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Planning of peatland management under contrasting economic and environmental targets requires application of ecosystem models that can account for complex interactions and feedbacks between biogeochemical, hydrological and forest-related processes. Here we present a further developed version of Peatland simulator SUSI (Lauren et al. 2021) that calculates formation, transport and biodegradation of dissolved organic carbon (DOC). We tested the new model structure against laboratory incubation results containing peat columns from Finland, Estonia, Sweden and Ireland. The drainage strategy (distance between ditches and ditch depth) is considerably different in all these countries: In Finland the ditch network forms a dense fish-bone pattern with an average ditch distance of 40 m, in Estonia the ditch distance is longer but the ditches are arranged to square blocks, in Sweden the network is often irregular, and in Ireland shallow ditches are spaced densely. Then we applied SUSI and assessed the impacts of changing ditch depth and distance on stand and soil C balance, lateral C flux and forest growth. We found that DOC export originated mainly from the close proximity of the ditches because the rate of decomposition is highest and the transport time is shortest. Further from the ditches, water residence time can be several months or even longer enabling biodegradation of a large part of DOC during the transport. The results revealed that even small slopes had a remarkable impact on WT, residence time and DOC export; and that the effect of the slope could exceed that of drainage dimensions per se. Overall results indicated that drainage strategy in Finland was particularly sensitive to changes in ditch depth and distance. In contrast, changes in irregular, sparse ditch network in Sweden caused only minor effects on forest growth, C balance and lateral C fluxes.

Lateral carbon (C) flux results from complex interplay of formation, transport and biodegradation of dissolved organic carbon (DOC), and is an important but rather scarcely studied component of the C balance in peatlands. Temperature and water table (WT) are the primary factors regulating peat CO2 emissions and the release of DOC. DOC dynamics in soil is complicated because the DOC storage is continuously increased by the decomposition of solid organic matter, but simultaneously decreased by biodegradation. Any upscaling of lateral C fluxes requires understanding these coinciding processes. We studied the effect of temperature and WT on CO2 emission and DOC concentration in pore water while incubating peat columns (diameter 0.2 m height 0.5 m) in laboratory conditions for eight months. Peat columns were extracted from drained forested peatlands in Finland, Estonia, Sweden and Ireland. WT was set to -0.2 m and -0.4 m distance from the column upper end. During the incubation, the temperature ranged between 18 and 34 ⁰C. DOC samples were extracted in monthly intervals from the columns using Rhizon soil water samplers. At the same time CO2 emission was measured from the headspace of the column. DOC biodegradation to CO2 and its temperature sensitivity was studied by incubating soil water samples in controlled conditions. The quality (aromaticity) of DOC was investigated with a UV-VIS spectrophotometer. The effect of temperature on DOC concentration was not straightforward unlike in the case of CO2 emission. DOC concentration increased steepest when the temperature exceeded 25 ⁰C, whereas with lower temperatures DOC was unchanged or slightly decreased. This can be due to different temperature sensitivities of DOC release and its biodegradation. Low WT resulted in high CO2 emissions and DOC concentrations. These results are important in developing ecosystem models accounting for lateral C fluxes and the effects of forest management, drainage and climate change in managed peatlands.

Peatlands are globally significant C storage because waterlogged conditions slow down organic matter (OM) decomposition. Changes in the water table (WT) because of global warming or drainage, consecutive vegetation succession, and enhanced root exudation causing priming may transform peatlands from C sinks to sources. We studied how glucose addition, WT, and forest harvesting affect the chemical composition of peat and decomposition rate by incubating peat columns collected from drained clear-cut (CC) and forested (FD) peatlands. Columns were divided into high or low WT, and half were labeled with C-13 to study the priming effect on peat decomposition and peat chemical quality. We measured CO2 fluxes, peat OM, and water quality. There was no detectable priming effect after glucose addition. Lowering of the WT led to increased CO2 efflux, which during the measurements averaged between 39 and 291 mu g m(-2) s(-1). Low WT also decreased the proportion of water-soluble OM in CC areas but not in FD areas. The proportion of recalcitrant OM in surface peat was higher in forest than in clear cut. Forest management also affected the quality of dissolved OM in soil water, with CC showing higher concentrations of recalcitrant compounds. Decomposition and OM quality were governed by forest management practices and WT manipulation. In the future, the C sink capacity of forested peatlands will be regulated by changes in WT level, forest management, and quality of OM.

