Fen Sites Research Articles

Long‐term drainage for forestry inhibits extracellular phenol oxidase activity in Finnish boreal mire peat

Drainage for forestry has been amongst the most extensive of land management practices applied to northern latitude peatlands, particularly in northern Europe. Extracellular phenol oxidases play an important role in the carbon cycle of soils. This study investigated the effects of long‐term (45 years) drainage for forestry upon surface peat extracellular phenol oxidase activity, soluble phenolic concentrations and pH at ombrotrophic bog, oligotrophic fen and mesotrophic fen sites at a Finnish mire complex. Phenol oxidase activity was reduced by drainage at all three sites. Phenol oxidase activity was positively correlated with peat pH across all sites irrespective of drainage treatment, suggesting that pH is a major factor influencing peat phenol oxidase activity at the mire complex. Peat pH became more acidic with drainage at the fen sites, and it is likely that this contributed to the suppression of peat phenol oxidase activity. The reduction of peat phenol oxidase activity with drainage was accompanied by increased concentrations of water‐soluble phenolics at all three sites, and the potential contribution of this to changes in peat carbon stocks following drainage is discussed.

Dependence of volume (oven dry weight) of harvesting residues on forest site type

Kasvukohatingimuste mõju raiejäätmete kuivmassile To limit the emissions of greenhouse gases the wider utilization of renewable energy is mandatory for all EU countries. The aim of the present study was to estimate the potential quantities of harvesting residues as a source of renewable fuel. The sample plots were selected to cover the majority of site types. Based on the characteristics of the stand and the weight of the harvesting residues from different site types 2 formulas of linear regression were composed. As a result it was determined that depending on the forest site type the oven dry weight of harvesting residues per m3 of the stem varies from 22 m3/ha (bog whortleberry site type) to 144 m3/ha (alder fen site type). If to consider the average bulk density to be 500 kg/m3, the share of harvesting residues from the volume of the stand varies from 4.4 to 28.8%.

Evapotranspiration in intermediate‐aged and mature fens and upland black spruce boreal forests

AbstractThe Canadian boreal forest consists of a mosaic of landscapes of varying soil drainage and forest age driven by wildfire. The hydrological consequences are complicated by plant responses to soil moisture and forest age, both potentially influencing evapotranspiration. Evapotranspiration was measured using the energy balance residual technique in 2006 and 2007 at forested upland and fen sites that originated following fire in 1964, 1930 and about 1850, near Thompson, Manitoba, Canada. Both net radiation and sensible heat flux density were greater at the older sites than those at the younger sites. Evapotranspiration was also greater at the older sites by between 4 and 19% for the 1930–1964 comparison, and 15% for the 1930–1850 comparison. There was no difference in net radiation between upland and fen sites of the same age, although upland sites had a higher sensible heat flux density. Albedo was greater at the fen sites. Evapotranspiration was greater at the upland sites by 11–20%, likely driven by greater leaf area at the upland sites. These intermediate to mature boreal forest sites still show the persistence of the impact of fire, and it is clear that changes in drainage and local hydrology will also have an impact on local evapotranspiration. The implication is that even these small changes in evapotranspiration can have a great regional and global effect because of the large land area of the boreal forest. Copyright © 2009 John Wiley & Sons, Ltd.

N2O concentration and isotope signature along profiles provide deeper insight into the fate of N2O in soils†

