PREDICTING RECOVERY IN ACIDIFIED FRESHWATERS BY THE YEAR 2010, AND BEYOND

Contract EVK1-1999-00087 - RECOVER:2010

Part of the 'Sustainable Management and Quality of Water'

Ecosystem Functioning

Directorate General Research
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THE REGIONS

RESULTS

Trends in nitrogen deposition and leaching in acid-sensitive streams in Europe

R.F.Wright1, C.Alewell2, J.Cullen3, C.D.Evans3, A.Marchetto4, F.Moldan5, A.Prechtel2and M.Rogora4
1Norwegian Institute for Water Research, P.O. Box 173 Kjelsås, N-0411 Oslo, Norway
2Institute for Terrestrial Ecosystem Research (BITÖK) University of Bayreuth, D-95440 Bayreuth, Germany
3Centre for Ecology and Hydrology, Wallingford, Oxon OX10 8BB,UK
4Consiglio Nazionale delle Richerche- Istituto Italiano di Idrobiologia, 28922 Verbania Pallanza (VB), Italy
5Swedish Environmental Research Institute (IVL), Box 47086, S-402 58 Göteborg, Sweden

Full Reference

Wright, R.F., Alewell, C., Cullen, J., Evans, C.D., Marchetto, A., Moldan, F., Prechtel, A. and Rogora. M. (2001). Trends in nitrogen deposition and leaching in acid-sensitive streams in Europe. Hydrology and Earth System Sciences Vol. 5, No. 3, 299-310.

Summary of Research

Long-term records of nitrogen in deposition and streamwater were analysed at 30 sites covering major acidification sensitive regions in Europe. Large regions of Europe have received high inputs of inorganic nitrogen for the past 20-30 years, with an approximate 20% decline in central and northern Europe during the late 1990s. Nitrate concentrations in stream waters are related to the amount of N deposition. All sites with less than 10 kgN ha-1 yr-1 deposition have low concentrations of nitrate in streamwater, whereas all sites receiving > 25 kgN ha-1 yr-1 have elevated concentrations. Very few of the sites exhibit significant trends in nitrate concentrations; similar analyses on other datasets also show few significant trends. Nitrogen saturation is thus a process requiring many decades, at least at levels of N deposition typical for Europe. Declines in nitrate concentrations at a few sites may reflect recent declines in N deposition. The overall lack of significant trends in nitrate concentrations in streams in Europe may be the result of two opposing factors. Continued high deposition of nitrogen (above the 10 kgN ha-1 yr-1 threshold) should tend to increase N saturation and give increased nitrate concentrations in runoff, whereas the decline in N deposition over the past 5-10 years in large parts of Europe should give decreased nitrate concentrations in run-off. Short and long-term variations in climate affect nitrate concentrations in streamwater and, thus, contribute "noise" which masks long-term trends. Empirical data for geographic pattern and long-term trends in response of surface waters to changes in N deposition set the premises for predicting future contributions of nitrate to acidification of soils and surface waters. Quantification of processes governing nitrogen retention and loss in semi-natural terrestrial ecosystems is a scientific challenge of increasing importance.

Fig.1.Map of Europe showing RECOVER:2010 stream sites

One objective of RECOVER:2010 is to analyse systematically long-term records of deposition and surface water chemistry at acid-sensitive sites characteristic of the major types of acidified waters in Europe. RECOVER:2010 includes sites in the regions Scandinavia (Norway, Sweden and Finland), the British Isles (UK), central Europe (Germany, Czech Republic, and Slovakia) and the southern Alps (Italy). Here we present the long-term trends in inorganic N concentrations in deposition and streamwater at 30 stream sites in Europe (Figure 1).












Fig 2.Measured wet deposition of N at several EMEP stations in Europe.







Deposition Data

Measured wet deposition of N compounds at EMEP sites, and sites included here from RECOVER:2010, show relatively large year-to-year variations (Figure 2), probably mainly due to natural variations in meteorological conditions such as the amount of precipitation. This "noise" in the record means that trends in N deposition must be relatively large before they become statistically significant. This probably explains why there are no significant trends in N deposition during the 1990s at many of the EMEP and RECOVER sites.





