The acidification of the Herrenwieser See, Black Forest, Germany, before and during industrialisation

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Wat. Res. Vol. 31, No. 5, pp. 1194-1206, 1997 © 1997ElsevierScienceLtd. All rights reserved Printed in Great Britain 0043-1354/97$17.00+ 0.00

Pergamon

PII:S0043-1354(96)00381-8

THE ACIDIFICATION OF THE HERRENWIESER SEE, BLACK FOREST, GERMANY, BEFORE AND DURING INDUSTRIALISATION I N G R I D J U T T N E R 1., J U T T A L I N T E L M A N N I, B E R N H A R D M I C H A L K E ' , R A I M U N D W l N K L E R 2, C H R I S T I A N E. W. S T E I N B E R G ' t @ and A N T O N I U S K E T T R U W ~GSF-Forschungszentrum ffir Umwelt- und Gesundheit GmbH, Institut fiir 13kologische Chemic, Neuherberg, D-85764 OberschleiBheim, Germany and 2GSF-Forschungszentrum fiir Umwelt- und Gesundheit GmbH, Institut fiir Strahlenschutz, Neuherberg, D-85764 OberscheiBheim, Germany (Received March 1996; accepted in revised form November 1996) Abstract--Past trends in the biology and chemistry of the Herrenwieser See in the base-poor Bunter Sandstone Black Forest were reconstructed from a sediment core. Diatom inferred pH indicated pre-industrial acidification periods with subsequent recovery. For the most recent acidification, multiple regression indicated a pH decline by 0.78 pH units to a minimum ofpH 3.91 in the early 1980s; weighted averaging also indicated a pH minimum in the 1980s, but the lowest value was pH 4.58 and the overall decline only 0.30 units. The most important indicator species were Asterionella ralfsii for moderate acidification and Tabellaria quadriseptata for extreme acidification. Community diversity H' and floristic composition, as shown by cluster analysis, were sensitive to pH changes in the lake. Chlorophyll pigments offered another indicator for pH trends since periods of acidification were accompanied by higher concentrations of chlorophyll derivatives. Acidic inputs into the lake were indirectly detected via analysis of persistent pollutants, metals and polycyclic aromatic hydrocarbons. Characteristic chemical changes indicated a metal burden from atmospheric deposition, and the release of base cations and aluminium from weathering. PAH concentrations rose simultaneously with the pH decline in the 19th century. After the input maximum in the 1960s the flux rates for PAHs decreased and are now <20% of their peak value. The simultaneous trends in biological indicators and persistent pollutants demonstrate that recent acidification was caused by atmospheric acid deposition. So far there has been no significant reverse trend despite signs of recent changes indicated by the diatoms. However, pre-industrial acidification and recovery were also related to acid deposition, and indicate that reversal is possible in this lake. © 1997 Elsevier Science Ltd Key words--acidification, lakes, diatoms, chlorophyll, heavy metals, polycyclic aromatic hydrocarbons, recovery

INTRODUCTION Paleolimnological studies represent the only way of reconstructing past environmental changes caused, for example, by acid deposition (Smol, 1992). The acidification of surface waters in base-poor geological regions has been convincingly demonstrated in Europe and North America (e.g. Arzet et al., 1986; Battarbee et al., 1989; Charles et al., 1990). Paleolimnological techniques have also allowed investigation of the relative roles of land use change and deposition in pH trends. Land use modification did not result in lake acidification in areas unaffected by acid deposition (Battarbee and Charles, 1994; Renberg et al., 1990), but effects by the scavenging of

pollutants in conifer forests (Hepp and Hildebrand, 1993) have accelerated acidification in other locations (Harriman et al., 1994). The Northern Black Forest has been subject to large changes in natural vegetation (Zeitvogel and Feger, 1990; Jahn et al., 1990) and anthropogenic acid deposition over recent centuries (Jiittner et al., 1996). In view of the past controversy about their relative effects, further case studies which use paleolimnology are required. In this paper we present results from the Herrenwieser See as a multi-parameter investigation of past trends in chemistry and biology, investigating in particular the role of past and current influences of acid deposition. STUDY SITE

*Author to whom all correspondence should be addressed. tPresent address: Institut for Gew~isser6kologie und Binnenfiseherei, Miiggelseedamm 310, D-12587 Berlin, Germany.

The Northern Black Forest (Fig. 1) is one of Germany's most acid-sensitive regions due to its geological background of base-poor Bunter Sand-

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Acidification in the Black Forest stone. The acidification of its freshwater systems has been studied intensively since the 1980s (e.g. Feger, 1986; Arzet, 1987; Steinberg et al., 1987; B6hmer and Rahmann, 1992; Thies, 1994; Hinderer, 1995; Feger et al., 1995; Jiittner et al., 1996). The dystrophic Herrenwieser See lies at 832 m a.m.s.1, in a glacial cirque, has a maximum depth of 9.5 m and a surface area of 1.8 ha; it is surrounded by Sphagnum mats and the catchment is covered by conifer forest dominated by spruce (73%) with pine (17%) and fir (10%) (Zeitvogel, 1986). These species have replaced the former natur~Ll fir-beech forest due to human activity throughout centuries (forest grazing, resin production, mining, logging, production of charcoal and potash, glass factories, plantation forestry). Soils in the catchment are podsols and stagnogleys. The lake receives water from three springfed rivulets, from groundwater seepage and from direct precipitation. Prevailing 'winds from south-southwestern to western directions; transport air masses from the densely populated and industrialised Rhine valley to the Black Forest, which receives its highest precipitation of more than 2000 mm (long-term annual mean) in its northern part at the Hornisgrinde (1160 m, Fig. 1). At higher elevations precipitation peaks during the winter and snow can persist from December to March. During snow melting periods in winter and in April large amounts of acids, stored in the snowpack, are transported into surface waters (Thies, 1994). In April 1992, when the sediment core was taken, the lake had a mean pH of 4.3 and a mean alkalinity of - 3 7 . 9 #eq/l (Table 1). At 8 m, pH was 4.9 (oxygen concentration 9%), and hence some in-lake alkalinity generation is likely. The Herrenwieser See is presently fishless. Since 1980 calcareous material was used for path restorations around the lake. In 1989, parts of the catchment, but not the lake, were limed. These activities, however, ceased immediately and the area around the lake is now designated as a nature reserve; liming was not reported prior to this date.

