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Lichens are a bottleneck resource for circumpolar populations of reindeer, and as such, for reindeer husbandry as an indigenous Sami land-use tradition in northern Sweden. This study uses ground lichen data and forest information collected within the Swedish National Forest Inventory since 1953, on the scale of northern Sweden. We found a 71 % decline in the area of lichen-abundant forests over the last 60 years. A decline was observed in all regions and age classes and especially coincided with a decrease of >60 year old, open pine forests, which was the primary explanatory factor in our model. The effects of reindeer numbers were inconclusive in explaining the decrease in lichen-abundant forest. The role that forestry has played in causing this decline can be debated, but forestry can have a significant role in reversing the trend and improving ground lichen conditions.

During the last six decades, forest biomass has expanded in the Northern basins, mainly due to forest management. This expansion should imply an increasing effect on evapotranspiration. However, increasing global CO2 emissions also trigger physiological plant water saving responses that induce an opposite effect on evapotranspiration. The dominant long-term and large-scale effect on evapotranspiration is still a matter of debate. In this study, we determined the dominant effect on evapotranspiration in Northern forests during the period 1961–2012 by studying change-effects on the ratio of actual evapotranspiration to precipitation, known as the evaporative ratio. We used the Budyko framework of water and energy availability at the basin scale to study the hydroclimatic movements in Budyko space of 65 Swedish basins. We found that changes in the evaporative ratio in 60 % of these basins could not be explained by climatic changes in precipitation and potential evapotranspiration. In both the temperate and boreal basin groups studied, a positive residual effect on the evaporative ratio counteracted the negative climatic effect. Furthermore, temporal change of this residual effect during the period 1961–2012 agreed with that of the standing forest biomass in both the temperate and boreal basin groups as well as with that of the forest cover area in the temperate group. Hence, our long-term and regional-scale results indicate that a positive effect on evapotranspiration from the increasing forest biomass overrode any possible negative stomatal water saving response from increasing atmospheric carbon dioxide concentration. Thus, we suggest that forest expansion is the dominant driver of long-term and large-scale evapotranspiration changes in Northern forests.

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.

The negative effects of elevated concentrations of inorganic aluminium on aquatic organisms are well documented. Acid deposition is often cited as a main driver behind the mobilisation and speciation of aluminium in soils and surface waters. In the study, we tested the hypothesis that sulphur deposition is the main driver for elevated concentrations of inorganic aluminium in 114 base poor, boreal Swedish streams. However, the deposition of anthropogenic sulphate has decreased substantially since it peaked in the 1970s, and at the current deposition levels, we hypothesise that local site parameters play an important role in determining vulnerability to elevated concentrations of inorganic aluminium in boreal stream waters. Presented here are the results of a principal components analysis of stream water chemistry, acid deposition data and local site variables, including forest composition and stem volume. It is shown that the concentrations of both organic and inorganic aluminium are not explained by either historical or current acid deposition, but are instead explained by a combination of local site characteristics. Sites with elevated concentrations of inorganic aluminium were characterised by small catchments (

[1] 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 (∼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, pCO2 (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 pCO2, 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 pCO2 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.

Summary Data from four soil water and groundwater transects from three small, boreal catchments situated along a south–north sulphur deposition gradient in Sweden were studied to assess whether the soils in the near stream zone can significantly modify the groundwater aluminium (Al) chemistry just before it enters the stream and to what extent different levels of acid deposition influences this. The results show that the groundwater aluminium species composition (Alt = total, Alo ∼ organic, Ali ∼ inorganic) and concentrations reflected the variations in groundwater pH ( r Al i 2 = 0.74 ) or TOC ( r Al o 2 = 0.93 ) or a combination of both ( r Al t 2 = 0.89 ). The highest Al concentrations were recorded in shallow groundwater, creating the prerequisites for large lateral Al-fluxes along the hillslopes during episodes of high flow when superficial flow paths are active. A downhill gradient was also seen, with increasing Alo and TOC concentrations towards the stream. Reduced Ali, in absolute as well as relative terms, but increased Alt concentrations in the discharge areas, indicate complex reactions favouring Alo formation and a local input of Alo from the soils. Results from the transect with the most detailed riparian sampling showed that in the last few meters before lateral flow reaches the stream, the mixing of superficial acid soil/groundwater and well-buffered groundwater that had moved along deeper flow paths increased pH and reduced the Ali and Alt concentrations, tangibly. The Alo concentrations were little affected by this pH increase, but at the soil and stream water interface Ali formation was favoured due to the low pH and DOC concentrations in the surface water. Hydrological and soil forming processes within the catchments were more important than acid deposition for the Al dynamics along the hillslopes.