Calcium inputs and transport in a base-poor forest ecosystem as interpreted by Sr isotopes

Transcription

1 WATER RESOURCES RESEARCH, VOL. 32, NO. 3, PAGES , MARCH 1996 Calcium inputs and transprt in a base-pr frest ecsystem as interpreted by Sr istpes Sctt W. Bailey, James W. Hrnbeck,: Charles T. Driscll, 3 and Henri E. Gaudette 4 Abstract. Depletin f Ca in frests and its effects n frest health are prly quantified. Depletin has been difficult t dcument due t limitatins in determining rates at which Ca becmes available fr ecsystem prcesses thrugh weathering, and difficulty in determining changes in ecsystem strage. We cupled a detailed analysis f Sr istpic cmpsitin with a mass balance at Cne Pnd Watershed, New Hampshire, in rder t further cnstrain estimates f these prcesses. Strntium acted as an analg fr Ca in mst prcesses except translcatin f nutrients within frest vegetatin. Variability in mineralgic and Sr istpic cmpsitin f bedrck and sils cmplicated assessment f the Sr/ Sr rati released t slutin by weathering reactins. By cnducting a mass balance n atmspherically derived Ca, it is pssible t distinguish Ca weathering lsses frm Ca leached frm ecsystem pls. The calcium weathering rate estimated by this methd was less than half f that determined by mass balance assuming steady state cnditins. Intrductin t lessen leaching f Ca, requires a determinatin f rates at Acidificatin f surface waters and decline in frest health which lst Ca is replaced by weathering. Unfrtunately, direct measurement f mineral weathering is prblematic [Drever, may result frm depletin f basic catins (Ca, Mg, Na, K) in available pls in frest ecsystems [Tmlinsn, 1990; A. H. Jhnsn et al., 1992]. Strng acids in precipitatin may facili- 1982]. Althugh weathering prcesses have been generally understd fr sme time, specific mechanisms and rates in the field remain difficult t determine [Crnan, 1985; Schtt and tate the release f basic catins frm frest sils, enhancing Petit, 1987]. Furthermre, mass balance studies, typically used leaching lsses in drainage waters. In mst ecsystems, precipitatin supplies nly a small fractin f Ca inputs [Likens et al., 1977]. When the supply f basic catins frm weathering is insufficient neutralize acid inputs, acidificatin f sil and surface waters ccurs IReuss and Jhnsn, 1985]. Calcium depletin may result in declines in frest health, including a t quantify basic catin inputs t, and lsses frm frested ecsystems [Likens et al., 1977], are limited in their ability t dcument the surces f leaching lsses which may be derived frm atmspheric inputs, mineral weathering reactins, r decreases in ecsystem pls, including bimass, frest flr, and the sil catin exchange cmplex. decrease in cld hardiness [Dellayes, 1992]. Increases in Al t Ca ratis in sil are assciated with an inhibitin f Ca uptake Backgrund [Shrtle and Smith, 1988]. Given increasing nitrgen depsitin T circumvent the difficulties in direct measurement f in many temperate ecsystems, Ca depletin culd result in Ca weathering, we used the Sr istpe methd t further define replacing nitrgen as the limiting element fr tree grwth n basic catin inputs and transprt in a frest ecsystem. Strnsensitive sites. tium acts as an analg t Ca because bth are alkaline earth Large areas in the eastern United States are at risk with elements with similar inic radius and the same valence [Elias respect t the depletin f basic catins [Gallway and Cwlet al., 1982; Jacks et al., 1989]. Additinally, gelgic surces ing, 1978; Federer et al., 1989]. In regins where silicate weath- are reflected in varied istpic cmpsitin f Sr as expressed ering is dminant, weathering inputs may nt be sufficient by the rati 87Sr/86Sr. In small watersheds, where the 87Sr/86Sr replace the accelerated lsses f basic catins assciated with ratis f atmspheric inputs and weathering inputs are distinct disturbancesuch as acidic depsitin r intensive frest har- and relatively cnstant ver time, this methd can be used t vest. Hwever, a cmplete assessment f the prblem, as well trace the transprt f Sr thrugh the ecsystem [Graustein, as the need t develp air pllutin emissin cntrl strategies 1989]. This technique has been used t identify weathering prd- Nrtheastern Frest Experiment Statin, USDA Frest Service, ucts in stream water [ berg et al., 1989] and t determine Camptn, New Hampshire. 2Nrtheastern Frest Experiment Statin, USDA Frest Service, prprtins f canpy leachate and atmspheric depsitin in Durham, New Hampshire. thrughfall [Gsz and Mre, 1989]. Miller et al. [1993] used Sr 3Department f Civil and Envirnmental Engineering, Syracuse istpe data t shw that sil basic catin pls were stable University, Syracuse, New Yrk. and that atmspheric depsitin supplied the majrity f Sr 4Institute fr Study f Earth, Oceans, and Space, University f New and Ca in bimass and frest flr pls at a relatively Ca- Hampshire, Durham. enriched site in the Adirndack Muntains. In the present Cpyright 1996 by the American Gephysical Unin. Paper number 95WR /96/95WR study we cmbined the surce infrmatin gained frm Sr istpic determinatins with a detailed annual watershed mass balance t partitin the Ca cycle and determine separate mass 707

2 ,I 708 BAILEY ET AL.' CALCIUM DEPLETION IN FOREST ECOSYSTEM Methds Cne Pnd Watershed cnsists f 53 ha f all-aged (maximum 260 years) frest within the White Muntain Natinal Frest, Thrntn, New Hampshire (43ø54'N, 71ø36'W; Figure 1). The watershed is 80% mixed cnifer frest, dminated by red spruce, balsam fir, and eastern hemlck; 15% nrthern hardwds, dminated by American beech, yellw birch, and sugar maple; and 5% bedrck utcrp. The watershed is underlain by sillimanite-grade metapelites f the Silurian Perry Muntain Frmatin, cmpsed f quartz, muscvite, bitite, and almandine, with accessry sillimanite, Fe-Ti xides, and retrgrade chlrite. Bedrck is expsed alng ridges, whereas the remainder f the watershed is mantled by glacial till (<2.5 m thick) derived primarily frm lcal metapelitic and granitic rcks [Bailey and Hrnbeck, 1992]. Sils include Typic, Lithic and Aquic Haplrthds, with lesser areas f Typic and Terric Brhemists in wetlands assciated