effects of acid anion additions (trifluoroacetate and bromide) on soil solution chemistry of a...

EFFECTS OF ACID ANION ADDITIONS (TRIFLUOROACETATE ANDBROMIDE) ON SOIL SOLUTION CHEMISTRY OF A NORTHERN

HARDWOOD FOREST SOIL

TORSTEN W. BERGER∗ and GENE E. LIKENSInstitute of Ecosystem Studies, Millbrook, New York 12545-0129, U.S.A.

(∗ author for correspondence, e-mail: [email protected]; fax: +43 1 4797896; address forcorrespondence: Institute of Forest Ecology, Universität Bodenkultur, Peter Jordanstraße 82,

A-1190 Vienna, Austria)

(Received 19 January 1998; accepted 19 November 1998)

Abstract. Experimental plots within the Hubbard Brook Experimental Forest, NH, were treatedwith sodium trifluoroacetate (TFA) and lithium bromide (Br), to study the impact of TFA alone andin the presence of increased anion concentrations (e.g. acid deposition) on the soil solution chemistryof a northern hardwood forest soil. Trifluoroacetate is a major atmospheric degradation product ofreplacement compounds of chlorofluorocarbons (CFC) and Br is widely used as a hydrologic tracer.Calculated drainage losses via soil water flow were less than 60% of inputs, added during the summer,and TFA and Br were temporarily retained in the soil until fall. The initial indication of an acid inputof the treatments (HTFA, HBr) in the Bs2 horizon, which reflects stream water chemistry as well,was an increase of base cations in the soil solution, decreasing the soil’s acid neutralizing capacity.Thereafter, trifluoroacetate and Br concentrations peaked after the peak in base cations, synchronouswith peaks in H+ and Al concentrations. Organic anions, nitrate and chloride played the major rolein accompaning base cations out of the solum. Sulfate retention at soil adsorption sites was increasedby the presence of TFA and Br, reducing its role as a mobile anion of base cations in this experiment.Relative retention of anions for the whole profile of this northern hardwood forest soil was estimatedby correlation analyses and input-output balances in decreasing order on an equivalant basis: SO4 >

TFA = Br≥Cl> NO3> organic anions. Recovery from acid additions were recorded within severalweeks after the treatments were stopped. Evaluating the impact of added chemical compounds to soilsmust be considered within the context of linkages among element cycles and pools.

Keywords: acidification, base cations, bromide, forest ecosystems, mobile anion, soil solution, TFA,trifluoroacetate

1. Introduction

The mobile anion concept is a model for understanding base cation biogeochem-istry. According to that concept the concentration of anions in solution will controlthe total concentrations of cations, while the composition of cations in solutionshould be controlled by equilibration with what is usually a large pool of cationsadsorbed on soil particles (Reuss and Johnson, 1986; Christet al., 1997).

Research on the effects of acid rain in North America and Europe has focusedprimarily on the biogechemistry of sulfur and of nitrogen (Johnson and Lindberg,

Water, Air, and Soil Pollution116: 479–499, 1999.© 1999Kluwer Academic Publishers. Printed in the Netherlands.

480 T. W. BERGER AND G. E. LIKENS

1992; Likenset al., 1996; Ulrich, 1988) and the scientific community has madesignificant progress in defining the mechanisms of repsonse to these chemicalinputs. Atmospheric inputs of S and N not chemically or biologically taken upin the soil moves through the soil solution primarily as NO3 or SO4 anions andare accompanied by cations to maintain charge neutrality (e.g. Fasthet al., 1990;Rustadet al., 1996; Rutherfordet al., 1985). As a result large quantities of the basecations Ca, Mg, K, and Na have been lost from the soil complex and exported bydrainage water. Base cations play essential roles in forest ecosystems and in thequality of surface water (Lawrenceet al., 1995; Likenset al., 1996).

Trifluoroacetate (TFA) must be considered an additional mobile anion in theacid rain issue, although little is known of its effect on soil solution chemistry.Average global concentration of TFA in rainfall is predicted to be 0.16µg L−1 by2010 (Trompet al., 1995), but recent survey data already suggest levels of TFA inthe range predicted for 2010 (Franket al., 1996). Trifluoroacetate is formed as animportant breakdown product by atmospheric degradation of chlorofluorocarbon(CFC) replacements (Franklin, 1993).

Trifluoroacetate is highly soluble in water and is transported to Earth’s surfacein precipitation (Franklin, 1993; Franket al., 1995). Trifluoroacetic acid (molecularweight, 114 g mol−1) is an acidic organic compound that predominantly occurs asan anion under environmental conditions.

Expected environmental concentrations of TFA are of little concern with re-spect to human health (Ball and Wallington, 1993), but there are reports of growthinhibitions of algae by TFA at low concentrations (100–300µg L−1, Thompson,1994).

Bromide (Br), widely used as a hydrologic tracer (e.g. Flury and Papritz, 1993),was used to compare transport via soil water in combination with TFA, and tosimulate effects of increased anion concentrations (e.g. sulfate from atmosphericdeposition) in the soil solution. The main objective of this paper is to evaluatepossible effects of strong anion additions, which currently are present in only tracequantities in the soil system, on solute concentrations and fluxes of major elementsfrom the soil. Two experimental plots were treated with A) sodium TFA and lithiumBr and B) sodium TFA only. This study was performed to address the followingquestions by calculating sources or sinks of analyzed ions within the soil profile,performing correlation analyses among these ions and studying changes of soilsolution chemistry over time: (1) Recent investigations (Bergeret al., 1997; Richeyet al., 1997; Likenset al., 1997) showed retention of TFA in soils, but what are thepossible retention mechanisms? (2) How do additional anions fit into the mobileanion concept? Are different anions equivalent in mobilizing base cations? (3) Arethe biogeochemical changes caused by the strong anion treatments reversible andhow rapidly do small experimental plots recover?

