Peatland Carbon Accumulation Rates Research Articles

To better detect drivers of peatland carbon accumulation rates and patterns

Abstract

Solar and ENSO activity affecting Late Holocene carbon accumulation rates in peatlands from Northeast Asia: Evidence from periodic signal analysis

Peatlands are well developed in large areas of Northeast Asia, where changes in Late Holocene carbon accumulation rate (CAR) have played an important role in influencing the regional carbon cycle. However, the driving mechanisms and periodic signals of these important peatlands have rarely been investigated. The Zhibian peatland is a subalpine peatland, which has a continuous CAR record covering the entire Late Holocene. This peatland is located in Northeast Asia, its carbon dynamics were directly influenced by the East Asian summer monsoon. This peatland recorded direct interactions between the CAR dynamics, solar and El Niño–Southern Oscillation (ENSO) activity. Thus, we selected this peatland as a representative peatland for Northeast Asia. We used spectrum analyses and wavelet analyses to study the periodic signals of CAR dynamics, total solar irradiance (TSI), mean annual precipitation (Pann) and ENSO activity during the Late Holocene. The correlation relationships between the above parameters were investigated to explore the driving mechanisms for CAR dynamics in Northeast Asia peatlands. Our analyses indicate that CAR dynamics show 88a, 210a and 1000a periodicity over the Late Holocene. The potential driving factors, such as the Pann, ENSO and TSI, also indicate similar periodic signals. These relationships further indicate that the Pann, ENSO and TSI played an important role in controlling the CAR variations of Northeast Asia peatlands. Wavelet analyses results suggest that the CAR, Pann and TSI negatively corresponded with the ENSO variations. From the relationship model between these parameters, we concluded that strong solar activity resulted in fewer ENSO events and more precipitation in Northeast Asia. Wet conditions contributed to higher CAR, and vice versa.

A Model Intercomparison Analysis for Controls on C Accumulation in North American Peatlands

AbstractPeatland biogeochemical processes have not been adequately represented in existing earth system models, which might have biased the quantification of Arctic carbon‐climate feedbacks. We revise the Peatland Terrestrial Ecosystem Model (PTEM) by incorporating additional peatland biogeochemical processes. The revised PTEM is evaluated by comparing with Holocene Peatland Model (HPM) in simulating peat physical and biogeochemical dynamics in three North American peatlands: a permafrost‐free fen site, a permafrost‐free bog site and a permafrost bog site. Peatland carbon dynamics are simulated from peat initiation to 1990 and then to year 2300. Model responses to the changes in temperature and precipitation are analyzed to identify key processes affecting peatland carbon accumulation rates. We find that the net C balance is sensitive to water table depth and nutrient availability. Future simulations to year 2300 are conducted with both models under RCP 2.6, RCP 4.5, and RCP 8.5. PTEM predicts these peatlands to be C sources or weaker C sinks when insufficient precipitation suppresses soil moisture and thereby net N mineralization and net primary production, while HPM predicts the same when drier climate leads to increasing water table depth. Our results highlight the importance of water balance and C‐N feedback on peatland C dynamics. With a warmer climate, these peatlands could become a weaker C sink or a source under drier conditions, otherwise a larger C sink if wetter. Improved understanding to peatland processes can help future quantification of peatland C dynamics in the boreal and Arctic regions.

Ecological response of a glacier-fed peatland to late Holocene climate and glacier changes on subantarctic South Georgia

Sedimentary deposits from glacier-fed peatlands provide records of past glacier variability, but the dynamics of these peat-forming ecosystems have rarely been investigated. Through multi-proxy analyses of a 204-cm peat core, we reconstructed the ecological response of a glacier-fed peatland on subantarctic South Georgia to climate and glacier variability over the last 4300 years. A stable peatland with rapid carbon accumulations and dynamic turnovers between brown mosses and monocots persisted between 4300 and 2550 cal yr BP when the up-valley cirque glacier was small under a regional hypsithermal climate. Carbon accumulation rates showed two peak periods driven by climate warming, reaching 140 g C m−2 yr−1 at 4000–3500 cal yr BP and 70 g C m−2 yr−1 at 3200–2700 cal yr BP. Paired δ13C and δ18O data from brown moss cellulose reveal several intervals of glacial meltwater inundation that caused short-term disturbances of the peatland vegetation, indicating that glacial meltwater potentially still affected the peatland ecosystem during this warm period. Moss-dominated vegetation was disrupted and peatland carbon accumulation rates decreased to 15 g C m−2 yr−1 after around 2550 cal yr BP when a cooling-driven glacier advance shifted the erosion and meltwater regime enhancing the glacial sediment influx onto the peatland. Although this enhanced regime of meltwater disturbance has continued since this transition, the brown moss habitat was gradually re-established during the medieval climate warming between 1200 and 600 cal yr BP and then became dominant shortly after that. This re-establishment of brown mosses might have benefited from a period of increased carbon accumulation rates up to 100 g C m−2 yr−1 at 1200–900 cal yr BP that built up the organic matter matrix and stabilized the habitat. We conclude that the ecosystem dynamics of glacier-fed peatlands is strongly shaped by the interplay between regional climate and glacier activity. This study also demonstrates the potential of stable isotope analysis in studying the paleohydrology of non-Sphagnum peatlands.

