Response of soil solution chemistry to recent declines in atmospheric deposition in two forest ecosystems in Berlin, Germany
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.Geoderma 83 1998 83101
Response of soil solution chemistry to recentdeclines in atmospheric deposition in two forest
ecosystems in Berlin, Germany
Bernd Marschner a,), Andreas Gensior b,1, Uwe Fischer c,2a Technical Uniersity Berlin, Institute of Ecology and Biology, Soil Science Dep.,
Salzufer 11 12, 10587 Berlin, Germanyb Humboldt Uniersity Berlin, Institute of Fundamentals in Plant Production, Resource Ecology
Dep., Inalidenstr. 42, 12587 Berlin, Germanyc Bundesalle 89, 12161 Berlin, Germany
Received 3 June 1996; accepted 11 November 1997
As part of a long-term monitoring program to study the effects of acid deposition on forestecosystems, throughfall and soil solutions from 50 and 200 cm depth have been collected andanalyzed from 1986 to 1995 in a young pine stand and a mixed pineoak forest in Berlin. Before1990, atmospheric SO inputs of 1.52.1 kmol hay1 ay1 were among the highest reported for4Western Europe. Between 1990 and 1992 they declined sharply to below 0.7 kmol hay1 ay1 andcontinued to decrease until 1995. Most other elements followed a similar time trend, except formineral-N compounds that decreased by only 30%. The assessment of soil solution reactions tothese changes was complicated by high temporal fluctuations of solute concentrations in responseto soil water content changes. This problem was overcome with a regression model, wheretime-trend corrected Cl concentrations were introduced to account for these fluctuations. The datathen show that in both stands soil solution composition reacts similarly to the changed inputsituation. Due to the concentration reductions of the major anion SO2y in the soil solutions,4concentrations of most major cations decreased and alkalinity increased. Still, acidity is transferred
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0016-7061r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. .PII S0016-7061 97 00139-0
( )B. Marschner et al.rGeoderma 83 1998 8310184
to the subsoil, indicating that soil acidification is continuing despite the strongly decreased aciddeposition rates. q 1998 Elsevier Science B.V.
Keywords: deposition rates; time trends; soil water chemistry; soil acidification; forest ecosystem;Germany
In most regions of Western Europe and North America acid deposition hasdeclined gradually since the mid 1970s Driscoll et al., 1989; Hedin et al., 1994;
.Kirchner and Lydersen, 1995; Wesselink et al., 1995 . These changes are mainlydue to reductions in SO emissions through increased use of low-S fuels and the2installation of filter systems in power plants and industry. However, the declinein ecosystem inputs of the acid anion SO is generally accompanied by the4
.reduced deposition of base cations Hedin et al., 1994 so that changes in netacidity may be small. As a consequence, the base cation status of the soilswould not be expected to improve and soil acidification could actually continue
. .as shown in the review of Wright and Hauhs 1991 . Wesselink et al. 1995modeled the reaction of the soil base saturation to changing deposition scenariosand showed that soils with low pools of base cations are especially sensitive tochanges in deposition rates. Small differences in declining deposition rates ofbase cations and acid anions can determine whether soil acidification continuesor recovery of base cation status occurs, as they demonstrate for two adjacentforest stands with slight differences in deposition rates.
Reduced base cation inputs were also held responsible for the failure ofstreamwater acidity at the Hubbard Brook catchment to respond to a 60%
.decline in SO inputs between 1964 and 1987 Driscoll et al., 1989 . Similar4 .observations were made in Norway Kirchner and Lydersen, 1995 and at-
tributed to the severe base cation depletion in earlier years.In the roof experiments of the NITREX project in southwestern Sweden and
central Germany, where irrigation water was adjusted to pre-industrial levels,soil solution NO and SO concentrations declined sharply in the O and E3 4horizons but SO only showed a gradual decrease in the Bs horizon within the4
.first 22.5 years Bredemeier et al., 1995; Giesler et al., 1996 . This wasattributed to the release of adsorbed SO in the Bs horizon where pools of4
.exchangeable SO apparently had accumulated. Rustad et al. 1996 also4demonstrated that SO dynamics in the soil solution in response to an artificial4acidification and subsequent recovery period were delayed due to reversibleadsorption processes.