Economic, climate and water protection targets need to be balanced in acceptable peatland management. This is not a simple task as the targets are not necessarily synergetic, and hydrology, carbon (C) and nutrient cycles are tightly connected forming a complex network of feedbacks and interactions. Thus, planning of peatland management calls for holistic simulation models. Recently, we have developed Peatland simulator SUSI (Lauren et al. 2021) as a platform for a combined modelling of hydrology, biogeochemistry, and tree stand growth under different water table (WT) management (drainage) regimes. SUSI simulates WT, organic matter decomposition, nutrient release and tree growth between two parallel ditch drains in daily time step, and allows us to change meteorological input data, stand and peat characteristics, ditch depth and the distance between the ditches. Here, we extended SUSI to account for forest thinning and ash fertilization as management practises. To allow simulation of logging residue decomposition, we substituted the earlier empirical decomposition model with a simple compartmental process model describing separately the decomposition of tree stand litter and peat. Effect of ash fertilization was modelled so that the leaf biomass was adjusted according to the prevailing nutrient supply and the stand nutrient demand. Improving nutrient supply allows a higher leaf mass and elevated light and water use efficiency. The new modifications allow unraveling the feedback loop extending from improved nutrient availability → increased leaf mass, light and water use efficiency → lowering WT → increased nutrient release from peat → improved stand growth → increased litterfall → changed C and nutrient balance → further lowering WT. The new model also includes lateral C fluxes. Release of dissolved organic carbon (DOC) in labile and recalcitrant form was calculated using computed WT, soil temperature, peat bulk density, and literature-derived release rates. The DOC release and the biodegradation of DOC to CO2 were connected as a source term to a 2-dimensional advection equation describing water movement and the equation was solved using a finite volume method. The model conceptualization, structure and the significance of the feedback mechanisms are analyzed and discussed. The new model enables, for the first time, internally coherent balancing among the economic, climate and water protection targets in management of boreal and tropical peatlands.

Peatlands contain a significant fraction of global soil carbon, but how these reservoirs will respond to the changing climate is still relatively unknown. A global picture of the variations in peat organic matter chemistry will aid our ability to gauge peatland soil response to climate. The goal of this research is to test the hypotheses that 1) peat carbohydrate content, an indicator of soil organic matter reactivity, will increase with latitude and decrease with mean annual temperatures (MAT), 2) while peat aromatic content, an indicator of recalcitrance, will vary inversely, and 3) elevation will have a similar effect to latitude. We used Fourier Transform Infrared Spectroscopy (FTIR) to examine variations in the organic matter functional groups of 1034 peat samples collected from 10-20, 30-40, and 60-70 cm depths at 165 individual sites across a latitudinal gradient of 79˚N to 65˚S and from elevations of 0 to 4773 meters. Carbohydrate contents of high latitude peat were significantly greater than peat originating near the equator, while aromatic content showed the opposite trend. For peat from similar latitudes but different elevations, the carbohydrate content was greater and aromatic content was lower at higher elevations. Higher carbohydrate content at higher latitudes indicates a greater potential for mineralization, whereas the chemical composition of low latitude peat is consistent with their apparent relative stability in the face of warmer temperatures. The combination of low carbohydrates and high aromatics at warmer locations near the equator suggests the mineralization of high latitude peat until reaching recalcitrance under a new temperature regime.