Nitrous oxide is an important greenhouse gas and its origin and fate are thus of broad interest. Most studies on emissions of nitrous oxide from soils focused on fluxes between soil and atmosphere and hence represent an integration of physical and biological processes at different depths of a soil profile. Analysis of N2O concentration and isotope signature along soil profiles was suggested to improve the localisation of sources and sinks in soils as well as underlying processes and could therefore extend our knowledge on processes affecting surface N2O fluxes. Such a mechanistic understanding would be desirable to improve N2O mitigation strategies and global N2O budgets. To investigate N2O dynamics within soil profiles of two contrasting (semi)natural ecosystem types (a temperate acidic fen and a Norway spruce forest), soil gas samplers were constructed to meet the different requirements of a water-saturated and an unsaturated soil, respectively. The samplers were installed in three replicates and allowed soil gas sampling from six different soil depths. We analysed soil air for N2O concentration and isotope composition and calculated N2O net turnover using a mass balance approach and considering diffusive fluxes. At the fen site, N2O was mainly produced in 30–50 cm soil depth. Diffusion to adjacent layers above and below indicated N2O consumption. Values of δ15N and δ18O of N2O in the fen soil were always linearly correlated and their qualitative changes within the profile corresponded with the calculated turnover processes, suggesting further reduction of N2O. In the spruce forest, highest N2O production occurred in the topsoil, but there was also notable production occurring in the subsoil at a depth of 70 cm. Changes in N2O isotope composition as to be expected from local production and consumption processes within the soil profile did hardly occur, though. This was presumably caused by high diffusive fluxes and comparatively low net turnover, as isotope signatures approached values measured for ambient N2O towards the topsoil. Our results demonstrate a highly variable influence of diffusive versus production/consumption processes on N2O concentration and isotope composition, depending on the type of ecosystem. This finding indicates the necessity of further N2O concentration and isotope profile investigations in different types of natural and anthropogenic ecosystems in order to generalise our mechanistic understanding of N2O exchange between soil and atmosphere. Revised version of a paper presented at the 30th Annual Meeting of the German Association for Stable Isotope Research (GASIR), 8–10 October 2007, Bayreuth, Germany.

Annual variation of temperature sensitivity of soil organic carbon decomposition in North peatlands: implications for thermal responses of carbon cycling to global warming

Temperature sensitivities of microbial respiration and dissolved organic carbon (DOC) production were investigated by using a novel method, thermal gradient (2–20°C) temperature bar, in two typical peatlands (bog and fen) in North Wales, UK over 12 months. The study indicated that temperature sensitivity of soil organic carbon decomposition in North peatlands was regulated not only by temperature but soil water content, dry–rewet event and phenologies. Potential decreases of Q10 (CO2) with increasing soil temperature were confirmed in both peatlands, but Q10 (DOC) increase with increasing soil temperature in both bog and fen sites. These results imply, if other factors such as the so-called CO2 fertilization effect are simultaneously taken into account, that the feedback of global warming induced CO2 release from peatlands to climate change may be overestimated in current biogeochemical models. However, global warming might have been nonlinearly accelerating DOC thermal production, and therefore it helps explaining the causes of remarkable increase of DOC in surface water in the Northern Hemisphere during last several decades.

Interannual Ecosystem CO2 Dynamics in The Alpine Zone of The Eastern Alps, Austria

ABSTRACTInformation about the annual carbon fluxes of fen and meadow ecosystems in alpine environments is rare. We studied the influence of photosynthetic active radiation (PAR), plant green area index (GAI), soil temperature, and water-filled pore space (wfps) on the net CO2 emission at four alpine sites (one meadow and three fen sites) differing in water balance and plant community. Measurements over two years were made in the Eastern Alps, Austria, including two snow-free periods and two snow periods. During snow-free periods, net CO2 gain during daylight periods (NEElight , PAR > 0) depended on PAR and GAI. The net CO2 emission rate at night (Rtot , PAR = 0) was positively related to soil temperature, while low wfps reduced the carbon loss via Rtot of the meadow and driest fen study site but reinforced carbon loss of the wetter fen sites. Daily average ecosystem net CO2 gain (NEEday ) during snow-free periods (averaged over both years) at the meadow was 3.5 g CO2 m−2 d−1 and ranged from 1.5 to 3.4 g CO2 m−2 d−1 at the fen sites. Mean average daily wintertime CO2 emission was low, being only −0.9 g CO2 m−2 d−1 for meadow and between −0.2 and −0.7 g CO2 m−2 d−1 for all fen sites. All sites function as significant annual net carbon sinks, with a net carbon gain from 50 to 121 g C m−2 a−1 (averaged over both years) irrespective of water balance. Our results indicate that these alpine fen sites that have built up a large carbon stock in the past do not gain a further carbon surplus compared with the meadow under the current climate.

