Theses and Dissertations

Date of Award

7-1-2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean, Coastal, and Earth Sciences

First Advisor

James Jihoon Kang

Second Advisor

Engil Isadora Pujol Pereira

Third Advisor

Rafael Almeida

Abstract

Green fields around the world are being converted to urban land uses to cope with population growth and urbanization. The objective of this study was to investigate how urban lawn soils can contribute to greenhouse gas (GHG) emissions in relation to soil saturation-drainage cycles. We measured carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions as well as redox potential (Eh) from garden soils amended with biochar, compost, or biochar + compost under a mesocosm scale. Bermuda turfgrass seed was seeded in each column (5-gallon bucket) and three water saturation conditions (half-saturated, full-saturated, and unsaturated soils) were maintained for two weeks followed by a 4-week drying period. Mean CO2 flux for Bermuda grass soil columns, bare soil (no grass), control, biochar, compost, and biochar-compost columns were 6.92, 7.64, 3.86, 12.6, and 9.61 g CO2 m-2 d-1 under saturated conditions, and 11.09, 11.66, 10.89, 17.81, and 16.39 g CO2 m-2 d-1 in unsaturated soils. Mean CH4 flux was low (0-2 g CO2 eq m-2 d-1 ) throughout the pre-saturated and saturated phases. CH4 pulses over 5 g CO2 eq m-2 d-1 were observed upon the drainage of full-saturated soils. CO2 flux showed positive correlation with soil temperature and was negatively correlated with soil moisture. The Eh values corresponded to the established water conditions with negative readings (<100 mV) under half- or full-saturated conditions while the Eh values in unsaturated conditions measured positive values (100-450 mV) throughout the experiment. Compost-amended soils maintained higher concentrations of nitrogen (NH4, NO3, and NO2) in soil solution following saturated conditions. The saturated conditions did not show a significant effect on the reductive dissolution of iron and manganese. This study investigates the biogeochemical processes in soil that cause the emission of GHG’s, affected by biochar and compost amendments and contrasting water table conditions, from soil columns treated with two popular turfgrass species, St. Augustine (Stenotaphrum secundatum) and Bermuda turfgrass (Cynodon dactylon) and the related biogeochemical reactions. Compost amended soils consistently led to significantly higher CO2 emissions compared to control and biochar amendments, with the most notable differences observed during the saturated and drainage periods. Saturated conditions significantly increased CH4 emissions, particularly in compost-amended soils, with the highest CH4 fluxes recorded during the drainage period following saturation.

Comments

Copyright 2024 Angel Salinas. https://proquest.com/docview/3115368783

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