EFFECTS OF ACID ANION ADDITIONS 481

2. Study Sites and Methods

2.1. STUDY AREA

The experiment was conducted in the Norris Brook watershed at an elevationof about 320 m within the Hubbard Brook Experimental Forest (HBEF) in NewHampshire (Likens and Bormann, 1995). The HBEF has northern hardwood vege-tation growing on Typic Haplorthods that developed in sandy till. The average pHof the humus layer (Oa horizon) is 3.9. The mineral soil pH increases from 4.2 to4.7 with depth (Johnsonet al., 1991). Soil characteristics for the Oa-, Bhs- and Bs2-horizon of the study area are: organic matter (79.5, 12.6 and 0.5%), clay (8, 5 and3%) and cation exchange capacity (17.2, 7.4 and 0.05 cmolc kg−1), respectively(Richey et al., 1997). Bhs is a combination of Bh and Bs1 horizons, which arethin and frequently discontinuous in this area of the HBEF. The main tree speciesin the study area are American beech (Fagus grandifolia; 60% of stems), yellowbirch (Betula alleghaniensis; 15%) and sugar maple (Acer saccharum; 13%). Meanannual precipitation during the study was 1230 mm. More detailed informationabout the study area is given by Christet al. (1995).

2.2. PLOT INSTALLATIONS

During the spring of 1995 two lysimeter plots (Plots A and B, each 1.5- along thecontour x 1-m upslope) were installed within 10 m of each other on a southwestfacing slope in the Norris Brook watershed. Both plots were equipped with ceramiccup tension lysimeters (Soilmoisture Equipment Corp.; 5 replications each in 10-,30- and 50-cm depth; applied suction: –40 kPa). Fixed soil depths at 10-, 30- and50-cm enabled hydrologic flux calculations and matched approximately the aver-age lower boundary of the three soil horizons, Oa, Bhs and Bs2. All lysimeters wereset into cleared, vertical upslope faces of the two pits (just below the treated areas),which were then backfilled. The small area of the plots was free of soil vegetation.The study sites were equipped with 3 bulk samplers for collecting throughfall. Soilmoisture tensions were recorded by tensiometers (6 replications per horizon).

2.3. TREATMENTS

Trifluoroacetate additions (Table I) were calculated to meet the detection limitof an ion chromatograph (0.5µmol L−1 TFA), representing a rather ‘worst casescenario situation’ of expected TFA deposition by 2010 (Trompet al., 1995).Plot A received three additions of sodium TFA (total of 0.81 g TFA m−2) andlithium Br (total of 10 g Br− m−2). Similar amounts of added Br were used inother experimental studies (e.g. Jemison and Fox, 1991; Kung, 1990; Schnabeletal., 1995, Owens and Edwards, 1992). Trifluoroacetate and Br data of Plot A wereused previously by Bergeret al. (1997), where Plot 2 is identical with Plot A of thisstudy. Plot B was treated twice with TFA only (total of 0.54 g TFA m−2), to separate


TABLE I

Additions of trifluoroacetate (TFA) and bromide (Br) in mmolc m−2 (c: charge; addedas sodium TFA and lithium Br). Amounts of collected throughfall during the singletreatment periods and total period are given in mm

Treatment Plot A Plot B Throughfall

No. Date (day of the year) TFA Br TFA Br per period

1 08 July 1995 (189) 2.39 42.2 2.39 – 182

2 12 August 1995 (224) 2.39 42.2 2.39 – 44

3 15 September 1995 (258) 2.39 42.2 – – 192

08 July–01 November 7.17 126.6 4.78 – 418

between effects of TFA and Br (questions 2 and 3). On occasion of treatments, theplots were covered just before expected precipitation and treated directly after thecessation of rain. Sodium TFA (98% NaTFA, provided by E. I. DuPont de Nemours& Co.) and lithium Br were mixed with water from nearby Mirror Lake (seeLikens, 1985), because of lack of actual throughfall. The volume of water addedvaried for each treatment corresponding to the amount of the previous precipitationevent, indicated by throughfall collectors. Therefore, no additional input variablewas necessary to run the hydrologic model (see below). Volume-weighted elementconcentrations (µmolc L−1) were higher in Mirror Lake water (Likens, 1985) thanin measured throughfall (this study) for Ca (Mirror Lake vs. throughfall: 119 vs.22), Mg (41.1 vs. 12.1), SO4 (119 vs. 36.9) and Cl (30.7 vs. 13.2). Because of smalladded volumes the impact of Mirror Lake water on the soil solution chemistry isconsidered negligible (treatment no. 1: 1.5 mm, no. 3: 2.0 mm) or small (treatmentno. 2: 17.6 mm), when compared to collected throughfall during the total period ofthe experiment (418 mm).

2.4. SAMPLING AND ANALYSIS

Soil solutions were sampled twice a week from 19 June 95 to 1 November 95 (firsttreatment on 8 July), except for two weeks after each treatment when samples werecollected 3 times a week. During the dry summer of 1995, sampling was limited oc-casionally in the upper horizons because of high soil moisture tensions (Figure 1).Lysimeters were emptied into clean, high-density polyethylene bottles and storedat 4◦C until analysis. Concentrations of TFA, Br, SO4, Cl and NO3 were measuredby ion chromatography, Ca and Mg by inductively coupled plasma emission (ICP)spectrophotometry, Na, Li and K by atomic absorption spectroscopy and NH4 byauto-analyzer. pH was determined electrometrically. Total monomeric and organ-ically complexed monomeric Al was measured by automated colorimetry usingpyrocatechol violet (Mc Avoyet al., 1992). The equivalents of charge of inorganic


Figure 1.Throughfall (mm), soil moisture (kPa) and concentrations of TFA, Na, Br, Li, Ca, Mg and K(µmolc L−1) in Plot A from 12 June to 1 November 1995. Upside down triangles indicate additionsof TFA and Br according to Table I.


monomeric Al (Aln+), which was removed from solution by ion exchange column(difference between total monomeric and organically complexed monomeric Al),was calculated at the measured pH of the sample (based on 3 equilibrium equationsfor Al3+, Al(OH)2+, Al(OH)2

+ and Al(OH)4−; Schecher and Driscoll, 1987).Throughfall was collected twice a week and analyzed for SO4, Cl, NO3, Ca, Mg,

K, Na, NH4 and pH as described for the soil solution samples. Throughfall fluxeswere calculated according to measured solution volumes per area of the collector.

2.5. CALCULATIONS

The amounts of elements transported through the soil profile were estimated bymultiplying the element concentration in each sample of soil water by the wateroutput from the related soil horizon and time. The Brook2 model (Federer andLash, 1978a, b), developed and parameterized for the HBEF (adjacent watershedW3), was used to calculate drainage from the rooting zone as described by Bergeret al. (1997).