with the inlet (Figure 1). These sils have develped in a firm, slwly permeable, dense basal till, which limits deep perclatin f drainage waters. Hydrlgic flw paths are largely cnfined t upper sil hrizns. A seasnal, perched water table develps n tp f the C hrizn in less well drained sites. Mass balances were prepared fr the water year Octber 1991 t September 1992 fr the 33.4-ha watershed f the inlet :' "' t Cne Pnd. Cmparisn f precipitatin and streamflw ' //, ": Stream amunts and Ca cncentratins between the study year and the tw prir and tw subsequent years (Figure 2) suggests that the 600 '%.: % 25-m cntur study year is representative f lnger-term cnditins. ' a ' -: Wetland Atmspheric precipitatin was measured with standard and / [ Weather statin recrding rain gauges at the pnd shre and at an pen ledge Stream g e in the upper watershed (Figure 1). Bulk precipitatin fr = B rck mple Sil Sample chemical analysis was cllected weekly via a plyethylene funnel at the upper weather statin. Thrughfall samples were :' 7'* a Bimes Sample 5 ß Thrughfall Clle r cllected weekly at tw plts representing cniferus and deciduus frest cver types. At each plt, thrughfall frm 10 randmly lcated cllectrs was cmpsited int a single sample. Cllectrs cnsisted f plyethylene funnels with cleaned plyester wl filters t minimize particulate inputs during the warmer mnths, and pen plyethylene bags stretched ver a cylindrical plyvinyl chlride (PVC) frame during the snw seasn. Sil water samples were cllected with zer-tensin pan lysimeters at the base f the Oa hrizn and within the Bs hrizn at each f three sites which span the range f sil and frest cver types present. Stream water utputs frm the watershed were measured cntinuusly at a V ntch weir. Figure 1. Cne Pnd Watershed map and sample site lca- Grab samples fr chemical analysis f stream water were cltins. lected at the weir at a maximum f weekly intervals, fr a ttal f 61 samples. In rder t btain basic catin cncentratin and Sr istpic balances fr Ca derived frm atmspheric and mineral weath- cmpsitin data that culd be cupled t an annual waterering inputs. shed mass balance with a reasnable analytical effrt, mnthly The study site, Cne Pnd Watershed (CPW), is lcated vlume-adjusted samples f bulk precipitatin, thrughfall within the White Muntain Natinal Frest, New Hampshire, frm cniferus and deciduus stands, and streamwater were U.S.A. There may be significant depletin f basic catins in prepared frm weekly cllectins. Resulting cmpsites were CPW as evidenced by lw cncentratins f basic catins in representative f the verall time perid cvered; hwever, any drainage waters, depressed p H, and elevated transprt f A1 infrmatin frm event-based variability r with changes in [Bailey et al., 1995]. Mineral Sr istpicmpsitin (87Sr/a6Sr hydrlgic cnditins was lst. Sil water samples, taken at > 0.712) was well separated frm atmspheric inputs (87Sr/a6Sr ), prviding an pprtunity t apply the Sr istpe methd t a site that is likely susceptible t catin depletin OO 7OO Water Year Figure 2. Precipitatin (millimeters; pen circles), streamflw (millimeters; pen squares), and calcium cncentratins (/ M) in bulk precipitatin (slid circles) and stream water (slid squares) fr 5 years at the Cne Pnd Watershed. Detailed Ca and Sr mass balances were prepared fr the 1991 water year. 10 6

3 BAILEY ET AL.: CALCIUM DEPLETION IN FOREST ECOSYSTEM 709 lnger time intervals, were nt cmpsited. All water samples were preserved at p H 2 with Tefln-distilled HNO3, filtered with a 0.45-/am cellulse nitrate filter, evaprated, and taken up and stred in either 2 N HC1 r 3 N HNO3. All labratry wrk was dne with distilled reagents in class 100 filter units. multiple cllectr machine (cmpared t an accepted value f ). The blank Sr was less than 1 ng, generally much less than 1% f the Sr islated frm each sample. Prprtins f Sr frm atmspheric and mineral weathering end-members in watershed pls and fluxes were calculated Annual in uptake by trees was calculated by multiplying in with a linear mixing mdel [Graustein, 1989]: cntent times annual mass prductin f individual tree cm- RatiOatm(X) + Ratimin(1 -X) = RatiOmix pnents (bles, branches, leaves, and rts) [Waring and Schlesinger, 1985]. Samples f fliage, branches, bark, wd, Rati = 87Sr/(87Sr + 86Sr) and rts were taken frm tw trees each f red spruce, balsam (1) fir, eastern hemlck, American beech, yellw birch, and sugar maple fr chemical analysis. Litter fall (leaves and small branches) was sampled with plastic traps at 45 lcatins. Return t the frest flr via fallen bles, branches, and dead rts was nt determined. where X is the prprtin f Sr frm the atmsphere, mix indicates the watershed flux r pl t be mdeled, atm indicates the atmspheric end-member, and min indicates the mineral weathering end-member. Using Sr istpic cmpsitins and assuming that Sr be- Samples f wd, fliage, and rts fr istpic analysis haves as a prxy fr Ca, the Ca mass balance was partitined were btained frm a red spruce remved frm the frest adjacent t the cniferus thrughfall site. In rder t examine int atmspheric and mineral weathering cmpnents. The atmspheric end-member was taken as the mean Sr istpic interspecific variability in bimass chemistry, wd samples cmpsitin f bulk precipitatin. Uncertainty in the Sr iswere als analyzed frm American beech and sugar maple. All bimass samples were ven dried, grund with a Wiley mill, and disslved in a ht nitric-perchlric acid mixture. Bimass strage was determined by measuring all trees n a tpe cmpsitin released t slutin by weathering reactins results frm hetergeneity in mineral Sr istpic cmpsitin in sils and bedrck. Thus a range f mineral weathering end-members were cnsidered, with the implicatins fr each stratified randm sample f nine 0.04-ha plts in 1991 and again in A paired differences test fr independent samn mdeled mixtures discussed. ples (p = 0.05) shwed n significant difference between the Results and Discussin tw data sets, suggesting that in strage in vegetatin changes little frm year t year in the "ld-grwth" frest at Cne Istpic Cmpsitin Pnd. Bedrck samples were cllected with a prtable saw at 12 