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This thesis presents temporal perspectives of lake acidification in Sweden. Sediment records have been used to study timing, trends and causes of acidification, and two different techniques for assessing past lake-water acidity are presented. A new technique for pH prediction, based on near-infrared (NIR) spectroscopy of surface sediments, is developed. This study shows that there is a pH related fraction of lake sediments that can be recorded by NIR analysis. Relationships between NIR spectra of surface sediment samples and measured lake-water pH values, and between NIR spectra of sediment cores and historical pH values inferred by diatom analysis, are modelled by partial least squares regression. The prediction errors of the models are comparable to those obtained by modelling of diatom and lake-water pH data. By further development NIR spectroscopy can become useful for inferring past pH, as well as several other lake-water parameters, from sediment cores. Diatom-based predictive models, using multivariate calibration methods, are developed for inferences of lake-water pH, alkalinity and colour. These models are used to provide a regional assessment of recent lake acidification in the provinces of Västerbotten and Norrbotten, northern Sweden. The study shows that a pH decline has occurred in some southeastern lakes, but that most of the lakes have not faced significant changes in lake-water pH, alkalinity and colour. The inferred water chemistiy changes are discussed in relation to atmospheric deposition and land-use. In a study of eight acid-sensitive Swedish boreal-forest lakes a past-analogue approach is used to test whether contemporary expansion of conifers could cause lake acidification. Water chemistry changes associated with the natural pre-historic colonization and expansion of spruce in Sweden (≈3000 years B.P.), at times of background atmospheric acidity, are inferred to evaluate the acidification ability of spruce per se on surface waters. This study shows that under natural, unpolluted conditions spruce colonization and expansion did not cause lake acidification. In a synthesis of palaeolimnological acidification research in Sweden a general model for pH- development for acid clear-water lakes in southern Sweden is presented. The pH-development from the last deglaciation to present time can be divided into four different periods; (i) a natural long-term acidification period (12000 B.P. - 2300 B.P., or later), with a gradual decrease in pH resulting from declining fluxes of base cations from catchment soils; (ii) a human induced alkalization period (2300 B.P. - 1900 A.D.), with a pH increase due to human activities in the catchments; (iii) the recent acidification period (about 1900 A.D. - present), when pH decreased towards 4.5 due to acid deposition and possibly ceased land-use; and (iv) the liming period (1970s - present), when pH often increases to values above 7 following lime treatment to counteract acidification. The implications of these past pH changes for the concept of contemporary lake acidification and for liming policy are outlined. / digitalisering@umu

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No description available.

Seasonally snow covered alpine areas play a larger role in the hydrologic cycle than their area would indicate. Their ecosystems may be sensitive indicators of climatic and atmospheric change. Assessing the hydrologic and bio- geochemical responses of these areas to changes in inputs of water, chemicals and energy should be based on a detailed understanding of watershed processes. This dissertation discusses the development and testing of a model capable of predicting watershed hydrologic and hydrochemical responses to these changes. The model computes integrated water and chemical balances for watersheds with unlimited numbers of terrestrial, stream, and lake subunits, each of which may have a unique, variable snow -covered area. Model capabilities include 1) tracking of chemical inputs from precipitation, dry deposition, snowmelt, mineral weathering, basefiow or flows from areas external to the modeled watershed, and user -defined sources and sinks, 2) tracking water and chemical movements in the canopy, snowpack, soil litter, multiple soil layers, streamflow, between terrestrial subunits (surface and subsurface movement), and within lakes (2 layers), 3) chemical speciation, including free and total soluble species, precipitates, exchange complexes, and acid -neutralizing capacity, 4) nitrogen reactions, 5) a snowmelt optimization procedure capable of exactly matching observed watershed outflows, and 6) modeling riparian areas. Two years of data were available for fitting and comparing observed and modeled output. To the extent possible, model parameters are set based on physical or chemical measurements, leaving only a few fitted parameters. The effects of snowmelt rate, rate of chemical elution from the snowpack, nitrogen reactions, mineral weathering, and flow routing on modeled outputs are examined.

