| 1. |
- Akselsson, Cecilia, et al.
(författare)
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Weathering rates in Swedish forest soils
- 2019
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 16:22, s. 4429-4450
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Forskningsöversikt (refereegranskat)abstract
- Soil and water acidification was internationally recognised as a severe environmental problem in the late 1960s. The interest in establishing “critical loads” led to a peak in weathering research in the 1980s and 1990s, since base cation weathering is the long-term counterbalance to acidification pressure. Assessments of weathering rates and associated uncertainties have recently become an area of renewed research interest, this time due to demand for forest residues to provide renewable bioenergy. Increased demand for forest fuels increases the risk of depleting the soils of base cations produced in situ by weathering. This is the background to the research programme Quantifying Weathering Rates for Sustainable Forestry (QWARTS), which ran from 2012 to 2019. The programme involved research groups working at different scales, from laboratory experiments to modelling. The aims of this study were to (1) investigate the variation in published weathering rates of base cations from different approaches in Sweden, with consideration of the key uncertainties for each method; (2) assess the robustness of the results in relation to sustainable forestry; and (3) discuss the results in relation to new insights from the QWARTS programme and propose ways to further reduce uncertainties. In the study we found that the variation in estimated weathering rates at single-site level was large, but still most sites could be placed reliably in broader classes of weathering rates. At the regional level, the results from the different approaches were in general agreement. Comparisons with base cation losses after stem-only and whole-tree harvesting showed sites where whole-tree harvesting was clearly not sustainable and other sites where variation in weathering rates from different approaches obscured the overall balance. Clear imbalances appeared mainly after whole-tree harvesting in spruce forests in southern and central Sweden. Based on the research findings in the QWARTS programme, it was concluded that the PROFILE/ForSAFE family of models provides the most important fundamental understanding of the contribution of weathering to long-term availability of base cations to support forest growth. However, these approaches should be continually assessed against other approaches. Uncertainties in the model approaches can be further reduced, mainly by finding ways to reduce uncertainties in input data on soil texture and associated hydrological parameters but also by developing the models, e.g. to better represent biological feedbacks under the influence of climate change.
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| 2. |
- Ameli, Ali A., et al.
(författare)
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Primary weathering rates, water transit times, and concentration-discharge relations : A theoretical analysis for the critical zone
- 2017
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Ingår i: Water resources research. - : AMER GEOPHYSICAL UNION. - 0043-1397 .- 1944-7973. ; 53:1, s. 942-960
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Tidskriftsartikel (refereegranskat)abstract
- The permeability architecture of the critical zone exerts a major influence on the hydrogeochemistry of the critical zone. Water flow path dynamics drive the spatiotemporal pattern of geochemical evolution and resulting streamflow concentration-discharge (C-Q) relation, but these flow paths are complex and difficult to map quantitatively. Here we couple a new integrated flow and particle tracking transport model with a general reversible Transition State Theory style dissolution rate law to explore theoretically how C-Q relations and concentration in the critical zone respond to decline in saturated hydraulic conductivity (K-s) with soil depth. We do this for a range of flow rates and mineral reaction kinetics. Our results show that for minerals with a high ratio of equilibrium concentration ( Ceq) to intrinsic weathering rate ( Rmax), vertical heterogeneity in K-s enhances the gradient of weathering-derived solute concentration in the critical zone and strengthens the inverse stream C-Q relation. As CeqRmax decreases, the spatial distribution of concentration in the critical zone becomes more uniform for a wide range of flow rates, and stream C-Q relation approaches chemostatic behavior, regardless of the degree of vertical heterogeneity in K-s. These findings suggest that the transport-controlled mechanisms in the hillslope can lead to chemostatic C-Q relations in the stream while the hillslope surface reaction-controlled mechanisms are associated with an inverse stream C-Q relation. In addition, as CeqRmax decreases, the concentration in the critical zone and stream become less dependent on groundwater age (or transit time).
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| 3. |
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| 4. |
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| 5. |
- Bishop, Kevin, et al.
