Rio Conchos Research Articles

The Pine-Oak Forest of the Rio Conchos Basin, Mexico: Key to Rain Production and Soil Erosion Control

Under the current climate crisis, the ecological integrity of forest ecosystems is key to increasing resilience and the sustainability of water and soil resources. Most forests around the world have experienced deforestation and degradation in the past few decades; however, the rate at which these occur varies depending on many factors, including the type of trees, management, and climate. We conducted a review of the deforestation, degradation, and soil erosion of the pine-oak forest within the Rio Conchos basin in northern Mexico. Preference was given to recent studies (last 10 years) conducted within this basin. Out of 27 recent publications on oak forests in Mexico, 19 focused on this forest and half of them were in Spanish. The results show that pine trees are more affected than oak trees, also that the deforestation rate has increased with time and is greater at higher elevations, making this area vulnerable to loss of topsoil during extreme hydrological events. Studies report an annual change in cover rate between 1985 and 2016 of −1.2% for pine, oak and mix vegetation. More recently, between 2000 and 2018, the change in pine cover was calculated as −2.8% concurrent with a +3.4% increase in cover of oak and other secondary vegetation. Proposed conservation strategies vary from runoff control to increased collaboration between landowners, government agencies, and stakeholders.

The future of water in a desert river basin facing climate change and competing demands: A holistic approach to water sustainability in arid and semi-arid regions

Study regionThe Middle Rio Grande (MRG), defined by the portion of the basin from Elephant Butte Reservoir in New Mexico to the confluence with the Rio Conchos in Far West Texas, U.S.A. and Northern Chihuahua, Mexico. Study focusThe future of water for the MRG and many other arid and semi-arid regions of the world is challenged by a changing climate, agricultural intensification, growing urban populations, and a segmented governance system in a transboundary setting. The core question for such settings is: how can water be managed so that competing agricultural, urban, and environmental sectors can realize a sustainable future? We synthesize results from interdisciplinary research aimed at “water futures”, considering possible, probable, and preferable outcomes from the known drivers of change in the MRG in a stakeholder participatory mode. We accomplished this by developing and evaluating scenarios using a suite of scientifically rigorous computer models, melded with the input from diverse stakeholders. New hydrological insights for the regionUnder likely scenarios without significant interventions, relatively cheap and easy to access water will be depleted in about 40 years. Interventions to mitigate this outcome will be very costly. A new approach is called for based on “adaptive cooperation” among sectors and across jurisdictions along four important themes: information sharing, water conservation, greater development and use of alternative water sources, and new limits to water allocation/withdrawals coupled with more flexibility in uses.

Evaluation of climate variability on sustainability for transboundary water supply in Chihuahua, Mexico

Study regionThis is study of the Rio Conchos Watershed, Chihuahua, Mexico. Study focusThis study provides assessment of climate variability from analysis of instrumental climate and reservoir operations data, plus nearby tree-ring indices in Chihuahua, Mexico. Water demand include international treaty deliveries, growing agricultural land use, and intensified crop production. Analysis of climate cycles includes frequency analysis of local multidecadal instrumental hydrologic time series and multi-century tree-ring indices. In addition, tree-ring indices were compared with 14C content in tree rings to assess the presence of the millennial solar cycle. New hydrological insights for the regionMost of the climate variability within inter-annual to interdecadal periods are aligned with Pacific Decadal Oscillation (PDO)-like climate cycles. New multi-century climate cycles were discovered from tree-ring indices that have a profound impact on sustainability of food and water security. Historical droughts of 8-year average duration within PDO-like cycles that span longer (12–43 year) periods were newly identified which are longer than the 5-year delivery cycles used in the 1944 International Treaty of the Rivers. Mega-droughts were discovered to occur within multi-century climate cycles. Multi-century cycles identified in tree-ring indices were likely driven by solar luminosity changes from the millennial solar cycle and not just recent anthropogenic climate change. Climate variability and temperature increases will further amplify cycles of supply and demand and exacerbate sustainability, mitigation, and management strategies. Conjunctive use combined with reservoir operations will broaden sustainability portfolio of options, reducing demand effects as well as enhance supply options and replenishment effects.

