Recipient Organization
UNIVERSITY OF ILLINOIS
2001 S. Lincoln Ave.
URBANA,IL 61801
Performing Department
Natl Res & Env Sci
Non Technical Summary
Phosphorus loss from agricultural fields in the Midwestern US occurs through surface runoff and tile drainage. Illinois has just developed a Nutrient Loss Reduction Strategy, which develops a plan for reducing P loads by 45%. Many management practices are proposed to reduce P losses, but there is great uncertainty about sources, transport, and forms. We will: 1) develop a rapid and simple method for determining which fields have large P losses through tile lines; 2) identify the forms of colloidal P (CP) and particulate P (PP) in tile and river water; 3) understand how soil P pools in fields control the dissolved reactive P (DRP), CP, and PP losses; and 4) assess the contribution of various P sources, including tiles, surface runoff, and riverine sources to overall watershed export of P. We will apply cutting edge chemical techniques including zetasizer (surface charge properties), dynamic light scattering (particle size distribution), high-resolution transmission electron microscopy (morphology, structure, and elemental distribution with P), synchrotron based XRD (characterization of amorphous or crystalline materials), and microfocused X-ray microprobe spectroscopy (solid state P speciation) to better understand and determine sources and transport. In addition to automatic and grab sampling of tile and river water, we will install a continuous DRP sensor in the watershed outlet. Samples will be primarily collected in the Embarras River watershed of Illinois. This knowledge will allow for better targeting and application of management practices, helping us reduce P losses by the large amounts needed in nutrient loss reduction strategies.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
There is great interest but also great uncertainty about controls on and forms of P from tile-drained agricultural watersheds. Therefore, our long-term goal is to use cutting edge chemical techniques to better quantify and understand the movement of P from fields to watershed outlets, which will allow for better targeting and selection of management changes that could reduce these critically important losses. As part of this goal we will better understand not only reactive P movement, but also the critically important colloidal and particulate forms of P that move via both surface runoff and tile drainage from fields. By examining these same P forms with these techniques at the watershed outlet, we will be able to more fully understand how field scale transport relates to watershed scale transport. Our specific objectives are therefore:1. To develop a rapid and simple method for determining which fields have large P losses through tile lines;2. To identify the forms of colloidal and particulate P in tile and river water;3. To understand how soil P pools in fields control the reactive, colloidal, and particulate P losses; and4. To assess the contribution of various P sources, including tiles, surface runoff, and riverine sources to overall watershed export of P.The primary hypotheses we will test are:1. Soil test and other soil chemical signatures of P, tile system design, and surface soil properties can be related to a simple method for determining which fields have large tile dissolved reactive P losses.2. Colloidal and particulate P from tile lines during high flow events is an important component of both field and watershed scale P losses, and is related to chemical properties of P found in the field soils.3. Particulate P eroded by surface runoff in the river will be different chemically than colloidal and particulate P transported by tile drainage.
Project Methods
Field SitesThis project will build on field and watershed infrastructure already in place in the Embarras River watershed of east-central Illinois, as well as additional agricultural fields in surrounding watersheds of this same area.Approach and MethodologyObjective 1: Develop a rapid and simple method for determining which fields have large P losses through tile linesWe will test a wide array of sorption media that we will suspend in the tile outlets that we are currently monitoring. This will follow exploratory laboratory work where we will use tile water collected from some of our monitored tiles that have a range of DRP and PP in them, and tile water that is spiked with phosphate as well. We will take non-perforated tile pipe and pump the tile water from a reservoir at a defined flow rate under laboratory conditions, with the sorption and filtration media suspended in the flow.We use a Lachat QuikChem 8000 continuous flow analyzer for DRP and total P (following digestion with sulfuric acid and ammonium persulfate) analysis. Once we find possible candidates we will choose tiles with a range of P concentrations and forms, and determine if these techniques can be used in the field to identify tiles with greater concentrations of P. We envision 1 to 2 week field deployments, depending on flow rates and storm events.Objective 2: Identify the forms of colloidal and particulate P in tile and river waterWe propose to collect large volumes of tile water from our network of monitored tiles to allow for chemical analysis of P present. This will need to be done during high flow events throughout the tile drainage period, typically January through June in east-central Illinois, where we can obtain tens of liters of tile water for this in-depth chemical analysis using novel techniques. We will select about 10 tiles in year 1 with higher total P and greater PP concentrations at high flow for this work. During high flow events, our team will manually collect the large volumes required using carboys