This thesis presents results from several studies that have focused on the carbon and nutrient dynamics in soils at the forest – tundra ecotone in Fennoscandia. The main objectives of the study were: (i) to investigate the links between the physical environment, above-ground vegetation communities, soil carbon storage, nutrient status and the chemical composition of the soil organic matter (SOM), and (ii) to quantify trace gas fluxes (methane and carbon dioxide) between mesic soils and the atmosphere. Four main field areas spanning an 8 degree latitudinal gradient were established at the ecotone in 1998 and studied for four years. In addition to the natural gradients we also established a warming treatment. Decomposition rates (i.e. carbon dioxide efflux and litter decomposition) were higher at our forest sites. This was linked principally to the more favourable physical environment at the forest sites, rather than to SOM quality, despite some indications of higher SOM quality at forest sites based upon conventional chemical analysis and 13C NMR techniques. Tundra soils stored large amounts of potentially labile carbon that could readily be accessed by microorganisms when transferred to a forest environment. The interrelation between increased soil temperature and reduced soil moisture content is likely to moderate the response of decomposition rates to increased temperatures. Generally, these mesic soils showed net methane uptake from the atmosphere, which was enhanced by the warming treatment. No differences between forest or tundra soils could be detected. The major conclusions presented here are that (1) soil carbon storage is likely to be reduced if mountain birch forest replaces tundra heath and (2), methane uptake in mesic soils in the Fennoscandian mountains represents a negative feedback to further environmental change in a warmer climate.

Environmental sustainability in Sweden is challenged by rising greenhouse gas emissions from transportation, input-intensive agriculture and potentially unsustainable removal of organic material from forests and farmland. The Swedish government is working towards sixteen environmental quality objectives in order to overcome these problems, among others.  The past decade gave rise to an international research community dedicated to investigate the age-old practice of applying charcoal to soil, practiced most notably by ancient civilisations in the Amazon region of South America. The high level of interest and controversy around this subject inspired this investigation of biochar’s potential benefits in Sweden.  A scientific study was conducted to examine the potential of biochar to enhance environmental sustainability in Sweden. This was largely a desk study, supplemented by expert interviews, GIS map work, an experiment and mathematical analysis.  It was found that there was insufficient research to date to prove the agronomic benefits of biochar in Sweden. More field studies are required to build up the evidence of its potential. Furthermore, as the rate of mineralization of the carbon content is dependent on numerous factors, including the composition of the soil to which the biochar is applied, it is difficult to conclusively define biochar’s carbon storage potential.  This study adds to the existing body of knowledge on the subject by integrating the conclusions from a variety of studies and expert opinions, as well as by providing maps indicating land areas in Sweden that would be likely to benefit from biochar application.

