Bog Surface Research Articles

The use of k-values to examine plant ‘species signals’ in a peat humification record from Newfoundland

Peat humification analysis has been used widely over the last three decades to reconstruct bog surface wetness (BSW) for use as a palaeoclimate proxy. The technique has the advantage that it is quick and relatively inexpensive to perform, allowing for high resolution and contiguous sampling of peat archives. However, some concerns have been raised over the quality of the resultant proxy-climate records because changes in the plant species composition of peat may contribute a ‘species signal’ to records, potentially confusing the relationship between bog water table position and the apparent degree of peat humification. This paper uses the k-values of fresh plant material (sensuOverbeck, 1947 – i.e. the absorption value of the alkali extracts of fresh plant material) to explore the impact of changing plant colouration in a Holocene peat humification-based palaeoclimate archive from Newfoundland. We calculate k-scores for peat samples, using plant macrofossil data and the k-values of individual species to provide a down-core visualisation of the plant species signal. Although, overall, the humification data are validated, comparison of the original humification data with a k-adjusted version shows that the species signal is sometimes sufficient to change the timing and number of decadal to centennial-scale events recorded in the data as well as millennial to multi-millennial-scale trends.

Regional climate change from peat stratigraphy for the mid- to late Holocene in central Ireland

At the millennial scale bog surface wetness (BSW) records show a clear Holocene climate event stratigraphy, with major phases comparable with other regional climate proxies such as chironomid inferred temperature records. Moving towards the centennial scale, however, and towards the limits of chronological certainty within the records, regional differences are apparent which likely reflect the more heterogeneous precipitation patterns which occur on shorter timescales. The BSW data presented in this paper are reconstructed from testate amoebae assemblages from central Ireland and are compared with other regional records. The results suggest that this region is in phase with the North of Ireland in terms of timings and durations of climate change, but the comparisons are less clear with a stacked and tuned record from Northern Britain that shows an apparent offset compared to the Irish records. This may reflect variations in past regional precipitation or be a function of the tuning and stacking process. The broad phases of comparison between the Irish records, and the extension of the central Irish record back to 6000 cal BP, allow comparisons with low frequency temperature reconstructions from chironomids, which also show a broad level of correlation, with cooler temperatures relating to wetter BSW at centennial to millennial timescales.

The Effects of Permafrost Thaw on Soil Hydrologic, Thermal, and Carbon Dynamics in an Alaskan Peatland

Recent warming at high-latitudes has accelerated permafrost thaw in northern peatlands, and thaw can have profound effects on local hydrology and ecosystem carbon balance. To assess the impact of permafrost thaw on soil organic carbon (OC) dynamics, we measured soil hydrologic and thermal dynamics and soil OC stocks across a collapse-scar bog chronosequence in interior Alaska. We observed dramatic changes in the distribution of soil water associated with thawing of ice-rich frozen peat. The impoundment of warm water in collapse-scar bogs initiated talik formation and the lateral expansion of bogs over time. On average, Permafrost Plateaus stored 137 ± 37 kg C m -2 , whereas OC storage in Young Bogs and Old Bogs averaged 84 ± 13 kg C m -2 . Based on our reconstructions, the accumulation of OC in near-surface bog peat continued for nearly 1,000 years following permafrost thaw, at which point accumulation rates slowed. Rapid decomposition of thawed forest peat reduced deep OC stocks by nearly half during the first 100 years following thaw. Using a simple mass-balance model, we show that accumulation rates at the bog surface were not sufficient to balance deep OC losses, resulting in a net loss of OC from the entire peat column. An uncertainty analysis also revealed that the magnitude and timing of soil OC loss from thawed forest peat depends substantially on variation in OC input rates to bog peat and variation in decay constants for shallow and deep OC stocks. These findings suggest that permafrost thaw and the subsequent release of OC from thawed peat will likely reduce the strength of northern permafrost-affected peatlands as a carbon dioxide sink, and consequently, will likely accelerate rates of atmospheric warming.

