Peat Water Content Research Articles

Determining parameters of peat soil for finite-element analysis using the Cam Clay model

A practical procedure for determining soil parameters when analysing the deformation of peat by finite-element analysis (FEA) using the Cam Clay model is presented. FEA has not been frequently used to predict the deformation of peat soil, even though it can be a powerful prediction tool. The main reason for this is that a practical method for determining parameters has not been established. In this paper, the remarkable correlation between the soil parameters required for FEA using the Cam Clay model and the natural water content (wn) and ignition loss (Li) of peat and organic clay is presented. Then, based on this correlation, a flow chart for determining the soil parameters of peat and organic clay is proposed. Using this chart, it is possible to determine soil parameters directly from triaxial compression, oedometer and other detailed tests or to estimate them from wn, Li and other physical indexes. A trial embankment on peat soil in Hokkaido, Japan, was also created. FEA was performed on the trial embankment using the proposed procedure for determining the soil parameters. The results of the FEA corresponded to the measured settlement behaviour in the trial embankment with an accuracy in the range −4% to +8%. The FEA results also modelled the measured behaviour of pore water pressure and lateral and vertical displacements in the trial embankment very well.

Pengaruh Aplikasi Bioarang dan Zeolit pada Fluks CO2, Populasi Mikrob, dan Aktivitas Enzim Mikrob pada Gambut

Oil palm plantation on peatlands is considered to contribute to increasing global warming by releasing CO2 as one of the greenhouse gases that cause global warming. The addition of ameliorants, such as biochar and zeolite, can absorb CO2 from soil respiration and store and filter it in their molecular pores. This research aimed to study the effect of ameliorant application on the CO2 flux, water content, microbial population, and enzyme activities. Ameliorant was applied to peat soil with two factors. The first factor was an ameliorant combination with 6 treatment levels: control (A0); zeolite (A1); biochar (A2); zeolite:biochar 75:25; zeolite:biochar 25:75; zeolite:biochar 50:50, and the second factor was 3 levels dose of treatment (% w/w): 1.5%, 3%, and 4.5%. Peat flux CO2 and water content were measured monthly for four months in the laboratory. Without mixing with biochar (A1), the results showed that zeolite suppressed CO2 flux and suppressed the decrease of water content better than other ameliorant combinations. However, different ameliorant dosage percentages did not show any significant results. Ameliorant application and incubation affected the microbial population and enzyme activities, and the results were varied. Chemical characteristics changed after 4 months of incubation. In conclusion, our results indicate that only zeolite amendment can suppress CO2 flux and decrease water content but did not affect microbial population dynamics and enzyme activities.
 
 Keywords: ameliorant, CO2 flux, enzyme activities, lignocellulolytic microbes, peat

Quantifying the Sorptive Behavior of Traditional Horticultural Substrate Components Based on Initial Hydraulic Conditioning

The ability of a substrate component (organic or inorganic) to capture and retain water (hydration and wettability) is important to investigate and promote water-use–efficient practices. Many factors may play a role in the wettability of the material, including the processing of the material and its initial handling. The goal of this experiment was to determine the effect of moisture content (MC) on the sorptive behavior of substrates after an initial and secondary hydration cycle. Coir, peat, and aged pine bark were evaluated at a 33%, 50%, and 66% MC by weight. At all moisture levels, coir and bark were minimally affected by MC or the initial hydration cycle. Peat was the most vulnerable to changes in sorptive behavior as a result of wetting and drying cycles. After a wetting and drying cycle, the maximum volumetric water content of peat from surface irrigation was reduced 21.5% (volumetrically), more than three times any other treatment. The hydration efficiency of peat was improved when blended with as little as 15% coir. These experiments provide evidence that MC and initial handling of the substrate can lead to differences in initial water use efficiency.