Brook2 requires daily precipitation and daily mean air temperatures as input.These data for the simulation were measured at the U.S.D.A. Forest Service RobertS. Pierce Ecosystem Laboratory site and at rain gage 22, some 0.9 km distant. Thevariable Edrain, which represents drainage from the rooting zone, was interpretedas the amount of water flowing past the plane of the lysimeters at 50-cm soil depth(Bs2 horizon), even though a few roots may be found below this plane. Their effectis assumed to be negligible. Water flux through each horizon was calculated fromEdrain according to Yanai (1990), that is, transpiration was distributed through thesoil profile according to the distribution of fine root biomass (Faheyet al., 1988).

3. Results and Discussion

3.1. SOIL SOLUTION CHEMISTRY

Volume-weighted means of element concentrations in the soil solution are given inTable II, which were calculated from modeled fluxes between the horizons. Sulfatedominated the soil solution chemistry at Plot B, while Br was quantitatively themost important anion at Plot A. Lithium decreased more rapidly with soil depththan Br, indicating much higher soil retention of this cation. Potassium and bothAl species (inorganic and organic Al) declined with increasing soil depth, withthe exception of an inorganic Al (Aln+) peak at 30-cm soil depth (Plot A). Nitrateconcentrations remained elevated in the lower horizons and were higher in Plot A.

Throughfall, mean soil moisture tensions, and concentrations of TFA, Na, Br,Li, Ca, Mg and K for Plot A are given in Figure 1. Sulfate, Cl, pH, Aln+ and orgAl concentrations for Plot A, as well as NO3 concentrations and the differencesbetween analyzed cations minus analyzed anions (Cat-An) for both plots are plot-ted in Figure 2. Trifluoroacetate and Br concentrations show similar patterns for


Figure 2. pH, org Al (µmol L−1), concentrations of NO3, SO4, Cl, Aln+ (µmolc L−1) and thedifferences between analyzed cations minus analyzed anions (Cat-An,µmolc L−1) for Plot A (threetreatments with TFA and Br are indicated by upside down triangles according to Table I), as well asNO3 and Cat-An concentrations for Plot B (two treatments with TFA only).


TABLE II

Volume-weighted means of element concentrations (calculated from mod-eled fluxes between the horizons) of the soil solution for different soilhorizons at Plots A and B from 19 June to 1 November 1995 inµmolcL−1, except organic aluminium (org Al) which is expressed inµmol L−1

Site TFA Na Br Li NO3 SO4 Cl

Plot A

Oa (10 cm) 13 36 222 168 24 95 36

Bhs (30 cm) 12 34 201 31 32 83 38

Bs2 (50 cm) 9 42 107 2 41 99 40

Plot B

Oa (10 cm) 4 63 0 128 35

Bhs (30 cm) 5 51 15 94 28

Bs2 (50 cm) 4 47 13 82 32

Site H Ca Mg K NH4 Aln+ org Al

Plot A

Oa (10 cm) 8 86 63 41 2 11 8

Bhs (30 cm) 18 107 89 23 1 40 6

Bs2 (50 cm) 15 91 92 14 1 27 4

Plot B

Oa (10 cm) 14 101 79 39 4 26 36

Bhs (30 cm) 11 29 46 35 2 10 12

Bs2 (50 cm) 8 34 35 6 1 3 3

all horizons. Because TFA was added as NaTFA and Br as LiBr similar patternsbetween these ions are not surprising. However, even the base cations (Ca, Mg, K),which were not added, show similar responses to the additions of TFA and Br inthe upper soil horizon. Sulfate concentrations at 10-cm soil depth decline sharplyafter each treatment and increase until the end of the treatment (Figure 2). The pHdecreases continuously from the beginning until the end of the experiment.

3.1.1. Correlations Between Added IonsBecause TFA was added as NaTFA, correlation coefficients between TFA and Nain Plot A were 0.90 (10 cm, p< 0.001), 0.82 (30 cm, p< 0.001) and 0.39 (50 cm,

EF

FE

CT

SO

FA

CID

AN

ION

AD

DIT

ION

S487

TABLE III

Correlation coefficients between anions and analyzed ions of the soil solution. The level of significance is less than 0.001, except indicated as n.s.:notsignificant, p> 0.05; a: p< 0.05; b: p< 0.01

Site TFA Br Na Li SO4 NO3 Cl H Ca Mg K NH4 Aln+ org Al Cat-An

Plot A

Br

Oa 1.00 – 0.90 0.96 –0.74 –0.20n.s. 0.75 0.65 0.95 0.88 0.57 0.20n.s. 0.76 0.28n.s. –0.85

Bhs 0.98 – 0.81 0.91 –0.72 –0.29n.s. 0.70 0.91 0.82 0.63 0.12n.s. –0.41a 0.97 0.92 –0.71

Bs2 0.98 – 0.34a –0.15n.s. –0.55 0.18n.s. 0.80 0.86 0.49b 0.00n.s. –0.17n.s. 0.10n.s. 0.81 0.79 –0.75

TFA

Oa – 1.00 0.90 0.97 –0.73 –0.20n.s. 0.77 0.66 0.94 0.87 0.56 0.20n.s. 0.76 0.29n.s. –0.86

Bhs – 0.98 0.82 0.87 –0.72 –0.28n.s. 0.72 0.89 0.79 0.66 0.09n.s. –0.42b 0.95 0.91 –0.73

Bs2 – 0.98 0.39a –0.16n.s. –0.50b 0.16n.s. 0.81 0.84 0.43b 0.01n.s. –0.25n.s. 0.08n.s. 0.75 0.76 –0.77

SO4

Oa –0.73 –0.74 –0.69 –0.63 – –0.06n.s. –0.61 –0.45b –0.85 –0.75 –0.55 0.04n.s. –0.57 0.13n.s. 0.74

Bhs –0.72 –0.72 –0.93 –0.48b – –0.40b –0.92 –0.49b –0.88 –0.91 –0.58 0.17n.s. –0.64 –0.61 0.68

Bs2 –0.50b –0.55 –0.37a 0.40a – –0.76 –0.70 –0.47b –0.83 –0.36a –0.46b –0.01n.s. –0.49b –0.56 0.71

NO3

Oa –0.20n.s. –0.20n.s. 0.15n.s. –0.09n.s. –0.06n.s. – –0.31n.s. 0.71 –0.01n.s. 0.26n.s. 0.54b 0.52b 0.59 –0.77 0.27n.s.

Bhs –0.28n.s. –0.29n.s. 0.20n.s. –0.48b –0.40b – 0.21n.s. –0.49b –0.24n.s. 0.48b 0.79 0.30b –0.36a –0.31n.s. –0.04n.s.

