2003 Progress Report: Measuring and Modeling the Source, Transport and Bioavailability of Phosphorus in Agricultural WatershedsEPA Grant Number: R830669
Title: Measuring and Modeling the Source, Transport and Bioavailability of Phosphorus in Agricultural Watersheds
Investigators: Lathrop, Richard C. , Armstrong, D. E. , Hoopes, John A. , Karthikeyan, K. G. , MacKay, David Scott , Nowak, Peter , Panuska, John C. , Penn, Michael R. , Potter, Kenneth W. , Wu, Chin H.
Institution: Wisconsin Department of Natural Resources , The State University of New York at Buffalo , University of Wisconsin Madison , University of Wisconsin - Platteville
EPA Project Officer: Packard, Benjamin H
Project Period: December 17, 2002 through December 16, 2005 (Extended to December 16, 2006)
Project Period Covered by this Report: December 17, 2002 through December 16, 2003
Project Amount: $749,307
RFA: Nutrient Science for Improved Watershed Management (2002) RFA Text | Recipients Lists
Research Category: Water , Water and Watersheds
The objectives are to:
- Quantify effects of manure management and crop production systems on runoff phosphorus (P) losses, particularly related to the portion that is biologically available.
- Determine spatial patterns of sediment and associated P in streams.
- Determine in-stream fate and transport processes of P including bioavailable P (BAP).
- Evaluate and improve modeling tools used to assess P transport in agricultural watersheds over a wide range of spatial scales.
- Determine relation of P losses with the scale of animal operation.
- Integrate outreach into on-going research efforts.
Part I: Effects of Manure Management and Crop Production Systems on Runoff P Losses
The following is an update and progress report for the edge-of-field research aspects of our project. The focus of part I is on the characteristics of particulate P (PP) losses at the edge of a conservation-till corn agricultural production system. This work improves our understanding of the impact of levels and sources of organic matter ([OM], residue or manure) on aggregate stability and runoff PP content. In addition, we are integrating the results of previous studies using a systems monitoring approach to characterize the edge-of-field PP losses with the following subobjectives:
- Investigate the size distribution of primary particles and soil aggregates in runoff.
- Investigate the total P mass distribution across particle-size fractions in runoff.
- Investigate the physical stability of aggregates and the factors impacting aggregate stability in runoff.
- Compare the runoff volume and pollutant loading determined by a bulk sample collection system against an automatic continuous flow monitoring system.
- Develop general regression relationships to predict PP transport in similar soil environments with different sets of physical (rainfall intensity, runoff volume, slope length, gradient, etc.) and chemical (OM, soil test P, etc.) factors.
Beginning in the spring of 2003, we began monitoring the impact of two corn harvesting systems (grain and silage) and manure application (with silage) on edge-of-field runoff particle characteristics. This work is leading to a greater understanding of the size distribution and P content in particles and the role of soil aggregation processes. Because aggregates play an important role in PP transport, this study is providing additional insights into the effect of land management practices on aggregate stability and particle P content. Having this information will lead to better best management practice (BMP) selection and design. BMPs, such as buffers and contour strips, are an important means to control P loss from agricultural management systems. To minimize PP movement, a BMP must have the ability to trap nutrient rich particles. The proposed study will result in a better understanding of the physical and chemical characteristics of runoff particles being delivered to the edge-of-field for the conditions represented in the study. The proposed investigation is also evaluating different sampling protocols to obtain reliable samples to determine edge-of-field sediment and P losses.
On-Going and Recently Completed Activities:
- Collection and analysis of base line soil samples (0–5 cm depth) on a 150 ft square grid. These samples have been analyzed for Bray-1 P, OM, and pH. The particle-size distribution (% of sand, silt, and clay) of the parent material has been determined for 24 of the 35 samples collected.
- Completion of a detailed GPS topographic survey for all 3 fields and the creation of topographic maps.
- Installation of a flume with continuous flow and automatic sampling in series with the bulk collector for the field in corn silage (no manure).
- Installation of three edge-of-field surface runoff bulk collection stations and three continuous automatic recording rain gages.
