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Title: Spatial variation related to hydroloigc patterns and vegetation in greenhouse gas fluxes from the Mississippi Delta agricultural region

item KEATING, MICHAEL - Mississippi State University
item BALACHANDRAN, DEVIKA - Princeton University
item OCHS, CLIFFORD - University Of Mississippi
item HOLLAND, MARJORIE - University Of Mississippi
item Lizotte, Richard
item YU, KEWEI - Troy University

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2015
Publication Date: 10/27/2015
Citation: Keating, M.P., Balachandran, D., Ochs, C.A., Holland, M.M., Lizotte Jr, R.E., Yu, K. 2015. Spatial variation related to hydroloigc patterns and vegetation in greenhouse gas fluxes from the Mississippi Delta agricultural region. Applied Soil Ecology. 98:278-281 DOI: 10.1016/j.apsoil.2015.09.012.

Interpretive Summary: Agricultural activity such as fertilizer applications can increase soil bacteria activity and contribute greenhouse gasses such as methane, nitrous oxide, and carbon dioxide. This study measured soil bacterial gas emissions in the field along with genetic and chemical analyses to determine greenhouse gas hotspots on farmland, riparian, and wetland soils within the Mississippi Delta agricultural region. Methane and nitrous oxide emissions were greatest on farmland soils while carbon dioxide emissions were greatest in riparian soils. Genetic analysis indicated nitrous oxide from farmland soils likely come from bacterial nitrification while nitrous oxide from riparian soils come from bacterial denitrification. Differences in greenhouse gas emissions from wetland soils were related to soil saturation and water flow indicating these variables as influencing emission rates. This information can be used to better manage agriculturally influenced greenhouse gas emissions because it can be used to get a better understanding of which conditions will mitigate these emissions.

Technical Abstract: Methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) fluxes from agricultural landscapes may contribute significantly to regional greenhouse gas budgets due to stimulation of soil microbial activity through fertilizer application and variable soil moisture effects. In this study, measurements of microbial gas emissions made with field collection chambers were combined with soil genetic and chemical analyses to determine hotspots of greenhouse gas emissions from cropland, drainage ditch, riparian zone and wetland sites in Tunica and Sunflower Counties of the north Mississippi Delta agricultural region. CH4 emissions increased from cropland to wetland, concomitantly with soil moisture. CO2 emissions peaked in the riparian zone, the region of intermediate soil moisture. N2O emissions were highest in the cropland and riparian zones, although soil genetic and chemical data suggest a difference in N2O source between these two sites. Genes involved in the denitrification pathway (nosZ gene) were recovered and indicate denitrification-derived N2O products in intermittently-flooded sites, while soil [NO3- + NO2-] concentrations suggest nitrification-derived N2O products in dry cultivated sites. Differences in gas emissions between paired neighboring wetland sites were related to hydrologic flow regime. This study demonstrates the importance of hotspots of gas emissions in this agricultural landscape with hydrological condition, particularly soil saturation and flow rate, a critical driver affecting emission rates.