Bs2 0.16n.s. 0.18n.s. 0.71 –0.11n.s. –0.76 – 0.52n.s. 0.18n.s. 0.78 0.81 0.62 –0.01n.s. 0.24n.s. 0.38n.s. –0.54

488T.W

.BE

RG

ER

AN

DG

.E.L

IKE

NS

TABLE III

(continued)

Site TFA Br Na Li SO4 NO3 Cl H Ca Mg K NH4 Aln+ org Al Cat-An

Cl

Oa 0.77 0.75 0.63 0.72 –0.61 –0.31n.s. – 0.84 0.66 0.53b 0.18n.s. –0.02n.s. 0.77 0.36a –0.74

Bhs 0.72 0.70 0.85 0.45b –0.92 0.21n.s. – 0.52 0.72 0.77 0.34a –0.20n.s. 0.61 0.58 –0.72

Bs2 0.81 0.80 0.60 –0.51 –0.70 0.52 – 0.76 0.62 0.23n.s. –0.02n.s. 0.06n.s. 0.62 0.75 –0.88

Plot B

TFA

Oa – – –0.11n.s. – 0.09n.s. –0.03n.s. 0.31n.s. –0.19n.s. –0.14n.s. –0.18n.s. –0.28n.s. 0.04n.s. –0.36n.s. –0.45n.s. –0.51

Bhs – – 0.96 – 0.11n.s. –0.04n.s. 0.12n.s. –0.23n.s. 0.35a 0.47b 0.85 –0.15n.s. –0.21n.s. –0.08n.s. 0.30

Bs2 – – 0.00n.s. – –0.32a 0.48b 0.13n.s. 0.36a –0.01n.s. –0.09n.s. 0.49b –0.07n.s. 0.58 0.68 –0.25

SO4

Oa 0.09n.s. – 0.40n.s. – – 0.63a 0.36n.s. –0.18n.s. –0.28n.s. 0.11n.s. –0.01n.s. 0.69b –0.29n.s. –0.54n.s. –0.56a

Bhs 0.11n.s. – 0.30n.s. – – –0.52b 0.15n.s. 0.05n.s. 0.04n.s. 0.32n.s. 0.30n.s. 0.46b 0.01n.s. 0.19n.s. 0.29n.s.

Bs2 –0.31∗a – –0.50b – – –0.84 –0.43b 0.23n.s. –0.78 –0.60 –0.44b 0.31a –0.12n.s. –0.14n.s. –0.28n.s.

NO3

Oa –0.03n.s. – 0.10n.s. – 0.63a – 0.04n.s. –0.07n.s. –0.32n.s. –0.11n.s. –0.15n.s. 0.84 –0.05n.s. –0.24n.s. –0.33n.s.

Bhs –0.04n.s. – –0.10n.s. – –0.52b – –0.58 –0.53b 0.56 0.30n.s. 0.01n.s. 0.28n.s. –0.49b –0.59 0.14n.s.

Bs2 0.48b – 0.34a – –0.84 – 0.28n.s. –0.11n.s. 0.58 0.37a 0.25n.s. –0.14n.s. 0.14n.s. 0.12n.s. –0.11n.s.

Cl

Oa 0.31n.s. – –0.40n.s. – 0.36n.s. 0.04n.s. – –0.55a –0.46n.s. –0.60a –0.75b 0.15n.s. 0.32n.s. –0.05n.s. –0.71b

Bhs 0.12n.s. – 0.12n.s. – 0.15n.s. –0.58 – 0.70 –0.33n.s. –0.24n.s. –0.15n.s. –0.30n.s. 0.62 0.20n.s. –0.34n.s.

Bs2 0.13n.s. – 0.43b – –0.43b 0.28n.s. – 0.15n.s. 0.23n.s. 0.22n.s. –0.08n.s. 0.10n.s. –0.08n.s. –0.08n.s. –0.02n.s.


p < 0.05, Table III). When Na is calculated as the dependant variable, the linearregression coefficient is between 0.6 and 0.7 and the constant is between 29 and 37.Hence, Na concentrations decline more rapidly than TFA concentrations in the soilsolution (between 30 and 40%), while background concentrations of Na inµmolcL−1 are given by the regression constant. At Plot B (30 cm), where no LiBr wasadded, relative retention of Na in comparison to TFA was much higher (60% Na:40% TFA; Na = 0.4×TFA + 51, p< 0.001). No significant correlation between Naand TFA was measured at 50-cm soil depth in Plot B. These data indicate that Nain the soil matrix exchange sites was replaced by Li, increasing Na concentrationsin the soil solution at Plot A.

Bromide and Li were correlated highly at 10- (r = 0.96, p< 0.001) and 30-cm soil depth (r = 0.91, p< 0.001), showing similar temporal patterns (Figure 1).No significant correlation is given for 50-cm soil depth (Table III). The regressioncoefficients were 0.5 (10 cm) and 0.1 (30 cm), indicating a 50 and 90% relativeretention of Li in comparison to Br.

3.1.2. Direct Impacts of the Treatments on Base Cation ConcentrationsAlthough the treatments did not include Ca, Mg or K, additions of NaTFA andLiBr obviously had a strong impact on the soil solution chemistry of these cations(Figure 1). Both TFA and Br (Plot A) were correlated highly with Ca, Mg and Kconcentrations at 10-cm and with Ca and Mg at 30-cm soil depth (p< 0.001). AtPlot B, TFA was correlated with K (p< 0.001) and with Ca and Mg (p< 0.05) at30-cm soil depth (Table III). These data indicate that additions of TFA only causedleaching of base cations into the lower mineral soil horizons, and the combinedeffect of TFA and Br treatments must be considered detrimental by reducing theacid neutralizing capacity of these already acid soils.

3.2. INPUT-OUTPUT BUDGETS

The first treatment on 8 July was performed when mean soil moisture tensions ofthe study area (Figure 1) were very low (–62 kPa at 10-cm soil depth) after anextraordinarily dry month of June (42 mm rain). At the second treatment on 12August, the soil was close to field capacity, indicated by soil moisture tensionsaround –10 kPa for all soil horizons. Subsequently, very dry weather conditionsfrom mid-August to mid-September (44 mm rain) decreased soil moisture tensionsat 10-cm depth to –69 kPa. During the third treatment on 15 September (Plot Aonly) the soil was moist but well drained (tensions between –18 and –25 kPa). AtPlot B the two dry periods resulted in lower and longer lasting soil moisture ten-sions in the Oa horizon than at Plot A (not shown), limiting the success of samplingdramatically. As a result, data from Plot B are either not given or interpretationsfor the Oa horizon must be treated cautiously.

