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Chapter 4 Geology, Climate, land, and Water Quality

Douglas G. Fox USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado

Roy Jemison USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Flagstaff, Arizona

Deborah Ulinski PoHer USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Albuquerque, New Mexico

H. Maurice VaieH University of New Mexico, Albuquerque, New Mexico

RayWaHs U.S. Geological Survey, Fort Collins, Colorado

GEOLOGY small extensions into Torrance, Santa Fe, Cibola, Rio Arriba, and Catron counties. The Middle Rio Grande is part of the chain of struc­ The principal landforms of the Middle Rio Grande tural basins, known as the Rio Grande depression, include: (1) pediments, (2) dissected slopes, (3) fault that extends from the San Luis Valley in Colorado to scarps, (4) terraces, (5) alluvial slopes, (6) alluvial fans El Paso, Texas, and through which the Rio Grande and cones, (7) major stream floodplains or valley flows (Chapin and Seager 1975). Bryan (1938) is cred­ bottoms, (8) eolian blankets and dunes, and (9) vol­ ited with designating this reach as the Rio Grande canic fields, ridges, and cones (Kelly 1977; "depression," because of his early research and the Fitzsimmons 1959). level of understanding he provided on the geology of the region. This area is also known as the Rio CHANNEL AND BASIN DESCRIPTIONS Grande "rift," a term coined by Kelly (1952), based on his belief in the possibility of significant longitu­ Lagasse (1981) described the channel of the Middle dinal displacement in the "trough" or depression Rio Grande as a shifting sand substratum with low, (Baltz 1978). The Rio Grande rift will be the term used poorly defined banks. The floodplain contains a mix­ in this discussion. ture of cottonwood, willow, Russian olive, and The Middle Rio Grande, as presented in this chap­ saltcedar, which together form a dense growth of ri­ ter, includes the area of the Rio Grande rift between parian woodland known as bosque interspersed with Cochiti Dam, southwest of Santa Fe and Elephant pasture and cultivated land. The configuration of the Butte dam, south of Socorro, New Mexico (refer to river may be described as one of low sinuosity with Fig. 2 in Chapter 1). The linear distance between these some straight reaches. Formation of sediment bars locations is about 257 km. The Middle Rio Grande in the channel during low-flow periods and, in par­ includes the four principle basins of Albuquerque, ticular, during the recession of flood flows, together Socorro, La Jencia, and San Marcial (Fig. 1). The with rapid growth of vegetation, generally determine Middle Rio Grande is located in the counties of the channel configuration within the levees. The Socorro, Valencia, Bernalillo, and Sandoval, with slope of the river drops about 0.95 m/km from Cochiti

52 106' 105' + base level and limit upstream and downstream river response of the Rio Grande.

Albuquerque Basin The Albuquerque Basin is the largest and most important basin in the Middle Rio Grande. The im­

36'+ portance of this basin is that it houses the aquifer from which most of the city of Albuquerque draws water. The geology of the Albuquerque Basin has been the subject of numerous studies and publica­ tions (Thorn et ~l. 1993; Kelly 1977). Hawley and Haase (1992) present the status of the geology as it relates to the hydrology of this area in "Hydro­ geologic Framework of the Northern Albuquerque 35·+ +35· .c c .c Basin." Thorn et al. (1993) summarized much of o o" o Hawley and Haase's work in "Geohydrologic Frame­ U I work and Hydrologic Conditions in the Albuquer­ que Basin, Central New Mexico." The discussion pre­

Rio Grande sented here on the Albuquerque Basin is edited from depression the work of Thorn et al. (1993), except where noted. Of note is the conclusion from these recent studies of 34'+ groundwater: that the water supply for the City of Al­ buquerque and surroundings is considerably more re­ stricted than earlier studies suggested. The Albuquerque Basin,located in the central part of the Rio Grande rift, is the third largest basin in the rift. The basin extends about 100 miles in length from north to south and about 35 miles in width, with an 33·+ 2 area of about 7,925 km . The northern boundary of the Albuquerque Basin, and the Middle Rio Grande,

.J.. are defined by the Nacimiento and Jemez uplifts. The 106' Nacimiento Uplift is characterized by Precambrian plutonic and metamorphic rocks overlain by Paleo­ zoic strata. Cenozoic volcanic rocks form the Jemez Figure 1.-Tectonic map of Rio Grande rift system (Kelly 1977). uplift (Hawley and Haase 1992). The topographically prominent eastern boundary is the eastward-tilted to just below Albuquerque, and about 0.76 m/km fault blocks of the Sandia, Manzano, and Los Pinos from just below Albuquerque to the confluence of uplifts; the Sandia uplift is the largest and highest. the Rio Puerco. Within the unstabilized floodway, These three uplifted areas are composed of Precam­ the channel has virtually no banks, and the bed of brian plutonic and metamorphic rocks uncon­ the river is at or above the level of areas outside the formably overlain by Paleozoic limestone and sand­ levees due to sediment deposition between the stone (Hawley and Haase 1992). The southern bound­ levees. ary is defined by the Joyita and Socorro Uplifts. This The Middle Rio Grande is broken by short can­ area, often referred to as the "San Acacia constric­ yons or narrows at San Felipe, Isleta, and San Aca­ tion," is formed by the convergence of the eastern cia, which in turn define the subvalleys or basins of and western structural boundaries of the Albuquer­ Santo Domingo, Albuquerque, Belen, and Socorro. que Basin. The Ladron and Lucero uplifts define the The diversion dams at Angostura, north of the Jemez southwestern boundary. Precambrian granite and River confluence and Isleta, midway between Albu­ metamorphic rocks compose the Ladron Uplift. The querque and Belen, act as "geologic" controls of river westward-titled Lucero uplift is composed of Paleo-

53 zoic limestone, sandstone, and shale capped by late series of river incision and backfilling episodes; the Cenozoic basalt flows (Hawley and Haase 1992). The latest cut and fill episode of the Rio Grande and Rio topographically subdued northwestern boundary is Puerco systems produced the channel and floodplain defined by the Rio Puerco Fault Zone. deposits of the present inner valley (Hawley and The fill material in the Albuquerque Basin is mostly Haase 1992). For the last 10,000 to 15,000 years, the Cenozoic fill deposits of the Santa Fe Group. The river valleys have been aggrading due to tributary Santa Fe Group was deposited during the middle input of more sediment than the regional fluvial sys­ Miocene to early Pleistocene (15 to 1 Ma). During that tem can remove. This young valley fill, as much as time the Albuquerque Basin received alluvial sediment 61 m thick, functions as a shallow source of water from the adjacent highlands and fluvial sediments from and as a connection between the surface-water sys­ Northern New Mexico and southern Colorado. The tem and the underlying Santa Fe Group (Hawley and current sedimentary sequence is intertonguing basin­ Haase 1992). I floor fluvial deposits and piedmont-slope alluvial de­ posits. Within the Albuquerque area, the source for Socorro Constriction the piedmont-slope alluvial deposits was the Sandia Mountains east of the City; they provided, for the The Socorro Basin or constriction as defined by most part, weathered granitic and limestone mate­ Kelly (1952) extends about 64 km from the San Aca­ rial to the basin. The fluvial deposits consist of a va­ cia channel on the north to the San Marcial basin on riety of material characteristic of the geology north the south. South of the Albuquerque Basin there is, of the Albuquerque Basin, including volcanic rock in addition to a pronounced narrowing of the Rio fragments from volcanic centers north and west of Grande rift, a marked change in the structural align­ the Albuquerque Basin. ment of the bordering uplifts. Furthermore, volcanic Hawley and Haase (1992) divided the Santa Fe rocks are prominent especially along the west side Group and post-Santa Fe Group deposits into four of the depression. The Socorro Channel is the main hydrostratigraphic units and 10 lithofacies units. The linkage of the Albuquerque Basin with the San hydrostratigraphic units consist of major valley and Marcial basin through this constriction. The channel basin-fill units that are grouped on the basis of ori­ lies between the Joyita uplift on the east and the gin and age of a stratigraphic sequence of deposits. Socorro uplift on the west. The Rio Grande rift along Examples include basin-floor playa, ancestral river this channel is only 8 to 16 km wide. Pre-Cambrian valley, alluvial-fan piedmont, and present river val­ rocks are at the surface locally in the bordering up­ ley depositional environments. Time-stratigraphic lifts (Kelly 1952). Work by Bruning (1973) has shown classes include units deposited during early, middle, that the Socorro Basin is actually part of a structure and late stages of basin filling (lower, middle, and known as the Popotosa Basin which is almost 64 km upper parts of the Santa Fe Group deposits, respec­ wide. Extensive late Tertiary to Quaternary erosion tively). Post-Santa Fe Group valley and basin-fill surfaces are developed on both sides of the Rio deposits consist of channel and floodplain deposits Grande in the area of the Socorro constriction. beneath the modern inner valley or preserved as al­ The basin fill in this area is part of the Popotosa luvial terraces (Hawley and Haase 1992). The 10 Formation, which is part of the Santa Fe Group lithofacies represent different depositional settings, (Chapin and Seager 1975; Baldwin 1963). Denny each recognizable by characteristic bedding and com­ (1940) and Bruning (1973) provide in-depth descrip­ positional properties having distinctive geophysical, tions of the Socorro Basin. In addition to fan, playa, geochemical, and hydrologic characteristics (Hawley and transitional facies (plus interbedded volcanic and Haase 1992). Also dispersed throughout the Santa rocks), the Popotosa Formation contains strikingly Fe Group are mafic volcanic flows and ash beds. different compositional facies. The bulk of the unit Thickness of the Santa Fe Group ranges from less consists of reddish, well-indurated volcanic conglom­ than 2,400 to greater than 3,000 feet along the mar­ erates composed mainly of clasts of basaltic ande­ gins of the basin to 14,000 feet in the central part of sites and ash-flow tuffs derived from the upper part the basin. Santa Fe Group deposition ceased about of the Datil volcanic section and from the La Jara Peak 1 million years ago when the Rio Grande and Rio Basaltic Andesite (Chapin and Seager 1975). Puerco started to cut their valleys (Hawley and Haase The Socorro area and the Las Cruces area are 1992). Post-Santa Fe units were deposited during a anomalous. They are the only areas along the Rio

