Agr-Ecsystems, 2 (1975) 127 132 127 Elsevier Scientific Publishing Cmpany, Amsterdam Printed in The Netherlands THE RELATIONSHIP BETWEEN NITRATE CONCENTRATION IN THE SOUTHERN APPALACHIAN MOUNTAIN STREAMS AND TERRESTRIAL NITR1FIERS R.L. TODD, W.T. SWANK,* J.B. DOUGLASS,* P.O. KERR,** D.L. BROCKWAY^" and C.D. MONKtt Department f Agrnmy and Institute f Eclgy, University f Gergia, Athens, Ga. 30102 (U.S.A.) *Cweeta Hydrlgic Labratry, U.S. Frest Service, Franklinf, N.C. 28734 (U.S.A.) **Department f Micrbilgy, University f Gergia, Athens, Ga. 30602 (U.S. A) 'U.S. Envirnmental Prtectin Agency, Sutheast Envirnmental Research Labratry, Athens, Ga. 30601 (U.S.A.) ft Department f Btany, University f Gergia, Athens, Ga. 30602 (U.S.A.) Cntributin N. 243 frm the Deciduus Frest Bime, US-IBP. (Received April 8th, 1975) ABSTRACT Tdd, R.L., Swank, W.T., Duglass, J.E., Kerr, P.O., Brckway, D.L. and Mnk, C.D., 1975. The relatinship between nitrate cncentratin in the Suthern Appalachian muntain streams and terrestrial nitrifiers. Agr-Ecsystems, 2: 127 132. The nitrate cntent f stream water and the nitrifying bacterial ppulatin f the terrestrial hrizn were measured in three suthern Appalachian watersheds ver a 22-mnth perid. The watersheds studied were a fescue grass catchment, a 15-year ld white pine plantatin, and a mature undisturbed hardwd frest. Mnthly averages f nitrate-nitrgen in stream water frm the three watersheds were 730, 190, and 3 ppb respectively; the respective nitrifying ppulatins averaged 16,000, 175 and 22 per gram f dry weight fr each 40 cm sil prfile. These ppulatins were cncentrated in the upper 10 cm f the prfile (grass = 98%, white pine = 90%, and hardwd = 88%). A crrelatin is evident between the number f nitrifying bacteria in the sil frm gaged watersheds and the NO 3 cntent f the streams. Nitrifying activity appears t be dependent n vegetatin type and suceessinal stage. INTRODUCTION Nitrgen transfrmatins ccurring within the bisphere are regulated almst cmpletely by terrestrial and aquatic micrrganisms. The bilgical frmatin f nitrate and/r nitrite frm cmpunds cntaining reduced nitrgen (ammnia) is a prcess termed nitrificatin. Nitrificatin in frest ecsystems was reviewed by Chase et al. (1968). Prpsals fr the imprtance f the nitrifying prcess n the functining f frested ecsystems have included an increase f nitrifying ppulatins (Smith et al.,
128 1968) and nitrate lsses (Likens et al., 1969) frm a cutver New Hampshire, watershed. Rice and Panchly (1972) suggest such increases are nt due t eliminatin f the cmpetitin fr nitrate by the vegetatin but result frm a de-repressin f the nitrificatin prcess. They prpse that the suppressin f nitrificatin is a prime factr in the establishment f a climax frest vegetatin. Recent evidence (Rice and Panchly, 1973; 1974) has been presented fr the rle f tannins and ther plyarmatic cmpunds as natural ccurring inhibitrs f nitrificatin. The cllatin f several investigatrs' effrts at the US- IBP Eastern Deciduus Frest Bime study site, lcated at Cweeta Hydrlgic Labratry in western Nrth Carlina, allws an in-depth assessment f the rle nitrificatin plays in nutrient cycling within suthern Appalachian frested watersheds. In this cmmunicatin the terrestrial nitrifying ppulatins are crrelated with the nitrate cntent in the streams fr a 22-mnth perid frm an area manifesting a grasst-frest serai stage after 4 years, a 15-year-ld white pine plantatin, and a mature undisturbed hardwd frest. The treatment histries and physical prperties f these adjacent catchments with similar sil types under differing vegetative regimes have