Mollusc diversity patterns in Central European fens: hotspots and conservation priorities

AbstractAim To assess mollusc species composition and diversity patterns of treeless fen sites and to find simple environmental parameters that characterize diversity hotspots and priority sites for conservation.Location Western Carpathian Mountains, Europe.Methods Mollusc communities were sampled quantitatively from a homogeneous area of 16 m2 in the central part of each of 145 treeless fen sites. Water conductivity and pH, geographical coordinates, altitude and habitat size of the sites studied, mean annual rainfall, mean annual temperature and mean January temperature were compiled for each plot. Nestedness in species composition was tested using the binmatnest program to confirm the ‘nested habitat‐quality hypothesis’. Patterns in species diversity were analysed using the regression trees method to isolate the main predictors of species diversity.Results Nested subset patterns of species composition were found along the gradient of mineral richness. Species distribution was highly nested (Tobs = 11.21, P << 0.001) in mineral‐poor sites (with water conductivity < 300 μS cm−1, n = 42) and was highly correlated with the site’s mineral richness (rs = 0.76, P << 0.001). By contrast, species distribution and richness of mineral‐rich sites (c.≥ 300 μS cm−1, n = 103) were not controlled by mineral richness. Variation in species richness was further explained by January temperature, landscape geomorphology, and total habitat area. The southern mineral‐rich low altitude fens were the most species rich, especially those of larger total area (23 species on average). These 24 sites (17% of all sites) harboured 90% of all recorded species, including all highly endangered ones. Mineral‐rich fens in montane valleys were the second most important group because they hosted the majority of populations of two rare glacial relict species (Vertigo geyeri and Pupilla alpicola).Main conclusions The significant nestedness raises the possibility of conserving the whole fen‐mollusc species pool within the most species‐rich sites. Thus, to select the conservation priority sites, easily available site characteristics for the prediction of species richness are needed. This knowledge can help us maintain fen biodiversity, which has become closely dependent on conservation management practices after the cessation of traditional mowing of fens for haymaking.

Long‐term effects of drainage and initial effects of hydrological restoration on rich fen vegetation

AbstractQuestions: What vegetational changes does a boreal rich fen (alkaline fen) undergo during a time period of 24 years after drainage? How is plant species richness affected, and what are the changes in composition of ecological groups of species? Is it possible to recover parts of the original flora by rewetting the rich fen? Which are the initial vegetation changes in the flora after rewetting? What are the major challenges for restoration of rich fen flora after rewetting?Location: Eastern central Sweden, southern boreal vegetational zone. Previously rich fen site, drained for forestry purposes during 1978–1979. The site was hydrologically restored (rewetted) in 2002.Method: Annual vegetation survey in permanent plots during a period of 28 years.Results: There were three successional stages in the vegetational changes. In the first stage there was a rapid (< 5 years) loss of rich fen bryophytes. The second step was an increase of sedges and early successional bryophytes, which was followed by an increase of a few emerging dominants, such as Molinia caerulea, Betula pubescens and Sphagnum spp. After rewetting, there are indications of vegetation recovery, albeit at slow rates. Depending on, for instance, initial species composition different routes of vegetation change were observed in the flora after drainage, although after 24 years, species composition became more homogenous and dominated by a few species with high cover.Conclusion: Major changes have occurred after changes in the hydrology (drainage and rewetting) with a severe impact on the biodiversity among vascular plants and bryophytes. Several rich fen bryophytes respond quickly to the changes in water level (in contrast to vascular plants). The recovery after rewetting towards the original rich fen vegetation is slow, as delayed by substrate degradation, dispersal limitation and presence of dominant species.

WATER ANALYSES FROM SOME IRISH BOGS AND FENS, WITH THOUGHTS ON 'THE <i>SCHOENUS</i> PROBLEM'

WATER ANALYSES FROM SOME IRISH BOGS AND FENS, WITH THOUGHTS ON 'THE <i>SCHOENUS</i> PROBLEM'

Influence of nested groundwater systems on reduction–oxidation and alkalinity gradients with implications for plant nutrient availability in four New York fens

