The response of two native Arizona plants, fourwing saltbush (Atriplex canescens) and greasewood (Sarcobatus vermiculatus), to five concentrations of nitrate (tap water only, 50 mg/L, 100 mg/L, 750 mg/L, and 2000 mg/L as nitrate) is investigated. Their growth, transpiration, and nitrate and percent nitrogen tissue concentrations were measured. All of the plants' responses were affected by nitrate concentration. In general, it can be concluded that both fourwing saltbush and greasewood tolerated nitrate concentrations as high as 2000 mg/L. However, greasewood's optimal growth was at Level 4 (750 mg/L nitrate) and its tissue nitrate approximately doubled from an average of 572 ± 255 mg/kg at Level 4 to 1020 ± 511 mg/kg at Level 5 (2000 mg/L nitrate). Fourwing saltbush demonstrated a remarkable ability to tolerate large quantities of nitrate and convert it to organic nitrogen at high concentrations. Fourwing saltbush's largest dry mass, 14.48 ± 2.03 g, was at 2000 mg/L of nitrate.

Nitrogen (N) cycling involves the gains, losses, and transformations of N from sources such as soil organic matter, crop residues, and fertilizers. These sources are the primary N supplies potentially available to non-leguminous crops. Through the use of a stable N isotope tracer (¹⁵N), transformations among various soil N pools can be studied. We conducted three separate studies using ¹⁵N. Two studies dealt with methodologies of ¹⁵N use and analysis, while the third study investigated mineralization of ¹⁵N labeled crop residues under field conditions. The first study evaluated a new apparatus for applying ¹⁵N by fertigation to subplots under buried drip irrigation. We determined that this method was an effective means of uniformly applying tracers using buried drip irrigation. The second study evaluated a new method for fine-grinding soils based on particle size distribution and variability of organic N and ¹⁵N analyses. Soils of varying texture were rapidly ground to achieve acceptable analytical precision for N and ¹⁵N analysis. The objectives of the third experiment were to: (i) evaluate mineralization of inorganic N from ¹⁵N -labeled crop residues with different C/N ratios and at different loading rates and (ii) evaluate the influence of residue loading rate and type on the percent net mineralization from ¹⁵N-labeled crop residues in a basin irrigated wheat cropping system in Southern Arizona. Mineralization of crop residues in this hyperthermic soil was rapid and was often followed by periods of re-immobilization. Net end-of-season mineralization of residue N was 30-50% for lettuce, and 30-40% for wheat.

Seven species in the phylum Microspora infect humans; four predominantly those patients with the human immunodeficiency virus (HIV). The number of documented infections in immunocompetent persons grows annually. Microsporidia are obligate, intracellular parasites that produce environmentally resistant spores. These spores are shed in feces and urine, making waterborne transmission possible. This work reports occurrence data for human infectious microsporidia species in environmental waters. Polypropylene-fiber cartridge filters (1DPPPY) of a nominal porosity of 1 micron (um) along with a modified Information Collection Rule protocol were used in the collection, elution, sample concentration, flotation, and analysis of surface water, groundwater, and wastewater samples. Fluorescently labeled, Encephalitozoon species-specific polyclonal antibodies were used to detect presumptive spores present in 46 samples. Overall, 12 samples were positive: 4 groundwater, 2 surface water, and 6 wastewater.

Two continuous cell lines, BGM and CaCo-2 were compared for the detection of viruses in mesophilic treated sludge (MIS) and secondary disinfected wastewater effluent (WWE) samples. Samples were inoculated in both cell lines and examined microscopically for cytopathogenic effect (CPE) for 14 days. Enumeration by the most probable number (MPN) method and statistical analysis revealed significantly greater MPN values for CaCo-2 than in BGM cells for WWE. Statistical analysis of MTS and WWE samples showed that CaCo-2 cells were more sensitive than BGM (p=0.0287). This suggests that CaCo-2 cells are more sensitive for the detection of enteroviruses in environmental samples. M-PCR was developed to detect and differentiate human adenovirus (Ad) from enteric adenovirus (Ead) from seeded environmental samples. Two sets of primers hexAA1885/1913 and K402/403 (308 bp and 152 bp amplicons respectively) were chosen for combination in M-PCR. The optimum MgC12 concentration was 1.25 mM with primer concentration of 100 pmol for hexAA1885/1913 and 50 pmol for K4021403 primers. Optimum primer annealing temperature was 60° C. Sensitivity of M-PCR was 10^2 TC1D50 for Ead and Ad mixed and 10^0 TCID50 for individual viruses per reaction. M-PCR has potential in the rapid and specific identification of these types of viruses in environmental samples.

