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Soil Sci. Soc. Am. J. 71:829–835doi:10.2136/sssaj2006.0020Received 13 Jan. 2006.*Corresponding author (jnorton4@uwyo.edu).©Soil Science Society of America677 S. Segoe Rd. Madison WI 53711 USAAll rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Traditionally farmed corn (Zea mays L.) fi elds on alluvial fans of the Zuni Indian Reservation in west-central New

Mexico represent some of the oldest agricultural soils in North America (Damp et al., 2002; Homburg et al., 2005). In a south-western North American version of runoff agriculture (Sandor et al., 2002; Sandor et al., 2007), Native American farmers rely on winter moisture stored in alluvium-derived soils for germination and early crop growth and then on summer rain-fall for later growth and grain production (Muenchrath et al., 2002). Soil fertility is not maintained by applications of nutri-ent-supplying amendments, but is thought to be a function of watershed processes that transport and decompose forest-fl oor organic materials from uplands (Cushing, 1920; Norton et al., 1998, 2001).

Properly functioning ephemeral channel-fan systems store and transform runoff, sediments, and nutrients washed from

uplands high in headwater watersheds (Bull, 1997). This process may underlie long-term sustainability of southwestern Native American agriculture but it also protects downstream aquatic systems (Peterson et al., 2001) and creates diverse and produc-tive microclimates in arid and semiarid landscapes. Channel erosion—often called arroyo cutting—prominent across the Southwest during the 20th century, disconnects ephemeral chan-nels from alluvial fans (Cooke and Reeves, 1976; Elliot et al., 1999). This eliminates storage and nutrient cycling functions, drying out and slowly depleting the fertility of existing alluvial soils as water and nutrients are taken up without being replen-ished (Bull, 1997). The Zuni and other southwestern Native American farmers actively manipulate ephemeral stream chan-nels to maintain and enhance depositional processes (Cushing, 1920; Hack, 1942; Nabhan, 1979; Norton et al., 2002).

Norton et al. (2003) established that soil organic matter contents measured along summit to toeslope transects in the study watersheds follow parabolic trends that peak in soils of wooded backslopes, while plant-available N and P increase lin-early and peak in soils of toeslopes. This suggests that organic materials are mixed and decomposed as they move downslope toward agricultural fi elds. Norton et al. (2007) showed that sediment and soil organic matter movement on the hillslopes refl ects the distribution of soils and vegetation and that fre-quent, minor rainfall events may be important drivers of nutri-ent movement and transformation. This study investigated sediment and organic materials in ephemeral stream channels that link hillslopes to alluvial fans where traditional cornfi elds

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.Organic Matter Transformations through Arroyos and Alluvial Fan Soils within a Native American AgroecosystemJay B. Norton*Dep. of Renewable ResourcesUniv. of WyomingLaramie, WY 82071-3354

Jonathan A. SandorDep. of AgronomyIowa State Univ.Ames, IA 50011-1010

Carleton S. WhiteDep. of BiologyUniv. of New MexicoAlbuquerque, NM 87131

Vanissa LaahtyZuni Conservation ProgramPueblo of ZuniP.O. Box 339Zuni, NM 87327

Linked biochemical and fl uvial processes in discontinuous ephemeral streams may sup-port sustained productivity of soils farmed by southwestern Native Americans for ≥3000 yr. Ephemeral stream channels transport forest fl oor litter and soil materials from upland hillslopes to alluvial fans. Improved understanding of how ephemeral streams transport and process forest-fl oor organic materials could improve conservation of ecologically important and productive headwater alluvial fans. We analyzed organic and mineral materials from source to mouth along two ephemeral streams and analyzed suspended sediments from four collection traps in each. Results suggest that decomposition processes differ by reach and fre-quent, low-energy fl ows preferentially transport organic detritus as it decomposes. Processing of organic-rich sediments in canyon reaches is dominated by microbial immobilization (low inorganic N and available P, high C/N ratio). Arroyo reaches receive organic materials chiefl y from upstream so mineralization plays in increasing role as materials are transported and decomposed downstream without fresh inputs. The frequency of fl ow decreases in a down-stream direction as water infi ltrates sandy streambeds. In lower arroyo and fan reaches, inputs of organic-rich sediments are infrequent. Relatively frequent wetting and drying stimulates mineralization of organic materials so concentrations of inorganic N and available P in detri-tus are relatively high. Results suggest that organic-rich sediments processed through ephem-eral streams and deposited on unincised alluvial fans are important in sustaining one of the most productive landscape positions in semiarid regions.