54 Grande rift where horsts have been elevated through along the Rio Puerco drainage is a series of volcanic several thousand feet of late Cenozoic sedimentary plugs that form prominent peaks above the softer fill near the centers of basins. The combination of Cretaceous sediments (Fitzsimmons 1959). It is as­ thin-skinned distension, high heat flow, and other sumed that the tops of the plugs represent former geophysical anomalies suggests the possibility of positions on the Rio Puerco Valley floor, and that the major intrusions into the rift structure (Chapin and Mesozoic bedrock (shales and sandstones) and allu­ Seager 1975). vial material through which the basalt was extruded were subsequently stripped away by the river (Slavin San Marcial Basin 1991). The Rio Puerco is presently in a phase of incising South of the Socorro Basin constriction the Rio in its northern reaches. Photographic evidence from Grande depression again widens into an irregular the late 1880s indicates that the river has incised up basin about 48 km long and 16 to 24 km wide. It is to 15 m (50 ft) in 100 years, an extremely rapid inci­ terminated on the south by the Pankey Channel sion rate. Paleochannels within the walls of the river's which connects it with the Engle Basin to the south­ channel indicate that it has undergone many cycles west. The main axis of the San Marcial Basin trends of cutting and filling. It is possible that the incision essentially south-southwest and coincides with the of the Mesozoic shales and alluvial material sur­ Rio Grande. It is bounded on the east by a low edge rounding the Puerco necks was similarly rapid, and of the Jornada del Muerto that lies to the east. This that an extraordinarily fast base-level change is re­ border is here termed the San Pascual Platform, and corded in the surfaces of the Rio Puerco valley. It is may be a sort of sub-alluvial bench surmounted by conceivable that 400 m or more (>1,312 ft.) of bed­ local basalt flows. The sub-alluvial bench of Santa Fe rock and alluvial material were removed over a very sediments probably does not connect with deep short span of time (e.g., tens of thousands to only Pliocene basins in the Jornada del Muerto. The west­ thousands of years, based on the above incision rate ern border is more complicated and marked by the for the alluvial material eroded over the past 100 in-echelon Socorro, Magdalena, and San Mateo up­ years). Even if the erosion of 400 to 500 m (1,312- lifts. The intervening troughs or down-thrown parts 1,640 ft.) of material has occurred over as much as of the fault blocks merge with the San Marcial basin the last 2.2 million years, these postulated incision and appear to be embayments from the latter. The rates may force a reconsideration of previously held extensive, although much dissected, erosion surface notions that geologic processes occur slowly over that exists on both sides of the Rio Grande in the San long periods of time (Slavin 1991). Marcial Basin is largely cut upon slightly deformed The general features of the landscape as we see Santa Fe beds (Kelly 1952). them today began to appear in the Cretaceous as a consequence of incipient Laramide deformation. The first deformation may have been by warping, but The Rio Puerco Drainage faulting soon followed. Mountainous areas formed The Rio Puerco drainage is a major drainage that to the north and the Rio Grande depression began to merges with the Rio Grande south of Albuquerque. appear on the east in the middle Tertiary. Erosion of The Rio Puerco Basin is more than 200 km long, en­ the highlands caused filling of the basins and, as the compassing approximately 19,036 km2 straddling mountains were worn down, erosion surfaces devel­ the boundaries among the Colorado Plateau, South­ oped arroyos and edges of older and younger beds ern Rocky Mountains, and Basin and Range physi­ were beveled. Subsequent uplift has caused streams ographic provinces. The upper portions of the drain­ to cut into these surfaces and to initiate at lower lev­ age basin are under lain by bedrock, whereas the els new erosional surfaces that have not yet had suf­ middle and lower portions are underlain by thick, ficient time to become large regional features. Fault­ semi-consolidated deposits in the Albuquerque struc­ ing and accompanying volcanic eruptions have oc­ tural basin. Although most of the drainage basin is curred throughout the Tertiary and Quaternary. less than 2,000 m above sea level, the headwaters lie Lavas intercalated between basin-filling sediments in the Nacimiento Mountains (up to 3,176 m), the and faulted lavas, and basin sediments attest to con­ Zuni Mountains (2,281 m), and Mount Taylor (3,345 tinued and contemporaneous faulting, sedimenta­ m) (Popp et al. 1988). A principal erosional feature tion, and volcanic activity (Fitzsimmons 1959).

55 The major landscape features of the Rio Puerco are nel. The dynamics of the Rio Puerco arroyo system sloping valley margins commonly cut into bedrock will be discussed in greater detail below. or in semi-consolidated basin fill. The valley floor is underlain by thick alluvial deposits and the incised HUMAN ACTIVITIES, GEOLOGY, axial stream channel. The Rio Puerco and its major AND THE RIO GRANDE tributaries have developed distinct geomorphic fea­ tures within confined arroyo walls that range from 8 Over 10,000 years of human occupation is pre­ to 13 m high and 145 to 245 m wide (Popp et al. 1988). served in the Rio Grande rift. This occupation was Love et al. (1983) and Shepherd (1976) described the and continues to be intimately related to the geologi­ inner channel as a complex of meanders, straight cal processes. The rifting that created the Rio Grande reaches, and slightly arcuate reaches. The inner chan­ trough concentrated the runoff and created a drainage nel and floodplain include sandbars and ripple corridor and a perennial water source (Ware 1984). marked surfaces along the floor, slightly finer-grained The rift almost certainly influenced the seasonal sandbars along the margins of the inner channel natu­ movements of early hunters and gatherers in north­ rallevees along the outer margins, and coppice dunes. ern New Mexico. The region's first PaleoIndian in­ The Rio Puerco is an ephemeral stream for most of habitants were undoubtedly drawn to the water its length and flows only in direct response to rain or source, as were the herds of Pleistocene animals they snowmelt. This stream is infamous for large dis­ hunted. As water became increasingly scarce during charges and high sediment loads. It has been esti­ the millennia-long droughts that followed the close mated that the Rio Puerco contributes more than 50 of the Pleistocene, the river exerted an important in­ percent of the sediment load to the Rio Grande in fluence on settlement patterns and seasonal popula­ central New Mexico while carrying less than 16 per­ tion movements. cent of the water (Waite et al. 1972; Popp and Laquer The rift concentrated important resources other 1980). The Rio Puerco is also highly mobile. Studies than water. Volcanism associated with rifting pro­ of the lower channel (Young 1982) determined that duced obsidian for stone tools, altered land forms, more than 90 percent of the lower channel has shifted and created elevations, ecological diversity, and a laterally since 1954. In this same time, the channel greater variety of wild plant and animal resources. changed from being relatively wide with low banks The floodplain of the Rio Grande eventually attracted and unvegetated in the 1930s to relatively narrow farming settlements. When large areas of the Colo­ with high banks in the 1980s. rado Plateau were abandoned by prehistoric farm­ The lower Rio Puerco is a losing stream, that is, it ers during the first centuries of the present millen­ loses water to its bed. A flow of as much as 0.14 m3/s nium, many of those who were displaced migrated at the stream gauge along Highway NM-6, west of to the rich bottomlands of the Rio Grande and its Los Lunas, is lost to seepage and evaporation before tributaries, where there was perennial stream flow it reaches the stream gauge at Bernardo (Heath 1983). and longer growing seasons (Ware 1984). In this reach west of Belen, the permanent water table is 10-13 m below the base of the modern channel, The Effect of Dam Construction on the but there are seasonally fluctuating perched water Middle Rio Grande tables on clay layers within the alluvium above the permanent water table. These perched water lenses Dams were constructed across the Rio Grande at tend to be recharged from the Rio Puerco when it is Elephant Butte, Cochiti, Angostura, and Isleta to con­ flowing on loose sand and can be depleted by seep­ trol river flow for irrigation, flood control, and sedi­ age to lower levels and by transpiration by tamarisks ment detention. Studies near Elephant Butte and and willows. Cochiti dams have shown that these dams have had The channel shape of the lower Rio Puerco reflects significant effects on the Rio Grande channel above repeated attempts at adjustment to extremely vari­ and below the locations of the dams. able flows and an extremely high sediment load. Flows much larger than bankfull tend to scour the Elephant Butte Dam base of the channel and the floodplain locally. Smaller Elephant Butte Dam, completed in 1916, was built flows tend to build sand bars attached to both sides to provide continuous and regulated river flow to of the channel and to aggrade the floor of the chan- the agricultural districts downriver from the dam.

56 The response of the Rio Grande channel, below the collected from 1936 to 1941, along the course of the dam, was monitored from 1917 to 1932. After the clo­ Rio Grande from Cochiti Dam to the head of Elephant sure of the dam there were two primary sources of Butte Reservoir, indicated that the average annual sediment for flows through the Rio Grande below increment of sediment added to the channel was the dam: riverbed scour by the clear water released about 15 cubic hectometers (Happ 1948). About half from the reservoir, and tributary inflow. The mate­ of that settled in the 23 km stretch immediately above rial derived from the steep-sloped, ephemeral tribu­ the head of the lake (Fitzsimmons 1955). This will be tary channels (arroyos) ranged from sand and gravel discussed further in the section on arroyo dynamics. to boulder size, and was deposited in a fan or delta at the tributary outlet, where it was available for trans­ Cochiti Dam port by main channel flows. Scour of the river channel Cochiti Dam was built in November 1973. Cochiti itself by clear water released from storage was consid­ Dam permits control of the main stem of the Rio ered to be the principal sediment source, particularly Grande above the Middle Valley. This dam was origi­ in the sand size range. It was expected that this would nally intended for flood control and sediment con­ remain the primary source of sands so long as the read­ trol only. Multipurpose development objectives in­ justment of the river channel to the changed conditions cluded arresting damaging flood flows, retaining of clear regulated flows continued (Lagasse 1981). sediment, and inducing degradation. Concern for Where an arroyo or tributary deposited directly into recreation led to a modification of the authorization, the main channel in a valley section below Elephant and a permanent pool has been formed. Butte Dam, the coarser material, which was beyond the The floodway between Cochiti and Bernardo is competence of regulated main channel flows, forced generally confined by levees and averages 458 m the Rio Grande channel away from the tributary outlet wide through intensively developed rural and urban through erosion of the opposite bank. Where the tribu­ areas. The Bureau of Reclamation and the Corps of tary channel entered the Rio Grande in a canyon sec­ Engineers installed jetties in this reach, varying the tion, the deposits of heavier debris created obstructions density and widths as guided by hydraulic model stud­ in the river channel, causing backwater above and rap­ ies. Design channel widths decrease in a downstream ids over the tributary delta. Regulated high flows were direction from 274 m in the Cochiti reach to 168 m at not of sufficient magnitude or duration to transport this Bernardo. Operated in conjunction with upstream coarser material downstream. Thus, arroyo and tribu­ reservoirs, this channel work was intended to reverse tary deposits created base-level controls along the main­ the trend of aggradation and to allow the channel to stream and strongly influenced the processes of degra­ degrade back to essentially a 1936 condition. dation and aggradation (Lagasse 1981). Before construction of Cochiti Dam and upstream An analysis of the effects of clear-water scour along tributary dams, the flood way of the Rio Grande was the Rio Grande below Elephant Butte Dam using aggrading at rates as high as 0.6 m every 50 years successive cross sections indicated that there was a near Albuquerque and as much as 5 m in 50 years lowering of the river channel near the dam of ap­ near San Marcial. The ultimate result of aggradation proximately 0.6 m during the first 15 years of reser­ is an increase in the height of the river bed or flood­ voir operation (Lagasse 1981). way above the adjacent flood plain. By 1960, the river The Rio Grande above Elephant Butte Reservoir is channel near Albuquerque was 1.8 to 2.4 m above aggrading. The cause of this is, in part, the raising of the elevation of lands outside the levees. Woodson effective local base level by delta building in the lake. and Martin (1963) provide an excellent summary of This is not the only cause of aggradation, however, the effects of the Rio Grande Comprehensive Plan and probably not the most important. Arroyo cut­ on the river regime throughout the middle valley of ting, contributing great qualities of sediment from the Rio Grande. As of 1963 it was apparent that the tributary streams, may be the most significant pro­ "Rio Grande within the Middle Valley is still an ag­ cess of all. Other causes are: windblown silt, increased grading stream, and construction of the floodway has loss of water because of domestic and irrigation us­ not halted aggradation. Aggradation has occurred in age, and prevention of flooding by artificial levee amounts varying from practically zero in the Cochiti building, thus preventing a natural discharge of de­ Division at the upstream end of the valley to a maxi­ bris flow over the floodplain and consequently con­ mum of about 0.01 m per year in the Albuquerque fining all aggradation to the channel. Measurements Division" (Woodson and Martin 1963: 359).