Peat macropore networks – new insights into episodic and hotspot methane emission

Abstract. Peatlands are important natural sources of atmospheric methane (CH4) emissions. The production and emission of CH4 are strongly influenced by the diffusion of oxygen into the soil and of CH4 from the soil to the atmosphere, respectively. This diffusion, in turn, is controlled by the structure of macropore networks. The characterization of peat pore structure and connectivity through complex network theory approaches can give conceptual insight into how the relationship between the microscale pore space properties and CH4 emissions on a macroscopic scale is shaped. The evolution of the pore space that is connected to the atmosphere can also be conceptualized through a pore network modeling approach. Pore regions isolated from the atmosphere may further develop into anaerobic pockets, which are local hotspots of CH4 production in unsaturated peat. In this study, we extracted interconnecting macropore networks from three-dimensional X-ray micro-computed tomography (µCT) images of peat samples and evaluated local and global connectivity metrics for the networks. We also simulated the water retention characteristics of the peat samples using a pore network modeling approach and compared the simulation results with measured water retention characteristics. The results showed large differences in peat macropore structure and pore network connectivity between vertical soil layers. The macropore space was more connected and the flow paths through the peat matrix were less tortuous near the soil surface than at deeper depths. In addition, macroporosity, structural anisotropy, and average pore throat diameter decreased with depth. Narrower and more winding air-filled diffusion channels may reduce the rate of gas transport as the distance from the peat layer to the soil–air interface increases. The network analysis also suggests that both local and global network connectivity metrics, such as the network average clustering coefficient and closeness centrality, might serve as proxies for assessing the efficiency of gas diffusion in air-filled pore networks. However, the applicability of the network metrics was restricted to the high-porosity near-surface layer. The spatial extent and continuity of the pore network and the spatial distribution of the pores may be reflected in different network metrics in contrasting ways. The hysteresis of peat water content between wetting and drying was found to affect the evolution of the volume of connected air-filled pore space in unsaturated peat. Thus, the formation of anaerobic pockets may occur in a smaller soil volume and methanogenesis may be slower when the peat is wetting compared to in drying conditions. This hysteretic behavior might explain the hotspots and episodic spikes of CH4 emissions, and therefore, it should be taken into account in biogeochemical models.

Minnesota peat viromes reveal terrestrial and aquatic niche partitioning for local and global viral populations

BackgroundPeatlands are expected to experience sustained yet fluctuating higher temperatures due to climate change, leading to increased microbial activity and greenhouse gas emissions. Despite mounting evidence for viral contributions to these processes in peatlands underlain with permafrost, little is known about viruses in other peatlands. More generally, soil viral biogeography and its potential drivers are poorly understood at both local and global scales. Here, 87 metagenomes and five viral size-fraction metagenomes (viromes) from a boreal peatland in northern Minnesota (the SPRUCE whole-ecosystem warming experiment and surrounding bog) were analyzed for dsDNA viral community ecological patterns, and the recovered viral populations (vOTUs) were compared with our curated PIGEON database of 266,125 vOTUs from diverse ecosystems.ResultsWithin the SPRUCE experiment, viral community composition was significantly correlated with peat depth, water content, and carbon chemistry, including CH4 and CO2 concentrations, but not with temperature during the first 2 years of warming treatments. Peat vOTUs with aquatic-like signatures (shared predicted protein content with marine and/or freshwater vOTUs) were significantly enriched in more waterlogged surface peat depths. Predicted host ranges for SPRUCE vOTUs were relatively narrow, generally within a single bacterial genus. Of the 4326 SPRUCE vOTUs, 164 were previously detected in other soils, mostly peatlands. None of the previously identified 202,371 marine and freshwater vOTUs in our PIGEON database were detected in SPRUCE peat, but 0.4% of 80,714 viral clusters (VCs, grouped by predicted protein content) were shared between soil and aquatic environments. On a per-sample basis, vOTU recovery was 32 times higher from viromes compared with total metagenomes.ConclusionsResults suggest strong viral “species” boundaries between terrestrial and aquatic ecosystems and to some extent between peat and other soils, with differences less pronounced at higher taxonomic levels. The significant enrichment of aquatic-like vOTUs in more waterlogged peat suggests that viruses may also exhibit niche partitioning on more local scales. These patterns are presumably driven in part by host ecology, consistent with the predicted narrow host ranges. Although more samples and increased sequencing depth improved vOTU recovery from total metagenomes, the substantially higher per-sample vOTU recovery after viral particle enrichment highlights the utility of soil viromics.3EUUqCyiCvMAAvxFuvvQVmVideo abstract The importance of Minnesota peat viromes in revealing terrestrial and aquatic niche partitioning for viral populations

Utilization of low plants peat brickets for macadamia (Macadamia integrifolia) planting