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A sediment core (30 cm length x 6 cm diameter) w a s taken at the deepest part of the lake using a gravity corer (Core-Stecher System Niederreiter, Limnological Station Mondsee, Austria) and sectioned in 0.5 cm slices; these were transported at ca. 4°C and finally freeze-dried. Subsequently, except the surface sample, only every second slice (full cm) was analysed for diatoms, chlorophyll, elements and PAHs. However, for the sediment dating every 0.5 cm slice was measured.

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MATERIALSAND METHODS Water chemistry and sediment coring Water samples (1(3 !) from 0, 2, 4, 6 and 8 m depth were taken in April 1992 and pH and conductivity were measured immediately (portable meters: LF 90 and pH 90 WTW, Weilheim, German~; pH-electrode for low conductivity waters 405-60-88 T1:',-57 Ingold, Steinbach/Ts., Germany). Five ml of water were filtered (0.45/zm) for the analysis of anions, and 3ml for the determination of metals, base-cations and silica, the latter fixed with 20/~l HNO3. The anions were determined photometrically (Segmented Continuous Flow Analysis System, Skalar, Erkelenz, Germany), and other determinations were clone by Inductively Coupled Plasma Optic Emission Spectrometry (ICP-OES, Jobin Yvon, Longjumeau, France). Reactive aluminium (Aim) W,'tS determined photometrically (Spektroquant, Merck, Darmstadt, Germany). Alkalinity measurements were carried out within 6 h of sampling and followed the procedure described by Wetzel and Likens (1991).

SI

Fe I

Fig. 1. Location of the study area. B: Bfihlertal; BB; Baden-Baden; F: Freudenstadt; H: Herrcnwies; L: Herrenwieser See; M: Hornisgrinde; O: Offenburg; R: Rastatt; S: Strasbourg; h Rhein; 2: Murg; 3: Rench; 4: Kinzig.

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1196 Table 1. Water chemistry of the Herrenwieser See, Northern Black Forest, Germany, in April 1992; water samples were taken in 2 m depth. Mean (+S.D.) pH, conductivity and alkalinity (ANC) were calculated from four measurements at 0, 2, 4 and 6 m depth pH Conductivity ANC CI SO4 Na K Mg Ca AI,o, Aim Mn Fe Cu Zn Si

(Stevenson et al., 1991; Birks, 1995). Harmonisation with the SWAP data set resulted in the inclusion of > 9 5 % o f the Black Forest taxa in 23 sediment samples, and > 90% o f the taxa in eight sediment samples, respectively, to derive past lake-water pH. Hierarchical agglomerative cluster analysis (Ward's method based on Pearson correlation) was used to classify the species communities (SPSS for Windows 6.0.1.).

4.3 (0.0) 51.3 (2.4) #S cm t -37.9 (8.9) #eq l -~ 2.8 mg 17.1 mg l1.2 izg I2.3 mg I t 447.0/~g l1.6 mg l-t 726.0/lg l431.0/lg I ~ 58.7/tg 1151.0/tg I t 20.5 Itg 1 48.9 #g I1.6 mg 1-

Chlorophyll The total chlorophyll content (chlorophyll-a + phaeopigments) of the sediment was measured according to the method of Wasmund (1984), modified for sediments, following a 20-h extraction with 90% (v/v) acetone (Jiittner et al., 1996).

Sediment dating The sediment core was dated over the past 100 years using the radioisotopes 2~°Pb(constant rate of supply model, c.r.s.) and ~37Cs(Robbins et al., 1978; Oldfield and Appleby, 1984). ~TCs dating points (atomic bomb tests 1963, Chernobyl radioactive fallout 1986) were in accordance with the :~°Pb dating. The mean sedimentation rate was 4.03 mg cm -2 yrand the 30-cm long sediment core embraced probably more than 500 yr. Diatoms Diatom preparations followed standard methods (Jiittner et al., 1996). We counted 400-500 valvae at 1000× magnification (interference contrast, Zeiss Axioplan). Taxonomy and nomenclature followed Krammer and Lange-Bertalot (1986-1991) and Krammer (1992). To reconstruct pH we applied two methods: (1) multiple regression of pH groups using the equation of Arzet (1987) and (2) weighted averaging (WA) with classical de-shrinking and bootstrapping (WACALIB version 3.3; Line et al., 1994) using the SWAP data set from Northern Europe

Elements Elements were detected from an aqua regia extraction with atomic absorption spectrometry (AAS) and inductively coupled plasma optic emission spectrometry (ICP-OES; hydride generating AAS for As, graphite furnace AAS for Pb, ICP-OES for S and ICP-OES or direct current plasma atomic emission spectroscopy, DCP-AES, for the remaining elements). Intercorrelations between element concentrations were assessed using principal component analysis (PCA) on z-transformed data (SPSS for Windows 6.0.1.). Polycyclic aromatic hydrocarbons (PAH) PAHs were analysed according to a method developed by Martens (1991 ). Sediment samples (200 mg dry weight) were extracted with tetrahydrofuran for 2.5 h under ultrasound, centrifuged, and the extract directly analysed with fluorescence-HPLC (Lintelmann et al., 1993; Jiittner et al., 1996). RESULTS

Bioindication D i a t o m c o m m u n i t y a n d inferred p H . F r o m 74 d i a t o m species f o u n d in the s e d i m e n t o f H e r r e n w i e s e r See only 12 species were c o m m o n , with relative a b u n d a n c e s c h a n g i n g m a r k e d l y t h r o u g h o u t the core (Fig. 2). Aulacoseira distans v. nivalis (W. Smith)

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Fig. 2. Relative abundance of common diatom species in the sediment core of the Herrenwieser See, Northern Black Forest.