- Collection and analysis of storm event runoff samples from the 2003 growing season.
- Completion of manure application, tillage, and harvest prior to the 2003 growing season, and manure and tillage operations completed for the 2004 growing season.
- Collection and analysis of manure samples.
- Development of a laboratory procedure to process bulk field samples.
Part II: Relation of P Losses With the Scale of Animal Operation
The installation of field equipment began during summer 2003. The study area in the Pheasant Branch subwatershed (located in the western part of the Lake Mendota watershed) comprises a series of nested sampling stations that have been deployed to monitor and sample runoff at the field scale, and also at small and large catchment scales. When all stations are fully deployed in 2004, two sheet-flow samplers and four automated runoff samplers will be gathering data on runoff and acquiring samples during each storm event. To facilitate our watershed modeling work, we have acquired a 3-m resolution digital elevation model (DEM) for the entire study area.
The location of the study matches the goals set forth in the original proposal. The selected catchment is divided into two subcatchments with two groups of contrasting animal feeding operations (AFOs). The first group occupies the southern subcatchment, where detailed information has been gathered on the animal equivalent units (AEUs), land base, and operation for these operations (Cabot and Nowak, in review). Approximately 4,000 AEUs are managed in this southern subcatchment, and this includes the animals of two dairy farms that are currently regulated under the Wisconsin Pollutant Discharge Elimination System (WPDES). These two farms occupy the majority of the land base for this subcatchment. An aspect of the data collection in the southern subcatchment also involves detailed manure application monitoring, through the use of a precision agriculture system mounted to the manure side-slinger being used on the fields where the sheet-flow samplers collect runoff. We are currently collecting information on the second group of AFOs in the northern subcatchment. Site visits and available data from the Dane County Land Conservation Department (DCLCD) indicate that there are 500–600 AEUs in an area approximately equal to the southern subcatchment.
During the 2003 storm season, we were able to collect runoff data from the two sheet-flow samplers during eight storms that totaled approximately 68 cm of precipitation, which was considerably below normal for this region of Wisconsin. One sequence of storms occurred directly after manure had been placed to a field that is monitored by one of the sheet-flow samplers. Data from this sequence is currently being analyzed to address questions regarding effects of manure application timing on sediment and P migration at the field scale.
Dorn Creek, a rural stream that drains into Lake Mendota, was chosen for our stream hydrodynamic and phosphorus study area because land use within the watershed is entirely agricultural (Figure 1). The stream begins as a spring and travels approximately 6 km where it enters the Dorn Creek Wetland leading to the lake. Dorn Creek flows through properties owned by seven different landowners, six of which have granted access to the stream. The six properties from which data were gathered represent approximately 90% of the total stream main channel by length upstream of the Dorn Creek wetland. Sampling sites were selected to represent typical stream reaches (riffles, glides, pools, and wetlands).
Figure 1. Dorn Creek Subwatershed Map Indicating Major Hydrologic Features and Mostly Nonurban Land Use in the Lake Mendota Watershed. The thicker stream line signifies the perennially flowing section of Dorn Creek.
Stream Survey Work
Stream and channel width, water depth, sediment thickness (depth), stream gradient, sediment particle size, volatile solids, and total sediment phosphorus were measured at 33 sites located along Dorn Creek. Additional measurements were made within the wetland complex at the terminus of the stream. Sediment thickness and water depth measurements were taken at one- or two-foot intervals along a cross-section of the stream at each site. Sediment thickness was defined as distance from top of sediment to the consolidated layer through which the probing device (hollow 2 cm-diameter aluminum rod) would not penetrate. Samples were collected at 18 sites from the top 2 cm of sediment for particle size analysis, which was determined by sieves for sands and the hydrometer method for silts and clays.
At least two sediment cores were collected at each site, one collected in the thalweg of the stream and the other approximately half of the distance from thalweg to bank. If sufficient sediment was present, the top 15 cm was collected from each core. The top 5 cm of sediment was separated into 1-cm subsamples, and the remaining sediment into 2.5-cm slices. Each sediment slice was analyzed for total phosphorus (persulfate digestion and ascorbic acid method).