57 Lagasse (1981) reported on a qualitative analysis During the extended low-flow period following of the effects of the construction of the Cochiti Dam closure of Cochiti Dam, the well-developed gravel on the Rio Grande. In the Cochiti to Isleta reach, sedi­ armor above Angostura and stabilization of point ment inflow from arroyos and tributaries has domi­ bars and closure of chute channels by vegetation nated the response of the main-stem Rio Grande to "locked" the Rio Grande into the low-flow channel altered conditions of flow and sediment transport pattern. Flows in excess of 170 m 3 / s were required following closure of Cochiti Dam. Regulated flows to initiate a transition to a high-flow channel pattern. of the post-dam period generally are not capable of To prevent the development of a channel pattern transporting the coarser sediment load and volume "locked in" to low-flow conditions and recurrence of material carried to the main stem by arroyos and of problems associated with the April- July 1979 sus­ tributaries. Between Cochiti and the Jemez River, tained high flows, releases from Cochiti Dam of about deltaic deposits at the confluence of tributaries and 170 m3 / s should be scheduled annually. arroyos are sufficiently stable to influence planform, Processes set in motion by the closure of Cochiti to create reaches of base-level control, and to influ­ Dam will eventually limit the effectiveness of the ence the processes of aggradation, degradation, and existing jetty fields. In the post-dam period less fre­ armoring on the Rio Grande. quent inundation of floodplain areas, a reduction in The reach immediately below the dam from Cochiti sediment supply from major source areas such as the to Galisteo Creek had essentially completed adjust­ Jemez River, and degradation and armoring in the ment to the closure of Cochiti Dam by 1975. Degra­ upstream channel all dictate against the installation dation and armoring progressed downstream of new jetty fields for channel stabilization. As the through the San Felipe reach, and by summer 1979 Kellner jetties become a less effective device for chan­ the upper portion of the study reach had attained a nel stabilization in the post-dam period, protection level of stability yet to be achieved in the study area of the banks by vegetation will become increasingly below the Jemez River. The Cochiti to Isleta reach of important. Control of the beaver community along the Rio Grande will continue to respond to the clo­ the banklines may be required, and traditional flood­ sure of Cochiti Dam. Even the upstream reach that fighting techniques that involve cutting of trees along has adjusted to the altered conditions of flow and the bankline should be reconsidered. sediment transport will experience sequences of The problem of predicting river response below a aggradation and degradation as sediments move dam and the extent to which development of an ar­ through the system. mor layer will limit degradation is extremely com­ Recent evidence indicates that arroyos and tribu­ plex. While it is recognized that bank erosion, dis­ taries below the Jemez River will play an increasingly charge variability, meandering, and sediment inflow important role in main-stem processes as degrada­ from tributaries affect channel response below dams, tion and armoring progress downstream. Response analytical techniques currently available in the lit­ in the lower portion of the study reach will eventu­ erature do not address response in the complex en­ ally parallel that above the Jemez River. However, vironment implied by these variables. Physical pro­ the level of stability between the Jemez River and cess computer modeling offers the most promising Isleta may never reach that of the Cochiti to Angos­ approach to solving this complex problem. tura reach, primarily because tributaries and arroyos with a drainage area necessary to influence main­ GEOLOGY AND ENVIRONMENTAL stem processes are less common below Angostura. CONCERNS The response at the Jemez River confluence sup­ ports the conclusion that the base level of the main The Middle Rio Grande along with the whole of stem is extremely sensitive not only to coarse mate­ New Mexico faces a special set of environmental rial carried in from steeper arroyos, but also to a large problems associated with rich mineral resources, a volume of finer material contributed by a major tribu­ dry climate, and vast areas of low population. Com­ tary. As a result, a decision to establish a permanent plex interactions between geology and environmen­ pool at an existing dam on a major tributary or to tal concerns involve geologic processes that have construct sediment-detention dams on smaller ar­ adverse effects on human activities and our use of royos must be supported by a detailed analysis of mineral, land, and water resources. Geologic pro­ potential response of the main-stem Rio Grande. cesses include moderate-intensity earthquakes, sur-

58 face subsidence due to rock solution, stream floods, debris flows, and landslides. Geologically related human impacts on the environment include surface 10 m ALAMOSA and subsurface extraction of economic mineral de­ • AlBUQUERQUE o El.£PHANT 8II11l DAM posits (primarily energy minerals), groundwater de­ t- mEl. PASO W 70 velopment, construction of dams and power plants, :::c disposal of hazardous wastes, and establishment of ~ m 10 W~ a: large-area reserves for military operations and sci­ a::::C 50 entific research (Hawley and Love 1981). ::>« t- LL « en 40 Geologists have a major role in helping to solve a: w environmental problems resulting from effects of WW a. a: 30 geomorphic processes and the development of min­ :EC) WW eral, water, and land resources. Inventories must be t- C 20 made of these processes and resources in order to put complex process-resource-human interactions in 10 proper space and time perspective. Guidelines can m'l FEB WAR APR MAY JUNE MY AUG sur OCT HCN OfC then be formulated for mitigation or prevention of geology-related problems. For example, mined lands need to be reclaimed, cities need to be planned, and sites need to be selected for hazardous waste disposal Figure 2a. -Mean monthly temperature for selected sites, 1951- (Hawley and Love 1981). 1980 (from Ellis et al. 1993; permission to reprint granted by American Water Resources Association).

CLIMATE Dorroh (1946) presents data for average annual and seasonal precipitation in New Mexico. His results il­ lustrate that two factors, topography and general o AlAMOSA en • AlBUOO(RCl.( atmospheric circulation patterns, exert the major in­ W o ELEPHAHT It1TTt DAM :::c • B. PUO fluences on climate of middle Rio Grande region. 0 1.5 Thornthwaite et al. (1942) identified five principal ~ source regions of air contributing to the Southwest ~ Z climate: (1) Cold Dry Continental; (2) Cool, Moist 0 North Pacific; (3) Hot Dry Continental; (4) Warm, i=« Moist Gulf; and (5) Warm, Moist South Pacific. t: a. Bryson & Hare (1974) provide monthly mean stream­ (3 W Q.5 lines of circulation for all of North America. Their a: January map is illustrative of a rather complex cir­ a. culation pattern that is the norm in the Rio Grande. Because of this complex circulation, the climate is o I ~ 1 I prone to exhibit swings of substantial variation from .we F£I lIAR APR MAY .AlE MY AUG SEPT OCT IIOY DEC mean conditions. These variations are a prominent feature of the climate in the region. Figure 2b.-Mean monthly precipitation for selected sites, 1951- 1980 (from Ellis et al. 1993; permission to reprint granted by A modern map of annual precipitation for the American Water Resources Association). Middle Rio Grande was published by Ellis et. al in 1993. They make the point that precipitation varies from a high of greater than 50 inches annually in the tral New Mexico. Figure 2 illustrates the annual mean headwaters in Colorado to less than 6 inches near monthly temperature and precipitation for the head­ Albuquerque. A similarly wide variation in tempera­ waters (Alamosa), north central (Albuquerque), ture is exhibited from the northern headwaters re­ south central (Elephant Butte Dam), and southern gion where mean January temperatures are below (EI Paso) region of the Middle Rio Grande. A map 25°F to mean July temperatures above 75°F in cen- presented by Ellis et al. also illustrates that mean

59 annual evapotranspiration as high as 80 inches oc­ ENSO is, however, only one of many signals that curs near Elephant Butte; that value falls to 75 inches determine regional weather; it is certain that at El Paso, 60 inches at Albuquerque, and 50 inches uncorrelated weather patterns and events are super­ at Alamosa. imposed on ENSO signals. It is particularly interest­ Of perhaps greater interest is the variation of wet ing that a dramatic shift from sustained drought to and dry years (Diaz 1991; Diaz et al. 1985). In areas unusually wet climatic conditions occurred between such as the middle Rio Grande, dry years and their 1895-1904 (strong drought) and 1905-1928 (wet). This persistence are particularly important. The relation­ was evident in a thousand-year reconstruction of the ship between these manifestations of climate and northern New Mexico paleoclimate (D' Arrigo and other natural and human disturbances may be among Jacoby 1991). the most significant factors influencing ecological In recent wor~ with the NCAR regional climate systems in New Mexico (Betancourt et al. 1993). model, RegCM, Mearns et al. (1994) have compared Of particular interest is the effect of global climate simulated current U.S. climate with a simulated on the Rio Puerco basin as represented by the El Nifio­ double CO2 climate. For the Southwest, their results Southern Oscillation (ENSO) meteorological distur­ show a significant increase in diurnal temperature bance. Investigators have identified relationships range, a decrease in cloud cover, and a significant between ENSO events and southwestern United decrease in precipitation frequency for summer con­ States climate (Ropelowski and Halpert 1986, 1987; ditions. A more uncertain increase in summer pre­ Andrade and Sellers 1988; Kiladis and Diaz 1989; cipitation intensity is also suggested. Although these Molles and Dahm 1990; Betancourt et al. 1993). results are too preliminary to draw any conclusions D' Arrigo and Jacoby (1991) developed a thousand­ from, they suggest that it is possible for the middle year record of winter precipitation for northwestern Rio Grande to experience an increase in temperature, New Mexico based on dendrochronology and corre­ a decrease in cloudiness, a reduction in precipitation lated it with ENSO. Dahm and Moore (1994) recently events, and possibly an increase in storm intensity. demonstrated a statistically significant correlation Weather and climate questions can be studied with between observed precipitation at Socorro, New a "nested" hierarchy of increasingly finer-resolution Mexico, and ENSO events of both polarities. The cor­ climate models. The objective of such a model link­ relation is strongest in October, significant from No­ age would be to provide a realistic simulation of the vember through May, but not significant during the spatial and temporal distributions of the middle Rio summer (convection) season. Correlation of ENSO Grande's climate, in particular of the climate's fea­ or other large-scale climate indicators with regional tures that influence sediment production and trans­ meteorological conditions is important for model de­ port. It is likely that high intensity rainfall events are velopment because weather records are sparse and the most significant climatic feature for land man­ represent conditions at only a single point, while agement concerns. Preliminary inspection of the weather has significant spatial variation. Large-scale weather records suggest that such precipitation indicators are expected to correlate more closely with events are infrequent. Hourly (and daily) time series whole-basin conditions. Furthermore, since ENSO of precipitation can be used to develop a history of events are predictable phenomena of the global cli­ significant events. Each of these significant events mate (Latif et al. 1994), it is possible that regional ef­ can be developed as an historical case study. The syn­ fects of global change may be somewhat more pre­ optic patterns in which these events are embedded dictable when correlated with ENSO events. can be developed from archived analyses (the initial A sustained La Nina condition in 1917 may have condition field for routinely performed numerical been a contributor to the high sedimentation rates weather predictions). Analysis fields consisting of observed in the Elephant Butte Reservoir during its temperature, pressure, and humidity distributions first decade. A single dry year, however, seems un­ over a O.5-degree latitude and longitude grid (ap­ likely to degrade vegetation condition to such a de­ proximately 50 km) can be obtained. gree that a decade or more of enhanced sedimenta­ These analysis fields can be used to initiate tion would ensue. Thus, multi-annual variations may "nested" runs of the RAMS model (Tremback et al. be a better indicator of vegetation stress and erosion 1986) and / or of the RegCM model (Dickenson et al. risk factor. The 3-year period that ended in 1919 was 1989; Giorgi et al. 1994; Mearns et al. 1994) ata grid one of potential stress on the region (Watts et al. 1994). resolution on the order of 10-50 km. Precipitation pre-

