Plant functional types define magnitude of drought response in peatland CO2 exchange
Kuiper, J.J. ; Mooij, W.M. ; Bragazza, L. ; Robroek, B.J.M. - \ 2014
Ecology 95 (2014)1. - ISSN 0012-9658 - p. 123 - 131.
sphagnum mosses - nitrogen availability - removal experiment - species-diversity - moisture controls - water-content - carbon - ecosystems - grassland - bog
Peatlands are important sinks for atmospheric carbon (C), yet the role of plant functional types (PFTs) for C sequestration under climatic perturbations is still unclear. A plant-removal experiment was used to study the importance of vascular PFTs for the net ecosystem CO2 exchange (NEE) during (i.e., resistance) and after (i.e., recovery) an experimental drought. The removal of PFTs caused a decrease of NEE, but the rate differed between microhabitats (i.e., hummocks and lawns) and the type of PFTs. Ericoid removal had a large effect on NEE in hummocks, while the graminoids played a major role in the lawns. The removal of PFTs did not affect the resistance or the recovery after the experimental drought. We argue that the response of Sphagnum mosses (the only PFT present in all treatments) to drought is dominant over that of coexisting PFTs. However, we observed that the moment in time when the system switched from C sink to C source during the drought was controlled by the vascular PFTs. In the light of climate change, the shifts in species composition or even the loss of certain PFTs are expected to strongly affect the future C dynamics in response to environmental stress.
Carbon accumulation in peat deposits from northern Sweden to northern Germany during the last millennium
Linden, M. van der; Heijmans, M.M.P.D. ; Geel, B. van - \ 2014
Holocene 24 (2014)9. - ISSN 0959-6836 - p. 1117 - 1125.
climate-change - human impact - bog - sphagnum - temperature - rates - vegetation - peatlands - growth - ams
Historic carbon accumulation rates in four bogs on a north to south transect from Sweden to Germany were calculated by using the bulk densities and carbon concentrations of 1-cm peat layers and a fine-resolution radiocarbon chronology. Carbon accumulation rates were compared to environmental data to explore the effects of climatic factors. Carbon accumulation rates in a period without clear human impact on the bog ecosystems (c.ad 1700–ad 1800) ranged from 25 g C/m2/yr in the most northern site to 50 g C/m2/yr in the southernmost site, which coincided with increasing annual temperatures from north to south. This suggests that temperature or growing season length is a major factor influencing carbon accumulation rates at different geographical sites. The temporal variations in carbon accumulation rates within the sites tentatively suggest that carbon accumulation rates may still increase with further warming in northern peat bogs, but decrease in southern peat bogs.
Can frequent precipitation moderate the impact of drought on peatmoss carbon uptake in northern peatlands?
Nijp, J.J. ; Limpens, J. ; Metselaar, K. ; Zee, S.E.A.T.M. van der; Berendse, F. ; Robroek, B.J.M. - \ 2014
New Phytologist 203 (2014)1. - ISSN 0028-646X - p. 70 - 80.
sphagnum mosses - climate-change - water-content - co2 exchange - soil respiration - vegetation - accumulation - desiccation - boreal - bog
Northern peatlands represent a large global carbon store that can potentially be destabilized by summer water table drawdown. Precipitation can moderate the negative impacts of water table drawdown by rewetting peatmoss (Sphagnum spp.), the ecosystem's key species. Yet, the frequency of such rewetting required for it to be effective remains unknown. We experimentally assessed the importance of precipitation frequency for Sphagnum water supply and carbon uptake during a stepwise decrease in water tables in a growth chamber. CO2 exchange and the water balance were measured for intact cores of three peatmoss species (Sphagnum majus, Sphagnum balticum and Sphagnum fuscum) representative of three hydrologically distinct peatland microhabitats (hollow, lawn and hummock) and expected to differ in their water table–precipitation relationships. Precipitation contributed significantly to peatmoss water supply when the water table was deep, demonstrating the importance of precipitation during drought. The ability to exploit transient resources was species-specific; S. fuscum carbon uptake increased linearly with precipitation frequency for deep water tables, whereas carbon uptake by S. balticum and S. majus was depressed at intermediate precipitation frequencies. Our results highlight an important role for precipitation in carbon uptake by peatmosses. Yet, the potential to moderate the impact of drought is species-specific and dependent on the temporal distribution of precipitation.
