Journal of Conference Abstracts

Hydrochemical Budget Studies of a Clean Rain and a Drought Experiment: II. Element Budgets

Y.-J. Xu¹ (yxu1@gwdg.de), K. Blank² (kblanck@gwdg.de), M. Bredemeier³ (mbredem@gwdg.de),
N. P. Lamersdorf² (nlamers@ufbwserver.uni-forst.gwdg.de) & G. A. Wiedey³ (gwiedey@gwdg.de)

¹ 1619 Prairie Street, Victoria, B.C., V8N 5X9, Canada.

² Institute of Soil Science and Forest Nutrition, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany.

³ Forest Ecosystem Research Center, University of Göttingen, Büsgenweg 1, 37077 Göttingen, Germany.

Widespread observations have demonstrated that acid deposition may cause nutrient depletion and acidification of soils and waters, and may give rise to the destabilization of terrestrial ecosystems (e.g., Likens & Bormann, 1974; Ulrich, 1983). The problem is accompanied by increasing concern about global warming, which might cause weather extremes, e.g., long drought periods. Some observations (e.g., Matzner & Thoma, 1983; Ulrich, 1983) have indicated that pronounced drought periods may increase soil acidification on strongly acidified soils. The Solling roof experiments were carried out to study the responses of a spruce forest on an acidified soil to reduced deposition and to limited water supply during summers. In the first part of our contribution we presented the results on water budgets. In this paper we will focus on element fluxes and budgets.

From 1990 to 1994, nutrient inputs carried by precipitation at the study site totaled (in kg ha-1): 52.6 for Na⁺, 14.3 for K⁺, 21.7 for Ca²⁺, 6.2 for Mg²⁺, 50.4 for NH₄⁺, 34.7 for NO₃^- and 54.5 for SO₄^2-. For the same time period, nutrient inputs carried by throughfall were much higher (in kg ha^-1): 93.6 for Na⁺, 130.3 for K⁺, 86.9 for Ca²⁺, 19.6 for Mg²⁺, 88.0 for NH₄⁺, 94.4 for NO₃^-, and 211.9 for SO₄^2-. In the clean rain treatment, collected throughfall was chemically manipulated by reducing input loads of NH₄⁺ (by 86 %), NO₃^- (by 50 %), SO₄^2- (by 56 %), and H⁺ (by 87 %) and resprinkled immediately, whereas in the drought experiment collected throughfall was stored in tanks during the summers and resprinkled after 3-6 months. Another roof plot served as a control without any treatments.

For the clean rain experiment, rapid changes of the NH₄⁺, NO₃^-, SO₄^2-, and H⁺ budgets were observed immediately after the clean rain treatment. For the treatment period (1992-1994), the total outputs of NO₃^- and NH₄⁺ at the clean rain plot (7.4 and 0.4 kg ha^-1) were much lower than those at the control plot (30.6 and 0.8 kg ha^-1). In N budgeting (NO₃^- + NH₄⁺), the clean rain plot showed a considerably smaller surplus than the control plot (27.7 vs. 59.2 kg ha^-1). The clean rain plot showed a lower SO₄^2- output (122.8 kg ha^-1), but a larger deficit on budgeting (-67.1 kg ha^-1) than the control plot (151.3 and -34.9 kg ha^-1, respectively). In H⁺ budgeting, the clean rain plot presented a deficit (-0.2 kg ha^-1), whereas the control plot a surplus (2.3 kg ha^-1). The results showed that deposition rates largely controlled the element input/output budgets in the spruce forest on a strongly acidified soil. The greater deficits of SO₄^2--S and H⁺ and the decreased N accumulation in the clean rain treatment may indicate that acidified states in an ecosystem might be reversible when acid deposition is reduced.

For the drought experiment, in the first and second treatment years (1992 and 1993) with extremely pronounced drought periods (nearly 6 months), NH₄⁺ responded with a strongly decreased surplus, but the (NO₃^- budgets remained almost at the same level as before the drought treatment. From 1992 to 1994, NO₃^-, NH₄⁺ and Al³⁺ outputs in seepage water at the drought plot (9.7, 0.0, and 63.8 kg ha^-1) were considerably lower than at the control plot (30.6, 0.8, and 86.2 kg ha^-1). Beck (1983) and Sparling & Ross (1988) pointed out that a nitrification pulse in soil may occur after drought/rewetting due to an increased N-mineralisation rate. Matzner & Thoma (1983) and Ulrich (1983) supposed that an acidification pulse in soil may happen under drought/rewetting conditions probably due to increased release of Al³⁺ and nitrate-N. The results of our studies, however, did not wholly support these views. Also, the soil chemical concentrations during the whole treatment period could not provide any convincing evidence for such pulses (Lamersdorf et al. 1997).

References

Beck, T., Zeitschr. Pflanzenernährung Boden., 146, 243-252 (1983).

Lamersdorf, N.P., Beier, C., Blanck, K., Bredemeier, M., Cummins, T., Farrell, E.P., Kreutzer, K., Rasmussen, L., Ryan, M., Weis, W. & Xu, Y.-J., Forest Ecol. Manage., in press (1997).

Likens, G.E. & Bormann, F.H., Science, 184, 1176-1179 (1974).

Matzner, E. & Thoma, E., Allg. Forstzeitschr., 38, 677-682 (1983).

Sparling, G.P. & Ross, D. J., Plant and Soil, 105, 163-167 (1988).

Ulrich, B., In Effects of Accumulation of Air Pollutants in Forest Ecosystems (eds Ulrich, B. & Pankrath, J.), 1-29 (D. Reidel, Dordrecht, 1983).