<p>Afforestation, the conversion of historically treeless areas into forests, is a rapidly spreading land-use change with the potential to sequester carbon. Afforested plantations typically feature fast growing exotic tree species that give landowners rapid returns. The efficient growth of plantations compared to less intensively managed forests also can provide greater timber yields in a smaller area. This increased efficiency in turn could require fewer acres to meet global forest product demands and could also reduce the need to log intact primary forests. Reduced primary forest harvest and high primary productivity make afforestation a highly efficient carbon sequestration tool.</p><p> However, the rapid growth and planting disturbance due to afforestation can have deleterious effects on soils and hydrology that undermine its benefits in some locations. The effects on hydrology include depletion of groundwater and reduced or complete elimination of surface water flow. Additionally, groundwater use can lead to increased concentrations of salts and trace metals in soil that could be deleterious for future plant productivity. Plantations have also been shown to acidify surface soils and stream water and to reduce soil carbon and nitrogen.</p><p> Despite the known effects of afforestation on soils, there has been little research on the mechanisms controlling these effects. For instance, there have been few studies on the effects of afforestation on soil microbes which mediate most biogeochemical processes. There is also little knowledge on what controls the effects of afforestation on soil carbon and nitrogen, vital indexes of soil quality, across regions with high levels of afforestation. The overarching goal of this dissertation is to examine the effects of afforestation on soils, microbes, and biogeochemical processes across local, regional and global scales. Understanding the mechanisms by which afforestation alters soils and biogeochemical cycling and how these mechanisms change across different scales will aid in evaluating the true costs and benefits of afforestation. These results will be useful in determining if the benefits of afforestation will continue to outweigh its costs in the long-term.</p><p> The goal of Chapter 1 is to evaluate how afforestation across the globe affects mineral soil quality, including pH, sodium, exchangeable cations, organic carbon, and nitrogen, and to examine the magnitude of these changes in regions where afforestation rates are high. To control for different initial soil conditions across the globe, I examined paired sites of afforested plantations and controls. Controls included land-use types that are frequently afforested, such as grasslands, shrublands, and pastures. I also examined potential mechanisms to reduce the impacts of afforestation on soils and to maintain long-term productivity. Across diverse plantation types (153 sites) to a depth of 30cm of mineral soil, I observed significant decreases in nutrient cations (Ca, K, Mg), increases in sodium (Na), or both with afforestation. For the global dataset, afforestation reduced soil concentrations of the macronutrient Ca by 29% on average compared with native controls (p<0.05). Afforestation by Pinus alone decreased soil K by 23% (p<0.05). Overall, plantations of all genera also led to an average 71% increase of soil Na (p<0.05). Average pH decreased 0.3 units (p<0.05) with afforestation. Afforestation caused a 6.7% and 15% (p<0.05) decrease in soil C and N content respectively, though the effect was driven principally by Pinus plantations (15% and 20% decrease, p<0.05). Carbon to nitrogen ratios in soils under plantations were 5.7-11.6% higher (p<0.05). The major implication of these results are that in several regions with high rates of afforestation, cumulative losses of C, N, Ca, and Mg are likely in the range of tens of millions of metric tons. The decreases indicate that trees take up considerable amounts of nutrients from soils; harvesting this biomass repeatedly could impair long-term soil fertility and productivity in some locations. Based on this study and a review of other literature, I suggest that proper site preparation and sustainable harvest practices, such as avoiding the removal or burning of harvest residue, could minimize the impact of afforestation on soils. These sustainable practices could in turn slow erosion, organic matter loss, and soil compaction from harvesting equipment, maintaining soil fertility to the greatest extent possible. </p><p> Soil microbes are highly diverse and control most soil biogeochemical reactions. Given the observed changes in Chapter 1, in Chapters 2 and 3 I examined how microbial functional genes and biogeochemical pools responded to the altered chemical inputs accompanying afforestation. I examined paired native grasslands and adjacent Eucalyptus plantations (previously grasslands) in Uruguay, a region that lacked forests before European settlement. Along with measurements of soil carbon, nitrogen, and bacterial diversity, I analyzed functional genes using the GeoChip 2.0 microarray that simultaneously quantified several thousand genes involved in soil carbon and nitrogen cycling. Plantations and grasslands differed significantly in functional gene profiles, bacterial diversity, and biogeochemical pool sizes. Afforestation decreased both bacterial diversity and richness compared to grasslands, though diversity remained relatively high. Most grassland functional gene profiles were similar, but plantation profiles generally differed from grasslands due to differences in functional gene abundance across many microbial groups. Eucalypts decreased ammonification and N-fixation functional genes by 11% and 7.9% (p<0.01) which correlated with decreased microbial biomass N and more NH4+ in plantation soils. Chitinase, an important carbon polymer degrading enzyme, decreased in functional gene abundance 7.8% in plantations compared to grasslands (p=0.017), and C polymer degrading genes decreased by 1.5% overall (p<0.05), which likely contributed to 54% (p<0.05) more C in undecomposed extractable soil pools and 27% less microbial C (p<0.01) in plantation soils. In general, afforestation altered the abundance of many microbial functional genes corresponding with changes in soil biogeochemistry. These changes were driven by shifts in the whole community functional gene profile, not just one or two constituent microbial taxa. Such changes in microbial functional genes correspond with altered C and N storage and have implications for long-term productivity in these soils.</p><p> The area studied in Chapters 2 and 3 lies near the middle of a precipitation gradient that stretches across the Rio de la Plata grasslands. In Chapter 4 I studied if the effects of afforestation on soil C and N from Chapters 2 and 3 varied with different precipitation levels. The effect of afforestation on soil C has been shown to depend on mean annual precipitation (MAP), with drier sites gaining C and wetter sites losing C with afforestation. This precipitation dependence of soil C changes with afforestation may be controlled by changes in soil nitrogen (N) cycling. In particular, loss of N due to leaching after afforestation could lead to soil C losses. However, the link between C and N changes due to afforestation has primarily been suggested by models and to my knowledge has never been explicitly tested across a precipitation gradient. The goal of this study was to test how precipitation affects changes in labile and bulk pools of soil C and N across a precipitation gradient, which will provide novel insight into the linkage between land-use change, different pools of soil C and N, and precipitation. I conducted this study across a gradient of precipitation in the Rio de la Plata grasslands of Argentina and Uruguay which ranged from 600mm to 1500mm of precipitation per year. The sites were all former grasslands that had been planted with Eucalyptus. I found that changes in bulk soil C and N were related to MAP with drier sites gaining and wetter sites losing C and N (R2=0.59, p=0.003), which supports the idea that N losses are strongly linked to C losses with afforestation. C and N in microbial biomass and extractable pools followed similar patterns to bulk soil C and N. Interestingly, losses of C and N decreased as the plantations aged, suggesting that longer rotation times for plantations could reduce potential soil carbon and nitrogen losses. These results indicate that afforestation is still be a valuable tool for carbon sequestration, but calculations of the benefits of afforestation must take into account site factors such as age and precipitation to accurately calculate total sequestration benefit and ensure continued high productivity and carbon sequestration.</p><p> In conclusion, afforestation could be an effective tool for carbon sequestration. However, its benefits need to be carefully weighed against its costs for soil such as reduced microbial diversity, decreased soil microbial functional capacity, losses of soil organic matter, and nutrient depletion. Careful management and consideration of afforestation is needed to ensure the greatest benefits with the least long-term damage to soils.</p> / Dissertation