been described in detail by Jhnsn and Swank (1973). MATERIALS AND METHODS Cmpsite samples were cllected at biweekly intervals ver a 22-mnth perid frm the sil slum frm at least tw lcatins n each catchment. The samples were transprted back t the labratry at 5 C and prcessed within 24 h. The number f chemauttrphic nitrifying micrrganisms was determined using a mdificatin f the prcedure described by Alexander and Clark (1965). The chemauttrphic nitrifying ppulatin is defined in this investigatin as ne frming nitrate (NO 3 ~) in a chemically defined medium in which ammnium (NH 4 + ) is the sle nitrgen surce and calcium carbnate the nly added energy surce. Nitrate frmatin in the incubatin medium was detected fllwing 3 weeks incubatin at 25 C (Alexander and Clark, 1965). Ppulatin density was estimated by the mst prbable number (MPN) methd utlined by Alexander (1965). Results are expressed as numbers per gram f dry weight sil, and reprted values reflect the mean f each mnth's set f determinatins. Nitrate was quantified in the stream water frm each watershed n a twiceweekly basis. Samples, cllected just abve the weir settling basin, were filtered within 2 h after their cllectin (0.45 p.m, Millipre) and stred at lw (5 C) temperature in sterile plyethylene r plyprpylene bttles. Nitrate was analyzed by the autmated cadmium reductin methd (Envirnmental Prtectin Agency, 1971). Reprducibility f the nitrate determinatin at 100 ppb was ± 1 ppb (McSwain, 1973). Average cncentratin values were weighted fr streamflw fr each drainage basin.
129 RESULTS The mnthly mean f nitrifying bacteria (number/g f sil) and the average NO 3 -N cncentratin f stream water are illustrated in Figs 1 3. Data in Fig. 1 are taken frm a watershed in the furth and fifth year f a grass-t-frest successin. Similar activities fr a 15-year white pine plantatin and a mature mixed hardwd catchment are represented in Figs 2 and 3, respectively. The mnthly plttings generally shw lw levels f NO 3 -N and nitrifying bacteria thrughut the year fr the mature hardwd cver. In cntrast, the pine and grass cvered watersheds shw large seasnal fluctuatins in bacteria and NO 3 -N levels; the annual maximum and minimum levels fr the tw variables tend t cincide. In Table I the distributin f the nitrifying ppulatins in the sil prfiles is cmpared t the mean annual NO 3 -N cntent f the stream water. Fr a 40- cm prfile 98% f the micrbial nitrifying ppulatin is lcated within the upper 10 cm f the grass watershed prfile; fr the pine the value is 90% and fr the hardwd 88%. DISCUSSION A crrelatin f nitrate cntent in first rder muntain streams and terrestrial nitrifying bacterial ppulatins frm their respective drainage watersheds is bserved. The distributin f these ppulatins ccurs in the upper divisin f the e? 5 O CD O 4 Grss Nitrifying Bacteria 1.4 1.2 1.0 < K. UJ 0.8 0.6 CD CD Z! I u_ E 0 I 6 8 1971 10 12 2 4 TIME (MONTHS) 1972 10 0.4 0.2 0 12 Fig. 1. Cmparisn f the terrestrial nitrifying bacteria and stream nitrate (NO 3 ) cntent fr the furth and fifth year f a grass-t-frest successinal vegetatin.
130 O 4 QQ Pine Nitrifying Bacteria N0 3 -N 1.4 1.2 1.0 0.8 0.6 0.4 U. 4 6 8 1971 10 12 TIME (MONTHS) 6 8 1972 0.2 0 10 12 Fig.2. Cmparisn f the terrestrial nitrifying bacteria and stream nitrate (NO 3 ) cntent fr the fifteenth and sixteenth year f a white pine successinal vegetatin. O CO O 4 1' UJ 2 CD O Hardwd Nitrifying Bacteria N0 3 -N 1.4 1.2 1.0 0.8 0.6 0.4 0.2 1971 10 12 2 4 TIME (MONTHS) 1972 10 12 Fig. 3. Cmparisn f the terrestrial nitrifying bacteria and stream nitrate (NO 3 ) cntent fr a mature hardwd vegetatin.
