The effects of a changing pollution climate on throughfall deposition and cycling in a forested area in southern England

Abstract

This study compares two sets of measurements of the composition of bulk precipitation and throughfall at a site in southern England with a 20-year gap between them. During this time, SO(2) emissions from the UK fell by 82%, NO(x) emissions by 35% and NH(3) emissions by 7%. These reductions were partly reflected in bulk precipitation, with deposition reductions of 56% in SO(4)(2-), 38% in NO(3)(-), 32% in NH(4)(+), and 73% in H(+). In throughfall under Scots pine, the effects were more dramatic, with an 89% reduction in SO(4)(2-) deposition and a 98% reduction in H(+) deposition. The mean pH under these trees increased from 2.85 to 4.30. Nitrate and ammonium deposition in throughfall increased slightly, however. In the earlier period, the Scots pines were unable to neutralise the high flux of acidity associated with sulphur deposition, even though this was not a highly polluted part of the UK, and deciduous trees (oak and birch) were only able to neutralise it in summer when the leaves were present. In the later period, the sulphur flux had reduced to the point where the acidity could be neutralised by all species - the neutralisation mechanism is thus likely to be largely leaching of base cations and buffering substances from the foliage. The high fluxes are partly due to the fact that these are 60-80 year old trees growing in an open forest structure. The increase in NO(3)(-) and NH(4)(+) in throughfall in spite of decreased deposition seems likely due to a decrease in foliar uptake, perhaps due to the increasing nitrogen saturation of the catchment soils. These changes may increase the rate of soil microbial activity as nitrogen increases and acidity declines, with consequent effects on water quality of the catchment drainage stream.

Twenty-five year record of chemicals in open field precipitation and throughfall from a medium-altitude forest catchment (Strengbach - NE France): An obvious response to atmospheric pollution trends

“…The chemical concentrations in throughfalls were higher than in open field precipitation (Table 2, Suplementary materials, Fig. 7), as had already been observed in many places (Ulrich, 1983;Probst et al, 1990a,b;Draaijers and Erisman, 1995;Dambrine et al, 1998b;Balestrini and Tagliaferri, 2001;Balestrini et al, 2007;Vogt et al, 2006;Schrumpf et al, 2007;Berger et al, 2008;Staelens et al, 2008;Kopacek et al, 2009;Skeffington and Hill, 2012;Eisalou et al, 2013). the result of atmospheric deposits because of foliar uptake and biological excretions occurring at the water/leaf interfaces (Ulrich, 1983;Lovett and Lindberg, 1984;Skeffington and Hill, 2012).…”

“…7), as had already been observed in many places (Ulrich, 1983;Probst et al, 1990a,b;Draaijers and Erisman, 1995;Dambrine et al, 1998b;Balestrini and Tagliaferri, 2001;Balestrini et al, 2007;Vogt et al, 2006;Schrumpf et al, 2007;Berger et al, 2008;Staelens et al, 2008;Kopacek et al, 2009;Skeffington and Hill, 2012;Eisalou et al, 2013). the result of atmospheric deposits because of foliar uptake and biological excretions occurring at the water/leaf interfaces (Ulrich, 1983;Lovett and Lindberg, 1984;Skeffington and Hill, 2012). Pascaud et al (2016) highlighted the lack of a systematic relationship between the reduction in NOx emissions and the changes in NO 3 concentrations in open field precipitation from 37 French rural sites with both significant increasing and decreasing trends depending on the sites.…”

“…4). Similarly, NO 3 concentrations in throughfall under spruce (Nacetin site, Czech Republic; Oulehle et al, 2006) or under pine (Whitehead et al, 2002;Skeffington and Hill, 2012) had not changed significantly since the eighties or nineties. In contrast to sulfate, nitrate concentrations in throughfall were not only (period 1986-2012).…”

“…Because the measure of dry and occult deposition is very complicated (Lindberg and Garten, 1988a;Balestrini et al, 2007), the sampling and analysis of throughfall have been developed to estimate the entire atmospheric deposition of contaminants to forest ecosystems and thus indirectly determine the dry deposition. However, the main difficulty is that throughfall integrates various types of deposition and sorption processes when precipitation interacts with the trees: 1) wet deposition by rain or snow, 2) sedimentation of particles caught by the leaves during dry episodes and dissolution by the next rainfall, 3) impact of dry aerosols from fog and cloud droplets, 4) absorption of gases inside stomata and 5) recretion/absorption of elements by leaf cells following exchange processes with rainwater (Ulrich, 1983;Parker, 1983;De Vries et al, 2003;Probst et al, 1990a;Dambrine et al, 1998b;Thimonier et al, 2008;Berger et al, 2008;Kopacek et al, 2009;Adrianssens et al, 2012;Skeffington and Hill, 2012;Kato et al, 2013;Shen et al, 2013;Klos et al, 2014). Although throughfall result from a mixture of several processes, it currently remains an efficient way to estimate accurately the in-situ input flux of Numerous publications have concerned acid precipitation and acidification processes.…”

“…Nevertheless, few studies have examined in detail the long-term (several decades) evolution of atmospheric element inputs to ecosystems with different tree types, particularly in the context of the changes in pollutant emissions during the past decades. This study benefits from a 25-year record of chemical and water fluxes for most of the element deposition to forest ecosystems (e.g., Zimmermann and Zimmermann, 2014;Skeffington and Hill, 2012), except for a proportion of the nitrogen deposited which can be taken up by leaves and needle (Harrison et al, 2000).…”