Denitrification is a microbial process of anaerobic respiration in which nitrate (NO₃⁻) is chemically reduced to gaseous nitrous oxide (N₂0) and molecular N2. Fertilizer N can be lost to the atmosphere through this process. Subsurface drip irrigation may create favorable conditions for denitrification, such as high moisture and NO₃⁻ content. The objectives of this research were to: 1) determine the denitrification rate in drip-. irrigated cauliflower and sweet corn crops; 2) evaluate the effect of soil water tension on the denitrification rate, and; 3) estimate an N balance under subsurface drip irrigation, including denitrification losses. Two field experiments with subsurface drip-irrigated cauliflower were conducted during the 1996-98 winter growing seasons at the Maricopa Agricultural Center, in Maricopa, AZ. An additional study with subsurface drip-irrigated sweet corn was conducted at the Campus Agricultural Center in Tucson, AZ. All the experiments were complete factorial designs with two soil water tension levels (low, high), two levels of N fertilizer (zero, adequate), and three replications. The denitrification rates evaluated at ambient temperature were <12 g N ha⁻¹ d⁻¹ during the cauliflower winter seasons. When soil cores taken during the 1997-98 winter season were incubated at room temperature (24 ±2°C), denitrification rates were five to 50 times higher than the rates evaluated at ambient temperature. The denitrification rate measured at room temperature in the cauliflower winter season was similar to the rate observed in the sweet corn during summer. Soil cores from the cauliflower 1997-98 season that received 100 kg N ha⁻¹ had denitrification rates from 10 to 45 g N ha⁻¹ d⁻¹ ; when these cores were amended with additional soluble carbon, the denitrification rate increased to 800 to 3500 g N ha⁻¹ d⁻¹. All of the three experiments showed higher denitrification rates at the end of the season. This trend coincided with increases in denitrifying enzyme activity and soluble organic carbon. The denitrification loss of fertilizer N was <1% in cauliflower and almost 2% in summer sweet corn, when irrigated at the higher soil water tension. Lower soil water tension did not increase the denitrification rate in the winter, but in the summer the loss of N due to denitrification increased to almost 6% of the applied N.

Constructed wetlands manifest a significant potential for removing nitrogen from wastewater. The study was conducted at a free water surface constructed wetland receiving partially treated dairy wastewater. A series of four cells was lined with plastic and a parallel series lined with clay. The objectives were to evaluate 1) nitrogen removal from the wastewater stream and 2) nitrogen accumulation in the soil and plant biomass. Above and below ground plant tissues and soil samples were collected from twenty-four locations during one year. Total nitrogen removal from wastewater was about 17 percent. The clay-lined cells accumulated more nitrogen in the soil, and less in plant biomass compared with the plastic-lined cells. Nitrogen accumulated was distributed evenly among the soil, above, and below ground plant biomass. Maximum total nitrogen in the soil was found during the second sampling event (about 1100 mg kg') About 90 percent of the accumulated nitrogen was organic.

As we have come to depend on aquaculture to supplement natural fisheries, intensive culture methods have increased production. Accompanying environmental damage--non-point source pollution, loss of biodiversity and struggle for water--has offset food and financial gains. Problems surrounding food production are amplified in arid lands, as the potential of irrigated agriculture is weighed against the value of water. Through the following research, I studied integration of aquaculture and agriculture through multiple uses of water and nutrients, to reduce environmental impacts. When managed properly, integration can provide multiple cash crops, increased food and fiber production with reduced inputs. Integration allows for groundwater and nutrients in water and solid waste to be reused. Shrimp farms in Arizona use low-salinity ground water from aquifers for shrimp ponds and agricultural irrigation. On one of these farms, effluent is reused for irrigation of olive trees and other field crops. In Chapter 3, I described an experiment designed to quantify changes in the height of olive trees due to irrigation with shrimp effluent. Trees receiving effluent grew an average of 61.0 cm over the two-year experiment, 70.4 cm with fertilizer and 48.4 cm in the well water treatment. No negative effects due to effluent irrigation were found, while increases in water use efficiency were realized by producing two crops with the same irrigation water. Multiple uses of water are also possible in smaller scale agriculture systems. I performed a financial analysis of a small-scale aquaponics system, integrated hydroponics and aquaculture, in Chapter 4. Biological viability of such systems is clear. By building and managing this system for five months, I examined economic viability, by analyzing annual costs and revenue. Calculating net present value showed that the system was not financially viable unless labor costs were excluded. Financial returns were between 3,794 and 10,640 over six years. In five months, this system produced 181.4 kg of food, with fish feed, iron and water as the only inputs. This study showed potential for using small-scale aquaponics as a hobby, in schools, and as a tool for agricultural economics education, but not as a business opportunity.