Extensive draining at tropical ombrotrophic peatlands in Southeast Asia has made these landscapes a global ‘hot spots’ for greenhouse gas emissions. Management practices and fires have changed substrate status, which affects microbial processes. Here, we present data on how change in management practices affect carbon (C) mineralization processes at these soils. We compared the C mineralization potentials of undrained swamp forest peat to those of abandoned peat (deforested, drained and burned peatlands in degraded condition) at various depths, with and without additional substrates (glucose, glutamate and nitrate), under oxic and anoxic conditions through ex situ experiments. Carbon mineralization (CO2 and CH4 production) rates were higher in the forest peat, with higher litter deposition and C availability. Production rates decreased with peat depth coinciding with decreasing availability of labile C. Consequently, the increase in production rates after labile substrate addition was relatively modest in forest peat as compared to the abandoned site and from the top layers as compared to deeper layers. Methanogenesis had little importance in total C loss. Adding labile C and nitrogen (N) enhanced heterotrophic CO2 production more than only addition of N. Surprisingly, oxygen availability did not limit CO2 production rates, but anoxic respiration also yielded substantial rates, especially at the forest peat. Flooding of these sites will therefore reduce, but not completely cease, peat C-loss. Reintroduced vegetation and fertilization in abandoned peatlands can enrich the peat with labile C and N compounds and thus lead to increased microbiological activity.

Tropical peat carbon compound composition (CCC) is a highly understudied subject. Advanced understanding of peat CCC and carbon dynamics in differing conditions is desperately needed due to large-scale utilization of these peatlands. We studied the CCC—i.e. the hemicellulosic carbohydrate and uronic acid composition and concentrations of extractives, cellulose, acid-soluble lignin and acid-insoluble lignin—in association with peat profile depth and physical structure of peat, under representative, common land uses. Samples were gathered from an undrained forest and three sites altered 20–30 years prior to the study, which in aggregate form a continuum of increasing land-use intensity (drainage-affected forest; drained and deforested degraded open site; drained and deforested site under cultivation) in Central Kalimantan, Indonesia. Peat samples were taken from depths between 10 and 115 cm that covered mostly oxic, frequently waterlogged and permanently waterlogged, anoxic conditions. Our results demonstrated greater modification of peat properties when both vegetation and hydrological conditions were altered. The differences between sites were mainly present in the topmost peat and decreased with depth. Peat located at the surface contained more labile compounds (hemicelluloses, extractives, uronic acids, cellulose) on forest sites than at the most intensively altered open sites, where peat was enriched with recalcitrant acid insoluble lignin. The effect of drainage was evident in the drained forest site, where at the approximate median water table depth peat more closely resembled open sites in terms of the peat properties. The increased recalcitrance of peat in reclaimed areas has been a result of enhanced decomposition, reduced litter input rates and, at open sites also by repeated fires.

Swamp forests on deep tropical peatlands have undergone extensive deforestation and draining for agriculture and plantations, consequently becoming globally significant carbon (C) sources. To study the effects of land-use change on peat as a biological environment, which directly affects decomposition dynamics and greenhouse gas emissions, we sampled peat from four common land-use types representing different management intensities in Central Kalimantan, Indonesia. The near-pristine swamp forest was used to describe unmanaged conditions, and the three other sites in order of increasing management intensity were reforested; degraded; and agricultural. We examined peat substrate quality (total C & nitrogen (N), dissolved organic C (DOC) and N (DON)), organic matter quality characterized by infrared spectroscopy, and microbial biomass and extracellular enzyme activity, to describe both biotic and abiotic conditions in peat. We found that the peat at altered sites was poorer in quality, i.e. decomposability, as demonstrated by the higher intensity of aromatic and aliphatic compounds, and lower intensity of polysaccharides, and concentration of total N, DOC, and DON compared to the peat in the swamp forest. The observed differences in peat properties can be linked to changes in litter input and decomposition conditions altered after deforestation and draining, as well as increased leaching and fires. The quality of the peat substrate was directly related to its biotic properties, with altered sites generally having lower microbial biomass and enzyme activity. However, irrespective of management intensity or substrate quality, enzyme activity was limited primarily to the first 0–3 cm of the peat profile. Some differences between wet and dry seasons were observed in enzyme activity especially in swamp forest, where the most measured enzyme activities were higher in dry season. Reforestation 6 years before our measurements had not yet restored enzyme activity in the peat to the level of the swamp forest, although the topmost peat characteristics in the reforested site already resembled those in the swamp forest. This is likely contributed by the limited capacity of the young tree stand to produce litter to support peat formation and restore the quality and structure of the peat, and the chemical weed control performed at the site. Therefore, we conclude that intensive land management, including deforestation and draining, leads to the surface peat becoming poorer biological environment, and it may take long time to restore the peat properties.