(författare)
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Relation between land use change for long- term trends of organic carbon in lake water and its importance for acidification assessment
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This study examines the changes of total organic carbon (TOC) concentrations in 20 Swedish lakes throughout Sweden using pre-industrial (1860) TOC0 inferred from near-infrared spectrometry (TOCNIRS) of lake sediments to determine if land use change over time could be a plausible explanation for changes in lake water TOC. The study also focuses on the importance of using inferred pre-industrial data of lake water pH and TOC for acidification assessment, in particular ANC0. Most lakes in this study show a long-term decreasing trend of TOC from 1860 up to -0.45 mg/l/yr-1 to an identified breaking point where the TOC turns from decreasing to increasing. Fifteen of the lakes have a breaking point in the mid to late 20th century (1950-1980) while five lakes do not display a clear breaking point. The magnitude of the increasing trend of TOC after the breaking point is up to 0.16 mg/l/yr-1 . Changes in land use were studied by comparing historical maps with present databases of land use. Land use changes in the catchment area show substantial differences in forest cultivation; for instance the coniferous forest has increased by 26% on average. This increase is due to removal of native forest (deciduous forest) and removal of wetlands. Two major conclusions can be drawn from the effects of land use change on TOC levels: (I) No direct correlation between land use change and long-term trends of TOC could be identified in this study. Previous studies have identified the effects of land use change on the carbon storage in the catchment area that corresponds well with the findings of this study. (II) the character of the forest land plays an important role when discussing the effects of land use change for long term TOC trends. The change from open-ended forests with large trees to intense managed forest is considered as an important driving force for TOC. To determine reference conditions there is a need to make good estimations of ANC0 for acidification assessment in Swedish lakes. This study examines the precision of MAGIC model ANC0 calculations (ANC0-MAGIC) against ANC0 calculated with TOCNIRS, diatom-pH and calculated pCO2 (ANC0, diatom-NIRS). ANC0, diatom-NIRS shows a mean difference of (-31µeq/l) when comparing it with ANC0-MAGIC. In comparison, when using contemporary TOC (TOCt) mean lake value 1990-2005 (ANC0,diatom-TOC) the results show a mean difference of (-0.45 µeq/l) in comparison with ANC0-MAGIC. A better fit is generated with TOCNIRS then TOCt. This could be an indication that ANC0- MAGIC overestimates the acidification of Swedish lakes. The European Union’s “Water 8 Framework Directive”, which Sweden has implemented, requires that all surface waters within the Union’s authority have achieved good ecological status by 2015. According to the ecological quality standard the differences between the pre-industrial pH and contemporary pH, i.e. ΔpH=pH0-pHt, should not be more than 0.4 units. This study shows that the long-term trends have to be accounted for when calculating reference conditions and ecological status for acidification
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| 6. |
- Erlandsson Lampa, Martin, et al.
(författare)
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Catchment export of base cations : improved mineral dissolution kinetics influence the role of water transit time
- 2020
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Ingår i: SOIL. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 6:1, s. 231-244
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Tidskriftsartikel (refereegranskat)abstract
- Soil mineral weathering is one of the major sources of base cations (BC), which play a dual role in forest ecosystems: they function as plant nutrients and buffer against the acidification of catchment runoff. On a long-term basis, soil weathering rates determine the highest sustainable forest productivity that does not cause acidification. It is believed that the hydrologic residence time plays a key role in determining the weathering rates at the landscape scale. The PROFILE weathering model has been used for almost 30 years to calculate weathering rates in the rooting zone of forest soils. However, the mineral dissolution equations in PROFILE are not adapted for the saturated zone, and employing these equations at the catchment scale results in a significant overprediction of base cation release rates to surface waters. In this study, we use a revised set of PROFILE equations which, among other features, include retardation due to silica concentrations. Relationships between the water transit time (WTT) and soil water concentrations were derived for each base cation, by simulating the soil water chemistry along a one-dimensional flow path, using the mineralogy from a glacial till soil. We show how the revised PROFILE equations are able to reproduce patterns in BC and silica concentrations as well as BC ratios (Ca2+/BC, Mg2+/BC and Na+/BC) that are observed in the soil water profiles and catchment runoff. In contrast to the original set of PROFILE equations, the revised set of equations could reproduce the fact that increasing WTT led to a decreasing Na+/BC ratio and increasing Ca2+/BC and Mg2+/BC ratios. Furthermore, the total release of base cations from a hillslope was calculated using a mixing model, where water with different WTTs was mixed according to an externally modeled WTT distribution. The revised set of equations gave a 50% lower base cation release (0.23 eqm 2 yr 1) than the original PROFILE equations and are in better agreement with mass balance calculations of weathering rates. Thus, the results from this study demonstrate that the revised mineral dissolution equations for PROFILE are a major step forward in modeling weathering rates at the catchment scale.
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| 7. |
- Erlandsson, Martin, et al.
(författare)
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A comparison of MAGIC and paleolimnological predictions of preindustrial pH for 55 Swedish lakes.