This project was designed to assess the potential for contamination of produce during irrigation with wastewater from animal operations. Dairy wastewater from the University of Arizona Campus Dairy Research Center was used to irrigate three different types of vegetable crops: lettuce, carrot, and bell pepper. This study was conducted over two consecutive years. The crops were planted in February and vegetables were harvested from May through July. Irrigation water and vegetable samples were examined for Escherichia coli, Clostridium perfringens, Listeria monocytogenes, and coliphage. In the dairy wastewater, E. coli concentrations averaged 5.7 x 10⁵ MPN/100 mL in the first year (2000), and 9.9 x 10⁷ MPN/100 mL in the second year (2001). C. perfringens concentrations were nearly the same in both years (1.7 x 10⁴ and 3.4 x 10⁴ CFU per 100 mL). Coliphage averaged 2.0 PFU/mL in 2000 and 1.3 x 10⁴ PFU/mL in 2001 in wastewater. E. coli was detected with greater frequency on carrots (100 and 96%) succeeded by lettuce (67 and 96%) and bell peppers (63 and 58%). The same was true for C. perfringens : carrots (100%), lettuce (86 and 88%), and bell peppers (100 and 50%). Coliphages were not detected on any of the vegetable crops except for average concentrations of 2 PFU/g on lettuce in the first year. L. monocytogenes was not detected on any of the vegetable samples. ANOVA test results indicates that E. coli and C. perfringens concentrations on three crops were statistically different (p < 0.0001) which suggest that the degree of contamination on the surface of the vegetables depends on where the edible portion of the crop is situated (above the soil or under the soil). The greatest contamination occurred on the carrots followed by lettuce and bell peppers. E. coli and C. perfringens were recovered from the carrots, bell peppers, and soil 55 days after wastewater irrigation of the plots had ceased. Positive correlations (p < 0.05) were found between E. coli and C. perfringens density and soil moisture content. The greatest risk of infection from pathogenic E. coli (O157:H7) occurs from consumption of lettuce and carrots. The annual risk of infection from consumption of all three vegetables was above the acceptable risk of 1:10,000 per year. The results of this study suggest that a more strict irrigation water quality standard for root and leafy vegetables might be appropriate to prevent the risk of infection in exposed population.

The vegetation index products from the Moderate Resolution Imaging Spectroradiometer (MODIS) are designed to provide consistent, spatial and temporal comparisons of global vegetation conditions. The objective of this dissertation was to validate the robustness and global implementation of two MODIS VI algorithms, including the normalized difference vegetation index (NDVI) and "enhanced" vegetation index (EVI). Their performances have been evaluated in: (1) the normalization of canopy background (brightness) variations and the extraction of biophysical parameters across different canopy structures; (2) the characterization of seasonal vegetation profiles (phenological, intra-annual); and (3) spatial and temporal discrimination of vegetation differences (inter-annual). The validation was accomplished through multiple means, including canopy radiative transfer models which were utilized to extract pure vegetation spectra and "true" VI value free of background contamination for varying canopy structures and vegetation amount. The experimental field- and airborne-based radiometry and satellite imagery at multiple spatial resolutions were also coupled and scaled-up for comparison with coarse spatial resolution MODIS VI products to quantify characteristics of semiarid rangeland vegetation. The results showed that NDVI was advantageous in yielding biophysical relationships applicable across varying canopy types, but required knowledge of soils for biophysical estimations. The EVI provided biophysical relationships sensitive to canopy structure, thus requiring knowledge of canopy type for biophysical assessments. The MODIS VI products were successfully validated, radiometrically, by coupling field and the MODLAND Quick Airborne Looks (MQUALS) observations to high spatial resolution imagery (AVIRIS and ETM+), and appeared robust across the two parallel sites for depicting their ecological equivalents. MODIS multitemporal VI profiles were able to depict phenological activity, length of the growing season, peak and onset of greenness, and leaf turnover. Among the sensors tested, spatial resolution was found to be most important for discriminating the major land cover subtypes within the two parallel semiarid rangelands, and spectral resolution had major effects on capturing seasonal contrast due to atmosphere influences. The validation strategy utilized in this study to successively aggregate the integrity-inherent multiple fine spatial resolution data to the coarse MODIS pixel sizes appeared to perform well, thus showing potentials in the validation of other satellite products.

Three soils were tested as possible substrates for an evapotranspiration cover for a Uranium mill tailings disposal site in Moab, Utah. Small weighing field lysimeters were used to determine the field capacity of soils with the effect of a coarse-grained capillary barrier placed beneath the soil to increase water retention. Water was ponded on each lysimeter and then covered with plastic to prevent evaporation. Lysimeters were drained and weighed periodically throughout the experiment. Field capacity was determined by the weight of the lysimeter when drainage stopped. Results were compared to a mathematical model for estimating water storage of capillary barriers. Results from particle size analyses were also compared to water storage results and we found that both sand and clay were significant factors (p <0.05) in explaining water storage. After determining the water-holding capacity of the soils, recommendations on the most suitable soil for the Moab evapotranspiration cap will be made.

