Soils In Finland Research Articles

A Coupled Model of Hydraulic Eco-Physiology and Cambial Growth - Accounting for Biophysical Limitations and Phenology Improves Stem Diameter Prediction at High Temporal Resolution.

Traditional photosynthesis-driven growth models have considerable uncertainties in predicting tree growth under changing climates, partially because sink activities are directly affected by the environment but not adequately addressed in growth modelling. Therefore, we developed a semi-mechanistic model coupling stomatal optimality, temperature control of enzymatic activities and phenology of cambial growth. Parameterized using Bayesian inference and measured data on Picea abies and Pinus sylvestris in peatland and mineral soils in Finland, the coupled model simulates transpiration and assimilation rates and stem radial dimension (SRD) simultaneously at 30 min resolution. The results suggest that both the sink and phenological formulations with environmental effects are indispensable for capturing SRD dynamics across hourly to seasonal scales. Simulated using the model, growth was more sensitive than assimilation to temperature and soil water, suggesting carbon gain is not driving growth at the current temporal scale. Also, leaf-specific production was occasionally positively correlated with growth duration but not with growth onset timing or annual cambial area increment. Thus, as it is hardly explained by carbon gain, phenology itself should be included in sink-driven growth models of the trees in the boreal zone and possibly other environments where sink activities and photosynthesis are both restrained by harsh conditions.

Mapping, impacts, characterization and extent of acid sulfate soils in Finland

Acid sulfate soils (ASS) cause big problems worldwide due to their potential to form sulfuric acid during oxidation of sulfidic materials, resulting in very acid soil (pH <4.0). Impacts include acidification of soil and water, leaching of metals, decreased nutrient supply, deterioration of water fauna and flora, and corrosion of infrastructure. These soils also exhibit poor geotechnical properties. Finland has the largest occurrences of ASS in Europe, mainly along the coast of the Baltic Sea. The EU Water Framework Directive brought about wide co-operation to reduce the harmful impacts of ASS in Finland. One urgent step was to localize and characterize the occurrences of ASS. The more than 10 year-long programme, led by the Geological Survey of Finland (GTK), started in 2009 and field work was completed in 2021. During the programme observations, measurements, sampling and analyses were made at 23 000 sites in an area of 5 010 000 ha. Traditionally ASS in Finland have been considered to comprise fine-grained sulfidic sediments and/or their oxidized layers, occurring on agricultural land along the coast below the highest shoreline of the Littorina Sea transgression. This study recognized and classified significant occurrences of other types of potentially harmful ASS materials: (1) coarse-grained ASS (sand), (2) organic ASS (peat) and (3) unsorted ASS (till material). The methods, definition and classification of Finnish ASS have been revised. We calculated the extent of ASS along the coast to be about 1 000 000 ha corresponding to 21% of the area covered in the past by the Littorina Sea, and three to six times more than earlier estimates. In addition, some occurrences of ASS were recognized inland, mainly related to black shales and sulfidic ores. The mapping data can be accessed via the GTK map service (www.gtk.fi) providing information about the distribution and properties of ASS.

High organic carbon content constricts the potential for stable organic carbon accrual in mineral agricultural soils in Finland

Sequestering carbon into agricultural soils is considered as a means of mitigating climate change. We used agronomic soil test results representing c. 95% of the farmed land area in Finland to estimate the potential of the uppermost 15 cm soil layer of mineral agricultural soils to sequester organic carbon (OC) and to contribute to the mitigation of climate change. The estimation of the maximum capacity of mineral matter to protect OC in stable mineral-associated form was based on the theory that clay and fine-sized (fines = clay + silt) particles have a limited capacity to protect OC. In addition, we used the clay/OC and fines/OC ratios to identify areas with a risk of erosion and reduced productivity, thus indicating priority areas potentially benefitting from the increased soil OC contents. We found that 32–40% of the mineral agricultural soils in Finland have the potential to further accumulate mineral-associated OC (MOC), while in the majority of soils, the current OC stock in the uppermost 15 cm exceeded the capacity of mineral matter to protect OC. The nationwide soil OC sequestration potential of the uppermost 15 cm in mineral agricultural soils ranged between 5 and 10 Tg, which corresponds to less than the annual greenhouse gas emissions in Finland. The fields with the highest potential for SOC accrual were found in the southern and southwestern parts of the country, including some of the most intensively cultivated high-clay soils. Although the nationwide potential for additional OC sequestration was estimated to be relatively small, the current OC storage in Finnish arable mineral soils (0-15 cm) is large, 128 Tg. Farming practices enabling maximum OC input into the soil play an important role as a tool for mitigating the loss of carbon from high-OC soils in the changing climate. Furthermore, especially in high-clay areas with potential for MOC accrual, efforts to increase soil OC could help improve soil structural stability and therefore reduce erosion and the loss of nutrients to the aquatic environments.