Calculated outflows of added anions from the organic layer during the studyperiod at Plot A were 59% TFA and 57% Br. For other horizons, total fluxes of


TFA and Br could not be calculated because TFA and Br concentrations remainedelevated, indicating possible major outputs via soil water flow after the experimentwas stopped. Recoveries so far, at the end of the experiment, were slightly lowerat Plot B (Plot A: Bhs: 40% TFA and 38% Br, Bs2: 23% TFA and 16% Br; PlotB: Bhs: 26% TFA, Bs2: 15% TFA). Bergeret al. (1997) concluded that significantamounts of TFA and Br were taken up by plants or retained within the soil, andthat Bromide, widely used as a hydrologic tracer (e.g., Flury and Papritz, 1993),was not useful as tracer of conservative transport in these studies. However, suchstudies on TFA are rare.

Solute flux profiles for all elements, measured in throughfall (except Na, whichwas added as NaTFA) are given in Figure 3. Element fluxes in throughfall areassumed to be input to the forest floor. Element fluxes in the soil solution passingthe plane of 10-, 30- and 50-cm soil depth were estimated with the modified Brook2model. Input-output budgets, based on only one field season can provide relativebudgets, so that we can evaluate differences between the plots. Specifying sourcesor sinks of elements is to some extent justified, if the balance (input minus output)is different from zero.

Flux profiles (Figure 3) indicate that the whole soil profile at Plot A is a sourceof Ca and Mg, while Plot B is a net sink (throughfall minus solute flux passing the50-cm soil depth level) of these elements, although the Oa horizon is a Ca and Mgsource. Thus, the higher the amount of added anions the higher is the loss of basecations. Because the input of acidic anions was lower at Plot B, Ca and Mg weretransferred only from the Oa into the Bhs horizon, but not lost from the system(rooted zone). Loss (50-cm depth) of mobile K is negligible presumably due tohigh plant uptake and tighter retention on soil exchange surfaces.

Concentrations (Table II) and flux profiles (Figure 3) both indicate a sourceof Cl in the forest floor, which agrees with Christ (1993). While Christ did notfind any strong source or sink for SO4 in the same soil profile, SO4 was leachedfrom the Oa into the Bhs horizon in both plots. Sulfate fluxes measured at 30- and50-cm soil depth were similar. These data point strongly to competition betweenSO4 and TFA and Br for soil adsorption sites in the organic horizon. Because soilretention in the Oa horizon is relatively high for TFA (19-20%) and low in themineral soils (4–8%; Bergeret al., 1997; Richeyet al., 1997; Likenset al., 1997)most of the SO4 is probably displaced from the soil exchange complex by TFA andBr (similar behavior) in the organic layer, resulting in high SO4 fluxes through the10-cm level and less differences between SO4 fluxes at 30- and 50-cm soil depth.It is unclear, why both plots have relatively high SO4 concentrations in the forestfloor lysimeters even though Plot A received a much greater anion load than Plot B.One interpretation might be that the soil at Plot B is more sandy with less exchangesites than at Plot A.

Nitrate loss via soil water drainage equals (Plot B) or exceeds (Plot A) inputvia throughfall (Figure 3). This finding is thought to be the result in part to theunusual weather conditions during the summer of 1995 (Figure 1). Seventy five


Figure 3.Solute flux profiles for Plot A (TFA and Br additions) and Plot B (TFA only addition) from19 June to 1 November 1995 (mmolc m−2). 10-, 30- and 50-cm refer to soil depths. Theoretically,the difference between throughfall flux (input, I) and soil solution flux at 50-cm soil depth (output,O) for a given chemical constituent indicates whether that constituent is being accumulated (I> O),being lost (I< O) or quantitatively passing through the system (I = O).


percent of the NO3 (50-cm soil depth, 19 June to 1 November, at each plot) was lostduring the period of the first treatment, when a warm and hot period presumablyincreased nitrification rates and a large storm (54 mm throughfall within 24 hr on17 July 1995) flushed the accumulated NO3 through the soil system (Figure 2).Hydrogen fluxes in throughfall are similar to H fluxes draining through the planeof 50-cm soil depth. Significant positive correlations between H concentrations andestimated water movement through 30- and 50-cm soil depth (Plot A: 30 cm: r =0.35, p< 0.05; 50 cm: r = 0.50, p< 0.01; Plot B: 30 cm: r = 0.56, p< 0.001;50 cm: r = 0.59 p< 0.001) indicate that acid rain (current annual mean pH: 4.3;Likenset al., 1996) has a direct impact on the pH of the soil solution.

3.3. RESPONSE(ACIDIFICATION, LOSS OF BASE CATIONS) AND RECOVERY

OVER TIME

To evaluate the entire data set a factor analysis was performed, identifying the mainfactors over time for each horizon (Figure 4, Plot A only). A factor analysis is astatistical technique used to identify a relatively small number of factors that can beused to represent relationships among sets of many interrelated variables (compareTable III). Three factors were extracted from principal components analysis (PCA).The next step, the rotation phase of factor analysis, attempts to transform the initialmatrix into one that is easier to interpret. This rotation step is the only differenceto PCA (Backhauset al., 1994). The two main factors, which explain most of thetotal variance (%), were plotted after a varimax rotation (SPSS Inc. 1993) as x andy axes. A biplot of objects (events numbered from 1: 19 June to 44: 1 November)and variables (elements) is shown in Figure 4. The variables were plotted as vectorscorresponding to their correlations with the factors. Each vector shows the directionof the strongest increase of this variable, while its length quantifies the extent ofthis increase in that direction. The objects were plotted by given factor scores ascoordinates on the factor axes. The closer two objects are, the more similaritiesexist between them.

The whole data set (concentrations of TFA, Na, Br, Li, SO4, NO3, Cl, H, Ca,Mg, K, inorg Al (inorganic, Aln+), org Al (organic) and NH4 in the lysimetersolutions) was reduced into two main factors (Figure 4), which explain between80 and 88% of the total variance.