Figure 2 presents a typical cross-section taken near the end of the stream, as it approaches the Dorn Creek Wetland. Note the large zone of depositional sediments in the stream (between the sediment and consolidated layer levels). This feature of large sediment deposits was characteristic of many of the stream sites sampled in our stream survey work conducted during the initial summer. The survey work also allowed us to select individual sites for more detailed sampling, including selecting a site for our detailed hydrodynamic research.
Figure 2. Cross Section Showing Water Depth and Sediment Thickness at a Site in Dorn Creek Immediately Upstream of the Major Wetland
Data collected during 2003 indicate that stream sediment deposit characteristics, such as percentage sand, water content, volatile solids, and sediment thickness, all are useful predictors of the P content of the stream sediment deposits. Relationships between total phosphorus (TP) and stream/sediment properties will be evaluated for the surficial sediments (the uppermost 1 cm) as well. To date, the top 5 cm of sediment have been analyzed. TP concentrations ranged between 200 and > 3,000 ppm. At most sites it appears that TP concentrations remain constant or decrease with depth. Preliminary results show the average TP concentration in the stream sediment decreasing 11–124 ppm per cm of depth change. After the remainder of the core samples (depths greater than 5 cm) are analyzed, variations in parameter values with depth will be examined. This information will assist in the selection of sites for sediment phosphorus fractionation and sediment dating.
Stream Sediment Chemistry Work. The goal of this subproject is to determine the processes and factors controlling the distribution and mobility of BAP in sediments of a stream (Dorn Creek) located in an agricultural watershed. Our approach involves determining the amounts of BAP in sediment cores and examining relationships to sediment biogeochemistry, longitudinal stream position, sediment age (depth), and contributing watershed characteristics. This subproject relates closely to the work on determining the P mass deposited in stream sediments.
In the fall of 2003, we obtained an initial set of sediment core samples that are being used to set up and verify methods for analysis of P and related sediment components. Several core surface layers have been analyzed for total P using the persulfate digestion method. Our results will be compared to those obtained by the stream survey group to validate methods.
Stream Hydrodynamic Work. Using information obtained by the stream survey group, by early summer 2003 we chose Dorn Creek to represent a small stream with a suitable riffle and pool site for studying flow and sediment hydrodynamic processes. The research site is located just upstream from the Dorn Creek wetland in a relatively steep, meandering segment of the stream. In this reach the channel has numerous riffle and pool sequences. Large boulders are evident, sometimes forming riffles and sometimes along the bank. The bed consists of sticky, firm, fine-grained sediments along with some sand and gravel.
During the spring and summer 2003, a careful review of instrumentation needed for measuring flow velocity, water depth, bathymetry, and sediment concentration was conducted as part of a student independent study report. In fall 2003, an instrument package that would allow measurements of stream velocity and depth and suspended sediment was developed and deployed in Dorn Creek. An instrument support and positioning frame was also constructed, allowing accurate and repeatable positioning of instruments within the main study pool. The frame extends approximately 5.8 m along the length of the stream, which is sufficient to access the entire study pool.
Preliminary measurements were carried out in Dorn Creek to determine the suitability of the selected research site to address key scientific questions regarding sediment movement and channel morphology alterations during runoff events. Data were recorded for water level, turbidity, and temperature from September 17 through December 10, 2003. During that period, two major rainfall events occurred—November 3-4 with a rainfall total of 7.2 cm and November 22-23 with a total rainfall of 5.3 cm. During these events, the stream water level and turbidity had a strong response to the rainfall events, indicating that this site has the potential to yield interesting hydrodynamic data. Specifically, both water level and especially suspended sediment concentrations exhibited a bimodal character. In the case of the water level, this is likely due to storage upstream from the study site. An explanation for the sediment response is less obvious, and further exploration on this is needed.
