Trends in pH in the organic layer

• Link to a simulation showing how the estimated pH in the organic layer has changed during the period 1963–1999.
• Link to a map showing where in the country the changes can be considered statistically significant, expressed as probability values (p-values, *=p<0.05, **=p<0.01, ***=p<0.001) derived from the underlying functions. Red indicates decreasing pH, blue increasing pH, and yellow indicates that no statistically significant change has occurred (n.s.).
• Link to a map showing the magnitude of change expressed as hydrogen ion concentration ×10⁻⁶ year⁻¹. Blue indicates decreasing hydrogen ion concentration (higher pH), and red indicates increasing hydrogen ion concentration (lower pH).

The maps above show that certain parts of Sweden exhibited clear changes in pH in the organic layer during the period 1963–1999. Areas where the rate of acidification was greatest and most reliably determined include the coastal region of Västerbotten, northern Dalarna, Tiveden, southern Jönköping County and western Kronoberg County. Other areas were also likely affected by acidification, for example Ångermanland and parts of Tornedalen.

In other regions, no clear change in pH in the organic layer was observed.

The analyses are based on the entire available dataset of approximately 62,000 sample plots with measured pH values. An attempt is also made to divide this dataset into two equally large subsets with respect to site productivity and stand age in order to identify potential differences in the pattern of acidification. This is presented below.

• Link to a simulation showing how the estimated pH in the organic layer has changed during the period 1963–1999.
• Link to a map showing where in the country the changes can be considered statistically significant, expressed as probability values (p-values, *=p<0.05, **=p<0.01, ***=p<0.001) derived from the underlying functions. Red indicates decreasing pH, blue increasing pH, and yellow indicates that no statistically significant change has occurred (n.s.).
• Link to a map showing the magnitude of change expressed as hydrogen ion concentration ×10⁻⁶ year⁻¹. Blue indicates decreasing hydrogen ion concentration (higher pH), and red indicates increasing hydrogen ion concentration (lower pH).

The dataset has been divided into two equally large subsets with respect to stand age, one older and one younger, within grid cells of 75 × 75 km. These have subsequently been combined into a SAS table indicating to which subset each sample plot belongs with respect to stand age.

The maps show that pH is generally higher in the younger half of the dataset. Of particular interest, however, is to assess whether there are areas with altered acidification patterns compared with the full dataset.

Areas that deviate in the younger half include Blekinge, where acidification is observed, and northern Dalarna, where little to no change in pH is evident. In northern Sweden, largely the same areas that show acidification occur in both the younger and older halves of the dataset.

• Link to a simulation showing how the estimated pH in the organic layer has changed during the period 1963–1999.
• Link to a map showing where in the country the changes can be considered statistically significant, expressed as probability values (p-values, *=p<0.05, **=p<0.01, ***=p<0.001) derived from the underlying functions. Red indicates decreasing pH, blue increasing pH, and yellow indicates that no statistically significant change has occurred (n.s.).
• Link to a map showing the magnitude of change expressed as hydrogen ion concentration ×10⁻⁶ year⁻¹. Blue indicates decreasing hydrogen ion concentration (higher pH), and red indicates increasing hydrogen ion concentration (lower pH).

The dataset has been divided into two equally large subsets with respect to stand age, one older and one younger, within grid cells of 75 × 75 km. These have subsequently been combined into a SAS table indicating to which subset each sample plot belongs with respect to stand age.

Areas that deviate in the older half of the dataset include Tiveden, where substantially less acidification is observed. The area in northern Dalarna is considerably more extensive and shows pronounced acidification. The area in south-western Götaland has decreased in extent and is now found in the southern part of Jönköping County. A decrease in pH can also be discerned in north-eastern Uppland. In northern Sweden, largely the same areas that show acidification overall are found in both the younger and older halves of the dataset.

• Link to a simulation showing how the estimated pH in the organic layer has changed during the period 1963–1999.
• Link to a map showing where in the country the changes can be considered statistically significant,expressed as probability values (p-values, *=p<0.05, **=p<0.01, ***=p<0.001) derived from the underlying functions. Red indicates decreasing pH, blue increasing pH, and yellow indicates that no statistically significant change has occurred (n.s.).
• Link to a map showing the magnitude of change expressed as hydrogen ion concentration ×10⁻⁶ year⁻¹. Blue indicates decreasing hydrogen ion concentration (higher pH), and red indicates increasing hydrogen ion concentration (lower pH).

The dataset has been divided into two equally large subsets with respect to site productivity (m³sk ha⁻¹ year⁻¹), one higher and one lower, within grid cells of 75 × 75 km. These have subsequently been combined into a SAS table indicating to which subset each sample plot belongs with respect to site productivity.

The maps show that pH is generally lower in the lower-productivity half of the dataset. Of particular interest, however, is to assess whether there are areas with altered acidification patterns compared with the full dataset.

In the lower-productivity half, a trend towards acidification is observed at many locations across Sweden. A clear deviation from the overall pattern is found in north-eastern Uppland and the northern parts of Stockholm County. Other areas include parts of Skåne, southern Västergötland, and southern Örebro County.

• Link to a simulation showing how the estimated pH in the organic layer has changed during the period 1963–1999.
• Link to a map showing where in the country the changes can be considered statistically significant, expressed as probability values (p-values, *=p<0.05, **=p<0.01, ***=p<0.001) derived from the underlying functions. Red indicates decreasing pH, blue increasing pH, and yellow indicates that no statistically significant change has occurred (n.s.).
• Link to a map showing the magnitude of change expressed as hydrogen ion concentration ×10⁻⁶ year⁻¹. Blue indicates decreasing hydrogen ion concentration (higher pH), and red indicates increasing hydrogen ion concentration (lower pH).

The dataset has been divided into two equally large subsets with respect to site productivity (m³sk ha⁻¹ year⁻¹), one higher and one lower, within grid cells of 75 × 75 km. These have subsequently been combined into a SAS table indicating to which subset each sample plot belongs with respect to site productivity.

In the higher-productivity half of the dataset, only a very small decrease in pH has occurred, at least in Götaland and Svealand. The areas in northern Sweden with a trend towards acidification have generally decreased in extent and are found in Ångermanland, Västerbotten, Norrbotten, and in the border areas of Dalarna, Härjedalen, and western Hälsingland.