Nitrous oxide emissions from five fertilizer treatments during one year-High-frequency measurements on a Swedish Cambisol

Nitrous oxide (N2O) is a strong greenhouse gas, and the emissions from managed soils are increasing. Emissions of N2O are highly variable in time and space, and there are potential triggers for emission peaks both in crop season and no-crop season. The aim of this study was to compare how fertilizer treatments, differing in rate and source of nitrogen (N), influence direct N2O emissions from soil, in crop season as well as in no-crop season, with the use of automated, high-frequency chamber measurements. Emissions were measured from cereal production on a Swedish clay-rich soil fertilized with biogas digestate, pig slurry and two levels of mineral N, as well as from control plots receiving no fertilizer N. The results showed that N2O emissions per unit area were low in all treatments, compared to other studies. Emissions from the treatment with mineral fertilizers at recommended rates were similar to the emissions from the control (0.65 and 0.48 kg N2O-N ha(-1) yr(-1), respectively). One-year cumulative emissions from a mineral N input rate 50 % higher than recommended were about three times higher than the control. Emissions of N2O from the pig slurry and biogas digestate treatments per unit area were of the same magnitude as from the high mineral N treatment. While the emissions from the high mineral N treatment were associated with elevated concentrations of nitrate in the drainage water, the high emissions from the organic fertilizer treatments were probably a result of large input of ammonium and degradable organic matter both in the year studied and in the preceding year. Most (approximately 75 %) of the N2O emissions occurred between harvest in autumn and sowing in spring, mainly in periods of freeze-thaw cycles. The relative differences between treatments were roughly the same during crop season and no-crop season. This study concludes that it is possible to combine high yields with very low N2O emissions -even on a clay soil in a semi-humid climate -when using mineral fertilizers at recommended rates

Upscaling Northern Peatland CO2 Fluxes Using Satellite Remote Sensing Data

Peatlands play an important role in the global carbon cycle as they contain a large soil carbon stock. However, current climate change could potentially shift peatlands from being carbon sinks to carbon sources. Remote sensing methods provide an opportunity to monitor carbon dioxide (CO2) exchange in peatland ecosystems at large scales under these changing conditions. In this study, we developed empirical models of the CO2 balance (net ecosystem exchange, NEE), gross primary production (GPP), and ecosystem respiration (ER) that could be used for upscaling CO2 fluxes with remotely sensed data. Two to three years of eddy covariance (EC) data from five peatlands in Sweden and Finland were compared to modelled NEE, GPP and ER based on vegetation indices from 10 m resolution Sentinel-2 MSI and land surface temperature from 1 km resolution MODIS data. To ensure a precise match between the EC data and the Sentinel-2 observations, a footprint model was applied to derive footprint-weighted daily means of the vegetation indices. Average model parameters for all sites were acquired with a leave-one-out-cross-validation procedure. Both the GPP and the ER models gave high agreement with the EC-derived fluxes (R-2 = 0.70 and 0.56, NRMSE = 14% and 15%, respectively). The performance of the NEE model was weaker (average R-2 = 0.36 and NRMSE = 13%). Our findings demonstrate that using optical and thermal satellite sensor data is a feasible method for upscaling the GPP and ER of northern boreal peatlands, although further studies are needed to investigate the sources of the unexplained spatial and temporal variation of the CO2 fluxes.Peer reviewe

Effects of drought and meteorological forcing on carbon and water fluxes in Nordic forests during the dry summer of 2018

