Sirpa Kleemola

Ion mass budgets for small forested catchments in Finland

Ion mass and H+ budgets were calculated for three pristine forested catchments using bulk deposition, throughfall and runoff data. The catchments have different soil and forest type characteristics. A forest canopy filtering factor for each catchment was estimated for base cations, H+, Cl− and SO42− by taking into account the specific filtering abilities of different stands based on the throughfall quality and the distribution of forest types. Output fluxes from the catchments were calculated from the quality and quantity of the runoff water. Deposition, weathering, ion exchange, retention and biological accumulation processes were taken into account to calculate catchment H+ budgets, and the ratio between external (anthropogenic) and internal H+ sources.In general, output exceeded input for Na+, K+, Ca2+, Mg2+, HCO3− (if present) and A− (organic anions), whereas retention was observed in the case of H+, NH4+, NO3− and SO42−. The range in the annual input of H+ was 22.8–26.3 meq m−2 yr−1, and in the annual output, 0.3–3.9 meq m−2 yr−1. Compared with some forested sites located in high acid deposition areas in southern Scandinavia, Scotland and Canada, the catchments receive rather moderate loads of acidic deposition. The consumption of H+ was dominated by base cation exchange plus weathering reactions (41–79 %), and by the retention of SO42− (17–49 %). The maximum net retention of SO42− was 87% in the HietajÄrvi 2 catchment, having the highest proportion of peatlands. Nitrogen transformations played a rather minor role in the H+ budgets. The ratio between external and internal H+ sources (excluding net base cation uptake by forests) varied between 0.74 and 2.62, depending on catchment characteristics and acidic deposition loads. The impact of the acidic deposition was most evident for the southern Valkeakotinen catchment, where the anthropogenic acidification has been documented also by palaeolimnological methods.

Sensitivity of soil acidification model to deposition and forest growth.

We report an investigation concerning the impacts of acid deposition and forest growth scenarios on simulated soil effective base saturation for a forested catchment in eastern Finland. These forests have not been managed during the last 150 yr and the area receives low levels of acidifying deposition. The fluxes of sulphur, nitrogen and base cations were assessed with models simulating historic and future deposition, stand uptake and leaching. We tested the effects of calibrating the modelled deposition time series to high and low estimates of current levels of deposition. The highest future soil base saturation was predicted when using the year with the lowest observed sulphur and nitrogen deposition (1993) as representative of the present deposition. The lowest historical and future soil base saturation resulted for using the year with the highest observed deposition of sulphur and nitrogen (1988). All scenarios concerning nutrient uptake, emission reduction levels and timing of the reductions resulted in simulated future soil base saturation values located between those predicted with the high and low observed present deposition. The standard deviation in the soil base saturation introduced by varying the present forest biomass and growth was smaller than that produced by varying the present deposition values.

Trend assessment of deposition runoff water fluxes and water chemistry at European ICP Integrated Monitoring sites

Acidifying deposition has been recognized as a severe environmental issue in Europe and North America resulting in coordinated air pollution control strategies, induding monitoring and assessment of air pollutants and affected receptors. As part of the Effects Monitoring Strategy under the Long-Range Transboundary Air Pollution Convention of the United Nations Economic Commission for Europe {UN/ ECE), the International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICP IM) provides a framework to observe and understand complex changes occurring in the external ecosystems with the purpose of monitoring and assessing the effects of air pollutants in undisturbed reference areas. Following a sharp increase up to the early 1970s, the European SO, emissions have experienced a dear downward trend over the past few decades. Development in NO, emissions is characterized by relatively high releases in the late 1980s followed by gende decrease both in NO, and NH, emissions during the 1~90s (OLENDRZYNSKI 1997). Thus, the empirical ev1dence on the development of environmental effects is obviously of central importance for the assessment of the success of international emission reduction policy (e.g. LOKEWILLE et al. 1997, VuoRENMAA 1997). The objective of this study was to evaluate trends ( 1988-1996) for deposition and runoff water fluxes and runoff water chemistry in acidification-related variables at 14 forested catchments belonging to the ICP IM network in Europe. The study sites are located in Scandinavia, in the UK and in central and eastern Europe. The geographically extensive dataset permits an evaluation of the responses to emission reductions in different subregions o f Europe.

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

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 (xSO4) and base cations x(Ca+Mg), hydrogen ion (H+), inorganic N (NO3 and NH4) 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 xSO4 deposition resulted in decreases in concentrations and fluxes of xSO4 in runoff, being significant at 90% and 60% of the sites, respectively. Bulk deposition of NO3 and NH4 decreased significantly at 60-80% (concentrations) and 40-60% (fluxes) of the sites. Concentrations and fluxes of NO3 in runoff decreased at 73% and 63% of the sites, respectively, and NO3 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 xSO4 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.