STATUS OF FRESHWATER MUSSELS (UNIONIDAE) OF THE RÍO CONCHOS BASIN, CHIHUAHUA, MEXICO

Before this study, researchers had not systematically surveyed the Rio Conchos, a tributary of the Rio Grande located in northern Mexico, for freshwater mussels. The Texas hornshell, Popenaias popeii, an endangered species under the United States Endangered Species Act, occurs in the main stem of the Rio Grande near its confluence with the Rio Conchos. The Texas hornshell's proximity to the Rio Conchos prompted us to survey to determine whether P. popeii also occurs within the Conchos basin. Additionally, previous researchers described the Conchos disk, Disconaias conchos, from the Rio Conchos but, to date, no one has reported live individuals of this species. The goal of this study was to determine the status of mussels within the Rio Conchos basin and to provide a baseline for future monitoring efforts. We qualitatively surveyed 11 sites within the Rio Conchos basin in May 2018. In total, we found two live individuals of the paper pondshell, Utterbackia imbecillis, at one site in the Rio San Pedro, a tributary of the Conchos River, and as shells of recently live individuals at two sites in the Rio Conchos. We found D. conchos as relict shells only at three sites, two in the Rio Conchos and one in a tributary of the river at Coyame. The lack of live or fresh-dead material suggests that D. conchos is extinct. We also found live individuals of nonnative Asian clams (Corbicula spp.) at 10 sites. Sand and gravel mining, high organic pollution, and inadequate instream flows were evident throughout the basin and might explain the general absence of mussels.

Impacts of Urbanization and Intensification of Agriculture on Transboundary Aquifers: A Case Study

AbstractThe objectives were to (1) delineate the complex set of rules governing the fate and transfer of water rights as agricultural land is urbanized in Texas and New Mexico in the United States and Chihuahua in Mexico and (2) estimate the change in water use as a result of such urbanization. Important additional determinants of water use in the region include intensification of agriculture and the hydroschizophrenic policy framework. We conducted interviews with key informants to identify the possible outcomes for changes in water rights as land is urbanized. We constructed decision trees for each of the three jurisdictions, Chihuahua, Texas, and New Mexico, that identified the possible outcomes from urbanization. For each of the possible outcomes in the decision tree, we estimated a range of potential water use outcomes and the most likely water use outcome on a per unit of land area basis. Results show that urbanization of agricultural land has almost no impact on the aggregate demand for or use of surface water. However, the impacts of urbanization on groundwater use vary considerably over the region from Texas to New Mexico to Chihuahua. In New Mexico and Chihuahua where groundwater rights can be leased or sold to other users, the likely impact is a net increase in groundwater use as land is urbanized, ranging from 0 to 3,000 m3/ha in New Mexico and averaging 3,000 m3/ha or more in Chihuahua. In Texas, there is a net benefit in groundwater savings, but those savings are subject to being offset by increased groundwater pumping to meet the needs of expanding pecan production. The net result is continued groundwater depletion, threatening the life of the transboundary aquifers, the Hueco Bolson and the Mesilla Bolson, in the Middle Rio Grande basin (defined as the part of the basin between Elephant Butte Reservoir in New Mexico to the confluence of the river with the Rio Conchos from Mexico).

Identity and distribution of the Nearctic otter (Lontra canadensis) at the Rio Conchos Basin, Chihuahua, Mexico

We have identified a scarcely known river otter population from the Upper Rio Conchos basin, northern Mexico, finding a well-established population of the Nearctic otter Lontra canadensis. A pioneer study of these otters at Rio San Pedro, a tributary of the Rio Conchos, described them as Neotropical otters, Lontra longicaudis; at that time, no specimens or photographs of these otters were available from the locality. Therefore, its taxonomic status remained unclear for various decades. Rio Conchos is one of the major tributaries of Rio Grande (Rio Bravo in Mexico) and its headwaters are located high in the Sierra Madre Occidental. A juvenile otter fur obtained from Rio San Pedro was compared to two furs of Neotropical otters from Oaxaca and Sonora, with the aim to compare the structure of primary hairs (PH) and secondary hairs (SH) in order to know their specific status. Camera traps were set-up at Rio San Pedro in Chihuahua and in Arroyo Bamochi (occupied by L. longicaudis) in Sonora in 2015 to compare individuals, population structure and occupation in both places. Two other places were surveyed to confirm the presence of river otters: Rio Conchos and Rio Santa Isabel. Based on hair characteristics (primary and secondary hairs from the juvenile) and photographic evidence from camera-traps, we confirm that otters from Rio San Pedro, belong to the Nearctic otter, Lontra canadensis. And presumably in other localities visited in the Concho’s river basin that also has presence of otters, such as Rio Santa Isabel and Rio Conchos. The population structure from Arroyo Bamochi and Rio San Pedro were similar in both areas, but the density of otters is higher at Arroyo Bamochi than at Rio San Pedro, even though there is no significant difference between the two sites. Specimens of river otters from Rio Grande basin have been identified as L. canadensis lataxina, Cuvier, 1823. The former distribution area of this species ranges from inland US across the Rio Grande basin in the Rocky Mountains, the Rio Pecos, further East, flowing south and southeast into the Gulf of Mexico. The finding reported here represents a major area occupied by this species, and a significant conservation issue for their protection in Mexico, as well as an indicator of the healthy conservation status of the upper Rio Conchos

