Changes in emission regime for nitrogen and sulfur in Germany and its impact on a spruce forest measured over a period of 35 years

TL;DR

A 35-year study in a German spruce forest shows how reduced sulfur emissions led to significant changes in soil chemistry and sulfur remobilization.

Contribution

The study demonstrates the long-term effects of reduced sulfur emissions on forest ecosystems and highlights the importance of sustained monitoring.

Findings

Sulfur inputs decreased by almost 95% between 1985 and 2020 due to pollution control measures.

Stored sulfur in the topsoil was remobilized over 28 years, leaving only 11% of the initial sulfur in the topsoil by 2020.

High nitrogen inputs continue to cause soil acidification despite reduced emissions.

Abstract

In Germany during several decades, emissions and thus the chemical climate affecting forests have changed significantly. The effects of these changes on the element balance of forests can be documented only by long‐term observations, as has been done at the Höglwald site (Southern Bavaria) since 1985. Since then, structural changes in agriculture have led to a reduction in emissions of reduced nitrogen (NH3). There was also a slight decrease in emissions of oxidized nitrogen (NOx). Air pollution control measures, especially in the 1980s, led to a particularly drastic reduction of sulfur emissions (SO2). Consequently, inputs to the ecosystem decreased by almost 95% between 1985 and 2020. Dry deposition nowadays plays practically no role for this element. High nitrogen inputs, dominated by reduced nitrogen, have led to a high proton production through N transformations. This has gradually reduced the buffering capacity of the topsoil. Comparing measured fluxes shows that with decreasing sulfur inputs, the sulfur stored in the topsoil from times of high deposition was remobilized. At the Höglwald, this process occurred rather clearly over a period of about 28 years and has resulted in only about 11% of the initial amount of sulfur being still present in the topsoil (humus layer + mineral soil down to 40 cm) in 2020. Forestry should take the changed chemical conditions into account in its nutrient management.

Changes in the emission regime should be detectable in the input into a forest ecosystem.Changes in input result in changes in soil–chemical properties and in changes in output by seepage.There may be a delay between changes in input and changes in output.This study demonstrates the importance and value of long‐term forest ecosystem monitoring.

Changes in the emission regime should be detectable in the input into a forest ecosystem.

Changes in input result in changes in soil–chemical properties and in changes in output by seepage.

There may be a delay between changes in input and changes in output.

This study demonstrates the importance and value of long‐term forest ecosystem monitoring.

Air pollutants emitted from agriculture, industry, and transportation (NH3, NOx, SO2) affect natural ecosystems. In a spruce forest (Höglwald) in southern Bavaria, Germany, the input and output of nitrogen and sulfur were studied over 35 years (1985–2020). The study revealed that sulfur emissions, and thus sulfur inputs into the forest, decreased significantly due to successful air pollution control measures. The sulfur reserves stored in the soil during periods of high sulfur emissions were remobilized and discharged with the seepage water over a period of approximately 30 years. Despite a slight decrease in nitrogen deposition, the proton turnover associated with nitrogen conversion still leads to high soil acidification. The consequences of air pollution on forestry can only be documented and assessed through long‐term measurements.

Figures