Table 1.Results of trend analyses in streamwater.

Mean concentrations of NO3 in streamwater were lowest in northern Scandinavia and northwestern UK and highest in central Europe (Table 1). This is the same geographic pattern as N deposition. Ammonium concentrations at all these sites are very low, often below the analytical detection limit. (Detection limit for NH4 varies between laboratories, and has changed over time, but is generally 0.5-1.0 µeq L-1). Mean concentrations of NO3in streamwater at the Scandinavian catchments were < 10 µeq L-1 with a clear gradient of increasing concentrations from north to south (Table 1).



Fig 4. Concentrations of NO3 (ueql-1) in streamwater-UK



The 11 stream sites in the UK also showed pronounced geographic gradient, with low concentrations (< 5 µeq L-1) at sites on the periphery (northern Scotland, western Northern Ireland, southwestern and southeastern England) and higher concentrations (> 10 µeq L-1) at sites in southern Scotland, central England, central Wales, and southernmost Northern Ireland (Table 1, Figure 4)

 Fig.3a.Concentrations of NO3 in streamwater in Sweden and Finland.













The records begin in the 1970s at the Norwegian sites, the mid-1980s at the Swedish sites and 1988 at the Finnish Sites. Only the sites Pipbäcken Nedre in southernmost Sweden and Storgama and Birkenes in southernmost Norway exhibited signs of elevated nitrate concentrations in streamwater (Figures 3a,b).













Fig 3(b) Concentrations of NO3 (ueql-1) in streamwater-Norway















 

 





Fig.5.Concentrations of NO3 in streamwater at catchments in Germany.




With the exception of Villingen in the Black Forest, all the German sites had very high concentrations of NO3 in streamwater with mean concentrations for the 12 year period 1987-99 exceeding 50 µeq L-1at Lehstenbach (Fichtelgebirge) and Markungsgraben (Bavarian Forest) (Table 1, Figure 5). These sites also receive very high N deposition (> 25 kg ha-1yr-1). The three streams in northern Italy all had high concentrations of nitrate (> 40 µeq L-1) (Table 1, Figure 6).


Fig 6. Concentrations of NO3(ueql-1) streamwater-Italy.

References

Alewell, C., Prechtel, A., Bittersohl, J., Moritz, K., Meesenburg, H. and Armbruster, M., 2001. Are there signs of recovery after two decades of reduced acid input in the low mountain ranges of Germany? Hydrol. Earth Syst. Sci., 367-378.

Barrett, K., Aas, W., Hjellbrekke, A.G., Tarrason, L. and Schaug, J., 2000a. An evaluation of trends for concentrations in air and precipitation. In: Transboundary Acidification and Eutrophication in Europe (L. Tarrason and J. Schaug (Eds.)), 41-58. EMEP Summary Report 2000, Norwegian Meteorological Institute, Oslo, Norway.

Evans, C.D. and Monteith, D.T., 2001. Chemical trends at lakes and streams in the UK Acid Waters Monitoring Network, 1988-2000: evidence for recent recovery at a national scale. Hydrol. Earth Syst. Sci., 351-366.

Monteith, D.T. and Evans, C.D., 2000. 10 Year Report. Analysis and Interpretation of Results, April 1988 - March 1998. UK Acid Waters Monitoring Network. ENSIS Publishing, London, 363 pp.

Moldan, F., Wright, R.F., Löfgren, S., Forsius, M. and Skjelkvåle, B. L., 2001b. Long-term changes in acidification and recovery at nine calibrated catchments in Norway, Sweden and Finland. Hydrol. Earth Syst. Sci., 339-349.

Rogora, M., Marchetto, A. and Mosello, R., 2001. Trends in the chemistry of atmospheric deposition and surface waters in Lake Maggiore watershed. Hydrol. Earth Syst. Sci., 379-390.

SFT, 2000. Overvåking av langtransportert forurenset luft og nedbør. Årsrapport - Effekter 1999. Statlig program for forurensningsovervåking Rapport Statens forurensningstilsyn, Oslo, Norway, 198 pp.

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