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Fig. 3. Cluster analysis (Ward's method) of the diatom species community in the sediment core of the Herrenwieser See, Northern Black Forest. Haworth, Asterionella ralfsii W. Smith and Tabellaria quadriseptata Knudson were the most common species but dominated during different times. Whereas A. distaws v. nivalis was characteristic for most of the older sediments, A. ralfsii was very abundant at 30, 23, 16 and between 13-6cm, but disappeared abruptly in the early 1950s (5 cm depth) and has not recovered since. T. quadriseptata dominated for a short time at 15 cm depth, was abundant from 12 cm depth, then increased even further after the d,~cline of A. ralfsii to peak at 65% relative abundance in the early 1980s; it has since decreased slightly but is still by far the most abundant species. Tabellaria flocculosa (Roth) Kiitzing appeared after Tabel, raria quadriseptata's abrupt decline at 14--13 cm, and has been more common since 1990. Eunotia rhomboidea Hustedt also increased suddenly in the early 1959s to become the second most abundant species :~ince then. Species which declined in the upper third of the core (post and mid-late 19th century) were Eurwtia incisa Gregory, Anomoeoneis brachysira v. brac,~ysira (Breb. in Rab.) Grunow in Cleve, Eunotia rneisteri Hustedt and Navicula

mediocris Krasske. Pinnularia subcapitata Gregory and Frustulia rhomboides v. saxonica (Rab.) De Toni were regularly present throughout the core but most common at 25-24 cm, 19-16 cm and since the 1930s. These changes in community composition were reflected by the cluster analysis (Fig. 3). Three cluster groups (CG) represent diatom communities dominated by T. quadriseptata (CG I), A. ralfsii (CG II) and A. distans v. nivalis (CG III). In CG II a T. quadriseptata and A. ralfsii were equally important, but nevertheless the overall community composition was not very different from CG II b. CG III a and b were very similar to each other, but distinct from CG I and II. pH inferred from multiple regression of ca. 4.7 changed little between 30 and 17cm depth, then decreased by 0.4 pH units from 16 to 15 cm, but recovered at 14 cm. Between 13 and 8 era, probably during the 19th century and the beginning of the 20th century, the inferred pH fluctuated repeatedly by about 0.2 pH-units. In the 20th century there was a constant decrease in pH, accelerating at the beginning of the 1960s to reach its lowest values in the mid

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1980s. Since then, there has been a small but insignificant pH increase (Fig. 4). pH inferred from weighted averaging indicates three pre-industrial acidification periods at 30, 23 and 16-15 cm, where the pH decreased between 0.11 and 0.23 pH-units from an average pH of 4.91. From 13 cm upwards inferred pH decreased to reach minima of 4.66 at 10 cm (ca. mid 19th century), 4.61 at 7 cm (beginning 20th century) and 4.58 at 2 cm (1982). Since then there has been an insignificant pH increase of 0.05 (Fig. 4). Generally, diversity H ' of the diatom community decreased only slightly during the investigated time period, due to a parallel decrease in evenness E. Species richness S tended to increase. However, there were exceptional periods with markedly depressed H ' and E at 30cm depth, H', E and S at 23 cm, S at 16-15 cm, H ' and E at 10, H', E and S at 8-7 and at 2-0.5 cm depth (Fig. 5). Total chlorophyll (chlorophyll-a + phaeopigment). Chlorophyll, largely present as phaeopigment, changed markedly throughout the sediment core with

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increased concentrations measured between 2623cm and 17-14cm and an increase from 10cm upwards. Between the early 1960s and the early 1970s the chlorophyll concentrations nearly doubled and they were still rising up to the present day (Fig. 6). There was a highly significant negative correlation between chlorophyll and multiple regression inferred pH (Spearman correlation r = -0.7927, p < 0.001; Fig. 7). Sediment chemistry Elements. Characteristic changes in base cation and metal contents in the sediment core were reflected by five principal components (Table 2 and Fig. 8a and b). Base cations, aluminium, titanium and iron loaded positively on PC 1, which mostly decreased in the upper half of the core. Exceptions were at 15 cm and 8-7 cm depth when these elements increased. Copper, chromium, zinc, cadmium and lead, scoring high on PC 2, increased substantially from the 1950s. Copper, zinc and nickel, the latter scoring highly on PC 1 and 5, increased also in 15 cm depth, with

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Acidification in the Black Forest

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copper and nickel concentrations being higher than background levels since 18 and 21 cm, respectively. Calcium (PC 3) c,oncentrations were lower in the upper part of the core, with the exception of very high concentrations at 7cm probably caused by allochthonous input following a severe flooding event. Arsenic (PC 4) increased prior to the heavy metals but has decreased since the 1960s. Polycyclic aromatic hydrocarbons. Concentrations of phenanthren, tluoranthene, chrysene, benzo(b)fluoranthen, benzo(k)fluoranthen, benzo(a)pyrene, benzo(g,h,i)-perylene and indenopyrene were usually less than 0.3mg/kg (0.01 mg.m-2.yr -') prior to 12 cm depth and anthracene, benz(a)anthracene and dibenz(a,h)anthracene were not detectable. Pyrene concentrations were higher than background values at 15 cm depth, and had peaked already in the 1910s. Phenanthrene peaked just prior to pyrene. Sediment concentrations of the other PAHs increased slowly since 12cm depth, presumably during the 19th century, then increased considerably since the turn of the century and peaked in the early 1970s. Since then, there has been a marked decrease to 20-30% of the 1970s values (Fig. 9). PAH-flux rates (Table 3), calculated for this century based on time-specific sedimentation rates (c.r.s.-model), were higher in the 1960s than in the 1970s; the most recent flux rates were on average 19% (S.D. 3.0) of the 1960s flux rates with the exception of anthracene (40%) and pyrene (74%). DISCUSSION Biological and chemical approaches have long been applied separately to assess historical changes in lake

status (e.g. Flower and Battarbee, 1983; Renberg and Hultberg, 1992; Hites et al., 1977; Heit et al., 1981; Sanders et al., 1993), but recently the power of using various methods simultaneously for demonstrating ecological changes and their causes has been acknowledged. In our study we have applied this multi-parameter approach to five lakes in the Northern Black Forest, knowing of their severe acidification problems from previous studies (Arzet, 1987; Steinberg et al., 1987). By analysing concurrently paleolimnological trends in diatom communities, inferred pH, chlorophyll, elements and PAHs we can demonstrate several acidification periods in the Herrenwieser See. Reconstruction of the lake's acidification history The naturally acidic pH of the Herrenwieser See supported a diatom community prior to anthropogenie acidification of mainly acidophilic species such as Aulacoseira distans v. nivalis, Anomoeoneis brachysira v. brachysira and several Eunotia species, which are also frequently found in similar types of lakes elsewhere (e.g. Whitehead et al., 1986). Another common species, Asterionella ralfsii, dominated repeatedly and had a marked effect on community diversity. At 16 and 13-6crn it preceded the occurrence of the acidobiontic T. quadriseptata, a well known indicator of severe acidification (e.g. Anderson et al., 1993). Thus we suggest that A. ralfsii might indicate increasing acid conditions. Davis et al. (1988) found an increase of Asterionella ralfsii v. americana during a period when agricultural activities caused nutrient input into Sagamore Lake, Adirondack Mountains, U.S.A. At the beginning of

