Marja Maljanen

Fluxes of N2O, CH4 and CO2 on afforested boreal agricultural soils

After drainage of natural boreal peatlands, the decomposition of organic matter increases and peat soil may turn into a net source of CO2 and N2O, whereas CH4 emission is known to decrease. Afforestation is a potential mitigation strategy to reduce greenhouse gas emission from organic agricultural soils. A static chamber technique was used to evaluate the fluxes of CH4, N2O and CO2 from three boreal organic agricultural soils in western Finland, afforested 1, 6 or 23 years before this study. The mean emissions of CH4 and N2O during the growing seasons did not correlate with the age of the tree stand. All sites were sources of N2O. The highest daily N2O emission during the growing season, measured in the oldest site, was as high as 29 mg N2O m−2d−1. In general, organic agricultural soils are sinks for methane. Here, the oldest site acted as a small sink for methane, whereas the two youngest afforested organic soils were sources for methane with maximum emission rates (up to 154 mg m−2d−1) similar to those reported for minerogenous natural peatlands. Soil respiration rates decreased with the age of the forest. The high soil respiration in the younger sites, probably resulted from the high biomass production of herbs, could create soil anaerobiosis and increase methane production. Our results show that afforestation of agricultural peat soils does not abruptly terminate the N2O emissions during the first two decades, and afforestation can even enhance methane emission for a few years. The carbon accumulation in the developing tree stand can partly compensate the carbon loss from soil.

Carbon dioxide and methane dynamics in a sub‐Arctic peatland in northern Finland

We studied carbon dynamics on various surface parts of a highly patterned fen, typical in northern Finland, to examine the importance of different microsites to the areal carbon fluxes. The studies were carried out in June-September 1995 on a mesotrophic flark fen (an aapa mire) in Kaamanen (69°08’N, 27° 17’E). Wet flarks, moist lawns and dry strings accounted for 60%, 10% and 30% of the surface area, respectively. A static chamber technique was applied to measure the CH4 exchange, the instantaneous net ecosystem exchange (NEE, transparent chamber) and the ecosystem respiration (Rtot, opaque chamber) in several microsites. The static chamber results were compared with those obtained by the eddy covariance technique. The mean daytime areal net ecosystem CO2 exchange rate measurement in conditions where photosynthesis was light saturated (PAR>400 ?mol m-2 s-1) varied during the measurement period from -59 mg CO2-C m-2h-1 (release) to 250 (uptake). The mean CH4 emission during the measuring period was 78 mg CH4-C m-2 d-1 on the flarks, 68 mg on the lawn and 6.0 mg on the strings. The strings without shrubs (mainly Betula nana) were in general net sources of CO2, even during the middle of the growing season, whereas the lawns, flarks and also strings growing B. nana showed a daytime net uptake of CO2. Areally integrated chamber results showed lower CO2 and higher CH4 fluxes than predicted from the eddy covariance measurements.

Fluxes and production of N2O, CO2 and CH4 in boreal agricultural soil during winter as affected by snow cover

Agricultural soils are important source of atmospheric nitrous oxide (N2O) and a considerable part of annual N2O release occurs during the cold season in the boreal region. According to recent studies N2O can be produced in soils at low temperatures, below 0°C. We studied if removal of the snowcover lowers soil temperatures and whether this would affect flux rates of N2O, carbon dioxide (CO2) and methane (CH4) from an agricultural soil in eastern Finland. Gas flux rates and concentrations in soil were measured from study plots with undisturbed snow cover and from plots with snow removed. This experiment simulates changes in the soil thermal conditions with less snowfall. Plots without snow had even 15°C lower temperature at the depth of 5 cm and they had higher N2O emissions during soil freezing and thawing. However, there were only minor changes in CH4 or CO2 flux rates after removal of snow over the cold season. N2O and CO2 accumulated in the soil during winter and were then released rapidly during thawing in spring. CH4 concentrations in the soil remained lower than the atmospheric levels during winter and subsequently increased to the ambient levels after thawing. Future climate scenarios suggest possible decline in snowfall in northern Europe resulting in lower soil temperatures. This could lead to higher N2O emissions from boreal agricultural soils.

Cold-season nitrous oxide dynamics in a drained boreal peatland differ depending on land-use practice

Drained peat soils are important sources of greenhouse gases such as nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2). These gases are produced in soil and they can be emitted year-roun...