Contribution of water erosion to organic carbon and total nitrogen loads in agricultural discharge from boreal mineral soils

While organic carbon (OC) in agricultural mineral soils is widely studied in terms of soil carbon sequestration and gaseous emissions, discharge-induced OC loss from soil is still poorly understood and estimations of boreal soil OC loads within water erosion are lacking. Loss of organic matter from arable soils is a concern for surface water quality, climate change and soil productivity. The main aim of this study was to quantify the role of water erosion in total OC and nitrogen (N) loads exported in agricultural discharge from boreal mineral soils under various cultivation practices. Surface water and subsurface drainage were collected near-continually over 2 years in two clayey and one sandy soil in Finland. Eroded sediment was mechanically separated by centrifugation from all discharge samples to detect sediment OC% and N% by dry-combustion method. Dissolved OC and N concentrations in selected discharge samples were measured with high-temperature catalytic oxidation of unfiltered supernatant. A multiple linear regression model was used to study the significant factors affecting dissolved, sediment and total OC loads. In the clayey soils, the sediment OC (2–24 kg ha−1 y−1) and N (0.2–1.1 kg ha−1 y−1) export accounted for up to 35 % and 20 % of the annual discharge-induced total loads of OC (19–85 kg ha−1) and N (2–8 kg ha−1), respectively. In the sandy soil, erosion was negligible and dissolved loads of 17–35 kg OC ha−1 y−1and 4–7 kg N ha−1 y−1 were detected. Subsurface drainage exported most of the sediment-associated OC and N loads from clayey soils. For the total OC loads, the distribution varied between the discharge routes, while the total N loads were mostly exported in subsurface drainage in both soil types. Sediment OC and N exports were related to soil plowing and discharge intensity, while dissolved OC loss was promoted by high surface soil OC%. Our results also indicated that a single cultivation practice may affect sediment and dissolved loads in opposite ways. These findings can be used to complement carbon budget estimations for mineral agricultural soils, and to assess soil management effects on terrestrial organic matter loading to boreal surface waters.

A new method for estimating carbon dioxide emissions from drained peatland forest soils for the greenhouse gas inventory of Finland

Abstract. In peatlands drained for forestry, the soil carbon (C) or carbon dioxide (CO2) balance is affected by both (i) higher heterotrophic CO2-C release from faster decomposing soil organic matter (SOM) and (ii) higher plant litter C input from more vigorously growing forests. This balance and other greenhouse gas (GHG) sinks and sources in managed lands are annually reported by national GHG inventories to the United Nations Climate Change Convention. In this paper, we present a revised, fully dynamic method for reporting the CO2 balance of drained peatland forest soils in Finland. Our method can follow temporal changes in tree biomass growth, tree harvesting and climatic parameters, and it is built on empirical regression models of SOM decomposition and litter input in drained peatland forests. All major components of aboveground and belowground litter input from ground vegetation as well as live trees and trees that died naturally are included, supplemented by newly acquired turnover rates of woody plant fine roots. Annual litter input from harvesting residues is calculated using national statistics of logging and energy use of trees. Leaching, which also exports dissolved C from drained peatlands, is not included. The results are reported as time series from 1990–2021 following the practice in the GHG inventory. Our revised method produces an increasing trend of annual emissions from 0.2 to 2.1 t CO2 ha−1 yr−1 for the period 1990–2021 in Finland (equal to a trend from 1.4 to 7.9 Mt CO2 yr−1 for the entire 4.3 Mha of drained peatland forests), with a statistically significant difference between the years 1990 and 2021. Across the period 1990–2021, annual emissions are on average 1.5 t CO2 ha−1 yr−1 (3.4 Mt CO2 yr−1 for 2.2 Mha area) in warmer southern Finland and −0.14 t CO2 ha−1 yr−1 (−0.3 Mt CO2 yr−1 for 2.1 Mha area) in cooler northern Finland. When combined with data on the CO2 sink created by the growing tree stock, in 2021 the drained peatland forest ecosystems were a source of 1.0 t CO2 ha−1 yr−1 (2.3 Mt CO2 yr−1) in southern Finland and a sink of 1.2 t CO2 ha−1 yr−1 (2.5 Mt CO2 yr−1) in northern Finland. We compare these results to those produced by the semi-dynamic method used earlier in the Finnish GHG inventory and discuss the strengths and vulnerabilities of the new revised method in comparison to more static emission factors.

