Murray State University
Does Taxodium distichum “knee” density affect greenhouse gas fluxes in bottomland hardwood wetlands?
Grade Level at Time of Presentation
Senior
Major
Environmental Science
Minor
Wildlife and Conservation Biology
KY House District #
5
KY Senate District #
1
Faculty Advisor/ Mentor
Dr. Jessica Moon
Department
Department of Earth and Environmental Science
Abstract
With rising greenhouse gas emissions, it is crucial to include natural sources of carbon dioxide (CO2) and methane (CH4) in the global carbon budget. Wetland soils and vegetation can play a significant role in these source-sink dynamics. However, regional carbon budgets often do not include emissions from woody root structures, such as the “knees” of Taxodium distichum (bald cypress) trees in bottomland hardwood wetlands, because little has been done to study their effects. We are examining how the density of knees (e.g., surface area for gas movement) affects the balance between CO2 and CH4 uptake and emissions. Knee density was surveyed in 120 1m2 plots within a 10 m stretch of Dunn Slough in Clarks River Wildlife Refuge, which contained a source population of Taxodium distichum. Densities ranged from no knees to 24 knees per m2 (mean +/- s.d. = 3.3 +/- 3.6 knees per m2). Twenty-four plots with varying knee densities were randomly selected to measure CO2 and CH4 fluxes over six hour time periods using large-framed chambers. Additionally, twelve of these plots were randomly selected to measure fluxes from the soil alone, adjacent to knees. During drought conditions in the Fall of 2022, soils within higher density plots had higher CO2 emissions and slightly higher CH4 uptake compared to lower density knee plots. When knees were included in flux measurements, they negated differences in CH4 uptake within the soils alone. We hypothesize, this is due to the knee’s ability to transport CH4 from deep soils pools, which we have found in a complementary study. Upscaling the results of this study could provide more accurate flux rates to regional carbon budgets of areas with varying cypress knee densities.
Does Taxodium distichum “knee” density affect greenhouse gas fluxes in bottomland hardwood wetlands?
With rising greenhouse gas emissions, it is crucial to include natural sources of carbon dioxide (CO2) and methane (CH4) in the global carbon budget. Wetland soils and vegetation can play a significant role in these source-sink dynamics. However, regional carbon budgets often do not include emissions from woody root structures, such as the “knees” of Taxodium distichum (bald cypress) trees in bottomland hardwood wetlands, because little has been done to study their effects. We are examining how the density of knees (e.g., surface area for gas movement) affects the balance between CO2 and CH4 uptake and emissions. Knee density was surveyed in 120 1m2 plots within a 10 m stretch of Dunn Slough in Clarks River Wildlife Refuge, which contained a source population of Taxodium distichum. Densities ranged from no knees to 24 knees per m2 (mean +/- s.d. = 3.3 +/- 3.6 knees per m2). Twenty-four plots with varying knee densities were randomly selected to measure CO2 and CH4 fluxes over six hour time periods using large-framed chambers. Additionally, twelve of these plots were randomly selected to measure fluxes from the soil alone, adjacent to knees. During drought conditions in the Fall of 2022, soils within higher density plots had higher CO2 emissions and slightly higher CH4 uptake compared to lower density knee plots. When knees were included in flux measurements, they negated differences in CH4 uptake within the soils alone. We hypothesize, this is due to the knee’s ability to transport CH4 from deep soils pools, which we have found in a complementary study. Upscaling the results of this study could provide more accurate flux rates to regional carbon budgets of areas with varying cypress knee densities.