Mats G. Öquist

Inventorying emissions from nature in Europe

As part of the work of the Economic Commission for Europe of the United Nations Task Force on Emission Inventories, a new set of guidelines has been developed for assessing the emissions of sulphur, nitrogen oxides, NH3, CH4, and nonmethane volatile organic compounds (NMVOC) from biogenic and other natural sources in Europe. This paper gives the background to these guidelines, describes the sources, and gives our recommended methodologies for estimating emissions. We have assembled land use and other statistics from European or national compilations and present emission estimates for the various natural/biogenic source categories based on these. Total emissions from nature derived here amount to ∼1.1 Tg S yr−1, 6–8 Tg CH4 yr−1, 70 Gg NH3 (as N) yr−1, and 13 Tg NMVOC yr−1. Estimates of biogenic NO x emissions cover a wide range, from 140 to 1500 Gg NO x (as N) yr−1. In terms of relative contribution to total European emissions for different pollutants, then NMVOC from forests and vegetation are clearly the most important emissions source. Biogenic NO x emissions (although heavily influenced by nitrogen inputs from anthropogenic activities) are very important if the higher estimates are reliable. CH4 from wetlands and sulphur from volcanoes are also significant emissions in the European budgets. On a global scale, European biogenic emissions are not significant, a consequence of the climate and size (7% of global land area) of Europe and of the destruction of natural ecosystems since prehistoric times. However, for assessing local budgets and for photochemical oxidant modeling, natural/biogenic emissions can play an important role. The most important contributor in this regard is undoubtedly forest VOC emissions, although this paper also indicates that NMVOC emissions from nonforested areas also need to be further evaluated. This paper was originally conceived as a contribution to the collection of papers arising as a result of the Workshop on Biogenic Hydrocarbons in the Atmospheric Boundary Layer, August 24–27, 1997. (Several papers arising from this workshop have been published in Journal of Geophysical Research, 103(D19) 1998.)

Cold winter soils enhance dissolved organic carbon concentrations in soil and stream water

Concentrations of dissolved organic carbon ([DOC]) have increased in lakes, streams and rivers across a large part of the northern hemisphere and raised an animated scientific debate about the unde ...

Nitrous oxide production in a forest soil at low temperatures – processes and environmental controls

Recent investigations have highlighted the relative importance of the winter season for emissions of N(2)O from boreal soils. However, our understanding of the processes and environmental controls regulating these emissions is fragmentary. Therefore, we investigated the potential for, and relative importance of, N(2)O formation at temperatures below 0 degrees C in laboratory experiments involving incubations of a Swedish boreal forest soil. Our results show that frozen soils have a high potential for N(2)O formation and subsequent emission. Net N(2)O production rates at -4 degrees C equaled those observed at +10 to +15 degrees C at moisture contents >60% of the soils water-holding capacity. The source of this N(2)O was found to be denitrification occurring in anoxic microsites in the frozen soil and temperature per se did not control the denitrification rates at temperatures around 0 degrees C. Furthermore, both net nitrogen-mineralisation and nitrification were observed in the frozen soil samples. Based on these findings we propose a conceptual model for the temperature response of N(2)O formation in soils at low temperatures.

Temporal and spatial variability of dissolved inorganic carbon in a boreal stream network: Concentrations and downstream fluxes

[1] Carbon dioxide (CO 2 ) and dissolved inorganic carbon (DIC) concentrations and export were analyzed throughout a 67 km 2 boreal stream network in northern Sweden. 700 DIC and CO 2 samples from 14 subcatchments were collected in 2006 and 2007. All sites were consistently supersaturated in CO 2 with respect to the atmosphere. Temporal variability of DIC and CO 2 concentration was best correlated with discharge, with concentrations generally diluting at high discharge. However, the variability in CO 2 concentration was also dependent on the specific pH range of the stream, as variability was greatest in acidic headwater streams and lowest in larger circumneutral streams. In the larger ones the increase in the CO 2 proportion of DIC at increased discharge counteracts the dilution of CO 2 . The shift toward proportionally more CO 2 of the DIC at higher discharge is caused by decline in pH. Spatial patterns showed that DIC and CO 2 concentrations were best correlated with peatland coverage of the subcatchment. The highest concentrations were found in headwater streams draining peatlands. The downstream export of DIC from the catchment outlet constitutes 19% of the total downstream export of carbon (DIC + DOC), or 0.7 (±0.09) g C m -2 yr -1 . This study demonstrates the importance of including fluvial fluxes of inorganic carbon in landscape carbon budgets via runoff, and also highlights the need to account for stream evasion of CO 2 to the atmosphere in such estimates since it can be larger than the downstream DIC export.

