EFFECTS OF ACID PRECIPITATION ON NUTRIENT CYCLING IN TERRESTRIAL ECOSYSTEMS OF SOUTHERN APPALACHIAN AND PIEDMONT WATERSHEDS (Task Force Project T-20)

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1 swank and Duglass EFFECTS F ACID PRECIPITATIN N NUTRIENT CYCLING IN TERRESTRIAL ECSYSTEMS F SUTHERN APPALACHIAN AND PIEDMNT WATERSHEDS (Task Frce Prject T-20) Wayne T. Swank and James E. Duglass USDA, Frest Service Sutheastern Frest Experiment Statin Cweeta Hydrlgic Labratry Rute 1, Bx 216 tt, NC IMPRTANCE At the Cweeta Hydrlgic Labratry, a 1,600-ha experimental frest maintained by the Frest Service in the Blue Ridge Muntains f Nrth Carlina, the effects f man's use f the frest n the quality and quantity f streamflw has been under study fr 50 years. Because future prductivity f the terrestrial and aquatic ecsystems are dependent n management practices applied t the landscape, detailed studies f mineral cycling n selected undisturbed and managed watersheds was begun 15 years ag. Atmspheric depsitin is a majr surce f nutrients fr frests, but chemical cmpsitin f precipitatin, particularly its high acid cntent, can adversely impact terrestrial and aquatic ecsystems. Therefre, a netwrk was established t quantify and mnitr lng term atmspheric input t the basin. Studies were begun t quantify the nutrient budgets fr selected watersheds, t describe the cycling f nutrients thrugh the system, and t determine changes in cycle prduced by management, natural disturbances, r changes in atmspheric input. In perspective, acid depsitin is ne cmpnent f a larger research effrt t define the nutrient budget f frested ecsystems in rder t prperly manage them. Descriptin f recent acid precipitatin research fllws. HYPTHESES (1) Hw des atmspheric depsitin vary between lcatins within the basin, between mnths, and between years? Is there a time trend? (2) Hw is precipitatin chemistry altered as it passes thrugh the canpy, litter, and int sil? (3) What is the fate f anins and catins in the sil system? Reprt presented by Duglass at EPA/NCSU Natinal Acid Precipitatin Assessment Prgram Effects Research Review, Raleigh, NC, February 21-24, 1983.

2 Swank--and Duglass TECHNICAL APPRACH Rainfall input is measured at 12 sites within the Cweeta basin. At eight f these, samplers are installed t cllect weekly bulk precipitatin samples fr chemical analysis. Samples are analyzed fr ph, N03-N, NH^-N, P^-P, Cl, Si0 2, S^, Ca, Mg, K, and Na as described by Swank and Duglass (1977). These same parameters are als measured n weekly grab samples frm each gaged watershed in the basin. Annual budgets are calculated by multiplying cncentratins by vlumes and subtracting utput frm input. Analysis f variance and regressin techniques were applied t determine whether input varied between lcatins, mnths, r years and whether any time trend in H"*" cncentratin was apparent fr the 10 years f recrd. Changes in bulk precipitatin chemistry as water mved thrugh canpy, litter, and sil were examined fr a nixed hardwd frest at Cweeta and a pitch pine (Pinus rigida Mill.) stand 13 km away in Franklin, Nrth Carlina. The number f thrughfall and lysimeter cllectrs varied between stands. Instrumentatin and methds used in the tw stands are described by Best and Mnk (1976) and Swank and Swank (in press) and chemical analytical methds are described by Swank and Duglass (1977). Differences in mean cncentratins f nutrients passing thrugh successive cmpartments were determined by t-test. Input-utput S^ budgets f undisturbed watersheds in the Cweeta basin shw large accumulatins f elemental S varying frm 5.9 t 8.9 kg ha-1 year~^ (Swank and Duglass, 1977). Sil samples cllected frm the A-, B-j, and C hrizns were analyzed and fund t have large adsrptin capacity f S (Jhnsn, et al., 1980). Because f high input f S^ and a finite adsrptive capacity f sils, sil samples frm fur watersheds were cllected t study the transfrmatin f S within the sil system. Carrier-free Na2 -^S^ was added t samples which were incubated and extracted t yield sluble, adsrbed, and nn-salt extractable (rganic) frms f S (Fitzgerald, et al., in press). Precipitatin Acidity RESULTS Mean annual IT*" cncentratin f bulk precipitatin at the eight lcatins within the Cweeta basin did nt differ significantly (Table 1) with elevatin r with any identifiable tpgraphic r gemrphic characteristic. The mean annual cncentratin was JJ eq with a standard deviatin f 2.2 u eq i~. Expressed as ph, the range in mean annual cncentratin was frm t 4.54> r 0.08 ph units.

