| 1. |
- Djukic, Ika, et al.
(författare)
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Early stage litter decomposition across biomes
- 2018
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Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 628, s. 1369-1394
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Tidskriftsartikel (refereegranskat)abstract
- Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from −9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.
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| 2. |
- Grandin, Ulf, et al.
(författare)
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Assessing critical load exceedances and ecosystem impacts of anthropogenic nitrogen and sulphur deposition at unmanaged forested catchments in Europe
- 2021
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 753
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic emissions of nitrogen (N) and sulphur (S) compounds and their long-range transport have caused widespread negative impacts on different ecosystems. Critical loads (CLs) are deposition thresholds used to describe the sensitivity of ecosystems to atmospheric deposition. The CLmethodology has been a key science-based tool for assessing the environmental consequences of air pollution. We computed CLs for eutrophication and acidification using a European long-term dataset of intensively studied forested ecosystem sites (n = 17) in northern and central Europe. The sites belong to the ICP IM and eLTER networks. The link between the sitespecific calculations and time-series of CL exceedances and measured site data was evaluated using long-term measurements (1990-2017) for bulk deposition, throughfall and runoff water chemistry. Novel techniques for presenting exceedances of CLs and their temporal development were also developed. Concentrations and fluxes of sulphate, total inorganic nitrogen (TIN) and acidity in deposition substantially decreased at the sites. Decreases in S deposition resulted in statistically significant decreased concentrations and fluxes of sulphate in runoff and decreasing trends of TIN in runoffweremore common than increasing trends. The temporal developments of the exceedance of the CLs indicated the more effective reductions of S deposition compared to N at the sites. There was a relation between calculated exceedance of the CLs and measured runoff water concentrations and fluxes, and most sites with higher CL exceedances showed larger decreases in both TIN and H+ concentrations and fluxes. Sites with higher cumulative exceedance of eutrophication CLs (averaged over 3 and 30 years) generally showed higher TIN concentrations in runoff. The results provided evidence on the link between CL exceedances and empirical impacts, increasing confidence in the methodology used for the European-scale CL calculations. The results also confirm that emission abatement actions are having their intended effects on CL exceedances and ecosystem impacts. (C) 2020 The Author(s). Published by Elsevier B.V.
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| 3. |
- Lundin, Lars, et al.
(författare)
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Long-term changes (1990-2015) in the atmospheric deposition and runoff water chemistry of sulphate, inorganic nitrogen and acidity for forested catchments in Europe in relation to changes in emissions and hydrometeorological conditions
- 2018
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 625, s. 1129-1145
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Tidskriftsartikel (refereegranskat)abstract
- The international Long-Term Ecological Research Network (ILTER) encompasses hundreds of long-term research/monitoring sites located in a wide array of ecosystems that can help us understand environmental change across the globe. We evaluated long-term trends (1990-2015) for bulk deposition, throughfall and runoff water chemistry and fluxes, and climatic variables 10 25 forested catchments in Europe belonging to the UNECE International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICP IM). Many of the IM sites form part of the monitoring infrastructures of this larger ILTER network. Trends were evaluated for monthly concentrations of non-marine (anthropogenic fraction, denoted as x) sulphate (xSO(4)) and base cations x(Ca + Mg), hydrogen ion (H+), inorganic N (NO3 and NH4) and ANC (Acid Neutralising Capacity) and their respective fluxes into and out of the catchments and for monthly precipitation, runoff and air temperature. A significant decrease of xSO(4) deposition resulted in decreases in concentrations and fluxes of xSO(4) in runoff, being significant at 90% and 60% of the sites, respectively. Bulk deposition of NO3 and NH4 decreased significantly at 60-80% (concentrations) and 40-60% (fluxes) of the sites. Concentrations and fluxes of NO3 in runoff decreased at 73% and 63% of the sites, respectively, and NO3 concentrations decreased significantly at 50% of the sites. Thus, the LTER/ICP IM network confirms the positive effects of the emission reductions in Europe. Air temperature increased significantly at 61% of the sites, while trends for precipitation and runoff were rarely significant. The site specific variation of xSO(4) concentrations in runoff was most strongly explained by deposition. Climatic variables and deposition explained the variation of inorganic N concentrations in runoff at single sites poorly, and as yet there are no clear signs of a consistent deposition-driven or climate-driven increase in inorganic N exports in the catchments. (C) 2017 Elsevier B.V. All rights reserved.