High-Calorific Biogas Production by Selective CO2 Retention at Autogenerated Biogas Pressures up to 20 Bar
Lindeboom, R.E.F. ; Weijma, J. ; Lier, J.B. van - \ 2012
Environmental Science and Technology 46 (2012)3. - ISSN 0013-936X - p. 1895 - 1902.
anaerobic-digestion - methane enrichment - thermodynamic model - waste-water - low ph - solubility - bacteria - sludge - energy - bog
Autogenerative high pressure digestion (AHED) is a novel configuration of anaerobic digestion, in which micro-organisms produce autogenerated biogas pressures up to 90 bar with >90% CH4-content in a single step reactor. The less than 10% CO2-content was postulated to be resulting from proportionally more CO2 dissolution relative to CH4 at increasing pressure. However, at 90 bar of total pressure Henry's law also predicts dissolution of 81% of produced CH4. Therefore, in the present research we studied whether CO2 can be selectively retained in solution at moderately high pressures up to 20 bar, aiming to produce high-calorific biogas with >90% methane. Experiments were performed in an 8 L closed fed-batch pressure digester fed with acetate as the substrate. Experimental results confirmed CH4 distribution over gas and liquid phase according to Henry's law, but the CO2-content of the biogas was only 1-2%, at pH 7, that is, much lower than expected. By varying the ratio between acid neutralizing capacity (ANC) and total inorganic carbon (TICproduced) of the substrate between 0 and 1, the biogas CO2-content could be controlled independently of pressure. However, by decreasing the ANC relative to the TICproduced CO2 accumulation in the aqueous medium caused acidification to pH 5, but remarkably, acetic acid was still converted into CH4 at a rate comparable to neutral conditions.
Holocene vegetation and hydrologic changes inferred from molecular vegetation markers in peat, Penido Vello (Galicia, Spain)
Schellekens, J. ; Buurman, P. ; Fraga, I. ; Martinez-Cortizas, A. - \ 2011
Palaeogeography Palaeoclimatology Palaeoecology 299 (2011)1-2. - ISSN 0031-0182 - p. 56 - 69.
climate-change - atmospheric pb - proxy climate - bog - reconstruction - precipitation - temperature - deposition - millennia - pollen
Peat molecular chemistry reflects a combination of plant input and decomposition. Both vegetation community and the degree of decomposition of plant remains are highly dependent on depth and fluctuation of the water table and thus peat organic matter (OM) chemistry reflects past hydrological conditions. Changes in hydrology according to the OM composition (by pyrolysis-gas chromatography/mass spectrometry, pyrolysis-GC/MS) in a high-resolution sampled monolith of an 8000 years old peat deposit are presented. Analysis of 18 modern vegetation species resulted in molecular markers for Erica spp., Deschampsia flexuosa, Juncus bulbosus and Carex binervis, in addition to more general markers which enabled differentiation between woody, grass and moss vegetation. Factor analysis of 106 pyrolysis products quantified for all peat samples enabled identification of mineral (Factor 1) and hydrological (Factor 2) conditions of the bog. Depth profiles of vegetation markers showed good agreement with those of the scores of both factors and enabled the identification of 14 relatively wet periods, dating to 1430-1865 AD, 930-1045 AD, 640 AD, 270-385 AD, 190-215 AD, 135 AD, 45 BC-15 AD, 260-140 BC, 640-440 BC, 1055-960 BC, 1505-1260 BC, 2300 BC, 41902945 BC and 5700-5205 BC, which show excellent agreement with other palaeoclimatic studies in Europe. The results emphasize the importance of high-resolution sampling, in combination with the use of multiple vegetation markers and other peat OM characteristics for a proper interpretation of a peat record.
