Location: Water Reuse and Remediation Research2012 Annual Report
1a. Objectives (from AD-416):
Objective 1: Evaluate a multi-sensor platform for salinity and irrigation management for the use of combined sensor technology, such as high resolution satellite imagery, EMI, and RTK-GPS (high resolution 3-D spatial information) for management of degraded waters. Objective 2: Improve our ability to predict the impact of degraded waters on infiltration into soils and plant response to irrigation with these waters by; a) determining the impact of using degraded waters for irrigation, including the effect of solution chemistry, high dissolved organic matter, and application of organic wastes, on soil physical and chemical properties; b) developing a new plant response sub model which considers salinity, soil water ion composition, drought stress, and evapotranspiration based on existing data sets, suitable for making field scale management decisions; and c) develop decision tools for use of waters impacted by salinity and potentially toxic elements, with emphasis on boron. Objective 3: Evaluate management strategies for use of degraded waters; a) test and validate applications of stream tube technology for field-scale parameterization of transport models that are applicable as decision tools for determination of plant response, leaching needs and management recommendations; b) develop a decision support tool for the field that utilizes salinity mapping, stream tube technology for delineating regions in the field and simplified modeling for salinity management of these regions.
1b. Approach (from AD-416):
Objective 1: We will evaluate the ability of a multi-sensor platform (ER, EMI, gamma-ray spectrometry) coupled to RTK-GPS to characterize the spatial distribution of texture, water content, salinity, and sodicity. Statistical analysis will be performed by determining correlation coefficients between sensor measurements and soil properties followed by a more extensive analysis using spatial regression models. Linear model-based statistical tests will be used to assess the adequacy and precision of the regression equations derived from the single and multi-sensor directed sampling strategies. Objective 2: a) We will examine the effects of a high dissolved organic carbon (DOC) treated municipal waste water on infiltration. We will next examine the effects of DOC and its interaction with SAR and pH on infiltration clay flocculation and saturated hydraulic conductivity on soils selected with a range in properties to develop new soil stability relationships. b) Plant relative yield functions will be developed and incorporated into UNSATCHEM model. c) We will develop a new B soil test for adsorbed and soluble B. d) Treated municipal waste waters will be measured for DOC, EC, pH and major ion composition, next utilized in boron adsorption experiments, and the boron adsorption as related to DOC described using a chemical surface complexation model. We will also investigate B desorption on soils having varying amounts of organic matter and examine B adsorption-desorption reaction on hysteretic soils after organic matter removal. If needed, we will develop a predictive model relating hysteresis to organic matter content. Objective 3: a) An intensive geospatial ECa survey will be used to delineate stream tubes in each of the two fields at a site with different quality irrigation water. Geospatial ECa measurements will be obtained with the multiplatform sensors from Objective 1. Eight classes of stream tubes will be identified using the EMh/EMv ratio and geometric mean of EMh and EMv as the classification criteria. Within each of 16 sub-classes a stream tube will be selected and 4 random sites within the tube will be selected for parameterization. Irrigation frequency, volumes of water applied and infiltration rates will be measured, soil samples collected and analyzed for EC and ion composition. b) We will evaluate changes in soil physical and chemical properties due to differences in irrigation water quality.