Both catabolic and anabolic heterotrophic microbial activity proceed in frozen soils

A large proportion of the global soil carbon pool is stored in soils of high-latitude ecosystems in which microbial processes and production of greenhouse gases proceed during the winter months. It has been suggested that microorganisms have limited ability to sequester substrates at temperatures around and below 0 °C and that a metabolic shift to dominance of catabolic processes occurs around these temperatures. However, there are contrary indications that anabolic processes can proceed, because microbial growth has been observed at far lower temperatures. Therefore, we investigated the utilization of the microbial substrate under unfrozen and frozen conditions in a boreal forest soil across a temperature range from −9 °C to +9 °C, by using gas chromatography-isotopic ratio mass spectrometry and 13C magic-angle spinning NMR spectroscopy to determine microbial turnover and incorporation of 13C-labeled glucose. Our results conclusively demonstrate that the soil microorganisms maintain both catabolic (CO2 production) and anabolic (biomass synthesis) processes under frozen conditions and that no significant differences in carbon allocation from [13C]glucose into [13C]CO2 and cell organic 13C-compounds occurred between +9 °C and −4 °C. The only significant metabolic changes detected were increased fluidity of the cell membranes synthesized at frozen conditions and increased production of glycerol in the frozen samples. The finding that the processes in frozen soil are similar to those in unfrozen soil has important implications for our general understanding and conceptualization of soil carbon dynamics in high-latitude ecosystems.

A 12-year record reveals pre-growing season temperature and water table level threshold effects on the net carbon dioxide exchange in a boreal fen

This study uses a 12-year time series (2001-2012) of eddy covariance measurements to investigate the long-term net ecosystem exchange (NEE) of carbon dioxide (CO2) and inter-annual variations in relation to abiotic drivers in a boreal fen in northern Sweden. The peatland was a sink for atmospheric CO2 in each of the twelve study years with a 12-year average (+/- standard deviation) NEE of -58 +/- 21 g C m(-2) yr(-1). For ten out of twelve years, the cumulative annual NEE was within a range of -42 to -79 g C m(-2) yr(-1) suggesting a general state of resilience of NEE to moderate inter-annual climate variations. However, the annual NEE of -18 and -106 g C m(-2) yr(-1) in 2006 and 2008, respectively, diverged considerably from this common range. The lower annual CO2 uptake in 2006 was mainly due to late summer emissions related to an exceptional drop in water table level (WTL). A positive relationship (R-2 = 0.65) between pre-growing season (January to April) air temperature (Ta) and summer (June to July) gross ecosystem production (GEP) was observed. We suggest that enhanced GEP due to mild pre-growing season air temperature in combination with air temperature constraints on ecosystem respiration (ER) during the following cooler summer explained most of the greater net CO2 uptake in 2008. Differences in the annual and growing season means of other abiotic variables (e.g. radiation, vapor pressure deficit, precipitation) and growing season properties (i.e. start date, end date, length) were unable to explain the inter-annual variations of NEE. Overall, our findings suggest that this boreal fen acts as a persistent contemporary sink for atmospheric CO2 that is, however, susceptible to severe anomalies in WTL and pre-growing season air temperature associated with predicted changes in climate patterns for the boreal region. (Less)

Temperature response of litter and soil organic matter decomposition is determined by chemical composition of organic material