- 2008
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 42:1, s. 43-8
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Tidskriftsartikel (refereegranskat)abstract
- Two fundamentally different approaches to define reference conditions for acidification assessments are hydrogeochemical modeling and paleolimnological reconstructions. Both methods have been applied to calculate the preindustrial chemistry for 55 Swedish lakes in two independent studies. This paper investigates whether these methods give similar reconstructions of the preindustrial pH for these lakes. Special focus has been attached to the importance of total organic carbon concentrations and CO2 partial pressure (pCO(2)) in the conversion from ANC to pH in the hydrogeochemical modeling. With a uniform pCO(2) value for all the lakes of 0.63 matm, the mean absolute difference between pH from the hydrogeochernical model and the paleolimnological pH was +0.23 units (mean absolute difference 0.36 units). If instead a lake specific preindustrial pCO(2) is assumed, equal to contemporary pCO(2), the mean difference in the predicted preindustrial pH between the two methods was reduced to +0.03 units (mean absolute difference 0.22 units). Statistical analyses indicated that with a lake specific pCO(2), the difference between the reconstructions is smaller than 0.13 pH-units at a 95% level of significance. The results of this study build confidence in the reliability of both methods, providing that lake-specific estimates of pCO(2) are used.
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| 8. |
- Erlandsson, Martin, et al.
(författare)
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Direct and indirect effects of increasing dissolved organic carbon levels on pH in lakes recovering from acidification
- 2010
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Ingår i: Journal of Geophysical Research: Biogeosciences. - 2169-8953 .- 2169-8961. ; 115:G3, s. G03004-
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we examine the impact of increasing concentrations of dissolved organic carbon (DOC) on the recovery from acidification for 66 lakes in Southern Sweden. The lakes are small, weakly buffered, and have all been affected by acidifying deposition. A majority of the lakes (similar to 75%) showed an increase in DOC concentrations between 1990 and 2008. The method used in this study was to model pH in 2008 from DOC, acid neutralizing capacity, pCO(2) (partial carbon dioxide pressure), and Al speciation, using both the DOC observed in 2008 and the "unelevated" DOC of 1990. Furthermore, we consider the indirect effects of increasing DOC on acidity, i.e., the ancillary effects from DOC on pCO(2), Al transport and speciation, and release of base cations (BCs). Our results indicate that the DOC increase in the latest decades has retarded the recovery from acidification by 0.13 pH units (median for all lakes) and by more than 1 unit for individual lakes. The effects of elevated pCO(2) and BC concentrations accompanying the DOC increase compensated for each other for the average lake, whereas the effects of higher Al transport on pH were minor. The estimate of the amount of BCs released with the organic anions is however uncertain, and further studies on this topic are needed.
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| 9. |
- Erlandsson, Martin, et al.
(författare)
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Increasing Dissolved Organic Carbon Redefines the Extent of Surface Water Acidification and Helps Resolve a Classic Controversy
- 2011
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Ingår i: BioScience. - : Oxford University Press (OUP). - 0006-3568 .- 1525-3244. ; 61:8, s. 614-618
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Tidskriftsartikel (refereegranskat)abstract
- Concentrations of organic acids in freshwaters have increased significantly during recent decades across large parts of Europe and North America. Different theories of the causes (e.g., recovery from acidification, climate change, land use) have different implications for defining the preindustrial levels for dissolved organic carbon (DOC), which are crucial for assessing acidification and other aspects of water quality. We demonstrate this by classifying the acidification status of 66 lakes with long-term observations, representative of about 12,700 acid-sensitive lakes in nemoral and boreal Sweden. Of these lakes, 47% are classified as significantly acidified (Delta pH >= 0.4), assuming preindustrial DOC levels were equal to those observed in 1990. But if instead, the higher DOC levels observed in 2009 define preindustrial conditions, half as many lakes are acidified (24%). This emphasizes the need to establish reference levels for DOC and casts new light on the classic controversy about natural versus anthropogenic acidification.
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| 10. |
- Erlandsson, Martin, et al.
(författare)
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Natural variability in lake pH on seasonal, interannual and decadal time scales : implications for assessment of human impact
- 2008
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 42:15, s. 5594-5599
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Tidskriftsartikel (refereegranskat)abstract
- Reference values define the natural state with respect to environmental stressors and are commonly used for assessments of ecological impacts and to set restoration targets. These reference values are often treated as constants, whereas in reality they can be highly variable. Here, we study the significance of this variability for assessments of human impact on the environment, by using almost two decades of observations from 95 acid-sensitive Swedish lakes. Our approach was to first estimate the preindustrial, steady-state reference level of acid neutralization capacity (ANC) for each lake with the hydro-geochemical model MAGIC. Then the variability in pH around this "baseline" was reconstructed from the contemporary, "natural" variability in the ANC, total organic carbon (TOC) and Al-concentrations, and partial CO2 pressure. The variability in reference pH was then examined for the period 1990-2004, on seasonal (single measurements), interannual (1-year median), and decadal (5-year median) scales. On the seasonal scale, the variability in reference pH ranged between 0.40 and 1.7. The range on the interannual time scale was up to 1.3 units and for the decadal scale up to 0.76 units. Since an anthropogenic pH decline of more than 0.4 units is deemed significant according to the Swedish Environmental Quality Criteria, this natural variability clearly needs to be accounted for when assessing acidification.
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