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acidification temporary eutrophication has been discussed by Renberg et al. (1985) and Renberg and Hultberg (1992), and occurs due to increased inputs of nitrogen, phosphorus and base cations from catchment and atmospheric sources. However, the complete absence of A. ralfsii during severe acidification might reflect the species' susceptibility to the high aluminium concentrations found in the lake water (Gensemer, 1991). According to the WA inferred pH and the dominance ofA. ralfsii at 30 and 23 cm, and A. ralfsii and T. quadriseptata at 16 and 15 cm, there have already been major impacts on the lake ecosystem long before industrialisation. This is supported by higher chlorophyll concentrations which provided an additional indication of acidification. Reasons for this are still unclear, but increasing water transparency following acidification has been demonstrated (e.g. Yan, 1983; Steinberg and Kiihnel, 1987; Schindler et al., 1980) and might provide better

conditions for benthic primary producers. No effect has been detected for planktonic biomass or primary production following experimental acidification (Schindler, 1994); however, Shearer et al. (1987) found a slight increase in phytoplankton and benthic filamentous green algae (metaphyton) proliferate in acid waters (Lazarek, 1985; Stokes, 1986; Howell et al., 1990). Another possible explanation might be the invasion of Sphagnum into the litoral as discussed by Melzer and Rothmeyer (1983). Although the causal mechanisms must yet remain unclear, enhanced chlorophyll concentrations in lake sediments during acidification were a valuable indication of acidification in other Black Forest lakes (cf. Guilizzoni and Lami, 1988; Jiittner et aL, 1996). Possible anthropogenic impacts causing pre-industrial acidification include emissions from mining and ore smelting in the Black Forest, the production of charcoal and potash, and emissions from glass factories. Detailed historical records are scarce before

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totalchlorophyll(chlorophylla + phaeopigment,mg/g) Fig. 6. Total chlorophyll content (chlorophyll-a + phaeopigment, mg/g dwt) in the sediment core of the Herrenwieser See, Northern Black Forest.

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inferred pH Fig. 7. Spearman correlation between diatom inferred pH (multiple regression) and total chlorophyll in the sediment core of the Herrenwieser See, Northern Black Forest. the 18th century but since then precise information about some ongoing activities is available (Metz, 1977). Iron ores, found at the western ridge of the Black Forest, were exploited from the 17th century and smelted in Biahlertal 10 km west-northwest of the Herrenwieser See between 1683 and 1802. These emissions might ihave had an impact on the lake as indicated by increased concentrations of nickel, copper and zinc, but also elevated chlorophyll and pyrene between 17 and 14cm. A much closer emission source ]probably affected the lake between 1724 and 1778, when a glass factory operated only 2.5 km west-southwest of the lake in the village of Herrenwies (Metz, 1977). T. quadriseptata increased from 0.7% relative abundance to 9.3% at 16 cm and 39.4% at 15 cm, but declined rapidly at 14 cm, as did Table2. Principalcomponentsderivedfromthe elementcomposition in the sedimentof HerrenwieserSee PC 1 PC2 PC 3 PC4 PC5 K 0.84 0.21 -0.22 0.37 -0.13 Mg 0.84 0.41 0.01 - 0 . 0 1 -0.16 Ca 0.24 -0.05 0.72 0.43 -0.23 Sr 0.85 0.26 0.23 - 0.26 0.11 Ba I].77 -0.36 0.26 -0.02 0.32 A1 I].82 0.51 -0.02 0.09 -0.13 P 13.45 0.68 0.22 -0.45 -0.15 As -13.64 0.43 0.16 0.55 0.13 Ti 13..77 0.41 0.02 0.09 -0.22 Cr 13.09 0.81 -0.15 -0.13 -0.18 Mn -C.I1 0.60 0.43 -0.14 0.55 Fe tL66 0.32 -0.20 0.35 0.25 Ni 13..52 0.22 -0.42 0.09 0.51 Cu -13,.37 0.84 -0.07 0.01 0.17 Zn -C,.56 0.79 -0.12 0.03 -0.10 Cd -0.57 0.78 -0.12 0.03 -0.16 Pb -13p.55 0.66 0.26 -0.01 0.10 Variance (%) 38.1 29.5 7.5 6.4 6.1

the chlorophyll concentration from 14 to 13 cm. In addition, both the pH increase inferred from multiple regression and WA suggest that the lake recovered as soon as these probable emission sources disappeared. In the 19th century community change and fluctuating pH probably reflected acidifying emissions due to the beginning industrialisation, as indicated by rising PAH concentrations. According to the multiple regression inferred pH, it was not until the early 20th century that pH finally declined dramatically. Although PAH flux rates in the 1940/50s are unknown, they were highest in the 1960s, when the multiple regression inferred pH decline accelerated again. The lowest inferred pH according to both pH reconstructions was during the early 1980s despite decreasing PAH flux rate during the 1970s and 1980s. However, in contrast to the pH inferred from multiple regression, pH inferred from WA was very low in the early 20th century, accompanied by high phenathrene and pyrene flux rates (Table 3; Jiittner et al., 1996). Additionally pH inferred from WA increased between the 1930s and 1950s despite high PAH concentrations (Fig. 9). Discrepancies in the pH optima for species from Northern Europe, as used in the SWAP data set, and pH optima for species occuring in the Black Forest cannot be excluded and might account for this contradictory result (cf. Niederhauser, 1993). PAHs, which are formed during incomplete combustion of fossil fuels, are transported by aerosols over long distances and have been used successfully for documenting airborne pollution (e.g. Heit et al., 1988; Steinberg et al., 1988; Sanders et al., 1993). Since they originate from the same sources as

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Fig. 8. (a and b) Elements (in order of factor loading on principal components) in the sediment core of the Herrenwieser See, Northern Black Forest.

