Glacial–interglacial variations in CO₂ and methane in polar ice cores have been attributed, in part, to changes in global wetland extent, but the wetland distribution before the Last Glacial Maximum ...(LGM, 21 ka to 18 ka) remains virtually unknown. We present a study of global peatland extent and carbon (C) stocks through the last glacial cycle (130 ka to present) using a newly compiled database of 1,063 detailed stratigraphic records of peat deposits buried by mineral sediments, as well as a global peatland model. Quantitative agreement between modeling and observations shows extensive peat accumulation before the LGM in northern latitudes (>40°N), particularly during warmer periods including the last interglacial (130 ka to 116 ka, MIS 5e) and the interstadial (57 ka to 29 ka, MIS 3). During cooling periods of glacial advance and permafrost formation, the burial of northern peatlands by glaciers and mineral sediments decreased active peatland extent, thickness, and modeled C stocks by 70 to 90% from warmer times. Tropical peatland extent and C stocks show little temporal variation throughout the study period. While the increased burial of northern peats was correlated with cooling periods, the burial of tropical peat was predominately driven by changes in sea level and regional hydrology. Peat burial by mineral sediments represents a mechanism for long-term terrestrial C storage in the Earth system. These results show that northern peatlands accumulate significant C stocks during warmer times, indicating their potential for C sequestration during the warming Anthropocene.
Simple and robust hydrological modelling is critical for peat studies as water content (θ) and water table depth (d
WT
) are key controls on many biogeochemical processes. We show that near-surface θ ...can be a good predictor of θ at any depth and/or d
WT
in peat. This was achieved by further developing the formulae of an existing model and applying it for Mer Bleue bog (Ontario, Canada) and a permafrost peat plateau at Scotty Creek (Northwest Territories, Canada). Simulated θ dynamics at various depths in hummocks and hollows at both sites matched observations with R
2
, Willmott's index of agreement (d), and normalized Nash-Sutcliffe efficiency coefficient (NNSE), reaching 0.97, 0.95, and 0.86, respectively. Simulated bog WT dynamics matched observations with R
2
, d, and NNSE reaching 0.67, 0.87, and 0.72. Our approach circumvents the difficulties of measuring subsurface hydrology and reveals a perspective for large spatial scale estimation of θ and d
WT
in peat.
Rapid, ongoing permafrost thaw of peatlands in the discontinuous permafrost zone is exposing a globally significant store of soil carbon (C) to microbial processes. Mineralization and release of this ...peat C to the atmosphere as greenhouse gases is a potentially important feedback to climate change. Here we investigated the effects of permafrost thaw on peat C at a peatland complex in western Canada. We collected 15 complete peat cores (between 2.7 and 4.5 m deep) along four chronosequences, from elevated permafrost peat plateaus to saturated thermokarst bogs that thawed up to 600 years ago. The peat cores were analysed for peat C storage and peat quality, as indicated by decomposition proxies (FTIR and C/N ratios) and potential decomposability using a 200-day aerobic laboratory incubation. Our results suggest net C loss following thaw, with average total peat C stocks decreasing by ~19.3 ± 7.2 kg C m
over <600 years (~13% loss). Average post-thaw accumulation of new peat at the surface over the same period was ~13.1 ± 2.5 kg C m
. We estimate ~19% (±5.8%) of deep peat (>40 cm below surface) C is lost following thaw (average 26 ± 7.9 kg C m
over <600 years). Our FTIR analysis shows peat below the thaw transition in thermokarst bogs is slightly more decomposed than peat of a similar type and age in permafrost plateaus, but we found no significant changes to the quality or lability of deeper peat across the chronosequences. Our incubation results also showed no increase in C mineralization of deep peat across the chronosequences. While these limited changes in peat quality in deeper peat following permafrost thaw highlight uncertainty in the exact mechanisms and processes for C loss, our analysis of peat C stocks shows large C losses following permafrost thaw in peatlands in western Canada.
Abstract Implementation lessons • Generating demand is an important part of the care delivery value chain. When new health interventions are designed based on recent clinical trial findings, demand ...generation activities prove all the more critical. • Demand generation activities need to iterate on their design, and tailor to the risk profile of target populations. • Leaders need to balance fidelity to a model and local innovation. • Cultural and contextual factors must be considered in designing public health campaigns.
Ombrotrophic bogs can comprise a mosaic of vegetation patches and open-water pools, with hydrological and biogeochemical connections between pools and the surrounding peat and vegetation. To ...establish these connections, we studied the spatial heterogeneity of hydrology and water chemistry in two zones of distinct vegetation assemblages in the subboreal Grande plée Bleue peatland, southern Québec, Canada. We show that seasonal water-level fluctuations are greater and organic C, N and P concentrations are higher in the peat pore water of a forested zone than in a neighboring open-bog zone; that vegetation is responsible for 69% of the spatial variations in hydrology and water chemistry. Vegetation also explains 31% of the temporal variation in water chemistry, with higher increases in C, N and P concentrations over the growing season in the forested peat and pools than in the open-bog zone. We also show that C, N and P concentrations and water-level fluctuations in pools, especially during precipitation events, were lower than in the surrounding peat. Our results suggest the existence of small “watersheds” to the pools with water flowing in during wet and out during dry periods. Localized patterns emerge from the vegetation–hydrology–water chemistry interactions, with pools influencing the persistence of trees in the central part of an ombrotrophic bog.