131 TABLE I Cmparisn f NO 3 -N cntent (weighted annual mean) in stream run-ff with mean number f nitrifying bacteria in the sil Frest type NO 3 -N (ppm) Grass- t-frest successin 0.792 White pine 0.190 Mature hardwd 0.003 Nitrifying bacteria (number/g ven-dry sil) by sil depth 0 10 cm 15,750 160 15 10 20 cm 90 4 2 20 40 cm 250 13 5 Ttal 16,000 175 22 prfile as wuld be expected fr these rganisms. The bservatin that nitrate lss and nitrifying ppulatins decrease as vegetatin appraches climax supprts the hypthesis prpsed by Rice and Panchly (1972). They prpse that the nitrifiers are inhibited in the climax s that ammnium nitrgen is nt xidized t nitrate as readily as in the successinal stages. Climax vegetatin can either inhibit the nitrificatin prcess (Rice and Panchly, 1973) r can better utilize ammnium-nitrgen directly than can the preceding serai stages. In spite f the psitive crrelatin between lwer nitrate lsses with decline in nitrifying ppulatins, it may be premature t speculate that these activities are respnsible fr nitrate lss frm the terrestrial ecsystems. Hwever, it certainly appears that the nitrate cntent f these streams culd be largely due t bilgical activity in the terrestrial envirnment and nt t bilgical activity within the stream. ACKNOWLEDGEMENT Research supprted by the Eastern Deciduus Frest Bime, US-IBP, funded by the Natinal Science Fundatin under Interagency Agreement AG-199, BMS69-01147 A09 with the Energy Research and Develpment Administratin Oak Ridge Natinal Labratry. REFERENCES Alexander, M., 1965. Mst-prbable-number methd fr micrbial ppulatins. In: C.A. Black et al. (Editrs), Methds f Sil Analysis, Part 2. Am. Sc. Agrn.,Madisn, Wise., pp. 1467 1472. Alexander, M. and Clark, F.E., 1965. Nitrifying bacteria. In: C.A. Black et al. (Editrs), Methds f Sil Analysis, Part 2. Am. Sc. Agrn., Madisn, Wise., pp. 1477 1483. Chase, F.E., Crke, C.T. and Rbinsn, J.B., 1968. Nitrifying bacteria in sil. In: T.R.G. Gray and D. Parkinsn (Editrs), The Eclgy f Sil and Bacteria. Univ. f Trnt Press, Trnt, Ont, pp. 593 611. Envirnmental Prtectin Agency, 1971. Methds fr chemical analysis f water and wastes. Envirnm. Prt. Agency, 16020, pp. 175 183.
132 Jhnsn, P.L. and Swank, W.T., 1973. Studies n catin budgets in the suthern Appalachians n fur experimental watersheds with cntrasting vegetatin. Eclgy, 54: 70 80. Likens, G.E., Brmann, F.H. and Jhnsn, N.M. 1969. Nitrificatin: Imprtance t nutrient lsses frm a cutver frested ecsystem. Science, 163: 1205 1206. McSwain, M.R., 1973. Prcedures fr chemical analysis f streamflw and precipitatin at the Cweeta Hydrlgic Labratry. Eastern Deciduus Frest Bime Rep. N. 73, p.12. Rice, E.L. and Panchly, S.K., 1972. Inhibitin f nitrificatin by climax ecsystems. Am. J. Bt., 59: 1033 1040. Rice, E.L. and Panchly, S.K., 1973. Inhibitin f nitrificatin by climax ecsystems. II. Additinal evidence and pssible rle f tannins. Am. J. Bt., 60: 691 702. Rice, E.L. and Panchly, S.K., 1974. Inhibitin f nitrificatin by climax ecsystems. III. Inhibitrs ther than tannins. Am. J. Bt, 81: 1095 1103. Smith, W., Brmann, F.H., and Likens, G.E., 1968. Respnse f chemauttrphic nitrifiers t frest cutting. Sil Sci., 106: 471 473.