Published online April 5, 2007

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are located. Our objective was to describe how the composi-tion of stream-deposited organic materials and suspended sedi-ments change through ephemeral channels from their source to runoff agricultural fi elds. We hypothesized that, as in the hillslope system, ephemeral streams process organic materials as they transport them toward traditional agricultural fi elds

with increasing proportions of available nutrients nearer the fi elds.

MATERIALS AND METHODSSite Description

We analyzed the properties of organic-rich deposits and suspended sediments along channels from watershed divides to distal alluvial fans in two watersheds above long-term traditional alluvial runoff agricultural fi elds on the Zuni Indian Reservation (Fig. 1 and 2). The Sanchez watershed drains 68 ha near the eastern edge of the reservation and the Weekoty watershed drains 125 ha about 10 km to the northwest. Each of the watersheds lies at about 2300-m elevation and is characterized by steep-walled canyons cut into sandstones and shales of the Gallup Sandstone formation (Anderson et al., 1989; Zschetzsche et al., 2005). Layered shale and sandstone members underlie shallow Entisols on mesa top caprocks; thickly bedded sand-stone creates fall faces; thick, weathered shale underlies Alfi sols on transportational back-slope and colluvial footslope positions; and sandy and silty alluvium underlies Alfi sols on toeslopes and alluvial fans (Fig. 3; Norton et al., 2003; Homburg et al., 2005). Mesas and

hillslopes in the two study watersheds are dominated by pinyon pine (Pinus edulis Engelm.)–juniper (Juniperus spp.)–oak (Quercus gambelii Nutt.) woodlands with appreciable ponderosa pine (Pinus ponderosa P. Lawson & C. Lawson) on upper watershed slopes (Norton et al., 2003). The canyon-fl oor alluvium in each watershed is bisected by an arroyo ranging up to 6 m deep. In each case, the arroyo channel ends

above a runoff agricultural fi eld, near the canyon mouth. Each of the two ephemeral stream sys-tems we studied are divided into three distinct reaches we called canyon, arroyo, and fan (Fig. 2). Canyon reaches are channels with bedrock beds at the foot of steep slopes and escarpments in upper watersheds. This corre-sponds to the “production zone” described by Schumm (1977). Arroyo reaches are deeply incised (>6 m) sections of upper allu-vial fans near the outlets of the channel reaches and correspond to Schumm’s (1977) “transfer zone.” Fan reaches correspond to Schumm’s (1977) deposition zone and are the active alluvial fans where traditional agricul-tural fi elds are located.

Rainfall averages 300 mm annually but is highly vari-able and comes mostly dur-

Fig. 1. Study area location and physiographic provinces of the Southwest.

Fig. 2. Study watersheds showing channel reaches and suspended sediment trap locations.

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ing thunderstorms in July, August, and September (Tuan et al., 1973). Although rainfall at the core of the localized storms can be intense, most of the annual rainfall comes as low-inten-sity, but relatively frequent, events (Balling and Wells, 1990; Norton et al., 2003). The frequent, low-inten-sity rains often generate hillslope run-off that is absorbed in deeper soils of footslopes and toeslopes (Norton et al., 2003). Streamfl ow that just exceeds transmission losses through these sys-tems occurs less than once per year on average, while larger fl ows that inundate alluvial fans are less frequent (Thomas et al., 1997; Norton, 2000; Norton et al., 2002).

Field and Laboratory Procedures

Stream-Deposited Organic MaterialsWe analyzed how fl uvial transport affects forest litter by collect-

ing samples of water-deposited forest fl oor materials in stream chan-nels. Samples were collected each 100 m from channel source (defi ned as the upper end of the longest continuous channel) to distal alluvial fan (see Fig. 2) (samples from each clump of organic material 7.5 m upstream and 7.5 m downstream from the 100-m point were mixed and subsampled). Organic-rich deposits were somewhat scarce in the lower reaches of the alluvial fans, forcing us to collect organic mat-ter samples opportunistically and note locations (as meters from the source) along channel trajectories.

