No description available.

No description available.

<p> To investigate how biogeochemical processes affect the concentrations and fluxes of dissolved organic matter (DOM) in forested watersheds, I studied the quantity and quality of DOM at the Arbutus Lake Watershed, Adirondack Park (NY, USA). First, to understand the biogeochemical changes of DOM for surface waters in the watershed, I studied spatial and temporal patterns of the quantity (bioavailable/refractory concentrations) and quality (&delta;¹³C, aromaticity, and low (LMW; &lt; 1kDa) and high molecular weight (HMW; > 1kDa) of dissolved organic carbon (DOC), nitrogen (DON), and sulfur (DOS). DOC and DON constituents passing through a wetland were composed of highly refractory, aromatic HMW components compared to upland streams. DOS was dominated by the refractory, LMW form. I developed a &ldquo;bioavailability-molecular size model&rdquo; showing the refractoriness of the LMW DOS compared to the HMW DOC and DON. </p><p> Second, to evaluate how a lake nested in a forested watershed affects the dynamics of DOC and DON, I analyzed a mass balance of DOC, DON and dissolved inorganic nitrogen (DIN) from 2000 to 2009. Annual DOC and DON mass balances were strikingly uncoupled, and Arbutus Lake generally acted as a sink for DOC. But a periodic source for DON was observed, indicating that internal recycling between DIN and DON might be important in affecting DON concentrations in this oligo-mesotrophic lake. </p><p> Third, isotopic signatures of DOS in the inlet catchment of the Watershed revealed that the incorporation of reduced S (e.g., SH-) derived from bacterial dissimilatory sulfate reduction contributed to generating DOS in ground and surface waters. These results provide new information on mechanisms for geochemical DOS formation in forested catchments. </p><p> Last, to better understand isotopic changes in DOS, three isotopic pretreatment methods for sulfate widely used were compared. I found an excellent agreement of the &delta;³⁴S-sulfate values among the three methods. However, some differences were observed in the &delta;¹⁸O-sulfate values associated with possible O contamination before isotopic measurements. </p><p> Overall, my studies highlighted novel approaches comparing sources and transformation of three elemental DOM fractions of DOC, DON, and DOS along various watershed components and a lake nested forested watersheds.</p>

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No description available.

<p> High-latitude ecosystems store large amounts of carbon in soil organic matter and are among the most vulnerable to climate change. In particular, fire severity and frequency are increasing in boreal ecosystems, and these events are likely to have direct and indirect effects on climate feedbacks via increased emission of carbon (C) from soil and changes in vegetation composition, respectively. In this study we created experimental burns of three severities in the northeastern Siberian arctic, near Cherskiy, RU, and quantified dissolved C, nitrogen (N), and phosphorus (P), and microbial respiration and extracellular enzyme activities at 1-day, 8-days, and 1-year post-fire. </p><p> Our objective was to determine how fire affects C, N, and P pools, soil microbial processes, and how these effects scale across severity and time since fire. We found labile C and nutrients increased immediately post-fire, but appeared similar to unburned controls within a week. Phosphorus alone remained elevated through 1-year post-fire. Leucine aminopeptidase activities initially increased with fire severity, but by 1-year, activities decreased with fire severity at a rate an order of magnitude faster. Fire severity suppressed phosphatase and ?-glucosidase activities at all time points. Soil respiration was reduced by half in high severity plots 1-year post-fire, while net rates of N mineralization increased by an order of magnitude. We found that changes in soil C and nutrient pools, soil respiration, and net N mineralization rates responded in a threshold-fashion to fire severity, although P was uncoupled from C and N by changing at a distinct severity threshold. Extracellular enzyme activities and edaphic variables scaled linearly with fire severity. The interaction of threshold and linear response curves to fire severity may help explain the variability across studies in soil microbial community responses to fire. Microbial communities recovering from more severe fires have the possibility to decrease future ecosystem C losses through reduced respiration. The changing fire regime in permafrost ecosystems has the potential to alter soil microbial community dynamics, the retention of nutrients, and the stoichiometry of C, N, and P availability.</p>