Because of immediate effects of the treatments on the upper horizon (Oa, 10 cm,Plot A, Figure 4, compare Section 3.1.2) factor 1 (Ca, Mg, Br, TFA, -SO4, Na, Li,Cl, K; elements were sorted by absolute size of the first coordinate; a negativesign indicates a negative correlation; 58.3%) includes TFA and Br as well as basecations. Sulfate behaves contrary to TFA and Br. Factor 2 (org Al, -NO3, H, inorgAl, 26.0%), representing acidification, is well defined by org Al and NO3 (negativecorrelation). During the pretreatment events (1–6; 19 June to 5 July) the soil so-lution chemistry changed from being SO4 dominated to NO3 dominated. This fact


Figure 4.Results of a factor analysis, plotted as biplot of objects (number of events: 1: 19 June to44: 1 November) and variables (elements) for each horizon (Oa, 10 cm; Bhs, 30 cm; Bs2, 50 cm) inPlot A. The two main factors explain between 80 and 88% of the total variance (see text). The dottedarrow indicates a trend over time for the Bh2 horizon, which reflects stream water chemistry as well.


indicates that nitrification rates increased during the rainless and warm weatherconditions of this period (see Figure 1).

At 30-cm soil depth (Bhs horizon, Figure 4), factor 1 (Br, inorg Al, TFA, H, Li,org Al, Ca, Na; 60.3%) represents mainly acidifying ions, including Br and TFA,while factor 2 (K, NO3, Mg, -SO4, NH4, Cl; 28.1%) is best explained by the basecation potassium. This shift is completed in the Bs2 horizon (50-cm soil depth):factor 1 is called ‘acidification’ (Br, TFA, H, org Al, inorg Al, Cl; 46.5%) and doesnot include any base cations (Li, Ca). Factor 2 is interpreted ‘loss of base cations’(NO3, Mg, K, Ca, -SO4, Na; 23.0%), including all base cations and NO3, whichobviously functions as a mobile anion (Reuss and Johnson, 1986) for these basecations.

A factor analysis was also performed for Plot B, but because of less intercor-related variables (Table III) and consequently lower communality values for TFA,no figure is given. (The proportion of variance explained by the common factors iscalled the communality of the variable: Plot A (TFA and Br): 10 cm, TFA: 98.2%,Br: 97.9%; 30 cm, TFA: 95.8%, Br: 98.9%; 50 cm, TFA: 92.8%, Br: 93.8%; PlotB (TFA only): 10 cm, 46.9%; 30 cm, 97.7%; 50 cm, 73.8%). A similar trend asdescribed for Plot A, however, is also indicated by a linear correlation matrix(Table III): positive significant correlation coefficients between TFA and cationsat 30-cm soil depth and between TFA and elements, representing acidification (orgAl, inorg Al, H; Reuss and Johnson 1986), at 50-cm soil depth. In general, theimpact on the soil solution chemistry of TFA only (Plot B) was small in comparisonto the combined effects of TFA and Br at Plot A, because of the smaller amount ofanions added to Plot B.

Soil solution chemistry changed over time in all horizons from being SO4 dom-inated, to base cations dominated, before acidifying effects of the treatment weremeasured. However, this change did not occur simultaneously but delayed withincreasing soil depth, caused by soil matrix flow. The importance of hydrology,driving the whole experiment (compare Bergeret al., 1997), is obvious from thefact that the soil solution chemistry did not change during the dry period of thesecond treatment in the mineral horizons. The time lag can be studied by lookingat the end of the experiment, that is, collection event 44 (1 November, Figure 4).The shift in soil solution chemstry, dominated by the acidifying effects of the treat-ments, toward the orignal SO4 dominated chemistry is clear in the Oa horizon, inprogress in the Bhs horizon, and not detectable in the Bs2 horizon.

Trifluoroacetate and Br were added as neutral salts (NaTFA, LiBr). Because thereservoir of ions on the exchange complex is much larger than that in solution, theresult would be very similar, at least in the short term, if the input causing increasedTFA and Br concentration were added as HTFA or HBr. The effect of increasingsolution concentrations as a result of TFA and Br, however, is always to depresspH as long as the soil has a net negative charge. This pH depression is knownas the ‘salt effect’ and is not the result of the acidity of the input solution (Reussand Johnson, 1986). While depleting the cation exchange capacity of the soil, the


formation of trifluoroacetic acid (Richeyet al., 1997), bromic acid or bromous acid(Flury and Papritz, 1993) will be pronounced, as indicated in Figure 4 (50 cm) byalmost identical vectors for H, TFA and Br, causing low pH (Figure 2) and soilacidification. As shown in Figure 4 for 50-cm soil depth (dotted arrow) the acidi-fication by additions of NaTFa and LiBr began with measureable high base cationconcentrations of the soil solution, and much later high concentrations of TFA andBr, coupled with low pH and increased Al species, analyzed in the Bs2 horizon.This time lag indicates that both TFA and Br were not transported conservativelyin water (also see, Likenset al., 1997; Bergeret al., 1997). Many similar results,suggesting plant uptake or soil retention, are reported for Br (Jemison and Fox,1991; Kung, 1990; Schnabelet al., 1995, Owens and Edwards, 1992).

If this study were seen as a time lapse picture, it would show many similarities tothe impact of acid rain. The focus on acidifying compounds only (e.g. SO4 via acidrain; in this case TFA and Br) obscures the role of other elements in the regulationof the long-term, acid-base status of precipitation, soil, and surface waters, as wellas linkages between element cycles. Likenset al. (1996) suggest that ecosystemacidification may be reversible, but only very slowly. Trends of recovery from acidadditions at 10- and 30-cm soil depth (Figure 4) are more compareable with resultsof Rustadet al. (1996). Those authors conclude that a hardwood forest soil of a fieldstudy was not irreversibly altered after 4 years of experimental acid inputs (HNO3

and H2SO4), because soil and soil chemistry after the following 2 years were re-markable unchanged, indicating quick recovery. However, it is very important todifferentiate clearly between results of these experimental plot manipulations andthe long-term, whole watershed results of the effects of acid rain.

3.4. RELATIVE RETENTION OF ANIONS AND THEIR ROLE IN LEACHING BASE

CATIONS

Christ (1993) concluded, that base cation movement within and through the soilprofile at HBEF was controlled tightly by the movement of anions in solution.Because retention time for TFA and Br in the soil was longer than for base cations(Figure 4, e.g. 50-cm soil depth), other anions must have caused leaching of thesecations. As already stated, TFA and Br behave very similarly. Hence, this studycan be focused simply on effects of strong acid anions, where the amount of addedanions to Plot A (125580µmolc m−2 Br + 7170µmolc m−2 TFA) was 28 times asmuch as was added to Plot B (4780µmolc m−2 TFA).