Small lentic freshwater ecosystems play a disproportionate role in global biogeochemical cycles by processing large amounts of carbon (C), nitrogen (N), and phosphorus (P), but it is unlikely that ...they behave as one homogenous group for the purpose of extrapolation. Here, we synthesize biogeochemical data from >12,000 geographically distinct freshwater systems: lakes, peatland ponds, and thermokarst waterbodies. We show that peatland ponds are biogeochemically distinct from the more widely studied lake systems, while thermokarst waterbodies share characteristics with peatland ponds, lakes, or both. For any given size or depth, peatland ponds tend to have dissolved organic carbon concentrations several‐fold higher and are 100‐fold more acidic than lakes because of the organic matter‐rich settings in which they develop. The biogeochemical distinctiveness of freshwater ecosystems highlights the need to account for the fundamental differences in sources and processing of organic matter to understand and predict their role in global biogeochemical cycles.
Plain Language Summary
Small freshwater bodies are major (but under‐studied) contributors to the global cycling of carbon and nutrients. A large number of these ecosystems develop in climate‐sensitive organic soils. Using a dataset of >12,000 geographically distinct freshwater bodies, we show that many of these ecosystems, namely peatland ponds and some waterbodies developing in permafrost, are structurally and functionally different than their more widely studied lake counterparts. Peatland ponds have distinct combinations of pH, nutrients, and organic carbon concentrations compared to lakes, and they are commonly much more acidic and richer in organic carbon for any given size or depth. Biogeochemically, permafrost waterbodies behave either as peatland ponds, as lakes, or as a combination of both. Our results emphasize the need to consider the distinction between peatland ponds, permafrost waterbodies, and lakes to better understand and forecast the role of small freshwater ecosystems in global biogeochemical cycles.
Key Points
Peatland ponds are distinct from lakes; thermokarst waterbodies behave either like peatland ponds or lakes, or are a combination of both
The distinctiveness of peatland ponds and some thermokarst waterbodies is due to their setting in climate‐sensitive organic soils
The biogeochemistry of a large portion of the world's freshwater ecosystems should not be predicted using current lake‐based models and data
Fossil testate amoeba assemblages have been used to reconstruct peatland palaeohydrology for more than two decades. While transfer function training sets are typically of local-to regional-scale in ...extent, combining those data to cover broad ecohydrological gradients, from the regional-to continental- and hemispheric-scales, is useful to assess if ecological optima of species vary geographically and therefore may have also varied over time. Continental-scale transfer functions can also maximise modern analogue quality without losing reconstructive skill, providing the opportunity to contextualise understanding of purely statistical outputs with greater insight into the biogeography of organisms. Here, we compiled, at moderate taxonomic resolution, a dataset of nearly 2000 modern surface peatland testate amoeba samples from 137 peatlands throughout North America. We developed transfer functions using four model types, tested them statistically and applied them to independent palaeoenvironmental data. By subdividing the dataset into eco-regions, we examined biogeographical patterns of hydrological optima and species distribution across North America. We combined our new dataset with data from Europe to create a combined transfer function. The performance of our North-American transfer function was equivalent to published models and reconstructions were comparable to those developed using regional training sets. The new model can therefore be used as an effective tool to reconstruct peatland palaeohydrology throughout the North American continent. Some eco-regions exhibited lower taxonomic diversity and some key indicator taxa had restricted ranges. However, these patterns occurred against a background of general cosmopolitanism, at the moderate taxonomic resolution used. Likely biogeographical patterns at higher taxonomic resolution therefore do not affect transfer function performance. Output from the combined North American and European model suggested that any geographical limit of scale beyond which further compilation of peatland testate amoeba data would not be valid has not yet been reached, therefore advocating the potential for a Holarctic synthesis of peatland testate amoeba data. Extending data synthesis to the tropics and the Southern Hemisphere would be more challenging due to higher regional endemism in those areas.
•Dataset of ca. 2000 North American peatland testate amoeba surface samples compiled.•Palaeohydrological transfer functions tested statistically, applied to independent palaeo data.•New model an effective tool for palaeohydrological reconstruction across North America.•Biogeographical patterns occur at taxonomic resolution applied; taxa hydrological optima mostly robust across North America.•Combined North American and European dataset illustrates potential for Holarctic synthesis.