Currently, the use of organic materials as organic fertilizer has been widely used by farmers. The awareness of farmers to use organic fertilizers has made organic fertilizers increasingly difficult to obtain. Organic fertilizers from chicken, goat and cow farms have generally been ordered and purchased by certain farmers. Therefore, alternative uses of other organic fertilizers need attention. Lowland peat is quite widely available in Indonesia, especially in North Sumatra. Peatlands are spread from the east coast of Aceh Province to the east coast of the Riau Province border. This potential makes it possible for peat to be modified into alternative organic fertilizers. One of the disadvantages of organic fertilizers is the large volume and weight. To overcome this problem, peat is made into briquettes through a pressing process so that its volume can be reduced to 1/3 times its previous volume. In addition, the acidic nature of peat is also expected to be greatly reduced by wasting peat water content. After being made into briquettes, the briquettes are used as organic fertilizer treatment for planting macadamia plants in the field. The results showed that the provision of briquettes from peat could increase the growth of macadamia plants compared to control. However, giving briquettes at a dose of 0.5 kg was not significantly different from giving briquettes up to 1.5 kg.

EFFECT OF WATER CONTENT AND SOIL IMPROVEMENT (HYDROGEL) ON PEAT FIRE SUPPRESSION

Forest and land fires are Indonesia's biggest problem which has continued from 2014 to the present. The number of activities to find the best solution in fire is something that has been done until now. Various methods, both preventive and repressive, have been implemented to prevent forest and land fires from occurring. This research aims to be a sureextinguishing gel, namely hydrogel, which can be used in efforts to extinguish forest and land fires. Extinguishing forest and land fires using hydrogel is a new method that is expected to prevent forest and land fire zones from spreading. This research shows that the tendency of decreasing the average water content of peat due to the drying process based on different intervals of oven time, namely the lowest yield ranged from 61.25% to the highest with a water content of 109.57%.

Effects of rainfall and groundwater level on soil subsidence, water content, and yield of oil palm

Peatlands have long been cultivated for various agricultural crops in Indonesia. However, nowadays land fires are often associated with drained peatlands. We present a four-year study looking at the effects of groundwater level (GWL) on peat reduction, moisture content, and yield. Observations were made on oil palm plantations in tropical peatlands of Riau Province. GWL was observed in 417 plots of 139 blocks and recorded once a week. Peat moisture was monitored automatically and recorded every hour. Subsidence poles were made in 36 blocks and recorded once a month. The results showed that peat subsidence, water content, and yield were affected by GWL fluctuations. There is a relationship between GWL and changes in peat subsidence (R2 = 0.26). A strong relationship was seen between the GWL and the water content of the peat soil at the 10 cm layer (R2 = 0.65). A strong relationship was also found between GWL and oil palm yield 20 months later (R2 = 0.65). In conclusion, by maintaining GWL at a depth of 40-60 cm, peat moisture at the surface can be maintained, peat subsidence can be minimized and oil palm production remains high at an average of 22 tonnes year-1, thereby also reducing susceptibility to fire.

PENGARUH PEMBAKARAN BERULANG PADA LAHAN GAMBUT TERHADAP BEBERAPA KARAKTERISTIK TANAH DI DESA RASAU JAYA UMUM KABUPATEN KUBU RAYA KALIMANTAN BARAT

