Shifting environmental controls on CH4 fluxes in a sub-boreal peatland

We monitored CO2 and CH4 fluxes using eddy covariance from 19 May to 27 September 2011 in a poor fen located in northern Michigan. The objectives of this paper are to: (1) quantify the flux of CH4 from a sub-boreal peatland, and (2) determine which abiotic and biotic factors were the most correlated to the flux of CH4 over the measurement period. Net daily CH4 fluxes increased from 70 mg CH4 m−2 d−1 to 220 mg CH4 m−2 d−1 from mid May to mid July. After July, CH4 losses steadily declined to approximately 50 mg CH4 m−2 d−1 in late September. During the study period, the peatland lost 17.4 g CH4 m−2. Both abiotic and biotic variables were correlated with CH4 fluxes. When the different variables were analyzed together, the preferred model included mean daily soil temperature at 20 cm, daily net ecosystem exchange (NEE) and the interaction between mean daily soil temperature at 20 cm and NEE (R2 = 0.47, p value \u3c 0.001). The interaction was important because the relationship between daily NEE and mean daily soil temperature with CH4 flux changed when NEE was negative (CO2 uptake from the atmosphere) or positive (CO2 losses to the atmosphere). On days when daily NEE was negative, 25% of the CH4 flux could be explained by correlations with NEE, however on days when daily NEE was positive, there was no correlation between daily NEE and the CH4 flux. In contrast, daily mean soil temperature at 20 cm was poorly correlated to changes in CH4 when NEE was negative (17%), but the correlation increased to 34% when NEE was positive. The interaction between daily NEE and mean daily soil temperature at 20 cm indicates shifting environmental controls on the CH4 flux throughout the growing season

Variation in carbon and nitrogen concentrations among peatland categories at the global scale

Publisher Copyright: © 2022 This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.Peatlands account for 15 to 30% of the world's soil carbon (C) stock and are important controls over global nitrogen (N) cycles. However, C and N concentrations are known to vary among peatlands contributing to the uncertainty of global C inventories, but there are few global studies that relate peatland classification to peat chemistry. We analyzed 436 peat cores sampled in 24 countries across six continents and measured C, N, and organic matter (OM) content at three depths down to 70 cm. Sites were distinguished between northern (387) and tropical (49) peatlands and assigned to one of six distinct broadly recognized peatland categories that vary primarily along a pH gradient. Peat C and N concentrations, OM content, and C:N ratios differed significantly among peatland categories, but few differences in chemistry with depth were found within each category. Across all peatlands C and N concentrations in the 10-20 cm layer, were 440 ± 85.1 g kg-1 and 13.9 ± 7.4 g kg-1, with an average C:N ratio of 30.1 ± 20.8. Among peatland categories, median C concentrations were highest in bogs, poor fens and tropical swamps (446-532 g kg-1) and lowest in intermediate and extremely rich fens (375-414 g kg-1). The C:OM ratio in peat was similar across most peatland categories, except in deeper samples from ombrotrophic tropical peat swamps that were higher than other peatlands categories. Peat N concentrations and C:N ratios varied approximately two-fold among peatland categories and N concentrations tended to be higher (and C:N lower) in intermediate fens compared with other peatland types. This study reports on a unique data set and demonstrates that differences in peat C and OM concentrations among broadly classified peatland categories are predictable, which can aid future studies that use land cover assessments to refine global peatland C and N stocks.Peer reviewe

Carbon storage and long-term rate of accumulation in high-altitude Andean peatlands of Bolivia