60 dicted by these models can be used to drive other to protect pueblo lands from off-reservation pollu­ components in a simulation of the land response to tion. Standards were subsequently adopted by the this significant event. Even finer-scale spatial reso­ Pueblo of Sandia, San Juan Pueblo, and the Jicarilla lution in predicted precipitation and temperature Apache Nation outside of the Middle Rio Grande fields can be obtained from the higher resolution cli­ Basin. Northern Pueblos that have published a no­ mate modeling efforts currently underway at Utah tice of intent to adopt water quality standards include State University in collaboration with the USDA-FS Nambe, Picuris, Pojoaque, Santa Clara, and Tesuque Intermountain Research Station (Bowles et al. 1994; (Blane Sanchez, water resources specialist for Isleta Bingham et al. 1995; Luce et al. 1995). Pueblo, personal communication). The State is pri­ Mesoscale and local-scale (if necessary) models can marily concerned about the level of pollution from be "driven" by the larger-scale synoptic analysis (e.g., nonpoint source9 (NMWQCC 1992), but Isleta Pueblo the larger scale represents both initial and boundary is concerned about point source discharges from the conditions for the higher resolution models), to simu­ City of Albuquerque (Blane Sanchez, personal late the most significant precipitation events. Assum­ communication). ing the number of these events is small, it will be Two recent reviews discuss water quality in the possible to "drape" a finely resolved precipitation Rio Grande Valley, but not throughout the entire distribution (order 1 km or less) over the Rio Puerco Middle Rio Grande Basin (Ellis et al. 1993; Crawford watershed. The significant events will be simulated et al. 1993). Water quality throughout the state is re­ from within a time series that simulates the long term ported to Congress every two years in the 305(b) re­ climate. The ENSO phenomena would be incorpo­ port of the New Mexico Water Quality Control Com­ rated in the global scale initialization analyses, thus mission (NMWQCC 1992). carrying the global signal to precipitation on the Rio There are four U.s. Geological Survey monitoring Puerco. stations along the main stem of the Rio Grande be­ tween Cochiti Lake and Elephant Butte Reservoir (at WATER QUALITY San Felipe, Isleta, San Acacia, and San Marcial). Land uses upstream of these sites include various commu­ Background nities, ski areas, summer homes, silviculture, graz­ ing, molybdenum mining, and irrigated agriculture. The Middle Rio Grande Basin includes 257 km Water quality from Isleta upstream to Cochiti Reser­ along the main stem of the Rio Grande between voir is affected by the City of Albuquerque and other Elephant Butte Reservoir and Cochiti Dam. Tribu­ urban areas, wastewater discharges, runoff from dair­ taries in the Middle Rio Grande Basin are the Jemez ies, and grazing. The lower portion of the Middle River, Rio Salado, and Rio Puerco. Other streams in­ Rio Grande Basin is affected by irrigation return clude Abo Arroyo in the Manzano Mountains, Tijeras flows, uranium mining in the Rio San Jose watershed, Creek, Las Huertas Creek, Galisteo Creek, and the and sediment contributions from three intermittent Santa Fe River below Cochiti Dam. Secondary tribu­ streams (the Rio Puerco, the Rio San Jose, and the taries include the Rio San Jose, Bluewater Creek, Rio Rio Salado) channeled over unconsolidated sedi­ Paguate, Rio Guadalupe, Vallecito Creek, Rio ments. Trends for the following parameters are re­ Moquino, and Seboyeta Creek. Designated uses and ported: conductivity, bacteria, alkalinity, sulfate, dis­ corresponding water quality are classified in the state solved solids, dissolved nitrite plus nitrite, and sus­ standards and vary from that suitable for a high qual­ pended sediment concentrations. For example, sus­ ity coldwater fIshery (e.g., the Jemez River above pended sediment concentrations at the mouth of the State Highway 4 near Jemez Springs, and the Rio Puerco are as high as 200,000 mg/L (USGS 1992), Guadalupe River and its tributaries) and domestic with a mean annual suspended sediment load of water supply, to limited warmwater fishery in the 2,580,000 tons per year (Ellis et al. 1993; USDI 1994). main stem above Elephant Butte Reservoir Others, however, note that sediment concentrations (NMWQCC 1991). in the Rio Puerco reach 680,000 mg/L during major The state authority for water quality is the New storm events (USDI 1994). Mexico Water Quality Control Commission. The In addition to the fixed monitoring sites listed Pueblo of Isleta was the first tribe to adopt water above, the USGS is conducting a study of the Rio quality standards in New Mexico (in December 1992) Grande Valley in the United States as part of the

61 National Water Quality Assessment Program define rate constants and transport mechanisms (Wil­ (NAWQA). Nine sites, including three on the main son and Babcock 1979; Wilson, Tague, Snavely, and stem plus floodway and conveyance channel sites, Babcock 1984). The state sampled the Rio Grande are located on the Rio Grande from just below Cochiti conveyance channel and Socorro Main Canal to Dam to San Marcial. Additional tributary stations evaluate the effects of irrigation return flow on Rio include the Rio Puerco near Bernardo and the Jemez Grande water quality, and it concluded that irrigated River below Jemez Canyon Dam (Ellis et al. 1993). agriculture did not noticeably contribute to the ni­ The state Environment Department (NMED) has trogen and phosphorus loading of the river. Similarly, sampled tributaries in the Middle Rio Grande Basin a New Mexico State University study indicated that as well as the main stem during intensive surveys, less than 20 percent of the nutrients contained in ir­ e.g., sampling a suite of stations for water chemistry, rigation waters vyere discharged to the central drain flow, and biological data at various times through­ (Wierenega, Duff, Senn, and Gelhar 1981; NMEID out a week-long survey. These data are available 1982). through the EPA STORET system, are published by A study by Tague and Drypolcher (1979) indicated survey, and catalogued through the NM State Library that the annual mass loading rates of both Nand P (Pierce 1989; Potter 1987a, b; Potter 1986; Potter and from stormwater was low compared to the loading Tague 1986; Potter 1985a, b; Potter 1984a-c; Jacobi and rate from the Albuquerque wastewater treatment Smolka 1984). Reservoir water quality is also moni­ plant, although a single event generated a tempo­ tored by NMED, and data are available for Cochiti rarily high load. In another study, significant corre­ and Elephant Butte lakes, as well as upstream lations and regressions between urban runoff volume reservoirs. and stormwater quality were calculated using data for the Alameda floodway (Diniz 1984).. More recently, high concentrations of un-ionized Surface Flows ammonia, which is toxic to some fish and inverte­ Surface flows for the main stem are highly modi­ brate species, have been attributed to water use im­ fied for flood control, sediment control, irrigation, pairment in the main stem of the Rio Grande from hydroelectric power, recreation, and reservoir stor­ Isleta Diversion Dam to the Jemez River (NMWQCC age for water supply. Reservoirs affecting the Middle 1992). Rio Grande Basin hydrology include Heron, El Vado, Abiquiu, Cochiti, Jemez Canyon, Galisteo, and El­ Trace metals ephant Butte. These modifications have resulted in Trace metals occur at detectable levels at various intermittent or ephemeral flows in areas that were sites throughout the Basin due to a combination of probably historically perennial flows (Crawford et natural and anthropogenic sources. For example, al. 1993). Recent efforts to mimic natural hydrographs natural arsenic sources (geothermal springs) from the in the main stem include flooding of the bosque habi­ watershed of the Jemez River result in high concen­ tat. There is also interest in reestablishing the natu­ trations of arsenic. Outcrops of organic-rich rocks ral surface-water / groundwater exchange (Crawford such as humates and dark shales are a natural source et al. 1993). Long-term flow data are available for the of trace metals in the Rio Puerco Basin (USDI 1994). main stem at Otowi bridge above Cochiti Lake. Flow Popp et al. (1980) collected samples for trace-metal in the Rio Puerco is not controlled for flooding or and pesticide analysis at six river sites from Bernalillo water supply and contributes 4 percent of the annual to Elephant Butte Reservoir. Water-use impairment water yield for the Rio Grande at San Marcial in the Middle Rio Grande Basin is attributed to trace (Crawford et al. 1993). metals in the main stem of the Rio Grande from San Marcial to the Rio Puerco, Rio Puerco to Isleta Diver­ Contaminants sion Dam, from Isleta Diversion Dam to the Jemez River, and from Jemez River to Cochiti Dam (NMWQCC 1992). Nutrient enrichment Isleta Pueblo will be initiating a joint water qual­ A number of nutrient loading studies have been ity monitoring program in accordance with an April conducted in the Middle Rio Grande Basin. Anutri­ 1994 settlement agreement regarding the City of ent transport simulation model was developed to Albuquerque's National Pollutant Discharge Elimi-

62 nation System (NPDES) permit for discharge of mu­ Other causes of water use impairment nicipal waste. Concentrations of four metals­ Other causes of water-use impairment in portions aluminum, arsenic, cyanide and silver-will be moni­ of the Middle Rio Grande Basin include chlorine, tored from San Felipe to Los Lunas (Blane Sanchez, pathogens, siltation, reduced riparian vegetation, and personal communication). streambank destabilization. Sources that contribute to Several studies have been directed at the water quality degradation resulting in use-impairment bioaccumulation of metals. Mercury, arsenic, and zinc are as follows: agriculture, municipal point sources, concentrations are higher in fish tissue collected at urban runoff, storm sewers, spills, hydromodification, Middle Rio Grande sites than other sites (Ellis et al. and "others" (NMWQCC 1992). The primary in-ba­ 1993). As a result of statewide sampling for mercury sin concerns related to water quality are non-point contamination in fish tissue, the state has issued fish sources of pollu~ion, water quantity and timing, and consumption guidelines (NMWQCC 1992). ecosystem integrity.