Leaching of nitrogen, phosphorus and other solutes from a controlled drainage cultivated peatland in Ruukki, Finland

Cultivated peatlands are important for grass production in Northern Europe, but the potential impact of nutrients leaching to surface waters is a major concern. Due to a lack of data on nitrogen (N), phosphorus (P) and organic carbon leaching, a monitoring programme was established at Ruukki (Siikajoki, Finland), an agricultural, subsurface drained peat site with a peat thickness of 20–80 cm. Concentrations and loading of N, P, and total organic carbon (TOC) were monitored, along with other water quality parameters for the field discharge, in 2018–2021. We observed N leaching from subsurface discharge to be 25 kg N ha−1 year−1 (range 11–40 kg N ha−1 year−1, 74 % as nitrate NO3-N). The least N leaching was recorded from plots of thinner peat topsoil and those with grass cover, while the majority of N leaching originated from thicker peat plots (bare or under barley) in spring. Leaching of N strongly decreased during periods of thick grass cover. Significant N leaching also occurred during the mild winter of 2019–2020, characterized by alternating freeze and thaw periods. Annual P loading from subsurface drainage was 0.30 kg P ha−1 (0.20–0.43 kg P ha−1), low compared to that of average cultivated soils in Finland. It was estimated that 13 % of the total N leaching and 50 % of the total P leaching occurred in surface runoff. Leaching of TOC was significant at 87 kg ha−1 year−1 (31–137 kg ha−1 year−1). Leaching of dissolved P and TOC increased with peat thickness. Abundant loading of sulfur and acidity indicates the oxidation of sulfidic material in the subsoil. Leaching concentrations correlated with discharge quantity, suggesting that mobilization processes during the dry periods resulted in leaching during high discharge periods. The results show the importance of avoiding bare peat soil for NO3-N leaching reduction, even during wintertime in cultivated peatlands.

Water Retention Characteristics of Mineral Forest Soils in Finland: Impacts for Modeling Soil Moisture

Soil hydraulic properties are central for soil quality and affect forest productivity and the impacts of climate change on forests. The water retention characteristics (WRC) of mineral forest soils in Finland are not well known, and practical tools to predict them for hydrological, biogeochemical and forest models are lacking. We statistically analyzed mineral forest soils WRC from over 130 sites in Finland, focusing on the humus layer and main root zone (0–19 cm depth). We showed that mineral forest soils can be grouped into five WRC classes that are well predictable from soil bulk density, organic matter content and clay fraction. However, the majority of the forest soils are hydrologically rather similar. We found that neither topsoil maps nor any combination of open geospatial data were able to predict WRC. Thus, in the absence of site-specific soil data, parameterizing WRC as a function of forest site fertility type was proposed. We demonstrated the approach in soil moisture modeling at a small forest headwater catchment and showed that the soil moisture response to weather conditions is jointly affected by WRC, stand attributes and topography. We showed that drought risks are highest for dense mature forests at nutrient-poor, coarse-textured sites and lower for young stands on peatlands and lowland herb-rich sites with groundwater influence. The results improve hydrological predictions for Finnish forests, and the open dataset can contribute to the larger synthesis and development of boreal forest soil pedo-transfer functions.