Observations on Habitat Use of Age-0 Rio Grande Blue Sucker (Cycleptus sp. cf. elongatus)

During April 2018, we collected 23 age-0 (33–55 mm total length) Rio Grande Blue Sucker (Cycleptus sp. cf. elongatus) from 3 locations in the Rio Grande near the confluence with the Rio Conchos where the species is rarely reported. Age-0 Rio Grande Blue Suckers occurred in habitats ranging from 6 to 81 cm deep, with current velocities ranging from 0 to 1.03 m/s over silt, sand, gravel, cobble, and bedrock substrates. There was limited evidence for greater detection in slower-velocity habitats with bedrock, silt, and sand substrates, but the habitats we sampled were not unique from habitats sampled in a previous year-round study reporting only a single individual. We conclude that our sampling occurred shortly after successful recruitment, and that age-0 Rio Grande Blue Suckers use a wide variety of habitats.

The spatial scale of homogenisation and differentiation in Chihuahuan Desert fish assemblages

Abstract We examined riverine desert fish assemblages in the Chihuahuan Desert, U.S.A. at multiple spatial scales of similarity to assess long‐term changes to assemblage distinctiveness, identify individual species responsible for changes, and determine the importance of geographic context and species resolution in interpreting patterns of change. We used a well‐documented historical data set on fish distribution and abundance, and recent collections of fishes that provided a paired analytical design across 36 localities spanning nearly 3 decades. Patterns of faunal homogenisation and differentiation were assessed at basin‐wide, sub‐basin and river‐reach scales with species occurrence and relative abundance data. Individual species responses were examined to identify the drivers of assemblage change across time. Patterns of assemblage similarity varied across spatial scales and produced seemingly incongruous trends across time. Assemblage distinctiveness depended on the spatial extent of the analyses, the geographical structuring of the fish assemblages, and whether occurrence or relative abundance data were used. These dependencies led to interesting and conflicting patterns of homogenisation and differentiation. The Rio Grande sub‐basin showed strong homogenisation with convergence between upstream and downstream reaches that corresponded to declining water quality and quantity from the Rio Conchos in Mexico. In contrast, the Pecos River sub‐basin showed strong differentiation between upstream and downstream reaches that corresponded to the successful colonisation and spread of the non‐native gulf killifish (Fundulus grandis) in the upper reach, where water quantity and quality have declined. Spatial variability in fish assemblages and their degree of change from historical conditions were largely congruent with anthropogenic modifications to the flow regime and variability in the success of invasive gulf killifish in the basin. The use of species occurrence as opposed to relative abundance data, and the spatial scale of analysis are crucial choices in studies of faunal homogenisation and differentiation, and we have demonstrated how these choices lead to variable results for our study system. Our multi‐scale approach and examination of individual species responses identified the ultimate drivers of these differences and illustrated the importance of scale‐dependent effects and geographical context on patterns of assemblage distinctiveness, especially with regard to species invasion, species loss and relative abundance shifts.