Summary This study compares hydrologic investigations of four New York fens designed to characterize spatial variability in groundwater flow (GWF) and the resulting hydrochemical patterns that influence plant nutrient availability. At the marl fen and two rich fen sites, hydrometric data and pore water samples collected from nested piezometers set along the GWF-path showed spatial patterns consistent with a mixing gradient established by the intersection of local (i.e., hill slope), relatively dilute groundwater discharge and mineral-rich groundwater discharged from a larger-scaled (i.e., intermediate) system. Distinct redox and carbonate gradients along the GWF-paths of three rich fens reflected strong interactions between groundwater supply of terminal electron acceptors and microbial processes affecting speciation of iron, nitrogen and phosphorus. Decreased nitrate concentrations, increased dissolved iron, and removal of sulfate along flowpaths indicated that redox conditions became more reduced as groundwater moved down-gradient. Nitrate removal occurred across the interface between the upland mineral soil and the organic-rich fen peat. Lack of ammonium accumulation indicated that denitrification limits N-supply to plants in down-gradient fen areas. Further down-gradient, sulfate-enriched groundwater discharge sustained sub-oxic conditions and enhanced phosphorus mobility through effects on iron–sulfur–phosphorus dynamics, alkalinity generation, and dissolution of mineral-bound P. In contrast, the poor fen was sustained by an isolated surficial groundwater system; a thick lacustrine clay aquitard limited intermediate or regional-scaled groundwater discharge. As a result, water table fluctuations were more responsive to short-term weather events and imposed the strongest influence on redox status. A redox gradient, evidenced by increasing iron and ammonium concentrations, extended downward with depth from the aerated peat surface. The dilute water supply and lack of additional internal alkalinity generation limited buffer capacity and decomposition. Overall, ammonium accumulation increased N-availability whereas reduced decomposition rates further limited P availability. Our results show that interaction of multiple GWF systems within the fens was the critical determinant of water table stability (rich fens) or fluctuation (poor fen), as well as the supply of dissolved ions that influence geochemical processes affecting plant nutrient availability. Together these factors accounted directly or indirectly for observed spatial patterns in redox and alkalinity gradients, which in turn controlled speciation of phosphorus-reactive minerals. Differences among fens in spatial patterns could be accounted for by differences in the geomorphometry of the basins within which the fens developed and the stratigraphy and hydraulic characteristics of underlying sediments. Results suggest that Fe–S dynamics, rather than carbonate precipitation, likely influences inorganic phosphorus pools and release mechanisms.

Design and Operability of a Large Weighable Fen Lysimeter

In principle, conventional lysimeters are suitable for the investigation of vertical water and solute fluxes. Lateral fluxes in water-saturated fen sites are characterized by heterogeneities and abnormities due to anisotropic layering. But due to lack of adequate monitoring techniques, these fluxes have been insufficiently analyzed. The newly developed large weighable fen lysimeter (LWFL) overcomes the limitations of conventional lysimetry and enables the measurement of vertical and horizontal transport processes in undisturbed large volume soil monoliths. The LWFL has a volume of 6 m3 (4 m length, 1 m width and 1.5 m depth) and was tested by filling the lysimeter with an undisturbed fen monolith. A special extraction procedure for the horizontal sliding of the lysimeter vessel through the natural fen was developed. In front of the vessel a converted cutting tool assisted in carving the soil monolith out of the peat, both vertically and horizontally. Inlet and outlet of the LWFL was constructed to allow the adjustment of a wide range of hydraulic gradients to depict natural occurring lateral transport processes. The LWFL including the measurement techniques was tested successfully for 3 years. On the basis of these tests, we conclude that complex physical and biogeochemical research problems involving lateral flows can be tackled now with multiphase observations and measurements at high spatial and temporal resolution, transdisciplinary data evaluation and numerical modelling approaches.