n-Alkane distributions as palaeoclimatic proxies in ombrotrophic peat: The role of decomposition and dominant vegetation
Schellekens, J. ; Buurman, P. - \ 2011
Geoderma 164 (2011)3-4. - ISSN 0016-7061 - p. 112 - 121.
organic-matter sources - holocene climate - pyrolysis-gc/ms - lipid biomarker - south-america - bog - stratigraphy - indicators - sphagnum - origin
n-Alkane distributions are frequently used as palaeoclimate proxies in ombrotrophic peat deposits. Although n-alkane distributions differ strongly between plant species, n-alkanes are not species-specific molecules. For a proper interpretation, it is important to understand the different abundances of n-alkanes in various plant species as well as the changes that occur when plant litter is transformed to peat. In particular because molecular markers are especially valuable in highly decomposed peat where plant remains are no longer recognizable, it is important to understand the effects of decomposition on n-alkane distributions. The organic matter (OM) of a high-resolution sampled, 9 m thick, ombrotrophic peat deposit from Tierra del Fuego was analysed with pyrolysis-gas chromatography/mass spectrometry (pyrolysis-GC/MS). The same samples were analysed for carbon (C) and nitrogen (N) content. Depth profiles of C:N ratio, the summed lignin and summed polysaccharide pyrolysis products, and markers specific for Sphagnum spp., Empetrum rubrum and Nothofagus antarctica, enabled a reconstruction of changes in vegetation composition to be made. This reconstruction was used to examine the validity of the n-C23 alkane to indicate Sphagnum and the summed long chain n-alkanes (C29 and C31) to reflect leaf input of the woody species E. rubrum and N. antarctica. Our results show that even in Sphagnum-dominated peat, the n-alkane distribution is not determined by Sphagnum but by leaf input of E. rubrum and N. antarctica. However, good correlations between the n-C23 alkane and the Sphagnum marker 4-isopropenylphenol, and between the summed n-C29 and n-C31 alkanes and the marker of N. antarctica support that their relative change with depth can be used to indicate the abundance of these species in Sphagnum-dominated peat. In peat with relatively low contributions of Sphagnum, both n-alkane proxies (C23 and C29 + C31) reflect the degree of decomposition. We evaluated the influence of Sphagnum dominance, decomposition, and pyrolysis on the n-alkane distributions in peat OM
Resource contrast in patterned peatlands increases along a climatic gradient
Eppinga, M.B. ; Rietkerk, M. ; Belyea, L.R. ; Nilsson, M.B. ; Ruiter, P.C. de; Wassen, M.J. - \ 2010
Ecology 91 (2010). - ISSN 0012-9658 - p. 2344 - 2355.
boreal mire - ecosystems - phosphorus - vegetation - nitrogen - wetlands - bog - plants - temperature - mechanisms
Spatial patterning of ecosystems can be explained by several mechanisms. One approach to disentangling the influence of these mechanisms is to study a patterned ecosystem along a gradient of environmental conditions. This study focused on hummock–hollow patterning of peatlands. Previous models predicted that patterning in drainage-dominated peatlands is driven by a peat-accumulation mechanism, reflected by higher nutrient availability in hollows relative to hummocks. Alternatively, patterning in evapotranspiration (ET)-dominated peatlands may be driven by a nutrient-accumulation mechanism, reflected by reversed nutrient distribution, namely, higher nutrient availability in hummocks relative to hollows. Here, we tested these predictions by comparing nutrient distributions among patterned peatlands in maritime (Scotland), humid temperate (Sweden), and humid continental (Siberia) climates. The areas comprise a climatic gradient from very wet and drainage-dominated (Scotland) to less wet and ET-dominated (Siberia) peatlands. Nutrient distribution was quantified as resource contrast, a measure for hummock–hollow difference in nutrient availability. We tested the hypothesis that the climatic gradient shows a trend in the resource contrast; from negative (highest nutrient availability in hollows) in Scotland to positive (highest nutrient availability in hummocks) in Siberia. The resource contrasts as measured in vegetation indeed showed a trend along the climatic gradient: contrasts were negative to slightly positive in Scotland, positive in Sweden, and strongly positive in Siberia. This finding corroborates the main prediction of previous models. Our results, however, also provided indications for further model development. The low concentrations of nutrients in the water suggest that existing models could be improved by considering both the dissolved and adsorbed phase and explicit inclusion of both nutrient-uptake and nutrient-storage processes. Our study suggests that future climate change may affect the ecosystem functioning of patterned peatlands by altering the contribution of pattern-forming mechanisms to redistribution of water and nutrients within these systems
Sphagnum re-introduction in degraded peatlands: the effects of aggregation, species and water table
Robroek, B.J.M. ; Ruijven, J. van; Schouten, M.G.C. ; Breeuwer, A.J.G. ; Crushell, P.H. ; Berendse, F. ; Limpens, J. - \ 2009
Basic and Applied Ecology 10 (2009)8. - ISSN 1439-1791 - p. 697 - 706.