Fertilizer-derived nitrous oxide, N20, may cause an increase of tropospheric N20, which could contribute to the destruction of the ozone layer and enhance the "greenhouse effect". The impact of fertilizer on tropospheric N20 may be enhanced by increased carbon dioxide, CO2, which may alter soil N dynamics. The goal of this research was to measure N20 emissions from soil within a field of wheat grown under two levels of atmospheric CO2 (ambient and ambient plus 200 ppm), two irrigation levels (15 and 30% depletion of available water in the root zone), and two levels N-fertilizer (15 and 350 kg N/ha). Spring wheat (Triticum aestivum L. cv. Yecora Rojo) was planted at the University of Arizona Agricultural Center, Maricopa, Arizona, December 1996 and harvested May 1997 in conjunction with a Free Air CO2 Enrichment (FACE) experiment. Chamber measurements of N20 emissions were made five days during the season. The results showed that emissions were not different for the two different irrigation levels. There was, however, a positive correlation between emissions and air temperature. The elevated CO2 had no statistically significant effect on the N20 emissions.

Respirometric experiments were performed to evaluate the role of nitrogen in aerobic diesel biodegradation. Specific objectives included 1) evaluating the effects of water potential induced by various nitrogen amendments on diesel biodegradation rates in arid region soils, 2) comparing concurrent effects of C:N ratios and soil water potential on diesel degradation rates, and 3), measuring gross rates of nitrogen cycling processes in diesel-contaminated soil to determine duration of fertilizer bioavailability. In all studies, increasing nitrogen fertilization resulted in a decrease in total water potential and correlated with an increase in lag phase and overall reduction in microbial respiration. Highest respiration and estimated diesel degradation was observed in the 250 mg N/kg soil treatments regardless of diesel concentration, nitrogen source, or soil used, suggesting an inhibitory osmotic effect from higher rates of nitrogen application. The depression of water potential resulting in a 50% reduction in respiration was much greater than that observed in humid region soil, suggesting higher salt tolerance by microbial populations of arid region soils. Due to the dependence on contaminant concentrations, use of C:N ratios was problematic in optimizing nitrogen augmentation, leading to over-fertilization in highly contaminated soils. Optimal C:N levels among those tested were 17:1, 34:1, and 68:1 for 5,000, 10,000 and 20,000 mg/kg diesel treatments respectively. Determining nitrogen augmentation on the basis of soil pore water nitrogen (mg N/kg soil H₂0) is independent of hydrocarbon concentration but takes into account soil moisture content. In the soil studied, optimal nitrogen fertilization was observed at an average soil pore water nitrogen level of 1950 mg N/kg H₂0 at all levels of diesel contamination. Based on the nitrogen transformation rates estimated, the duration of fertilizer contribution to the inorganic nitrogen pool at 5,000 mg/kg diesel was estimated at 0.9, 1.9, and 3.2 years in the 250, 500, and 1000 mg/kg nitrogen treatments respectively. The estimation was conservative as ammonium fixation, gross nitrogen immobilization, and nitrification were assumed as losses of fertilizer with only gross mineralization of native organic nitrogen contributing to the most active portion of the nitrogen pool.