Mean sulfate concentrations in the soil solution (Table II) were in the samerange as reported by Christ 1993 (between 80 and 94µmolc L−1), for the samestudy area, collected by zero tension lysimeters. Significant negative correlationsbetween base cations and SO4 for all horizons in Plot A (e.g. for Ca: between–0.83 and –0.88, p< 0.001; Table III, Figure 4) are surprising and indicate that SO4

is retained at soil adsorption sites in much higher amounts, when concentrations ofTFA and Br are high. At Plot B, significant negative correlations between SO4


and base cations were measured only in the Bs2 horizon. Negative correlationsbetween SO4 and the added anions as well as the fact that there was no impact ofthe treatments on SO4 solute concentrations within the mineral soil, indicate thatSO4 was adsorbed more strongly by the soil exchanger than TFA and Br. Accordingto Figure 2, SO4 concentrations in the Oa horizon peaked slightly just before eachtreatment was performed.

It is not known from this study, which cations accompanied SO4 anions to main-tain charge neutrality. We suggest that the combined treatment with TFA and Brcaused a mobilization of iron and manganese (cation acids, Fe2+ and Mn2+; Ulrich,1984), which are leached commonly with SO4 in podzolized soils (Ulrich, 1987).This would explain, why differences between analyzed cations (Fe and Mn wasnot analyzed) minus analyzed anions (Cat-An) were negative as a direct responseto the treatments in Plot A (Figure 2).

Dissociated organic anions concentrations, calculated as anion deficit, matchexactly between Christ’s (1993) untreated plots (Oa: 147µmolc L−1, Bhs: 54µmolcL−1); and Plot B (Oa: 149µmolc L−1, Bhs: 55µmolc L−1, Bs2: 19µmolc L−1).For that reason Cat-An is assumed to be organic anions for Plot B, while thisdifference includes both organic anions and Fe and Mn for Plot A. The importantrole of organic anions in moving base cations is documented by significant positivecorrelations between Cat-An and Ca, Mg and K for all horizons in Plot B (e.g. forCa: between 0.57 and 0.77, p< 0.001). Negative correlations between Cat-An andbase cations in Plot A (e.g. for Ca: 10 cm, –0.85, p< 0.001; 30 cm, –0.56,<0.001;50 cm, –0.49, p< 0.01) are caused by contrary behavior between acid and basecations.

Nitrate is not correlated with TFA or Br, as indicated by vectors in approxi-mately right angles to each other (Figure 4, compare Table III), probably becauseof a seasonal pattern of NO3 concentrations (compare Figure 2, Plot B). Higherand longer lasting NO3 concentrations in Plot A are suggested to be caused byeffects of increased anion additions. Also a net loss of NO3 in Plot A (Figure 3)indicates that some NO3 was replaced from the soil exchanger by TFA and Br,which is considerd an important counter anion of base cations in the mineral soil(see Figure 4).

Positive correlations between chloride concentrations and estimated water move-ment through 30- and 50-cm soil depth in Plot B (30 cm: 0.47, p< 0.01; 50 cm:0.61, p< 0.001) indicate that transport of Cl was controlled by hydrologic processes.At Plot A, however, Cl concentrations are driven by TFA and Br concentrations(Table III), resulting in slightly higher means of Cl than at Plot B. The Cl vectorsat 30- and 50-cm soil depth indicate retention times between those for base cations(short) and TFA and Br (long).

TFA and Br are of minor importance in accompaning base cations out of thesolum (Table III). Hence, NO3, Cl, and organic anions are suggested to maintaincharge neutrality, and SO4 does not seem to play a major role in moving basecations in this experiment. However, if the variability between high average SO4


concentrations and high average base cation concentrations is not correlated, itprobably does not mean that background SO4 plays no role in moving the back-ground base cations through the soil profile. Because the sum of NO3 and Cl fluxesout of the solum accounts for approximately 35% of base cation fluxes (see Fig-ure 3), organic anions are suggested as dominant mobile anions for these cations.This fact is different to Likenset al. (1996), where SO4 and NO3 account almostfully for long term annual loss of base cations in streamwater. This differencebetween plot and watershed scale is stated by Christet al. (1997), who conclude,that organic anions are usually removed from the soil solution befores drainagewater leaves a watershed, but they play important roles in moving cations withinsoil horizons. Based on these findings in the soil solution over time (Figure 2, 50-cm soil depth) relative temporal retention of anions for the whole profile of thisnorthern hardwood forest soil is estimated in decreasing order: SO4 > TFA = Br≥Cl > NO3 > organic anions. Richeyet al. (1997) measured relative soil retentionfor the A horizon of an oxisol as follows: F = SO4 > Cl = TFA> Br > NO3.

4. Conclusions

This study supports recent findings that loss of TFA via soil water flow is 40–80%(Bergeret al., 1997; Likenset al., 1997; Richeyet al., 1997) of inputs, which wereadded between 8 July and 15 September. Both TFA and Br (similar loss as TFA)are temporarily retained in the soil. The first indication of an acid input effect ofthe treatments in the Bs2 horizon, which reflects stream water chemistry as well(Christ, 1993), was an increase of base cations in the soil solution, decreasing thesoil’s acid neutralizing capacity (not measured). Trifluoroacetate and Br concen-trations peaked after the peak in base cations, coupled with low pH and increasedAl concentrations. In the organic layer, however, TFA and Br concentrations andbase cations peaked simultaneously. This temporal retention probably is causedby anion exchange. Sulfate retention at soil adsorption sites was increased by thepresence of TFA and Br, reducing its role as a mobile anion of base cations inthis experiment. Organic anions, nitrate and chloride are suggested to maintaincharge neutrality for the increase in base cation concentrations in the mineral soil.Relative retention of anions for the whole profile of this northern hardwood forestsoil was estimated in decreasing order: SO4 > TFA = Br ≥ Cl > NO3 > organicanions. Hence, evaluating the impact of added chemical compounds to soils mustbe considered within the context of linkages among element cycles and pools.Because TFA and Br behave very similarly, this study could be focused simplyon strong anion additions, showing many similarites to the deposition of acid rain.Trends of recovery were recorded within several weeks after the treatments werestopped.


