Evaluating Edge of Field Phosphorus in Agricultural Watersheds

John Gabrysiak

Kelly Westhelle

Lindsay Cotnoir

Zachary Neal

Kevin Schiavone

Client: Julie Moore, Stone Environmental, Inc.

Problem Statement

Stone Environmental, Inc. is evaluating the effectiveness of Best Management Practices (BMPs) utilized by farmers in the Lake Champlain basin to reduce sediment and nutrient losses via overland runoff. Additional analysis is needed to determine the conditions which cause the most significant runoff losses to occur to ensure that BMPs are targeting the factors responsible.

Justification

Excessive phosphorus loading in Lake Champlain has resulted in the degradation of its water quality. Non-point sources of runoff in particular are of utmost concern, as they are the main contributor to phosphorus loading throughout the Champlain Basin (VTANR, 2008). Agriculture contributes approximately 40% of the non-point phosphorus load, and farms have been under increased pressure to reduce runoff after the U.S. EPA withdrew their approval of the Vermont Lake Champlain Basin Total Maximum Daily Load (TMDL) for phosphorus in 2011 (Troy et al., 2007).To address this issue, farmers have shown interest in implementing Best Management Practices (BMPs) such as conservation tillage to reduce sediment and nutrient losses via runoff into neighboring bodies of water. Although farmers have anecdotally reported improved water quality attributed to these practices, the actual effectiveness of BMPs in reducing sediment and phosphorus runoff has not been quantitatively documented. The USDA-NRCS and Vermont Agency of Agriculture, Food, and Markets (VAAFM) addressed the need for documentation by hiring Stone Environmental, Inc. to collect non-point source runoff data from fields on seven farms spread throughout the Vermont portion of the Champlain Watershed. Runoff data was collected on fields practicing three common agricultural BMPs: soil aeration on hayland, reduced tillage, and cover cropping (Moore et al., 2013; Braun et al., 2015).

This study followed a paired watershed design which assumed that proximate, comparable watersheds respond to runoff in a similar manner (USEPA, 1993). This experimental design included a control and treatment watershed. The control watershed in each pair provided baseline data that accounted for year-to-year and seasonal climate variations while land management practices remained the same. Treatment watersheds employed BMPs (USEPA, 1993). This design was comprised of two phases: a calibration period, where all watersheds were treated the same and paired water quality data was collected, and a treatment period, where one watershed employed a BMP treatment but paired water quality data was collected (USEPA, 1993). For the edge of field monitoring conducted by Stone Environmental, Inc., twelve watersheds paired and studied on six operational dairy farms.

While the effectiveness of the BMPs is the primary focus of the analysis by Stone Environmental, Inc., their extensive dataset affords opportunity to isolate other factors that can influence the quality of agricultural runoff. The calibration period provides extensive data on soil chemistry, water quality and runoff events along other climatic factors that can aid in understanding the dynamics of the site. This data also reflects the weather events, site conditions, and timing of manure and chemical fertilizer applications that can degrade the quality of water. Conducting a thorough analysis of the calibration period data could identify environmental factors that significantly affect quality and quantity of agricultural runoff on conventional fields. These findings could assist in understanding how existing site and weather conditions affect the quality and quantity of runoff to inform the selection of the most suitable BMPs for reducing phosphorus and sediment losses, providing valuable information to farmers and agencies for future implementation.

Objectives

  1. Create a multivariate regression model to evaluate whether hydrologic soil group, soil test phosphorus, sample period discharge per acre of field, field area, mean field slope, total suspended solids (TSS) concentration, and/or antecedent dry days affect the edge of field phosphorus concentrations.
  2. Create a multivariate regression model to evaluate whether precipitation depth, storm duration, hydrologic soil group, mean field slope, and field area affect the mean runoff volume per acre (L/acre) from storm events.
  3. Compare the Modified Morgans method and the Mehlich method’s ability to predict the amount of phosphorus runoff from agricultural soils.
  4. Interpret results of statistical analyses to assess what environmental factors impact phosphorus concentration and runoff, and identify what BMPs would best mitigate these factors.

Proposed Approach

The methodology to complete the objectives combines a review of the literature with several statistical analyses of the large dataset consisting of environmental and water quality data provided by Stone Environmental, Inc. The provided dataset was collected over the 2-year study calibration period (2013 - 2015), during which no conservation measures were applied to any of the study fields. We will review literature on the factors identified in the objectives that may create conditions for significant runoff events (in terms of water quality) to determine if our objectives are targeting appropriate factors of statistical significance. Microsoft Excel and JMP will be the platforms used to test for statistical significance between the parameters identified in the objectives. We will use a linear regression model and/or a two-tailed T-test to interpret whether the variables in our objectives have any correlation. To ensure we are conducting the correct statistical analyses, we will consult Dr. Jennifer Pontius of the Rubenstein School of Environment and Natural Resources at the University of Vermont. Finally, we will compile our results into a written report for Stone Environmental, Inc. outlining our findings and their possible significance in the study of BMP effectiveness. This report could be used to complement the finding of Stone Environmental. Inc. to determine if the BMPs are targeting the runoff events that produce the most significant sediment and nutrient loads.