A set of error/uncertainty analyses were performed on several "improved" vegetation indices (VIs) planned for operational use in the Moderate Resolution Imaging Spectroradiometer (MODIS) VI products onboard the Terra (EOS AM-1) and Aqua (EOS PM-1) satellite platforms. The objective was to investigate the performance and accuracy of the satellite-derived VI products under improved sensor characteristics and algorithms. These include the "atmospheric resistant" VIs that incorporate the "blue" band for normalization of aerosol effects and the most widely-used, normalized difference vegetation index (NDVI). The analyses were conducted to evaluate specifically: (1) the impact of sensor calibration uncertainties on VI accuracies, (2) the capabilities of the atmospheric resistant VIs and various middle-infrared (MIR) derived VIs to minimize smoke aerosol contamination, and (3) the performances of the atmospheric resistant VIs under "residual" aerosol effects resulting from the assumptions in the MODIS aerosol correction algorithm. The results of these studies showed both the advantages and disadvantages of using the atmospheric resistant VIs for operational vegetation monitoring. The atmospheric resistant VIs successfully minimized optically thin aerosol smoke contamination (aerosol optical thickness (AOT) at 0.67 μm < 1.0) but not optically thick smoke (AOT at 0.67 μm > 1.0). On the other hand, their resistances to "residual" aerosol effects were greater when the effects resulted from the correction of optically-thick aerosol atmosphere. The atmospheric resistant VIs did not successfully minimize the residual aerosol effects from optically-thin aerosol atmosphere (AOT at 0.67 μm ≤ ∼0.15), which was caused mainly by the possible wrong choice of aerosol model used for the AOT estimation and correction. The resultant uncertainties of the atmospheric resistant Vls associated with calibration, which were twice as large as that of the NDVI, increased with increasing AOT. These results suggest that the atmospheric resistant VIs be computed from partially (Rayleigh/O₃) corrected reflectances under normal atmospheric conditions (e.g., visibility > 10 km). Aerosol corrections should only be performed when biomass burning, urban/industrial pollution, and dust storms (larger AOT) are detected.

A new concept of dispersion (cross) covariance has been introduced for the modeling of spatial scale dependent multivariate correlations. Such correlations between attributes depend on the spatial size of the domain and size of samples in the population and have been modeled by first time in this research. Modeled correlations have been used to introduce a new scale dependent principal component analysis (PCA) method. This method is based on computation of eigen values and vectors from dispersion covariance matrices or scale dependent correlations which can be modeled from integrals of matrix variograms. For second order stationary random functions this PCA converges for large domains to the classic PCA. A new technique for computing variograms from spatial variances have also been developed using derivatives. For completeness, a deeper analysis of the linear model of coregionalizations widely used in multivariate geostatistics has been included as well. This last part leads to a new more sophisticated model we termed "linear combinations coregionalization model." This whole research explains the relationship between different average states and the micro- state of vector random functions in the framework of geostatistics. Examples have been added to illustrate the practical application of the theory. This approach will be useful in all earth sciences and particularly in soil and environmental sciences.

Aquatic nuisance species (ANS) represent a growing problem in Arizona that is receiving little funding attention. With the objective of addressing this problem in a coordinated manner between state and federal agencies, the task of writing the Arizona State Aquatic Nuisance Species Management Plan was undertaken, this process and its results will be discussed. Section 1204 of the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 (P.L. 101-646), provides opportunity for federal cost-share upon adoption of a state management plan. Methodology included gathering input towards reworking an early draft of the plan at a number of meetings, including the Lower Colorado Giant Salvinia Task Force, the Salvinia molesta National Convention, and Southwest Vegetation Management Association, and researching the format and process used in writing plans recently adopted in other states. Developments in management needs were incorporated, several of the plan's tasks were initiated and the plan was presented to agency members for comments and review. The resulting management plan is now ready to be signed into action, requiring approval by the state governor as a final step towards providing additional funds to fight ANS.

A finite-element model was developed to simulate the water flow underneath a surface point source using the Galerkin method of weighted residuals and the mixed formulation of the Richards' equation. The saturated radius usually formed during a point source test was estimated by the numerical model. Comparisons with published experimental and analytical results indicated that the model is accurate and reliable. The numerical model aids in understanding the water regime under different point source scenarios. The finite element model was coded in C++ by using an object oriented approach. This allows flexibility for future updating. Finite and infinite elements were combined to obtain a numerical solution for unbounded 1-D flow domains. The results showed that the use of infinite elements may reduce the computational time when solving the flow equations for deep profiles. Although the transient point-source problem can be solved numerically, generalized solutions were developed and their coefficients calculated by best fitting numerical results of dimensionless saturated radius and time. The solutions allow calculation of the transient saturated radius given values of the van Genuchten hydraulic function parameter "m" and dimensionless point-source application rate. The resulting generalized solutions have the advantage of reducing large volumes of data. The estimation of soil hydraulic parameters from field data by using existing flow theory is analyzed. The results obtained from these studies verified that soil type and conditions can limit field estimation of steady state data for some soils. As a consequence, estimation of steady data is highly recommended by fitting field data to empirical equations. An empirical equation for transient saturated radius as a function of time was proposed. This equation is robust to predict steady-state saturated radius. To test the applicability of point source tests, hydraulic properties were estimated from field disc and point source tests. The parameters obtained from the disc and point-source methods matched closely. An overall methodology is also given for conducting point-source tests.