Water retention characteristics of mineral forest soils in Finland: impacts for modeling soil moisture

Water retention characteristics of mineral forest soils in Finland: impacts for modeling soil moisture

Geochemistry of multiple sclerosis in Finland

Multiple sclerosis (MS) affects some 3 million people around the world and the prevalence is increasing. The MS incidence increases with distance from the equator forming a north-to-south gradient. The cause of this gradient and the cause of MS in general are largely unknown. Sulphide-bearing marine and lake sediments, when exposed to oxygen after drainage, form sulphuric acid resulting in the development of acid sulphate soils. From these soils major neurotoxic metals such as iron, aluminum and manganese and trace metals such as nickel, copper and cadmium are released into the surrounding environment. As these soils are largely used for farming, obvious routes to human metal exposure exist. Here we compare the distribution of acid sulphate soils in Finland to the geographic localisation of MS cases using data from a national acid sulphate soil mapping project and historical MS distribution data. Finland has among the highest MS prevalences in the world and several independent nationwide surveys have shown the highest prevalence in western Finland, stable over time. Acid sulphate soil distribution colocalizes with MS, both on a regional (nationwide) scale and local (proximity to rivers) scale. A toxicokinetic LADME model for MS pathogenesis is presented. We propose that neurotoxic metals leaching from acid sulphate soils contribute to the clustering of MS in Finland.

Biochar Capacity to Mitigate Acidity and Adsorb Metals—Laboratory Tests for Acid Sulfate Soil Drainage Water

A 96-h laboratory experiment was conducted to assess the potential of biochar as a water protection tool for acid sulfate soil runoff. Acid sulfate soils pose a risk to water bodies due to acid, metal-rich runoff, especially in drained peatland forests. New water protection methods, such as adsorption with biochar, are needed. We investigated the capability of spruce and birch biochar to adsorb metals and reduce acidity in the water. Water from an acid sulfate site was stirred with biochar, biochar with lime, and biochar with ash. We determined water Al, S, Fe, Cu, Co, Cd, Ni, and Zn concentrations periodically, as well as pH and total organic carbon at the beginning and the end of the experiment. The studied substances are considered the most abundant and environmentally harmful elements in the acid sulfate soils in Finland. Biochar surface characteristics were analyzed with FTIR spectroscopy. Concentration changes were used to parametrize adsorption kinetics models. Biochar adsorbed metals and increased pH, but lime and ash additives did not always improve the adsorption. Spruce biochar and ash addition had generally higher adsorption than birch biochar and lime addition. The adsorption was dominated by Al and Fe at lower pH, while increasing pH improved the adsorption of Cd and Zn. The results show that biochar can increase the water pH, as well as adsorb Al, Fe, Co, Cd, Ni, and Zn. Further work could include an actual-scale biochar reactor in a laboratory and field conditions.

CPTU-based settlement modelling for Kujala test embankments on overconsolidated silty clay: A probabilistic approach

Sounding resistance, such as CPTU cone tip resistance, is often used to estimate the settlement of the subsoil when designing ground-supported structures. This paper utilizes CPTU-based probabilistic modelling to estimate the settlement of two test embankments located in Finland. The model is based on an empirical correlation between CPTU net cone resistance and constrained modulus (M0 ), described by factor α. Besides the existing correlation (prior distribution of α), this paper also considers the site-specific observations via Bayes’ theorem. By means of Monte Carlo simulation, the settlement histograms were produced and the results compared to the observed settlements. Lastly, the effect of dry crust on the embankment load transmission was considered in order to decrease the model bias. The results indicate that for the other embankment the effect of dry crust has to be considered in order to acquire satisfactory results. It is concluded that this CPTU-based settlement model might be suitable for stiff, overconsolidated silty clay soils in Finland. However, model calibration using site-specific oedometer test data is recommended. On the other hand, such simplified model with a singular modulus should not be used for normally consolidated clay subsoils.

Denitrification is the major nitrous acid production pathway in boreal agricultural soils

Nitrous acid (HONO) photolysis produces hydroxyl radicals—a key atmospheric oxidant. Soils are strong HONO emitters, yet HONO production pathways in soils and their relative contributions are poorly constrained. Here, we conduct 15N tracer experiments and isotope pool dilution assays on two types of agricultural soils in Finland to determine HONO emission fluxes and pathways. We show that microbial processes are more important than abiotic processes for HONO emissions. Microbial nitrate reduction (denitrification) considerably exceeded ammonium oxidation as a source of nitrite—a central nitrogen pool connected with HONO emissions. Denitrification contributed 97% and 62% of total HONO fluxes in low and high organic matter soil, respectively. Microbial ammonium oxidation only produced HONO in high organic matter soil (10%). Our findings indicate that microbial nitrate reduction is an important HONO production pathway in aerobic soils, suggesting that terrestrial ecosystems favouring it could be HONO emission hotspots, thereby influencing atmospheric chemistry.