In contrast to the emission reductions in Western Europe and North America,emissions in Eastern European countries continued to increase until the late
1980s due to growing energy needs and lacking filter technology Umwelt-.bundesamt, 1992; Landesumweltamt Brandenburg, 1995a . In East Germany,
( )B. Marschner et al.rGeoderma 83 1998 83101 85
the predominant combustion of brown coal also resulted in high emissions ofalkaline dusts so that acid deposition was relatively low despite high SO inputs4 .Hofmann and Krauss, 1988; Marschner et al., 1991 . As a consequence of thepolitical and economic changes after 1989, industrial production and energyconsumption in East Germany was greatly reduced within one year, resulting inrapid responses of improved air quality in the former industrial centers and
.leeward regions Landesumweltamt Brandenburg, 1995a .In Berlin where air quality and atmospheric deposition were largely con-
.trolled by these external inputs Marschner et al., 1991 , measurements of bulkdeposition, throughfall and soil solution chemistry are conducted in two forestecosystems since 1986. Based on the 9-year monitoring period until 1995, thedrastic changes in deposition rates at these sites since 1989 are presentedtogether with the respective soil solution data. This paper mainly focuses on thetime scale and magnitude of the soil solution response to these changes andevaluates differences between the two stands.
2. Materials and methods
The investigation area is located about 6 km southwest of the center of Berlinon a glacial till plain in the Grunewald, a forest area of about 3000 ha. Theclimate is continental, with mean annual precipitation of 580 mm with nodistinct seasonality and a mean annual temperature of 8.98C. One study plot is a
. .young Scots pine stand Pinus sylestris with few oaks Quercus robur ,planted about 45 years ago. The adjacent other plot is a mixed forest with pinesof about 130 years and oaks of 7080 years. Both soils are classified as acidicCambic Arenosols with negligible clay content and less than 5% silt. The
chemical soil properties at the two sites are very similar in the subsoils Tables 1. .and 2 . In the mineral topsoils 020 cm , the higher values for CEC, C , Norg t
Table 1 .Chemical properties of the Cambic Arenosol from the pineoak stand 1995
aDepth pH CEC BS C N Seff org t ty1 y1 y1 y1 . . . . . .cm CaCl mmol kg % g kg g kg mg kg2 c
b80 3.4 100.7 56 250 10.8 n.d.05 3.6 25.6 9 20.5 0.85 247510 3.8 20.9 5 18.2 0.83 240
1020 4.0 18.7 6 13.6 0.55 2032040 4.3 11.5 6 6.3 0.28 2144080 4.3 5.8 4 1.8 0.09 14280200 4.4 5.7 15 1.0 0.05 n.d.a Base saturation.b Not determined.
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Table 2 .Chemical properties of the Cambic Arenosol from the young pine stand 1995
aDepth pH CEC BS C N Seff org t ty1 y1 y1 y1 . . . . . .cm CaCl mmol kg % g kg g kg mg kg2 c
30 3.5 124.5 71 311.0 14.1 180005 3.2 46.8 19 60.0 2.35 750510 3.6 27.8 9 24.7 0.88 335
1020 3.8 23.5 9 17.8 0.64 2412040 4.2 12.5 6 7.5 0.30 1684080 4.4 6.1 8 1.9 0.09 105
b80200 4.5 4.2 12 1.0 0.05 n.d.a Base saturation.b Not determined.
and S in the young pine stand are due to the incorporation of forest floortmaterial when the site was ploughed prior to plantation. As a result, a microre-lief of ridges and furrows exists and the forest floor is only poorly developed incomparison to the pineoak stand, where distinct layers of different degrees of
.decomposition L, Of, Oh exist.Field measurements of bulk deposition, throughfall and soil solution have
been carried out almost continuously since April 1986, with only a 6-monthinterruption in soil solution sampling between November 1992 and April 1993.Until October 1993, throughfall in the pineoak stand was gathered with 12rectangular polyethylene collectors of 0.25 m2 surface area and led into asubterranean 10 l bottle which were sampled weekly or biweekly. In November1993 these collectors were replaced by round samplers of only 83.3 cm2 surfacearea. From April to October of that year, both sampling systems were in use andshowed no methodological effects on the measured throughfall fluxes. From1986 to 1992, throughfall was also collected and analyzed in the young pinestand. Since element fluxes were not significantly different from fluxes in the
.adjacent pineoak stand Marschner et al., 1991 , the latter data are valid forboth sites.
Soil solution was collected with ceramic suction cups in 50 and 200 cm depthwith 12 replicates for each depth and each stand. The spatial distribution of thecups in the plots was selected to represent the variability in microsites, asindicated by different distances to trees and in the young stand ridges andfurrows. Every week after sampling, vacuum was applied to each suction cupindividually and adjusted to y300 to y500 hPa depending on the amount of thesolution gathered. The collected soil solutions were combined to form fourcomposite samples for each depth and plot and stored at y308C.
