San Pedro River

Riparian fire studies in the American Southwest have focused on flow-regulated rivers and typically show increase in introduced Tamarix, a species with high resprout capacity, and declines in Populus. Effects of fire, however, can vary with environmental setting. We examined riparian fire along the free-flowing Upper San Pedro River (Arizona) by making temporal comparisons supplemented by spatial contrasts between burned and unburned sites. Pre-fire, Populus fremontii and Salix gooddingii were dominant species, with Tamarix sparse in the understory. Species differed in mortality and resprout rates, producing post-fire vegetation change. Mortality was highest for Tamarix, intermediate for Salix, and lowest for Populus, and also varied among size classes. Resprout rate was low for Populus, high for Salix, and also high for the few surviving Tamarix. The net effect was changes in population size structure (relative shifts towards larger Populus but smaller individuals of other species) and forest composition (decreased abundance of Tamarix relative to Populus and Salix), and in spatial distribution of stems. Tamarix’s low ability to survive fire resulted from competitive suppression by Populus and Salix, with their dominance a product of the site’s flow regime. Results indicate that post-fire outcomes within the riparian Southwest are variable and context-dependent.

We combined remote sensing and in-situ measurements to estimate evapotranspiration (ET) from riparian vegetation over large reaches of western U.S. rivers and ET by individual plant types. ET measured from nine flux towers (eddy covariance and Bowen ratio) established in plant communities dominated by five major plant types on the Middle Rio Grande, Upper San Pedro River, and Lower Colorado River was strongly correlated with Enhanced Vegetation Index (EVI) values from the Moderate Resolution Imaging Spectrometer (MODIS) sensor on the NASA Terra satellite. The inclusion of maximum daily air temperatures (Ta) measured at the tower sites further improved this relationship. Sixteen-day composite values of EVI and Ta were combined to predict ET across species and tower sites (r2 = 0.74); the regression equation was used to scale ET for 2000–2004 over large river reaches with Ta from meteorological stations. Measured and estimated ET values for these river segments were moderate when compared to historical, and often indirect, estimates and ranged from 851–874 mm yr− 1. ET of individual plant communities ranged more widely. Cottonwood (Populus spp.) and willow (Salix spp.) stands generally had the highest annual ET rates (1100–1300 mm yr− 1), while mesquite (Prosopis velutina) (400–1100 mm yr− 1) and saltcedar (Tamarix ramosissima) (300–1300 mm yr− 1) were intermediate, and giant sacaton (Sporobolus wrightii) (500–800 mm yr− 1) and arrowweed (Pluchea sericea) (300–700 mm yr− 1) were the lowest. ET rates estimated from the flux towers and by remote sensing in this study were much lower than values estimated for riparian water budgets using crop coefficient methods for the Middle Rio Grande and Lower Colorado River.

A portion of Arizona’s San Pedro River is managed as a National Riparian Conservation Area but is potentially affected by ground-water withdrawals beyond the conservation area borders. We applied an assessment model to the Conservation Area as a basis for monitoring long-term changes in riparian ecosystem condition resulting from changes in river water availability, and collected multi-year data on a subset of the most sensitive bioindicators. The assessment model is based on nine vegetation bioindicators that are sensitive to changes in surface water or ground water. Site index scores allow for placement into one of three condition classes, each reflecting particular ranges for site hydrology and vegetation structure. We collected the bioindicator data at 26 sites distributed among 14 reaches that had similar stream flow hydrology (spatial flow intermittency) and geomorphology (channel sinuosity, flood-plain width). Overall, 39% of the riparian corridor fell within condition class 3 (the wettest condition), 55% in condition class 2, and 6% in the driest condition class. Condition class 3 reaches have high cover of herbaceous wetland plants (e.g., Juncus and Schoenoplectus spp.) along the perennial stream channel and dense, multi-aged Populus-Salix woodlands in the flood plain, sustained by shallow ground water in the stream alluvium. In condition class 2, intermittent stream flows result in low cover of streamside wetland herbs, but Populus-Salix remain abundant in the flood plain. Perennial wetland plants are absent from condition class 1, reflecting highly intermittent stream flows; the flood plain is vegetated by Tamarixa small tree that tolerates the deep and fluctuating ground water levels that typify this reach type. Abundance of herbaceous wetland plants and growth rate of Salix gooddingii varied between years with different stream flow rates, indicating utility of these measures for tracking short-term responses to hydrologic change. Repeat measurement of all bioindicators will indicate long-term trends in hydro-vegetational condition.

The giant 1960 earthquake, with a 1000 km-long rupture, between the Nazca and South American plates, triggered three landslides damming the channel of the San Pedro
River near the mouth of the Riñihue Lake during two months (named “tacos” 1, 2 and 3). Such damming implied a serious threat for the human downstream settlements, including Valdivia city. Afortunatelly, disaster was avoided by a controlled opening. Historical evidence shows the occurrence of a similar process nearby triggered by the 1575 earthquake. However,
in 1575 the dam accumulated water for five months, collapsing catastrophically and claiming thousands of Indian lives. Based on geomorphological evidence, previous works have located
the evidence of such landslide on the southern river bank. It is a huge 2.6 km-long escarpment including equally large landslide deposits. Here, using primary historical sources, geomorphic dating, and geomorphometric analysis, we propose the 1575 landslide was actually smaller than the proposed one and it was on the northern bank. Finally, we propose the potential of our approach as a tool for paleoseismic studies in south-central Chile.

