Greenhouse Gas Emissions from Big Meadow Bog: Influence of Gull-Derived Phosphate as a Biogeochemical Driver

Greenhouse gas (GHG) emissions (CO2, CH4, N2O) were measured in the two years prior to, and the year of, the hydrological restoration of the ditched Big Meadow Bog (BMB). The total greenhouse gas emission from the south of BMB in recovery succession after abandonment of the area by nesting Herring Gulls 20 years earlier (‘BMB Recovering’) was twice that of the pristine raised ‘Reference Bog’. The emissions from the north of BMB, the zone of current gull nesting (‘BMB Gull’), was twice that of the ‘BMB Recovering’ site. The coefficient of variation (CV) for CO2 evolution measurements at all sites was comparatively low (average = 36%) but extreme for N2O and CH4 (average in each case = 139%); regardless, for each measurement year, the N2O values (17–92 CO2 equivalent units) at BMB Gull were significantly greater than either the Reference Bog or BMB Recovering sites. While CO2 evolution accounted for nearly all (88–100%) of total GHG emissions prior to blocking the ditches (hydrological restoration) N2O levels were greatest (92 CO2 eq.) in the restoration year when the water table was elevated. Phosphate levels in peat at the two BMB sites—the legacy of gull guano inputs—accounted for 73% of CO2 evolution variation in its measurement year (2016). Three types of nitrogen in peat (NO3, NH4 and total soluble N) accounted for less variation (r2 = 42–52%) in N2O than phosphate (r2 = 66%). Overall, greenhouse gas emissions have been exacerbated by the changing hydrology and eutrophication of BMB; however, the long-term management goal of reducing gull numbers could return BMB to a carbon sink.