Human populations in Colorado, New Mexico and Texas depend on the Rio Grande for municipal water, agricultural irrigation, and recreation. The Rio Grande and its riparian corridor also support thousands of species of plants, invertebrates and vertebrates, some of which include over 300 species of migratory birds and the endangered Rio Grande silvery minnow and southwestern willow flycatcher. Eutrophication and salinization are the two most important types of water quality degradation which negatively impact the human and nonhuman biological communities in this water poor region. In spite of their significance, few published studies have investigated anthropogenic and natural sources of nutrients and dissolved solids to the Rio Grande. This study investigated the patterns and trends of nutrients and dissolved solids in the Middle Rio Grande (MRG) on a monthly basis from September 2005 – January 2008. During all months, wastewater treatment plants were the major source of nutrients to the MRG. Under high flow conditions, nutrient levels remained elevated for 260 river kilometers below the wastewater inputs. During months when significant portions of the river flow were diverted for irrigation, nitrate and phosphate were removed from the MRG and concentrations at the downstream end of the reach were returned to levels comparable to the un-impacted northern reach of river. Dissolved solids were added to the river by both wastewater and saline tributary inputs. Both anthropogenic and natural inputs of dissolved solids were found to affect water quality in the MRG. Continuous real-time measurements of temperature, pH, turbidity, dissolved oxygen, and conductivity also were initiated at four sites above and through the urban reach of the City of Albuquerque. Preliminary results show increasing turbidity and dissolved oxygen depletions associated with storm runoff from urban areas.
The objectives of this study were to: 1) conduct a detailed assessment of the temporal and spatial trends in water quality of the MRG, 2) determine sources of eutrophication and salinization along the MRG, 3) estimate instream nutrient processing and retention, 4) calculate the effects of urbanization on dissolved oxygen and stream metabolism values in the MRG, and 5) provide baseline data for future water-quality monitoring and assessment in the MRG.
Samples were collected along the lenth of the MRG over a two to three day period, approximately monthly. Single grab samples were collected at each site. During 'Monthly' collections samples were taken from just the mainstem of the MRG. During 'Synoptic' collections samples were taken from both the mainstem sites and all of the major tributaries to the MRG. Mainstem sites were located ~ 5 km downstream of each major tributary to the MRG to allow complete mixing of the tributary and mainstem water bodies and tributaries were sampled just prior to their convergence with the mainstem of the Rio Grande. Samples were collected during periods of stable flow (samples were not collected during storm pulses).
Surface-water samples were collected for measurement of temperature, pH, and conductivity, and analysis of major dissolved inorganic nutrients (nitrate, phosphate, and ammonium), major cations (sodium, potassium, magnesium and calcium), major anions (sulfate, bromide and chloride), dissolved organic and inorganic carbon (DOC, DIC), specific ultraviolet absorbance (SUVA), and chlorophyll a at each site. Sampling began in September 2005 and continued through February 2008. All samples were collected as close to the stream thalweg as flows permitted. Water samples for analysis of nutrients, cations, and anions were collected as grab samples in 130 ml syringes and immediately filtered in the field through ashed 0.7 um pore size glass fiber filters. Unfiltered water samples for chlorophyll-a analysis were collected in acid washed or unused HDPE bottles. All samples were placed on ice and transported to the laboratory for analysis.
Ammonium samples were analyzed using the phenyl hypochlorite method and a 10 cm flow path modified from Hansen and Koroleff (Hansen and Koroleff 1983). Bromide, chloride, nitrate, phosphate and sulphate were analyzed by ion chromatography (Dionex, Standard Method EPA 300.1, 2). Organic and inorganic carbon were analyzed using a Shimadzu TOC-5050A carbon analyzer using Standard Method 5310 B (Clesceri et al. 1998). Sodium, potassium, magnesium, and calcium were analyzed using a Perkin Elmer Optima 5300 DV ICP using Standard Method 3120 B (EPA 200.7) (Clesceri et al. 1998). Clesceri, L. S., A. E. Greenberg, and A. D. Eaton, editors. 1998. Standard Methods for the Examination of Water and Wastewater. 20 edition. American Public Health Association, American Water Works Association, Water Environment Federation, Baltimore. Hansen, H. P. and F. Koroleff. 1983. Determination of Nutrients. Pages 159-226 in K. Grasshoff, K. Kremling, and M. Ehrhardt, editors. Methods of Seawater Analysis. Weinheim: Verlag Chemie.
* Instrument Name: Carbon Analyzer
* Manufacturer: Shimadzu
* Model Number: TOC-5050A
* Instrument Name: Ion Chromatograph
* Manufacturer: Dionex
* Model Number:
* Instrument Name: Inductively Coupled Plasma Optical Emission Spectrometer
* Manufacturer: Perkin Elmer
* Model Number: Optima 5300 DV ICP