acidifying substances such as SO]- and N O ; , PAH patterns might provide the possibility of identifying sources. However, in such remote lakes as this, atmospheric mixing of combustion products during transport prevents clear identification of their sources from core samples (Morselli and Zapolli, 1988). With the exception of pyrene, which was indicative of emissions before the industrialisation in Black Forest lakes (Jiittner et all, 1996), individual PAHs have not shown well differentiated trends during recent acidification, and similar PAH composition has also been found elsewhere (Sanders et al., 1993). Since their formation is highest during low efficient combustion processes such as domestic heating (Dasch, 1982), they indicate acidifying substances only from this source. Heit et al. (1988) found a

significantly positive correlation between coal consumption for domestic heating and fluoranthene flux in sediments of Cayuga Lake (U.S.A.), whereas commercial use of coal in power stations or the use of oil and gas showed no clear correlation with fluoranthene flux. The change from coal to oil and gas in domestic heating has been regarded as a major reason for declining PAH emissions (e.g. Christensen and Zhang, 1993; Heit et al., 1988). Therefore, as in Lake Cayuga, other sources are probably also responsible for the present acidification of the Herrenwieser See such as emissions from power plants, industry and traffic. From the 3.0 Mio tons of SOs emitted in Germany in 1982, 62% came from power plants, 25% from industry, but only 9% from domestic sources and 3%

Acidification in the Black Forest Phe "

0,5.

• mmmm 2: m m 4[ m m 6] m m mm a] m . m , . m m • lo'm •

Ant

Fin

m mm •m m m m m mmm mm•m m mmm

mm m ~. m m ,.,ms. m . ~ ~ , • •

Baa i l i I i i I i mm mm •

Bbf

1203

Bkf

Dba

• • a i

mm •l I

• • i

BE

i

l

/ Hi

i / i / i • i • •

i i i i i I •

I i i i i i s

/ i l i l • • • s

/ i i / I • • m

i I i i I i • s

Ind

•

mm

atom

• BE i I i I l l I I i mm • • m m

m m

BB

l l i i i / i I i m • s mm

.'

.m

18~m

n

2o: } 22: l

26: •• 2S: • • 30" i

•• i a g

i ~

O

~

O

r

~

O

~

O

~

O

~

O

o- o-

~

O

~

O

~

d

Fig. 9. Polycyclicaromatic hydrocarbons in the sediment core of the Herrenwieser See, Northern Black Forest. from traffic; from 3.1 Mio tons of NOx emissions, 55% came from traffic, 28% from power plants, 14% from industry and 4% from domestic sources (UBA, 1985). Increasing concentrations of heavy metals since the 1950s, with no or little decline, suggest that other types of pollution are also contributing to changes in these freshwaters. Heavy metals accumulated in organic soil horizons in the catchment of the Herrenwieser See are mainly from atmospheric origin, and are mobilised during strong precipitation events (Biihler, 1993). Worldwide, the emissions of heavy metals have increased dramatically in the 20th century (Nriagu et al., 1979) but the importance of different sources have changed (Sanders et al., 1993). Whereas emissions from mining, heavy metal industry and coal have decreased, traffic and metal-processing industries have contributed most to atmospheric emissions in more recent decades (Pacyna et al., 1991). Metals accumulated in the recent sediments of the Herrenwieser See such as copper, zinc, cadmium and chromium are widely used in non-ferric metal industries; chromium also in the production of ceramics and leather goods. Such industries are very common in the nearby centres of Offenburg, Rastatt, Baden-Baden and Freudenstadt.

Depth (cm) 0.5 1 2 3 4 5

6 7

In contrast to the heavy metals, base cations and aluminium decreased in the sediment during the actual acidification period probably as a result of dissolution at low pH: there are now extremely high concentrations of aluminium found in the water column (Table l). Higher concentrations during the acidification period in the 18th century (15 cm) might reflect release from the catchment as a result of increased acid deposition. Recent recovery. One of the most important issues in acidification research has centered on the potential recovery of acidified ecosystems in response to air pollution control. Historic acidification periods caused by mining in the Bavarian Forest have shown recovery after the emissions stopped (Bruckmeier, 1994; Steinberg et al., 1984) comparable to our results in the Herrenwieser See before the most recent acidification. At present, the question is whether recent emission reductions are sufficient to be reflected in ecological recovery. Although SOs emissions in southwest Germany have decreased by 50% since the implementation of clean air legislation in the 1980s, and lower SO2- and H + concentrations have been found in precipitation, NO~- inputs remained unchanged, while NH~ even increased in

Table 3. PAH flux rates in the sediment of the Herrenwieser See Phe Ant Fla Pyr Baa Cry Bbf 0.008 0.002 0.029 0.111 0.010 0.027 0.026 0.037 0.002 0.043 0.063 0.020 0.050 0.067 0.020 0.002 0.048 0.108 0.015 0.037 0.056 0,031 0.003 0.074 0.113 0.032 0.078 0.117 0,052 0.004 0.129 0.150 0.051 0.108 0.149 .

0,010 0,027

.

.

0.001 0.004

.

0.035 0.088

.

0.041 0.327

.

0.015 0.040

.

.

0.028 0.074

.

0.042 0.125

since 1914 (rag m -2 yr -~)

Bkf 0.013 0.035 0.023 0.048 0.068 .

0.020 0.058

Bap 0.015 0.052 0.023 0.045 0.076 .

Dba 0.000 0.020 0.004 0.010 0.013

Bgh 0.021 0.052 0.046 0.002 0.124

0.027 0.058 0.023 0.074 0.150

0.004 0.009

0.042 0.002

0.047 0.085

Ind

.

0.024 0.074

Note: calculation based on time-specific sedimentation rates (c.r.s.-model). Flux rates were not calculatedin 5 cm depth due to extremelyhigh sedimentationrates. Phe: Phenanthrene; Ant; Anthracene; Fla: Fluoranthene;Pyr: Pyrene;Baa: Benz(a)anthracene;Cry: Chrysene;Bbf: Benzo(b)fluoranthene,

Bkf: Benzo(k)fluoranthene;Bap: Benzo(a)pyrene;Dba: Dibenz(a,h)anthracene;Bgh: Benzo(g,h,i)perylene;lnd: Indeno(I,2,3-cd)pyrene.

