Location: Water Reuse and Remediation Research2013 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:
Integration of the real-time kinetics GPS, electromagnetic induction (e.g. EM38 and DUALEM-2 electrical conductivity meters), and gamma-ray spectrometer onto a single mobile platform for Objective 1 is near completion. Preliminary testing of the gamma-ray spectrometer investigating the depth of measurement indicated variation in depth from 5-15 cm from one location to the next. The cause for the variation in depth of penetration is currently unknown. The inability to find a field site meeting all the criteria needed to evaluate management strategies for degraded water reuse in Objective 3 resulted in the use of a contingency site (32.4-ha Westlake Farm field) to evaluate stream tubes. An apparent soil electrical conductivity survey of the site using electromagnetic induction equipment has been completed along with associated soil sampling (192 cores). Soil sample preparation (i.e., grinding, sieving) and saturation extracts has been completed. Analyses of the soil properties of interest for the samples are 30% complete. Preliminary stream tubes have been established. Recycled waste waters have been identified as sources of dissolved organic matter and are currently being collected to evaluate the impact of this material on boron complexation and boron transport in soils. Laboratory soil flocculation studies have been initiated. Solutions for the soil flocculation study were prepared according to chemical compositions calculated using the EXTRACTCHEM program. The solutions range in electrical conductivity from 0.5 to 4 dS/m, sodium adsorption ratio from 2 to 16, and pH values from 5 to 9. A protocol for measuring percent clay dispersed by optical methods has been developed and is being tested on the first soil. Selenate adsorption was measured on a set of Midwestern soils as a function of solution pH. Chlorpyrifos adsorption on Turkish soils was described using a surface complexation model. The newly developed soil B test was evaluated for its ability to quantitatively recover B added to a set of soils from California, Iowa, and Oklahoma. The test was found to recover much higher amounts of adsorbed boron as compared to the present recommendations. A study on the impact of organic components of recycled wastewater on infiltration as related to irrigation water pH and sodium adsorption ratio has been completed. We compared the infiltration rate of wastewater adjusted to various pH and sodium adsorption ratios to the infiltration rate of prepared waters of the same chemical composition as the wastewater (only without the dissolved organic matter). In this outdoor study, we measured both the infiltration rate of the irrigation water as well as infiltration under the rain simulator. We also examined the impact of varying sodium adsorption ratios and pH on infiltration of two additional soils that will also be utilized in the flocculation studies. A study was conducted on the water retention as related to the water potential in soil samples collected at the termination of the infiltration study.
1. Updated protocols for mapping salinity with ECa-directed soil sampling. Mapping and monitoring the spatial variability of soil salinity at field scale is a valuable piece of information due to the detrimental impact of salinity on crop yields and surface and ground water quality. Soils are highly spatially variable in their properties, e.g., within-field variation in soil salinity can be an order of magnitude, which presents a technological challenge. An ARS scientist in Riverside, California, has updated the protocols developed earlier in Riverside for mapping and monitoring soil salinity with detailed guidelines of special considerations necessary to obtain reliable, accurate measurements. The implementation of these new protocols will assure users of ECa-directed soil sampling, such as National Resources Conservation Service (NRCS) staff, soil scientists, agricultural geophysicists, and agricultural consultants, of reliable, repeatable, and accurate maps of soil salinity for use in inventorying, monitoring, and site-specifically managing salinity.
2. New boron soil test to measure plant available boron. Boron (B) soil tests currently in use, do not extract all plant available B but relate the extractable amount of B to plant B content. There is a need to accurately measure all plant available or adsorbed B because B can be toxic to plants at elevated concentrations and can cause marked yield decrements. ARS scientists in Riverside, California, developed a new B soil test that was able to provide quantitative recovery of B added to a diverse set of seven soils from California, Iowa, and Oklahoma. Results from this soil test can be used in chemical speciation-transport models such as the unsaturated water and solute transport model (UNSATCHEM) to obtain accurate predictions of B transport and partitioning in soils. This research is important because it will allow extension agents to make accurate recommendations for the management of waters and soils high in B.
3. Arsenate adsorption by unsaturated alluvial sediments. Arsenic is a toxic element that can occur naturally in excess of drinking water standards. ARS scientists in Riverside, California, evaluated arsenate adsorption behavior on a set of sediments from the Antelope Valley of California as a function of solution and described the data using a chemical surface complexation model. Equimolar phosphate concentrations did not affect the extent of arsenate adsorption (As) indicating that the As remediation process will be unaffected by the low amounts of native phosphate. An extensive column study of arsenic adsorption by these sediments indicated that adsorption was sufficient to reduce arsenic concentrations from 300 micrograms per liter (ug/L) in the input water down to 2 ug/L in the outlet water at the bottom of the column, for up to 50 pore volumes, in both pH 6 and 8. This study demonstrates the viability of a treatment process using naturally occurring oxide minerals present in sediments located in the unsaturated zone to adsorb and thereby to remediate high As concentrations to below drinking water standards. Our findings are important for farmers, irrigation districts and municipal water districts as it indicates a potential for extending the availability and use of scarce water resources by remediating water degraded by elevated arsenic.Goldberg, S.R., Suarez, D.L. 2013. Arsenate adsorption by unsaturated alluvial sediments. Soil Science Society of America Journal. 77(3):782-791.