Environmental applications of pyrogenic carbon, aka black carbon (BC), have been hampered due to the poor characterization and quantification of environmental BC. This dissertation was dedicated to the better characterization of environmental char/charcoal BC (char-BC), the most heterogeneous and the less identifiable group in the BC continuum. The analytical approach developed for char-BC was further incorporated with other BC methods in environmental samples for a comprehensive assessment of combustion-derived carbon inputs in different environmental systems. The present study firstly evaluated the feasibility of using levoglucosan, a marker derived from cellulose/hemocellulose combustion, to characterize and quantify char-BC in the environment. Levoglucosan was found exclusively in BC materials derived from biomass combustion albeit in highly variable yields across different char-BC. A further examination of synthetic chars showed that temperature is the most influential factor affecting levoglucosan yield in char. Notably, levoglucosan was only detectable in low temperature char samples (150-350 degrees C), regardless of plant species. These results demonstrated that levoglucosan could serve as a good qualitative indicator for the presence of char produced under low temperature conditions in soil, sediments, and aerosols. Results of lignin analysis on the synthetic chars further reveal that combustion can greatly decrease the yield of the eight major lignin phenols with no lignin phenols detected in any synthetic char produced at greater than or equal to 400 degrees C. The values of all lignin parameters show significant shifts with increasing combustion severity (temperature and/or duration), indicating that thermal alteration is an important abiotic lignin degradation process. Hence the input of char-BC in the environments represents a terrestrial organic matter source with highly altered lignin signatures. Finally, a multi-proxy approach, including elemental (soot-BC) and molecular (levoglucosan, polycyclic aromatic hydrocarbons (PAHs), and lignin oxidation products) proxies, was adopted to investigate the centennial-scale temporal distribution of combustion products in four sediment cores from Puget Sound basins, WA. The observed temporal trends of soot-BC and combustion PAHs fluxes reflect the evolution of energy consumption and the positive effects of environmental regulations. The distinct temporal patterns of soot and PAHs among cores demonstrate that urbanization is a crucial factor controlling the inputs of combustion byproducts to the environment. On the other hand, the trends of levoglucosan may be more relevant to the climate oscillation and thus show a regional distribution pattern. Our results demonstrate that environmental loading of combustion byproducts is a complex function of urbanization and land use, fuel usage, combustion technology, environmental policies, and climate changes.

Irrigation using reclaimed wastewater can introduce organic contaminants and dissolved organic matter (DOM) to soils. Sorption of three common organic wastewater contaminants to five soils of diverse organic matter composition was studied both before and after the removal of soil carbohydrate and peptide components using acid hydrolysis. Results suggest that these polar components may block organic contaminants from accessing higher affinity sorption sites in soil organic matter. The sorptive fractionation of DOM by three mineral soils was studied to assess the terrestrial fate of this complex environmental matrix. Carboxyl- and aromatic-containing moieties appear to preferentially and reversibly sorb to mineral soils. Conversely, carbohydrate and peptide components of DOM preferentially remain in the aqueous phase while aliphatic moieties were selectively retained only by a soil with high surface area. This thesis illustrates that reclaimed wastewater should be applied to soils cautiously as it may degrade soil and groundwater quality.

Irrigation using reclaimed wastewater can introduce organic contaminants and dissolved organic matter (DOM) to soils. Sorption of three common organic wastewater contaminants to five soils of diverse organic matter composition was studied both before and after the removal of soil carbohydrate and peptide components using acid hydrolysis. Results suggest that these polar components may block organic contaminants from accessing higher affinity sorption sites in soil organic matter. The sorptive fractionation of DOM by three mineral soils was studied to assess the terrestrial fate of this complex environmental matrix. Carboxyl- and aromatic-containing moieties appear to preferentially and reversibly sorb to mineral soils. Conversely, carbohydrate and peptide components of DOM preferentially remain in the aqueous phase while aliphatic moieties were selectively retained only by a soil with high surface area. This thesis illustrates that reclaimed wastewater should be applied to soils cautiously as it may degrade soil and groundwater quality.