1204

I. Ji.ittner et al.

agricultural regions (Hepp and Hildebrand, 1993), the latter also playing an increasing role in acidification elsewhere (Van D a m and Mertens, 1995). In our study on five lakes in the Northern Black Forest we found no significant increase in inferred p H despite early visible changes in the diatom community since 1990 (J/ittner et al., 1996). In the Herrenwieser See catchment, the use of limestone for path restoration together with a catchment liming campaign in 1989, might have had an influence on the lake; but since 1990 no more lime was used in the catchment and similar changes in diatom communities have also occurred in a nearby lake where no liming has been performed. Battarbee et al. (1988) found floristic changes of diatom communities in surface sediments of Scottish lochs in the 1980s with a delay of 10 yr since SO2-deposition in Britain declined. According to Hochstein and Hildebrand (1992) the critical load in forests in southwest Germany is still exceeded. This also applies to the upper rock strata in the lake's catchment (Hinderer, 1994) and, in addition, accumulated stores of sulfur may well continue to prevent immediate recovery (Einsele and Hinderer, 1995). Moreover, Likens et al. (1996) suggest that large losses in base cations from soils in forest ecosystems can result in a long-term hysteresis in recovery. CONCLUSIONS F r o m this paleolimnological study we conclude that the pre-industrial and present severe acidification of the Herrenwieser See was caused by atmospheric acid deposition; this is shown by simultaneous trends in biological indicators and persistent pollutants, associated with the deposition of acidifying substances. So far there has been no significant reverse trend despite signs of recent changes indicated by the diatoms. However, trends in heavy metals and also dioxins (Jiittner et al., in press) suggest that there is still significant exposure to airborne pollutants. Furthermore, continued N O ; and increasing N H ~ emission, but also release of SO~- stored in the soils during high deposition periods and base cation loss from the catchment might delay the recovery of the lakes in the Northern Black Forest. Notwithstanding these current patterns, one important result from our data is that the Herrenwieser See has recovered from previous periods of acidification, That such reversal can occur clearly has relevance for the future of this region. Acknowledgements--This work was partly funded by the Landesanstalt fiir Umweltschutz, Baden-Wiirttemberg. We thank the forest commission for support and access to the lake, Prof. Dr Rahmann, Universit/it Hohenheim, Prof. Dr A. Melzer and Dr U. Raeder, Technische Universit~it Miinchen, for the supply of technical equipment, Dr J. B6hmer, Universit~it Hohenheim and Mr E. Wildi, GSF, for help in the field, Dr H.-J. Thies, Universit~it Freiburg, for informations and discussions, Mrs U. Gerstberger, Miinchen, for her introduction to diatom taxonomy, Dr A.

Zwick, GSF, for providing the chlorophyll method, Dr D. Martens, GSF, for providing the method for analysis of PAHs, Dr M. Hinderer, Universit~it Tiibingen, and Dr S. J. Ormerod, University of Wales, Cardiff, for their useful comments on the manuscript. Special thanks to Dr T. Allot, ECRC, University College London, for his help in applying the weighted averaging approach and to Prof. R. Battarbee, ECRC, University College London, for access to the SWAP data set. REFERENCES

Anderson D. S., Davis R. B. and Ford M. S. J. (1993) Relationships of sedimented diatom species (Bacillariophyceae) to environmental gradients in dilute northern New England lakes. J. Phycol. 29, 264-277. Arzet K. (1987) Diatoms as pH-indicators in sediments of base-poor lakes (in German). PhD-thesis, University of Innsbruck, Austria. Arzet K., Krause-Dellin D. and Steinberg C. (1986) Acidification of four lakes in the Federal Republic of Germany as reflected by diatom assemblages, cladoceran remains and sediment chemistry. In Diatoms and Lake Acidity (Edited by Smol J. P., Battarbee R. W., Davis R. B. and Merilainen J.), pp. 227 250. Dr W. Junk Publishers, Dordrecht. Battarbee R. W. and Charles D. F. (1994) Lake acidification and the role of paleolimnology? In Acidification of Freshwater Ecosystems: Implications for the Future (Edited by Steinberg C. E. W. and Wright R. F.), pp. 51-65. Report of the Dahlem Workshop, Berlin 1992. John Wiley & Sons, Chichester. Battarbee R. W., Flower R. J., Stevenson A. C., Jones V. J., Harriman R. and Appleby P. G. (1988) Diatom and chemical evidence for reversibility of acidification of Scottish lochs. Nature 322, 530-532. Battarbee R. W., Stevenson A. C., Rippey B., Fletcher C., Natkanski J., Wik M. and Flower R. J. (1989) Causes of lake acidification in Galloway, south-west Scotland: a paleoecological evaluation of the relative rates of atmospheric contamination and catchment change for two acidified lakes with non-afforested catchments. J. Ecol. 77, 651-672. Birks H. J. B. (1995) Quantitative paleoenvironmental reconstructions. In Statistical Modelling of Quaternary Science Data (Edited by Maddy D. and Brew J. S.), pp. 161-254. Quaternary Research Association, Technical Guide No. 5, Cambridge. B6hmer J. and Rahmann H. (1992) Acidification of freshwaters. Limnological investigations of the acidification of standing waters in the Northern Black Forest with special consideration of amphibians (in German). Ecomed Verlag, Landsberg and Lech, Germany. Bruckmeier B. (1994) Input of acids, PCB, PCDD und PCDF in the GroBer Arbersee between 1860 and 1990 (in German). Diplom-thesis, Technical University of Munich, Germany. Biihler B. B. (1993) Investigations of the mobility of atmospheric and lithogenic heavy metals with consideration of the acidification of soils and waters in a forested watershed (Bunter Sandstone Black Forest, in German). Diplom-thesis, Part 1, University of T/Jbingen, Germany. Charles D. F., Binford M. W., Furlong E. T., Hites R. A., Mitchell M. J., Norton S. A., Oldfield F., Paterson M. J., Smol J. P., Uutala A. J., White J. R., Whitehead D. R. and Wise R. J. (1990) Paleoecological investigation of recent lake acidification in the Adirondack Mountains, N.Y.J. Paleolimnol. 3, 195-241. Christensen E. R. and Zhang X. (1993) Sources of polycyclic aromatic hydrocarbons to Lake Michigan determined from sedimentary records. Environ. Sci. Technol. 27, 139-146. Dasch J. M. (1982) Particulate and gaseous emissions from