sites chsen randmly frm all expsures in the watershed. Whle rck samples were crushed in a shatter bx. Mineral Rck and sil. Bedrck was the mst radigenic and istpically variable cmpnent f the ecsystem with a mean 87Sr/86Sr rati f fr the 12 whle rck samples (Figure 3; all istpic data are listed in Table 1). The variability f Sr separates were hand picked fr almandine, bitite, muscvite, istpic cmpsitin within the Perry Muntain Frmatin and chlrite frm a disk-milled cmpsite f the 12 bedrck samples and plagiclase and hrnblende frm ne C hrizn illustrates bth the pwer and the challenge f applying the Sr istpe methd t ecsystem studies. The ischrn plt (Figsil sample. Whle rck and mineral separates were disslved ure 3) demnstrates the ratinale f Sr istpe systematics. in ht hydrfluric and perchlric acid fr 24 hurs in a Tefln capsule. Sil samples frm each hrizn in three prfiles were air-dried, crushed in a shatter bx and disslved using the same methd. Calcium was measured by flame atmic absrptin spectrphtmetry [Slavin, 1968]. Strntium was separated by in exchange chrmatgraphy using Dwex 50WX-8 r Eichrm Sr-spec resin. Samples laded nt Dwex clumns were disslved in 2 N HC1, then laded nt clumns that were previusly calibrated using radiistpes f Rb, Ca and Sr. Ultrapure 2 N HC1 was washed thrugh the clumn, and Rb and Sr were cllected after specific vlumes f acid had passed thugh (Rb was cllected at 6.5 t 8.0 ml; Sr was cllected at 14 t 18 ml). Sr-spect clumns were als utilized fllwing the methd f Hrwitz et al. [1991]. This invlved cleaning the clumn with 4 free clumn vlumes f H20; cnditining the clumn with 4 free clumn vlumes f 3 N HNQ3; lading the sample; rinsing with 30 free clumn vlumes f 3 N HNO3 t strip Ca, Rb, and ther catins; and cllecting Sr with 10 free clumn vlumes f H20. Strntium and Rb were measured by istpe dilutin with thermal inizatin mass spectrmetry with bth When the rck riginally crystallized, 87Sr/86Sr was hmgeneus thrughut the frmatin. Over time, as 8?Rb decayed t 8?St ( = 1.42 x 10- /yr), minerals with a higher Rb/Sr rati became increasingly enriched in radigenic 8?St. Individual samples with a greater prprtin f Rb-rich minerals thus have higher present-day 87Rb/86Sr and 87Sr/86Sr ratis (Figure 3). Of the fur mineral separates analyzed, bitite was the mst radigenic, with a 87Sr/86Sr rati f 2.59, reflecting a crystal structure that des nt readily accept divalent alkaline earths. In cntrast, chlrite had the lwest rati, Minerals lacking mnvalent alkali sites in the lattice but rich in Ca, such as plagiclase r apatite, wuld be expected t have a 87Sr/86Sr similar t the initial rati f the rck, given by the rdinate intercept f the ischrn [Faure, 1986], calculated at by Yrk regressin [Yrk, 1969]. While this variability cmplicates the simple assessment f the verall istpic cmpsitin f Sr released frm weathering reactins, it prvides the pprtunity t trace the prducts frm weathering f individual minerals if mineral cmpsitins and abundance are well knwn. Sil C hrizns, representing relatively unweathered till (the sil parent material), had relatively cnstant 87Sr/86Sr at single and multiple cllectr machines. Each mass spectrme (Figure 4). The degree f weathering can be expected t ter run cnsisted f at least 100 individual measurements f 87Sr/86Sr. Measurements were nrmalized t 86Sr/88Sr -- decrease in mineral sil frm the highly altered E hrizn, just belw the rganic surface hrizns, t the parent till in the C NBS-987 was peridically measured t check accuracy; hrizn. This is cnsistent with the pattern f increasing cn- 28 analyses yielded a mean 87Sr/86Sr _ n the single cllectr machine and _ n the centratin f Ca and Sr with depth (Figure 4). Variatin f 87Sr/86Sr within sil prfiles was incnsistent between sample

4 710 BAILEY ET AL.' CALCIUM DEPLETION IN FOREST ECOSYSTEM 2.6 weathered frm the sil, including the relatively unweathered C hrizn Plagiclase and hrnblende samples were separated frm the C hrizn sample at prfile b in rder t assess the ptential cntributin f these tw sil minerals. Neither mineral is 1.8 cmmn in the bedrck, hwever bth are amng the mst Ca-rich f the sil minerals fund in the watershed [Hyman, ]. The Sr istpic cmpsitin f plagiclase was , lwer than any 87Sr/86Sr rati measured in this study with the exceptin f bulk precipitatin, while hrnblende had a 87Sr/ Sr rati f , clse t the value fr bulk sil in this 0.8 sample (Figure 4). These relatively lw values indicate the 0.6 cntributin frm rck units with a lwer ischrn Y intercept, l 200 I 300 I 400 I 500 I 600 than the underlying bedrck. b. 87Rb/86Sr Waters. The average rati in precipitatin (87Sr/86Sr ) was slightly higher than cean water (87Sr/86Sr = [Hess et al., 1986]). This pattern is cnsistent with ther studies which have fund an istpic cmpsitin f rainwater slightly M greater r less than cean water, depending n the influence f dust derived frm lcal gelgic surces [Graustein and Armstrng, 1983; berg et al., 1989; Anderssn et al., 1990; Miller et al., 1993]. In additin, it might be expected that minr amunts KEY f bilgic materials (pllen, leaf particles, insects) cntribute e.. "6 0 hle Rci t the 87Sr/86Sr signature f bulk precipitatin. As the samples Sample..( ' * Whle Rch were filtered and mineral dust cntaminants are relatively in- Mean B Bitite sluble, the deviatin frm seawater values might be expected G Garnet t reflect influence f the mre sluble bilgic cntributins. M ituscvite I, I, I C Chl,rite T the extent that bilgic materials reflect the Sr cmpsitin f the lcal gelgic substrate, either pssibility wuld have a 87Rb/86Sr similar influence n the 87Sr/86Sr rati f bulk precipitatin. Thrughfall shwed little tempral variatin in 87Sr/86Sr, Figure 3. Perry Muntain Frmatin ischrn plt with re- suggesting that the cmpsiting technique masked interstrm gressin line fr (a) all bedrck data and (b) samples excluding r weekly variability in canpy-atmsphere interactins. The the bitite separate and the mst radigenic whle rck sample. cnsistent deviatin frm bulk precipitatin indicates that canpy-atmsphere interactins were active year-rund, despite a lack f a deciduus canpy frm Nvember