3. Progress Report:
Fifteen soils are being collected and homogenized for characterization and use in the flocculation and column studies to examine the impact of degraded waters on soil physical and chemical properties. We have conducted an outdoor container study with one soil on the effect of tertiary treated municipal waste water on infiltration rates as related to sodium adsorption ratio. Potential waste waters are being identified as sources of dissolved organic matter. Boron (B) soil tests, as presently applied, do not extract all of the B available to plants but relate the extractable amount to plant growth. An optimal soil test would measure all plant available B. Sugar alcohols form strong bonds between B and cis-diol groups and are ideal candidates for a quantitative B soil test. We tested various sugar alcohols: sorbitol, mannitol, xylitol and varying soil to solution ratios and reaction times. We selected sorbitol, soil:solution ratio of 10 g/L, and reaction time of 24 hours. The new B soil test will be used to determine plant available B in soils that have been irrigated with standard irrigation waters and various types of recycled waste waters. Arsenate (As) adsorption was evaluated on a set of sediments from the Antelope Valley of California. These experiments are part of a study to determine the effectiveness of the oxide minerals in the sediments to adsorb and thereby treat high arsenic water. Arsenate adsorption experiments were conducted as a function of solution As concentration and solution pH and described using a chemical surface complexation model. We have initiated an arsenate transport study using different unsaturated zone materials, arsenate concentrations and pH. The chemistry of phosphate is very similar to arsenate, thus arsenate adsorption is also being investigated in the presence of competing phosphate concentrations. Gamma-ray spectrometer equipment has been purchased that meets the specification necessary for obtaining geospatial measurements of clay content for Objective 1. Two study sites have been evaluated for Objective 3. We evaluated a site at Westlake Farm and another on the Maricopa Agricultural Center (MAC). Each site lacks all the qualities desired for the degraded water reuse study, but are possible alternatives if other potential sites do not meet critical criteria needed for Objective 3.
1. Modeling selenite adsorption envelopes on oxides, clay minerals, and soils using the triple layer model. Elevated selenium (Se) concentrations in agricultural drainage waters are common in the Western U.S. and are a major ecological concern when these waters are discharged to surface environments, hence there is a need to understand and predict selenium transport in and below the rootzone. Selenite adsorption on amorphous aluminum and iron oxides, clay minerals: kaolinite, montmorillonite, and illite, and 45 surface and subsurface US soil samples as a function of solution pH was described using the triple layer surface complexation model. The fit of the triple layer model was much improved over that obtained previously utilizing other chemical models such as the constant capacitance model. This information is of interest to modelers developing combined chemical and transport models for prediction of selenium transport in the subsurface and for development of management practices to reduce Se discharge to meet regulatory standards.
2. Geophysical techniques help to map and monitor saline-sodic soils at field scales during remediation. Field-scale monitoring and mapping of soil salinity with mobile geophysical techniques is based on statistical sampling strategies that use geospatial measurements of apparent soil electrical conductivity (ECa) as a surrogate for characterizing spatial variability in soil salinity. Design-based sampling strategies, such as stratified random sampling are commonly used, but a response surface sampling design offers the advantage of minimizing the sampling requirement. ARS scientists at the Salinity Laboratory compared sampling strategies for characterizing the spatial variability of soil salinity with ECa-directed soil sampling. The model-based response surface sampling approach resulted in better model discrimination, more precise parameter estimates, and smaller prediction variances that the design-based strategies, thus enabling reduction in sampling needs. Implementation of this sampling design will facilitate more rapid and less costly salinity mapping, benefiting producers and irrigation districts that utilize mobile geophysical techniques.
3. Role of organic matter on boron adsorption-desorption hysteresis ( dependence of a system not only on its current environment but also on its past environment) of soils. Boron (B) is a specifically adsorbing anion that has a narrow range between deficiency and toxicity for plants. Boron adsorption-desorption reactions of six soils were evaluated and the extent to which organic matter content, as well as incubation time, affected B release was established. The B adsorption-desorption behavior of all six soils was found to be non-hysteretic (readily reversible) in a short-term (23 hour) experiment regardless of organic matter content. Apparent hysteresis (non-reversibility) of B adsorption was found to result from difficulties in the experimental procedure itself, such as precipitation of calcium carbonate, soil clumping resulting in poor equilibration of soil and solution, and loss of soil particles in the supernatant during washing steps. Our results do not support the hypothesis that B desorption hysteresis increases in soils with increasing organic matter content. Our results will benefit scientists who are developing models of B movement in arid zone soils, and can be used to aid action and regulatory agencies in the management of soils and waters that contain elevated concentrations of B.Lebron, I., McGiffen, Jr, M.E., Suarez, D.L. 2012. The effect of total carbon on microscopic soil properties and implications for crop production. Journal of Arid Land. 4(3):251-259.