THE EFFECTS OF ACID RAIN AND FOREST DIE-BACK ON GROUNDWATER - CASE STUDIES IN BAVARIA, GERMANY (FRG)

Transcription

1 Atmospheric Deposition (Proceedings of the Baltimore Symposium, May 1989). IAHS Pub!. No THE EFFECTS OF ACID RAIN AND FOREST DIE-BACK ON GROUNDWATER - CASE STUDIES IN BAVARIA, GERMANY (FRG) Thomas Haarhoff Bayerisches Landesamt filr Wasserwirtschaft, Lazarettstrafie 61, D-800L Miinchen, West Germany ABSTRACT Concern over increasing airborne pollution and the acceleration of acidification of the water paths has led to investigation programs of the water balance and water quality in forest stands. Here case studies are presented in which the entire water cycle i.e. precipitation, seepage, groundwater and surface run-off in forest stands is observed. The approaches and methods are described, as are the specific hydrological and geological situations in the case study areas and first results of data collection are presented. BACKGROUND OF THE PROJECT Over recent years in various parts of the world, concern has been increasing over growing airborne pollution and the accelerating acidification of the environment even in less industrialized regions. In Bavaria, the forests are an important part of the natural environment, particularly with regard to the water balance. In 1986 investigations were initiated by the Bavarian Government into the effects of acid rain and forest die-back on the groundwater. The project is being carried out by the Bavarian Water Authority in cooperation with the Bavarian Forestry Research Institute. Data collection will take place over five years. AIM OF THE PROJECT Recent research at home and abroad has covered the acidification of individual sections of the water cycle (run-off, erosion, infiltration rates and groundwater quality). The goal of this project is to carry out integrated investigations of the entire water cycle in order to achieve the following: a. to show the functional interconnections between the sections of the water cycle in forest areas. b. to forecast long-term changes in the water chemistry processes subject to continuous pollution. c. to establish possible counteractive water management and forestry strategies to secure the groundwater supply. The goal is to research the effects of acidification in the seepage zone, with concern for transport and mobilization of substances which endanger the groundwater. APPROACHES AND METHODS Overall Concept Figure 1 shows the overall concept of the project, the past and current 229

2 230 Thomas Haarhoff programs which can be divided into the following groups: a Mapping programs over the entire area: A soils and forestry installations, B aerial survey, b Mapping programs on specific plots: C Classification of forest die-back, D Investigation of upper soil layers, E Geological subsurface, c Data collection programs: precipitation in open areas including trace metals, precipitation in stands and flow off tree trunks, seepage water, groundwater, sources, surface water and run-off. Input Output (I,ET) Figure 1 Diagram of the overall concept. Measurement Methods In forest stands the data collection is realized in integrated measurement points. To measure the atmospheric pollution bulk collectors are used for both wet and dry deposits. The data are compared with similarly collected data from open areas (with additional separate collection of dry and wet deposit data planned) (Figure 2). The main emphasis is on the unsaturated seepage zone and the groundwater. Samples are taken from the unsaturated zone by means of suction plugs (AI3O2). The groundwater observation wells were set up on recommendation of the guideline of LAWA. Evaluation and Interpretation Two approaches are used to achieve input and output in the areas and also numerous internal processes depending on area-specific changes: a. Data collected at certain points are transferred to (topological-synthetic approach) wid er areas

3 Effects of Acid Rain on Groundwater 231 b. Data collected over wide areas are analyzed to show the influence on smaller areas (chorological-analytical approach) Both approaches aim to achieve substance balances for the specific areas. From these substance balances and their possible future development possible water management strategies are to be deduced. Open Area Deposition quantity and precipitation recorder precipitation collector heavy metat collector Seepage Zone water quality and water content Groundwater groundwater level and quality Figure 2 Measurement points in stands and open areas. CASE STUDY AREAS Three relatively small catchments (4-15 km") in the source areas of rivulets with corresponding aquifers were selected in various regions of Bavaria according to the following criteria: a. area used exclusively for forestry purposes, no fertilizers/biocide used. b. current or expected forest die-back accompanied by thinning of the stands. c. aquifers at risk due to the low buffering capacity of the soils and rock strata. d. water supply plants existing in the area. The areas are: 1. Metzenbach/Birkwasser in the Spessart (red sandstone, locally weathered and weakened),