thrugh April (Figure 5). Deciduus thrughfall had an istpic cmpsitin lcatins. The expected pattern f an increase 87Sr/86Sr in weathered cmpared t unweathered materials, due t mre rapid weathering f Ca/Sr-rich minerals cmpared t K/Rbrich minerals [Bttin and Fullagar, 1968; Dasch, 1969] was nt always evident at CPW. This discrepancy may be due t spatial variatins in sil mineralgy [Hyman, 1993], the influence f Sr assciated with rganic matter, the prevalence f lateral rather than vertical hydrlgic flw paths, r sil mixing due t tree thrw by wind, which is extensive in White Muntain sils [Pilgrim and Harter, 1977]. Sil prfiles at tw lcatins (Figures 4a and 4c) shwed an increase 87Sr/86Sr frm the C t the Bs hrizn, whereas a third site (Figure 4b) shwed a slight decrease. Upper sil prfiles shwed the mst variability, reflecting variatins in rganic matter cntent and prbably als in mineralgy. While the till is partially derived frm the underlying bedrck, there are als cntributins frm ther lcal bedrck almst identical t that f bimass (see belw), suggesting that the increase in Sr cncentratin between bulk precipitatin and thrughfall under the deciduus canpy was due t leaching f catins frm the canpy bimass. Cniferus thrughfall was intermediate in istpic cmpsitin between bimass and bulk precipitatin, indicating a greater influence f atmspheric Sr in cniferus thrughfall. This pattern is cnsistent with ther studies which have fund greater dry depsitin in cniferus versus deciduus canpies. Gsz and Mre [1989] fund little evidence f canpy leaching in thrughfall frm an Engelmann spruce canpy in New Mexic in cntrast t a mixture f atmspheric and canpy Sr in thrughfall under a nearby aspen canpy. The data frm CPW imply a pattern f greater canpy leaching than nted in the New Mexic study, pssibly due t elevated inputs f acidic depsitin at CPW. Sil water Sr cmpsitin was similar t, r had a lwer 87Sr/86Sr rati than bulk sil at each site (Figure 4), cnsistent units, especially ther Silurian metasedimentary units and the with the mdel f Sr in sil water derived frm a mixture f Devnian Kinsman Quartz Mnznite [Bailey and Hrnbeck, 1992]. One might expect all f these units t be unifrm with respect t Sr istpe systematics (i.e., t lie alng the same ischrn), as all were subject t Acadian reginal metamrphism. Hwever, the till samples (C hrizn, Figure 4) wuld plt well belw the bedrck ischrn (Figure 3). Either the till atmspheric inputs and sil mineral weathering. The unadjusted mean sil water 87Sr/86Sr f was intermediate between bulk sil and stream water values (belw). Little tempral variatin in stream water 87Sr/86Sr was bserved (Figure 5), again likely due t cmpsiting f samples. These results suggest that n a mnthly basis there was a has been influenced by cntributins frm rck units with cnsistent mixture f surce areas fr stream water. Individual lwer initial 87Sr/86Sr, r radigenic Sr has been preferentially stream water samples cllected during a pilt sampling pr-

5 BAILEY ET AL.' CALCIUM DEPLETION IN FOREST ECOSYSTEM 711 Table la. Rck and Sil Istpic Data Strntium Rubidium Sample Mean Mean Deviatin, Sr, Deviatin, 87Sr/86Sr x 10 -s ppm 8SRb/87Rb x 10 -s Rb, ppm Perry Muntain Frmatin, Whle Rck Samples Sp Sp Sp Sp Sp Sp Sp Sp Sp Sp Sp Sp Perry Muntain Frmatin, Mineral Separates Muscvite Bitite Chlrite Garnet Sil Samples 1-Oa E Bh Bs Cd Oa A Bs C Oa E Bhs BC Sil Mineral Separates Plagiclase Hrnblende gram shwed great variatin in 878r/86Sr with varying hydr- Sr as an Analg t Ca lgic cnditins. A grab sample cllected during extreme base Within each type f sample analyzed there was a cnsistent flw cnditins cntained 87Sr/86Sr f , reflecting inputs Sr/Ca rati, suggesting parallel surces and behavir f these frm much mre radigenic surces, prbably bedrck weathelements. Mnthly fluxes f these tw elements revealed simering. Therefre while the cmpsiting technique may ensure ilar patterns in precipitatin, thrughfall, and stream water that the data are quantitatively representative f the Sr cm- (Figure 6). Mlar Sr/Ca ratis ranged frm an average f 1.3 x psitin lst frm the watershed in stream water n a mnthly 10-3 in cniferus thrughfall t 3.3 x 10-2 in bulk sil. This basis, any prcess level infrmatin n variatin in surce areas r hydrlgic flw paths has been lst. variability is greater than that fund by,, berg et al. [1989], wh Bimass. Istpic cmpsitin f Sr was least variable in reprted Sr/Ca ratis f 1 x 10-2 t 2 x 10-2 in rain, thrughbimass f all materials analyzed, with the lwest rati fr fall, runff, sil exchangeable catins, sil minerals, and vegetatin in a cniferus watershed in Sweden. sugar maple wd within 0.1% f the highest rati fr American beech wd (Table 2). Wd, fliage, and rt samples In cntrast t the relative istpic hmgeneity f bimass cllected frm a single red spruce were essentially identical in samples, the Sr/Ca rati was much mre vahable in bimass 878r/S6Sr. Bimass 878r/S6Sr was in the same range but less than in ther ecsystem cmpnents. This resulted frm a variable than shallw sil water 878r/S6Sr (Figure 4), which rather cnstant Sr cncentratin in bimass, with a factr f 4 ranged frm t Shrt-term tempral variatin in between the lwest and highest cncentratins, cmpared t sil water might be expected due t changing flw paths with Ca, which varied by a factr f 20. Wd samples fr the three varying hydrlgic cnditins. The vegetatin appears t at- species analyzed were relatively unifrm, with a mlar Sr/Ca tenuate variatins in Sr istpic cmpsitin as assimilatin rati f abut 3.3 x 10-3, similar t that f sil water. Red ccurs ver a number f grwing seasns. spruce rts and fliage had much lwer ratis (Table 2),