(1) The high-altitude (4,500+ m) Andean mountain range of north-western Bolivia contains many peatlands. Despite heavy grazing pressure and potential damage from climate change, little is known about these peatlands. Our objective was to quantify carbon pools, basal ages and long-term peat accumulation rates in peatlands in two areas of the arid puna ecoregion of Bolivia: near the village of Manasaya in the Sajama National Park (Cordillera Occidentale), and in the Tuni Condoriri National Park (Cordillera Real). (2) We cored to 5 m depth in the Manasaya peatland, whose age at 5 m was ca. 3,675 yr. BP with a LARCA of 47 g m-2 yr-1. However, probing indicated that the maximum depth was 7–10 m with a total estimated (by extrapolation) carbon stock of 1,040 Mg ha-1. The Tuni peat body was 5.5 m thick and initiated ca. 2,560 cal. yr. BP. The peatland carbon stock was 572 Mg ha-1 with a long-term rate of carbon accumulation (LARCA) of 37 g m-2 yr-1. (3) Despite the dry environment of the Bolivian puna, the region contains numerous peatlands with high carbon stocks and rapid carbon accumulation rates. These peatlands are heavily used for llama and alpaca grazing

Shifting environmental controls on CH₄ fluxes in a sub-boreal peatland

We monitored CO₂ and CH₄ fluxes using eddy covariance from 19 May to 27 September 2011 in a poor fen located in northern Michigan. The objectives of this paper are to: (1) quantify the flux of CH₄ from a sub-boreal peatland, and (2) determine which abiotic and biotic factors were the most correlated to the flux of CH₄ over the measurement period. Net daily CH₄ fluxes increased from 70 mg CH₄ m⁻² d⁻¹ to 220 mg CH₄ m⁻² d⁻¹ from mid May to mid July. After July, CH₄ losses steadily declined to approximately 50 mg CH₄ m⁻² d⁻¹ in late September. During the study period, the peatland lost 17.4 g CH₄ m⁻². Both abiotic and biotic variables were correlated with CH₄ fluxes. When the different variables were analyzed together, the preferred model included mean daily soil temperature at 20 cm, daily net ecosystem exchange (NEE) and the interaction between mean daily soil temperature at 20 cm and NEE (<i>R</i>² = 0.47, <i>p</i> value < 0.001). The interaction was important because the relationship between daily NEE and mean daily soil temperature with CH₄ flux changed when NEE was negative (CO₂ uptake from the atmosphere) or positive (CO₂ losses to the atmosphere). On days when daily NEE was negative, 25% of the CH₄ flux could be explained by correlations with NEE, however on days when daily NEE was positive, there was no correlation between daily NEE and the CH₄ flux. In contrast, daily mean soil temperature at 20 cm was poorly correlated to changes in CH₄ when NEE was negative (17%), but the correlation increased to 34% when NEE was positive. The interaction between daily NEE and mean daily soil temperature at 20 cm indicates shifting environmental controls on the CH₄ flux throughout the growing season

The effect of water table levels and short-term ditch restoration on mountain peatland carbon cycling in the Cordillera Blanca, Peru

Many tropical mountain peatlands in the Andes are formed by cushion plants. These unique cushion plant peatlands are intensively utilized for grazing and are also influenced by climate change, both of which alter hydrologic conditions. Little is known about the natural hydroperiods and greenhouse gas fluxes of these peatlands or the consequences of hydrologic alteration for these fluxes. Therefore, our objectives were to assess how carbon dioxide (CO2) and methane (CH4) fluxes varied across a hydrological gradient caused by ditching and evaluate how short-term carbon cycling responds after rewetting from ditch blocking in a tropical mountain peatland. The study was carried out in Huascarán National Park, Peru using static chamber methods. Comparing reference to highly drained conditions, mid-day net ecosystem exchange (NEE) was higher (1.07 ± 0.06 vs. 0.76 ± 0.11 g CO2 m−2 h−1), and the light compensation point for CO2 uptake was lower. Gas fluxes were relatively stable in the rewetted and reference treatments, with small positive responses of NEE to rising water tables. CH4 emissions averaged 2.76 ± 1.06 mg CH4 m−2 day−1, with negative fluxes at water tables \u3e10 cm below the soil surface, and positive fluxes at higher water levels. Our results indicate that undrained peatlands appear to be carbon sinks, highly drained peatlands were likely carbon sources, and rewetting of moderately drained peatlands increased NEE and the ability to store carbon to undrained reference conditions. Ditching of peatlands will likely increase their susceptibility to negative climate change impacts, and hydrologic restoration could moderate these impacts