Samples from organic-rich deposits were air dried in the fi eld and then analyzed for concentrations of total C and N in subsam-ples oven dried at 105°C and ground to pass a 76-μm sieve using a Fissions EA1100 dry combustion CNSHO analyzer (Fissions Inst., Milan, Italy). Total P concentrations were determined in similar sub-samples by alkaline oxidation (Dick and Tabatabai, 1977). Available P concentrations were measured by the Olsen extraction method (Olsen and Sommers, 1982). Ammonium- and NO3–N concentra-tions were determined in 2 M KCl extracts using the Berthelot reac-tion for NH4–N (Willis et al., 1993) and nitration of salicylate for NO3–N (Yang et al., 1998).

Suspended SedimentsMovement and transformation of fi ne organic particulate trans-

ported in ephemeral streamfl ows were analyzed by sampling sus-pended sediments in upper canyons and below the three reaches of each ephemeral stream system (Fig. 2). Samples were collected during the summers of 1997 and 1998 in the Weekoty and during 1998 in the Sanchez watershed. Samplers were based on USGS samplers designed to collect water samples during rising stages of runoff events. Each USGS sampler consists of four or more 1-L sample bottles stacked inside 10.16-cm (4-inch) i.d. polyvinyl chloride (PVC) pipe, each with an inlet tube piercing the upstream side of the PVC pipe and a vent tube extending out the top of the pipe. We modifi ed the samplers to fi t the scale of the small channels at our study sites by stacking two 1-L bottles and embedding the encasing PVC pipe verti-cally in the center of the channel bed, leaving about 15 cm exposed.

Inlet tubes were 1 and 5 cm above the channel bed surface. Samples were collected after each runoff event, preserved with dilute phenyl mercuric acetate solution, and allowed to settle in refrigerators at 4°C. The total volume of each sample was recorded and clear super-natants were analyzed for cation concentration by atomic absorption spectrophotometry and anion concentration by ion chromatography. Sediment samples were air dried (oven temperature 60°C), weighed for calculation of sediment concentration, and analyzed for total C, N, and P by methods described above for samples of organic-rich deposits. Samples were generally too small for analysis of mineral N and P fractions or particle size distribution.

Precipitation volume, intensity, and duration were measured only at the Weekoty watershed at a tipping-bucket rain gauge and a CRX-20 data logger (Campbell Scientifi c, Logan, UT) located near sediment trap no. 3 in the Weekoty watershed (Fig. 2).

Concentrations of each measured constituent in stream-depos-ited organic material and suspended sediments were analyzed by regression analysis (SPSS 14.0, Chicago, IL) as functions of distance from the channel source for each watershed separately. Suspended sediment concentration as a function of rainfall intensity and the C/N ratio of organic matter in suspended sediments as a function of sediment concentration were also analyzed by regression analysis for the Weekoty watershed only (where the tipping-bucket rain gauge was located). The signifi cance of each model was tested by ANOVA (SPSS 14.0, Chicago, IL) and reported P values are based on those analy-ses. Ratios, including C/N, available P/total P, NO3–N/total N, and NH4–N/NO3–N, were log10 transformed for analyses. Reported r2 and P values are based on the log10 transformations. Untransformed values are reported on Fig. 4 to 8 and equations are based on those values (calculated with the trendline function in Microsoft Excel).

RESULTSOrganic-Rich Deposits

Regression analyses show that concentrations of total C, N, and P, as well as available N and P, in organic-rich deposits change along distinct parabolic and linear functions through Weekoty and Sanchez fl uvial systems (Fig. 4). Available N concentration, both NH4– and NO3–N (only NO3–N is pre-

Fig. 3. General topography, slope positions, and soils within the three watershed study sites on the Zuni Indian Reservation (from Norton et al., 2003).

832 SSSAJ: Volume 71: Number 3 • May –June 2007

sented), increases distinctly with distance from the source at the Weekoty watershed but not at the Sanchez watershed (Fig. 4d and 4i). Phosphorus contents, both total (Fig. 4c and 4h) and available (Fig. 4e and 4j), follow especially strong parabolic relationships along the channels.

