The Effects of Temperature, Flooding, and Goose Feces Addition on Greenhouse Gas Emissions and Ammonification in Four High-Latitude Soils from Western Alaska

The large carbon (C) stock of wetlands is vulnerable to climate change, especially in high latitudes that are warming at a disproportional rate. Likewise, low-elevation Arctic coastal areas will flood more frequently under climate change and sea-level rise, which may alter goose herbivory and fecal deposition patterns if geese move inland. While temperature, flooding, and feces impact soil C emissions, their interactive effects have been rarely studied. Here, I explore the impact of these interactions on CO2 and CH4 emissions and nitrogen (N) mineralization (ammonification) in soils collected from four plant communities in the Yukon-Kuskokwim (Y-K) Delta, a high latitude coastal wetland in western Alaska. Plant communities follow an elevational gradient and vary in their flooding and grazing susceptibility. These communities include an intensely grazed and susceptible to flooding grazing lawn (“Grazing Lawn”), two wetlands that experience moderate grazing and frequent (“Lowland Wetland”) and less frequent (“Upland Wetland”) flooding, and a rarely grazed and flooded upland tundra community (“Tundra”) located at the highest elevation. Soils were incubated for 16 weeks at 8°C or 18°C in microcosms and subjected to flooding and feces addition treatments with no-flood and no-feces controls. I quantified C emissions weekly and ammonification over the course of the experiment. I found that warming, which favors maintenance respiration over growth, increased ammonification, reflecting increased microbial demand for C relative to N in the Lowland Wetland. While warming always increased CO2 and CH4 emissions, interactions with flooding complicated warming impacts on C emissions in the Grazing Lawn and Tundra. In the Grazing Lawn, flooding increased CH4 emissions at 8°C and 18 °C, but in the Tundra, flooding suppressed CH4 emissions at 18°C. Flooding alone reduced CO2 emissions in the Upland Wetland. Feces addition increased CO2 emissions in all communities, but feces impacts on CH4 emissions and ammonification were minimal. When feces and flooding occurred together in the Lowland Wetland, CH4 emissions decreased compared to when feces was added without concomitant flood. Feces decreased the immobilization of ammonium (N-NH4 +) and therefore microbial N demand in the Tundra only. My results suggest that flooding could partially offset C emissions from warming in less frequently flooded, higher elevation communities, but this offset could be negligible if flooding and warming drastically increase C emissions in more flooded lowland areas.

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