Mapping peatlands in boreal and tropical ecoregions

© 2018 Elsevier Inc. All rights reserved. Peatlands are a class of wetlands that are defined as having saturated soils, anaerobic conditions, and large deposits of partially decomposed organic plant material (peat). Occurring in ecozones from the tropics to the arctic, peatlands are estimated to cover just under 4.5 million km2, roughly 3-5% of the Earth’s land surface (Maltby and Proctor, 1996). Although they cover a small amount of land globally, peatlands are estimated to store ~ 30% of the Earth’s soil carbon (C) (Gorham, 1991, Botch et al., 1995, Lappalainen, 1996, Zoltai and Martikainen, 1996, Clymo et al., 1998, Moore et al., 1998, Yu et al., 2010, Page et al., 2011), making them crucial to the global C cycle. Therefore, it is vital to obtain improved estimates of peatland distribution across the globe, as well as to monitor disturbances due to climate change or human activity. Efforts to map global wetlands from MODIS or other coarse resolution optical sources are ineffective in detecting and mapping peatlands. With coarse (250 m-1 km resolution) data, peatlands typically are grouped with a more general wetland class. Since peatlands are often small and interspersed with upland and other wetland types, it is essential to use finer resolution data (~ 30 m or better) to distinguish peatland types as described further in this article. Advanced remote sensing methods that use a combination of data sources and imagery from multiple seasons are necessary to capture the hydrologic and phenological variation that characterizes the diversity of peatlands that exist on the landscape. This article reviews the need for peatland mapping in boreal and tropical systems and summarizes applications of remote sensing for this purpose. Before mapping any landscape, it is necessary to have an understanding of the systems to be mapped. Knowledge of the characteristics of the ecosystems allows for informed decision making when choosing the combination of remote sensing data sources to best distinguish and classify the region of interest. In this article, we begin with background information on peatlands, followed by a review of mapping approaches from the literature and lastly, provide three examples of using multisensor, multitemporal optical, and radar data for mapping peatlands. The multisensor and multidate approaches are shown through examples to be more effective than using a single date of imagery and/or a single sensor

6.04 - Mapping peatlands in boreal and tropical ecoregions

Peatlands are a class of wetlands that are defined as having saturated soils, anaerobic conditions, and large deposits of partially decomposed organic plant material (peat). Occurring in ecozones from the tropics to the arctic, peatlands are estimated to cover just under 4.5 million km2, roughly 3–5% of the Earth’s land surface (Maltby and Proctor, 1996). Although they cover a small amount of land globally, peatlands are estimated to store ∼ 30% of the Earth’s soil carbon (C) (Gorham, 1991, Botch et al., 1995, Lappalainen, 1996, Zoltai and Martikainen, 1996, Clymo et al., 1998, Moore et al., 1998, Yu et al., 2010, Page et al., 2011), making them crucial to the global C cycle. Therefore, it is vital to obtain improved estimates of peatland distribution across the globe, as well as to monitor disturbances due to climate change or human activity. Efforts to map global wetlands from MODIS or other coarse resolution optical sources are ineffective in detecting and mapping peatlands. With coarse (250 m–1 km resolution) data, peatlands typically are grouped with a more general wetland class. Since peatlands are often small and interspersed with upland and other wetland types, it is essential to use finer resolution data (∼ 30 m or better) to distinguish peatland types as described further in this article. Advanced remote sensing methods that use a combination of data sources and imagery from multiple seasons are necessary to capture the hydrologic and phenological variation that characterizes the diversity of peatlands that exist on the landscape. This article reviews the need for peatland mapping in boreal and tropical systems and summarizes applications of remote sensing for this purpose. Before mapping any landscape, it is necessary to have an understanding of the systems to be mapped. Knowledge of the characteristics of the ecosystems allows for informed decision making when choosing the combination of remote sensing data sources to best distinguish and classify the region of interest. In this article, we begin with background information on peatlands, followed by a review of mapping approaches from the literature and lastly, provide three examples of using multisensor, multitemporal optical, and radar data for mapping peatlands. The multisensor and multidate approaches are shown through examples to be more effective than using a single date of imagery and/or a single sensor