The peatlands in Southeast Asia have been impacted and turned to vast carbon dioxide sources (CO2) by land management often involving drainage and deforestation. The amount of released CO2 in decomposition is related to management intensity likely resulting from altered conditions for decomposition. However, the link between decomposition processes and land-use change are poorly understood. To provide insight to the effects of land-use change intensities to decomposition processes in Central Kalimantan, Indonesia, we examined physical (dry bulk density, total pore space, particle size) and chemical properties (pH, loss-on-ignition; total concentrations of N, P, K, C, Ca, Mg, Mn, Zn, Al, Fe, S, Si, DOC and DON; organic matter quality characterized by infrared spectroscopy and on compound level), which together were used to determine the decomposition stage and decomposability (i.e., substrate quality) of peat. The peat biological properties (microbial biomass and enzyme activity) were used to provide insight to the decomposition activity at various land-use types and as a response to known peat properties. The study sites were: near-pristine swamp (i) and drained (ii) forest, deforested and drained degraded (iii), agricultural (iv) and reforested (v) sites. At the most intensively altered deforested sites the peat was denser, finer and enriched with recalcitrant compounds. The highest enzyme activity and microbial biomass were in the surface peat of swamp forest, where the amount of labile carbohydrates was highest. The six years ago reforested site did not yet show signs of recovery in peat properties, which was likely due the limited litter production capacity of the young plantation and microbial activity limited by chemical weeding. The main conclusion is that the litter input, or rather the lack of it after land-use change, and intensive management practices forms the main factors affecting to decomposition processes and leading to poorer substrate quality and reduced biological activity. Maankäyttömuutos, joka usein sisältää suoalueen kuivatuksen sekä alkuperäisen suosademetsän korvaamisen vähemmän biomassaa tuottavalla kasvillisuudella, on muuttanut Kaakkois-Aasian suoalueet hiilen nieluista hiilen lähteiksi. Suolta vapautuvan hiilidioksidin (CO2) määrän on havaittu riippuvan maankäyttömuutoksesta, mikä johtunee turpeen hajotettavuuden heikentymisestä, mutta yhteys hajotusprosessien ja maankäyttömuutoksen välillä on heikosti tunnettu. Lisätäksemme tietämystä maankäyttömuutoksen vaikutuksista hajotusprosesseihin, tutkimme turpeen fyysisiä (kuivatuoretiheys, huokoisuus, hiukkasjakauma) sekä kemiallisia ominaisuuksia (pH, tuhka, N, P, K, C, Ca, Mg, Mn, Zn, Na, Al, Fe, S, Si sekä liuenneen typen ja hiilen kokonaispitoisuudet ja turpeen kemiallinen rakenne), jotka kummatkin määrittävät turpeen maatumisastetta sekä hajotettavuutta (s.o. substraatin laatu mikrobeille). Turpeen biologisia ominaisuuksia (mikrobibiomassa sekä entsyymiaktiivisuus) käytettiin selittämään hajotusaktiivisuutta useilla maankäyttömuodoilla sekä vasteena turpeen laatua määrittäviin ominaisuuksiin. Tutkimusalueet olivat: lähes luonnontilainen ja kuivatettu suosademetsä, sekä kolme avohakattua ja kuivatettua aluetta, joista yksi oli uudelleen metsitetty, yksi maatalousmaana ja kolmas jättömaana. Turve oli tiiviimpää, hienompaa ja sisälsi enemmän heikosti hajoavia hiiliyhdisteitä (esim. ligniini) alueilla, jotka oli sekä avohakattu että kuivatettu. Mikrobibiomassa ja hajotusaktiivisuus olivat korkeampia suosademetsän pintaturpeessa, jossa oli myös eniten helposti hajoavia hiiliyhdisteitä (esim. hemiselluloosa). Kuusi vuotta sitten uudelleen metsitetyllä alueella turpeen ominaisuudet eivät olleet palautuneet metsän kaltaiseksiTähän vaikuttivat luultavasti puuston ikä ja pieni koko, jolloin se ei vielä tuottanut riittävästi kariketta, sekä mikrobeihin negatiivisesti vaikuttava kemiallinen heinäntorjunta. Kasvillisuus, ja erityisesti sen puuttuminen maankäyttömuutoksen myötä, sekä maanmuokkaus ovat tärkeimmät turpeen hajotukseen vaikuttavat tekijät. Voimakkaimmin muokatuilla alueilla, jotka on kuivatettu ja avohakattu, turpeen kemiallinen laatu heikkenee, mikä johtaa pienempään mikrobiaktiivisuuteen.