Latitudinal limits to the predicted increase of the peatland carbon sink with warming

The carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. The rates of both these processes will increase with warming but it remains unclear which will dominate the global peatland response. Here we examine the global relationship between peatland carbon accumulation rates during the last millennium and planetary-scale climate space. A positive relationship is found between carbon accumulation and cumulative photosynthetically active radiation during the growing season for mid- to high-latitude peatlands in both hemispheres. However, this relationship reverses at lower latitudes, suggesting that carbon accumulation is lower under the warmest climate regimes. Projections under Representative Concentration Pathway (RCP)2.6 and RCP8.5 scenarios indicate that the present-day global sink will increase slightly until around ad 2100 but decline thereafter. Peatlands will remain a carbon sink in the future, but their response to warming switches from a negative to a positive climate feedback (decreased carbon sink with warming) at the end of the twenty-first century.

A multi-proxy record of Holocene environmental change, peatland development and carbon accumulation from Staroselsky Moch peatland, Russia

Despite their huge extent, the peatlands of Russia are an under-exploited source of data on palaeoenvironmental change. We investigated the Holocene history of Staroselsky Moch, an ombrotrophic peatland in the Tver Region of European Russia by analysis of testate amoebae, peat physical properties, plant macrofossils and pollen. The peatland developed through a classic hydroseral succession in the early Holocene with a sharp decline in mineral input to 6200 cal. BC followed by an abrupt transition from fen to bog vegetation around 5500 cal. BC. Through the Holocene, the peatland has accumulated carbon at a mean apparent rate of 21.5 g C m−2 yr−1 suggesting that carbon accumulation rates in peatlands of European Russia lie close to the global average, and contrasting with a short sequence of eddy-covariance data which implies a net loss of carbon. The testate amoeba record shows considerable variability which may be driven by climate, but changes are not well replicated in the macrofossil or pollen data. We tentatively infer (1) a phase of early Holocene warming commencing around 7200 cal. BC, (2) dry peatland surface conditions c. 3700–3900 cal. BC, (3) a shift to wetter conditions from c. 3900 cal. BC, and (4) drier conditions from c. 400 cal. BC onwards. More robust and precise hydroclimatic reconstructions for this region will require the development of a regional transfer function and the replication of results between cores and sites.

Hydrology-mediated differential response of carbon accumulation to late Holocene climate change at two peatlands in Southcentral Alaska

Peatlands are among the largest reservoirs of terrestrial carbon in the northern hemisphere. Understanding how this reservoir will respond to climate changes is critical to assessing potential climate feedbacks. Peatland carbon accumulation rates (PCAR) are controlled by the difference between production and decomposition, which is affected by local and climatic factors including hydrology and temperature. To better understand how local controls can influence the response of PCAR to climate change, we investigated modern hydrology, paleohydrology, and PCAR at two nearby Sphagnum-dominated peatlands with different surficial geology (lowland and moraine settings) in Southcentral Alaska. Modern hydrological data indicated a higher rate of subsurface drainage at the lowland site, suggesting greater hydrologic sensitivity to prolonged dry periods of the past. We investigated past responses of these peatlands to well-documented climatic changes, like the Medieval Climate Anomaly (MCA) at ∼1000–600 cal yr BP and Little Ice Age (LIA) at ∼600–200 cal yr BP, using water-table depth (WTD) inferred from testate amoebae and PCAR calculated from loss-on-ignition and 14C-dating analyses. Our results indicate that WTD and PCAR remained relatively stable at the moraine site throughout the last 1100 years, including the MCA and LIA. However, the lowland site experienced relatively stable WTD and higher PCAR during the MCA, but highly variable WTD and lower PCAR during the LIA. These differences suggest that hydrology and likely decomposition were the primary control on PCAR at these peatlands. Our results highlight the importance of local-scale controls, like surficial geology, in mediating the response of peatland hydrology and carbon accumulation to climate change.