Preliminary velocity measurements were also made using a Sontek 10 Mhz Acoustic Doppler Velocimeter. A number of factors, including ice and insufficient battery life, combined to make the results of this test less than ideal, although the utility of the positioning frame was proven. The problems encountered here should be easily resolved in the spring. The results of the phase 1 study indicate the suitability of the selected research site and feasibility of the instrumentation and infrastructure. The preliminary measurements also pose several scientific questions regarding sediment movement and channel morphology responses to rainfall events.
The activities pertaining to the modeling aspects of the project were primarily: (1) completion of a paper on modeling sediment transport within the Lake Mendota watershed; (2) GIS and database work to support phosphorus modeling in the Mendota watershed as the focus of a graduate practicum course; and (3) initial work with the Agricultural Policy/Environmental eXtender (APEX) model. An investigation on how the Soil and Water Assessment Tool (SWAT) model structure and input data representation affect sediment predictions was published (Chen and Mackay, 2004). The study focused on SWAT’s integration of the Modified Universal Soil Loss Equation (MUSLE) with hydrologic response units (HRU). The results show that HRUs do not conserve sediment with scale of watershed representation. Instead, HRUs introduce almost half of the variability in sediment generation, which other researchers have previously attributed to input data aggregation. This occurs for two reasons. First, MUSLE defines a nonlinear relationship between sediment generation and HRU area, but the sediment load is scaled linearly from the HRU level to the subwatershed level. Second, HRUs aggregate land areas without regard for the surface connectivity assumptions, which are implicit in MUSLE. These conflicts caused by the integration of HRU and MUSLE make it difficult to determine the effect of different land use on soil erosion. This study indicates that greater attention should be made to structuring the data inputs to match the underlying assumptions of submodels within SWAT. This finding provides new insight on the appropriate scales for interfacing field- and watershed-scale process representation, which will help focus future project-related simulation work with both SWAT and its companion model APEX.
A full range of runoff sampling activities associated with the agricultural uplands and streams are planned for 2004 as the sampling equipment and other instrumentation have been purchased/constructed, installed, and utilized during runoff events sampled in 2003. Further work on mapping and characterizing the stream sediment deposits will also be done during the Summer 2004 field season. In early 2004, we will be initiating analyses of BAP, total organic P, and total inorganic P using sequential NaOH and HCl extraction procedures on samples collected during 2003. In addition, we plan on measuring additional sediment characteristics including organic C and N and amorphous Fe for use in evaluation of sediment diagenesis and P retention characteristics. Another aspect of our work in 2004 will involve the use of natural radionuclides (Be-7 and Pb-210) to evaluate sediment age and dynamics. Be-7 will provide information on short-term (week to month) dynamics, while Pb-210 will provide sediment age information for undisturbed sediment deposits.
In addition to the detailed storm event sampling for the stream hydrodynamic work, we are planning to investigate sediment residence times in the riffle-pool stream using a dye tracer. While the dye tracer technique may place a lower limit on sediment travel times through the system, it can provide a good approximation of travel times for small particles. In addition, we plan to install two instrument packages to examine possible sediment storage within the riffle/pool system. These observations will be coupled with an examination of changes in bed morphology, using various techniques. We also plan to develop a stage/discharge rating curve that will allow us to determine flow rate and sediment flux from data like those collected in the fall of 2003.
Modeling work will continue with applications of APEX and SWAT to our study watershed. In addition, we are planning to conduct an analysis on the impact of using a high-resolution DEM in assessing GIS-based watershed P loads. Most watershed studies, including previous work on the Mendota watershed, have utilized coarser DEMs readily available through the U.S. Geological Survey. In our glaciated basin with many shallow depressions, flow pathways, and the amount of noncontributing area may change dramatically using the high-resolution DEM, which was recently made available for the Mendota watershed.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 50 publications||9 publications in selected types||All 9 journal articles|
||Cabot PE, Nowak P. Planned versus actual outcomes as a result of animal feeding operation decisions for managing phosphorus. Journal of Environmental Quality 2005;34(3):761-773.||
||Chen E, Mackay DS. Effects of distribution-based parameter aggregation on a spatially distributed agricultural nonpoint source pollution model. Journal of Hydrology 2004;295(1-4):211-224.||