6 712 BAILEY ET AL.: CALCIUM DEPLETION IN FOREST ECOSYSTEM Table lb. Water Istpic Data Mean Deviatin Sample 878r/86Sr x 10 -s Sr Bulk Precipitatin Oct Nv Jan March May July Sept Cniferus Thrughfall Oct Nv Dec Jan Feb March April May June Aug Deciduus Thrughfall Oct Nv Dec Jan June July Aug Sept Inlet Oct Nv Dec Jan Feb March April May June July Aug Sept Grab 1' Grab Sil Water Samples: July a Bs a Bs a Bs a Bs Bs$ Bimass Spruce wd Spruce needle Spruce needle Spruce needle NA Spruce needle Spruce rt Beech wd Maple wd Bimass Sr cncentratins are in parts per millin; all thers are in parts per billin. *May 12, 1989.?Sept. 12, $March pssibly indicating discriminatin by trees in the assimilatin f Ca and Sr in these tissues. This finding cntrasts with the findings f,, berg et al. [1989], which shw n discriminatin between these elements by vegetatin. Elias et al. [1982] fund a cnstant Sr/Ca rati in analyses f humus, sil water, and sedge in a grassland ecsystem. In wdy plants, differences in Sr/Ca rati between sil misture and rts were nt substantive. Hwever, reductin did appear t ccur during xylem transprt frm stem t leaf. The data frm CPW are mre cnsistent with the cnclusins f Elias et al. [1982] in that sil water and wd had similar Sr/Ca ratis whereas a much lwer Sr/Ca rati was evident in the fliage sample. Furthermre, the lw ratis in thrughfall cmpared t bulk precipitatin suggesthat thrughfall is influenced by canpy leaching f bimass with a relatively lw Sr cntent. Catin Surce Mdeling: Identificatin f End-Members Ecsystem pls and fluxes were mdeled as mixtures f atmspheric and mineral weathering end-members n the basis f Sr istpic cmpsitin (Figure 7). Precisin in measurement f 87Sr/86Sr ratis leads t an uncertainty f 3% in md- eled mixtures. The atmspheric end-member was taken as the vlumeadjusted mean f the bulk precipitatin samples. Several studies, including this ne, have fund 87Sr/86Sr in atmspheric precipitatin t be clse t the seawater cmpsitin, varying abve r belw this value depending n the cmpsitin f 87Sr/86Sr in lcal gelgic materials. As bimass is als influenced by the Sr cmpsitin f its substrate, particles f bimass in atmspheric precipitatin wuld have the same effect n 87Sr/86Sr as wuld particles f mineral dust. In a silicate terrain such as the White Muntains, dust cmpsed f plant material is likely t be much mre sluble than mineral dusts and thus have a greater influence n Sr cncentratins and istpic cmpsitin f atmspheric precipitatin. The influence by lcal materials n bulk precipitatin can be cnsidered as material recycled frm within the watershed rather than as an atmspheric input. If bulk precipitatin is mdeled via equatin (1) as a mixture f bimass cntaminatin and atmspheric input with a cmpsitin f cean water, then 3% f Sr in bulk precipitatin wuld be derived frm bimass inputs. This value represents a cnservative verestimate f the atmspheric input due t the ptential impact f dusts derived frm within the watershed. Given the range in istpic cmpsitin f varius minerals, the validity f a single end-member t describe the weathering cntributin needs t be qualified. The istpic cmpsitin f Sr released by weathering reactins is the cmpsite f the istpic cmpsitins f each weathering reactant. Thus given a suite f minerals, each with its wn weathering rate and istpic cmpsitin, there is a unique istpic cmpsitin f Sr released t slutin. The cnstraint n defining such a system with a single end-member is that the end-member may nly be valid fr the area and time perid specified. As mineralgic cmpsitin f the weathering substrate varies spatially, an end-member which describes the watershed is nt necessarily the same as an end-member fr any subset f the watershed, be it a subwatershed r a specific sil prfile. Furthermre, if the weathering rate f any mineral varies ver time, then the end-member culd change. Fr example, ver a lng time perid (e.g., thusands f years f sil develpment), easily weathered minerals might becme depleted in the sil prfile relative t mre resistant minerals. This culd

7 ... BAILEY ET AL.' CALCIUM DEPLETION IN FOREST ECOSYSTEM 713 Ca (ppm) I E -,30 -,30, ß I Sr/86Sr Sr ppm Ca (ppm) ,, I ' c Sr/86Sr Sr (pprn) Ca (ppm),10 0 c I I I I ,., u a , Sr/86Sr Sr (ppm) Figure 4. Sil Sr and Ca chemistry at three prfiles (a, b, and c). The left clumn shws 87Sr/86Sr with depth fr bulk sil (circles) and sil water (triangles) samples. The right clumn shws Ca (slid circles) and Sr (pen circles) cncentratin fr the same three prfiles. The central clumn indicates hrizns at each site. result in a change in the istpic cmpsitin f Sr released t slutin. Within shrter time perids (e.g., hundreds f years) cntributins mre radigenic than the bulk sil, pssibly frm bitite r garnet in the sil r bedrck. ne wuld nt expect variatin in the relative weathering cn- If the end-member were as lw as then this wuld tributins f individual minerals due t depletin. indicate that bimass Sr is exclusively derived frm weathering. Althugh hetergeneity in sil mineral and bedrck 87Sr/ The spruce- and fir-dminated frest at CPW is characterized 86Sratis prevents assignment f an exact mineral weathering as having essentially all f its active feeder rts within the end-member withut further data n mineralgi cmpsitin frest flr. This wuld suggesthat atmspheric depsitin and depletin in weathering znes, there are cnstraints that can be made n the range f pssibilities. Overall, minerals ranged in 87Sr/86Sr rati frm fr sil plagiclase t 2.59 shuld be an imprtant surce f base catins fr vegetatin uptake. Sr istpe studies in New Mexic [Gsz and Mre, 1989] and New Yrk [Miller et al., 1993] have fund a high in bedrck bitite. Within this range, a minimum pssible percentage f atmspheric Sr in spruce bimass. value fr the weathering end-member f is predicated by the cmpsitin f bimass and stream water at this value. If A prvisinal assignment f the mineral weathering Sr endmember at 878r/86Sr: , r clse t that f bulk sil bimass and stream water represent mixtures f atmspheric (Figure 7) was made by mass balance cmparisns f adjacent and weathering Sr, then the weathering end-member must sil hrizns within the weathering prfile. This number was have a higher 87Sr/86Sr rati. Sil water 87Sr/86Sr ratis as high calculated by cmparing Sr cncentratin and cmpsitin as and a grab stream water sample at indicate between adjacent sil hrizns. This methd relies n the