Radionuclides Water Quantity and Timing Uranium-rich rock of the Rio Puerco Basin is a source of radionuclides. The Rio Puerco has elevated Stream flow rate is affected by reservoir releases, levels of uranium, gross alpha, and gross beta, and irrigation withdrawals, irrigation return flows, and high concentrations of cesium 137 and lead 210 in precipitation variability. Changes in precipitation can Paguate Reservoir on the Paguate Creek tributary of have a disproportionate (e.g., nonlinear) change on the Rio Puerco (Ellis et al. 1993). Uranium mining streamflow. For example, under global warming sce­ and milling activities near Grants, New Mexico, have narios, a 2° C temperature increase is predicted to accelerated the downstream transport of radionu­ result in a 10 percent decline in precipitation, but a clides and metals. Eroding tailings piles may con­ 75.7 percent decline in annual stream discharge is tinue to result in water pollution. predicted within the Rio Grande Basin (Revelle and Waggoner 1989). This is the largest predicted percent Biocides change per basin in the United States. Biocide contamination occurs from agriculture, as In 1990, total water withdrawal (groundwater and well as from the cumulative impact of residential and surface water) from the Rio Grande Basin in New commercial landscaping activities. Potter (1987b) Mexico was 2,258 x 106 m 3 (1,830,628 acre feet), sig­ sampled pesticide and herbicide concentrations at nificantly exceeding a sustainable rate (Schmandt three Rio Grande main-stem sites in Socorro County. 1993). Average annual outflow of the Rio Grande In general, concentrations were below detection lim­ from Colorado to New Mexico is 370 x 106 m 3 (300,000 its. Although chlordane and 2,4-0 were detected at acre-feet) (Schmandt 1993). Significant changes in the San Antonio station, only the former exceeded water supply in the main stem ultimately affect the the recommended chronic criterion for aquatic life distribution of water as defined by existing treaties and limits for fish consumption. and compacts. The International Boundary and Wa­ Other pesticides found at detectable concentrations ter Commission has already exercised its authority in the Rio Grande main stem include diazinon. Also, to protect water quality (e.g., salinity of the Colorado p-p' DOE was detected in the Middle Rio Grande by River) delivered to Mexico, and similar requirements the U.S. Fish and Wildlife Service (Ellis et al. 1993). could be imposed for the Rio Grande in the future Water-use impairment in the Rio Grande is attrib­ (DuMars 1993). Both streamflow and reservoir stor­ uted to pesticides in the main stem from Isleta Di­ age are affected by terms of the interstate Rio Grande version Dam to Jemez River and from San Marcial to Compact and treaty with Mexico, while the Recla­ the Rio Puerco (NMWQCC 1992). mation Act of 1902 addresses irrigation uses. Such legal implications of changes in water supply extend Volatile organiC compounds to various state and federal regulations of water qual­ VOC detectable in the Middle Rio Grande at Isleta ity and appropriation. For example, "conjunctive man­ include trichlorofluoromethane, chlorpyrifos, and agement" of surface and groundwater requires that to trichlorofluoromethane (Ellis et al. 1993). Organic obtain rights to drill a well in an underground aquifer compounds are not considered to impose a major that recharges a surface stream, an equivalent surface impact on New Mexico streams (NMWQCC 1992). water right must be purchased and retired (Gosz 1992).

63 The hydrologic effects of floods and droughts in is less extensive and thinner than was previously semiarid regions is quite different from mesic regions. estimated, and it has dropped 40 feet from 1989 to In the Rio Salado, for example, loss of streamflow in 1992 in the eastern, northwestern and south-central the summer occurs after wet winter / springs, while areas (Thorn et al. 1993). Over 1.5 x 1011 1 (40 billion summers with high flooding occur after dry winter / gallons) of water a year are withdrawn from the aqui­ springs. Hypothetical reasons for this observation fer, at a rate exceeding that of recharge (City of Albu­ include: less vegetation biomass is available after a querque 1994). Consumption rate is 947 1 (250 gal­ dry winter / spring to slow overland flow so runoff lons) per person per day, and residential use is 71 therefore increases; wet winter / springs result in re­ percent of total. The remainder is consumed by com­ duced hydrophobic tendency of the soils and in­ mercial use (17 percent), institutional use (9 percent), creased infiltration; and due to the effect of soil tem­ and industrial u;;e (3 percent) (City of Albuquerque peratures, more intense summer storms may occur 1994). Mayor Martin Chavez states that reducing after a dry winter/spring and produce high runoff water use is "the most important issue facing the City (Molles et a1. 1992). of Albuquerque, bar none." Groundwater quality is also lower than previously believed, including areas Anthropogenic Effects on Water Quality that are unsuitable for drinking. Human activities may result in regional changes Anthropogenic effects on water quality in the in the water cycle, water quality, and sediment trans­ Middle Rio Grande Basin are the result of activities port systems (Huggett 1993). These changes are mod­ associated with irrigation, urbanization, mining, eled at various scales, including the global and con­ grazing, timber harvest, construction, and recreation tinental scales. Predictions can be made for variables (Crawford et a1. 1993; NMWQCC 1991, 1992; Ellis et such as runoff, stream discharge, soil moisture, and a1. 1993; USGS 1992). Additional activities upstream evapotranspiration (Huggett 1993). There is a grow­ from Cochiti Dam to the San Luis Valley in Colorado ing, interdisciplinary interest in water resources is­ also contribute to the cumulative effect on water sues that relate to sustainable development in the quality. entire Rio Grande Basin (Gosz 1992; Crawford et a1. Irrigation return flows and runoff affect both wa­ 1993; Schmandt 1994). Those efforts include sharing ter quantity and quality. Irrigated agriculture is the scientific information and collaborative projects that principal water use and a main economic activity in will improve water and riparian area quality, as well the Basin. Water withdrawals from irrigated agricul­ as economic sustainability. Such partnerships, insti­ ture are declining, e.g., from 1,536 x 106 m 3 to 1,227 x tutional cooperation, and joint decision-making are 106 m 3 (1,244,900 to 995,000 surface water acre-feet) necessary to address global change issues related to in the New Mexico portion of the Rio Grande Basin climate, population, economy, the environment, and (Schmandt 1993). DuMars distinguishes between culture (Gosz 1992). In the Rio Grande Basin, total "commercial agriculture" and"culturally significant water consumption is greater than the supply. This marginal agriculture" of rural communities and In­ water deficit is allowed to continue through diver­ dian Pueblos (DuMars 1993). sion systems and groundwater mining (DuMars Urbanization has resulted in commercial and in­ 1993). It is well recognized that sustainable economic dustrial activities that have the potential to affect development depends on efficient water use, water water quality. It has also resulted in increased levels conservation, and water pollution control. of treated sewage discharged to streams. Perhaps most importantly, it has increased the demand for ARROYO DYNAMICS OF water supply, although municipal use relies on THE RIO PUERCO BASIN groundwater. Urban population growth is predicted to continue in the next century, e.g., when the effects Background of accelerated climate change may be evident. In con­ trast, rural populations have remained rather con­ The Rio Puerco basin is composed of federally stant in the Basin (Schmandt 1993). managed lands (FS, Bureau of Land Management, The rate of depletion of Albuquerque's water sup­ National Park Service, and Fish & Wildlife Service: ply is currently a great concern. The aquifer on which 30 percent,), Indian lands (20 percent), state (10 per­ the City of Albuquerque depends for water supply cent), and private (40 percent) lands. This broad

64 mosaic of ownerships and management objectives tion of the key storage and management facility is a makes the Rio Puerco an excellent candidate for eco­ legal, as well as a practical, necessity. The popula­ system management-oriented studies. tion of this area is growing rapidly, as much as 20 The Rio Puerco, a tributary of the Rio Grande, is percent per year in selected locations, as is its de­ one of the highest sediment-yielding streams of the pendence on reliable water supplies. While most United States (Aguilar et al. 1990); as much as 20 drinking water needs are currently supplied by percent of the Rio Puerco's historical discharge into groundwater pumping, there is increasing concern the Rio Grande is suspended solids (Laquer 1981). about the quality and continuity of this source as well From its 19,036 km2 drainage basin, it produces an as its relationship to the Rio Grande. average of 2.4 Mt./y (million metric tons per year) The high sedimentation rates of the early part of of suspended sediment, or an average of 130 t/km2 /y. this century have, fortunately, moderated. At current Bryan and Post (1927) estimated that 500xl06 m 3 of sedimentation rates the projected lifetime of Elephant sediment was eroded from arroyo walls during the Butte Reservoir is beyond 300 years. The Bureau of period 1885-1927; this translates to an average rate Reclamation's Albuquerque Projects Office recently of 12xl06 m 3 /Y or approximately 24 Mt./y based on (August I, 1994) issued a "Draft Preliminary Find­ an estimated pre-erosion sediment density of 2 gl cm3. ings Report-Rio Puerco Sedimentation and Water These calculations suggest that approximately 90 Quality Study" (USDI Bur. Rec. 1994) that contains percent of the sediment mobilized in arroyo incision an excellent review of the literature and available is redeposited within the basin; the remaining 10 data. This report recommends against construction percent is exported as suspended sediment load. of control structures to manage sediment from the Dortignac (1956) estimated that two-thirds of Rio Rio Puerco, but rather recommends interagency Puerco's sediment was derived from arroyo deep­ analysis and model development to improve under­ ening and widening processes, and one-third from standing of the system. sheet and rill erosion of hill slopes; this estimate re­ Table 1 summarizes published statistics on the Rio duces the redeposited:exported ratio further, to 93 Puerco's sediment production. Some statistics can­ percent:? percent, or 13:1. Miller (1985) estimated not be compared directly because, for example, they transport rates of 500 t/km2 Iy in regional dune fields, represent different time periods. There are, neverthe­ which represents a surface-material mobility:average less, apparent discrepancies and interpretation diffi­ export ratio of 4:1. The Rio Puerco basin clearly ex­ culties. For example, Bryan's estimate of a mean ar­ hibits high mobility of surface and near-surface sedi­ royo excavation rate of 12xl06 m 3 /y pales (by a fac­ ments; the great majority of material is redistributed tor of 2.5) in comparison to the Elephant Butte within the basin, but the fluvial channel system nev­ Reservoir's measured rate of sediment influx of ertheless receives and exports a significant amount 30xl06 m 3 /Y during the period 1915-1925. Was Rio of mobilized material. These have been observed and Puerco's erosion rate higher during the decade 1915- dated only on an incidental basis. 1925 than for the period 1885-1927? Did other tribu­ The current arroyo system developed during the taries contribute more than half of the sediment load latter part of the 19th century. Kirk Bryan (1925), one during the 1915-1925 decade? Are pre-erosion sedi­ of the earliest students of the Rio Puerco, cited 1880 ments substantially denser than post-deposition sedi­ as the approximate time of erosion initiation. Sedi­ ments? Answers to these questions lie in field obser­ mentation rates were particularly high during the 40 vations of the Rio Puerco Basin and of Elephant Butte years that followed (1880-1920). Elephant Butte dam Reservoir. was closed in 1916. Its reservoir immediately was subjected to high deposition rates-so high that the In-Basin Concerns reservoir would be filled with sediment by 2022 if early deposition rates had been sustained. This sce­ The foregoing discussion focused narrowly on nario is disquieting because Elephant Butte Reser­ sedimentary processes and on the out-of-basin effects voir is the primary management facility for delivery on the Rio Grande surface water supply. There are also of water to the lower Rio Grande Basin in New concerns regarding in-basin land and water resources. Mexico, Texas, and Mexico. Elephant Butte While the Rio Grande channel system and Reservoir's delivery is governed by interstate com­ Elephant Butte Reservoir accumulated large quanti­ pacts and by international treaty; enduring opera- ties of sediment, the Rio Puerco landscape lost it. The

65 Table 1.-Values taken from the literature indicate magnitudes of various types of mass redistributions in the Rio Puerco watershed.

