Methane Emissions from a Grassland-Wetland Complex in the Southern Peruvian Andes

Abstract

Wet organic-rich mineral and peat soils in the tropical Andes represent a potentially significant, but little studied, source of methane to the atmosphere. Here we report the results of field and laboratory measurements of soil–atmosphere methane exchange and associated environmental variables from freely draining upland and inundation prone wetland soils in a humid puna ecosystem in the Southeastern Andes of Peru. Between seasons and across the landscape soil–atmosphere exchange varied between uptake and emission. Notable hotspots of methane emission, peaking during the wet season, were observed from both upland and wetland soils with particularly strong emissions from moss-accumulating topographic lows. This variability was best explained by the influence of oxygen concentration on methane production in superficial soil horizons.

Formation and Fluxes of Soil Trace Gases

“…Vargas et al (2018) and Roby et al (2019) both extend this concept to the natural patchiness of the semi-arid landscape, which supports patches of relatively little (bare soil) or dense (near grass) root density [1,3]. Suppressing soil processes may directly or indirectly affect the process of interest, as noted by Miller et al (2019) for inhibitors of methanogenesis [8], consistent with observations by Jones et al (2018) of co-varying gross trace gas fluxes (e.g., CH 4 consumption and production) [4], which must be considered when applying this method.…”

“…Jones et al (2018) highlight the spatial variability in soil CH 4 emissions and illustrate the power of high coverage of measurements (here, spatially) and the potential to infer temporal dynamics from spatial data (space-for-time substitution) [4]. The study was conducted in a wetland in the Peruvian Andes with soils ranging from freely draining upland to inundated wetland.…”

“…They isotopically enriched soil cores with 13 CH 4 in anaerobic laboratory incubations to quantify anaerobic methane oxidation from measurements of 13 CO 2 production and quantify this cryptic carbon cycling process alongside CO 2 production from soil organic matter respiration and CH 4 production by methanogenesis [8]. Jones et al (2018) constrained aerobic methane oxidation and partitioned net CH 4 fluxes through 13 CH 4 isotope enrichment in aerobic laboratory incubations [4]. In both cases, isotope mixing models are used to interpret measurements.…”

“…In both cases, isotope mixing models are used to interpret measurements. Stable isotope approaches often require assumption and/or measurement of various factors (e.g., fractionation factors, substrate isotope ratio), which may be more feasible to measure in the laboratory where isotope labeling typically occurs [4,8], but are likely impractical to measure at the same temporal resolution as in-situ natural abundance isotope studies (e.g., [2]). Taken together, these isotope approaches reveal otherwise-hidden contributions of various biogeochemical processes to the overall soil flux and advance understanding of soil gas formation and fluxes.…”

Assessing Methane Emissions From Tropical Wetlands: Uncertainties From Natural Variability and Drivers at the Global Scale

“…Even though, temperature is generally not a limiting factor of ecological processes over the tropics, inland shallow‐water wetlands may occur at different altitudes and thus temperature may become a controlling factor of methanogenesis (Jones et al., 2018; Otter & Scholes, 2000). For example, peatlands in the Peruvian Andes occur at 4,000 masl and a mean annual temperature of 11°C (Jones et al., 2018), which contrasts with the average temperature over the tropics of 24 to 27°C. This is a relevant difference since temperature has been positively related to methanogenesis (Masamba et al., 2015).…”