8 714 BAILEY ET AL.' CALCIUM DEPLETION IN FOREST ECOSYSTEM ß v ß _ 0 KEY r-. deciduus thrughfall streamwater ß ß cnifer thrughfall ß bulk precipitatin ß ß ß Oct Dec Feb Apr Jun Aug Mnth Figure 5. Tempral variatin in 87Sr/86Sr fr mnthly cmpsite water samples. questinable cnditin that weathering has resulted in a negligible lss f mass. Additinally, the influence f rganic matter depsitin in mineral hrizns is nt accunted fr. Given these limitatins, the value calculated is slightly higher than that f the bulk sil mean, cnsistent with a weathering input dminated by sil weathering, with a small additinal input derived frm bedrck. With this end-member, equatin (1) gives 32% f bimass Sr derived frm atmspheric surces, a value that indicates that the prvisinal end-member may be cnservatively lw as a greater influence f atmspheric surces n bimass Sr is expected. Althugh plagiclase had by far the highest cncentratin f Sr f all minerals analyzed, its extremely lw 87Sr/86Sr rati cmpared t the pssible range fr the mineral weathering end-member indicates that it is relatively unimprtant as a weathering reactant. Plagiclase was nt fund in an electrn micrprbe scan f Perry Muntain Frmatin thin sectins taken frm CPW bedrck samples. In additin, plagiclase in sil samples appears t have fresh surfaces, in cntrast the highly pitted, spnge-like appearance f hrnblende grains. Pitted rinds f bedrck samples reveal active disslutin f bitite and garnet n utcrp surfaces. Bth these physical indicatrs, as well as the likely range f strntium istpic tants. Mass Balance Partitin Given the atmspheric and mineral weathering prprtins f measured watershed fluxes and pls (Figure 7), the Ca cycle was partitined int separate mass balances fr each f the atmspheric and weathering surces (Figure 8). A methd t estimate the prprtin f watershed lsses due t weathering was devised based n a mass balance fr Ca derived frm the atmsphere (A detailed example calculatin illustrating this methd is given in the appendix). The mdel was calculated fr the prvisinal weathering end-member as well as a range f pssible end-members t illustrate the effect f endmember chice n calculated weathering and ecsystem depletin rates. In rder t assess additinal atmspheric inputs beynd thse measured in bulk precipitatin, thrughfall was mdeled as a mixture f catins leached frm the canpy and catins depsited frm the atmsphere. A pair f simultaneus equatins were slved assuming that Sr leached frm the canpy had the same istpic cmpsitin as the canpy and that additinal atmspheric depsitin had the same istpic cmpsitin as bulk precipitatin. This methd yielded an estimate f 3 ml/(ha yr) fr additinal depsitin f Ca t the canpy, cmpared t 17 ml/(ha yr) fr bulk depsitin (Figure 8). These results are cnsistent with the findings f Baker [1990], wh fund that artificial cllectrs are relatively etficient cllectrs f dry depsitin f chemicals, such as Ca, which are assciated with carse particle sizes. Thus little additinal dry depsitin f Ca t the canpy wuld be expected, beynd that caught in a bulk precipitatin cllectr. The ttal input f Ca frm the atmsphere f 20 ml/(ha yr) was abut ne half f the lss f atmspherically derived Ca in stream water (37 ml/(ha yr)). This pattern suggests that an ecsystem pl f Ca was being depleted (i.e., a net lss f strage within the frest). Net depletin f stred Ca culd be derived frm the bimass pl, mineralizatin f rganic matter in the frest flr, r lss f exchangeable catins. At the nearby Hubbard Brk Experimental Frest (HBEF) there is evidence f declining Ca cntent in the frest flr ver the last 20 years [Yanai et al., 1993]. Fr each f these pls at CPW, the Sr istpic cmpsitin was similar t that f bimass, suggesting that depleted material was apprximately 32% atmspheric and 68% mineral in rigin. Therefre depletin f ne f these pls by 17 ml/(ha yr) f atmspheric Ca was accmpanied by depletin f 36 ml/(ha yr) f Ca derived frm weathering reactins (Figure 8). Figure 9 illustrates the effect f weathering end-member chice n mdeled Ca fluxes. At end-members less than 87Sr/ 868r = 0.722, there is a net retentin f atmspheric Ca in the ecsystem, and the weathering rate is equal t the watershed lss f 103 ml Ca/(ha yr). Fr end-members greater than 87Sr/86Sr = 0.722, the mdel predicts lesser weathering rates with cnsequently greater depletin rates, with a minimum weathering rate f abut 10 ml Ca/(ha yr) fr end-members in the vicinity f the mean bedrck Sr istpe cmpsitin. Within this range the mst likely cmpsitin f the weather- cmpsitin released by weathering, argue fr a cmbinatin f hrnblende, garnet, and bitite as the dminant weathering reactants. Mre detailed studies f mineral depletin in sil hrizns and bedrck weathering rinds as well as further 8?Sr/ 86Sr analyses f mineral materials are needed t further cn- Table 2. Bimass Sr and Ca Chemistry at Cne Pnd Watershed strain the weathering end-member istpic cmpsitin and t determine relative weathering cntributins f dminant reac- Sample 87Sr/86Sr Sr, ppm Ca, ppm Sr/Ca* Red Spruce Wd X 10-3 Fliage X 10-6 Rts X 10-4 American Beech Wd X 10-3 Sugar Maple Wd x 10-3 *Sr/Ca expressed as a mlar rati.

9 BAILEY ET AL.: CALCIUM DEPLETION IN FOREST ECOSYSTEM ¾ E 10 E 0.0, I i 0 Oct Dec Feb Apr Jun Aug 20 b t ' i i, I ' i, 6 ß 20 v 8 18 Oct Dec Feb Apr Jun Aug d. ß u 9 ß ' E 6-40 E 3 ]20 cn I ' I I, I Oct Dec Feb Apr Jun Aug Figure 6. Tempral variatin in Ca (pen circles) and Sr (slid squares) fluxes fr (a) bulk precipitatin, (b) cniferus thrughfall, (c) deciduus thrughfall, and (d) stream water. ing end-member is at 87Sr/86Sr = In this range the Stcks f Ca in the sil exchange pl were nly ne third f rati f atmspheric t weathering input rates is reasnably the amunt f Ca stred in the bimass pl, whereas reserves reflected in the mdeled bimass cmpsitin (Figures 7 f Ca in <2-mm mineral sil were 6 times larger than the and 8). amunt f Ca stred in the bimass pl. This is in cntrast The Ca weathering rate f 30 ml/(ha yr) estimated by this HBEF, where the exchangeable Ca pl is 39 times larger than methd is abut 5% f recent estimates frm nearby HBEF the bimass pl [C. E. Jhnsn et al., 1992]. This pattern [Jhnsn et al., 1994]. If ecsystem pls are assumed t be at suggests that the ecsystem at CPW wuld be very sensitive t steady state, then the weathering rate estimate at CPW wuld disturbance and might nt