A 1.16 Ma record of carbon accumulation in western European peatland during the Oligocene from the Ballymoney lignite, Northern Ireland

The Oligocene Ballymoney lignite in Northern Ireland is one of the thickest lignites in Europe and provides the potential for comparing Holocene and pre-Holocene peatland evolution and its response to long-term climate change on time scales much greater than 10 ka. Samples were collected from 50 m of lignite and analysed for δ 13 C. Spectral analysis of the δ 13 C record reveals that the record contains significant frequencies at 0.21 m −1 and 1.12 m −1 . These cycles are interpreted as the c . 100 ka eccentricity and 20 ka precession cycles, respectively. These cycles were then tuned and the duration was determined as 1.16 Ma with a carbon accumulation rate of 27 g C m −2 a −1 . If long-term changes in lignite δ 13 C are related to changes in the δ 13 C of the exogenic carbon reservoir, and if the lignite Chattian age is accepted, then the lignite probably formed between 24.6 and 25.8 Ma. Comparison of the estimated carbon accumulation rate with other Cenozoic peatland carbon accumulation rates indicates that this rate appears to be insensitive to changes in the concentration of atmospheric CO 2 .

The Influence of Permafrost and Fire upon Carbon Accumulation in High Boreal Peatlands, Northwest Territories, Canada

Carbon and peat accumulation rates over the past 1200 yr were measured in relation to permafrost aggradation, maturity, ground fires, and degradation in a peatland with discontinuous permafrost near Fort Simpson, N.W.T., Canada. The White River volcanic ash layer, deposited 1200 yr ago, was used as a chronostratigraphic marker to compare peat and carbon accumulation among peat cores collected along transects over a consistent period of time. The aggradation of permafrost results in a change from unfrozen bog to forested peat plateau, and approximate decreases of 50 and 65% in carbon and vertical peat accumulation rates, respectively. Carbon and peat accumulation continue to decrease significantly with both increasing permafrost maturity and the number of ground fires. The transition from peat plateau to collapse bog through internal permafrost degradation results in up to a 72 and 200% increase in carbon and vertical peat accumulation rates, respectively. Permafrost degradation at the margins of a peat plateau can result in the formation of collapse fens, in which vertical peat accumulation increases significantly yet the carbon accumulation rates remain similar to the peat plateau. A warming climate may result in a shift towards higher carbon accumulation rates in peatlands associated with bog vegetation following peat plateau collapse, yet warmer peat temperatures, greater soil aeration, greater rates of peat decomposition, and an increase in burning may provide limits to the increase.

The Influence of Permafrost and Fire upon Carbon Accumulation in High Boreal Peatlands, Northwest Territories, Canada

Carbon and peat accumulation rates over the past 1200 yr were measured in relation to permafrost aggradation, maturity, ground fires, and degradation in a peatland with discontinuous permafrost near Fort Simpson, N.W.T., Canada. The White River volcanic ash layer, deposited 1200 yr ago, was used as a chronostratigraphic marker to compare peat and carbon accumulation among peat cores collected along transects over a consistent period of time. The aggradation of permafrost results in a change from unfrozen bog to forested peat plateau, and approximate decreases of 50 and 65% in carbon and vertical peat accumulation rates, respectively. Carbon and peat accumulation continue to decrease significantly with both increasing permafrost maturity and the number of ground fires. The transition from peat plateau to collapse bog through internal permafrost degradation results in up to a 72 and 200% increase in carbon and vertical peat accumulation rates, respectively. Permafrost degradation at the margins of a peat plateau can result in the formation of collapse fens, in which vertical peat accumulation increases significantly yet the carbon accumulation rates remain similar to the peat plateau. A warming climate may result in a shift towards higher carbon accumulation rates in peatlands associated with bog vegetation following peat plateau collapse, yet warmer peat temperatures, greater soil aeration, greater rates of peat decomposition, and an increase in burning may provide limits to the increase.