Estimating the Natural Flow Regime of Rivers With Long‐Standing Development: The Northern Branch of the Rio Grande

AbstractAn estimate of a river's natural flow regime is useful for water resource planning and ecosystem rehabilitation by providing insight into the predisturbance form and function of a river. The natural flow regime of most rivers has been perturbed by development during the 20th century and in some cases, before stream gaging began. The temporal resolution of natural flows estimated using traditional methods is typically not sufficient to evaluate cues that drive native ecosystem function. Additionally, these traditional methods are watershed specific and require large amounts of data to produce accurate results. We present a mass balance method that estimates natural flows at daily time step resolution for the northern branch of the Rio Grande, upstream from the Rio Conchos, that relies only on easily obtained streamflow data. Using an analytical change point method, we identified periods of the measured flow regime during the 20th century for comparison with the estimated natural flows. Our results highlight the significant deviation from natural conditions that occurred during the 20th century. The total annual flow of the northern branch is 95% lower than it would be in the absence of human use. The current 2 year flood has decreased by more than 60%, is shorter in duration, and peaks later in the year. When compared to unregulated flows estimated using traditional mass balance accounting methods, our approach provides similar results.

Economic effects of a reservoir re-operation policy in the Rio Grande/Bravo for integrated human and environmental water management

Abstract Study region The study region is the Big Bend Reach of the Rio Grande/Bravo, from Luis L. Leon reservoir in the Rio Conchos to Amistad reservoir in the Rio Grande/Bravo mainstem. This reach is part of the Rio Grande trans-boundary river basin between United States and Mexico, an area of recognized environmental and socioeconomic significance by both countries. Study focus A central challenge of Integrated Water Resources Management is the design and implementation of policies to allocate water to both humans and the environment in a sustainable manner. This study uses the results from a water-planning model of the Big Bend Reach of the Rio Grande/Bravo to quantify and compare the economic benefits of two water management policies: business as usual (Baseline) policy and a proposed reservoir re-operation policy to provide environmental flows (EFs). New hydrological insights This study determines the economic feasibility of the EF policy. Results show that a proposed Environmental Flow policy would increase irrigated agriculture profit, slightly decrease recreational activities profit, and reduce costs from flood damage and environmental restoration compared to the baseline policy. In addition to supporting ecological objectives, the proposed EF policy would increase the economic benefits of water management objectives.

Arsenic, lead, and uranium concentrations on sediments deposited in reservoirs in the Rio Grande Basin, USA–Mexico border

The El Granero reservoir is the last reservoir of the Rio Conchos before it joins the Rio Grande at the Mexico–USA border. This reservoir, together with the San Marcos reservoir, is located in the arid region of Chihuahua, Mexico. High, naturally occurring radioactivity levels, as well as high arsenic (As) concentrations, have been found in both reservoirs. The main goal of this research was to establish the spatial and temporal distribution of trace and radioactive elements in surface sediments and cores collected from these reservoirs. Sediment cores were dated using 210Pb and 137Cs measurements and applying the constant rate of supply (CRS) model. Major, trace, and radioactive elements were determined in surface samples and three sediment cores. Radioactive elements were determined by both alpha and gamma spectrometry. Major and trace elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using the EPA 3051a method. Enrichment factors (EF), contamination factors (CF), and pollution load indexes (PLI) were calculated in order to identify the human impact in both reservoirs, whereas the chemical index weathering (CIW) was used to assess differences in the degree of weathering. High uranium (U) enrichment (EFs = 24.9–54.7) was observed in core layers at the San Marcos reservoir, while in surface sediments, this enrichment was lower. The high variability of lead (Pb) and As in sediment cores from the Granero reservoir was attributed to human influence. Arsenic and Pb enrichment differences between entry and exit sediment cores were explained by the filtering capabilities of the elongated shape, the topography, and the presence of plants on the reservoir’s bed. The highest PLI was found at the entrance core of the Granero reservoir. The natural element concentration levels of As, Pb, and U were established at the Granero reservoir. High EFs for As and Pb suggest an anthropogenic origin of these pollutants at specific time intervals. High U concentrations in the San Marcos area are explained as naturally occurring. The concentrations of As in most of the studied sediments could pose a risk to human health by As ingestion, since they are above the probable effect level (PEL).