The National Disaster Management Agency (BNPB) identifies eight provinces considered prone to forest and land fires in Indonesia. Four provinces are in Sumatra and four are in Kalimantan, one of which is West Kalimantan. Forest and land fires seem to have become a disaster in West Kalimantan, especially every dry season. Burning activies in the preparation of land for agriculture in the village of Rasau Jaya General is still using a relatively simple technology, namely the method of "slash and burn". The impacts caused by the peat fire process are in the form of water vapor from the combustion process in the air so that smoke formed which is very thick, causes environmental pollution and can affect soil conditions such as physical and chemical properties of peat soils. The purpose of this study was to obtain information about the effects of repeated burning on peatlands on soil characteristics in Rasau Jaya Umum Village, Kubu Raya Regency, West Kalimantan. This research was conducted by survey method and carried out with purposive sampling on 3 research sites, which were on land that had repeated burning twice, 4 times and 5 times. Soil physical properties observed were peat maturity (fiber content), water content, soil moisture, water level and bulk density. The level of fertility of peatlands is influenced by the chemical nature of the soil. The chemical nature of the soil is one of the limiting factors for knowing nutrients in the soil that are beneficial for plant growth. Determination of the level of soil fertility in peatlands can be done by analyzing the chemical properties of the soil. Analysis of the soil chemical properties includes analysis of the main element content such as acidity (pH), nitrogen (N), phosphorus (P), potassium (K) and cation exchange capacity (CEC). The physical properties of the soil consisting of the weight of the contents, the moisture content varies with different levels of burning, the higher the value of the weight of the contents, the more dense a soil and vice versa. In the value of water content, the amount of combustion influences the amount of ground water content, the more number of combustion, the value of water content also increases. Peat environmental conditions observed in the field consisted of soil moisture, soil temperature and ground water level measured for 7 days and obtained a mean value that also varied did not show its effect on the number of repeated fires. The chemical properties of peat soils on the number of repeated burning can increase and decrease each nutrient value consisting of N, P, K and also CEC. Nutrients that increase in the amount of combustion are pH, N, and CEC while the value of nutrients that decrease is K and P. This shows that the greater the level of combustion, the pH, N, and CEC greater.Keywords: peatlands, repeated burning, soil characteristics

Identification of factors that influence carbon emissions in tropical peatland

Abstract. The research aimed to find out the relationship between water table and soil as well as the influence of chemical (peat water content, pH) and physical (cation exchange capacity = KTK) factors on CO2 emission. The research used simple mathematic analysis using secondary data. The research was conducted in oil palm plantation in Koto Gasib districk, Siak Regency, Riau. Objects researched were water table level, rainfall and peatland chemical-physical factors in oil palm plantation. Research result indicated that rainfall and days of rain had linear relationship with water table level. Water table level contributed 71.48% to GRK emission and the remaining 28.52% was influenced by other factors. Peatland pH contributed 91.41% to emission, and the remaining 8.59% was influenced by other factors. The influence of KTK on emission was 88.66 % and the remaining 11.34% was influenced by other factors. Water content of peatland had influence on GRK emission of 96.19% and the remaining 3.81 % was influenced by other factors. Conclusion: water table level, water content, pH, and KTK had significant influence on CO2 emission. Research result shows that water content has the biggest influence on CO2 release compare to water table, KTK and pH.

Relationship between electrical conductivity and water content of peat and gyttja: implications for electrical surveys of drained peatlands

ABSTRACTThe application of electrical resistivity tomography to peatlands supports conventional coring by providing data on the current condition of peatlands, including data on stratigraphy, peat properties and thickness of organic deposits. Data on the current condition of drained peatlands are particularly required to improve estimates of carbon storage as well as losses and emissions from agriculturally used peatlands. However, most of the studies focusing on electrical resistivity tomography surveys have been conducted on natural peatlands with higher groundwater levels. Peatlands drained for agriculture have not often been studied using geophysical techniques. Drained sites are characterized by low groundwater levels and high groundwater fluctuations during the year, which lead to varying levels of water saturation. To validate better electrical resistivity tomography surveys of drained peatlands, the aim of this laboratory study is to investigate the influence of varying water saturation levels on electrical conductivity (reciprocal of resistivity) for a variety of peat and gyttja types, as well as for different degrees of peat decomposition. Results show that different levels of water saturation strongly influence bulk electrical conductivity. Distinct differences in this relationship exist between peat and gyttja substrates and between different degrees of peat decomposition. Peat shows an exponential relationship for all degrees of decomposition, whereas gyttja, in particular organic‐rich gyttja, is characterized by a rather unimodal relationship. The slopes for the relationship between electrical conductivity and water content are steeper at high degrees of decomposition than for peat of low degrees of decomposition. These results have direct implications for field electrical resistivity tomography surveys. In drained peatlands that are strongly susceptible to drying, electrical resistivity tomography surveys have a high potential to monitor the actual field water content. In addition, at comparable water saturations, high or low degrees of decomposition can be inferred from electrical conductivity.