Multi-proxy Holocene palaeoclimate records from Walton Moss, northern England and Dosenmoor, northern Germany, assessed using three statistical approaches

Plant macrofossil analysis is a robust and established method for estimating palaeoclimatic changes from raised peat bogs. There remains uncertainty, however, over the best statistical method to use for converting the palaeoecological data to an index of bog surface wetness (BSW). To test this, a 9 m core (WLM22) from Walton Moss, northern England was analysed for changes in plant macrofossils, testate amoebae and humification. The plant macrofossil data were then converted to a single curve of bog surface wetness (BSW) using three different techniques: weighted averaging by the Dupont Hydroclimatic Index (DHI) and ordination by Detrended Correspondence Analysis (DCA) and by Non-metric Multidimensional Scaling (NMDS). Through comparison with testate amoebae and humification data from the same core, it was observed that a statistically better fit was found with the wetness curve from DHI than that from either ordination. It is suggested that the weighted averaging method of DHI can provide a good indicator of BSW variation in long peat records, where the profile incorporates data from both Sphagnum-dominated and Eriophorum/ericaceous-dominated bog deposits, which is common to NW European bogs. The data also imply that, with sufficient diversity of taxa, there is potential for the further development of plant macrofossil transfer functions. Application of DHI to an additional data set from Dosenmoor, northern Germany and comparison with published records from NW Europe revealed coherent regional climatic variations.

The relationship of fine-resolution, multi-proxy palaeoclimate records to meteorological data at Fågelmossen, Värmland, Sweden and the implications for the debate on climate drivers of the peat-based record

Fluctuations in bog surface wetness (BSW) over an 86-year period were reconstructed using fine-resolution analyses of testate amoebae, plant macrofossils and peat humification from Fågelmossen, an ombrotrophic bog in western Sweden. Results were compared with local instrumental temperature and precipitation data and reconstructed values of total seasonal water table deficit using an age–depth model based on spheroidal carbonaceous particle analysis and a historically dated, geochemically typed tephra layer. Statistically significant correlations between decadal means of the fine-resolution data and climate parameters lend support to the notion that a climate signal may be present in those data, enhancing confidence in the peat-based record to address pressing research questions on abrupt climate change. All three proxies were correlated most significantly with annual precipitation, plant macrofossils only when correlations were time-lagged by 10 years, suggesting that precipitation, rather than temperature, is the primary driver of the BSW record at Fågelmossen. However, plant macrofossils also correlated significantly with annual temperature when time-lagged by 10 years. The correlation of individual physical and biological proxies with climate parameters on different time-scales, coupled with the significant correlation of plant macrofossil results with annual temperature in addition to annual precipitation, may bring into question the use of composite curves of BSW that combine results from multi-proxy studies. The correlations reported here partly support those from other similar studies, but highlight that regional variability may be greater than previously hypothesised and that it may not be possible to apply a single explanation of climatic forcing where bog surface wetness reconstructions are concerned.

Contrasting responses to environmental changes by pine (Pinus sylvestris L.) growing on peat and mineral soil: An example from a Polish Baltic bog

A comparison of the tree-ring width of pines growing in areas adjacent to a peat bog and on a Baltic raised bog dome suggests that cambium activity in each tree group is affected by different factors. The study was aimed at pinpointing effects of meteorological factors on two pine populations growing under different hydrological conditions. The study further sought to identify periods during which anthropogenic pressure affected the two populations. The pines growing on mineral soil were characterised by ring-width growth–climate responses typical of this part of Europe, whereas the tree-ring growth of the pines growing on the peat bog showed no unequivocal relationship with meteorological conditions. The tree-ring width growth dynamics of that population responded primarily to changes in the level of the groundwater table. These changes were associated with human activities over the last two centuries. The development of the tree stands on the peat bog and in its immediate vicinity was reconstructed using this assumption and available historical evidence. A banding drainage ditch dug around 1880 resulted in the drying of the peat bog, the introduction of pines, and the forestation of the bog. Digging of central ditches (in the 1960s) resulted in periodic desiccation of the bog surface and reduction of the tree-ring widths; similar responses were observed in the 1980s as a consequence of the deepening and opening of the drainage ditches. The recent years are characterised by decreasing ring-width growth as a result of the damming of drainage ditches. Damming resulted in an increase of the groundwater table level in the bog and in a partial inundation of tree roots. This partial inundation interfered with gas exchange and adversely affected the health status of the pines studied. Our results allow conclusions to be drawn regarding peat bog palaeohydrology and facilitate absolute dating of changes associated with anthropogenic transformations. In active nature protection, such data are of key importance for understanding the functioning of a peatland and for planning active conservation measures.