Seasonal and Diurnal Net Methane Emissions from Organic Soils of the Eastern Alps, Austria: Effects of Soil Temperature, Water Balance, and Plant Biomass

ABSTRACTAlthough the contribution of methane emission to global change is well recognized, analyses of net methane emissions derived from alpine regions are rare. Therefore, three fen sites differing in water balance and plant community, as well as one dry meadow site, were used to study the importance of soil temperature, water table, and plant biomass as controlling factors for net methane emission in the Eastern Alps, Europe, during a period of 24 months. Average methane emissions during snow-free periods in the fen ranged between 19 and 116 mg CH4 m−2 d−1. Mean wintertime emissions were much lower and accounted for 18 to 59% of annual flux. The alpine dry meadow functions as a methane sink during snow-free periods, with mean flux of −2.1 mg CH4 m−2 d−1 (2003) and −1.0 mg CH4 m−2 d−1 (2004). Seasonal methane emissions of the fen were related to soil temperature and groundwater table. During the snow-free periods the water table was the main control for seasonal methane emission. The net methane flux related to water table was much higher for the distinctly drier year 2003 than for the wetter year 2004. Methane emissions differed diurnally at sites where the water table position was high or very low. The influence of total above-ground plant biomass on methane emission was apparent only for those sites with high water table positions. Seasonal and diurnal methane uptake of the dry meadow was related to soil temperature and water-filled pore space, whereas plant biomass did not significantly influence methane fluxes. Our studies gave evidence that fens in the Eastern Alps act as a source of methane throughout the whole year and that a dry meadow site acts as a net methane sink during snow-free periods.

Factors affecting variation in seed production in the heterostylous herbPrimula modesta

AbstractSpatial and temporal variation in the seed production of a species and the various factors affecting seed production provide essential information for understanding biotic and abiotic controls on reproduction and for assessing population trends. We conducted a 4‐year study combining field observations and pollination experiments to evaluate the major factors causing variation in seed production ofPrimula modestaat two sites (fen and grassy sites) on Mt Asama in central Japan.Primula modestaswitched from a vegetative to reproductive life phase at a stage that depended on its accumulation of biomass, and the number of flowers produced by each plant was also highly correlated with plant size. Plants at the grassy site, where snow melts 2–3 weeks earlier than at the fen site, can accumulate more biomass and, thus, bear more flowers and ovules than those at the fen site. AlthoughP. modestais distylous with both self and intramorph incompatibility, pollen availability did not limit seed production at either site. Annual seed production was relatively constant at both sites over the four seasons except 2002, but it was influenced by many environmental factors, including stochastic events, and by antagonistic interactions with herbivores and pathogens. In 2002, many flowers failed to bloom at the fen site. This was likely caused by frost damage to flower buds because of an unusually early snowmelt in that year. Unusual climatic events may be a crucial factor causing spatial and temporal variation in seed production at our study sites. Longer‐term observations are needed to evaluate the effect of unusual climatic events on reproduction.

Plant indicator values as a tool for land mollusc autecology assessment

Abstract The aim of this paper was to utilize Ellenberg's plant indicator system for assessing mollusc autecology and to highlight possibilities and advantages of that approach in the case of fen mollusc communities. Molluscs and plants from 137 fen sites in the Western Carpathian Mountains were recorded quantitatively from homogeneous areas of 16 m2. Water conductivity and pH were measured in the field. Values of Ellenberg's “light, temperature, continentality, moisture, soil reaction, and nutrients” were estimated for each site. The whole data set was processed using ordinations (PCA, DCA, and CCA) and generalized additive models (GAMs). We observed a strong correlation between water pH and Ellenberg soil reaction estimated by plant indicator values (r = 0.72, P

An integrated sampling/speciation method for inorganic arsenic in soil solution

AbstractArsenic mobility, bioavailability, and toxicity in soil‐water systems are strongly affected by species distribution. In spite of species‐selective analytical tools, results may be biased by postsampling oxidation or reduction of compounds. The scope of this study was to delineate a speciation method for inorganic arsenic integrated with pore‐water sampling to prevent problems related to postsampling species transformation. Experiments were performed with exchange cartridges packed with quaternary amine (nitrate‐form) to separate anionic arsenate from uncharged arsenite. Standard solutions with varied As(III) : As(V) ratios as well as groundwater and soil‐solution samples were studied. Analyses were performed by ICP‐MS using either extraction cartridges directly coupled to the instrument or samples obtained by offline speciation tests. Results showed that As(III) passes the packed bed with the rinsing solution, while As(V) is retained on the column and can be released by elution with 0.25 M NH4NO3. Recoveries between 98% and 116% were insensitive to pH variation (pH 3–8) and competing anions. Groundwater samples from a contaminated site yielded recoveries between 92% and 125% when the sum of As(III) and As(V) was compared to total As. Integration of the speciation scheme with pore‐water sampling was tested in a soil‐column experiment. Soil material from a fen site with elevated geogenic As contents was subjected to a varying moisture regime. Reducing conditions during prolonged saturation caused a marked increase of As(III) concentrations. Conversely, when the soil was drained, total As levels decreased and were dominated by As(V). Overall, extraction results with standard solutions and natural samples indicate reliable performance of the method in experimental investigations and field studies.