Chemical analysis of all solutions was performed on monthly samples and . included pH glass electrode Ca, Mg, K, Al, Mn and Na atomic absorption. . .spectroscopy , Fe colorimetrically and Cl, NO , SO ion chromatography .3 4
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For the determination of solution acidity and quantification of acidity transfer .within the ecosystems, we adapted the concept of Van Breemen et al. 1983
and extended it for the characterization of precipitation chemistry. According to .Van Breemen et al. 1983 , alkalinity, also termed acid neutralization capacity
. ..ANC is defined as Eq. 1 :2q 2q q q 2y yANC s2 Ca q2 Mg q K q Na y2 SO y NO4 3
yy Cl 1 .w xwhere X are molar concentrations. ANC is positive if there is a surplus of the
basic cations over the strong acid anions, indicating the presence of HCOy or3OHy. If organic anions are present in the solutions, as it is the case inthroughfall and soil solution from the topsoil, ANC calculated according to Eq. . q1 is overestimated. However, a negative ANC indicates the presence of H , Aland Fe cations and therefore a transfer of acidity with the solution.
For the calculation of throughfall acidity, we introduced NHq in the equation4since it contributes to the acid load of the soil by the release of Hq upon itsuptake by plants or by the production of an equimolar amount of Hq during
.nitrification and therefore reduces throughfall alkalinity according to Eq. 2 .2q 2q q q 2y yANC s2 Ca q2 Mg q K q Na y2 SO y NO4 3
y qy Cl y NH 2 .4For the calculation of time trends in soil solution composition, the approach
.of Wesselink et al. 1995 was adapted, where they used Cl to correct for soilwater fluctuations due to evapotranspiration and dilution, assuming the conser-
..vative behavior of Cl in the soil solution Eq. 3 :.X sA P tqA Cl qB 3 .X Cl X
w x where X is the element concentration in the soil solution, t is time months or.years and A , A and B are parameters estimated by the model. However,X Cl X
this approach fails if soil solution Cl concentrations themselves show a temporaltrend due to decreasing inputs, as it is the case at our study site where significant
.negative slopes were calculated according to Eq. 4 for 19901995:
Cl sA P tqB 4 .Cl Clw ) xTo overcome this problem, a time-trend-corrected Cl concentration Cl was
.calculated according to Eq. 5 by adding the previously determined time trend .component of Cl slope= time to the measured Cl concentration values:
))Cl s Cl qA P mo ymo 5 . .Cl i iy1i i
with isnumber of months since the begin of the study.
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The component that describes variations in element concentrations caused by .soil water content changes was thus described with Eq. 6 :
)X sA P Cl qB 6 .X Xww xwhere X are predicted element concentrations assuming only dilution andw
w ) xconcentration effects. Cl is the time-trend corrected Cl concentration from .Eq. 5 . For the period 19861991 when no time trends for Cl were observed,
.the actually measured Cl concentrations were used in Eq. 6 .Based on the above calculations, the temporal trend in soil solution concentra-
tions after 1990 for all elements was described with the following model Eq. ..7 :
))X sA P tqA P Cl qB 7 .X XCl X
w x w ) xwhere X is the element concentration, Cl the time trend corrected Cl . )concentration from Eq. 2 and A , A and B the estimated modelX XCl X
3.1. Element fluxes with throughfall
In comparison to bulk deposition outside of forest stands, throughfall fluxesof most elements are higher due to wash-off of dry deposits from the canopy andleaching from the foliage. These external and internal sources are difficult todifferentiate for most elements so that total inputs to forest ecosystems aredifficult to estimate. But the throughfall fluxes presented in Table 3 quantify thesolute inputs to the soil surface and therefore are more relevant for soil solutioncomposition.
Despite the large annual variability in throughfall fluxes, a drastic decline of .several elements is evident between 1989r1990 and 1991r1992 Table 3 .
Since these changes all occurred within one or two years and no temporal trendsin the earlier and later years are discernible for most elements, mean annualfluxes from 1986 to 1991 were compared with those from 1991 to 1995. Duringboth time periods, mean annual precipitation was around 570 mm whichcorresponds well with the long-term average of 580 mm for Berlin. With 733mm in 1987r1988 and 731 mm in 1993r1994 wet years were recorded in bothperiods. The extremely dry year 1988r1989 has no equivalent in the later timeperiod, when precipitation was always well above 400 mm. However, nocorrelations were found between precipitation and element fluxes, so that
Table 3 .Annual element fluxes with throughfall in the pineoak stand and total precipitation precip. in the Grunewald forest April 1986March 1995
.ANCsacid neutralizing capacitySO Ca Mg K Mn NO NH H Al Fe Na Cl ANC Precip.4 3 4 .kmol kmol kmol kmol kmol kmol kmol kmol kmol kmol kmol kmol kmol mmc
y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1. . . . . . . . . . . . .ha ha ha ha ha ha ha ha ha ha ha ha ha1986r1987 1.49 0.82 0.18 0.391 0.038 0.70 0.79 0.59 0.152 0.034 0.38 0.65 y2.34 6171987r1988 2.03 0.79...