The Nordic region was subjected to severe drought in 2018 with a particularly long-lasting and large soil water deficit in Denmark, Southern Sweden and Estonia. Here, we analyse the impact of the drought on carbon and water fluxes in 11 forest ecosystems of different composition: spruce, pine, mixed and deciduous. We assess the impact of drought on fluxes by estimating the difference (anomaly) between year 2018 and a reference year without drought. Unexpectedly, the evaporation was only slightly reduced during 2018 compared to the reference year at two sites while it increased or was nearly unchanged at all other sites. This occurred under a 40 to 60% reduction in mean surface conductance and the concurrent increase in evaporative demand due to the warm and dry weather. The anomaly in the net ecosystem productivity (NEP) was 93% explained by a multilinear regression with the anomaly in heterotrophic respiration and the relative precipitation deficit as independent variables. Most of the variation (77%) was explained by the heterotrophic component. Six out of 11 forests reduced their annual NEP with more than 50 g C m(-2)yr(-1)during 2018 as compared to the reference year. The NEP anomaly ranged between -389 and +74 g C m(-2)yr(-1)with a median value of -59 g C m(-2)yr(-1). This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.Peer reviewe

Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe's terrestrial ecosystems : a review

Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, spatial upscaling and modelling of observed ecosystem carbon and GHG dynamics. The applied sampling design was developed and formulated in protocols by the scientific community, representing a trade-off between an ideal dataset and practical feasibility. The use of open-access, high-quality and multi-level data products by different user communities is crucial for the Integrated Carbon Observation System in order to achieve its scientific potential and societal value.Peer reviewe

Land use effects on nitrous oxide emission from drained organic soils Land use effects on nitrous oxide emission from drained organic soils

Abstract Since industrialisation, the atmospheric concentration of greenhouse gases (GHG) has increased significantly. The most important anthropogenic GHGs are carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O). N 2 O is of major concern for two reasons; i) it is a potent GHG responsible for 6.2% of the observed anthropogenic radiative forcing and ii) it plays a major role in the destruction of stratospheric ozone. Soil processes are the largest contributor to the atmospheric N 2 O, with agriculture as the largest anthropogenic source, accounting for 65% to 80% of total emission. The N 2 O emissions are largely influenced by the land use and, due to the long half life time of N 2 O in the atmosphere, is it important to find mitigation options that will reduce N 2 O from agriculture. This is particularly important for drained organic soils, which are emitting large amounts of N 2 O and CO 2 . The main processes that produce N 2 O in soil are nitrification and denitrification. Several interacting factors control these processes and the magnitude of N 2 O emission, such as site fertility, ground water level, pH and competition from vegetation. Thus, because of the complexity of the driving variables, it is difficult to predict N 2 O emission from environmental factors. The articles in this thesis deals with measurements of N 2 O, CH 4 and CO 2 fluxes, although I in my summary of these, focus on mitigation options for N 2 O emissions from organic soils, as these are largely increased after drainage and have a large impact on the national GHG budget for Sweden. Main findings of my work are that cereals, row sown crops (e.g. vegetables) and forest emit larger amounts of N 2 O than pastures. However, due to the many controlling factors, the different soil properties as well as measurement periods it is difficult to generalise the findings for all peat soils. Soil pH was found to be a driving factor for N 2 O emission from the forest site, with enhanced N 2 O emission from low pH. Increased soil pH due to wood ash addition was found to reduce N 2 O emission at a spruce forest site, which might provide a mitigation option for organic forest soils. Based on the results from the thesis, a suggested mitigation strategy for N 2 O emission from drained agricultural peat soils is to avoid cereal and vegetable cultivation in favour of permanent meadows or pastures. Increasing pH by wood ash or lime can decrease N 2 O emission from forest soils. Although not a result in this thesis, liming of agricultural drained peat soils could also be an option. 1 Land use effects on nitrous oxide emissions… Sammanfattning Koncentration av växthusgaser i atmosfären har sedan industrialiseringen ökat kraftigt. De viktigaste antropogena växthusgaserna är koldioxid (CO 2 ), metan (CH 4 ) och lustgas (N 2 O). Lustgas är av stor betydelse av två skäl, dels för att det är en potent växthusgas som uppskattas stå för 6,2% av den antropogena växthuseffekten och dels för att det har en avgörande roll vid nedbrytningen av stratosfärisk ozon. Markprocesser är den största källan till atmosfärisk N 2 O, varav jordbruket är den största antropogena källan och står för 65% till 80% av de totala utsläppen. Då markanvändning i hög grad påverkar N 2 O-emissionerna är det viktigt att hitta begränsningsalternativ som kan minska lustgasutsläppen. Särskilt viktigt är det hitta metoder för att minska växthusgasutsläppen från åker och skogsmark på näringsrika dränerade torvjordar då dessa är stora punktkällor av såväl CO 2 som N 2 O. De viktigaste processerna som producerar N 2 O i jord är nitrifikation och denitrifikation. Flera samverkande faktorer såsom som bördighet, grundvattennivå, pH och konkurrens från vegetation påverkar båda processerna och därmed storleken på lustgasemissionerna. Det är således svårt att förutsäga storleken på lustgasemissionerna på grund av komplexiteten av de drivande variablerna. Trots att artiklarna i denna avhandling beskriver mätningar av både metan, koldioxid och lustgas, har jag i sammanställningen av dessa valt att fokusera på att hitta alternativ för att minska N 2 O-utsläppen från dränerade torvjordar, eftersom dessa har en stor inverkan på den nationella växthusgasbudgeten för Sverige. Viktigaste resultaten från mina undersökningar är att spannmål, radsådda grödor, såsom morötter och potatis, samt skog släpper ut mer N 2 O än betesvall på dränerade näringsrika torvjordar. Eftersom det finns många faktorer som styr emissionerna och att markegenskaperna och mätperioderna var olika för mätytorna, kan jag inte dra slutsatsen att detta gäller för alla dränerade torvjordar. pH visade sig vara en drivande variabel för lustgasemissionerna från björkskogen, med ökade lustgasemissioner vid lägre pH. Vidare fann vi att askåterföring till dränerad organogen granskog minskade lustgasemissionerna samtidigt som mark-pH ökade. Baserat på resultaten från undersökningarna i denna avhandling, föreslår jag att en strategi för att minska N 2 O utsläppen från organogen dränerad jordbruksmark skulle vara att undvika spannmål och grönsaker till förmån för permanent ängsmark eller betesmark. Emissionerna från dränerad organogen skogsmark kan minskas med askåterföring. Huruvida kalkning av organogen jordbruksmark kan minska lustgasemissionerna är inte ett resultat av mina undersökningar, men det skulle kunna vara en möjlighet. LIST OF PAPERS This thesis is based on the following papers, which are referred to as Paper I-V in the text