Relationships between the C, N, and P fractions are similar between the two study sites (Fig. 5). Carbon/N ratios are vari-able but decrease linearly (P < 0.05) in a downstream direction along the channels (Fig. 5a and 5e). Available P as a percentage of total P decreases slightly in the upper reach of the Weekoty watershed, but increases steadily (P < 0.01) through the arroyo and fan reaches of both watersheds (Fig. 5b and 5f). Nitrate-N as a proportion of total N increases along a highly signifi cantly trend (P < 0.0001) with distance from the source of the Weekoty

watershed (Fig. 5c) but does not follow a signifi -cant trend in the Sanchez watershed (Fig. 5g). The ratio of NH4– to NO3–N, an indicator of nitrifi cation rates, is relatively high and variable in the canyon reaches of the Weekoty system, but very constant at about 1:1 in the arroyo and allu-vial fan reaches (Fig. 5d and 5h).

Suspended SedimentsNine rainfall events at the Weekoty water-

shed in 1997 and 1998 and four events at the Sanchez watershed in 1998 produced samples in our sediment traps. While each trap received runoff during most of the events, it did not always appear to be the result of continuous fl ow from upper canyons to distal channel fans. Observations during sample collection suggest that fl ow intensity peaks where canyon reaches empty into arroyo reaches. There was consider-able scour at these traps (trap no. 2 at each site; Fig. 2) after several of the events in each water-shed. Transmission losses through the sandy arroyos below trap no. 2 appear to rapidly dimin-ish fl ows. The most distal trap at each site did not receive runoff during several of the events, and during others runoff apparently came from local sheet fl ow. Some the events in each watershed did generate continuous fl ow past all the traps. Most of our samples came from bottles connected to the lower intakes, 1 cm above ground level, and probably represent the very beginning of fl ow at the traps. Samples from both intake depths were essentially identical. They are combined for the data reported here.

Suspended sediment concentrations are highly variable and range from 0.6 to 128 g L−1 without predictable differences between sedi-ment trap locations. Both sediment concentra-tion and variability increase with increasing rainfall intensity (P < 0.10; Fig. 6), but many more of the relatively high-intensity rainfall events we measured yielded higher concentra-tions of suspended sediments than did the lower intensity events. Also, C/N ratios of the sus-pended sediments increase with increasing sedi-

ment concentration (P < 0.0001; Fig. 7). Although sediment concentration in runoff varies greatly among events and trap locations, concentrations of total C, N, and P in the sediments remain relatively constant among events and appear to vary systematically among traps (Fig. 8). Carbon/N ratios in sedi-ments decrease between the upper and lower traps at both sites, with the largest difference occurring between traps no. 2 and 3 at the Weekoty site and traps no. 3 and 4 at the Sanchez site (Fig. 8d and 8h).

DISCUSSIONOrganic Matter Movement and Transformation

The combination of rainfall intensity, sediment concentra-tion, and organic matter and nutrient contents of the sediment

Fig. 4. Composition of organic-rich stream deposits as a function of distance from channel source. Sampling of the Sanchez watershed began approximately 500 m from its source. Weekoty watershed is reported in left column (a–e) and San-chez watershed in right (f–j).

SSSAJ: Volume 71: Number 3 • May –June 2007 833

suggest that relatively frequent, low-intensity runoff events preferentially move organic materi-als with more favorable C/N ratios and higher mineral N and P concentrations. This pattern (materials being moved downslope as they are broken down) was also noted in hillslope soils (Norton et al., 2003) and sediments (Norton et al., 2007). The same pattern is known to be important in organic detritus processing by perennial streams (Boling et al., 1975; Maltby, 1992; Wagener et al., 1998). Our data suggest that dominant processes transforming organic materials vary by reach depending on the amount and composition of materials entering the stream from surrounding slopes.

In upper canyon reaches on relatively level mesa tops, gentle slope processes contribute to conditions that stimulate nutrient immobili-zation in decomposing organic matter. Forest fl oor materials under these mesa-top wood-lands decompose in situ, which, together with lower intensity runoff (because of shorter, fl at-ter slopes) that minimizes disturbance, leads to relatively stable plant and microbial communi-ties, rapid immobilization, and “tight” nutrient cycles (Stark and Hart, 1997; Norton et al., 2003). This is suggested by low available N and P concentrations in the organic-rich deposits of canyon reaches. Gentle runoff on the short, relatively level slopes preferentially moves partly decomposed materials toward channels (Norton et al., 2007). As this material is decomposed and moved downstream into lower canyon reaches, it mixes with large quantities of relatively fresh, high-C-content forest fl oor material from lon-ger, steeper slopes forested by ponderosa pine, Gambel oak, and pinyon–juniper. This infl ux of C-rich for-est litter probably stimulates immobilization in organic-rich deposits in lower canyon reaches (relatively high C/N ratios and low available P/total P). Steep gradients and the conver-gence of many tributaries through these reaches appear to cre-ate intense fl ows, however, even during relatively low-magni-

tude, high-frequency rainfall events. This frequent perturba-tion probably leads to a relatively “open” N cycle suggested by increasing inorganic N concentrations in the deposits.