Geothermal ecosystems as natural climate change experiments : The ForHot research site in Iceland as a case study

This article describes how natural geothermal soil temperature gradients in Iceland have been used to study terrestrial ecosystem responses to soil warming. The experimental approach was evaluated at three study sites in southern Iceland; one grassland site that has been warm for at least 50 years (GO), and another comparable grassland site (GN) and a Sitka spruce plantation (FN) site that have both been warmed since an earthquake took place in 2008. Within each site type, five ca. 50 m long transects, with six permanent study plots each, were established across the soil warming gradients, spanning from unwarmed control conditions to gradually warmer soils. It was attempted to select the plots so the annual warming levels would be ca. +1, +3, +5, +10 and +20 °C within each transect. Results of continuous measurements of soil temperature (Ts) from 2013-2015 revealed that the soil warming was relatively constant and followed the seasonal Ts cycle of the unwarmed control plots. Volumetric water content in the top 5 cm of soil was repeatedly surveyed during 2013-2016. The grassland soils were wetter than the FN soils, but they had sometimes some significant warming-induced drying in the surface layer of the warmest plots, in contrast to FN. Soil chemistry did not show any indications that geothermal water had reached the root zone, but soil pH did increase somewhat with warming, which was probably linked to vegetation changes. As expected, the potential decomposition rate of organic matter increased significantly with warming. It was concluded that the natural geothermal gradients at the ForHot sites in Iceland offered realistic conditions for studying terrestrial ecosystem responses to warming with minimal artefacts.

Greenhouse Gas Dynamics of a Northern Boreal Peatland Used for Treating Metal Mine Wastewater

Northern peatlands in their natural state are sinks of carbon dioxide (CO2) but sources of methane (CH4). They are often nitrogen limited and can act as sinks for greenhouse gas (GHG) nitrous oxide (N2O). Peatlands have been used to treat wastewaters from different point sources. Continuous nutrient and pollutant load to a nutrient limited peatland ecosystem may change the microbial processes and lead to increased productivity, which together are likely to change the GHG emissions. We studied the effect of wastewater derived from metal mining on N2O and CH4 emissions on two treatment peatlands in northern boreal zone. The measured CH4 fluxes from the reference point without any wastewater load were in the range of those reported from northern pristine peatlands while emissions from treatment peatlands were greatly reduced, presumably as result of high sulfate concentration in the porewater. N2O emissions were small in the reference point, but up to 300 times higher in the treatment peatlands. Methane emissions increased with increasing total organic carbon concentration and decreased with increasing sulfate concentration in the surface water, respectively, while N2O emissions increased with increasing nitrate concentrations. The data indicate drastic changes in GHG fluxes and related biogeochemical processes in treatment peatlands as compared to the reference point.

The effect of geothermal soil warming on the production of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), nitric oxide (NO) and nitrous acid (HONO) from forest soil in southern Iceland

The project was funded by the Academy of Finland (no. 297735 and no. 132045). This work also contributes to the ForHot-Forest (Project No.163272-051 of the Icelandic Research Council), as well as to the Nordic CAR-ES project and the ClimMani COST Action (ES1308) and the International Program CryoCARB and COUP. The Kuopio Naturalists’ Society is thanked for a travel grant. Jaana Rissanen is thanked for assisting in the laboratory at the University of Eastern Finland. We also want to acknowledge the staff at the Reykir campus of the Agricultural University of Iceland for great logistic support.

Effects of volcanic ash on GHG production rates and soil properties in a drained peat soil in Finland and a comparison to wood ash

INTRODUCTION Past volcanic eruptions in Iceland have sometimes led to long-distance distribution of fine volcanic tephra (volcanic ash). Evidence for volcanic ash from, for example, the ca. 4250 BP eruption in Hekla (H4) and the 17831784 AD Laki eruption in southern Iceland has been found in wetlands at Svalbard (Kekonen et al. 2005), Scotland (Charman et al. 1995) and Scandinavia (Thorarinsson 1981). Basaltic volcanic ash contains several compounds, e.g. mixed sulphates, ammonium (NH4 +) and nitrate (NO3 -) (Ayris and Delmelle 2012), all of which have the potential to affect various soil processes, such as N cycling and greenhouse gas (GHG) production. Such direct effects of long distance volcanic ash transport have, however, been little studied so far. The Eyjafjallajokull volcano eruption started in Iceland in March, 2010. A major outbreak of the central crater under the covering ice cap started on 14 April and continued until 24 May, ejecting a very large amount of gases and fine ash into the atmosphere. This ash contained mainly silicon dioxide, but also other compounds including sulphates (O’Dowd et al. 2012). This eruption gave us an opportunity to study the fresh volcanic ash and its effects on soil properties. Because this volcanic ash was alkaline, it could increase soil pH and affect the microbiological processes behind GHG emissions in a similar way to that suggested for wood ash (Maljanen et al. 2014, Klemedtsson et al. 2010). We used fresh volcanic ash from the Eyjafjallajokull volcano in a laboratory experiment conducted on samples of drained peat soil from western Finland that were also used for studying the effects of wood ash recycling from bioenergy power plants (Maljanen et al. 2014). The aim of this study was to test whether this volcanic ash affected GHG production rates in drained peat soil in our laboratory incubation experiments and to compare the results with wood ash.