Desertification, salinization, and biotic homogenization in a dryland river ecosystem

This study determined long-term changes in fish assemblages, river discharge, salinity, and local precipitation, and examined hydrological drivers of biotic homogenization in a dryland river ecosystem, the Trans-Pecos region of the Rio Grande/Rio Bravo del Norte (USA/Mexico). Historical (1977–1989) and current (2010–2011) fish assemblages were analyzed by rarefaction analysis (species richness), nonmetric multidimensional scaling (composition/variability), multiresponse permutation procedures (composition), and paired t-test (variability). Trends in hydrological conditions (1970s–2010s) were examined by Kendall tau and quantile regression, and associations between streamflow and specific conductance (salinity) by generalized linear models. Since the 1970s, species richness and variability of fish assemblages decreased in the Rio Grande below the confluence with the Rio Conchos (Mexico), a major tributary, but not above it. There was increased representation of lower-flow/higher-salinity tolerant species, thus making fish communities below the confluence taxonomically and functionally more homogeneous to those above it. Unlike findings elsewhere, this biotic homogenization was due primarily to changes in the relative abundances of native species. While Rio Conchos discharge was>2-fold higher than Rio Grande discharge above their confluence, Rio Conchos discharge decreased during the study period causing Rio Grande discharge below the confluence to also decrease. Rio Conchos salinity is lower than Rio Grande salinity above their confluence and, as Rio Conchos discharge decreased, it caused Rio Grande salinity below the confluence to increase (reduced dilution). Trends in discharge did not correspond to trends in precipitation except at extreme-high (90th quantile) levels. In conclusion, decreasing discharge from the Rio Conchos has led to decreasing flow and increasing salinity in the Rio Grande below the confluence. This spatially uneven desertification and salinization of the Rio Grande has in turn led to a region-wide homogenization of hydrological conditions and of taxonomic and functional attributes of fish assemblages.

Genesis of antibiotic resistance (AR) I: monitoring of microbial pathogens with AR by Texas Clean Water Program in Rio Grande Basin including Amistad Reservoir (986.1)

Water‐related (borne) diseases are categorized into four different classes: waterborne, water‐washed, water‐based, and water‐related insect vectors. The Pacific Institute Research Report (http://www.pacinst.org/) speculates that by 2020 a global mortality rate of 34‐76 million people will be observed due to water related diseases. One of the main sources for water in Southwest Texas is the Rio Grande River which receives its water influx from Las Vacas, Rio Conchos, Rio Rodrigo, and Rio Salado tributaries from Mexico. The Rio Grande River flows through the southwest border and is stored in the Amistad Reservoir located in Del Rio, Texas. The “Texas Clean Rivers Program” a collaborative program operated by The Amistad Reservoir ‐ International Boundary and Water Commission, US section(USIBWC) ‐ The Rio Grande Basin and The Texas Commission on Environmental Quality(TCEQ) monitor the microbial and water quality issues in Texas. As per the 2012 Basin Highlights Report for the Rio Grande Basin in Texas show that there were between 14,200 colonies/100 ml and 3,800,000 colony forming units/100ml of the fecal coli form bacteria in the water samples. High levels of Biological Oxygen Demand, and Chemical Oxygen Demand were also detected in the water samples tested in the urban areas of Del Rio, Eagle Pass and Laredo. Taken together the severity of the contamination, BOD and COD increases the mutagenic potential in the microbial pathogens (bacteria) to acquire antibiotic resistance through known and unknown mechanisms.Grant Funding Source: PROFESSIONAL DEVELOPEMENT FUNDS ‐

The geomorphic effectiveness of a large flood on the Rio Grande in the Big Bend region: Insights on geomorphic controls and post-flood geomorphic response

Since the 1940s, the Rio Grande in the Big Bend region has undergone long periods of channel narrowing, which have been occasionally interrupted by rare, large floods that widen the channel (termed a channel reset). The most recent channel reset occurred in 2008 following a 17-year period of extremely low stream flow and rapid channel narrowing. Flooding was caused by precipitation associated with the remnants of tropical depression Lowell in the Rio Conchos watershed, the largest tributary to the Rio Grande. Floodwaters approached 1500m3/s (between a 13 and 15year recurrence interval) and breached levees, inundated communities, and flooded the alluvial valley of the Rio Grande; the wetted width exceeding 2.5km in some locations. The 2008 flood had the 7th largest magnitude of record, however, conveyed the largest volume of water than any other flood. Because of the narrow pre-flood channel conditions, record flood stages occurred.We used pre- and post-flood aerial photographs, channel and floodplain surveys, and 1-dimensional hydraulic models to quantify the magnitude of channel change, investigate the controls of flood-induced geomorphic changes, and measure the post-flood response of the widened channel. These analyses show that geomorphic changes included channel widening, meander migration, avulsions, extensive bar formation, and vertical floodplain accretion. Reach-averaged channel widening between 26 and 52% occurred, but in some localities exceeded 500%. The degree and style of channel response was related, but not limited to, three factors: 1) bed-load supply and transport, 2) pre-flood channel plan form, and 3) rapid declines in specific stream power downstream of constrictions and areas of high channel bed slope. The post-flood channel response has consisted of channel contraction through the aggradation of the channel bed and the formation of fine-grained benches inset within the widened channel margins. The most significant post-flood geomorphic changes have occurred at and downstream from ephemeral tributaries that contribute large volumes of sediment.