Acidification in the Black Forest wood-burning fireplaces. Environ. Sci. Technol. 16, 639-649. Davis R. B., Ander~;on D. S., Charles D. F. and Galloway J. N. (1988) Two-hundred-year pH history of Woods, Sagamore, and Panther Lakes in the Adirondack Mountains, New York State. In Aquatic Toxicology and Hazard Assessment (Edited by Adams W. J., Chapman G. A. and Landis W. G.), Vol. 10, pp. 89-111. American Society for Testing and Materials, Philadelphia. Einsele G. and Hinderer M. (1995) Acid inputs and element cycling in the Bunter Sandstone Black Forest (Seebach catchment, 8 years of measurements) (in German). Z. dt. Geol. Ges. 146, 51-62. Feger K.-H. (1986) Biogeochemical investigations of waters in the Black Forest with specific consideration of atmospheric inputs (in German). Freiburger Bodenkundliche Abhandlungen, Heft 17. Feger K. H., Martin D. and Z6ttl H. W. (1995) Development of water acidity in the Black Forest--are there any change.s caused by deposition? (in German). Naturwissenschafi~n 82, 420~23. Flower R. J. and Battarbee R. W. (1983) Diatom evidence for recent acidification of two Scottish lochs. Nature 305, 130-133. Gensemer R. W. (1991) The effects of pH and aluminium on the growth of the acidophilic diatom Asterionella ralfsii var. americana. Limnol. Oceanogr. 36, 123-131. Guilizzoni P. and Lami A. (1988) Sub-fossil pigments as a guide to the phytoplankton history of the acidified Lake Orta (N. Italy). Verh. lnternat. Verein. Limnol. 23, 874-879. Harriman R., Likens G. E., Hultberg H. and Neal, C. (1994) Influence of management practices in catchments on freshwater acidification: afforestation in the United Kingdom and North America. In Acidification of Freshwater Ecosystems: Implications for the Future (Edited by Steinberg C. E. W. and Wright R. F.), pp. 83-101. Report of the Dahlem Workshop, Berlin 1992. John Wile)' & Sons, Chichester. Heit M., Tan Y., Klusek C. and Burke J. C. (1981) Anthropogenic trace elements and polycyclic aromatic hydrocarbon levels in sediment cores from two lakes in the Adirondack acid lake region. Water Air Soil Pollut. 15, 441-464. Heit M., Tan Y. L. and Miller K. M. (1988) The origin and deposition history of polycyclic aromatic hydrocarbons in the Finger Lake,,; region of New York. Water Air Soil Pollut. 37, 85-110. Hepp R. and Hildebrand E. E. (1993) Depositions in forests of Baden-Wiirttemberg (in German). Allg. Forstztg. 22,

1139-1142. Hites R. A., Lafiamme R. E. and Farrington J. W. (1977) Sedimentary polycyclic aromatic hydrocarbons: the historical record. Science 198, 829-831. Hinderer M. (1994) Simulation of long-term trends in soil and groundwater acidification based on long-term mass balances (in German). PhD-thesis, University of Tiibingen, Germany. Hochstein E. and Hildebrand E. E. (1992) Status and development of ~Ltmospheric deposition in forest ecosystems of Baden-Wiirttemberg. Allg. Forst Jagdztg. 163, 21-26. Howell T., Turner M. A., France R. and Stokes P. M. (1990) Ecological features of acidification-induced growth of metaphyton. Car~. J. Fish. Aquat. Sci. 47, 1085-1092. Jahn G., Miihlh~iuBer G., Hiibner W. and Bricking W. (1990) Changes in natural forest communities in montane areas of the Northwestern Black Forest (in German). Mitt~ Ver. Forstl. Standortkunde und Forstpflanzenziic~,!tung 35, 15-24. Jiittner I., Steinberg C. E. W. and Kettrup A. (1996) Acidification o f selected lakes in the Northern Black Forest. Paleolimnologicad' reconstruction and causation of

1205

recent acidification (in German). Landesanstalt f'tir Umweltschutz Baden-Wiirttemberg, Projekt "Angewandte t3kologie" PAO 15, Karlsruhe. Jiittner I., Henkelmann B., Schramm K.-W., Steinberg C. E. W., Winkler R. and Kettrup A. Occurrence of PCDD/F in dated lake sediments of the Black Forest, south western Germany. Environ. Sci. Technol. (in press). Krammer K. (1992) Pinnularia, a monograph of the European taxa (in German). Bibliotheca Diatomologica, Vol. 26, J. Cramer in der Gebriider Borntr~iger Verlagsbuchhandlung, Berlin. Krammer K. and Lange-Bertalot H. (1986-1991) Bacillariophyceae (in German), Vol. 1-4. Freshwater Flora of Middle Europe (Edited by Ettl H., G/irtner G., Gerloff J., Heynig H. and Mollenbauer D.). Gustav Fischer Verlag, Stuttgart. Lazarek S. (1985) Epiphytic algal production in the acidified Lake Gardsj6n, SW Sweden. Ecol. Bull. 37, 213-218. Likens G. E., Driscoll C. T. and Buso D. C. (1996) Long-term effects of acid rain and recovery of a forest ecosystem. Science 272, 244-246. Line J. M., ter Braak C. J. F. and Birks H. J. B. (1994) WACALIB version 3.3--a computer program to reconstruct environmental variables from fossil assemblages by weighted averaging and to derive sample-specific errors of production. J. Paleolimnol. 10, 147-152. Lintelmann, J., Giinther W. J., Rose E. and Kettrup A. (1993) Behaviour of polycyclic aromatic hydrocarbons (PAHs) and triazine herbicides in water and aquifer material of a drinking water recharge plant. I. The area of investigation and the determination methods for PAHs and triazine herbicides in the aqueous matrix. Fresenius J. Anal. Chem. 346, 988-994. Martens D. (1991) Development of a method to detect polycyclic aromatic hydrocarbons in sediments using high performance liquid chromatography (HPLC), in German. Diplom-thesis, University of Paderborn, Germany. Melzer A. and Rothmeyer E. (1983) The effects of the acidification of the G r o ~ r and Kleiner Arbersee in the Bavarian Forest on macrophyte vegetation (in German). Ber. Bayer. Bot. Ges. 54, 9-18. Metz R. (1977) Mineralogical-Geographical Walks in the Northern Black Forest (in German). Moritz Schauenburg Verlag, Lahr. Morselli L. and Zappoli S. (1988) PAH determination in samples of environmental interest. Sci. Total Environ. 73, 257-266. Niederhauser P. (1993) Diatoms as bioindicators of the impact of acids and nutrients on dilute high mountain lakes (in German). PhD-thesis University of Ziirich. Nriagu J. O., Kemp A. L. W., Wong H. K. T. and Harper N. (1979) Sedimentary record of heavy metal pollution in Lake Erie. Geochim. Cosmochim. Acta 43, 247-258. Oldfield F. and Appleby P. G. (1984) Empirical testing of z~°Pb-dating models for lake sediments. In Lake Sediments and Environmental History (Edited by Haworth E. and Lund J.), pp. 93-124. University Press, Leicester. Pacyna J. M., Miinich J. and Axenfeld F. (1991) European inventory of trace metal emissions to the atmosphere. In Heavy Metals in the Environment (Edited by Vernet J.-P.), pp. 1-20. Elsevier, Amsterdam. Renberg I. and Hultberg H. (1992) A paleolimnological assessment of acidification and liming effects on diatom assemblages in a Swedish lake. Can. J. Fish. Aquat. Sci. 49, 65-72. Renberg I., Hellberg T. and Nilsson M. (1985) Effects of acidification on diatom communities as revealed by analyses of lake sediments. Ecol. Bull. 37, 219-223. Renberg I., Korsman T. and Anderson N. J. (1990) Spruce and surface water acidification: an extended summary. Phil. Trans. R. Soc. Lond. B 327, 371-372. Robbins J. A., Edington D. N. and Kemp A. L. W. (1978) Comparative Pb-210, Cs- 137, and pollen geochronologies