Peatland pools are freshwater bodies that are highly dynamic aquatic ecosystems because of their small size and their development in organic‐rich sediments. However, our ability to understand and ...predict their contribution to both local and global biogeochemical cycles under rapidly occurring environmental change is limited because the spatiotemporal drivers of their biogeochemical patterns and processes are poorly understood. We used (1) pool biogeochemical data from 20 peatlands in eastern Canada, the United Kingdom, and southern Patagonia and (2) multi‐year data from an undisturbed peatland of eastern Canada, to determine how climate and terrain features drive the production, delivering and processing of carbon (C), nitrogen (N), and phosphorus (P) in peatland pools. Across sites, climate (24%) and terrain (13%) explained distinct portions of the variation in pool biogeochemistry, with climate driving spatial differences in pool dissolved organic C (DOC) concentration and aromaticity. Within the multi‐year dataset, DOC, carbon dioxide (CO2), total N concentrations, and DOC aromaticity were highest in the shallowest pools and at the end of the growing seasons, and increased gradually from 2016 to 2021 in relation to a combination of increases in summer precipitation, mean air temperature for the previous fall, and number of extreme summer heat days. Given the contrasting effects of terrain and climate, broad‐scale terrain characteristics may offer a baseline for the prediction of small‐scale pool biogeochemistry, while broad‐scale climate gradients and relatively small year‐to‐year variations in local climate induce a noticeable response in pool biogeochemistry. These findings emphasize the reactivity of peatland pools to both local and global environmental change and highlight their potential to act as widely distributed climate sentinels within historically relatively stable peatland ecosystems.
Peatland pool biogeochemistry is mostly driven by internal cycling of elements and exchanges with the surrounding soil. While peatland pool functioning is similar across regions, biogeochemical patterns vary in relation to small‐ and broad‐scale geographic properties.
Peatland open‐water pools can be net carbon (C) emitters within heterogeneous peatland ecosystems that are generally net C sinks. However, the intra‐ and inter‐regional patterns and drivers of CO2 ...and CH4 production, as well as their link with dissolved organic matter (DOM) quality and quantity, remain poorly understood. We analyzed a range of optical characteristics and chemical variables controlling DOM and CO2 and CH4 concentrations in peatland pools across two regions with contrasting geographical properties (i.e., climate, topography, morphometry, and vegetation cover) of eastern Canada and Chilean Patagonia. We found inter‐regional patterns in CO2, CH4 and DOM concentrations and composition that were coherent with patterns in mean annual temperature and precipitation, and vegetation cover. Cross‐regional patterns of CO2 and CH4 were driven by morphometry, vegetation cover, and protein‐like DOM composition, a proxy of high biological activity, whereas temporal variations of CO2 and CH4 concentrations were further influenced by seasonal changes in humic‐like DOM composition, dissolved organic carbon and nutrients (i.e., total phosphorus and total nitrogen) concentrations, as well as pH and oxygen levels. Our results suggest that geophysical constraints associated with local peat and pool characteristics as well as climate patterns are major drivers of DOM and greenhouse gases concentrations and the links between them in broadly distributed peatland pools.
Key Points
Broad‐scale patterns in peatland pools dissolved organic matter (DOM) and CO2 were driven by vegetation cover and pool morphometry
Broad‐scale patterns in CH4 were the most responsive among C‐species to long‐term climate averages across regions
Protein‐like DOM controls within‐pool greenhouse gases (GHG) concentrations across regions, while humic‐like DOM drives within‐site temporal GHG concentrations
Climatic change that occurred during the Holocene is often recognized as the main factor for explaining fire dynamics, while the influence of human societies is less apparent. In eastern North ...America, human influence on fire regime before European settlement has been debated, mainly because of a paucity of sites and paleoecological techniques that can distinguish human influences unequivocally from climate. We applied a multiproxy analysis to a 12 000-year-old paleoecological sequence from a site in the vicinity of known settlement areas that were occupied over more than 7000 years. From this analysis, we were able detect the human influence on the fire regime before and after European colonization. Fire occurrence and fire return intervals (FRI) were based on analysis of sedimentary charcoals at a high temporal and spatial resolution. Fire occurrence was then compared to vegetation that was reconstructed from pollen analysis, from population densities deduced from archeological site dating, from demographic and technological models, and from climate reconstructed using general circulation models and ice-core isotopes. Holocene mean FRI was short (164 ± 134 years) and associated with small charcoal peaks that were likely indicative of surface fires affecting small areas. After 1500 BP, large vegetation changes and human demographic growth that was demonstrated through increased settlement evidence likely caused the observed FRI lengthening (301 ± 201 years), which occurred without significant changes in climate. Permanent settlement by Europeans in the area around 1800 AD was followed by a substantial demographic increase, leading to the establishment of Gatineau, Hull and Ottawa. This trend was accompanied by a shift in the charcoal record toward anthropogenic particles that were reflective of fossil fuel burning and an apparent absence of wood charcoal that would be indicative of complete fire suppression. An anthropogenic fire regime that was characterized by severe and large fires and long fire-return intervals occurred more than 1000 years ago, concomitant with the spread of native agriculture, which intensified with European colonization over the past two centuries.
•The Holocene (past 12 000 years) fire regime was compared with trends in vegetation, human demography and climate.•Holocene Fire Return Intervals were short under slow-moving climate, and vegetation and sparse populations.•Late Holocene fire return intervals lengthening tracked demographic growth and vegetation changes.•Past 200 years are characterized by fire suppression and by spherical charcoals indicative of fossil fuel burning.
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