Middle Rio Grande River Research Articles

Linking Reclaimed Water Consumption with Quantitative Downstream Flow Impacts

Although reclaimed water—municipal wastewater treatment plant effluent—can serve as a locally sustainable alternative water resource, this additional consumptive use of reclaimed water may cause impacts downstream. This paper seeks to quantitatively assess these impacts by employing scenario analysis coupled with a two-sample t-test to evaluate the statistical significance of streamflow alteration. Further, the potential for lower volumes of streamflow is linked to impacts on downstream stakeholders through the use of stakeholder performance metrics. To demonstrate the applicability of this approach, two diverse regions are evaluated: (1) the Illinois River downstream from the greater Chicago, Illinois, area, and (2) the Middle Rio Grande River downstream from Albuquerque, New Mexico. In Illinois, impacts to barge transportation are marginal and decrease with distance downstream of effluent consumption. In the Rio Grande, impacts to the Rio Grande silvery minnow worsen downstream such that a proposed consumption would be unlikely to be established under federal regulations. The extent of downstream impacts is important in legal and policy contexts regarding the sustainability of reclaimed water projects.

Phenology-guided saltcedar (Tamarix spp.) mapping using Landsat TM images in western U.S.

Accurate distribution maps are essential to understand further and control the fast expansion of the introduced saltcedar (Tamarix spp.) in the western U.S. Remote sensing imagery, due to its broad spatial and temporal coverage, is well-suited for this task. More specifically, images acquired during late fall and early winter are used for saltcedar identification as the plant's foliage turns a unique orange-yellow color (coloration) during this time of a year, which makes them easily distinguishable from other plant species. However, saltcedar coloration usually lasts for only several weeks, and the timing of this phenological event varies across space. Therefore, without prior knowledge of saltcedar phenology, it is often challenging to select the remote sensing image collected at the optimal time of the year to capture the distinctive spectral signature of the coloring saltcedar. Moreover, the timing of saltcedar coloration also varies within a single remote sensing scene making it inappropriate to use an entire scene as the mapping unit. In our study, we found that the timing of saltcedar peak coloration and leaf drop were linearly correlated with each other and we were able to model this relationship using the MODIS End of Season–Time (EoST) product and Landsat TM images. Guided by a per-pixel model estimation of saltcedar coloration date, we constructed composite Landsat images at two study sites along the Rio Grande River such that each pixel in the composite images was acquired during saltcedar peak coloration. Classification results showed that the phenology-informed composite image was better for saltcedar identification than the single scene image as it was able to capture the within-scene variations in saltcedar phenology. In addition, given our lack of training data for the model, the successful classification results obtained at the Middle Rio Grande River site also demonstrated the potential of our proposed method to be applied for large-scale saltcedar mapping.

Water, climate, and social change in a fragile landscape

We present here and in the companion papers an analysis of sustainability in the Middle Rio Grande region of the U.S.‐Mexico border and propose an interdisciplinary research agenda focused on the coupled human and natural dimensions of water resources sustainability in the face of climate and social change in an international border region. Key threats to water sustainability in the Middle Rio Grande River region include: (1) increasing salinization of surface and ground water, (2) increasing water demand from a growing population in the El Paso/Ciudad Juarez area on top of an already high base demand from irrigated agriculture, (3) water quality impacts from agricultural, municipal, and industrial discharges to the river, (4) changing regional climate that portends increased frequency and intensity of droughts interspersed with more intensive rainfall and flooding events, and (5) disparate water planning and management systems between different states in the U.S. and between the U.S. and Mexico. In addition to these challenges, there is an increasing demand from a significant regional population who is (and has been historically) underserved in terms of access to affordable potable water. To address these challenges to water resources sustainability, we have focused on: (1) the determinants of resilience and transformability in an ecological/social setting on an international border and how they can be measured and predicted; and (2) the drivers of change … what are they (climate, social, etc.) and how are they impacting the coupled human and natural dimensions of water sustainability on the border? To tackle these challenges, we propose a research agenda based on a complex systems approach that focuses on the linkages and feedbacks of the natural, built/managed, and social dimensions of the surface and groundwater budget of the region. The approach that we propose incorporates elements of systems analysis, complexity science, and the use of modeling tools such as scenario planning and back‐casting to link the quantitative with the qualitative. This approach is unique for our region, as are our bi‐national focus and our conceptualization of “water capital”. In particular, the concept of water capital provides the basis for a new interdisciplinary paradigm that integrates social, economic, and natural sectors within a systems framework in order to understand and characterize water resources sustainability. This proposed approach would not only provide a framework for water sustainability decision making for our bi‐national region at the local, state, and federal levels, but could serve as a model for similar border regions and/or international rivers in arid and semi‐arid regions in the Middle East, Africa, Asia, and Latin America.

Transpirational Water Loss in Invaded and Restored Semiarid Riparian Forests

The invasive tree, Tamarix sp., was introduced to the United States in the 1800s to stabilize stream banks. The riparian ecosystem adjacent to the middle Rio Grande River in central New Mexico consists of mature cottonwood (Populus fremontii) gallery forests with a dense Tamarix understory. We hypothesized that Populus would compensate for reduced competition by increasing its water consumption in restored riparian plots following selective Tamarix removal, resulting in similar transpiration (T) among stands. The northern study site included a Populus stand invaded by Tamarix (INVN) and a restored Populus‐only stand (RESN), as did a southern site (INVS and RESS) approximately 80 miles south. At each site, 20 × 20–m plots were established where up to 16 stems were monitored throughout the 2004 growing season using thermal dissipation sapflow sensors. Populus sapflux rates were greater in restored stands, suggesting those trees compensated for understory removal by using more water. Sapflow was scaled to estimate stand‐level T based on a quantitative assessment of sapwood basal area (Asw) by species. Although exotic species represented 85 and 91% of the total stems in the invaded stands, it amounted to only 3% (INVS) and 4% (INVN) of the total Asw, contributing proportionately less to T compared to Populus. Our results indicate that removing Tamarix from the Populus understory in this riparian forest had a minimal impact on stand water balance. Riparian restoration of the type discussed herein should focus primarily on enhancing riparian health rather than generating water.