experimental plant-communities - interspecific competition - vascular plants - growth - bog - mosses - heterogeneity - restoration - vegetation - dynamics
In European peatlands which have been drained and cut-over in the past, re-vegetation often stagnates after the return of a species-poor Sphagnum community. Re-introduction of currently absent species may be a useful tool to restore a typical, and more diverse, Sphagnum vegetation and may ultimately improve the functioning of peatland ecosystems, regarding atmospheric carbon sequestration. Yet, the factors controlling the success of re-introduction are unclear. In Ireland and Estonia, we transplanted small and large aggregates of three Sphagnum species into existing vegetation. We recorded changes in cover over a 3-year period, at two water levels (¿5 and ¿20 cm). Performance of transplanted aggregates of Sphagnum was highly species specific. Hummock species profited at low water tables, whereas hollow species profited at high water tables. But our results indicate that performance and establishment of species was also promoted by increased aggregate size. This mechanism (positive self-association) has earlier been seen in other ecosystems, but our results are the first to show this mechanism in peatlands. Our results do not agree with present management, which is aimed at retaining water on the surface of peat remnants in order to restore a functional and diverse Sphagnum community. More than the water table, aggregate size of the reintroduced species is crucial for species performance, and ultimately for successful peatland restoration.
Towards spatial assessment of carbon sequestration in peatlands: spectroscopy based estimation of fractional cover of three plant functional types
Schaepman-Strub, G. ; Limpens, J. ; Menken, M. ; Bartholomeus, H. ; Schaepman, M.E. - \ 2009
Biogeosciences 6 (2009)2. - ISSN 1726-4170 - p. 275 - 284.
spectral reflectance measurements - growth forms - vegetation - sphagnum - leaf - boreal - bog - accumulation - stress
Peatlands accumulated large carbon (C) stocks as peat in historical times. Currently however, many peatlands are on the verge of becoming sources with their C sequestration function becoming sensitive to environmental changes such as increases in temperature, decreasing water table and enhanced nitrogen deposition. Long term changes in vegetation composition are both, a consequence and indicator of future changes in C sequestration. Spatial continuous accurate assessment of the vegetation composition is a current challenge in keeping a close watch on peatland vegetation changes. In this study we quantified the fractional cover of three major plant functional types (PFTs; Sphagnum mosses, graminoids, and ericoid shrubs) in peatlands, using field spectroscopy reflectance measurements (400-2400 nm) on 25 plots differing in PFT cover. The data was validated using point intercept methodology on the same plots. Our results showed that the detection of open Sphagnum versus Sphagnum covered by vascular plants (shrubs and graminoids) is feasible with an R-2 of 0.81. On the other hand, the partitioning of the vascular plant fraction into shrubs and graminoids revealed lower correlations of R-2 of 0.54 and 0.57, respectively. This study was based on a dataset where the reflectance of all main PFTs and their pure components within the peatland was measured at local spatial scales. Spectrally measured species or plant community abundances can further be used to bridge scaling gaps up to canopy scale, ultimately allowing upscaling of the C balance of peatlands to the ecosystem level.