The first International Peat Congress (IPC) held in the tropics – in Kuching (Malaysia) – brought together over 1000 international peatland scientists and industrial partners from across the world (“International Peat Congress with over 1000 participants!,” 2016). The congress covered all aspects of peatland ecosystems and their management, with a strong focus on the environmental, societal and economic challenges associated with contemporary large-scale agricultural conversion of tropical peat.

Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane-spanning lipids from Bacteria and Archaea that are ubiquitous in a range of natural archives and especially abundant in peat. Previous work demonstrated that the distribution of bacterial branched GDGTs (brGDGTs) in mineral soils is correlated to environmental factors such as mean annual air temperature (MAAT) and soil pH. However, the influence of these parameters on brGDGT distributions in peat is largely unknown. Here we investigate the distribution of brGDGTs in 470 samples from 96 peatlands around the world with a broad mean annual air temperature (-8 to 27 degrees C) and pH (3-8) range and present the first peat-specific brGDGT-based temperature and pH calibrations. Our results demonstrate that the degree of cyclisation of brGDGTs in peat is positively correlated with pH, pH = 2.49 x CBTpeat + 8.07 (n = 51, R-2 = 0.58, RMSE = 0.8) and the degree of methylation of brGDGTs is positively correlated with MAAT, MAAT(peat) (degrees C) = 52.18 x MBT'(5me) - 23.05 (n = 96, R-2 = 0.76, RMSE = 4.7 degrees C). These peat-specific calibrations are distinct from the available mineral soil calibrations. In light of the error in the temperature calibration (similar to 4.7 degrees C), we urge caution in any application to reconstruct late Holocene climate variability, where the climatic signals are relatively small, and the duration of excursions could be brief. Instead, these proxies are well-suited to reconstruct large amplitude, longer-term shifts in climate such as deglacial transitions. Indeed, when applied to a peat deposit spanning the late glacial period (similar to 15.2 kyr), we demonstrate that MAAT(peat) yields absolute temperatures and relative temperature changes that are consistent with those from other proxies. In addition, the application of MAAT(peat) to fossil peat (i.e. lignites) has the potential to reconstruct terrestrial climate during the Cenozoic. We conclude that there is clear potential to use brGDGTs in peats and lignites to reconstruct past terrestrial climate. (C) 2017 The Authors. Published by Elsevier Ltd.