Effects of Land Use Types on CH4 and CO2 Production Potentials in Subtropical Wetland Soils

Jiaxing Xu,Suvadip Neogi,Derrick Y F Lai

doi:10.3390/w12071856

Abstract

Changes in land use types can alter the soil and environmental characteristics of wetlands, which in turn influence the magnitude of greenhouse gas production by soil microbes. However, the effects of land use change on the production potential of methane (CH4) and carbon dioxide (CO2) in subtropical wetland soils and the underlying controls are still largely unknown. In this study, we examined the soil CH4 and CO2 production potentials under five different land use types (natural mangrove, Gei Wai water channel, Gei Wai forest, reedbed, and freshwater pond) and their relationships with soil physico-chemical properties in a subtropical wetland in Hong Kong using aerobic and anaerobic laboratory incubation experiments. Our results showed an overall decreasing trend of CH4 and CO2 production potentials down the soil profile at all sites, which could be attributed to a reduction in the concentrations of soil organic matter (SOM), total Kjeldahl nitrogen (TKN) and ammonium nitrogen (NH4+-N). Moreover, the soil CH4 and CO2 production potentials varied significantly in the surface soils among land use types, but were more similar across the sites in the deeper soils. The conversion of natural mangrove to other land use types significantly reduced both the aerobic and anaerobic CO2 production potentials in the top 10 cm soils, except for Gei Wai forest, which demonstrated significantly higher CO2 production rates (61.15–97.91 μg g−1 day−1). Meanwhile, the mean CH4 production potential in the surface soils of natural mangrove (0.05 μg g−1 d−1) was significantly lower than that in the Gei Wai forest and Gei Wai channel (0.26–0.27 μg g−1 day−1) but slightly higher than that in the freshwater pond and reedbed (0.00–0.02 μg g−1 day−1). The high soil CH4 and CO2 production potentials observed in the Gei Wai forest could be explained by the high soil concentrations of SOM, TKN and NH4+-N. On the other hand, the lower anaerobic CH4 and aerobic CO2 productions observed in the reedbed could be attributed to the lower concentrations of NH4+-N and available phosphorus. Our findings highlighted the significant impacts of land use types on the CH4 and CO2 production potentials of subtropical wetland soils, which had practical implications for wetland management for climate change mitigation.

Highlights

Carbon dioxide (CO2 ) and methane (CH4 ) are potent greenhouse gases (GHGs) in the atmosphere that can contribute significantly to global climate change
The anaerobic CH4 (an-CH4) production potentials were much lower in the mangrove, freshwater pond, and reedbed, with mean rates of 0.05, 0.02, and 0.004 μg g−1 day−1, respectively (Figure 2)
At a depth of 10–20 cm, the an-CH4 production was significantly higher in the Gei Wai water channel (0.05 μg g−1 day−1 ) and mangrove (0.06 μg g−1 day−1 ) than the other three land use types (0.00–0.03 μg g−1 day−1 )

Summary

Introduction

Carbon dioxide (CO2 ) and methane (CH4 ) are potent greenhouse gases (GHGs) in the atmosphere that can contribute significantly to global climate change. The net CH4 emission rate from wetlands depends on the balance between CH4 production, oxidation, Water 2020, 12, 1856; doi:10.3390/w12071856 www.mdpi.com/journal/water. The magnitude of soil CH4 production depends on various factors including pH, temperature, and the availability of substrate, oxygen, and other alternative electron acceptors [4,5,6,7]. Coles and Yavitt [14] found an increase in CH4 production rates following the addition of carbon substrates (e.g., glucose, ethanol and acetate) to forested fen peat samples, which indicated substrate availability was a limiting factor of CH4 production. Nitrate nitrogen has been shown to increase the soil redox potential and decrease CH4 production [16], while higher anaerobic CH4 production rate was observed in peatlands with higher soil organic carbon (SOC) and nitrogen (N)

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