Swift recovery of Sphagnum nutrient concentrations after excess supply
Limpens, J. ; Heijmans, M.M.P.D. - \ 2008
Oecologia 157 (2008)1. - ISSN 0029-8549 - p. 153 - 161.
atmospheric nitrogen deposition - vascular plants - phosphorus availability - boreal forest - vegetation - growth - bog - fertilization - resorption - mosses
Although numerous studies have addressed the effects of increased N deposition on nutrient-poor environments such as raised bogs, few studies have dealt with to what extent, and on what time-scale, reductions in atmospheric N supply would lead to recovery of the ecosystems in question. Since a considerable part of the negative effects of elevated N deposition on raised bogs can be related to an imbalance in tissue nutrient concentrations of the dominant peat-former Sphagnum, changes in Sphagnum nutrient concentration after excess N supply may be used as an early indicator of ecosystem response. This study focuses on the N and P concentrations of Sphagnum magellanicum and Sphagnum fallax before, during and after a factorial fertilization experiment with N and P in two small peatlands subject to a background bulk deposition of 2 g N m(-2) year(-1). Three years of adding N (4.0 g N m(-2) year(-1)) increased the N concentration, and adding P (0.3 g P m(-2) year(-1)) increased the P concentration in Sphagnum relative to the control treatment at both sites. Fifteen months after the nutrient additions had ceased, N concentrations were similar to the control whereas P concentrations, although strongly reduced, were still slightly elevated. The changes in the N and P concentrations were accompanied by changes in the distribution of nutrients over the capitulum and the stem and were congruent with changes in translocation. Adding N reduced the stem P concentration, whereas adding P reduced the stem N concentration in favor of the capitulum. Sphagnum nutrient concentrations quickly respond to reductions in excess nutrient supply, indicating that a management policy aimed at reducing atmospheric nutrient input to bogs can yield results within a few years.
Peat–water interrelationships in a tropical peatland ecosystem in Southeast Asia
Wösten, J.H.M. ; Clymans, E. ; Page, S.E. ; Rieley, J.O. ; Limin, S.H. - \ 2008
Catena 73 (2008)2. - ISSN 0341-8162 - p. 212 - 224.
climate-change - kalimantan - indonesia - forests - fires - bog
Interrelationships between peat and water were studied using a hydropedological modelling approach for adjacent relatively intact and degraded peatland in Central Kalimantan, Indonesia. The easy to observe degree of peat humification provided good guidance for the assignment of more difficult to measure saturated hydraulic conductivities to the acrotelm¿catotelm hydrological system. Ideally, to prevent subsidence and fire, groundwater levels should be maintained between 40 cm below and 100 cm above the peat surface. Calculated groundwater levels for different years and for different months within a single year showed that these levels can drop deeper than the critical threshold of 40 cm below the peat surface whilst flooding of more than 100 cm above the surface was also observed. In July 1997, a dry El Niño year, areas for which deep groundwater levels were calculated coincided with areas that were on fire as detected from radar images. The relatively intact peatland showed resilience towards disturbance of its hydrological integrity whereas the degraded peatland was susceptible to fire. Hydropedological modelling identified areas with good restoration potential based on predicted flooding depth and duration. Groundwater level prediction maps can be used in fire hazard warning systems as well as in land utilization and restoration planning. These maps are also attractive tools to move from the dominant uni-sectoral approach in peatland resource management toward a much more promising multi-sectoral approach involving various forestry, agriculture and environment agencies. It is demonstrated that the combination of hydrology and pedology is essential for wise use of valuable but threatened tropical peatland ecosystems.