and pumps. We plan to get 30 L of tile water from each tile and unique flow event for complete analysis. In addition, we will sample the Embarras River at Camargo at a range of flow events, obtaining the same sample volumes for a similar analysis. This type of sampling will be conducted each year of the project, giving us a large number of samples for our analysis techniques.In our study, we will first process 30L of tile sample through 0.45 µm filters to separate DRP from PP. And then, filtrates will be passed through an automated ultrafiltration device (AUD) (Tsao et al., 2009). Operationally defined CP, which is based on three filter membranes (CP50: <50 µm, CP100: 50-100 µm and CP450: 100-450 µm) will be recovered. All CP and PP values will be corrected after subtracting DRP values. Fractionated CPs and PPs will be preserved using two different methods: 1) re-suspended in 15 mL filtered solution in scintillation vials to preserve the chemical state of CP at steady state and stored at 3°C and 2) washed and freeze-dried for the solid state analysis in objective 3.Characterization of colloidal and particulate PUsing subsamples from drainage water collections, we propose zeta potential, hydrodynamic diameter of CP using dynamic light scattering. Since PP is too large for DLS, particle size of PP is measured using TEM described below. For the particle size analysis of CP (sonified CP, ~0.2 g/L), dynamic light scattering measurements will be performed using a Wyatt Dawn Heleos II particle separation system (Wyatt Technologies, Dernbach, Germany) in batch mode. Data will be analyzed with ASTRA V software from Wyatt Technologies. If the suspension density is low, concentrated samples will be prepared using ultra high speed centrifugation methods. We will also estimate zeta potential of CP using the Zeta Phase Analysis Light Scattering Zetasizer Nano S90 (Malvern Instruments Ltd. Worcestershire, United Kingdom). For this measurement, colloid suspensions will be in filtrate that is recovered from the AUD-particle separation procedure.Particle characterization (e.g., morphology, elemental association) of CP and PP will be carried out using Transmission electron microscopy (TEM) and SEM techniques at the UIUC Electron Microscopy Facility and synchrotron based X-ray microprobe spectroscopy. In addition to total C and total elemental analysis of CP and PP, both CP and PP samples (paste and freeze dry colloids) will be analyzed for P chemical speciation using microfocused synchrotron based X-ray microprobe techniques. This method will be used to understand the spatially resolved chemical speciation of P in CP separated in Objective 2. The techniques include microfocused-XRF, -XAS, and -XRD. The molecular scale synchrotron X-ray based measurements provide the only means of definition of the chemical forms of targeted element in heterogeneous samples containing crystalline, amorphous, and interfacial P coordination environments. We will use beam line 14-3 at Stanford Synchrotron Radiation laboratory (SSRL), Menlo Park, CA.Objective 3: Understand how soil P pools in fields control the reactive, colloidal, and particulate P lossesOn each of the fields that we are measuring P export through the tile systems we will sample soils for soil test P measurements, as well as other P information. Most soil sampling will be the upper 10 cm of soil, but at selected fields (that represent a range of P loss rates) we will also sample 10-30, 30-50, 50-100, and 100-140 cm soil depths for more complete information on P pools and soil test values.Using the methods described by Helmke and Sparks (Helmke and Sparks, 1996), soils will be characterized for particle size, texture, cation exchange capacity, total C and N, soil pH, buffering capacity, amorphous and crystalline Fe/Al (oxy) hydroxide content via chemical extractions, mineralogy via X-ray diffraction.For indirect P chemical speciation, sequential chemical extraction will be used to identify operationally defined extractable P (e.g., water soluble, oxalate extractable) in fractionated soil samples, which includes particles smaller than clay, according to the method described by Arai et al. (Arai et al., 2005). For direct chemical speciation, undisturbed soil core samples and fractionated soil samples will be freeze dried for thin section preparation according to the method described by Arai et al. (Arai et al., 2007). Microfocused XRF analysis and P K-edge X-ray absorption near edge structure spectroscopy (XANES) analyses will be conducted at beamline 14-3 at SSRL. Based on the XRF maps, we will conduct the advanced statistical analysis (moment analysis) to better assess the P distribution in soils using XRF software, SMAK (http://smak.sams-xrays.com/).Objective 4: Assess the contribution of various P sources, including tiles, surface runoff, and riverine sources to overall watershed export of PWe will have measured P forms in tile flow from a wide range of fields. Putting the tile results in the context of the overall watershed is a substantial challenge. We have available and will install at the Camargo outlet site a Sea-Bird Coastal Cycle Phosphate sensor from Wet Labs. When combined with ISCO samples during high flow events, we can fully characterize the P forms and loads in the Embarras River. Using our chemical characterization data from objectives 2 and 3, combined with the continuous DRP measurements, we will be able to see if the chemical signature of CP and PP forms in tile samples is similar to what we see in the river at the outlet of the watershed. We also will have surface soil chemistry from a great number of fields, and we can also see how that compares to the riverine P forms and loads during both tile flow and surface runoff dominated events.