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

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 in 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) and base cations x(Ca+Mg), hydrogen ion (H), inorganic N (NO and NH) 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 deposition resulted in decreases in concentrations and fluxes of xSO in runoff, being significant at 90% and 60% of the sites, respectively. Bulk deposition of NO and NH decreased significantly at 60-80% (concentrations) and 40-60% (fluxes) of the sites. Concentrations and fluxes of NO in runoff decreased at 73% and 63% of the sites, respectively, and NO 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 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.

Recovery of acidified Sudbury, Ontario, Canada, lakes: a multi-decade synthesis and update

“…The dominant trend in the Extensive lakes has been a decline in NO 3 concentrations (28 lakes) with no trend observed in 14 lakes. This generally agrees with other North American and European observations indicating either declines or no change in surface water NO 3 concentrations in recent decades (Garmo et al 2014;Vuorenmaa et al 2018).…”

Organic nitrogen steadily increasing in Norwegian rivers draining to the Skagerrak coast

“…Lastly, the long-term fate of the deposited N onto boreal catchments is still unresolved, as to date no strong leaching of inorganic N has been reported across Scandinavia 5 . However, given the increased runoff of organic material, part of the N stored in the terrestrial catchments may leach into aquatic systems in organic form 22 , 25 , 26 .…”

Wind farm development on peatlands increases fluvial macronutrient loading

“…Models often had high R 2 , but did not explain fully the field observations. The remaining unexplained variability in streamwater macronutrient concentration and export may relate to shortterm and seasonal variations in weather and climate and long-term trends in atmospheric N deposition (Vuorenmaa et al 2018). For example, enhanced streamwater [NO 3 -N] may occur for 2-3 years in upland UK catchments after severe summer drought (Reynolds et al 1992), but such effects are difficult to disentangle from land-use activities in this study.…”