be able t recver frm lng term be 84 ml Ca/(ha yr), still abut 20% f the HBEF estimate. depletin f Ca in sil pls. Cntinuatin f the input, utput, Despite similarity in gelgic substrate between these tw and depletin rates as determined fr the year f study culd sites, weathering rates may be different due t lcal variatin in result in the depletin f Ca cmparable t the size f the abundance f primary minerals r thickness f sils [Bailey and frest flr Ca pl in less than 60 years, suggesting the p- Hrnbeck, 1992]. Cmparisn f these tw appraches sug- tential fr a majr change in ecsystem functin. gests that determinatin f weathering by mass balance ap- It is unknwn hw lng the frest culd endure chrnic prach, assuming steady state ecsystem strage, substantially depletin f Ca pls withut substantial reductin in vigr r verestimates weathering inputs and may ignre eclgically changes in cmpsitin. Shrtle and Smith [1988] shwed that significant lsses f basic catins frm available pls. a mlar A1/Ca rati f >1 in the fine rt envirnment is In this study, net bilgic uptake was assumed t be zer. typical f sites exhibiting spruce decline. Sil water samples This frest has never been harvested and, based n bimass frm CPW typically have A1/Ca ratis f 5 t 6, suggesting the plt inventry appears t be at steady state cnditins. If, n ptential fr aluminum-induced calcium deficiency syndrme the ther hand, the frest were agrading, net bilgic uptake at this site. wuld cnstitute an additinal sink fr atmspherically derived This site has n unusual characteristics that wuld suggest it Ca. Higher weathering and/r sil depletin rates wuld be des nt represent large areas f eastern Nrth America with required t cmplete the mass balance in this case. thin sils and slwly weathering silicate mineralgy. Given the

10 . 716 BAILEY ET AL.: CALCIUM DEPLETION IN FOREST ECOSYSTEM ,t0 ' ' ' I I I I I ' ' ' Atmspheric, End-Member Weathering * End-Member I,I Precipitatin (100) I,I Cnifer thrughfall (43) I * I Deciduus Thrughfall (32) I,I Bimass (32) I * I Sil Water (24) I* I Stream Water (35) I ß I Bulk Sil Sr/86Sr Figure 7. Mean ecsystem 87Sr/86Sr ratis. The bars indicate +_ 1 standardeviatin. The mdeled percentage f atmspheric Sr in each mixture as calculated by equatin (1) is indicated in parentheses. lw base saturatin f the sil exchange cmplex, the small size f this pl in relatin t ther ecsystem pls, and the lw rate f basic catin inputs frm the atmsphere r mineral weathering, recvery f this site frm surface water acidificatin wuld prceed very slwly, even if Ca lsses are mderated by reductins in sulfur and nitrgen emissins. Cnclusins 1. Ratis f Sr/Ca suggest little discriminatin between these elements fr ecsystem prcesses except transprt f catins frm ble t fliage within trees. 2. Istpe end-member mdeling as well as lw Sr/Ca ra- ) b) Additinal Dep 3 IBulk pitatin Litter 112 ea0/?0 E+Bh exc 112 [ [ Thrughfall I I Atm. Canpy /xll Bs exch i... N'e't' ' 'i 1540 ::Depletin:: Stream 17 C exch... Output 41 ] 37 Litter ghfall \?l 1340/ JE +Bh,- m- I, ß Net.Depletin Strea mm.' < C exch ' Figure 8. Mass balance f Ca derived frm (a) atmspheric and (b) mineral weathering surces. Units are mles per hectare fr ecsystem pls and mles per hectare per year fr fluxes.

11 ß ß _ BAILEY ET AL.: CALCIUM DEPLETION IN FOREST ECOSYSTEM 717 A B C D Wea%heri,.el 60 ' ' 'Ttal Depletin I I O 10,, i /t......'...'"'...-'...' Depletin f Atmspheric-Ca,,,, I, J, I,,,, I,,,, I,,,, a7sr/a Sr. Weathering End-member Figure 9. Effect f chice f weathering end-member 87Sr/86Sr n variatin in mdeled annual depletin and weathering rates. Reference pints with respect t the weathering end-member are as fllws: A, , value at which there is n ecsystem depletin; B, , mean bulk sil cmpsitin; C, , prvisinal end-member; and D, 0.727, bedrck ischrn intercept. tis in thrughfall indicate that mst f the Sr and Ca in thrughfall is derived frm canpy leaching rather than frm wash-ff f dry depsitin. 3. Variability in mineral Sr istpic cmpsitin cmplicatin strage in the frest flr r frm the catin exchange cmplex. Given lw inputs via weathering and atmspheric depsitin cmpared t the depletin rate, as well as the relatively large rate f depletin cmpared t strage in available cates assessment f 87Sr/86Sr rati f Sr released by weathering sil pls, cntinuatin f basic catin depletin culd be reactins. Results f the present study as well as thse f Bain and Bacn [1994] demnstrate the imprtance f a thrugh knwledge f site mineralgy and mineral Sr systematics in rder t prperly interpret ecsystem Sr istpe studies. The effects f weathering, spatial variability in parent material, and rganic matter depsitin need t be taken int accunt when assessing patterns in 87Sr/86Sr within the sil weathering prfile. Althugh transprted sil parent material in this glaciated expected t have a majr impact n the functin f this ecsystem. 6. The striking difference in base status and estimated weathering rates between CPW and HBEF, tw similar sites which lie in clse prximity t each ther, underscres the need t better understand spatial variatin in site specific parameters such as sil mineralgy and disturbance histry, in rder t develp reginal mdels frm study f specific sites. regin cmplicates assessment f mineral weathering, even in regins with residual sils, mineral istpe hetergeneity is t be expected due t variatins in Sr/Rb rati in individual min- Appendix: Mass Balance Partitin Calculatins eral species. 1. Calculate the watershed thrughfall flux by multiplying 4. Watershed Ca lsses may be partitined int lsses d ue the flux at each site by the area f each cver type; sum fr the t weathering versus lsses due t depletin f ecsystem pls ttal. by cnducting a mass balance n atmspherically derived Ca. This apprach requires an estimate f ttal atmspheric dep- Cniferus x ml Ca/ha sitin as well as an indicatin f the rigins f Ca in ecsystem Deciduus 59.6 x 0.19 = 11.3 ml Ca/ha pls subject t depletin. Open 17.3 x 0.03 = 0.5 tl Ca/ha 5. Cupling f istpic end-member mdeling with a mass Ttal ml Ca/ha balance shwed that depletin f basic catin pls may be an imprtant cntributr t stream water lsses frm this watershed. This depletin is prbably due t a reductin in basic 2. Calculate the prprtin f each end-member in the watershed thrughfall flux by multiplying the flux at each site