Despite the importance of soil organic matter (SOM) in C storage and provision of ecosystem services, the magnitude and direction of the response of SOM to climate change remains debated. Particularly contested is the role of biochemical recalcitrance in determining the biological stability of SOM, which in turn, may also vary with climate. Employing a climosequence study design controlling for confounding pedogenic factors, the research described in this thesis aimed to uncover the response of both SOM chemistry and SOM biological stability to changes in climate and associated land use shifts at the grassland-forest ecotone in west-central Saskatchewan. Characterization of SOM chemistry was achieved using two advanced analytical techniques: X-ray absorption near edge structure (XANES) spectroscopy and pyrolysis-field ionization mass spectrometry (Py-FIMS). Agreements between XANES and Py-FIMS revealed only minor differences in SOM chemistry resulting from a 0.7 °C mean annual temperature (MAT) gradient and associated broad differences in land use, but revealed a clear influence of depth within soil profiles. In contrast, long-term aerobic incubations revealed that biological stability of SOM varied with both climate and climate-induced differences in land use, but was not largely influenced by depth. Together, these findings suggest a decoupling of SOM chemistry and its biological stability, indicating that factors other than biochemical recalcitrance are the primary drivers of SOM persistence in these soils.

In this dissertation, the intermolecular interactions between soil organic matter (SOM) and organofluorine compounds have been studied at the molecular-level using Nuclear Magnetic Resonance (NMR) spectroscopy. NMR probes the local magnetic environment surrounding atomic nuclei, and is uniquely capable as an analytical tool to probe molecular environments in complex disordered materials, such as soils. Several NMR techniques were employed in this work, including Pulse Field Gradient (PFG)-NMR based diffusion measurements, solid-state cross-polarization (CP), saturation transfer difference (STD) spectroscopy, and reverse-heteronuclear saturation transfer difference (RHSTD) spectroscopy. Using organofluorine compounds as molecular probes, xenobiotic interactions with SOM were studied. Using 1H{19F} RHSTD, the interaction sites in humic acid for organofluorine compounds were identified by direct molecular-level methods. Protein and lignin were identified as major binding sites, with different preferences exhibited for these sites by dissimilar organofluorine compounds: aromatic organofluorine compounds display varied preference for aromatic humic acid sites while perfluorooctanoic acid exhibits near total selectivity for protein-derived binding sites. The mechanisms underlying these preferences were probed in the solution state. Using crucial knowledge from the humic acid studies, a detailed molecular-level investigation of xenobiotic interactions in an intact and unmodified whole soil was made possible. A direct and in situ elucidation of the components in soil organic matter that interact with small organofluorine xenobiotic molecules has been presented, allowing, for the first time, resolution of multiple interactions occurring for xenobiotics simultaneously at different sites within a whole soil.

In this dissertation, the intermolecular interactions between soil organic matter (SOM) and organofluorine compounds have been studied at the molecular-level using Nuclear Magnetic Resonance (NMR) spectroscopy. NMR probes the local magnetic environment surrounding atomic nuclei, and is uniquely capable as an analytical tool to probe molecular environments in complex disordered materials, such as soils. Several NMR techniques were employed in this work, including Pulse Field Gradient (PFG)-NMR based diffusion measurements, solid-state cross-polarization (CP), saturation transfer difference (STD) spectroscopy, and reverse-heteronuclear saturation transfer difference (RHSTD) spectroscopy. Using organofluorine compounds as molecular probes, xenobiotic interactions with SOM were studied. Using 1H{19F} RHSTD, the interaction sites in humic acid for organofluorine compounds were identified by direct molecular-level methods. Protein and lignin were identified as major binding sites, with different preferences exhibited for these sites by dissimilar organofluorine compounds: aromatic organofluorine compounds display varied preference for aromatic humic acid sites while perfluorooctanoic acid exhibits near total selectivity for protein-derived binding sites. The mechanisms underlying these preferences were probed in the solution state. Using crucial knowledge from the humic acid studies, a detailed molecular-level investigation of xenobiotic interactions in an intact and unmodified whole soil was made possible. A direct and in situ elucidation of the components in soil organic matter that interact with small organofluorine xenobiotic molecules has been presented, allowing, for the first time, resolution of multiple interactions occurring for xenobiotics simultaneously at different sites within a whole soil.

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 3 uppsatser.