ABSTRACT The San Pedro River originates in northern Sonora near the town of Cananea and spans the U.S. - Mexico border into southeastern Arizona. The San Pedro Basin and perennial portions of its river support one of the most ecological diverse regions in the world. The regional groundwater aquifer which largely supports perennial flow and the associated riparian ecosystem is the primary water source for a number of communities, and for the Cananea copper mine in Sonora, which produces roughly two to three percent of the world's copper, and Ft. Huachuca, a major military installation in Arizona and the largest employer of southern Arizona. This presentation will discuss strategies and efforts over the past decade on both sides of the border to link hydrological, ecological and social sciences to aid elected officials and decision-makers in managing the basin, its growing population, and the water it so vitally depends upon. The disparate legal, cultural, economic and scientific environments, as well as the unequal degrees of decentralization and regional autonomy on the two sides of the border have resulted in distinct concerns and approaches to water resource management and varying rates of success. In the Sonoran portion of the basin water quality is the primary concern and in Arizona, water quantity is the major concern. The paper will report on sustained binational efforts and constraints encountered by researchers at the University of Arizona's NSF-funded SAHRA project and several NOAA-supported efforts in the basin region.

The San Pedro Basin sits within an intermountain ecotone with the Sonoran and Chihuahuan Deserts to the west and east and the Rocky Mountain and Sierra Madre Mountain habitats to the north and south. The headwaters of the basin originate in northern Sonora and flow north into southeast Arizona. As the region's only remaining perennial stream, the San Pedro River

Airborne lidar (light detecting and ranging) is a useful tool for probing the structure of forest canopies. Such information is not readily available from other remote sensing methods and is essential for modern forest inventories. In this study, small-footprint lidar data were used to estimate biophysical properties of young, mature, and old cottonwood trees in the Upper San Pedro River Basin, Arizona, USA. The lidar data were acquired in June 2003 and 2004, using Optech's 1233 ALTM (Optech Incorporated, Toronto, Canada). Canopy height, crown diameter, stem diameter at breast height (dbh), canopy cover, and mean intensity of return laser pulses from the canopy surface are estimated for the cottonwood trees from lidar data. The lidar estimates show a good degree of correlation with ground-based measurements. This study also demonstrates that other parameters of young, mature, and old cottonwood trees such as height and canopy cover, when derived from lidar, are significantly di...

We investigate one the Middle and Upper San Pedro River Valley during the AD 750-1450 time period and assess the extent to which major regional cultural shifts correspond to local cultural shifts. Specifically, we investigate diachronic trends in architecture and settlement layout, ceramic traditions and exchange, and mortuary practices and suggest that changes in these patterns represent two simultaneous processes—the integration of Hohokam, Mimbres, and northern Sonora cultural practices and populations into the area, and the continuity of underlying, locally contingent life ways maintained regardless of regional patterns of cultural cohesion and dissolution.

Data on geology and geophysics in the San Pedro River Basin in Sonora, Mexico were combined to develop a three-dimensional conceptual model of the alluvial-fill aquifer in the basin that is being used to construct a regional ground-water-flow model. In Mexico, the headwater region of the river encompasses approximately 1,800 square kilometers of an ungaged catchment system. This feeds a

This paper reviews regional climate knowledge and vulnerability in the northern Mexico San Pedro River Basin, with a focus on water quality, quantity, and management issues on the Mexican side of the border. A discussion based on the available literature is ...

Groundwater and surface flow depletions are altering riparian ecosystems throughout the southwestern United States. Due in large part to hydrologic alterations and land use changes, forests of the pioneer trees Populus fremontii (Fremont cottonwood) and Salix gooddingii (Goodding willow) have declined. In many areas these forests have been replaced by shrublands and woodlands of Tamarix ramosissima (salt cedar). Previous work

The Upper San Pedro River Basin in southeastern Arizona is well known for its avian diversity; however, water use by Sierra Vista, Fort Huachuca, and agriculture in the basin threatens to lower its water table. This, in turn, could alter vegetation in the basin in a way that ...

Groundwater and surface flow depletions are altering riparian ecosystems throughout the southwestern United States. Due in large part to hydrologic alterations and land use changes, forests of the pioneer trees Populus fremontii (Fremont cottonwood) and Salix gooddingii (Goodding willow) have declined. In many areas these forests have been replaced by shrublands and woodlands of Tamarix ramosissima (salt cedar). Previous work

Along the Upper San Pedro River in southeastern Arizona deep-rooted woody phreatophytes such as the non-native Tamarix ramosissima (salt cedar) and the native Prosopis velutina (velvet mesquite) are expanding their range, but we have little understanding about how this change in vegetation composition will change the cycling of water and nutrients in these riparian ecosystems. We compared water and carbon

MODFLOW is a groundwater flow model that has been used to model flow in the San Pedro River basin. The San Pedro flows into Arizona from northern Sonora, Mexico, and is the largest undammed river in the southwest US. A portion of it - the San Pedro Riparian National Conservation Area - is federally protected in recognition of the ecosystem's