Period Basin Amount/ start end total Units area Units

Areaa 1.9E+04 km2 Area 1.9E+ 10 m2 Area 1.9E+ 16 mm2 Mean water outflow 1941 1993 3.0E+07 m3/y 1.6E-03 m3/y Mean water outflow 1941 1993 3.0E+ 16 mm3/y 1.6 mm/y Mean sediment outflow 1941 1993 2.3E+06 t/y 1.21 E+02 t/km2/y Mean sediment outflowb 1941 1993 1.2E+06 rn3/y 6.1 E-05 m/y Mean sediment outflowb 1941 1993 1.2E+ 15 mm3/y 0.061 mm/y Arroyo excavation 1885 1927 5.0E+08 m3 0.026 m Arroyo excavation 1885 1927 1.2E+07 m3/y 6.1 E-04 m/y Arroyo excavation 1885 1927 1.2E+ 16 mm3/y 0.61 mm/y Eolian movement ? 1985 500 t/km2/y Eolian movement ? 1985 250 m3/km2/y Eolian movement ? 1985 0 mm/y EBR sedimentb 1915 1926 3.0E+07 m3/y

aincludes area of closed inferior drainages bassumed density = 2,000 kg/m3

arroyos, as suggested earlier, may have lost sediment tailings that are exposed on the land surface. Tail­ volume 10 times greater than was exported to the ings materials have episodically entered the drain­ Rio Grande. Natural excavation of such deep grooves age network and certainly do so on a continuous basis in the valley floors drained valley-fill aquifers and in a setting where surficial materials are highly mo­ defeated extant agricultural surface-water diversions; bile (Miller 1985). The presence of these materials in an apparent repetition of the demise of the settle­ poses both in-basin and downstream threats to wa­ ment at Chaco Canyon, several agrarian communi­ ter and environmental quality. In its recent study, the ties abandoned the Rio Puerco basin. Sediment that Bureau of Reclamation (1994) concluded: "Evidence remained in the basin (>90 percent of the excavated exists that heavy metal and radionuclide contami­ amount) has been redeposited in the lower reaches nants are carried into the Rio Grande by the Rio of the arroyos; vegetation has become established Puerco. The majority of these contaminants are at­ there and retards peak flows in the channel and fur­ tached to sediment particles. It is not known whether ther increases aggradation. Water tables rise as ar­ the Rio Puerco contributes trace metals or radionu­ royos continue to refill with sediment. Conditions clides to the Rio Grande in quantities sufficient to may be ripe for reinitiation of a basin-wide arroyo cause health risks to humans or adverse ecological cycle (Gellis 1991). effects." What factures or combinations of factors will ini­ tiate the next cycle of erosion? What measures might Research Problems be taken to ameliorate negative impact? Of measures that might be identified, which ones provide opti­ More than 1,200 technical references have been mum benefits? What observations or monitoring cited in a recent review of Rio Puerco literature; yet, would provide early warning of pending erosion? in spite of such extensive scientific scrutiny, the cause, These are practical questions of concern to landown­ character, and future of erosion in the basin remain ers and to land and water resource managers of the subjects of debate. Various authors have attributed Rio Puerco and downstream areas. arroyo incision to climatic variations or changes; to graz­ Mining is a substantial activity in the Rio Puerco ing; to roads and stock trails; to combinations of these Basin, particularly in its southwestern quadrant. Both factors; or to cyclic behavior of arroyo systems (coupled radioactive and toxic minerals are present in mine or uncoupled with climate variations). The ambiguity

66 of interpretation of the prehistoric and historic record slope, and vegetation conditions exhibits re­ encourages study of the Rio Puerco arroyo processes peated episodes of incision and high sediment through the use of numerical simulation models. discharge when driven with historical regional Arroyo-inducing conditions and high sediment weather. yields are not synchronous with climate conditions Implications: If hypothesis 1 was false but this owing to the critical role of vegetation as landscape hypothesis is true, then interaction among tribu­ armor. It takes several years for plants to succumb to taries, or between tributaries and main channel, stress and more for their physical soil-stabilizing is an essential driver of arroyo instability. If the structures to decompose. Other factors, such as graz­ hypothesis is true, then the factors of dynamic ing, accelerate the removal of sediment-fixing plant vegetation and soil disturbance may be con­ structures, but these also have their characteristic tributory b1)t are not essential to the gross be­ rates of progress. Thus, there are unknown delays havior of the arroyo system. If false, then the between climatic causative conditions and high ero­ effect of each of these additional factors must sion; there are further delays (transmission times) in be considered. the channel system itself. Development of an object-oriented arroyo dynam­ ics process simulation model is currently underway Conceptual Model at the TERRA laboratory (Watts et al. 1994). This model is based on geographic coverage of the Rio A simple model of influences over sediment­ Puerco. The hydrologic system of the Rio Puerco is generating processes can be conceptualized. mapped from digital elevation models at 30 m reso­ Hillslope conditions are interposed between major lution of the entire Basin. The resulting stream sys­ causative factors-weather and human activities­ tem can be analyzed automatically using geographic introducing characteristic time responses that delay, statistics. This allows the watershed to be analytically mask, and mix the driving signals. One could develop reduced into a combination of channel reach seg­ a model that incorporates the essentials of these dy­ ments. The model being developed at TERRA treats namics in a way that allows for substantial duplica­ each channnel reach as a separate object having a tion of historical observations. Such a model will be headwater, a right, and a left input. The system can used to investigate effects that would follow differ­ be simulated with whatever degree of complexity is ent driving conditions-primarily changes in climate necessary by linking these objects into a simulated and human-influenced conditions such as grazing. map of the channel system. Since the dynamics of A structured sequence of hypotheses and tests for arroyos depend on a number of features beyond sim­ this project could be: ply the hydrology, each object contains geomorphic, vegetation, and other characteristics. 1. Hypothesis: A linear arroyo characterized by typical but static Rio Puerco soil, slope, and veg­ etation conditions exhibits repeated episodes of NUTRIENT RETENTION, STREAM METABOLISM, incision and high sediment discharge when AND ARROYO FORMATION driven with historical regional weather. Implications: If the hypothesis is true, then the The perception of streams as inanimate pipes that factors of dynamic vegetation, soil disturbance, drain watersheds has been rejected by both hydrolo­ and drainage network geometry may be con­ gists and ecologists. Streams are no longer viewed tributory but are not essential to the gross be­ as receptacles for hillslope water; instead, ground­ havior of the arroyo system. Gross behavior of water and surface water fluxes are now considered the system can be used, at least qualitatively, to interactive and hydrologically integrate hillslope and investigate frequency and intensity of sediment channel systems (Bencala 1993; Harvey and Bencala production of the basin, including production 1993). Solute transport in all ecosystems is tied to the of entrained toxic materials. If the hypothesis is movement of water. Given the advective, unidirec­ false, then the effect of each of the named fac­ tional transport characteristic of lotic systems, the tors must be considered. retention of nutrients and organic matter is an in­ 2. Hypothesis: A simple, branched arroyo charac­ sightful measure of ecosystem functioning. A suite terized by typical but static Rio Puerco soil, of physical, chemical, and biological processes de-

67 lays the downstream flux of nutrients, and the inter­ sient storage. Surface complexities such as debris play of these factors influences the structure and func­ dams have been shown to increase hydrologic resi­ tioning of stream systems. Geomorphic differences dence time and enhanced retention of particulate among streams can have a large impact on the reten­ organic material (Speaker et a1. 1984; Trotter 1990; tion and cycling of nutrients (Lamberti et a1. 1988; Ehrman and Lamberti 1992). D'Angelo et a1. (1993) Coleman and Dahm 1990; Gregory et a1. 1991). In the examined the relationship between stream order and Rio Puerco drainage, arroyo formation is an agent of transient storage. They found an overall decrease in geomorphic change that is of great importance to storage zone size with increasing stream order. downstream environments and terrestrial systems The interaction of surface water with ground­ within the catchment. In this study plan, we describe water also contributes to transient storage in lotie eco­ a research program to assess the influence of arroyo systems (Bencal~ and Walters 1983). Surface and sub­ formation on the retention of nutrients by head­ surface systems of streams are linked by vertical gra­ water streams of the Rio Puerco, New Mexico. dients causing groundwater discharge (upwelling) and recharge (downwelling) that result from stream HydrologiC Retention bottom geometry (Vaux 1968; White et a1. 1987) and hillslope-channel water interaction (Harvey and Stream channel complexity, as well as surface Bencala 1993). The term "hyporheic zone" refers to water-groundwater interactions, entrain nutrients in the subsurface component of transient storage and is flowpaths that move at slower velocities than those defined as the region of groundwater that receives wa­ predicted by the average advective velocity of sur­ ter from the above-ground channel (Triska et a1. 1989). face flow. The resulting delay in transport is known Hyporheic flowpaths have been identified as a signifi­ as hydrologic retention and has been quantified us­ cant source of hydrologic retention in gravel-bottom ing conservative hydrologic tracers (Bencala and streams (Castro and Hornberger 1991; Bencala 1993). Walters 1983; Stream Solute Workshop 1990). Analy­ The magnitude of subsurface storage changes with sis of tracer response in wells provides point mea­ space and time. Constrained stream reaches occur surements of hydrologic retention in interstitial wa­ when the valley floor is less than two times the ac­ ter. Individual wells reveal the extent of penetration tive channel, reflecting geomorphic limits on the lat­ of surface water into the groundwater at specific lo­ eral extent of the fluvial system (Gregory et a1. 1991). cations. Average travel time to a sampling well ex­ Using the above definition, D'Angelo et a1. (1993) presses the rate of exchange between surface water showed that transient storage was higher in uncon­ and groundwater. In this manner, distribution of con­ strained segments of a stream in the Pacific North­ servative tracers in well networks can provide a west than in constrained reaches of the same stream. qualitative measure of hydrologic retention along a For a single stream reach, transient storage changes reach of stream (Triska et a1. 1989, 1993). with time. For headwater streams of Appalachian Downstream transport of water and tracer can be (D' Angelo et a1. 1991) and New Mexican (Morrice et simulated using numerical models to provide a quan­ a1., in review) mountains, there is a negative correla­ titative measure of hydrologic retention (Bencala and tion between discharge and hyporheic zone size. Walters 1983; Stream Solute Workshop 1990; Runkel Morrice et a1. (in review) identified hydraulic con­ and Broshears 1991). One such approach is the One­ ductivity as a parameter that influences hydrologic re­ dimensional Transport with Inflow and Storage tention through its affect on surface water-groundwater model (OTIS) developed by Runkel and Broshears exchange. Using hydrologic tracers, we compared the (1991). This model treats the stream as a two com­ transient storage of three headwater streams located partment system-a main stream channel and a tran­ in catchments of contrasting geologic material and sient storage zone. Transient storage reflects the tem­ differing alluvial properties (Morrice et a1. [in re­ porary delay of downstream transport and includes view], Valett et a1. [in review D. The rate and spatial hydrological and geomorphic features of surface and extent of hydrologic interaction between the streams subsurface systems. The size of the storage zone can be and their alluvial aquifers decreased with decreas­ determined by OTIS to provide a quantitative, compara­ ing alluvial hydraulic conductivity and decreasing tive, reach-scale measurement of hydrologic retention. channel complexity. Recent studies have sought to identify features of Hydrologic interaction between streams and stream ecosystems that influence and organize tran- their alluvial aquifers is heavily influenced by