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| 4. |
- Löfgren, Stefan
(författare)
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Decreased DOC concentrations in soil water in forested areas in southern Sweden during 1987-2008
- 2011
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 409, s. 1916-1926
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Tidskriftsartikel (refereegranskat)abstract
- During the last two decades, there is a common trend of increasing concentrations of dissolved organic carbon (DOC) in streams and lakes in Europe. Canada and the US. Different processes have been proposed to explain this trend and recently a unifying hypothesis was presented, concluding that declining sulphur deposition and recovery from acidification, is the single most important factor for the long-term DOC concentration trends in surface waters. If this recovery hypothesis is correct, the soil water DOC concentrations should increase as well. However, long-term soil water data from Sweden and Norway indicate that there are either decreasing or indifferent DOC concentrations, while positive DOC trends have been found in the Czech Republic. Based on the soil water data from two Swedish integrated monitoring sites and geochemical modelling, it has been shown that depending on changes in pH, ionic strength and soil Al pools, the DOC solubility might be positive, negative or indifferent. In this study, we test the acidification recovery hypothesis on long-term soil water data (25 and 50 cm soil depth) from 68 forest covered sites in southern Sweden, showing clear signs of recovery from acidification. The main aim was to identify potential drivers for the DOC solubility in soil solution by comparing trends in DOC concentrations with observed changes in pH, ionic strength and concentrations of Al(n+). As in earlier Swedish and Norwegian studies, the DOC concentrations in soil water decreased or showed no trend. The generally small increases in pH (median < 0.3 pH units) during the investigation period seem to be counterbalanced by the reduced ionic strength and diminished Al concentrations, increasing the organic matter coagulation. Hence, opposite to the conclusion for surface waters, the solubility of organic matter seems to decrease in uphill soils, as a result of the acidification recovery. (C) 2011 Elsevier B.V. All rights reserved.
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| 5. |
- Löfgren, Stefan, et al.
(författare)
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Decreasing DOC trends in soil solution along the hillslopes at two IM sites in southern Sweden : Geochemical modeling of organic matter solubility during acidification recovery
- 2010
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 409:1, s. 201-210
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Tidskriftsartikel (refereegranskat)abstract
- Numerous studies report increased concentrations of dissolved organic carbon (DOC) during the last two decades in boreal lakes and streams in Europe and North America Recently a hypothesis was presented on how various spatial and temporal factors affect the DOC dynamics It was concluded that declining sulphur deposition and thereby increased DOC solubility is the most important driver for the long-term DOC concentration trends in surface waters If this recovery hypothesis is correct the DOC levels should increase both in the soil solution as well as in the surrounding surface waters as soil pH rises and the ionic strength declines due to the reduced input of SO42- ions In this project a geochemical model was set up to calculate the net humic charge and DOC solubility trends in soils during the period 1996-2007 at two integrated monitoring sites in southern Sweden showing clear signs of acidification recovery The Stockholm Humic Model was used to investigate whether the observed DOC solubility is related to the humic charge and to examine how pH and ionic strength influence it Soil water data from recharge and discharge areas covering both podzols and riparian soils were used The model exercise showed that the increased net charge following the pH increase was in many cases counteracted by a decreased ionic strength, which acted to decrease the net charge and hence the DOC solubility Thus the recovery from acidification does not necessarily have to generate increasing DOC trends in soil solution Depending on changes in pH ionic strength and soil Al pools the trends might be positive negative or indifferent Due to the high hydraulic connectivity with the streams the explanations to the DOC trends in surface waters should be searched for in discharge areas and peat lands.
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| 6. |
- Zetterberg, Therese, et al.
(författare)
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Sensitivity analyses of MAGIC modelled predictions of future impacts of whole-tree harvest on soil calcium supply and stream acid neutralizing capacity
- 2014
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 494, s. 187-201
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Tidskriftsartikel (refereegranskat)abstract
- Forest biofuel is a main provider of energy in Sweden and the market is expected to grow even further in the future. Removal of logging residues via harvest can lead to short-term acidification but the long-term effects are largely unknown. The objectives of this study were to 1) model the long-term effect of whole-tree harvest (WTH) on soil and stream water acidity and 2) perform sensitivity analyses by varying the amounts of logging residues, calcium (Ca2+) concentrations in tree biomass and site productivity in nine alternate scenarios. Data from three Swedish forested catchments and the Model of Acidification of Groundwater in Catchments (MAGIC) were used to simulate changes in forest soil exchangeable Ca2+ pools and stream water acid neutralizing capacity (ANC) at Gammtratten, Kindla and Aneboda. Large depletions in soil Ca2+ supply and a reversal of the positive trend in stream ANC were predicted for all three sites after WTH. However, the magnitude of impact on stream ANC varied depending on site and the concentration of mobile strong acid anions. Contrary to common beliefs, the largest decrease in modelled ANC was observed at the well-buffered site Gammtratten. The effects at Kindla and Aneboda were much more limited and not large enough to offset the general recovery from acidification. Varying the tree biomass Ca2+ concentrations exerted the largest impact on modelled outcome. Site productivity was the second most important variable whereas changing biomass amounts left on site only marginally affected the results. The outcome from the sensitivity analyses pointed in the same direction of change as in the base scenario, except for Kindla where soil Ca2+ pools were predicted to be replenished under a given set of input data. The reliability of modelled outcome would increase by using site-specific Ca2+ concentrations in tree biomass and field determined identification of site productivity. (C) 2014 Elsevier B.V. All rights reserved.
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