An Overview of Atmospheric Deposition Chemistry over the Alps: Present Status and Long-term Trends

Abstract

Several research programs monitoring atmospheric deposition have been launched in the Alpine countries in the last few decades. This paper uses data from previous and ongoing projects to: (i) investigate geographical variability in wet deposition chemistry over the Alps; (ii) assess temporal trends of the major chemical variables in response to changes in the atmospheric emission of pollutants; (iii) discuss the potential relationship between the status of atmospheric deposition and its effects on forest ecosystems in the alpine and subalpine area, focusing particularly on nitrogen input. We also present results of studies performed at a local level on specific topics such as long-term changes in lead deposition and the role of occult deposition in total nitrogen input. The analysis performed here highlights the marked geographical variability of atmospheric deposition in the Alpine region. Apart from some evidence of geographically limited effects, due to local sources, no obvious gradients were identified in the major ion deposition. The highest ionic loads were recorded in areas in the foothills of the Alps, such as the pre-alpine area in North-Western Italy and the area of Canton Ticino, Switzerland. Trend analysis shows a widespread decrease in the acidity of precipitation in the last 15-20 years as a consequence of the reduced emission of S compounds. On the other hand, nitrate concentrations in rain have not changed so much, and ammonium has decreased significantly only at the Austrian sampling sites. The deposition of N is still well above the estimated critical loads of nutrient N at some forest sites in the alpine and subalpine areas, thus confirming the critical situation of both terrestrial and aquatic ecosystems regarding N inputs. Existing data highlights the importance of continuously monitoring atmospheric deposition chemistry in the Alpine area, taking account of acidifying elements, nutrients and other pollutants such as heavy metals and organic compounds. There is also a need for unifying sampling and analytical methods in order to obtain comparable data from the different regions of the Alps.

Biodiversity promotes primary productivity and growing season lengthening at the landscape scale

“…Similar effects are found from rainout of air pollution from traffic and fossil fuel-based heating along the pre-Alps (39). In such areas, species loss may be found as a consequence of eutrophication, which would go along with a negative rather than positive biodiversity-productivity relationship due to competitive exclusion.…”

Lake Orta chemical status 25 years after liming: problems solved and emerging critical issues

“…5d) peaked at 4.2 mg N L -1 in the whole water mass soon after the liming; thereafter concentrations decreased steadily due to the dilution from the tributary waters, with their much lower concentrations (1.3-2.8 mg L -1 ). At present, in-lake values are close to 1 mg N L -1 , not far from those of the nearby Lake Maggiore, whose nitrogen levels are currently controlled largely by atmospheric input of nitrogen, both as ammonium and nitrate (Rogora et al, 2006a). The epilimnetic nitrate concentration in Lake Orta has regular seasonal variations, with minima in the spring and summer, due to biological activity and to the more intense effect of the tributary waters during the period of thermal stratification.…”

Nitrate‐depleted conditions on the increase in shallow northern European lakes

“…This decrease has probably contributed to the decline in May to August NO 3 -N concentrations that we observed in the Swedish reference lakes since 1988. A decrease in atmospheric NO 3 -N deposition is not detectable everywhere in the Northern Hemisphere, the Alp region in Central Europe being an example (Rogora et al 2006). Lack of significant trends in atmospheric NO 3 -N deposition might be one of many explanations why, for instance, Evans et al (2001) and Skjelkvale et al (2005) found a variety of surface waters across the Northern Hemisphere without significant trends in NO 3 -N concentrations.…”