Methane emissions from two tundra wetlands in eastern Antarctica

During the summertime of 2005/2006 net methane ( CH 4 ) fluxes and environmental variables were investigated in two tundra wetlands Wolong Marsh and Tuanjie Marsh of eastern Antarctica, using the closed chamber technique. At Wolong Marsh, the measurements were made at four wet tundra sites, four mesic tundra sites, and two dry sites. CH 4 flux for wet tundra sites averaged 163.4 μ g m - 2 h - 1 and for the mesic sites 132.4 μ g m - 2 h - 1 . For the dry sites, all the CH 4 fluxes showed the negative values with an average of - 99.9 μ g m - 2 h - 1 . At Tuanjie Marsh, flux measurements were made at two open ponds, two shallow fens and two dry sites. The average CH 4 flux for the pond sites was 170.4 μ g m - 2 h - 1 and for the fen sites 134.7 μ g m - 2 h - 1 . For the dry sites CH 4 fluxes were approximately one order of magnitude lower than those for pond and fen sites and averaged 18.4 μ g m - 2 h - 1 . Spatial variations in CH 4 flux were primarily driven by the water table position at two tundra wetlands, whereas temporal variations in CH 4 flux from wet and mesic sites were related with the thermal regime of tundra soil layers. The fluxes from six observation sites showed a consistent diurnal cycle with the peak at 14:00 and the lowest at 2:00 (local time), which was correlated with ground temperature at the depth of 0–10 cm. The CH 4 emissions from coastal wetlands could constitute an important part of the annual CH 4 budget for Antarctic tundra ecosystems.

Effects of short‐ and long‐term water‐level drawdown on the populations and activity of aerobic decomposers in a boreal peatland

AbstractWe analysed the response of microbial communities, characterized by phospholipid fatty acids (PLFAs), to changing hydrological conditions at sites with different nutrient levels in a southern boreal peatland. Although PLFAs of Gram‐negative bacteria were characteristic of the peatland complex, microbial communities differed among sites (ombrotrophic bog, oligotrophic fen, mesotrophic fen) and sampling depths (0–5, 5–10, 10–20, 20–30 cm). The microbial communities in each site changed significantly following water‐level drawdown. The patterns of change varied among sites and sampling depths. The relative proportion of Gram‐negative bacteria decreased in the upper 10 cm but increased in deeper layers of the fen sites. Fungi benefited from water‐level drawdown in the upper 5 cm of the mesotrophic fen, but suffered in the drier surfaces of the ombrotrophic bog, especially in the 5–10 cm layer. In contrast, actinobacteria suffered from water‐level drawdown in the mesotrophic fen, but benefited in the drier surfaces of the ombrotrophic bog. Basal respiration rate correlated positively with pH and fungal PLFA, and negatively with depth. We suggest that the changes in microbial community structure after persistent water‐level drawdown follow not only the hydrological conditions but also the patterns of vegetation change. Our results imply that changes in structure and activity of the microbial community in response to climate change will be strongly dependent on the type of peatland.