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Assessment of the potentially acidic, heavy metal-ladenleachates that leave deposits of sulfide ore mill tailings andevaluation of various possible options for mill tailingremediation are scientific problems of increasing practicalimportance. High costs may be associated with the mill tailingremediation, not least after recent changes in Swedish andEuropean environmental legislation. This thesis presents amethodology for studying and quantifying geochemical processesthat contribute to generation of so-called acid mine drainage(AMD). The methodology builds from first principles regardinggeochemical processes, and is based on geochemicalcharacterisation of the mill tailings combined with explicitmodel quantification of the effect of factors, such astemperature, pH, and mineral (BET) surface area, that influencemineral weathering rates. Application of the modellingmethodology to a case study site, Impoundment 1, Kristineberg,northern Sweden, including quantification of slow processesthrough literature rate laws, successfully reproduced the pHand relative concentrations of major ions in the impoundmentgroundwater. Absolute concentrations of most major ions, withthe exception of Zn, were 1-2 orders of magnitude higher in themodel than in the field, which is consistent with the commonlyobserved scale dependence of mineral weathering rates; however,application of a single calibration factor, Xr=10-2, to all weathering rate expressions, sufficed toaccount for this apparent scale dependence. Subsequent laboratory determination of mineral weatheringrates in Impoundment 1 tailings indicated that rates for themajor minerals pyrite (FeS2) and aluminosilicates were in fact 1-2 orders ofmagnitude lower in the ~50-year-old tailings than ratesreported in the literature. Weathering rates of chalcopyrite(CuFeS2) and sphalerite (ZnS) were by contrast 1-3 ordersof magnitude greater than predicted by the literature rate lawsthat were used in the modelling study. While the mechanism ofZn release requires further investigation for improved forwardmodel prediction, the underestimation of Zn concentration inImpoundment 1 by the model was resolved. The laboratory studyfurthermore indicated that the weathering rates of most majorminerals exhibited the same dependence on pH, temperature andsurface area as reported in the literature, and therebysupported the use of literature rate laws for model assessmentof dominant geochemical processes in tailings deposits, onceallowance is made for lower rates in older tailingsmaterial. Analysis of the dominant geochemical processes in the modelof Impoundment 1 indicated that slow weathering ofaluminosilicate minerals provided the bulk of protonattenuation and, as a result, considerably affected the rate ofdepletion of fast-reacting pH-buffering minerals. Inclusion ofthe kinetics of aluminosilicate dissolution and of thefeedbacks between slow and fast processes is thus potentiallycrucial for prediction of pH and its long-term evolution. Thesensitivity of modelled groundwater composition and pH to ironredox reactions, such as may be accelerated by acidophilicbacteria, indicated that, while iron redox cycling was low atthe present case study site, quantification of microbialmediation of these reactions may be necessary for predictingAMD quality under other conditions. The laboratory studies alsoindicated that application of common sterilisation techniques,such as is necessary for study of relative contributions ofabiotic and biotic weathering processes, had little effect onthe long-term (&gt;30 days) abiotic element release rates inthe tailings. This study suggests that within certain limits, which appearnarrower than currently recognised in industrial predictionpractices, it is possible to predict the weathering behaviourof major minerals, and hence proton release and attenuation, inbase metal tailings under field conditions.

<p>Assessment of the potentially acidic, heavy metal-ladenleachates that leave deposits of sulfide ore mill tailings andevaluation of various possible options for mill tailingremediation are scientific problems of increasing practicalimportance. High costs may be associated with the mill tailingremediation, not least after recent changes in Swedish andEuropean environmental legislation. This thesis presents amethodology for studying and quantifying geochemical processesthat contribute to generation of so-called acid mine drainage(AMD). The methodology builds from first principles regardinggeochemical processes, and is based on geochemicalcharacterisation of the mill tailings combined with explicitmodel quantification of the effect of factors, such astemperature, pH, and mineral (BET) surface area, that influencemineral weathering rates. Application of the modellingmethodology to a case study site, Impoundment 1, Kristineberg,northern Sweden, including quantification of slow processesthrough literature rate laws, successfully reproduced the pHand relative concentrations of major ions in the impoundmentgroundwater. Absolute concentrations of most major ions, withthe exception of Zn, were 1-2 orders of magnitude higher in themodel than in the field, which is consistent with the commonlyobserved scale dependence of mineral weathering rates; however,application of a single calibration factor, X_r=10^-2, to all weathering rate expressions, sufficed toaccount for this apparent scale dependence.</p><p>Subsequent laboratory determination of mineral weatheringrates in Impoundment 1 tailings indicated that rates for themajor minerals pyrite (FeS₂) and aluminosilicates were in fact 1-2 orders ofmagnitude lower in the ~50-year-old tailings than ratesreported in the literature. Weathering rates of chalcopyrite(CuFeS₂) and sphalerite (ZnS) were by contrast 1-3 ordersof magnitude greater than predicted by the literature rate lawsthat were used in the modelling study. While the mechanism ofZn release requires further investigation for improved forwardmodel prediction, the underestimation of Zn concentration inImpoundment 1 by the model was resolved. The laboratory studyfurthermore indicated that the weathering rates of most majorminerals exhibited the same dependence on pH, temperature andsurface area as reported in the literature, and therebysupported the use of literature rate laws for model assessmentof dominant geochemical processes in tailings deposits, onceallowance is made for lower rates in older tailingsmaterial.</p><p>Analysis of the dominant geochemical processes in the modelof Impoundment 1 indicated that slow weathering ofaluminosilicate minerals provided the bulk of protonattenuation and, as a result, considerably affected the rate ofdepletion of fast-reacting pH-buffering minerals. Inclusion ofthe kinetics of aluminosilicate dissolution and of thefeedbacks between slow and fast processes is thus potentiallycrucial for prediction of pH and its long-term evolution. Thesensitivity of modelled groundwater composition and pH to ironredox reactions, such as may be accelerated by acidophilicbacteria, indicated that, while iron redox cycling was low atthe present case study site, quantification of microbialmediation of these reactions may be necessary for predictingAMD quality under other conditions. The laboratory studies alsoindicated that application of common sterilisation techniques,such as is necessary for study of relative contributions ofabiotic and biotic weathering processes, had little effect onthe long-term (>30 days) abiotic element release rates inthe tailings.</p><p>This study suggests that within certain limits, which appearnarrower than currently recognised in industrial predictionpractices, it is possible to predict the weathering behaviourof major minerals, and hence proton release and attenuation, inbase metal tailings under field conditions.</p>