12 718 BAILEY ET AL.: CALCIUM DEPLETION IN FOREST ECOSYSTEM by its atmspheric prprtin (Figure 7) and by its area; sum fr the ttal. Atmspheric Cniferus x 0.78 x 0.44 = 49.5 ml Ca/ha Deciduus 59.6 x 0.19 x 0.33 = 3.7 ml Ca/ha Open Ttal Weathering Cniferus Deciduus Ttal 17.3 x 0.03 x 1.0 = 0.5 ml Ca/ha 53.0 ml Ca/ha x 0.78 x 0.56 = 63.0 ml Ca/ha 59.6 x 0.19 x 0.67 = 7.6 ml Ca/ha 71.4 ml Ca/ha 3. Partitin thrughfall int atmspheric depsitin and canpy leachate. This was dne by assuming that atmspheric depsitin caught by the canpy in excess f bulk depsitin had the same istpic cmpsitin as bulk depsitin, whereas canpy leachate had the same istpi cmpsitin as bimass. Atmspheric Surce Weathering Surce Atmspheric depsitin x 0 Canpy leachate y z Cnstraints are y/(y + z) = 0.32 (atmspheric prtin f bimass), x + y = 53.0 (step 2), and z = 71.4 (step 2). Slve fr y (33.5 ml Ca/ha) and x (19.6 ml Ca/ha). 4. Calculate the lss f atmspheric Ca frm the watershed by multiplying the stream water flux by the prprtin f stream water derived frm atmspheric depsitin ml Ca/ha x 0.36 = 36.6 ml Ca/ha Calculate the depletin f Ca f atmspheric rigin by subtracting the ttal atmspheric depsitin rate f 19.6 ml Ca/ha (step 3) frm the lss f atmspheric Ca in stream water ml Ca/ha ml Ca/ha = 17.1 ml Ca/ha 5. Calculate the depletin f Ca f weathering rigin by assuming that the depleted pl has the istpic cmpsitin f bimass. x/(17.1 ml Ca/ha + x) = 0.32 x = 36.4 ml Ca/ha The ttal depletin rate is then = 53.5 ml Ca/ha 6. Calculate the weathering rate by subtracting the depletin f Ca f mineral rigin frm the watershed lss f Ca f mineral rigin ml Ca/ha x 0.64 = 65.9 ml Ca/ha 65.9 ml Ca/ha ml Ca/ha = 29.9 ml Ca/ha. Acknwledgments. This research was supprted by the Nrtheastern Frest Experiment Statin, USDA Frest Service, and by the Natinal Science Fundatin. Assistance in the labratry and field was prvided by J. Hislp, R. Smith, R. Perrn, and W. Olszewski. The manuscript was imprved by the thughtful cmments f T. D. Bullen and tw annymus reviewers. References berg, G., G. Jacks, and P. J. Hamiltn, Weathering rates and 87Sr/ 86Sratis: An istpic apprach, J. Hydrl., 109, 65-78, Anderssn, P., R. L6fvendahl, and G. berg, Majr element chemistry 2H, 180 and 87Sr/86Sr in a snw prfile acrss central Scandinavia, Atms. Envirn., Part A, 24, , Bailey, S. W., and J. W. Hrnbeck, LithlOgic cmpsitin and rck weathering ptential f frested, glacial-till sils, Res. Pap. NE-662, 7 pp., U.S. Dep. f Agric. Frest Serv., Nrtheast. Fr. Exp. Stn., Radnr, Pa., Bailey, S. W., C. T. Driscll, and J. W. Hrnbeck, Acid-base chemistry and aluminum transprt in an acidic watershed and pnd in New Hampshire, Bigechemistry, 28, 69-91, Bain, D.C., and J. R. Bacn, Strntium istpes as indicatrs f mineral weathering in catchments, Catena, 22, , Baker, L. A., Reginal estimates f atmspheric dry depsitin, in Acidic Depsitin and Aquatic Ecsystems: Reginal Case Studies, edited by D. F. Charles, pp , Springer-Verlag, New Yrk, Bttin, M. L., and P. D. Fullagar, The effects f weathering, Am. J. Sci., 266, , Crnan, C. S., Chemical weathering and slutin chemistry in acid frest sils: Differential influences f sil type, bitic prcesses, and H + depsitin, in The Chemistry f Weathering, edited by J. I. Drever, pp , D. Reidel, Nrwell, Mass., Dasch, E. J., Sr istpes in weathering prfiles, deep sea sediments, and sedimentary rcks, Gechim. Csmchim. Acta, 33, , Dellayes, D. H., Winter injury and develpmental cld tlerance f red spruce, in Eclgy and Decline f Red Spruce in the Eastern United States, edited by C. Eager and M. B. Adams, pp , Springer-Verlag, New Yrk, Drever, J. I., The Gechemistry f Natural Waters, Prentice-Hall, Englewd Cliffs, N.J., Elias, R. W., Y. Hira, and C. C. Pattersn, The circumventin f the natural bipurificatin f calcium alng nutrient pathways by atmspheric inputs f industrial lead, Gechim. Csmchim. Acta, 46, , Faure, G., Principles f Istpe Gelgy, 2nd ed., Jhn Wiley, New Yrk, Federer, C. A., J. W. Hrnbeck, L. M. Trittn, C. W. Martin, R. S. Pierce, and C. T. Smith, Lng-term depletin f calcium and ther nutrients in eastern US frests, Envirn. Manage. N.Y., 13, , Gallway, J. N., and E. B. Cwling, The effects f precipitatin n aquatic and terrestrial ecsystems: A prpsed precipitatin chemistry netwrk, J. Air Pllut. Cntrl Assc., 28, , Gsz, J. R., and D. I. Mre, Strntium istpe studies f atmspheric inputs t frested watersheds in New Mexic, Bigechemistry, 8, , Graustein, W. C., 87Sr/86Sr ratis measure the surces and flw f strntium in terrestrial ecsystems, in Stable Istpes in Eclgical Research, edited by P. W. Rundel, J. R. Ehleringer, and K. A. Nagy, pp , Springer-Verlag, New Yrk, Graustein, W. C., and R. L. Armstrng, The use f Strntium-87/ Strntium-86 ratis t measure atmspheric transprt int frested watersheds, Science, 219, , Hess, J., M. L. Bender, and J. G. Schilling, Evlutin f the rati f strntium-87 t strntium-86 in seawater frm Cretaceus t present, Science, 231, , Hrwitz, E. P., M. L. Dietz, and D. E. Fisher, Separatin and precncentratin f strntium frm bilgical, envirnmental, and nuclear waste samples by extractin chrmatgraphy using a crwn ether, Anal. Chem., 63, , Hyman, M. E., Rates f Mineral Weathering in the Cne Pnd Watershed, Graftn Cunty, New Hampshire, M.S. thesis, Syracuse Univ., Syracuse, N.Y., Jacks, J., G. berg, and P. J. Hamiltn, Calcium budgets fr catchments as interpreted by strntium istpes, Nrd. Hydrl., 20, 85-96, Jhnsn, A. H., et al., Synthesis and cnclusins frm epidemilgical and mechanistic studies f red spruce decline, in Eclgy and Decline f Red Spruce in the Eastern United States, edited by C. Eager, and M. B. Adams, pp , Springer-Verlag, New Yrk, Jhnsn, C. E., A. H. Jhnsn, and T. G. Siccama, Whle-tree clearcutting effects n exchangeable catins and sil acidity, Sil Sci. Sc. Am. J., 55, , Jhnsn, C. E., M. I. Litar, M. F. Billet, and O. P. Bricker, Chemical weathering in small catchments: Climatic and anthrpgenic influ-