Wetland soil greenhouse gas production in laboratory incubations under varying nutrient conditions across an estuarine salinity gradient

Background/Question/Methods

Wetlands within the Hudson River Estuary receives significant inputs of readily dissolvable carbon (C) and nitrogen (N) from fertilizer watershed runoff and incomplete wastewater treatment during storm events associated with NYC and other urban centers.  Nutrient deposition may alter carbon utilization in the estuarine water column, associated sediments and surrounding wetlands.  However, the extent to which nutrient additions alters C pools in anaerobic systems and the role microbial communities play in C transformation remains unclear.  In these anaerobic systems, we hypothesize that microbial activity is limited by the availability of easily-degradable C, which acts as a co-metabolite and provides energy for organic matter decomposition.  Sporadic transport of highly C enriched storm derived discharge may substantially enhance greenhouse gas (GHG) production rates through the utilization of stored C pools and/or added organic C.  To test our hypothesis carbon dioxide (CO₂) and methane (CH₄) production rates were evaluated from soil cores removed from three wetland sites (Saw Mill Creek, (SM), Piermont (PM), and Iona Island (II) Marsh(s)) located across a salinity gradient (22 – 0.5 ppt) and incubated under varying nutrient treatments.  Daily headspace GHG measurements were conducted while biogeochemical and 454 sequencing analyses were made at the conclusion of each incubation experiment. 

Results/Conclusions

Incubation experiments from wetland soil core experiments demonstrated that readily degradable C but not inorganic N additions stimulated GHG production 3X compared to negative controls.  CO₂ production rates for C amended soils were not significantly different between sites with an average of 10, 8, and 12 µg C day^-1 g^-1 of dry soil for SM, PM, and II incubations, respectively.  In contrast, CH₄ production rates for C amended soils were significantly different between treatments with 0.05, 6, and 9 µg C day^-1 g^-1 of dry soil for SM, PM, and PM incubations, respectively.  Salinity was negatively correlated with CH₄ production while only weakly correlated with CO₂ production.  The net warming potential effect from CO₂ and CH₄ emissions from C-amended soils were 25X greater in the two oligohaline marshes (II and PM) compared to 2X greater in the polyhaline marsh (SM).  Most significantly, 8%, 14%, and 23% of the C added to C treatments was mineralized as CO₂ and CH₄ for the SM, PM, and II incubations indicating that the native wetland soil C pools are resilient to anthropogenic additions and will remain critical C sinks in urban dominated ecosystems.