Site types revisited: Comparison of traditional Russian and Finnish classification systems for European boreal forests

AbstractQuestionsForest classifications are tools used in research, monitoring, and management. In Finland, the Cajanderian forest site type classification is based on the composition of understorey vegetation with the assumption that it reflects in a predictable way the site's productive value. In Russia, the Sukachevian forest classification is similarly based on understorey vegetation but also accounts for tree species, soil wetness, and paludification. Here we ask whether Cajander's and Sukachev's forest types are effectively the same in terms of species composition, site productivity, and biodiversity.LocationBoreal forests on mineral soils in Finland and the Russian part of Fennoscandia.MethodsWe use vegetation and soil survey data to compare the Cajanderian and the Sukachevian systems in terms of the understorey community composition (that is supposed to define them), soil fertility and tree productivity (that they are expected to indicate), and biodiversity (that is of interest for conservation purposes). We create and employ class prediction models to divide Russian and Finnish sites into Cajander's and Sukachev's types, respectively, based on vegetation composition. We perform cross‐comparisons between the two systems by non‐metric multidimensional scaling ordination and statistical tests.ResultsWithin both systems, the site types formed similar, meaningful gradients in terms of the studied variables. Certain site types from the two systems were largely overlapping in community composition and arranged similarly along the fertility gradient and may thus be considered comparable.ConclusionsThe Cajanderian and the Sukachevian systems were both developed in the European boreal zone but differ in terms of the exact rules by which site types are determined. Our results show that analogous types between the systems can be identified. These findings aid in endeavours of technology and information transfer between Finnish and Russian forests for the purposes of basic or applied ecological research and forest management.

Quantifying carbon stocks in urban parks under cold climate conditions

Removing CO2 from the atmosphere and storing carbon in vegetation and soil are important ecosystem services provided by urban green space. However, knowledge on the capacity of trees and soils to store carbon in urban parks - especially in the northern latitudes - is scarce. We assessed the amount of organic carbon stored in trees and soil of constructed urban parks under cold climatic conditions in Finland. More specifically, we investigated the effects of management, vegetation type and time since construction on the amount of carbon stored in park trees and soil. We conducted two tree surveys and collected soil samples (0–90 cm) in constructed parks managed by the city of Helsinki. The estimated overall carbon density was approximately 130 t per park hectare, when the carbon stock of trees was 22 to 28 t ha−1 and that of soil 104 t ha−1 at the very least. The soil to tree carbon storage ratio varied from 7.1 to 7.5 for vegetated, pervious grounds and from 3.7 to 5.0 for entire park areas. The effects of park management and vegetation type could not be entirely separated in our data, but time was shown to have a distinct, positive effect on tree and soil carbon stocks. The results indicate that park soils can hold remarkable carbon stocks in a cold climate. It also seems that park soil carbon holding capacity largely exceeds that of forested soils in Finland. Preservation and augmentation of carbon stocks in urban parks implies avoidance of drastic tree and soil renovation measures.

Incorporating a model for ground lichens into multi-functional forest planning for boreal forests in Finland