Measuring biodiversity across spatial scales in a raised bog using a novel paired‐sample diversity index

Summary 1. Biodiversity is an inherently spatial phenomenon. It is determined by environmental heterogeneity and by spatially structured ecological processes such as disturbance, competition and dispersal. However, conventional biodiversity indices are based on discrete samples or pooled sets of samples without sufficient consideration of the spatial relationships between the samples. 2. Here we describe a new method for spatial analysis of species diversity, based on a paired‐sample version of the widely used Gini–Simpson diversity index and its numbers equivalent. The index and its numbers equivalent are plotted as a function of lag distance between two samples along spatial and/or environmental gradients. 3. We demonstrate the potential of this approach by applying it to two transects of fine‐scale (5 × 5 cm quadrat) vegetation data from sites with contrasting hydrology within a raised bog, where the location of each quadrat is accurately recorded and the height of the bog surface above the water table is measured using a terrestrial laser scanner. 4. Both transects have similar alpha‐diversity as measured using the Gini–Simpson index, and the transition between alpha‐ and gamma‐diversity occurs at similar length scales, suggesting that species aggregate at similar scales along both transects. However, the transect from the central bog dome has higher gamma‐diversity than that from the bog margin, and shows more marked significant spatial structure at a length scale of 135–140 cm, corresponding to the typical hummock–hollow microtopography at the site. We show that beta‐diversity at both transects can be attributable to both species clustering along the hydrological gradient, consistent with niche partitioning, as well as independent spatial aggregation of species that is not explained by hydrology. 5. Synthesis. The paired‐sample diversity index described here is a potentially useful tool in detecting and attributing patterns of beta‐diversity along both spatial and environmental gradients.

Investigating water distribution in the Luitel Lake peat bog using MRS, ERT and GPR

ABSTRACTIn this paper we present the results of a geophysical study of water distribution in the peat bog at Luitel Lake. The goal of the study was to determine water distribution within the bog, which is part of a protected nature preserve. The small peat bog (17 ha) provides a good test site for developing and testing surface geophysical methods. For this study we used magnetic resonance sounding (MRS), electrical resistivity tomography (ERT) and ground‐penetrating radar (GPR). Because the water distribution in the bog is a 2D target for MRS, we had to develop a measuring procedure and 2D inversion routine for MRS. The fieldwork consisted in establishing seventeen MRS stations and conducting three ERT profiles and one GPR line. The MRS, ERT and GPR results on the reservoir geometry correlated well with each other. Pine and birch trees cover most of the bog surface but they have not yet populated the centre of the bog, the location where the maximum water content was observed. This result agrees well with vegetation distribution in the study area: at the centre of the bog, vegetation is typical of a swampy environment but outside the centre the vegetation is typical of a forest. According to MRS, the water content of the peat formation at the centre of the bog is 60–70%, whereas GPR estimated the water content to be between 64–70%. Outside the centre, MRS showed the water content of the peat to be about 30%.

‘The methodological basis for fine-resolution, multi-proxy reconstructions of ombrotrophic peat bog surface wetness’: Reply to comments

‘The methodological basis for fine-resolution, multi-proxy reconstructions of ombrotrophic peat bog surface wetness’: Reply to comments

‘The methodological basis for fine-resolution, multi-proxy reconstructions of ombrotrophic peat bog surface wetness’: Comments

‘The methodological basis for fine-resolution, multi-proxy reconstructions of ombrotrophic peat bog surface wetness’: Comments