Comparison of net ecosystem CO 2 exchange in two peatlands in western Canada with contrasting dominant vegetation, Sphagnum and Carex

Net ecosystem carbon dioxide exchange was measured in two contrasting peatlands in northern Alberta, Canada using the eddy covariance technique during the growing season (May–October). Sphagnum spp. made up approximately 66% of the total LAI (1.52 m 2 m −2) at the poor fen and the total N content of Sphagnum capitula was 7.8 mg g −1 at the peak of the growing season. In contrast, the dominant plant species at the extreme-rich fen site, the perennial sedge, Carex lasiocarpa, accounted for approximately 60% of the total LAI (1.09 m 2 m −2), and had leaf total N content of 19.3 mg g −1 at peak biomass. In addition, the peak aboveground biomass was higher at the poor fen (230.9 g m −2) than at the extreme-rich fen (157.1 g m −2). Both sites had maximum daily rates of net CO 2 uptake of approximately 5 μmol m −2 s −1, and typical nighttime rates of CO 2 loss of approximately 2 μmol m −2 s −1 during the peak of the growing season. Calculations of maximum photosynthetic and respiratory capacity were consistently higher at the extreme-rich fen. The poor fen was a net sink for CO 2 during 4 of the 6 months (peaking at 44 g C m −2 in July), while only slight net losses of CO 2 (3 g C m −2) occurred in May and September. In contrast, the extreme-rich fen was calculated to be a significant net sink for CO 2 only during 2 months of the growing season (peaking at 30 g C m −2 in August), while significant net losses of CO 2 occurred in May (8 g C m −2) and in October (13 g C m −2). The plant species at the poor fen site were active earlier and later in the growing season, while it took longer for C. lasiocarpa to develop leaf tissue, and leaf senescence and reduction in photosynthetic activity occurred earlier in the fall at the extreme-rich fen. When integrated over the 6-month growing season, the poor fen was a net sink (90 g C m −2) that was three times larger than the extreme-rich fen (31 g C m −2). The ratio of cumulative total ecosystem respiration to gross primary production was 0.7 at the poor fen and 0.9 at the extreme-rich fen.

Vegetation heterogeneity and ditches create spatial variability in methane fluxes from peatlands drained for forestry

Drainage of peatlands for forestry starts a succession of ground vegetation in which mire species are gradually replaced by forest species. Some mire plant communities vanish quickly following the water-level drawdown; some may prevail longer in the moister patches of peatland. Drainage ditches, as a new kind of surface, introduce another component of spatial variation in drained peatlands. These variations were hypothesized to affect methane (CH4) fluxes from drained peatlands. Methane fluxes from different plant communities and unvegetated surfaces, including ditches, were measured at the drained part of Lakkasuo mire, Central Finland. The fluxes were found to be related to peatland site type, plant community, water-table position and soil temperature. At nutrient-rich fen sites fluxes between plant communities differed only a little: almost all plots acted as CH4 sinks (−0.9 to −0.4 mg CH4 m−2 d−1), with the exception of Eriophorum angustifolium Honck. communities, which emitted 0.9 g CH4 m−2 d−1. At nutrient-poor bog site the differences between plant communities were clearer. The highest emissions were measured from Eriophorum vaginatum L. communities (29.7 mg CH4 m−2 d−1), with a decreasing trend to Sphagna (10.0 mg CH4 m−2 d−1) and forest moss communities (2.6 mg CH4 m−2 d−1). CH4 emissions from different kinds of ditches were highly variable, and extremely high emissions (summertime averages 182–600 mg CH4 m−2 d−1) were measured from continuously water-covered ditches at the drained fen. Variability in the emissions was caused by differences in the origin and movement of water in the ditches, as well as differences in vegetation communities in the ditches. While drainage on average greatly decreases CH4 emissions from peatlands, a great spatial variability in fluxes is emerged. Emissions from ditches constantly covered with water, may in some cases have a great impact on the overall CH4 emissions from drained peatlands.

Effect of varied fertilization and cutting frequency on forage yields, phosphorus and potassium contents and nutrient balance of fen grassland

The effect of fertilization and cutting frequency on forage yields, nutrient contents and nutrient balance was examined for seven years in a two-factorial plot trial laid out in strip design with eight variants on a medium-deep fen site in the Havelländisches Luch. The combination of different levels of fertilization and varied cutting frequency revealed significant differences in terms of forage yield, plant ingredients and in some cases also soil nutrient contents. With the management intensity practiced in the trial, between 20 and 28 kg P ha−1 would be optimal. Although up to 150 kg K ha−1 were extracted by the forage crop, application of about 120 kg K ha−1 would be sufficient.