Greenhouse gas dynamics in a freshwater wetland in southeastern Ontario: Field measurements and laboratory incubations

Concentrations of dissolved carbon dioxide (CO2), dissolved methane (CH4), and dissolved nitrous oxide (N2O) were measured in open water areas across a freshwater mineral wetland in the Ottawa Valley.268 samples were collected on 19 sampling days from September 16 th , 2022 to February 5 th , 2024.Average dissolved CO₂ ranged from 111 μmol/liter in the spring, to 2548 μmol/liter in mid-winter.Average dissolved CH₄ ranged from 3.33 μmol/liter in the autumn, to 1414 μmol/liter in mid-winter.Average dissolved N₂O concentrations ranged from 0.016 μmol/liter below ambient to 0.036 μmol/liter.CO2, CH4, and N2O accumulated under ice, resulting in high concentrations in winter.Concentrations of CO2 and CH4 declined in the autumn and increased from the spring until the end of summer.In late summer, CO2 and CH4 concentrations were higher than during the mid-summer despite lower temperatures.These higher gas concentrations coincided with the presence of dense flocks of migrating Canada geese.To further investigate the potential influence of the Canada goose migration and other nutrient sources on greenhouse gas emissions, two laboratory incubations of saturated soils in sealed jars were performed.The first incubation compared a control group with treatment groups of K₂SO₄, KH₂PO₄, KNO₃, and biochar.Each group had five replicates measured 17 times over 141 days for concentrations of CO2, CH4, and N2O.Additions of fertilizers and biochar did not have a large impact on measured gases.The second incubation compared a control group with treatment groups of two different application rates of goose feces and cattle manure.Each group had five replicates measured 20 times over 78 days for concentrations of CO2, CH4, and N2O.Goose feces and cow manure additions led to an increase in peak production of CO2, CH4, and N₂O.This research demonstrates the importance of year-round sampling across an entire wetland system and a new understanding of seasonality that includes the influence of nutrient additions from migrating species and local land use.iii Résumé:Les concentrations de dioxyde de carbone dissous (CO2), de méthane dissous (CH4) et d'oxyde nitreux dissous (N2O) ont été mesurées dans des zones d'eau libre à travers une zone humide minérale d'eau douce dans la vallée de l'Outaouais.268 échantillons ont été prélevés sur 19 jours d'échantillonnage du 16 septembre 2022 au 5 février 2024.La teneur moyenne en CO₂ dissous variait de 111 μmol/litre au printemps à 2 548 μmol/litre au milieu en hiver.La teneur moyenne en CH₄ dissous variait de 3,33 μmol/litre en automne à 1 414 μmol/litre au milieu de l'hiver.Les concentrations moyennes en N2O dissous variaient de 0,016 μmol/litre sous des concentrations de l'air ambiant à 0,036 μmol/litre.Le CO₂, le CH 4 et le N 2 O se sont accumulés sous la glace, ce qui donnait des concentrations élevées en hiver.Les concentrations de CO2 et de CH4 ont diminué en automne et ont augmenté du printemps jusqu'à la fin de l'été.À la fin de l'été, les concentrations de CO2 et de CH4 étaient plus élevées qu'au milieu de l'été malgré des

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