The global soil carbon pool is approximately three times larger than the contemporary atmospheric pool, therefore even minor changes to its integrity may have major implications for atmospheric CO2 concentrations. While theory predicts that the chemical composition of organic matter should constitute a master control on the temperature response of its decomposition, this relationship has not yet been fully demonstrated. We used laboratory incubations of forest soil organic matter (SOM) and fresh litter material together with NMR spectroscopy to make this connection between organic chemical composition and temperature sensitivity of decomposition. Temperature response of decomposition in both fresh litter and SOM was directly related to the chemical composition of the constituent organic matter, explaining 90% and 70% of the variance in Q10 in litter and SOM, respectively. The Q10 of litter decreased with increasing proportions of aromatic and O-aromatic compounds, and increased with increased contents of alkyl- and O-alkyl carbons. In contrast, in SOM, decomposition was affected only by carbonyl compounds. To reveal why a certain group of organic chemical compounds affected the temperature sensitivity of organic matter decomposition in litter and SOM, a more detailed characterization of the (13) C aromatic region using Heteronuclear Single Quantum Coherence (HSQC) was conducted. The results revealed considerable differences in the aromatic region between litter and SOM. This suggests that the correlation between chemical composition of organic matter and the temperature response of decomposition differed between litter and SOM. The temperature response of soil decomposition processes can thus be described by the chemical composition of its constituent organic matter, this paves the way for improved ecosystem modeling of biosphere feedbacks under a changing climate.

Winter climate controls soil carbon dynamics during summer in boreal forests

Boreal forests, characterized by distinct winter seasons, store a large proportion of the global terrestrial carbon (C) pool. We studied summer soil C-dynamics in a boreal forest in northern Sweden using a seven-year experimental manipulation of soil frost. We found that winter soil climate conditions play a major role in controlling the dissolution/mineralization of soil organic-C in the following summer season. Intensified soil frost led to significantly higher concentrations of dissolved organic carbon (DOC). Intensified soil frost also led to higher rates of basal heterotrophic CO2 production in surface soil samples. However, frost-induced decline in the in situ soil CO2 concentrations in summer suggests a substantial decline in root and/or plant associated rhizosphere CO2 production, which overrides the effects of increased heterotrophic CO2 production. Thus, colder winter soils, as a result of reduced snow cover, can substantially alter C-dynamics in boreal forests by reducing summer soil CO2 efflux, and increasing DOC losses.

Effects of a transient oxic period on mineralization of organic matter to CH4 and CO2 in anoxic peat incubations

Rates of organic matter mineralization in peatlands, and hence production of the greenhouse gases CH4 and CO2, are highly dependent on the distribution of oxygen in the peat. Using laboratory incub ...

Partitioning Litter Mass Loss into Carbon Dioxide and Methane in Peatland Ecosystems

Carbon is lost from peatland ecosystems as CO 2 -C, CH 4 -C, or organic C. Despite the obvious contributions of all three of these forms of carbon to total mass losses arising from the degradation of organic material in peatland ecosystems, our understanding of both the relative amounts of these C forms that are emitted, and the factors controlling their partitioning, is limited. In this chapter, we summarize and evaluate current knowledge regarding partitioning of terminally mineralized carbon into CO 2 and CH 4 to identify the main factors controlling the partitioning of mass loss of plant-derived biomass into these species; gaps in knowledge regarding the processes involved, their rates and their interactions; and important issues to address in future research initiatives. We first outline the main factors that influence the partitioning into CO 2 and CH 4 of organic matter degraded in northern peatlands, then evaluate their relative importance, and related issues, using available data in the scientific literature. We conclude that current knowledge of the partitioning between CO 2 and CH 4 production during the degradation of organic material in peatlands is very limited, and values of CO 2 /CH 4 reported in the literature differ by a factor of about 80,000. The main environmental factors affecting the partitioning are the composition of the plant litter entering the soil, the soil redox conditions, the age of the peat, and soil temperature. However, attempts to draw sound general conclusions supported by reliable quantitative data are hampered by the high variability reported in the literature.