The infl ux of fresh material from side slopes stops abruptly as channels emerge from canyons and enter arroyos cut through alluvial valley fi lls. Runoff intensity peaks at this transition from

Fig. 5. Relationships between total and available nutrients and stream course position in organic-rich stream deposits. Weekoty watershed is reported in left column (a–d) and Sanchez watershed in right (e–h).

Fig. 6. Sediment concentration as a function of rainfall inten-sity as measured at suspended sediment traps and tipping bucket rain gauge in the Weekoty watershed.

Fig. 7. Carbon/N ratio of sediment organic matter as a function of sediment concentration at suspended sediment traps in the Weekoty watershed.

834 SSSAJ: Volume 71: Number 3 • May –June 2007

steep bedrock channels to more gently sloping alluvial channels. The relatively high stream power is refl ected in low C, N, and P concentrations and high C/N ratios in suspended sediments (low-density, decomposed organic materials are preferentially removed by the fl owing water). Essentially, fl ows emerge from the forested bedrock canyon rich with both suspended sediments and organic materials. Sediments are deposited as stream gradi-ent decreases, but organic materials are carried farther down-stream and deposited as transmission losses diminish fl ows. Each fl ow mixes, moves, and sorts the organic-rich materials, causing increasing mineralization rates through arroyo reaches. The pre-dominance of low fl ows from minor rains preferentially moves fi ne, low C/N ratio particles downstream.

Alluvial fans receive infl uxes of coarse organic-rich mate-rials only during low-frequency, intense runoff events that

deposit loads of sandy and loamy sediments across valley fl oors. Some of the more frequent low-intensity runoff events also move across alluvial fans, but deposit only fi ne sediments and relatively highly decomposed fi ne-particu-late organic materials. This combination of wetting by frequent low-intensity rains, occa-sional infl ux of organic particles with low C/N ratios, and lack of coarse forest detritus infl ux contributes to increasing mineralization rates in organic-rich deposits with distance through the alluvial fans. Sala and Lauenroth (1982) emphasized the importance of frequent small rainfall events in driving organic matter dynam-ics in semiarid soils.

Figure 5d suggests that nitrifi cation in organic-rich deposits of the forested canyon reach may be inhibited. White (1994) described a mechanism for this type of inhibition in south-western conifer forests by volatile organic com-pounds called monoterpenes. This effect appears to diminish as organic materials are moved far-ther from their source on the ponderosa pine forested slopes, possibly because the volatile compounds are lost as materials decompose.

Differences between mineral N concentrations in organic-rich deposits from the Weekoty and Sanchez watersheds (Fig. 4), along with similarities in organic C, total N, and total P concentrations seem to suggest greater N immobilization in all the Sanchez samples and may refl ect differences in sam-pling times or inadvertent differences in handling of samples (i.e., the Sanchez samples were wetter at sampling and humid weather at the study site caused them to air dry slowly).

CONCLUSIONSOur results emphasize the importance of

hydrological connectivity that transports and transforms watershed soil and organic materials, which replenish alluvium-derived soils that have important cultural, ecological, and hydrological functions. Ephemeral storm-water fl ows that scour channels and transport and deposit fresh sediments are important drivers of hydrological

functions of alluvial fans. These relatively high-impact events shape the fl uvial system and have received a great deal of atten-tion. Our results show that minor rainfall and runoff, which occur much more frequently, may drive biochemical processes that link forested watersheds to alluvial fans. In contrast to dra-matic, bedload-transporting events that have multiyear average return intervals, minor low-energy fl ow events generally occur multiple times during the summer rainy season. These minor events repeatedly moisten, mix, and sort channel and hillslope materials as they move them downstream in a stepwise fashion. This results in mineralization rates that increase downslope through hillslope and fl uvial systems and in accumulation of decomposed, nutrient-rich organic materials in lower reaches where traditional runoff fi elds are located.