The effect of temperature on growth and competition between Sphagnum species
Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Robroek, B.J.M. ; Berendse, F. - \ 2008
Oecologia 156 (2008)1. - ISSN 0029-8549 - p. 155 - 167.
interspecific competition - litter quality - tussock tundra - climate-change - water-level - mosses - bog - decomposition - mire - photosynthesis
Peat bogs play a large role in the global sequestration of C, and are often dominated by different Sphagnum species. Therefore, it is crucial to understand how Sphagnum vegetation in peat bogs will respond to global warming. We performed a greenhouse experiment to study the effect of four temperature treatments (11.2, 14.7, 18.0 and 21.4°C) on the growth of four Sphagnum species: S. fuscum and S. balticum from a site in northern Sweden and S. magellanicum and S. cuspidatum from a site in southern Sweden. In addition, three combinations of these species were made to study the effect of temperature on competition. We found that all species increased their height increment and biomass production with an increase in temperature, while bulk densities were lower at higher temperatures. The hollow species S. cuspidatum was the least responsive species, whereas the hummock species S. fuscum increased biomass production 13-fold from the lowest to the highest temperature treatment in monocultures. Nutrient concentrations were higher at higher temperatures, especially N concentrations of S. fuscum and S. balticum increased compared to field values. Competition between S. cuspidatum and S. magellanicum was not influenced by temperature. The mixtures of S. balticum with S. fuscum and S. balticum with S. magellanicum showed that S. balticum was the stronger competitor, but it lost competitive advantage in the highest temperature treatment. These findings suggest that species abundances will shift in response to global warming, particularly at northern sites where hollow species will lose competitive strength relative to hummock species and southern species.
Variability of annual CO2 exchange from Dutch grasslands
Jacobs, C.M.J. ; Jacobs, A.F.G. ; Bosveld, F.C. ; Hendriks, D.M.D. ; Hensen, A. ; Kroon, P. ; Moors, E.J. ; Nol, L. ; Schrier-Uijl, A.P. ; Veenendaal, E.M. - \ 2007
Biogeosciences 4 (2007)5. - ISSN 1726-4170 - p. 803 - 816.
netto ecosysteem uitwisseling - kooldioxide - graslanden - nederland - net ecosystem exchange - carbon dioxide - grasslands - netherlands - greenhouse-gas balance - carbon-dioxide - water-vapor - flux densities - annual sums - respiration - temperature - soil - bog
An intercomparison is made of the Net Ecosystem Exchange of CO2, NEE, for eight Dutch grassland sites: four natural grasslands, two production grasslands and two meteorological stations within a rotational grassland region. At all sites the NEE was determined during at least 10 months per site, using the eddy-covariance (EC) technique, but in different years. The NEE does not include any import or export other than CO2. The photosynthesis-light response analysis technique is used along with the respiration-temperature response technique to partition NEE into Gross Primary Production (GPP) and Ecosystem Respiration (Re) and to obtain the eco-physiological characteristics of the sites at the field scale. Annual sums of NEE, GPP and Re are then estimated using the fitted response curves with observed radiation and air temperature from a meteorological site in the centre of The Netherlands as drivers. These calculations are carried out for four years (2002–2005). Land use and management histories are not considered. The estimated annual Re for all individual sites is more or less constant per site and the average for all sites amounts to 1390±30 gC m−2 a−1. The narrow uncertainty band (±2%) reflects the small differences in the mean annual air temperature. The mean annual GPP was estimated to be 1325 g C m−2 a−1, and displays a much higher standard deviation, of ±110 gC m−2 a−1 (8%), which reflects the relatively large variation in annual solar radiation. The mean annual NEE amounts to –65±85 gC m−2 a−1. From two sites, four-year records of CO2 flux were available and analyzed (2002–2005). Using the weather record of 2005 with optimizations from the other years, the standard deviation of annual GPP was estimated to be 171–206 gC m−2 a−1 (8–14%), of annual Re 227–247 gC m−2 a−1 (14–16%) and of annual NEE 176–276 gC m−2 a−1. The inter-site standard deviation was higher for GPP and Re, 534 gC m−2 a−1 (37.3%) and 486 gC m−2 a−1 (34.8%), respectively. However, the inter-site standard deviation of NEE was similar to the interannual one, amounting to 207 gC m−2 a−1. Large differences occur due to soil type. The grasslands on organic (peat) soils show a mean net release of CO2 of 220±90 g C m−2 a−1 while the grasslands on mineral (clay and sand) soils show a mean net uptake of CO2 of 90±90 g C m−2 a−1. If a weighing with the fraction of grassland on organic (20%) and mineral soils (80%) is applied, an average NEE of 28 ±90 g C m−2 a−1 is found. The results from the analysis illustrate the need for regionally specific and spatially explicit CO2 emission estimates from grassland.