CAPILLARY WATER RISE IN PEAT SOIL AS AFFECTED BY VARIOUS GROUNDWATER LEVELS

<p class="abstrakInggris">Capillary water in peatlands has a very important role in supplying water to the root zone of plants. The current water content in the root zone depends mainly on groundwater levels in some areas with shallow water levels. The study aimed to measure the capillary water dynamics in peat soils at various soil densities and groundwater levels which were observed from the changes in peat color, moisture distribution, water content and hydrophobicity of peat soil. The study was conducted in the greenhouse of Indonesian Swampland Agricultural Research Institute, Banjarbaru, South Kalimantan. The experiment was arranged in a randomized block design with two factors and three replications. The first factor was the bulk density (BD) of peat, namely BD-1 (on actual condition, 0.1 g cm-3) and BD-2 (compressed into 0.2 g cm-3). The second factor was simulated groundwater levels (GWL) consisting of GWL-1 (-100 cm), GWL-2 (-70 cm) and GWL-3 (-40 cm) from soil surfaces. The results showed that the rise of capillary water in peat soil reached a maximum height of 50 cm which was characterized by the increase in water content at the top layer in the range of 105–127% for BD-1 and 141–181% for BD-2. The highest value of water content (308%) was achieved in the treatment of GWL-3 with BD-2 and the lowest (37%) was in the treatment of GWL-1 with BD-1. The rate of capillary water rose progressively corresponded to the increase in BD value because the number of micropores of BD-2 was greater.</p>

DAMPAK PARIT DRAINASE TERHADAP TINGGI MUKA AIR, KONDISI TANAH DAN PERTUMBUHAN POHON DI HUTAN GAMBUT KALIMANTAN BARAT

Currently, tropical peatland forests are under considerable pressure because of increasing deforestation and degradation of forests. In Kalimantan, degradation and deforestation of peatland forests are driven primarily by industrial logging, expansion of agricultural activities through primarily conversion of forests to agricultural land and oil palm plantations. By the establishment of intensive drainage, it can induce wildfires in peatland. Unmanaged drainage ditches will alter water table levels within the site adjacent to the drainage including to surrounding peatland forest. Water table assessments were conducted before and after peatland drainage on 2007/2009 and 2012/2015 in Kubu Raya, West Kalimantan. This paper studies the effect of drainage ditches into the peatland water table. Results show the establishment of drainage ditches on this peatland landscape lowered the water table by more than 3 times from ~11.7 cm (SE = 1.5, n = 5) to ~37.3 cm (SE = 2.1 cm, n = 26). The effect on the water table was in drier months of July-August. Lowering the water table level altered worst the soil micro climate, peat temperature and peat water content. The results indicate the land use changes in peatland with the establishment of drainage affects peatland water table currently. In the area of less than 500 m from the drainage, the water level tends to lower toward the drainage feature. Therefore, recovery of peatland forests should be initiated by managing the landscape hydrology (i.e. water table) to restore the ecosystem and to protect the remaining peat swamp forest.

Modeling hydrological controls on variations in peat water content, water table depth, and surface energy exchange of a boreal western Canadian fen peatland

AbstractImproved predictive capacity of hydrology and surface energy exchange is critical for conserving boreal peatland carbon sequestration under drier and warmer climates. We represented basic processes for water and O2 transport and their effects on ecosystem water, energy, carbon, and nutrient cycling in a process‐based model ecosys to simulate effects of seasonal and interannual variations in hydrology on peat water content, water table depth (WTD), and surface energy exchange of a Western Canadian fen peatland. Substituting a van Genuchten model (VGM) for a modified Campbell model (MCM) in ecosys enabled a significantly better simulation of peat moisture retention as indicated by higher modeled versus measured R2 and Willmot's index (d) with VGM (R2~0.7, d~0.8) than with MCM (R2~0.25, d~0.35) for daily peat water contents from a wetter year 2004 to a drier year 2009. With the improved peat moisture simulation, ecosys modeled hourly WTD and energy fluxes reasonably well (modeled versus measured R2: WTD ~0.6, net radiation ~0.99, sensible heat >0.8, and latent heat >0.85). Gradually declining ratios of precipitation to evapotranspiration and of lateral recharge to discharge enabled simulation of a gradual drawdown of growing season WTD and a consequent peat drying from 2004 to 2009. When WTD fell below a threshold of ~0.35 m below the hollow surface, intense drying of mosses in ecosys caused a simulated reduction in evapotranspiration and an increase in Bowen ratio during late growing season that were consistent with measurements. Hence, using appropriate water desorption curve coupled with vertical‐lateral hydraulic schemes is vital to accurately simulate peatland hydrology and energy balance.