Expected Outcomes and Significance

Using the wealth of edge of field water quality and quantity data available, we will describe five relationships between environmental factors and agricultural runoff, including the significance of each factor as it contributes to runoff. This will assist in identifying statistically significant relationships between environmental factors and the quality of agricultural runoff across the study areas. These results will provide a basis of comparison for considering the combinations of site conditions and precipitation events that drives nutrient and sediment losses from Vermont farm fields. This in turn will complement the findings of Stone Environmental Inc., ensuring the BMPs tested are targeting the factors that produce the most polluted runoff.

Effort Assignment

Lindsay Cotnoir

I will investigate whether rain events of the same depth to see if they generate different amounts of runoff depending on the duration. I will review the literature, test for statistical significance, and assist in compiling the results into a final report.

John Gabrysiak

I will extract data from the reports provided by Stone Environmental on the contributing field area, slope, and soil type for each watershed. I will assist in determining the relationship between these factors and the amount of runoff from agricultural fields. I will review the literature, help assess statistical significance, and assist in writing the final report.

Zach Neal

I will determine whether timing of fertilizer application (time removed) from the most recent application of manure or chemical fertilizer affects nutrient runoff from similar storms. I will review the literature, test for statistical significance, and help to write the final report. Unfortunately there was not sufficient data to complete this first objective, so I focused on literature review and writing the report.

Kevin Schiavone

I will focus on whether the soil test phosphorus levels relate to phosphorus concentration measured in runoff from the monitoring fields. Also, compare soil characterization methods ability to predict P runoff. I will review the literature, test for statistical significance, and assist in compiling the results.

Kelly Westhelle

I will examine the relationship between the antecedent dry days of storms and the concentration and loads for phosphorus and sediments. I will review the literature, test for statistical significance, and assist in assembling and writing the final report.

Timeline

Project: / Edge of Field
Client: / Julie Moore, Stone Environmental, Inc.
Project team: / Lindsay Cotnoir
John Gabrysiak
Zachary Neal
Kevin Schiavone
Kelly Westhelle
Week of: / 18-Jan-16 / 25-Jan-16 / 1-Feb-16 / 8-Feb-16 / 15-Feb-16 / 22-Feb-16 / 29-Feb-16 / 7-Mar-16 / 14-Mar-16 / 21-Mar-16 / 28-Mar-16 / 4-Apr-16 / 11-Apr-16 / 18-Apr-16 / 25-Apr-16 / 2-May-16
Gantt Chart / Objectives Week: / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14 / 15 / 16
Pick Project
Coordinate with Group Members
Reach out to Project Partner
Coordinate Williston Site Visit
In-Class Progress Meeting
Send proposal to Julie for feedback
Project Proposal Due (Mar. 4)
Identify five relationships to be tested
Meet with Jennifer Pontius for statistical guidance
Perform data analyses
Check in with Julie with progress on data analyses
Write project report
Draft Project Report due (4/5)
Final Report due (4/29)

References Cited

Braun, D., Moore, J., Meals, D., & Sleeper, R. (2015). Agricultural Practice Monitoring and Evaluation: Year Three Report (draft) (No. 112540-W). Montpelier, VT: Stone Environmental, Inc.

Moore, Julie, Don Meals, and Dave Braun. (2013). Agricultural Practice Monitoring and Evaluation: Year One Report (draft). Rep. Montpelier: Stone Environmental, Inc. Print.

Smeltzer, Eric, and Fred Dunlap. (2015). "Lake Champlain Basin Program: State of the Lake 2015." Lake Champlain Basin Program: State of the Lake 2015. Lake Champlain Basin Program.

Troy, A., D. Wang, and D. Capen. (2007). Updating the Lake Champlain Basin Land Use Data to Improve Prediction of Phosphorus Loading. LCBP Technical Report #54. Lake Champlain Basin Program, Grand Isle, VT.

United States Environmental Protection Agency. (1993). Paired Watershed Study Design (National Service Center for Environmental Publications No. 841-F-93-009). Washington, D.C.: USEPA Office of Water.

Vermont Agency of Natural Resources. (2008). “Report on Progress in Establishing and Implementing the Total Maximum Daily Load (TMDL) Plan for Lake Champlain.” Submitted to the Vermont General Assembly in accordance with Act 43, Section 4.