1
|
Mayer AC, McFarlane KJ, Silver WL. The effect of repeated hurricanes on the age of organic carbon in humid tropical forest soil. GLOBAL CHANGE BIOLOGY 2024; 30:e17265. [PMID: 38553935 DOI: 10.1111/gcb.17265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 03/05/2024] [Accepted: 03/17/2024] [Indexed: 04/02/2024]
Abstract
Increasing hurricane frequency and intensity with climate change is likely to affect soil organic carbon (C) stocks in tropical forests. We examined the cycling of C between soil pools and with depth at the Luquillo Experimental Forest in Puerto Rico in soils over a 30-year period that spanned repeated hurricanes. We used a nonlinear matrix model of soil C pools and fluxes ("soilR") and constrained the parameters with soil and litter survey data. Soil chemistry and stable and radiocarbon isotopes were measured from three soil depths across a topographic gradient in 1988 and 2018. Our results suggest that pulses and subsequent reduction of inputs caused by severe hurricanes in 1989, 1998, and two in 2017 led to faster mean transit times of soil C in 0-10 cm and 35-60 cm depths relative to a modeled control soil with constant inputs over the 30-year period. Between 1988 and 2018, the occluded C stock increased and δ13C in all pools decreased, while changes in particulate and mineral-associated C were undetectable. The differences between 1988 and 2018 suggest that hurricane disturbance results in a dilution of the occluded light C pool with an influx of young, debris-deposited C, and possible microbial scavenging of old and young C in the particulate and mineral-associated pools. These effects led to a younger total soil C pool with faster mean transit times. Our results suggest that the increasing frequency of intense hurricanes will speed up rates of C cycling in tropical forests, making soil C more sensitive to future tropical forest stressors.
Collapse
Affiliation(s)
- Allegra C Mayer
- Department of Environmental Science, Policy and Management, University of California Berkeley, Berkeley, California, USA
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California, USA
- Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, USA
| | - Karis J McFarlane
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California, USA
| | - Whendee L Silver
- Department of Environmental Science, Policy and Management, University of California Berkeley, Berkeley, California, USA
| |
Collapse
|
2
|
Capooci M, Seyfferth AL, Tobias C, Wozniak AS, Hedgpeth A, Bowen M, Biddle JF, McFarlane KJ, Vargas R. High methane concentrations in tidal salt marsh soils: Where does the methane go? GLOBAL CHANGE BIOLOGY 2024; 30:e17050. [PMID: 38273533 DOI: 10.1111/gcb.17050] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 10/18/2023] [Accepted: 10/18/2023] [Indexed: 01/27/2024]
Abstract
Tidal salt marshes produce and emit CH4 . Therefore, it is critical to understand the biogeochemical controls that regulate CH4 spatial and temporal dynamics in wetlands. The prevailing paradigm assumes that acetoclastic methanogenesis is the dominant pathway for CH4 production, and higher salinity concentrations inhibit CH4 production in salt marshes. Recent evidence shows that CH4 is produced within salt marshes via methylotrophic methanogenesis, a process not inhibited by sulfate reduction. To further explore this conundrum, we performed measurements of soil-atmosphere CH4 and CO2 fluxes coupled with depth profiles of soil CH4 and CO2 pore water gas concentrations, stable and radioisotopes, pore water chemistry, and microbial community composition to assess CH4 production and fate within a temperate tidal salt marsh. We found unexpectedly high CH4 concentrations up to 145,000 μmol mol-1 positively correlated with S2- (salinity range: 6.6-14.5 ppt). Despite large CH4 production within the soil, soil-atmosphere CH4 fluxes were low but with higher emissions and extreme variability during plant senescence (84.3 ± 684.4 nmol m-2 s-1 ). CH4 and CO2 within the soil pore water were produced from young carbon, with most Δ14 C-CH4 and Δ14 C-CO2 values at or above modern. We found evidence that CH4 within soils was produced by methylotrophic and hydrogenotrophic methanogenesis. Several pathways exist after CH4 is produced, including diffusion into the atmosphere, CH4 oxidation, and lateral export to adjacent tidal creeks; the latter being the most likely dominant flux. Our findings demonstrate that CH4 production and fluxes are biogeochemically heterogeneous, with multiple processes and pathways that can co-occur and vary in importance over the year. This study highlights the potential for high CH4 production, the need to understand the underlying biogeochemical controls, and the challenges of evaluating CH4 budgets and blue carbon in salt marshes.
Collapse
Affiliation(s)
- Margaret Capooci
- Department of Plant and Soil Science, University of Delaware, Newark, Delaware, USA
| | - Angelia L Seyfferth
- Department of Plant and Soil Science, University of Delaware, Newark, Delaware, USA
| | - Craig Tobias
- Department of Marine Sciences, University of Connecticut, Groton, Connecticut, USA
| | - Andrew S Wozniak
- School of Marine Science and Policy, University of Delaware, Lewes, Delaware, USA
| | - Alexandra Hedgpeth
- Department of Geography, University of California, Los Angeles, Los Angeles, California, USA
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California, USA
| | - Malique Bowen
- School of Marine Science and Policy, University of Delaware, Lewes, Delaware, USA
| | - Jennifer F Biddle
- School of Marine Science and Policy, University of Delaware, Lewes, Delaware, USA
| | - Karis J McFarlane
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California, USA
| | - Rodrigo Vargas
- Department of Plant and Soil Science, University of Delaware, Newark, Delaware, USA
| |
Collapse
|
3
|
Broek TA, Moreland KC, Ognibene TJ, McFarlane KJ, Brown TA. Optimization of the LLNL/CAMS gas-accepting ion source and 1 MV compact AMS for natural abundance radiocarbon analysis of CO 2. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH. SECTION B, BEAM INTERACTIONS WITH MATERIALS AND ATOMS 2022; 530:1-7. [PMID: 38390228 PMCID: PMC10883299 DOI: 10.1016/j.nimb.2022.08.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2024]
Abstract
The Lawrence Livermore National Laboratory - Center for Accelerator Mass Spectrometry (LLNL/CAMS) 1 MV AMS system was converted from a biomedical AMS instrument to a natural abundance 14C spectrometer. The system is equipped with a gas-accepting hybrid ion source capable of measuring both solid (graphite) and gaseous (CO2) samples. Here we describe a series of experiments intended to establish and optimize 14CO2 measurement capabilities at natural abundance levels. A maximum instantaneous ionization efficiency of 8 % was achieved with 3 % CO2 in helium at a flow rate of approximately 220 μL/min (3.5 μg C/min). For modern materials (e.g., OX I) we measured an average of 240 ± 50 14C counts/μg C, equivalent to a total system efficiency of approximately 3 %. Experimental CO2 samples with F14C values ranging from 0.20 to 1.05 measured as both graphite and directly as CO2 gas produced equivalent values with an average offset of < 2σ.
Collapse
Affiliation(s)
- Taylor A.B. Broek
- National Ocean Sciences Accelerator Mass Spectrometry Facility, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, USA
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
| | - Kimber C. Moreland
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
| | - Ted J. Ognibene
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
| | - Karis J. McFarlane
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
| | - Thomas A. Brown
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
| |
Collapse
|