The Effects of Fire on Organic Functional Groups of Peat in Relation to Water Content

The aim of this research was to study the decline of organic functional group through the process of burning in peat. In addition, this study was also to examine the relationship between water content in peat and organic functional group after combustion (burning). Peat drying was conducted in an oven at a temperature of 75°C with the interval of 0, 1, 2, 3, 4, 5 and 6 hours. Each time interval had three replicates within two sets of experiments so that the total number of samples were 42 (experimental units). Variables measured were moisture content, total acidity, COOH groups, and OH-phenolate. The relationship between the water content with total acidity, COOH groups and OH-phenolate were determined by the equation y = bx + a. The results showed that the relationship between the water content with organic functional group was linear. While the relationship between peat water content with organic functional group after burning was irregular, although water levels through the process of burning have been greatly reduced. Keywords: Burning peat; organic functional groups; water content [How to Cite: Said R, FH Yusran, A Haris and S Asmawi. 2014. The Effects of Fire on Organic Functional Groups of Peat in Relation to Water Content. J Trop Soils 19: 143-149. Doi: 10.5400/jts.2014.19.3.143]

Water availability influences morphology, mycorrhizal associations, PSII efficiency and polyamine metabolism at early growth phase of Scots pine seedlings

Scots pine (Pinus sylvestris L.) is adapted to various soil types with diverse water availabilities. However, Scots pine seedlings are vulnerable to abiotic stress during the early growth, when they may be exposed to both dry and wet conditions. Here, we focused on the above and below ground coping strategies of Scots pine seedlings under controlled wet, optimal and dry soil conditions by investigating morphological traits including seedling biomass, number of root tips, proportion of mycorrhizal root tips and brown needles. In addition, we studied metabolic and physiological responses including gene expression involved in biosynthesis and catabolism of polyamines (PA), PSII efficiency and the expression of the catalase (CAT) late-embryogenesis abundant protein (LEA), pyruvate decarboxylase (PDC), glutamate-cysteine ligase (GCL) and glutathione synthetase (GS) genes. We found that seedlings invested in shoots by maintaining stable shoot water content and high PSII efficiency under drought stress. Free and soluble conjugated putrescine (Put) accumulated in needles under drought stress, suggesting the role of Put in protection of photosynthesizing tissues. However, the expression of the PA biosynthesis genes, arginine decarboxylase (ADC), spermidine synthase (SPDS) and thermospermine synthase (ACL5) was not affected under drought stress whereas catabolizing genes diamino oxidase (DAO) and polyamine oxidase (PAO) were down-regulated in shoots. The morphology of the roots was affected by peat water content. Furthermore, both drought stress and water excess restricted the seedling ability to sustain a symbiotic relationship. The consistent pattern of endogenous PAs seems to be advantageous to the Scots pine seedlings also under stress conditions.

Experimental warming differentially affects microbial structure and activity in two contrasted moisture sites in a Sphagnum-dominated peatland

Several studies on the impact of climate warming have indicated that peat decomposition/mineralization will be enhanced. Most of these studies deal with the impact of experimental warming during summer when prevalent abiotic conditions are favorable to decomposition. Here, we investigated the effect of experimental air warming by open-top chambers (OTCs) on water-extractable organic matter (WEOM), microbial biomasses and enzymatic activities in two contrasted moisture sites named Bog and Fen sites, the latter considered as the wetter ones. While no or few changes in peat temperature and water content appeared under the overall effect of OTCs, we observed that air warming smoothed water content differences and led to a decrease in mean peat temperature at the warmed Bog sites. This thermal discrepancy between the two sites led to contrasting changes in microbial structure and activities: a rise in hydrolytic activity at the warmed Bog sites and a relative enhancement of bacterial biomass at the warmed Fen sites. These features were not associated with any change in WEOM properties namely carbon and sugar contents and aromaticity, suggesting that air warming did not trigger any shift in OM decomposition. Using various tools, we show that the use of single indicators of OM decomposition can lead to fallacious conclusions.Lastly, these patterns may change seasonally as a consequence of complex interactions between groundwater level and air warming, suggesting the need to improve our knowledge using a high time-resolution approach.