Acknowledgements

This research was supported by funds from the E. I. DuPont de Nemours & Co.,Inc. and the A. W. Mellon Foundation to G. E. Likens and an Austrian ErwinSchrödinger Fellowship to T. W. Berger. We thank S. L. Tartowski for excellentrecommendations for field and lab work and helpful comments on the manuscript.C. A. Federer participated in helpful discussions. Rainfall data for the hydrologicmodel were provided by the USDA Forest Service Experiment Station at Hub-bard Brook. The HBEF is operated and maintained by the USDA Forest Service,Radnor, PA. This is a contribution to the Hubbard Brook Ecosystem Study.

References

Ball, J. C. and Wallington, T. J.: 1993,Air and Waste43, 1260.Berger, T. W, Tartowski, S. L. and Likens, G. E.: 1997,Environ. Sci. Technol. 31, 1723.Backhaus, K., Erichson, B., Plinke, W. and Weiber, R.: 1994,Multivariate Analysemethoden, eine

anwendungsorientierte Einführung, Springer-Verlag, Berlin Heidelberg.Christ, M.: 1993,Investigating the Role of Base Cation and Ammonium Deposition in Soil and Soil-

Water Acidification at the Hubbard Brook Experimental Forest, New Hampshire,Ph.D Thesis,Rutgers University.

Christ, M., Driscoll, C. T. and Likens, G. E.: 1997 (submitted).Christ, M., Zhang, Y., Likens, G. E. and Driscoll, C. T.: 1995,Ecol. Applic. 5, 802.Fahey, T. J., Hughes, J. W., Pu, M. and Arthur, M.: 1988,Forest Sci. 34, 744.Fast, W. J., Davi, M. B. and Vance, G. F.: 1990,Can. J. For. Res. 21, 23.Federer, C. A. and Lash, D.: 1978a,Water Resour. Res. 14, 1089.Federer, C.A. and Lash, D.: 1978b,Brook: A Hydrologic Simulation Model for Eastern Forests,Water

Resources Research Center, University of New Hampshire, Durham, Research Report No. 19.Brook2 freeware and documentation: United State Department of Agricultural Forest Service,P.O. Box 640, Durham, NH 03824.

Flury, M. and Papritz, A.: 1993,J. Eviron. Qual. 22, 747.Frank, H., Renschen, D., Klein, A. and Scholl, H.: 1995,J. High Resolut. Chromatogr. 18, 83.Frank, H., Klein, A. and Renschen, D.: 1996,Nature382, 34.Franklin, J.: 1993,Chemosphere27, 1565.Hoffman. J. S.: 1990,Ambio19, 329.Jemison, J. M. and Fox, R. H.: 1991,Commun. Soil Sci. Plant Anal. 22, 283.Johnson, C. E., Johnson, A. H. and Siccama, T. G.: 1991,Soil Sci. Soc. Am. J. 55, 502.Johnson, D. W. and Lindberg, S. E.: 1992,Atmospheric Deposition and Forest Nutrient Cycling. A

Synthesis of the Integrated Forest Study,Springer-Verlag, New York.Kung, K.-J. S.: 1990,Soil Sci. Soc. Am. J. 54, 975.Lawrence, G. B., David, M. B. and Shortle, W. C.: 1995,Nature378, 162.Likens, G. E. (ed.): 1985,An Ecosystem Approach to Aquatic Ecology: Mirror Lake and Its

Environment,Springer-Verlag, New York.Likens, G. E. and Bormann, F. H.: 1995,Biogeochemistry of a Forested Ecosystem, 2nd ed. Springer-

Verlag, New York.Likens, G. E., Driscoll, C. T. and Buso, D. C.: 1996,Science272, 244.Likens, G. E., Tartowski, S., Berger, T. W., Richey, D. G., Driscoll, C. T., Frank, H. C. and Klein, A.:

1997,Proc. Natl. Acad. Sci. 94, 4499.McAvoy, D. C., Santore, R. C., Shosa, J. D. and Driscoll, C. T.: 1992,Soil Sci. Soc. Am. J. 56, 449.


Nimitz, J. S. and Skaggs, S. R.: 1992,Environ. Sci. Technol. 26, 739.Owens, L. B. and Edwards, W. M.: 1992,J. Environ. Qual. 21, 406.Prather, M. J. and Watson, R. T.: 1990,Nature344, 729.Ravishankara, A. R., Turnipseed, A. A., Jensen, N. R., Barone, S., Mills, M., Howard, C. J. and

Solomon, S.: 1994,Science263, 71.Reuss, J. O. and Johnson, D. W.: 1986,Acid Deposition and the Acidification of Soils and Water,

Springer Verlag, New York.Richey, D. G., Driscoll, C. T. and Likens, G. E.: 1997,Environ. Sci. Technol. 31, 1723.Rowland, F. S.: 1990,Ambio19, 281.Rustad, L. E., Fernandez, I. J., David, M. B., Mitchell, M. J., Nadelhoffer, K. J. and Fuller, R. B.:

1996,Soil Sci. Soc. Am. J. 60, 1933.Rutherford, G. K., vanLoon, G. W., Mortenson, S. F. and Hern, J. A.: 1985,Can. J. For. Res. 15, 848.Schecher, W. D. and Driscoll, C. T.: 1987,Water Resour. Res. 23, 525.Schnabel, R. R., Stout, W. L. and Shaffer, J. A.: 1995,J. Environ. Qual. 24, 888.SPSS Inc.:1993,SPSS for Windows, Professional Statistics, Release 6.0.Thompson, R. S.: 1994,Proceedings of the Workshop on the Environmental Fate of Trifluoroacetic

Acid, in F. G. Chumley (ed.), Alternative Fluorocarbons Environmental Study, Washington, DC,Chapter 15.

Tromp, T. K., Ko, M. K. W., Rodríguez, J. M. and Sze, N. D.: 1995,Nature376, 327.Ulrich, B.: 1984,Atmos. Environ. 18, 621.Ulrich, B.: 1987,Forstarchiv58, 232.Ulrich, B.: 1988, ‘Effects of Acidic Precipitation on Forest Ecosystems in Europe’, in D. C. Adriano

and A. H. Johnson (eds),Acid Precipitation, 2, Springer Verlag, New York, pp. 198–272.Yanai, R. D.: 1990,The Effect of Disturbance by Whole-Tree Harvest on Phosphorous Cycling in a

Northern Hardwood Forest Ecosystem,Ph.D. Thesis, Yale University.

effects of acid anion additions (trifluoroacetate and bromide) on soil solution chemistry of a...

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