3 Swank and Duglass Table 1. Mean annual H cncentratin f bulk precipitatin (1973-, 1982). Cncentratin Gage Qi_ _illj 2H ' X + S The average weighted mnthly If* cncentratin f bulk precipitatin fr the 10-year perid differed significantly between mnths (Figure 1). Lwest cncentratins ccurred in fall and winter except fr February, which, alng with May thrugh September, had highest cncentratins f H*. The bserved ph extreme values fr weekly saaples were 6.30 and 3«35«Less than 4 percent f the mnths during the 10-year perid had mean bulk precipitatin mre acid than ph 4.0. Acidity f bulk precipitatin differed significantly between years with 1977 being ths year f least acidity and 1978 the year f greatest acidity, bth years being drier than nrmal (Figure 2). With a 10-year recrd f ph replicated at eight lcatins within a relatively small gegraphic area, we can say that there is n evident time trend tward either increasing r decreasing acidity f rainfall. It is bvius frm Figure 2 that a much larger perid will be required befre any cnclusive time trends fr acidity f bulk precipitatin can be established. Acidity Changes in Hydrl^ic As precipitatin passes thrugh the frest canpy, H* in cncentratin changes (Table 2). Hydrgen* cncentratin varied because measurements were made at diffrest times and lcatins. In the pitch pine stand, thrugafall was significantly leas acid than rain, water leaching thrugh the litter was sigaifleaatly less acid than thrughfall, but sil water was significantly mre acid at 25 cm depth than water passing thrugh the litter. A similar pattern f changes were bserved as water passed thrugh thase cmpartments f the hardwd stand, except that the prgressive neutralizatin f acidity f rain cntinued fra canpy int the sil. Changes in N03-N in water passing thrugh successive layers f the pitch pin and hardwd frest were similar t thse f H+ cncentratin. Hwever, 804 cncentratin tended t increase as water passed thrugh canpy and litter but were variable in sil depending n frest type. Fr detailed discussin f in dynamics, see Swank and Swank (in press).

4 MEAN MNTHLY H + CNCENTRATIN F BULK PRECIPITATIN (p eq/l) r cr a s en S. z HI Q.

5 3 t * i~** v, *>S»-^ - t» 0 I P» CD U ANNUAL H+ CNCENTRATIN F BULK 0 0 PRECIPITATIN f// eg/i) w en 0 M'Br c*- c is H a. a 3 0" t 0 I g C 2 rn t 13 c n T H *"$ H* > < i; *"* *t!3 C 00 0 t 1C p g- t H* H- (m t3 t3 H- H- r<- MJ p) H- <-«H- C (0 CD Q. t; T ( ' &> ta C

6 Swank and Duglass Table 2. Cmparisn f mean annual H* in cncentratin and ph in hydrlgic cmpartments f mixed hardwd and pitch pine frests (t-test between successive cmpartments, *p < 0.05; **p < 0.01). H Cncentratin Cmpartment (y eq I" 1 ) p_h A. Pitch Pine Precipitatin Thrughfall 52.9* 4.28 Litter water 5.6** 5.26 Sil water (25 cm) 17.4.** 4.76 B. Mixed Hardwds Precipitatin Thrughfall 5.1* 5.30 Litter water Sil water (25 en) 1.0* 6.01 Metablic Fate f Inrganic S Sils studied were frm an ld-grwth hardwd, tw recently clearcut hardwds, and a 26-year-ld white pine frest. All sils were fund t rapidly incrprate 35S^ int na~salt extractable S. A substantial prtin f th@ added 35SQ^ was adsrbed by these sils but was cmpletely released by the analytical prcedure used (Fitzgerald, et al., in press). Althugh sm differences existed between sils, 10 t 20 percent f the labaled inrganic S^ added t the sils was transfrmed int nn-salt extractable ester and carbn-bnded frms f S. Results supprt ther evidence (Jhnsn s et al., 1980) that S accumdatin is related t S^ adsrptin and that cnversin f S int nn-salt extractable rganic fres may als play an imprtant rle in accumulatin in these sils. DISCUSSII Thesa results indicate a clear seed fr cntinued lng term mnitring f ataspheric depsitin t datect changing patterns f acidity s if any, and t prvide basic data a nutrient cycling studies. Analyses f all nutrient input data and crrelatin f input and exprt cncentratins, and amunts are incmplete at this time. Reasns fr the large changes in H^* cncentratins as precipitatin passes thrugh varius cmpartaents aad ultimately drps t nearly neutral levels in streaaflw requires additlaal etu^, as des the linkage between H* and the nitrate and sulfata dynamics In the sil system.