An intercomparison is made of the Net Ecosystem Exchange of CO2, NEE, for eight Dutch grassland sites: four natural grasslands, two production grasslands and two meteorological stations within a rotational grassland region. At all sites the NEE was determined during at least 10 months per site, using the eddy-covariance (EC) technique, but in different years. The NEE does not include any import or export other than CO2. The photosynthesis-light response analysis technique is used along with the respiration-temperature response technique to partition NEE into Gross Primary Production (GPP) and Ecosystem Respiration (R-e) and to obtain the eco-physiological characteristics of the sites at the field scale. Annual sums of NEE, GPPand R-e are then estimated using the fitted response curves with observed radiation and air temperature from a meteorological site in the centre of The Netherlands as drivers. These calculations are carried out for four years (2002-2005). Land use and management histories are not considered. The estimated annual R-e for all individual sites is more or less constant per site and the average for all sites amounts to 1390 +/- 30 gC m(-2) a(-1). The narrow uncertainty band (+/- 2%) reflects the small differences in the mean annual air temperature. The mean annual GPP was estimated to be 1325 g C m(-2) a(-1), and displays a much higher standard deviation, of +/- 110 gC m(-2) a(-1) (8%), which reflects the relatively large variation in annual solar radiation. The mean annual NEE amounts to -65 +/- 85 gC m(-2) a(-1). From two sites, four-year records of CO2 flux were available and analyzed (2002-2005). Using the weather record of 2005 with optimizations from the other years, the standard deviation of annual GPP was estimated to be 171-206 gC m(-2) a(-1) (8-14%), of annual R-e 227-247 gC m(-2) a(-1)(14-16%) and of annual NEE 176-276 gC m(-2) a(-1). The inter-site standard deviation was higher for GPP and R-e, 534 gC m(-2) a(-1) (37.3%) and 486 gC m(-2) a(-1) (34.8%), respectively. However, the inter-site standard deviation of NEE was similar to the interannual one, amounting to 207 gC m-2a-1. Large differences occur due to soil type. The grasslands on organic (peat) soils show a mean net release of CO2 of 220 +/- 90 g C m(-2) a(-1) while the grasslands on mineral (clay and sand) soils show a mean net uptake of CO2 of 90 +/- 90 g C m(-2) a(-1). If a weighing with the fraction of grassland on organic (20%) and mineral soils (80%) is applied, an average NEE of 28 +/- 90 g C m(-2) a(-1) is found. The results from the analysis illustrate the need for regionally specific and spatially explicit CO2 emission estimates from grassland.
Woodlands of the past : The excavation of wetland woods at Zwolle-Stadshagen (the Netherlands): Reconstruction of the wetland wood in its environmental context
Kooistra, M.J. ; Kooistra, L.I. ; Rijn, P. van; Sass, U.G.W. - \ 2006
Netherlands journal of geosciences 85 (2006)1. - ISSN 0016-7746 - p. 37 - 60.