Conservation Genetics of an Undescribed Species ofDionda(Teleostei: Cyprinidae) in the Rio Grande Drainage in Western Texas

Abstract The systematic and conservation-genetic status of a population of the cyprinid genus Dionda in Alamito Creek, a tributary of the Rio Grande in Big Bend Ranch State Park, Presidio County, Texas, was assessed using mtDNA sequences and nuclear-encoded microsatellites. Phylogenetic analyses of the mitochondrial cytochrome b (cytb) gene revealed that the Dionda in Alamito Creek likely is conspecific with an undescribed species (Dionda species 1) known only from the Rio Conchos and Rio Nazas basins of Mexico and in the USA from Cibolo Creek, a small tributary of the Rio Grande drainage. Genetic variation of Dionda in Alamito Creek is extremely low. All 18 fish assayed for 1,533 base pairs of mitochondrial mtDNA (cytb and ND5 sequences) had the same haplotype, and 40 fish assayed for 34 nuclear-encoded microsatellites (25 monomorphic) averaged only 1.44 alleles/microsatellite (HE = 0.12). Estimates of current effective size (Ne) and effective number of breeders (Nb) were 22 and 28, respectively. Bayesia...

Rio Grande and Rio Conchos water supply variability over the past 500 years

The Rio Grande is a major source of water for parts of Mexico and the USA. The 2 main source regions for the Rio Grande system are the San Juan Mountains of the southern Rocky Mountains and the Sierra Madre Occidental in Mexico, which is the headwaters for the Rio Con- chos, the largest tributary of the Rio Grande. Precipitation and streamflow from these 2 source regions are largely independent of each other; winter snowpack is the dominant contributor to the annual streamflow north of the USAMexico border, and the North American monsoon is a key factor in the Rio Conchos basin. Reconstructions of water year (OctoberSeptember) streamflow for a gauge in the upper Rio Grande, 1508�2002, and of OctoberJuly precipitation in the Rio Con- chos watershed region, 1649�1993, also indicate a lack of correlation between the 2 basins over century time scales. Despite this lack of correlation, periods of concurrent multiyear drought have occurred over the past 4 centuries, most notably in the 1770s, 1890s and 1950s. These rare concur- rent droughts in the upper Rio Grande and Rio Conchos source regions may arise from large-scale forcing out of the Pacific Ocean and will be relevant to the binational planning of these water resources, which serve a large and growing population of users.

Development of a Hydrological Model for the Rio Conchos Basin

AbstractThis paper focuses on calibration and validation of a hydrologic model of the Rio Conchos Basin, a main Mexican tributary of the binational Rio Grande Basin. The Rio Conchos provides approximately 55% of the water deliveries to the United States under the 1944 water treaty signed between both countries. The hydrologic modeling has been developed using the one-dimensional, two-layer soil moisture accounting scheme embedded in the Water Evaluation and Planning (WEAP) model. A 10-year period was used to calibrate the model, which was achieved by a trial-and-error method for the adjustment of the model parameters. The results show a Nash-Sutcliffe coefficient of 0.84 at Ojinaga station (mouth of the basin) and 0.81 at La Boquilla, indicating good model performance. In general the model predicts well the monthly, annual, and maximum flows; but there are significant differences between the model values and undeveloped (naturalized) flows for low flow periods, especially at La Boquilla station. For model...