Fig. 8. Concentrations of organic C, total N, and total P in suspended sediment as a function of distance from channel source. Weekoty watershed is reported in left column (a–d) and Sanchez watershed in right (e–h).

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ACKNOWLEDGMENTSThis work was funded by National Science Foundation Grant no. DEB-9528458. We are indebted to the Zuni Sustainable Agriculture Project, the Zuni Conservation Project, and the Zuni Tribe. We thank Jeff Homburg, Todd Carlson, Marnie Criley, and Clara Wheeler for laboratory analysis and Troy Lucio, Lindsay Quam, and participants in Zuni’s Job Training Partnerships Act program for fi eld assistance. We are grateful to Tom DeLuca, Urszula Norton, and Stephen Siebert for technical advice and editorial review, and to the research team, including Deborah Muenchrath, Stephen Williams, Pete Stahl, and Mark Ankeny.

REFERENCESAnderson, O.J., S.G. Lucas, D.W. Love, and S.M. Cather. 1989. Southeastern

Colorado Plateau: New Mexico Geological Society 40th Annual Field Conference. 28 Sept.–1 Oct. 1989. New Mexico Geol. Soc., Albuquerque.

Balling, R.C.J., and S.G. Wells. 1990. Historical rainfall patterns and arroyo activity within the Zuni River drainage basin, New Mexico. Ann. Am. Assoc. Geograph. 80:603–617.

Boling, R.H., Jr., E.D. Goodman, J.A. Van Sickle, J.O. Zimmer, D.W. Cummins, R.C. Petersen, and S.R. Reice. 1975. Toward a model of detritus processing in a woodland stream. Ecology 56:141–151.

Bull, W.B. 1997. Discontinuous ephemeral streams. Geomorphology 19:227–276.Cooke, R.U., and R.W. Reeves. 1976. Arroyos and environmental change in

the American Southwest. Oxford Univ. Press, New York.Cushing, F.H. 1920. Zuni breadstuff. Museum of the American Indian, Heye

Foundation, New York.Damp, J.E., S.A. Hall, and S. Smith. 2002. Early irrigation on the Colorado

Plateau near Zuni Pueblo, New Mexico. Am. Antiq. 67:665–676.Dick, W.A., and M.A. Tabatabai. 1977. An alkaline oxidation method for

determination of total phosphorus in soils. Soil Sci. Soc. Am. J. 41:511–514.Elliot, J.G., A.C. Gellis, and S.B. Aby. 1999. Evolution of arroyos: Incised

channels of the southwestern United States. p. 153–185. In S.E. Darby and A. Simon (ed.) Incised river channels. John Wiley & Sons, New York.

Hack, J.T. 1942. The changing physical environment of the Hopi Indians of Arizona. p. 1–85. In Papers of the Peabody Museum of American Archaeology and Ethnology. Vol. 35(1). Harvard Univ. Press, Cambridge, MA.

Homburg, J.A., J.A. Sandor, and J.B. Norton. 2005. Anthropogenic infl uences on Zuni agricultural soils. Geoarchaeology 20:661–693.

Maltby, L. 1992. Detritus processing. p. 331–353. In P. Calow and G.E. Petts (ed.) The rivers handbook. Vol. 1. Blackwell Sci. Publ., Oxford, UK.

Muenchrath, D.A., M. Kuratomi, J.A. Sandor, and J.A. Homburg. 2002. Observational study of maize production systems of Zuni farmers in semiarid New Mexico. J. Ethnobiol. 22:1–33.

Nabhan, G.P. 1979. The ecology of fl oodwater farming in arid southwestern North America. Agro-Ecosystems 5:245–255.

Norton, J.B. 2000. Agroecology, hydrology, and conservation of ephemeral streams and alluvial fans, Zuni Pueblo, New Mexico. Publ. AAT 9993970. Univ. of Montana, Missoula.

Norton, J.B., F.J. Bowannie, P. Peynetsa, W. Quandelacy, and S.F. Siebert. 2002. Native American methods for conservation and restoration of

semiarid ephemeral streams. J. Soil Water Conserv. 57:250–258.Norton, J.B., R.R. Pawluk, and J.A. Sandor. 1998. Observation and experience

linking science and indigenous knowledge at Zuni, New Mexico. J. Arid Environ. 39:331–340.