Detailed mapping of riparian vegetation in the middle Rio Grande River using high resolution multi-spectral airborne remote sensing

This paper describes procedures used to map riparian vegetation in the middle Rio Grande River, New Mexico. Airborne multi-spectral digital images were acquired at 0.5 m spatial resolution over the riparian corridor of the Middle Rio Grande River in July 2001. The images were corrected for lens vignetting effects, lens radial distortions, rectified to a base map, mosaicked, calibrated in terms of reflectance and classified. The classification accuracy was assessed using ground truth information obtained through comprehensive field campaigns and independent ground truth information. Surface areas of vegetation classes and in-stream features were extracted from the classified imagery. A longitudinal vegetation distribution analysis was conducted to study the changes in vegetation and water surface areas along the river. This analysis showed an increase in surface areas of the invasive type of vegetation Tamarisk ( Tamarix ramosissima) in the downstream direction corresponding to decreases in water surface areas and flow. This indicates significant impacts on the river ecosystem due to many factors. The high resolution airborne remote sensing proved to be a powerful tool for mapping riparian vegetation which is very hard to map using satellite imagery due to its complexity, high diversity, and spatial variability occurring at finer scales.

Predicting riparian evapotranspiration from MODIS vegetation indices and meteorological data

A vegetation index (VI) model for predicting evapotranspiration (ET) from data from the Moderate Resolution Imaging Spectrometer (MODIS) on the EOS-1 Terra satellite and ground meteorological data was developed for riparian vegetation along the Middle Rio Grande River in New Mexico. Ground ET measurements obtained from eddy covariance towers at four riparian sites were correlated with MODIS VIs, MODIS land surface temperatures (LSTs), and ground micrometeorological data over four years. Sites included two saltcedar ( Tamarix ramosissima) and two Rio Grande cottonwood ( Populus deltoides ssp. Wislizennii) dominated stands. The Enhanced Vegetation Index (EVI) was more closely correlated ( r=0.76) with ET than the Normalized Difference Vegetation Index (NDVI; r=0.68) for ET data combined over sites and species. Air temperature ( T a) measured over the canopy from towers was the meteorological variable that was most closely correlated with ET ( r=0.82). MODIS LST data at 1- and 5-km resolutions were too coarse to accurately measure the radiant surface temperature within the narrow riparian corridor; hence, energy balance methods for estimating ET using MODIS LSTs were not successful. On the other hand, a multivariate regression equation for predicting ET from EVI and T a had an r 2=0.82 across sites, species, and years. The equation was similar to VI–ET models developed for crop species. The finding that ET predictions did not require species-specific equations is significant, inasmuch as these are mixed vegetation zones that cannot be easily mapped at the species level.

Nutrient cycling at the landscape scale: The role of diel foraging migrations by geese at the Bosque del Apache National Wildlife Refuge, New Mexico

Wildlife refuges are sites of dense aggregations of wintering waterfowl. Refuge managers are concerned about local water‐quality effects and the amount of birdborne nutrient load that might cause eutrophication in roosting ponds and(or) be exported to downstream systems. We initiated this research effort to test the hypothesis that daily feeding migrations by geese represented a significant source of nutrients to wetland systems at the Bosque del Apache National Wildlife Refuge in the middle Rio Grande River valley of New Mexico. We documented the role of geese in translocating nutrients through a combination of time budget and mass balance models for birds, bioassays of phytoplankton growth, and stable isotope methods that trace the source of nitrogen to food webs. Geese increased the nutrient loading rates in some wetland ponds by up to 40% for total nitrogen and 75% for total phosphorus. Bioassays revealed that nitrogen was consistently limiting to primary production by algae in the ponds. Chlorophyll levels increased in proportion to bird densities. Fish and crayfish from the ponds intensively used by birds had very low stable nitrogen signatures relative to those from the Rio Grande River. This result derived from the low 15N in alfalfa and corn, which were the primary forage for birds, and accumulated through food webs in proportion to bird use of individual ponds as roosting areas. In general, the wetland ponds functioned efficiently in retaining the birdborne, allochthonous nutrient load and only modest amounts of the total nitrogen or phosphorus were exported downstream.

Concentration distribution of sediment mixtures in open-channel flow

Rouse's equation and some of the recently developed equations for concentration distribution in the case of flow in an open channel have been checked for their accuracy with the help of data ofsuspended-sediment concentration-distribution of the individual fractions in a mixture. The agreement between predictions and measurements is not found to be satisfactory. It is found that the sediment distribution exponent for any size in the mixture is not constant over the whole depth of flow. A two-layer model is accordingly suggested herein to describe the sediment distribution in the vertical. A predictor for the reference concentration at 0.2D is also suggested. The model showed satisfactory agreement with the measurements on the Rhine river and the Middle Rio Grande river.