landschap - bodem - geologie - archeologie - palynologie - geschiedenis - hout - overijssel - landscape - soil - geology - history - archaeology - palynology - wood - overijssel - pollen - bog - teleconnections - sections - pipette - climate - remains - holland - rise - bc
Information on the vegetation and landscape history of a region is often limited, and available data are hard to interprete. A concept is presented here on how a more comprehensive picture of the structure and development of landscapes and vegetations of the past can be gained by integrating the information of several disciplines. Archaeological field methods have been combined with methods used in landscape studies (geology, soil science, micromorphology) and vegetation studies (ecology, palynology and dendrochronology). This concept has been applied and tested during an integrated study of a buried woodland at Zwolle-Stadshagen (Province of Overijssel, the Netherlands). Many large wood remnants were found in a peat layer preserved below a thick clay deposit. The wood remnants were dated by using dendrochronology to the period between ca. 150 BC and AD 580 (ca. 2200 - 1400 cal. BP). Two phases could be distinguished in the development of the peat. The woodland consisted of a closed stand with ash, alder and oak as main species, in the first phase mostly resembling an alder carr, and in the second one the near-extinct Filipendulo-Alnetum Passage et Hofmann 1968. No evidence of exploitation of the woodland by man nor of animal foraging was found. The followed integrated procedure has led to a more substantiated reconstruction of the palaeo-environment with its wetland wood, but also of the influence of human activities on the palaeo-landscape and its woodlands, that could not have been obtained otherwise.
Buoyancy-driven flow in a peat moss layer as a mechanism for solute transport
Rappoldt, C. ; Pieters, G.J.J.M. ; Adema, E.B. ; Baaijens, G.J. ; Grootjans, A.P. ; Duijn, C.J. van - \ 2003
Proceedings of the National Academy of Sciences of the United States of America 100 (2003)25. - ISSN 0027-8424 - p. 14937 - 14942.
horizontal porous layer - boundary-conditions - large peatlands - sphagnum - stability - carbon - modulation - convection - growth - bog
Transport of nutrients, CO2, methane, and oxygen plays an important ecological role at the surface of wetland ecosystems. A possibly important transport mechanism in a water-saturated peat moss layer (usually Sphagnum cuspidatum) is nocturnal buoyancy flow, the downward flow of relatively cold surface water, and the upward flow of warm water induced by nocturnal cooling. Mathematical stability analysis showed that buoyancy flow occurs in a cooling porous layer if the system¿s Rayleigh number (Ra) exceeds 25. For a temperature difference of 10 K between day and night, a typical Ra value for a peat moss layer is 80, which leads to quickly developing buoyancy cells. Numerical simulation demonstrated that fluid flow leads to a considerable mixing of water. Temperature measurements in a cylindrical peat sample of 50-cm height and 35-cm diameter were in agreement with the theoretical results. The nocturnal flow and the associated mixing of the water represent a mechanism for solute transport in water-saturated parts of peat land and in other types of terrestrializing vegetation. This mechanism may be particularly important in continental wetlands, where Ra values in summer are often much larger than the threshold for fluid flow. The upper part of a living mire consists of a sponge-like layer of predominantly moss species, the acrotelm (1), with a porosity above 95%. The green and brownish plants near the surface (Fig. 1) intercept light and fix CO2. Further down, the older plants turn yellow and start to decay. Aerobic decay in the acrotelm takes place relatively rapidly and makes nutrients available for recycling. Below the acrotelm, a denser layer, the catotelm, is present, where the hydraulic conductivity is much lower than in the acrotelm (2), and where the decay rate is several orders of magnitude smaller due to the anoxic conditions (3). It is the peat formation (4, 5) in the slowly growing catotelm that represents a sink of atmospheric CO2 (5, 6). The production of organic matter at the surface largely depends on the recycling of nutrients originating from decomposing plant material. Because decomposition and photosynthesis take place at different depths, the transport of oxygen, carbon compounds, and nutrients forms an important element in the functioning of the mire ecosystem. This transport takes place both inside (7) and outside the plants by diffusion and fluid flow. In this paper, we investigate a mechanism for fluid flow in a water-saturated peat moss layer, which does not depend on capillarity or an external hydraulic pressure. During the night, the surface cools, leading to relatively cold water on top of warm water, and if the temperature drop is sufficiently large, the cold water sinks and the warm water rises. This type of flow is called buoyancy flow, and it implies convective transport of the heat and solutes carried with the water. Buoyancy flow often occurs as ``cells¿¿ consisting of adjacent regions with upward and downward flow. We studied the phenomenon in a peat moss layer by means of a mathematical model, numerical simulation, and laboratory measurements.