Occurrence patterns of facilitation by shade along a water gradient are mediated by species traits

In disturbed habitats, shade often has facilitative effects on plants by ameliorating water and thermal stresses. Facilitation by shade tends to increase as water availability decreases. At the same time, several studies have suggested that facilitation by shade is not affected by water status or collapses under extremely dry conditions. We hypothesized that traits of beneficiary plants, specifically, the flexibility in the allocation of biomass between shoots and roots, would mediate variation in the relationship between facilitation by shade and water status. To test this hypothesis, we examined the responses of two bog species to shade under various water conditions in a post-mined peatland. The seeds of Rhynchospora alba and Moliniopsis japonica were sown under three water levels (dry: 53% peat water content, wet: 77%, and control: 71%) × two shading levels (50% shaded and unshaded). The survival, biomass, and biomass allocation between the shoots and roots of the two species were monitored for two years. Shade increased the survival and biomass of both species. However, the facilitation of R. alba by shade was independent of water level, whereas the strength of the facilitative effects on M. japonica increased as water content decreased. R. alba preferentially allocated biomass to roots under dry conditions and was highly drought tolerant. M. japonica did not alter the allocation of its biomass in response to either shade or water level and was drought intolerant. Our results suggest that flexibility in biomass allocation of beneficiary plants mediates occurrence patterns of facilitation by shade along a water gradient. The facilitation of species with inflexible biomass allocation by shade through the amelioration of water stress increases as water availability decreases, whereas the facilitation of species with flexible biomass allocation is independent of water status. Such species-specific facilitation would promote the coexistence of diverse species in a community.

Seasonal changes in peatland surface elevation recorded at GPS stations in the Red Lake Peatlands, northern Minnesota, USA

Northern peatlands appear to hold large volumes of free‐phase gas (e.g., CH4 and CO2), which has been detected by surface deformations, pore pressure profiles, and electromagnetic surveys. Determining the gas content and its impact in peat is challenging because gas storage depends on both the elastic properties of the peat matrix and the buoyant forces exerted by pore fluids. We therefore used a viscoelastic deformation model to estimate these variables by adjusting model runs to reproduce observed changes in peat surface elevation within a 1300 km2 peatland. A local GPS network documented significant changes in surface elevations throughout the year with the greatest vertical displacements associated with rapid changes in peat water content and unloadings due to melting of the winter snowpack. These changes were coherent with changes in water table elevation and also abnormal pore pressure changes measured by nests of instrumented piezometers. The deformation model reproduced these changes when the gas content was adjusted to 10% of peat volume, and Young's modulus was varied between 5 and 100 kPa as the peat profile shifted from tension to compression. In contrast, the model predicted little peat deformation when the gas content was 3% or lower. These model simulations are consistent with previous estimates of gas volume in northern peatlands and suggest an upper limit of gas storage controlled by the elastic moduli of the peat fabric.

Peat emission control by groundwater management and soil amendments: evidence from laboratory experiments

Peat respiration that releases carbon dioxide (CO2) to the atmosphere contributes to regional and global change. Aeration associated with soil water content levels controls emission rates, but soil amendments might mitigate respiration. The objectives of this study were to examine the effects of various water content levels and laterite application on microbial (heterotrophic) respiration in peat soil. Bulk samples of surface (0–20 cm depth) and subsurface (30–50 cm depth) layers were collected from an oil palm plantation in Riau Province, Indonesia. Peat water content was adjusted to 20, 40, 60, 80, and 100 % water filled pore space (WFPS). Laterite soil (clay containing high Al and Fe oxides) was applied to 3, 6, and 12 mg g−1 dry weight (1.2, 2.4, and 4.8 Mg ha−1) peat samples at 60 % and 100 % WFPS. Results showed peat respiration was notably affected by water content, but less affected by laterite application. Peat respiration increased sharply from wet (≥80 % WFPS) to moist soil (60 to 40 % WFPS), and decreased when soil dried (≤40 % WFPS). Laterite as a peat ameliorant accelerated rather than reduced peat respiration, and is therefore not a viable choice for CO2 emissions reduction.