The quantitative assessment of forest management impacts on ecosystem services calls for ecological models to be linked to forest planning systems. In these systems, such models are expected to produce valid and accurate predictions to quantify the effects of alternative forest management strategies on ecosystem services. As an example, we present an evaluation of the model for the percent cover of ground lichens in forests on mineral soils in Finland. First, the performance of the lichen cover model fitted to the data of forest vegetation surveyed in 1985–1986 was comprehensively validated with the data resurveyed on the same plots in 1995. The differences between the observed and predicted values in lichen cover were calculated and analysed. Second, stand-level analyses were conducted to validate the predicted development of lichen cover in accordance with the rotation length development and management of forest stands. Third, the impacts of forest management scenarios on the average lichen cover at regional level were calculated to validate the results over larger areas. Lichen cover was predicted by site fertility, growing stock, forest harvests, soil preparation and geographic location. Our evaluation suggested that the model logically predicted the 10-year change in lichen cover at the stand level. A negative bias was found in predictions especially on xeric sites in northern Finland, although this was not related to stand management, but probably to global greening and reindeer grazing. The model based on the cross-sectional vegetation survey data showed its ability to describe the long-term changes in lichen cover along with the development and management of stands in different site fertility classes. On xeric and barren sites, the analyses showed decreasing trends in the average lichen cover at the regional level during the 30-year simulation period. However, the development of the average lichen cover varied only slightly among the alternative forest management scenarios. This study provides a modelling approach to evaluate the impacts of forest management on ecosystem services, here the cover of ground lichens, as an indicator of forest biodiversity and quality of reindeer pastures.

Underground parking lot at Turku market square - Zero energy parking hall and the biggest solar energy storage in the world

This paper opens the case Turku market square underground parking lot from the energy perspective. Also constructional and historical aspects are presented. Heavily populated city center has faced several challenges, such as intense traffic. Uncomfortable local tailpipe emissions and lack of parking spaces have decreased living conditions for the citizens and visitors. Therefore, total renovation of main market square of Turku was started in autumn 2018. Together with that, municipality should respond not only to primary needs, but also to national and global environmental targets. One of the new strategy objectives for Turku is being carbon-neutral city by 2029. Hence, project was based on large-scale renewable resources utilization for urban underground spaces. Research and analysis of possible technical solutions was made. Modern time is characterized by climate change and strong measures that need to be taken to stop the global warming. The heat, cold and electricity should be produced in a carbon neutral manner. This doesn’t exclude heated multilevel car parking facilities either. As the parking capacity grows and finding a free place is easier, a positive environmental effect is expected to be reached. The described underground parking lot in Turku is first of its kind in many ways: 1) Never before underground parking lot has dug up and constructed into clay-based soils in Finland, 2) it is probably the first zero carbon energy parking hall in Europe and 3) it has the biggest solar thermal energy storage in the world.

Applying heatmaps in interpretation of geochemical baseline data on urban soils in Finland

Urban soil geochemical mapping was carried out, using the same sampling and analytical protocol, in seven Finnish towns in 2012–2017. All samples were taken from urban topsoil (0–10 cm), dried at <40 °C and sieved to <2 mm grain size. Aqua regia-extractable concentrations of 24 elements and total carbon content were assessed in this statistical study. Soil geochemical results are a typical example of compositional data. Thus, the data were isometric log-ratio (ilr) transformed before correlation analyses and heatmap production. Heatmapping involves colour coding of correlations, with different colours for positive and negative correlations. Elements were re-arranged for heatmaps by clustering the correlation matrix, using hierarchical clustering with distances based on the correlations. Heatmaps were produced for four general soil classes derived from samples taken from the urban topsoil: natural fine-grained sediments, natural coarse-grained sediments, man-made minerogenic soil material and man-made soil material rich in organic matter. The heatmaps revealed two distinct groups in all urban soil parent materials: elements related to abundance of trioctahedral mica minerals and elements bound to soil organic matter. Some man-made soil materials reflecting a single source of pollutants were also identified in the heatmaps.

Soil disturbance by cut-to-length machinery on mid-grained soils

Factors affecting soil disturbance caused by harvester and forwarder were studied on mid-grained soils in Finland. Sample plots were harvested using a one-grip harvester. The harvester operator processed the trees outside the strip roads, and the remaining residues were removed to exclude the covering effect of residues. Thereafter, a loaded forwarder made up to 5 passes over the sample plots. The average rut depth after four machine passes was positively correlated to the volumetric water content at a depth of 0–10 cm in mineral soil, as well as the thickness of the organic layer and the harvester rut depth, and negatively correlated with penetration resistance at depths of both 0–20 cm and 5–40 cm. We present 5 models to predict forwarder rut depth. Four include the cumulative mass driven over a measurement point and combinations of penetration resistance, water content and the depth of organic layer. The fifth model includes harvester rut depth and the cumulative overpassed mass and provided the best fit. Changes in the penetration resistance (PR) were highest at depths of 20–40 cm. Increase in BD and VWC decreased PR, which increased with total overdriven mass. After four to five machine passes PR values started to stabilize.