Norton, J.B., R.R. Pawluk, and J.A. Sandor. 2001. Farmer–scientist collaboration for research and agricultural development on the Zuni Indian Reservation, New Mexico, USA. p. 107–120. In W.A. Payne et al. (ed.) Sustainability of agricultural systems in transition. ASA Spec. Publ. 64. ASA, CSSA, and SSSA, Madison, WI.

Norton, J.B., J.A. Sandor, and C.S. White. 2003. Hillslope soils and organic matter dynamics within a Native American agroecosystem on the Colorado Plateau. Soil Sci. Soc. Am. J. 67:225–234.

Norton, J.B., J.A. Sandor, and C.S. White. 2007. Runoff and sediments from hillslope soils within a Native American agroecosystem on the Colorado Plateau. Soil Sci. Soc. Am. J. 71:476–473.

Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. p. 403–430. In A.L. Page et al. (ed.) Methods of soil analysis. Part 2: Chemical and biological methods. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.

Peterson, B.J., W.M. Wollheim, P.J. Mulholland, J.R. Webster, J.L. Meyer, J.L. Tank et al. 2001. Control of nitrogen export from watersheds by headwater streams. Science 292:86–90.

Sala, O.E., and W.K. Lauenroth. 1982. Small rainfall events: An ecological role in semiarid regions. Oecologia 53:301–304.

Sandor, J.A., J.B. Norton, J.A. Homburg, D.A. Muenchrath, C.S. White, S.E. Williams, C.L. Havener, and P.D. Stahl. 2007. Biogeochemical studies of a Native American runoff agroecosystem. Geoarchaeology (in press).

Sandor, J.A., J.B. Norton, R.R. Pawluk, J.A. Homburg, D.A. Muenchrath, C.S. White, S.E. Williams, C.I. Havener, and P.D. Stahl. 2002. Soil knowledge embodied in a Native American runoff agroecosystem. In Trans. World Congr. of Soil Sci., 17th, Bangkok, Thailand (CD-ROM). 14–21 Aug. 2002.

Schumm, S.A. 1977. The fl uvial system. John Wiley & Sons, New York.Stark, J.M., and S.C. Hart. 1997. High rates of nitrifi cation and nitrate

turnover in undisturbed coniferous forests. Nature 385:61–64.Thomas, B.E., H.W. Hjalmarson, and S.D. Waltemeyer. 1997. Methods

for estimating magnitude and frequency of fl oods in the southwestern United States. Water Supply Pap. 2433. U.S. Geol. Surv., Denver, CO.

Tuan, Y., C.E. Everard, J.G. Widdison, and I. Bennett. 1973. The climate of New Mexico. State Planning Offi ce, Santa Fe.

Wagener, S.M., M.W. Osgood, and J.P. Schimel. 1998. Rivers and soils: Parallels in carbon and nutrient processing. BioScience 48:104–109.

White, C.S. 1994. Monoterpenes: Their effects on ecosystem nutrient cycling. J. Chem. Ecol. 20:1381–1406.

Willis, R.B., G.J. Schwab, and C.E. Gentry. 1993. Elimination of interferences in the colorimetric analysis of ammonium in water and soil extracts. Commun. Soil Sci. Plant Anal. 24:1009–1019.

Yang, J.E., E.O. Skogley, B.E. Schaff, and J.J. Kim. 1998. A simple spectrophotometric determination of nitrate in water, resin, and soil extracts. Soil Sci. Soc. Am. J. 62:1108–1115.

Zschetzsche, S.A., S.S. Park, C.E. Montoya, C.L. Chavez, J.K. Melhus, and J. May. 2005. Soil survey of McKinley County area, New Mexico. NRCS, Washington, DC.

Soil Science Society of America Journal -- About the Cover (May 2007, 71, (3))

About the Cover

This issue's cover: These images show corn (Zea mays L.) grown on alluvium-derived soils of the Zuni Indian Reservation in New Mexico. Archaeological and historical evidence suggests that fields like the one in the background image have been farmed more or less continuously for over 1000 years. In traditional non-irrigated crop production in this semiarid environment, Zuni farmers do not use soil amendments but rely on watershed transport and deposition processes for productivity maintenance and renewal. Please see “Organic matter transformations through arroyos and alluvial fan soils within a Native American agroecosystem” by J.B. Norton, J.A. Sandor, C.S. White, and V. Laahty, pages 829–835.

http://soil.scijournals.org/content/vol71/issue3/cover.shtml [2/1/2008 8:49:53 AM]