Experiments were conducted in a flume (3.0 meter long, 0.3 meter wide by 0.3 meter deep) to examine chemical loss to surface runoff. The bottom of the flume was made of a perforated steel plate, which allowed infiltration to occur during the runoff event. Three experiments were conducted. The objective of the first experiment was to introduce a calcium chloride solution as surface flow into the flume which was pre-saturated with calcium bromide. This experiment allowed the transfer of chemicals from soil to runoff to be examined. The second experiment was the reverse of the first experiment, i.e. the soil was saturated with calcium chloride and the surface flow contained calcium bromide. This experiment was done to examine chemical transport from runoff to the soil. In the last experiment, the soil was saturated with a mixture of calcium bromide, sodium benzoate, and pentafluorobenzoic acid (PFBA), and the surface flow contained calcium chloride. The sodium benzoate was chosen to examine biodegradation. The PFBA and bromide, both non-reactive tracers, have different aqueous diffusion coefficients. The results obtained for these two were compared to help determine if the mass transfer in the soil mainly is due to flow, or if diffusion contributes. With this research it has been shown that there are several factors influencing chemical loss to runoff infiltration, biodegradation, and there are also suggestions that there is transfer due to diffusion processes.

Duckweed plants (Lemna spp) are increasingly being used to improve the quality of wastewater in many parts of the world. We investigated a duckweed (Lemna gibba L.)-covered pond for its ability to remove Gicrdiq Oyptosporidiurn, enteroviruses, coliphages, and enteric indicator bacteria from unchlorinated secondary effluent. Giardia cysts and Oyptosporidium oocysts were reduced by 98 and 89 percent, respectively; total coliforms by 61 percent; fecal colifoims by 62 percent; and bacteriophages by 40 percent. The results indicate that the larger organisms (parasites) settled to the bottom of the pond, while the removal of bacteriophages by the pond was not as effective. There was a significant correlation between the removal of Giardia cysts and Oyptosporidium oocysts by the pond (p <0.001). Influent turbidity and parasite removal were also significantly correlated (Oyptosporidium and turbidity, p 0.05; and for Giardia and turbidity, p 0.01). However, there appeared to be no correlation between the removal of these parasites and effluent turbidity.

Constructed wetlands can play a critical role in wastewater treatment for rural areas. It has been demonstrated that large constructed wetlands are useful in the reduction of enteric microorganisms. This study evaluated the ability of three small scale, subsurface wetlands to remove total coliforms, fecal coliforms, bacteriophage, Giardia, and Cryptasporidium. These wetlands have three different vegetation densities: no vegetation, partially vegetated, and completely vegetated. Influent and effluent water samples for each wetland were tested for the presence of the microorganisms. In the wetland with no vegetation, total coliform, fecal coliform, bacteriophage, Giardia, and Cryptosporidium percent reductions were 93.5, 95.4, 61.5, >97.8, and 77.1, respectively. In the partially vegetated wetland, percent reduction of total coliforms, fecal coliforms, bacteriophage, Giardia, and Cryptosporidium were 91.0, 96.1, 86.6, >98.6, and >44.3, respectively. Percent removal was greatest in the wetland that was completely vegetated. Total coliforms were reduced by 97.3 percent, fecal coliforms by 99.5 percent, and bacteriophage by 97.1 percent. These results indicate that small scale constructed wetlands can be useful in wastewater treatment and that vegetation may play a role in enteric microorganism removal.

The use of macrophytes for the treatment of wastewater in constructed wetlands has caused concern over the possible concentration of elements within plant tissues. To better understand the potential of constructed wetland systems for adverse impacts, research was conducted to determine ranges at which micronutrients and heavy metals naturally exist in the root, shoot and leaf tissues of wetland plants in southern Arizona. Lemna sp., Anemopsis californica and Scirpus americanus concentrated the highest levels of micronutrients and heavy metals. Leaves of tree and shrub species usually had the lowest micronutrient and heavy metal concentrations of the plants analyzed in this study. Root tissues generally had higher concentrations of most elements, although elevated concentrations of micronutrients and heavy metals were found in the shoots of Typha domingensis and the leaf tissues of Anemopsis californica.