68 hydrogeologic parameters (e.g., hydraulic conduc­ Morrice et a1. (in review) and Va lett et a1. (in re­ tivity) and surface channel features, as well as flu­ view), found that nitrate uptake length was corre­ vial geomorphology, including channel gradient, lated with storage zone size. Increased hydrologic sinuosity, and width-to-depth ratio (Larkin and Sharp exchange between surface water and groundwater 1992). Ecological consequences of arroyo formation promoted tighter cycling of nitrogen between sur­ on headwater streams probably reflect geomorpho­ face and interstitial systems. Mixing between surface logical responses of the fluvial system. We suggest water and groundwater integrates the biogeochem­ that because of its close relationship to reach com­ istry of these regions and generates nutrient fluxes plexity, hydrologic retention will be sensitive to the that may influence processes in both subsystems potential impacts of stream incision and arroyo (Gibert et a1. 1990; Valett et a1. 1994). formation. Metabolism and Nutrient Cycling in Biological Retention Stream Hyporheic Zones Nutrient transport in streams can also be attenu­ The size of the hyporheic zone and the direction ated by pathways involving biological retention. In and magnitude of groundwater-surface water inter­ lotic ecosystems, the competing processes of hydro­ action varies greatly among and within catchments, logic export and biological retention are expressed and has important implications for ecosystem me­ in the nutrient spiralling concept (Webster and Patten tabolism and nutrient cycling. For example, Valett et 1979; Elwood et a1. 1982; Newbold et a1. 1983). Down­ a1. (in review) found that interstitial dissolved oxy­ stream transport adds longitudinal displacement to gen concentrations were significantly correlated to nutrient cycles such that they act as nutrient spirals. the rate of exchange between surface and subsurface. Comparisons of solute loads (mass transported per This suggests that residence time in aquifer sediments unit time) at successive points along a reach provides governs oxygen availability and strongly influences a measure of nutrient uptake or release. Ecosystem redox potential along subsurface flow paths. Micro­ retention is then calculated as the net difference be­ bial respiration in groundwater proceeds through a 1 tween inputs and outputs from an established reach predictable series of electron acceptors (02' N03- , (Grimm 1987; Stream Solute Workshop 1990; Triska Mn+4, Fe/, S04-2, COl) reflecting the nature of their et a1. 1990). hydrologic supply (Chapelle and Lovely 1990). Ad­ Biological retention in streams can be measured in ditionally, respiration rates in stream systems (sur­ reach-scale experiments that involve the concomitant face and subsurface) are linked to the supply of dis­ release of conservative (non-active) and non­ solved organic carbon (Dahm 1981; Kaplan and Bott conservative (biologically active) solutes. Uptake 1982, 1989; Findlay et a1. 1993; Vervier et a1. 1993; lengths represent the average distance traveled by a Jones et a1. [in review]) and availability of terminal solute (sensu Newbold et a1. 1983) and are determined electron acceptors. Since residence time affects dis­ from analysis of plateau concentrations of conserva­ solved oxygen distribution, we predict that hyporheic tive and non-conservative solutes at successive points zones in basins with low rates of surface water­ along a reach. groundwater exchange will be dominated by anaero­ Hyporheic zones are historically known as habitat bic metabolism. In contrast, interstitial regions with for unique and diverse invertebrate assemblages (for high rates of surface water-groundwater exchange review see Williams 1984), but these groundwater / should be well oxygenated and dominated by aero­ surface water mixing zones also affect stream me­ bic processes. tabolism (Grimm and Fisher 1984; Metzler and Smock 1989) and nutrient dynamics (Triska et a1. Arroyo Formation and Lotic Ecosystem 1989; Duff and Triska 1990; Hill 1990; Hendricks and Functioning White 1991). Because subsurface sediments are meta­ bolically active, hyporheic zones may act as sources Across stream systems, basin lithology influences or sinks of nutrients depending on the relative mag­ the availability of biologically important solutes nitude of processes generating or immobilizing bio­ (Hynes 1975; Kruger and Waters 1983; Munn and logically important solutes (Triska et a1. 1989; Meyer 1990; Pringle and Triska 1991), properties of McDowell et a1. 1992). alluvial materials, sediment bed loads (Kelson and

69 Wells 1989), and groundwater/surface water inter­ fect the rates of groundwater-surface water exchange, action (Morrice et al. [in reviewD. Within catchments, ecosystem metabolism, and nutrient retention in nutrient retention has been shown to vary among perennial headwater streams of the Rio Puerco pools, riffles, and debris dams (Munn and Meyer drainage. 1990) and is influenced by varying geomorphology within similar reach types (Coleman and Dahm 1990) Research and frequency of woody debris (Trotter 1990; Ehrman and Lamberti 1992). Within streams, variation in Objectives channel geomorphology influences ecosystem func­ The structure and functioning of stream ecosys­ tioning. Just as D'Angelo et al. (1993) found lower tems are intimately linked to processes occurring at transient storage in constrained reaches, Lamberti et the watershed ~cale (Hynes 1975). For this reason, al. (1988) concluded that constrained reaches were the biogeochemistry of streams has been used as an far less retentive of dissolved and particulate matter indicator of disturbance and successional state in than were unconstrained reaches where channel com­ adjacent terrestrial ecosystems (Likens et al. 1970; plexity is higher. Vitousek and Reiners 1975). Cyclical arroyo forma­ In the semiarid southwest, stream-bed sediments tion impacts the structure and functioning of down­ of sandy-bottom streams are metabolically active stream reaches (e.g., Rio Grande, Elephant Butte Res­ (Grimm and Fisher 1984; Coleman and Dahm 1990; ervoir) and alters upland terrestrial systems, but Valett et al. 1990) and highly mobile (Wertz 1963; Graf nothing is known about its impact on the perennial 1988), reflecting variable precipitation (Molles and aquatic habitats of headwater streams. Dahm 1990) and the influence of flash floods (Graf The general objective of this research is to deter­ 1988). Under these conditions, movement of sedi­ mine the effect of arroyo formation on nutrient re­ ments may represent a significant disturbance to in­ tention in headwater streams of the Rio Puerco Ba­ stream aquatic communities of the surface (Gray sin. To do this, we will interact with researchers from 1980; Boulton et al. 1992a) and hyporheic zone (Boulton the Bureau of Land Management who have estab­ et al. 1992b) and to ecosystem processes (Fisher et al. lished study sites on a number of perennial streams 1978; Grimm and Fisher 1989; Valett et al. 1994). near the San Pedro Wilderness in the Jemez Moun­ Mobilization of vast quantities of sediments due tains of the Santa Fe National Forest. We will describe to arroyo formation has been a focus of concern for ecosystem structure in areas variably impacted by managing agencies in the southwestern United States arroyo formation and compare nutrient dynamics in (Hereford 1987; Lagasse et al. 1987; Watts et al. 1994). incised and unconstrained reaches. Finally, we will In New Mexico, the Rio Puerco contributes an enor­ compare retention in these sites to a similar stream mous amount of sediment to the Rio Grande (and (Rio Calaveras) in the Jemez Mountains where we ultimately to Elephant Butte Reservoir), but Watts et have studied hydrologic and biological retention and al. (1994) emphasized that over 90 percent of the stream/ groundwater interactions for the past three mobilized sediment is redeposited within the basin. years (see Wroblicky et al. 1992; Morrice et al. [in re­ Associated with convective thunderstorms, summer view]; Valett et al. [in reviewD. Our current study floods in the headwater streams of the Puerco restruc­ plan includes studies of arroyo influences within ture channel geomorphology, decimate benthic single streams and comparisons of retention between stream biota, and initiate stream incision and arroyo an arroyo-impacted catchment and a reference formation. In other sandy-bottom streams disturbed catchment not impacted by arroyo formation. by flash floods, rates of ecosystem recovery are in­ Specifically, we will: (1) describe the hydrogeologic fluenced by nutrient fluxes between groundwater and chemical conditions of surface water and and benthic environments (Valett et al. 1994). While groundwater environments in headwater catchments arroyo formation is recognized as a critical issue for of the Rio Puerco that are impacted by arroyo forma­ terrestrial and fluvial systems in terms of sediment tion, (2) determine the influence of arroyo formation erosion and transport, little is known about its local on the retention of water and nutrients, and (3) in­ implications on biological aspects of headwater vestigate the metabolic activity of sediments depos­ streams. Via its impacts on small-scale (e. g., 100-1000 ited in perennial reaches and imported from ephem­ m) stream geomorphology and its potential to dis­ eral tributaries (e.g., arroyos). We will pursue these turb aquatic communities, arroyo formation may af- objectives with three research elements: (1) structure

70 of the groundwater/surface water interface, (2) hy­ puts over a designated time period (e.g., retention = drologic and biological aspects of nutrient retention, and [nutrients in-nutrients out]/time). Biological activ­ (3) metabolism and carbon cycling in stream sediments. ity entrains nutrients in plant and animal biomass, reducing the movement across the downstream Study sites boundary. This is a significant component of nutri­ ent retention in streams. Similarly, nutrients may The initial phase of our research will focus on es­ enter volumes of water moving much slower than tablishing study sites in perennial reaches of head­ the main current. Pools, eddies, backwaters, and water streams that drain into the Rio Puerco near flowpaths routing surface water through the near­ Cuba, New Mexico, on the western slopes of the stream groundwater system are features of streams Jemez Mountains in the Santa Fe National Forest. We that result in hyqrologic retention. We will investigate will coordinate our efforts with ongoing research the influence of arroyo formation on the hydrologic and projects organized by the Bureau of Land Management biological retention of N03-N. We focus on N03-N be­ focusing on headwater restoration in the Rio Puerco cause it is the predominant form of plant-available ni­ basin. Perennial reaches of headwater streams near the trogen in streams and because nitrogen is the nutrient San Pedro Wilderness Area will be assessed. Potential commonly limiting biological processes in southwest­ study sites now include San Pablo Creek, the Rito Leche, ern streams and rivers (Grimm and Fisher 1986). and Nacimiento Creek near Senorito Canyon. This research element addresses the impacts of arroyo formation on hydrologic and biological Structure of the groundwater/surface mechanisms of nutrient retention. We will compare water interface transient storage and nutrient uptake lengths within individual streams and compare results to those al­ Initial field sampling will be aimed at characteriz­ ready analyzed for a nearby reference stream (Rio ing the hydrogeologic and biogeochemical conditions Calaveras, Jemez Mountains, New Mexico) to inves­ of surface and groundwater environments in our tigate the influence of arroyo formation on nutrient study streams. Using standard methods modified for retention. use in sandy-bottom streams, we will analyze Question 1: How does arroyo formation influence hydrogeologic properties (e.g., vertical hydraulic hydrologic retention in headwater streams of the Rio gradients, alluvial hydraulic conductivity) and the Puerco Basin? distribution and concentration of biologically impor­ Hypothesis 1: Decreased channel complexity and tant (e.g., redox-sensitive) solutes at the benthic/ deposition of silt in the beds of arroyo-cut streams hyporheic interface. We will compare biogeochemi­ results in decreased hydrologic retention. cal structure of incised and unconstrained reaches Predictions: (1) Transient hydraulic storage will be and the physical-chemical conditions of saturated lower in reaches where arroyo formation has im­ sands entering the main channel from ephemeral pacted the stream channel through incision and/ or tributaries (e.g., arroyos). Results from these surveys deposition of fine-grained sediments. (2) Average will be used to identify characteristic reach types and values for transient storage in Rio Puerco headwa­ locate sites for experimentation (see below). ters will be less than in the reference stream (Rio Calaveras). Hydrologic and biological aspects of Alternatively, sediment deposition may provide nutrient retention extensive sand bars and channel storage that pro­ motes subsurface flow and hydrologic retention.