Exploring the patterns and causes of land use changes in south-west Sweden

To study the causes of agricultural declines in south-west Sweden, a multi-proxy study including pollen analysis, bog surface wetness indicators and aeolian sediment influx reconstructions was carried out on the Store Mosse Bog, situated on the coastal plain of Halland. Patterns of agricultural changes during the past 6,000 years from this study were compared to one additional site on the coastal plain (Undarsmosse Bog) and to four sites in the forested upland region. First, we compared land use activity on the coastal plain and in upland regions of south-west Sweden. Three periods with reduced agricultural activities were observed, primarily in records from the coastal plain. Next, the causes for these declines were studied by comparing land use indicators in the pollen records from the Store Mosse and Undarsmosse peat bogs to independent climatic reconstructions based on the same core material (past storm activity based on aeolian sediment influx onto the peat bogs; bog surface wetness reconstructed from organic bulk density measurements). Since the climatic reconstructions and pollen analysis were carried out on the same peat cores, a direct comparison between the timing of climatic events and land use changes was possible. Results indicate that climatic perturbations prior to ca. 1,000 years ago contributed to or possibly caused agricultural declines. The agricultural expansions near the Store Mosse and Undarsmosse bogs from 3000 to 2600 cal. yrs b.p. ended at the time when climatic proxy indicators recorded climatic instability (from ca 2600 to 2200 cal. yrs b.p.). The same sequence of events was recorded around 1500 cal. yrs b.p. and from 1200 to 1000 cal. yrs b.p., suggesting a climatic cause for these agricultural declines as well. The well-known climatic perturbations associated with the Little Ice Age, however, did not have a visible impact on agricultural activities. By this time, advances in land use knowledge and technology may have drastically diminished society’s sensitivity to climatic changes.

The methodological basis for fine-resolution, multi-proxy reconstructions of ombrotrophic peat bog surface wetness

The need for Holocene peat-based palaeoclimatic records of increased temporal resolution has been widely identified in recent research. The often rapid growth rates of ombrotrophic bogs, when combined with fine-resolution (i.e. millimetre-scale) sampling, provide an as yet largely unexploited potential to derive sub-decadal palaeoclimatic data from this proxy-archive. However, multi-proxy, fine-resolution analyses require changes to standard methodologies, and the application of sampling techniques that are new to peat-based palaeoclimate research. A peat sampler was custom-built to allow precise and replicable millimetre-scale subsampling. Subsequent methodological testing revealed that, irrespective of sample thickness (i.e. resolution), halving the standard sample volume used for plant macrofossil (from 4 cm3 to 2 cm3) and testate amoebae (from 2 cm3 to 1 cm3) analyses and the sample weight used for peat humification analysis (from 0.2 g to 0.1 g dried peat) did not affect the interpretation of the results. A contiguous 1-mm sampling resolution for plant macrofossil analysis was also tested, but it was found that contiguous 5-mm samples provided a more reliable background record to fine-resolution testate amoebae and peat humification analyses. Based on these findings, a standardized and systematic methodological approach was developed, using the custom-built peat slicer to take millimetre-scale samples that provide enough sample material for both testate amoebae and peat humification analyses to be performed at 1-mm resolution. This approach will facilitate the testing of the palaeoclimatic reliability of multi-proxy, fine-resolution peat-based records.

Preliminary data on the bog surface wetness from the Sirok Nyírjes-tó peat bog, Mátra Mts, Hungary

Abstract The Sirok Nyirjes-to peat bog provides an almost full Holocene climatic record reconstructed by bog surface wetness investigations based on plant macrofossil analysis. The method of bog surface wetness reconstruction has not so far been adapted to the characterization of continental peat bogs. The emergence of a deep oligotrophic lake was dated to cc. 9500 cal. yr BP. The driest phase of the peatland was recorded at 6400 cal. yr BP, at the time of the Holocene climatic optimum. The deterioration of the climate, which began at 3500 cal BP, culminates here in the Carpathian Basin, as was shown by numerous records. An increase in the amount of Sphagna from 2800 cal. yr BP in the Nyires-to peat bog marks the cooling of the climate and the accompanying rise in rainfall. The first oligotrophic Sphagnum peatland developed at Sirok between 2300 and 1500 cal. yr BP. Since 2300 cal. yr BP a record of alternating phases of Sphagnum peatlands and sedge/reed peatlands was demonstrated. A sudden expansion of S...

Occurrence and distribution of glycerol dialkyl glycerol tetraethers in a French peat bog

