Elsevier

Environmental Pollution

Volume 159, Issue 12, December 2011, Pages 3571-3582
Environmental Pollution

Reduced European emissions of S and N – Effects on air concentrations, deposition and soil water chemistry in Swedish forests

https://doi.org/10.1016/j.envpol.2011.08.007Get rights and content

Abstract

Changes in sulphur and nitrogen pollution in Swedish forests have been assessed in relation to European emission reductions, based on measurements in the Swedish Throughfall Monitoring Network. Measurements were analysed over 20 years with a focus on the 12-year period 1996 to 2008. Air concentrations of SO2 and NO2, have decreased. The SO4-deposition has decreased in parallel with the European emission reductions. Soil water SO4-concentrations have decreased at most sites but the pH, ANC and inorganic Al-concentrations indicated acidification recovery only at some of the sites. No changes in the bulk deposition of inorganic nitrogen could be demonstrated. Elevated NO3-concentrations in the soil water occurred at irregular occasions at some southern sites. Despite considerable air pollution emission reductions in Europe, acidification recovery in Swedish forests soils is slow. Nitrogen deposition to Swedish forests continues at elevated levels that may lead to leaching of nitrate to surface waters.

Highlights

► S deposition to Swedish forests has decreased in parallel with European emissions. ► Soil water pH, ANC and inorganic Al-concentrations indicated a slow recovery. ► The bulk deposition of inorganic nitrogen over Sweden has not decreased. ► Continued N deposition to Swedish forests may cause leaching of N to surface waters.

Introduction

Anthropogenic emissions of sulphur and nitrogen have caused acidification and eutrophication of terrestrial and aquatic ecosystems in Europe (Reuss and Johnson, 1986, Galloway et al., 2004). The emissions have however decreased considerably since 1990 (Nyiri et al., 2009). Over the period 1990–2008, the emission reductions reported by EMEP for the 27 EU member countries were 73, 39 and 22% for oxidized sulphur, oxidized nitrogen and reduced nitrogen, respectively. The corresponding values for emission reductions for Sweden were 71, 49 and 8% for oxidized sulphur, oxidized nitrogen and reduced nitrogen, respectively.

The emission reductions have improved the situation to some extent e.g. in streams and lakes in Sweden (Skjelvåle et al., 2001, Fölster and Wilander, 2002). But the recovery is often slow and model simulations show that a full recovery is far away in the future in many regions, where the soils have been depleted of base cations (Sverdrup et al., 2005). Continuous evaluations of effects of the reduced emissions on air pollutant concentrations, on deposition to the forests and on soil and soil water chemistry are necessary in order to assess whether or not the emission reductions are large enough to allow for sufficient ecosystem recovery.

The Swedish Throughfall Monitoring (SWETHRO) network started in 1985, with the aim to measure air concentrations, deposition and soil water chemistry in managed forest ecosystems across Sweden. The measurements started in southern Sweden, where the acidification problems were largest, but the network has expanded and today measurements are carried out across the entire country. Evaluation of data for the period 1985–1994 has shown a gradient with the highest S and N deposition in the south-western part of Sweden (Hallgren Larsson et al., 1995). Furthermore, there was a temporal trend with decreasing sulphur deposition during this period.

In this article, air concentrations, deposition and soil water chemistry were evaluated with respect to trends over time and geographical gradients for the different monitoring sites within the SWETHRO network. Focus was on the period of October 1996–September 2008, for which continuous time series of measurements are available for more than 50 sites for throughfall and soil water chemistry, covering the entire country. Results are also shown from a few long time series in southern Sweden, starting in the late ‘80s or early ‘90s. The changes in air concentrations and deposition to Swedish forests are compared to the reported European emission reductions and discussed in relation to the progress of recovery of soil water chemistry.

Section snippets

Sites and measurements

The SWETHRO network is financed by regional air quality protection associations and local county administrative boards. They decide what to measure and when, in collaboration with the SWETHRO scientists. As a result, the measurements at different monitoring sites cover different time periods.

The SWETHRO network includes measurements of air concentrations and bulk deposition (BD) in open areas, as well as throughfall deposition (TF) and soil water chemistry inside forest stands (Table 1). In

Air concentrations

Several of the sites in the SWETHRO network with long-term air pollution concentration measurements were terminated 2006 and several other sites did not start air concentration measurements until the beginning of the 2000s. As a result there were relatively few sites with air concentration measurements covering the entire period 1996/97–2007/08. An example of the geographical distributions of yearly mean air concentrations of SO2, NO2 and NH3 across Sweden is shown in Fig. 2 for the

Discussion

The air pollution situation over Sweden, as well as the deposition rates, depends strongly on the weather conditions. However, there were no obvious trends in air temperatures or precipitation during the period 1996/97–2007/08 that might have systematically influenced the air pollution concentration or deposition during this period. This analysis was made for average values across Sweden with yearly and growing season time resolution (data not shown), based on official weather statistics

Conclusions

Changes over time in sulphur and nitrogen air concentrations, deposition and soil water concentrations in forest ecosystems in Sweden as well as in other Nordic countries were assessed in relation to European emission reductions for oxidized sulphur and oxidized and reduced nitrogen. The analysis of the time series 1996/97–2007/08 gave the following results.

  • The SO2 and NO2 air concentrations have decreased substantially, whereas there was no trend for NH3.

  • Reductions in SO4-deposition were found

Acknowledgements

This research has been funded by various regional air quality protection associations, county administrative boards and the Swedish Environmental Protection Agency. The Swedish Throughfall Monitoring Network (SWERHRO) is run by IVL Swedish Environmental Research Institute. The work with this publication was funded by the unit Monitoring at the Swedish Environmental Protection Agency. We would also like to thank all field and laboratory personnel and all other devoted colleagues.

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