Quantifying the Impacts of Nutrient Enrichment On the Greenhouse Gas Emissions and Water Quality Improvement Functions of a Tidal Freshwater Wetland.

We measured greenhouse gas production (CH₄, CO₂, N₂O) and nitrogen (N) removal via denitrification in anaerobic incubations of soil from plots in a tidal freshwater wetland (TFW) fertilized with either N, phosphorus (P), a combination of N and P (N&P) or left unfertilized (control) for 7 years, in order to quantify the effect of nutrient enrichment on TFW soils and associated ecosystem functions. CH₄ production in N and N&P amended plots (0.15-0.19 μg CH₄/g soil/hr) was more than double the production in P and control plots (0.07 μg CH₄/g soil/hr) indicating N limits methanogenesis in this TFW. Furthermore, the addition of labile carbon (C) increased CH₄ production 2-4x in N fertilized soils (0.39-0.84 μg CH₄/g soil/hr), but not in P or control plots (0.09 μg CH₄/g soil/hr). Rates of ambient CO₂ and N₂O production were not significantly different among treatments. Ambient denitrification rates, as measured by the acetylene block method, were highest in the N fertilized soils (0.04 μg N₂O/g soil/hr). However, the addition of NO₃^- to denitrification incubations increased denitrification rates in all soils to 0.12-0.14 μg N₂O/g soil/hr, indicating denitrifying populations responded equivalently to increased N among all treatments. Soil total P and labile P were highest in P and N&P fertilized plots, but P-sorption capacity was similar in all plots, indicating long-term P fertilization does not diminish the P retention capacity of TFW soils. Total soil N and C did not differ between treatments. These results indicate that long-term fertilization does not diminish the capacity of TFWs to remove N via denitrification or to retain P in the soil pool. However, N fertilization does increases the production of CH₄, a potent greenhouse gas.