The present study was aimed at examining the distribution and abundance of glycerol dialkyl glycerol tetraethers (GDGTs) of archaeal and bacterial origin in peat samples from surface and deep (ca. 50 cm) horizons of a peat bog in the Jura Mountains (northeastern France). Two principal types of GDGTs are present: extractable GDGTs, recoverable by solvent extraction, and non-extractable GDGTs, linked to the soil matrix. Within the extractable pool, “free” (i.e. core lipids) and “bound” (i.e. intact polar and/or ester-bound lipids) GDGTs can be distinguished. Extractable “free” and “bound” GDGTs were extracted using both accelerated solvent extraction (ASE) and a modified Bligh and Dyer technique. Both methods were shown to allow adequate extraction of “free” archaeal and bacterial GDGTs from soil samples. Both extraction protocols afforded similar relative distributions of archaeal and bacterial GDGTs, although poorer extraction of “bound” GDGTs was observed for ASE relative to Bligh and Dyer. Even though only low amounts of bacterial GDGTs were released after acid hydrolysis of solvent-extracted samples, non-extractable and total extractable GDGTs showed different distribution patterns in some samples. Consequently, these two lipid pools potentially reflect different proxy records of mean annual air temperature (MAAT) and pH. Last, the distribution of bacterial GDGTs differed between the different samples. Samples from deep horizons gave lower GDGT-derived MAAT values than those from surficial horizons, in agreement with measured soil temperatures at 7 cm and 50 cm depths from April to September. MAAT estimates more closely resemble spring and summer temperatures rather than annual soil temperature. The variability in bacterial GDGT distribution and resulting MAAT estimates probably also reflects the heterogeneity of peat samples and the variation in several environmental factors such as peat moisture level and oxygen availability.

Distribution of heаvy metals in the profile of peat bog Zhuravlyne (Skolivski Beskydy, Ukrainian Carpathians) as an indicator of changes in chemical composition of air precipitations in historical retrospective

Vertical distribution of ash, Pb, Cd, Zn, Fe, Mn, Cu, Al, Ca, Mg in oligotrophic bog „Zhuravlyne” (Skolivski Beskydy, Ukrainian Carpathians) was investigated. Vertical cores were sampled in 2006 and dated by 14 C method. Distribution of ash in peat slices increased considerably closer to the bog surface. Reasonable agreement exists in the comparison between the ash distribution and measurements of Al and Fe concentrations, what point to a decisive influence of aluminosilicate material formed from the rocks weathering on ash deposits. Historical trends of heavy metals levels in peat based on the absolute concentrations or their ratio to Al are identical and concomitant with the history of industrial development of Western Europe. Keywords: ombrotrophic peat bogs, heavy metals, Ukrainian Carpathians.

Differential hydrogen isotopic ratios of Sphagnum and vascular plant biomarkers in ombrotrophic peatlands as a quantitative proxy for precipitation—evaporation balance

We have developed a new approach to quantitatively reconstruct past changes in evaporation based on compound-specific hydrogen isotope ratios of vascular plant and Sphagnum biomarkers in ombrotrophic peatland sediments. We show that the contrast in H isotopic ratios of water available to living Sphagnum (top 20 cm) and in the rooting zone of peatland vascular plants can be used to estimate “ƒ”—the fraction of water remaining after evaporation. Vascular plant leaf waxes record H isotopic ratios of acrotelm water, which carries the D/H ratio signature of precipitation and is little affected by evaporation, whereas the Sphagnum biomarker, C 23 n-alkane, records H isotopic ratios of the water inside its cells and between its leaves, which is strongly affected by evaporation at the bog surface. Evaporation changes can then be deduced by comparing H isotopic ratios of the two types of biomarkers. We calibrated D/H ratios of C 23 n-alkane to source water with lab-grown Sphagnum. We also tested our isotopic model using modern surface samples from 18 ombrotrophic peatlands in the Midwestern United States. Finally, we generated a 3000-year downcore reconstruction from Minden Bog, Michigan, USA. Our new record is consistent with records of other parameters from the same peatland derived from different proxies and allows us to differentiate precipitation supply and evaporative loss.

Holocene climate variability revealed by oxygen isotope analysis of Sphagnum cellulose from Walton Moss, northern England

Stable isotope analyses of Sphagnum alpha-cellulose, precipitation and bog water from three sites across northwestern Europe (Raheenmore, Ireland, Walton Moss, northern England and Dosenmoor, northern Germany) over a total period of 26 months were used to investigate the nature of the climatic signal recorded by Sphagnum moss. The δ 18O values of modern alpha-cellulose tracked precipitation more closely than bog water, with a mean isotopic fractionation factor α cellulose-precipitation of 1.0274 ± 0.001 (1 σ) (≈27‰). Sub-samples of isolated Sphagnum alpha-cellulose were subsequently analysed from core WLM22, Walton Moss, northern England yielding a Sphagnum-specific isotope record spanning the last 4300 years. The palaeo-record, calibrated using the modern data, provides evidence for large amplitude variations in the estimated oxygen isotope composition of precipitation during the mid- to late Holocene. Estimates of palaeotemperature change derived from statistical relationships between modern surface air temperatures and δ 18O precipitation values for the British Isles give unrealistically large variation in comparison to proxies from other archives. We conclude that use of such relationships to calibrate mid-latitude palaeo-data must be undertaken with caution. The δ 18O record from Sphagnum cellulose was highly correlated with a palaeoecologically-derived index of bog surface wetness (BSW), suggesting a common climatic driver.