Challenges and Opportunities for Water of the Rio Grande

The Rio Grande has headwaters in Colorado, flows through New Mexico, and serves as the United States-Mexico border in Texas, emptying into the Gulf of Mexico. Snow melt in Colorado and northern New Mexico constitutes the water river supply for New Mexico and the El Paso region, whereas summer monsoonal flow from the Rio Conchos in Mexico and tributaries, including the Pecos River, provides the Rio Grande flow for southern Texas. The region is mostly semiarid with frequent long-term drought periods but is also characterized by a substantial irrigated agriculture sector and a rapidly growing population. International treaties and interstate compacts provide the rules for allocation of Rio Grande waters between the United States and Mexico and among Colorado, New Mexico, and Texas. Water rights in Texas have been adjudicated, but the adjudication process was based on a wet period; hence, contemporary Rio Grande water rights are overallocated. Issues related to the waters of the Rio Grande include frequent drought, increased municipal demand caused by a rapidly increasing population, supply variability, underdeliveries from Mexico, increasing salinity, inefficient delivery systems, health issues of the population, no economic/financial incentives for farmers to conserve, and water is not typically priced for efficiency. Stakeholders are interested in identifying solutions to limited water supplies while there is increasing demand. There are several activities in place addressing Rio Grande-related water needs, including enhancing delivery distribution efficiency of raw water, conversion of rights from agriculture to urban, improving both agricultural irrigation field distribution and urban use efficiency, developments in desalination, and litigation. None of the solutions are easy or inexpensive, but there are encouraging cooperative attitudes between stakeholders.

Temporal variations of natural soil salinity in an arid environment using satellite images

In many remote arid areas the scarce amount of conventional soil salinity data precludes detailed analyses of salinity variations for the purpose of predicting its impact on agricultural production. A tool that is an appropriate surrogate for on-ground testing in determining temporal variations of soil salinity is Landsat satellite data. In this study six Landsat scenes over El Cuervo, a closed basin adjacent to the middle Rio Conchos basin in northern Mexico, were used to show temporal variation of natural salts from 1986 to 2005. Natural salts were inferred from ground reference data and spectral responses. Transformations used were Tasseled Cap, Principal Components and several (band) ratios. Classification of each scene was performed from the development of Regions Of Interest derived from geochemical data collected by SGM, spectral responses derived from ENVI software, and a small amount of field data collected by the authors. The resultant land cover classes showed a relationship between climatic drought and areal coverage of natural salts. When little precipitation occurred three months prior to the capture of the Landsat scene, approximately 15%–20% of the area was classified as salt. This is compared to practically no classified salt in the wetter years of 1992 and 2005 Landsat scenes. En áreas remotas y áridas la cantidad de datos de salinidad obtenidos por métodos convencionales es escasa por lo general, siendo esto un impedimento para realizar estudios detallados de salinidad y su impacto a cultivos. El análisis de imágenes satelitales es una herramienta útil para la determinación de variaciones estacionales de salinidad de suelo en estas áreas. En este estudio utilizamos seis imágenes de satélite de la cuenca cerrada El Cuervo, situada en el norte de México y adyacente a la cuenca del rio Conchos, con el objeto de dar seguimiento a las variaciones naturales de salinidad de suelo entre 1986 y 2005. Los niveles de salinidad se establecieron a partir de mediciones de campo y de información espectrográfica de las imágenes. Se aplicaron las transformaciones de Tasseled Cap, Componentes Principales, y algunos cocientes de bandas. La clasificación de las imágenes se obtuvo por medio de la técnica de Regiones de Interés e integrando datos geoquímicos de sedimentos (Servicio Geológico Mexicano, SGM), técnicas espectrométricas de análisis incluidas en el programa de sensores remotos ENVI y resultados de muestras de campo (autores). Los resultados muestran una relación substancial entre salinidad y episodios de sequia. Para imágenes con escasa precipitación de tres meses o más, aproximadamente 15 a 20% del área clasificó como suelo salino, mientras que en años de más intensa precipitación como 1992 y 2005 ningún área fue clasificada como suelo salino.

Description of Gambusia zarskei sp. n. - a new poeciliid fish from the upper Rio Conchos system, Chihuahua, Mexico (Teleostei: Cyprinodontiformes: Poeciliidae)

Gambusia zarskei, new species, is described from the upper drainage of Rio Conchos, Rio Grande system, Chihuahua, Mexico. It is clearly distinguished by metrics, gonopodial and other morphological characteristics from all other species of the genus. A mitochondrial DNA-sequence based molecular phylogenetic analysis revealed similar results on the status of the new species as a separate taxon and its relation to other closely related species.