Measurement of net ecosystem exchange, productivity and respiration in three spruce forests in Sweden shows unexpectedly large soil carbon losses

Measurement of net ecosystem exchange was made using the eddy covariance method above three forests along a north-south climatic gradient in Sweden: Flakaliden in the north, Knottasen in central and Asa in south Sweden. Data were obtained for 2 years at Flakaliden and Knottasen and for one year at Asa. The net fluxes (N-ep) were separated into their main components, total ecosystem respiration (R-t) and gross primary productivity (P-g). The maximum half-hourly net uptake during the heart of the growing season was highest in the southernmost site with -0.787 mg CO2 m(-2) s(-1) followed by Knottasen with -0.631 mg CO2 m(-2) s(-1) and Flakaliden with -0.429 mg CO2 m(-2) s(-1). The maximum respiration rates during the summer were highest in Knottasen with 0.245 mg CO2 m(-2) s(-1) while it was similar at the two other sites with 0.183 mg CO2 m(-2) s(-1). The annual N-ep ranged between uptake of -304 g C m(-2) year(-1) (Asa) and emission of 84 g C m(-2) year(-1) (Knottasen). The annual R-t and P-g ranged between 793 to 1253 g C m(-2)year(-1) and -875 to -1317 g C m(-2) year(-1), respectively. Biomass increment measurements in the footprint area of the towers in combination with the measured net ecosystem productivity were used to estimate the changes in soil carbon and it was found that the soils were losing on average 96-125 g C m(-2)year(-1). The most plausible explanation for these losses was that the studied years were much warmer than normal causing larger respiratory losses. The comparison of net primary productivity and P-g showed that ca 60% of P-g was utilized for autotrophic respiration