Half-lives of PAHs and temporal microbiota changes in commonly used urban landscaping materials.

BackgroundPolycyclic aromatic hydrocarbons (PAHs) accumulate in urban soils, and PAH contamination can change soil microbial community composition. Environmental microbiota is associated with human commensal microbiota, immune system and health. Therefore, studies investigating the degradation of PAHs, and the consequences of soil pollution on microbial communities in urban landscaping materials, are crucial.MethodsFour landscaping materials (organic matter 1, 2, 13 and 56%) were contaminated with PAHs commonly found at urban sites (phenanthrene, fluoranthene, pyrene, chrysene and benzo(b)fluoranthene) in PAH concentrations that reflect urban soils in Finland (2.4 µg g -1 soil dry weight). PAHs were analyzed initially and after 2, 4, 8 and 12 weeks by gas chromatography-mass spectrometry. Half-lives of PAHs were determined based on 12-weeks degradation. Bacterial communities were analyzed at 1 and 12 weeks after contamination using Illumina MiSeq 16S rRNA gene metabarcoding.ResultsHalf-lives ranged from 1.5 to 4.4 weeks for PAHs with relatively low molecular weights (phenanthrene, fluoranthene and pyrene) in landscaping materials containing 1–2% organic matter. In contrast, in materials containing 13% and 56% organic matter, the half-lives ranged from 2.5 to 52 weeks. Shorter half-lives of phenanthrene and fluoranthene were thus associated with low organic matter content. The half-life of pyrene was inversely related to the relative abundance of Beta-, Delta- and Gammaproteobacteria, and diversity of Bacteroidetes and Betaprotebacteria. Compounds with higher molecular weights followed compound-specific patterns. Benzo(b)fluoranthene was resistant to degradation and half-life of chrysene was shorter when the relative abundance of Betaproteobacteria was high. Temporal microbiota changes involved increase in the relative abundance of Deltaproteobacteria and decrease in genera Flavobacterium and Rhodanobacter. Exposure to PAHs seems to adjust microbial community composition, particularly within class Beta- and Deltaproteobacteria.ConclusionsIn this study, PAH degradation depended on the organic matter content and bacterial community composition of landscaping materials. Contamination seems to alter bacterial community composition in landscaping materials depending on material type. This alteration includes changes in bacterial phyla associated with human health and immune system. This may open new possibilities for managing urban environments by careful selection of landscaping materials, to benefit health and wellbeing.

Soil CO2 balance and its uncertainty in forestry-drained peatlands in Finland

To understand the global carbon cycle and the impact of human activity on climate, it is necessary to quantify the net CO2 exchange of ecosystems in different land uses on a large scale. Methods to estimate soil net CO2 exchange (NECO2soil) for drained peatland forests have been largely based on chamber measurements and statistical models. The uncertainty in these methods has not been assessed. Yet, disturbed organic soils are a globally important, potential CO2 source due to their vast carbon storage and its sensitivity to changes in soil moisture.In this study, we estimated the countrywide NECO2soil for the 4.76 million ha of forestry-drained peat soils in Finland. We gathered available litter production and CO2 efflux data and constructed models to be used for the upscaling of NECO2soil from forest inventory data. The contribution of each model and the inventory sampling to the precision of the countrywide estimate was calculated. Also, the sensitivity to possible bias in selected model components was estimated.Compared to the estimated mean NECO2soil, ranging from a source of +20gm−2year−1 of C to a sink of −40gm−2year−1 of C, the uncertainty was high. The precision of the estimate (±1 standard deviation) was ±20gm−2year−1 of C. Due to possible bias in the estimated belowground litter input, the overall uncertainty was much higher, around ±60gm−2year−1 of C.The main reason for the high relative uncertainty was NECO2soil being on average close to zero in these boreal forestry-drained peatlands. Forest inventory sample size was large enough and the data for the models were mainly sufficient. To reduce the uncertainty, better understanding of belowground carbon fluxes in order to accurately determine the C input to soil, is crucial.