4 232 Thomas Haarhoff 2. Markungsgraben in the Bavarian Forest (weathered granite and gneiss), 3. Source brooks of the Lehstenbach in the Fichtelgebirge (granite blocks and weathered granite). In addition, one case study area without surface runoff but which is of extreme importance for public water supply was selected: 4. Ebersberger Forest in the Miinchner Schotterebene (Munich glacial gravel plain). The hydrological situations in the case study areas are very dissimilar while the forest usage and stands are relatively similar (see Figure 3). No. Area km2 Usage Altitude (m) rainfall mm year Forestry Nat. Park Forestry * Fore: stry *** No. run-off mm year-i evapotransp. mm year -1 recharge mm year-i < ** * KERN ** K0PF & ROTHASCHER *** SCHIRM Figure 3 Hydrological data on the case study areas. RESULTS Due to the as yet brief data collection period, only the data gained in the Spessart and the Ebersberger Forest are compared. In the other areas, the data can only be used to characterize the relevant areas. Precipitation in Stands and Open Areas The precipitation in the open areas in the Ebersberger Forest and in the Spessart showed similar concentrations but there were lower acid concentrations in the Ebersberger Forest. It is surprising that the precipitation in the Spessart beech stands shows

5 Effects of Acid Rain on Groundwater 233 ph values of various stands and open area(-) i N * A i i \\K \ \ vv/y- V I 1 1 1, \ < 1 4/ /88 Time (month) x x Plot 6 (spruce stand).. Plot 5 (beech stand) plot 3 (open area) Figure 4 Comparison of ph values of precipitation in the Spessart. a small basic increase over certain short periods (autumn) (Figure 4). Seepage Water In the Spessart the seepage water is acidic over the whole two meters of the profile, but remains above 4.0 ph. The metal ion concentrations (aluminum up to 3 ppm; chrome, cadmium up to 20 ppb) registered in the already acidic surface soils (ph approx. 4.5), would jeopardize the water supply if they reached the groundwater in these concentrations (Figure 5a). In the Ebersberger Forest the calcium-magnesium concentrations and the ph values increase rapidly below the decalcifying level (approx. 50 cm below surface). In view of the geological situation and the soil structure this is not surprising. Nevertheless in the upper part of the overburden (50 cm below surface) hazardous amounts of metal compounds (aluminum, cadmium, chrome) have already been observed (Figure 5b). Groundwater In the Spessart the conductivity as a measure of the sum of dissolved ions in the observation period shows only minimal deviations in time and locality, whereby individual ions vary widely in their concentrations. If ph values of 5-6 are regarded as natural, sulphate concentrations of ppm suggest anthropogenous influences. The chalky gravel waters of the Ebersberger Forst have not yet been acidified but have been exposed to nitrate, sulphate and chloride from the atmosphere and from boundary inflow. CONCLUSIONS AND OUTLOOK Results obtained to date confirm that to establish possible changes in the groundwater quality due to increased airborne contamination it is necessary to study most closely the unsaturated zone beneath the root zone.

6 234 Thomas Haarhoff Al content (mg I" 1 ) ot various soil depths ph value I-) m tom 0.5 m 1.0 m a) Spessart( Plot 5 (beech stand) 4 3 =V /87 Time 7 BS 6/88 (month) AI content (mg l" 1 ) ph valu al various soil depths (-) b) Ebersb.F., Plot 3 (spruce stand Figure 5 Seepage water data Ebersberger Forst and Spessart. Nevertheless an integrated survey including surface and vegetation changes is also necessary. Data on various sectors of the water cycle differ in their degree of accuracy. To reduce this major difficulty when attempting to set up water and substance balances, measurements of' additional metereologi'cal parameters are planned. However, it is doubtful whether the results obtainable during the five years of the project will be sufficient to provide long-term forecasts of the possible acidification of the groundwater. ACKNOWLEDGEMENTS The project is supervised by the Oberste Baubehorde (Supreme Building Authority) on behalf of the State of Bavaria. The author is grateful for permission to publish.

7 REFERENCES Effects of Acid Rain on Groundwater 235 Kern, H. (1954). Niederschlags-, Verdunstungs- und Abflu/?karten von Bayern (Bavarian maps of precipitation, évapotranspiration and runoff). Bayer L. Stelle fur Gew&sserkunde, Munich, FRG. Kopf, E & Rothascher, A., (1980). Das naturliche Grundwasserdargebot in Bayern (The natural yield in Bavaria). Schriftenreihe Bayer. Landesamt f. Wasserwirtschaft No. 13, Munich, FRG. LAWA-Arbeitskreis "Grundwasserbeschaffenheitsrichtlinie" (1987) Richtlinie fur Beobachtung und Auswertung (Guideline for observation and evaluation of groundwater quality). Unpublished draft. Schirm, H. (1963) Hydrogeologische Verhaltnisse in der Munchner Schotterebene (Hydrogeology of the Munich Glacial Gravel Plain). PhD Thesis, Univ. of Munich, Munich, FRG.

8