1206

I. Jiittner et al.

of sediments from Lake Ontario and Erie. Quart. Res. (NY) 10, 256-278. Sanders G., Jones K. C., Hamilton-Taylor J. and D6rr H. (1993) Concentrations and deposition fluxes of polynuclear aromatic hydrocarbons and heavy metals in the dated sediments of a rural English lake. Environ. Toxicol. Chem. 12, 1567-1581. Schindler D. W. (1994) Changes caused by acidification to the biodiversity: productivity and biogeochemical cycles of lakes. In Acidification of Freshwater Ecosystems: Implications for the Future (Edited by Steinberg C. E. W. and Wright R. F.), pp. 153-164. Report of the Dahlem Workshop, Berlin 1992. John Wiley & Sons, Chichester. Schindler D. W., Wegemann R., Cook R. B., Ruszczynski T. J. and Prokopowich J. (1980) Experimental acidification of Lake 223, experimental lakes area: background data and the first three years of acidification. Can. J. Fish. Aquat. Sci. 37, 342-354. Shearer J. A., Fee E. R., DeBruyn E. R. and DeClercq D. R. (1987) Phytoplankton primary production and light attenuation responses to the experimental acidification of a small Canadian Shield lake. Can. J. Fish. Aquat. Sci. 44, 83-90. Smol J. P. (1992) Paleolimnology: an important tool for effective ecosystem management. J. Aquat. Ecosyst. Health 1, 49-58. Steinberg C. and Kiihnel W. (1987) Influence of cation acids on dissolved humic substances under acidified conditions. Wat. Res. 21, 95-98, Steinberg C., Arzet K. and Krause-Dellin D. (1984) Acidification of Freshwaters in the Federal Republic of Germany as seen from paleolimnological studies (in German). Naturwissenschaften 71, 631-633. Steinberg C., Arzet K., Krause-Dellin D., Sanides S. and Frenzel B. (1987) A long core study on natural and anthropogenic acidification of the Huzenbacher See, Black Forest, Federal Republic of Germany. Global Biogeochem. Cycles 1, 89-95. Steinberg C., Hartmann H., Kern J., Arzet K., Kalbful3 W., Krause-Dellin D. and Maier M. (1988) Acidification of freshwaters by atmospheric pollutants (in German). In Hohenheimer Arbeiten (Edited by Kohler A. and Rahmann H.), pp. 79-103. Ulmer Verlag, Stuttgart.

Stevenson A. C., Juggins S., Birks H. J. B., Anderson D. S., Anderson N. J., Battarbee R. W., Berge F., Davis R. B., Flower R. J., Haworth E. Y., Jones V. J., Kingston J. C., Kreiser A. M., Line J. M., Munro M. A. R. and Renberg I. (1991) The Surface Waters Acidification Project Paleolimnology Programme: Modern Diatom/Lake-water Chemistry Data-set. ENSIS Ltd, London. Stokes P. M. (1986) Ecological effects of acidification on primary products in aquatic systems. Water Air Soil Pollut. 30, 421-438. Thies H. (1994) The Huzenbacher See--limnochemistry and mass balances of a dystrophic cirque lake in the Northern Black Forest (in German). PhD-thesis, University of Freiburg, Germany. UBA Umweltbundesamt (1985) Depositions of Atmospheric Pollutants in the Federal Republic of Germany (in German). Berlin. Van Dam H. and Mertens A. (1995) Long-term changes of diatoms and chemistry in headwater streams polluted by atmospheric deposition of sulphur and nitrogen compounds. Freshwat. Biol. 34, 579-600. Wasmund N. (1984) Problems of spectroscopic determination of chlorophyll (in German). Acta Hydrochim. Hydrobiol. 12, 255-272. Wetzel R. G. and Likens G. E. (1991) LimnologicalAnalysis. Springer, New York, pp. 111-115. Whitehead D. R., Charles D. F., Jackson S. T., Reed S. E. and Sheehan M. C. (1986) Late-glacial and Holocene acidity changes in Adirondack (N.Y.) Lakes. In Diatoms and Lake Acidity (Edited by Smol J. P., Battarbee R. W., Davis R. B. and Meril~iinen J.), pp. 251-274. Dr W. Junk Publishers, Dordrecht. Yan N. D. (1983) Effects of changes in pH on transparency and thermal regimes of Lohi Lake, near Sudbury, Ontario. Can. J. Fish. Aquat. Sci. 40, 621-626. Zeitvogel W. (1986) Pollen analysis in sediments of selected Black Forest lakes to reconstruct recent changes in forest communities (in German). Diplom-thesis, University of Freiburg, Germany. Zeitvogel W. and Feger K. H. (1990) Pollen analysis and investigations of historical use to reconstruct soil and water acidification in the Northern Black Forest (in German). Allg. Forst. Jagdztg. 161, 136-144.