Seasonally snow covered alpine areas play a larger role in the hydrologic cycle than their area would indicate. Their ecosystems may be sensitive indicators of climatic and atmospheric change. Assessing the hydrologic and bio-geochemical responses of these areas to changes in inputs of water, chemicals and energy should be based on a detailed understanding of watershed processes. This dissertation discusses the development and testing of a model capable of predicting watershed hydrologic and hydrochemical responses to these changes. The model computes integrated water and chemical balances for watersheds with unlimited numbers of terrestrial, stream, and lake subunits, each of which may have a unique, variable snow-covered area. Model capabilities include (1) tracking of chemical inputs from precipitation, dry deposition, snowmelt, mineral weathering, baseflow or flows from areas external to the modeled watershed, and user-defined sources and sinks, (2) tracking water and chemical movements in the canopy, snowpack, soil litter, multiple soil layers, streamflow, between terrestrial subunits (surface and subsurface movement), and within lakes (2 layers), (3) chemical speciation, including free and total soluble species, precipitates, exchange complexes, and acid-neutralizing capacity, (4) nitrogen reactions, (5) a snowmelt optimization procedure capable of exactly matching observed watershed outflows, and (6) modeling riparian areas. Two years of data were available for fitting and comparing observed and modeled output. To the extent possible, model parameters are set based on physical or chemical measurements, leaving only a few fitted parameters. Thc effects of snowmelt rate, rate of chemical elution from the snowpack, nitrogen reactions, mineral weathering, and flow routing on modeled outputs are examined.

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No description available.

The objective of this thesis was to validate the dynamic model SAFE (Soil Acidification in Forested Ecosystems) in a small deciduous watershed of southern Quebec. SAFE could then be used to: (1) identify which processes are governing acidification, and (2) assess the rates of acidification according to various forest conditions. / Soil and soil solution chemistry between unburned and burned zones following fire disturbance seventy-five years ago was examined within the watershed. Results showed two major, statistically significant, differences: (1) higher base status, and (2) lower soil solution N in the burned zone. High quality leaf litter of aspen and birch (burned zone) relative to that of sugar and red maple (unburned zone) has contributed to the enrichment of base cations in the forest floor. The enrichment of the forest floor did not however impoverish the B horizon as seen in other studies. Rather, fire enriched the soil in base cations and buffered the effect of forest regrowth in the B horizon. / The MAKEDEP model was used to reconstruct the time-series input files needed to run SAFE. In MAKEDEP, the availability of N determines tree growth which in turn, affects most of the processes involved in nutrient cycling. Regressions of measured deposition at the Hubbard Brook Experimental Forest and that of simulated deposition at the study site suggest MAKEDEP is suitable to model the deposition trends of all elements except Na. / SAFE was calibrated for the unburned and burned conditions at the study site. Fire disturbance and forest regrowth have produced different soil chemical composition within the zones as discussed above. SAFE was therefore validated at the study site as a function of its ability to reproduce soil chemistry under unburned and burned conditions. The simulated soil chemistry was in close agreement with the measured unburned soil conditions, but some processes would have to be clarified or accounted for with greater accurately, e.g., biological N fixation and N immobilization by myccorhizal fungi, to reproduce more accurately the measured burned soil chemistry. Simulated soil chemistry in the unburned zone reinforced nevertheless the conclusions of a few historical soil chemistry studies supporting the hypothesis that acid-sensitive forest sites of the United States underwent significant acidification during 1930--1980 during major input of acidity from the atmosphere. Model output suggests that cation nutrient deficiencies could occur in the long-term, but future Al phytotoxic responses are unlikely to occur due to a relatively high projected pH. (Abstract shortened by UMI.)

This thesis used novel methodologies in dendrochemistry to observe past nutrient and Al change in relation to incremental stem xylem growth to predict current and future forest health. The methods included (1) sequential digestion of wood tissue to remove the elemental fraction that is mobile across tree rings leaving the structurally intrinsic, residual (or less mobile) ion fraction for analysis and (2) transformation of elemental concentrations into multivariate ratios (compositional nutrient diagnosis (CND)) over a time series. Sampling of trees represented a gradient in acidity resilience using three regions of southern Quebec (St. Lawrence Lowlands; Lower Laurentians; and Appalachian Highlands) and three species (red maple ( Acer rubrum L.); sugar maple (Acer sacharum Marsh.); and American beech (Fagus grandifolia Ehrh.). The elemental residual fraction had differences from the mobile fraction over time for Ca, Mg and Mn, but not for K or Al. The base rich Saint-Lawrence region had the highest and slightly increasing incremental stem xylem Al of the regions yet had stable or increasing growth. By contrast the acid sensitive Appalachian region had the greatest increase in Al accompanied by a decrease in growth beyond 1970. The Appalachians also had the highest Mn, which had an adverse effect on growth of sugar maple. The acid-resilient species American beech had stable or decreasing Al while having stable or increasing growth in contrast to the less resilient sugar and red maple. The nutrient poor Laurentian region had a persistent deficiency of K over time but no relationships with Al. Aluminium had a general negative correlation with the other canons. Although Mn had the highest levels in red maple for each region, it appears to be limiting growth. The changes in wood chemistry and growth over time appear to be driven by the resilience of the region or species to increasing acidic load in the ecosystems.