7 1. Ten years f weekly measurements f K* in bulk precipitatin at eight lcatins in the Cweeta basin indicate: a. N significant difference between lcatins, b. Significant differences in H + cncentratin between ncnths, c. N apparent trend tward increasing r decreasing acidity. 2. Hydrgen* cncentratin f precipitatin decreases as it passes thrugh the canpy and litter f pitch pine and nixed hardwd frests. Hydrgen* cncentratin in sil beneath the litter cntinues t decline beneath hardwds but increases saewhat beneath pitch pine. 3. The large slfate accumulatins in Cweeta sils are due t bth adsrptin and cnversin int rganic ferns with adsrptin apparently mst imprtant. REFERENCES Beat, G. R. and C. D. Mnk Catin flux in hardwd and white pine watersheds. In Mineral cycling in sutheastern ecsystems. p F. G. Hwe11, J. B. Gentry, and M. H. Smith, eds. ERDA Sympsium Series, Cnf Fitzgerald, J. W., T. C. Strickland, and V. T. Swank. In Press. Metablic fate f inrganic sulphate in sil samples frm disturbed and managed frest ecsystems. Sil Bilgy and Bichemistry. Jhnsn, D. W., J. tf. Hrnbeck, J. M. Kelly, W. T. Swank, and D. E. Tdd Reginal patterns f sil sulfate accumulatin: relevance t ecsystem sulfur budgets. In Atmspheric sulfur depsitin: envirnmental inpact and health effects, p D. S. Shriner, C. R. Richmnd, and S. E. Lindberg, eds. Prc. 2d Life Sci. Syrup. CGatlinburg, Tenn., ct Ann Arbr Sci. Publ., Inc., Ann Arbr, Mich. Swank, W. T. and J. E. Duglass Nutrient budgets fr undisturbed and manipulated hardwd frest ecsystems In the muntains f Nrth Carlina, In Watershed research in eastern Nrth America, Vl. I. p D. L. Crrell, ecu Smithsnian Institutin, Edgeuater, Md. Swank, W. T. and M. T. S. Swank. In Press. Dynamics f water chemistry in hardwd a»d pins csystea. In Sympsium n catchment experiments in fluvial gemrphlgy. VT. T. Burt and D. E. Walling, eds. Prc. Intern. Gegraphical nin Cma, n Field Experiments in Gemrphlgy. EExeter and Huddersfield, UK, Aug J Gebks, Nrwich, UK.

8 Swank and Duglass f'vt 7'~^l? < 3T TTC ^i L i t Z r_h J Li (1) Data set f bulk precipitatin and strea-flv cher.istry fr the Cweeta basin fra 1972 t present. (2) See Swank and Swank, in press, and Fitzgerald, et al., in press. Bth shuld appear in print in RELATINSHIP T THER WRK This wrk is part f the Frest Service effrt at the Ccveeta Hydrlgic Labratry; anther part is ccr.tair.ed in the Aquatic Task Frce Reprts. In additin, research at the Jcweeta Kydrlgic Labratry bearing n the acid rain questin:; is spnsred by Natinal Science Fundatin under the Lcng-Ter_ Eclgical Research (LTE") prgram. Wrk n the fate f sulfate en Cve-'ita watersheds by J. W. Fitzgerald and supprted by a Natinal Science Fundatin grant is related, as Is the study f acid rain effects n whle tree harvesting (see D. W. Jhnsn, this meeting) supprted by Departsent f Energy and Envirnmental Prtectin Agency. In additin, cperative testing by Electric Pwer Research Institute f the ILVAS mdel n a watershed is underway at Cweeta. ACTIVITIES Sae Fitzgerald, et al. (in press) and Swank and Swank (in press). The latter was presented at the Syapsiusi n Catchiaent Experiisents in Fluvial Gemrphlgy in Bxetar, England. SUPPRT Frest Service, $45>000, cntinuing; Envirnmental Prtectin Agency, $15,000, PERSMEL J. E. Duglass, Principal Hydrlgist, W. T. Swank, Principal Eclgist, and L. V. Swift, Jr., Frest Meterlgist. USDA Frest Service, Sutheastern Frest Experiment Statin, Cweeta Hydrlgic Labratry, tt, Nrth Carlina. Abve persnnel at TELEPHNE CNTACTS