Vegetational response to human colonisation of the coastal and volcanic environments of Ketilsstaðir, southern Iceland

Tephra-dated, high-resolution pollen profiles from Ketilsstaðir, southern Iceland, indicate a largely unwooded pre-settlement environment, a probable consequence of the exposed coastal location. The degree of change associated with the Norse landnám is more limited than in many Icelandic pollen diagrams. There are three main periods of change in the post-settlement vegetational development of the area. Firstly, Norse settlement affected the hydrology of the bog, resulting in the near-disappearance of Sphagnum and agricultural activity led to a reduction of some species (e.g. Angelica spp. and, Salix). Secondly, the establishment of probable permanent settlement in the mid-11th century AD initiated expansion of such apophytic taxa as Plantago spp. Lactuceae, Ranunculus spp. and Pteridophytes. Thirdly, the ≥ 10 cm thick Katla tephra, deposited in AD 1357, enhanced drainage of the bog surface, favouring dryland taxa (e.g. Poaceae, Galium and Lactuceae). The tephra deposit and the associated drainage probably caused or contributed to the local extinction of the wetland beetle Hydraena britteni. The study has enabled a series of natural and humanly-related issues to be addressed including tephra-vegetation relationships, the anthropogenic reduction in plant diversity, and comparisons between historical and environmental settlement records.

Climate drivers for peatland palaeoclimate records

Reconstruction of hydroclimate variability is an important part of understanding natural climate change on decadal to millennial timescales. Peatland records reconstruct 'bog surface wetness’ (BSW) changes, but it is unclear whether it is a relative dominance of precipitation or temperature that has driven these variations over Holocene timescales. Previously, correlations with instrumental climate data implied that precipitation is the dominant control. However, a recent chironomid inferred July temperature record suggested temperature changes were synchronous with BSW over the mid-late Holocene. This paper provides new analyses of these data to test competing hypotheses of climate controls on bog surface wetness and discusses some of the distal drivers of large-scale spatial patterns of BSW change. Using statistically based estimates of uncertainty in chronologies and proxy records, we show a correlation between Holocene summer temperature and BSW is plausible, but that chronologies are insufficiently precise to demonstrate this conclusively. Simulated summer moisture deficit changes for the last 6000 years forced by temperature alone are relatively small compared with observations over the 20th century. Instrumental records show that summer moisture deficit provides the best explanatory variable for measured water table changes and is more strongly correlated with precipitation than with temperature in both Estonia and the UK. We conclude that BSW is driven primarily by precipitation, reinforced by temperature, which is negatively correlated with precipitation and therefore usually forces summer moisture deficit in the same direction. In western Europe, BSW records are likely to be forced by changes in the strength and location of westerlies, linked to large-scale North Atlantic ocean and atmospheric circulation.

Methane emission from the oligotrophic bog massif in the Northwestern Russia

Results of measuring methane emissions from the Lammin-Suo oligotrophic bog massif are considered. It is shown that emission intensity depends on the methane transport from the active layer of the peat bed. The highest emission intensity is observed in the sedge-sphagnum microlandscape and over swampy hollows of the hummock-ridge complex. It is found that the methane flux intensity approaches zero when the wetland level drops by 30–35 cm from the bog surface. Spatial methane emission variability is estimated within dominating bog landscapes. The methane emission reaches its maximum values (207%) in microlandscapes with oriented microrelief (hummock-ridge complex); in the central bog (sphagnum-suffrutescent-cottongrass landscape afforested with pine), it reaches its lowest level (76%). A model of methane emissions from bogs is developed. The model has been verified from the observational data. The comparison of model calculations with experimental data is indicative of their good agreement, which makes it possible to use the model in different calculations and assessments of the influence of natural factors on the methane emission intensity.