response of denitrification, greenhouse gas production (CO2, CH4, N2O), and the formation of reduced inorganic sulfur species following laboratory incubations simulating saltwater intrusion with salinity levels of 2 and 5. Ambient denitrification ranged from 0.03 μg N2O/g/hr in the Satilla River to 0.40 μg N2O/g/hr in the Altamaha River. Potential denitrification was two to eight times greater than ambient denitrification. Denitrification from Satilla River soils increased with salinity, while Altamaha and Ogeechee River soils were unaffected. Methane production, however, was inhibited by salinity, decreasing by 77% in the 2 treatment and 89% in the 5 treatment whereas CO2 generally increased with salinity, though exhibited a variable response between the three rivers. Formation of reduced sulfur species followed a similar trend to CO2 production. Our findings suggest that tidal forests are effective sinks for N, capable of producing anywhere from 0.032 to 1.9 μg N2O/g soil/hr. Overall, salinity increased the amount of C mineralized suggesting that low levels of salinity can alter the short-term C dynamics of tidal freshwater forests.