A case study in large-scale wetland restoration at Seney National Wildlife Refuge, Upper Michigan, U.S.A

A large wetland drainage project was initiated in 1912 near the town of Seney, Michigan, U.S.A. This project included the construction of a series of ditches through a large peatland to drain the land for agricultural use. The largest of these ditches was the 35 km long Walsh Ditch. Much of the drained wetland affected by the Walsh Ditch is now managed by the U.S. Fish and Wildlife Service as part of Seney National Wildlife Refuge. Between 2002-2003, nine large earthen ditch plugs were installed along a 4.5 km section of the ditch in an attempt to restore the hydrological and ecological integrity of the approximately 1400 ha of wetlands and streams. This study explores the effects that the ditch plugs had on the hydrology and vegetation structure of the adjacent landscape 8y later. Plot level measurements (707 m2 plots) of hydrology and vegetation, combined with an analysis of land cover change using aerial imagery, indicated that the ditch plugs had been successful in altering the hydrology and vegetation over portions of the area. Mortality of upland tree species more typical of xeric conditions and colonization by typical wetland species indicated that these sites should continue to develop into wetland ecosystems. Land cover change analysis showed an increase in wetland area of 152 ha. The areas of change were concentrated near the plugged ditch and near a large anthropogenic pool. © 2013, American Midland Naturalist

Peat porewater dissolved organic carbon concentration and lability increase with warming: a field temperature manipulation experiment in a poor-fen

Studies conducted across northern Europe and North America have shown increases in dissolved organic carbon (DOC) in aquatic systems in recent decades. While there is little consensus as to the exact mechanisms for the increases in DOC, hypotheses converge on such climate change factors as warming, increased precipitation variability, and changes in atmospheric deposition. In this study, we tested the effects of warming on peat porewater composition by actively warming a peatland with infrared lamps mounted 1.24 m above the peat surface for 3 years. Mean growing season peat temperatures in the warmed plots (n = 5) were 1.9 ± 0.4 °C warmer than the control plots at 5 cm depth (t statistic = 5.03, p = 0.007). Mean porewater DOC concentrations measured throughout the growing season were 15 % higher in the warmed plots (73.4 ± 3.2 mg L−1) than in the control plots (63.7 ± 2.1 mg L−1) at 25 cm (t = 4.69, p \u3c 0.001). Furthermore, DOC from the warmed plots decayed nearly twice as fast as control plot DOC in laboratory incubations, and exhibited lower aromaticity than control plot porewater (reduction in SUVA254 in heated plots compared with control plots). Dissolved organic nitrogen (DON) concentrations tracked DOC patterns as expected, but the amount of dissolved N per unit C decreased with warming. Previous work has shown that warming increased net primary production at this site, and together with measured increases in the activities of chitinases and glucosidases we suggest that the increased DOC concentrations observed with warming were derived in part from microbial-plant interactions in the rhizosphere. We also detected more nitrogen containing compounds with higher double bond equivalents (DBE) unique to the warmed plots, within the pool of biomolecules able to deprotonate (16 % of all compounds identified using ultrahigh resolution ion electrospray mass spectrometry); we suggest these compounds could be the products of increased plant, microbial, and enzyme activity occurring with warming. With continued warming in peatlands, an increase in relatively labile DOC concentrations could contribute to dissolved exports of DOC in runoff, and would likely contribute to the pool of efficient electron donors (and acceptors) in the production of CO2 and CH4 in terrestrial and aquatic environments