Rivers and streams are /I open" ecosystems, domi­ Tests: After identifying geomorphic reaches asso­ nated by physical transport of nutrients across up­ ciated with arroyo formation, we will compare the stream and downstream boundaries. The down­ transient storage of incised (or constricted) reaches stream flow of water accounts for the vast majority with intact reaches of greater channel complexity. of the input and output of materials for a reach of Bromide will be used as a biologically and chemi­ stream or river (Cummins et al. 1983; Grimm 1987). cally conservative solute to be injected into the sur­ Retention integrates the processes that retard the face waters of all study reaches. Bromide transport will movement of nutrients out of an ecosystem and is be simulated by a one-dimensional transport with in­ defined as the difference between inputs and out- flow and storage computer model (OTIS, Runkel, and

71 Broshears 1991). Transient storage size (As) is a param­ logic exchange between surface and interstitial zones eter of the OTIS model that is widely accepted as a on the metabolism of saturated sediments in head­ measure of hydrologic retention, and will be determined water streams of the Rio Puerco. and compared among reaches and streams. Compari­ Question 3: What is the influence of arroyo forma­ son of As among reach types will assess the extent and tion on aquatic microbial processes that cycle carbon? variation in transient storage with the Rio Puerco head­ Hypothesis 3a: Because of low organic matter con­ waters. Comparisons with past injections in the refer­ tent and frequent disturbance, metabolic demand of ence stream will be used to test the prediction that ar­ stream sediments will be low compared to the hy­ royo-impacted streams have less transient storage. drologic supply of oxygen, promoting aerobic me­ Increased hydrologic retention results in longer tabolism in the hyporheic zone. contact time between water and microbial commu­ Prediction: (1) IStream sediments will be low in or­ nities of benthic and hyporheic habitats. Our past ganic matter (e.g., < 1 percent by weight). research has shown that uptake lengths (the average (2) Porewater will be well oxygenated. (3) Metabolic downstream distance a molecule of nitrate travels in activity in sediment will occur aerobically. solution before being entrained by biological process­ Hypothesis 3b: Grain size and other alluvial prop­ ing) and transient storage are closely related (Valett erties of imported sediments will result in low rates et al. [in review]). of exchange between oxygenated surface water and Question 2: How does arroyo formation affect the metabolically active subsurface regions resulting in retention of N03-N in headwater streams of the Rio anaerobic metabolism and nutrient transformations Puerco Basin? in stream bed sediments. Hypothesis 2: Disturbance in the form of scouring Prediction: (1) Alluvial hydraulic conductivity will during elevated flow and instability of sediments at be low (e.g., less than 1 X 10-5 cm/ s) in reaches con­ base flow maintains lower biological activity in the taining imported sediments. (2) Interstitial water will stream channel resulting in reduced nitrate retention be anoxic. (3) Metabolic activity in sediments will be in streams affected by arroyo formation. anaerobic.

Predictions: (1) Uptake lengths for N03-N will be Tests: Sediment cores will be used for measures of greater in streams heavily impacted by arroyo for­ respiration, after which sediments will be analyzed mation (e.g., longer uptake lengths will occur in the for organic matter content. Evolution of CO2 and 02 Rio Puerco headwaters compared to the reference consumption will be used to differentiate between stream). (2) Uptake lengths will be longer in constrained aerobic and anaerobic metabolism in sediment cores. (incised) reaches compared to unconstrained reaches. Oxygen concentration in interstitial spaces and allu­

Tests: Uptake length for N03-N will be determined vial properties will be measured in accordance with from experiments in which nitrate is injected with a Research Element 1. conservative tracer (Tests for Hypothesis I, above). Climatic factors that will be investigated include Calculated uptake lengths will be compared among intense, sustained, or repeated La Nina (dry-winter) study streams (Rio Puerco streams vs. Rio Calaveras) conditions and Gulf moisture (intense summer pre­ and designated reaches (constrained vs. unconstrained) cipitation) conditions. Models will be used to simu­ to assess differences in biological nutrient retention. late conditions and effects of climate, land use, and vegetation condition on sheet and rill erosion and Metabolism and carbon cycling in on arroyo sediment dynamics. The studies have prac­ stream sediments tical application for evaluating water quantity risks imposed on the Elephant Butte Reservoir, located This research element focuses on carbon cycling downstream on the Rio Grande from the confluence and the rates and nature of metabolic processes in of the Rio Puerco, and other reservoirs in similar the sediments of arroyo-impacted streams and asso­ geoclimatic settings. Elephant Butte Reservoir has ciated shallow groundwater systems. Convective historically suffered high rates of sedimentation; if thunderstorms and intermittent flows in arroyo tribu­ these were to recur, then the utility of the dam as the taries are expected to result in the importation of fine­ major controlling structure for release of water to the grained sediments that are low in organic matter con­ lower Rio Grande (Texas and Mexico) would be im­ tent. This research element addresses the intensity paired. These studies also have practical application of biological activity and the implications of hydro- to evaluation of water quality risks because toxic and

72 radioactive mine tailings are copious in parts of the D.W., (ed) Pinon-Juniper Ecosystems for basin; their entrainment in sediments may adversely Sustainability and Social Needs. affect water and riparian habitat downstream. Al­ Bingham, G.E.; Kluzek, E.; Lamaye, A.s.; Riley, I.P. though these studies focus principally on sedimen­ 1995. A nested model chain between GCM scale tary processes, they will provide information that and river flow: A testbed for vegetation, erosion, benefit the integrated management of the Rio Puerco and water yield scaling studies. Preprint, Ameri­ and Rio Grande ecosystems. Issues as broad as the can Meteorological Society, Conference on Hydrol­ health of the bosque or wetland forests, the water ogy, Jan 15-20, 1995. Dallas, TX. supplies of El Paso and Albuquerque, and the gen­ Boulton, A.J.; Peterson, C.G.; Grimm, N.B. 1992a. Sta­ eral economy of the Rio 'Grande border region may bility of an aquatic macroinvertebrate community eventually be related to these analyses. in a multiyear hydrologic disturbance regime. Ecol­ ogy. 73: 2192-2207. REFERENCES Boulton, A.J.; Valett, H.M.; Fisher, S.G. 1992b. Spa­ tial distribution and taxonomic composition of the Aguilar, R.; Francis, R.E.; Stout, P.J. 1990. Erosion/ hyporheos of several Sonoran Desert streams. depositional cycles reflected by relict soil horizons, Archiv fur Hydrobiologie. 125: 37-61. Rio Puerco watershed. Agronomy Abstracts. Bretschko, G.; Leichtfried, M. 1987. The determina­ American Public Health Association. 1992. Standard tion of organic matter in river sediments. Archiv methods for the examination of water and waste­ fur Hydrobiologie. 68: 403-417. water, 18th ed. Amer. Water Works Assoc. Bruning, J.E. 1973. Origin of the Popotosa Formation, 1106 p. North Central Socorro County, New Mexico (Ph.D. Andrade Jr., E.R.; Sellers, W.D. 1988. El Nino south­ dissertation). New Mexico Institute of Mining and ern oscillation phenomenon and the Sevilleta Technology. 132 p. Long-Term Ecological Research Site. Unpublished Bryan, K. 1925. Date of channel trenching (arroyo manuscript available from Department of Biology, cutting) in the arid Southwest. Science. 62: 338- University of New Mexico, Albuquerque, NM. 16 p. 344. Baldwin, B. 1963. Part 2, Geology. In: Spiegel, Zane, Bryan, K. 1938. Geology and ground-water condi­ and B. Baldwin. Geology and Water Resources of tions of the Rio Grande Depression in Colorado the Santa Fe Area, New Mexico. U.S. Geological and New Mexico. In: (U.S.) Natural Resources Survey Water-Supply Paper 1525. 21-89 p. Committee, Regional Planning part VI-The Rio Baltz, E.H. 1978. Resume of Rio Grande Depression Grande Joint Investigations in the Upper Rio in North-Central New Mexico. In: Guidebook to Grande Basin in Colorado, New Mexico, and Texas, Rio Grande rift in New Mexico and Colorado, com­ 1936-37: U.s. Government Printing Office, Vol. 1. piled by Hawley, J.W. New Mexico Bureau of 197-225 pp. Mines and Mineral Resources, cir. 163.210-228 p. Bryan, K.; Post, G.M. 1927. Erosion and control of Bencala, K.E. 1984. Interactions of solutes and stream­ silt on the Rio Puerco, New Mexico. October, 1927. bed sediments 2. A dynamic analysis of coupled Report of the Chief Engineer, Middle Rio Grande hydraulic and chemical processes that determine Conservancy District, Albuquerque, NM. 174 p. solute transport. Water Resources Research. 20: Bryson, R.A.; Hare, F.K. 1974. Climates of North 1804-1814. America. World survey of climatology, Vol. 11, Bencala, K.E. 1993. A perspective on stream­ Elsevier Science Publishers B.V., Amsterdam. catchment connections. Journal of the North Castro, N.M.; Hornberger, G.M. 1991. Surface­ American Benthological Society. 12: 44-47. subsurface water interactions in an alluvia ted Bencala, K.E.; Walters, R.A. 1983. Simulation of sol­ mountain stream channel. Water Resources ute transport in a mountain pool-and-riffle stream: Research. 27: 1613-1621. a transient storage model. Water Resources Re­ Chapelle, F.H; Lovely, D.R. 1990. Rates of bacterial search. 19: 718-724. metabolism in deep coastal-plain aquifers. Applied Betancourt, J.L.; Pierson, E.A.; Rylander, K.A.; and Environmental Microbiology. 56: 1865-1874. Fairchild-Parks, J.A.; Dean, J.s. 1993. Influence of Chapin, C.E.; Seager, W.R. 1975. Evolution of the Rio history and climate on New Mexico Pinon-Juni­ Grande rift in the Socorro and Las Cruces areas. per Woodlands. pp. 42-62. IN: Aldon, E.F.; Shaw, In: New Mexico Geological Society Guidebook,

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