FIELD SCALE MODELING TO ESTIMATE PHOSPHORUS AND SEDIMENT LOAD REDUCTIONS USING A NEWLY DEVELOPED GRAPHICAL USER INTERFACE FOR SOIL AND WATER ASSESSMENT TOOL

Mittelstet Mittelstet

doi:10.3844/ajessp.2012.605.614

Abstract

Streams throughout the North Canadian River watershed in northwest Oklahoma, USA have elevated levels of nutrients and sediment. Soil and Water Assessment Tool (SWAT) was used to identify areas that likely contributed disproportionate amounts of Phosphorus (P) and sediment to Lake Overholser, the receiving reservoir at the watershed outlet. These sites were then targeted by the Oklahoma Conservation Commission (OCC) to implement conservation practices, such as conservation tillage and pasture planting as part of a US Environmental Protection Agency Section 319(h) project. Conservation practices were implemented on 238 fields. The objective of this project was to evaluate conservation practice effectiveness on these fields using the Texas Best Management Evaluation Tool (TBET), a simplified Graphic User Interface (GUI) for SWAT developed for field-scale application. TBET was applied on each field to predict the effects of conservation practice implementation on P and sediment loads. These predictions were used to evaluate the implementation cost (per kg of pollutant) associated with these reductions. Overall the implemented practices were predicted to reduce P loads to Lake Overholser by nine percent. The ‘riparian exclusion’ and ‘riparian exclusion with buffer’ practices provided the greatest reduction in P load while ‘conservation tillage’ and ‘converting wheat to bermuda grass’ produced the largest reduction in sediment load. The most cost efficient practices were ‘converting wheat to bermuda grass’ or ‘native range’ and ‘riparian exclusion’. This project demonstrates the importance of conservation practice selection and evaluation prior to implementation in order to optimize cost share funds. In addition, this information may lead to the implementation of more cost effective practices and an improvement in the overall effectiveness of water quality programs.

Highlights

In agricultural watersheds, non-point sources are often the dominate contributor to water quality impairment (Allan, 1995; Rao et al, 2009)
The average annual reduction from the 238 field sites due to the implementation of the conservation practices was 4,200 kg of P per year (0.65 kg ha-1 year-1) and 3,000 Mg of sediment per year (0.47 Mg ha−1 year−1). This corresponded to a nine percent average annual reduction in P load to Lake Overholser based on loads estimated by Storm et al (2007)
The majority of the total watershed reductions were from the ‘conservation tillage’ and ‘wheat to bermuda’ practices due to the large number of fields where these practices were implemented; the largest reductions in P and sediment per unit area were achieved with the ‘riparian exclusion with buffer’ and the ‘wheat to bermuda’ practices, respectively (Fig. 2)

Summary

Introduction

Non-point sources are often the dominate contributor to water quality impairment (Allan, 1995; Rao et al, 2009). Both the USEPA and the USDA have expressed significant interest in evaluating the effectiveness of these programs. The Canton-Overholser corridor of the North Canadian watershed (Fig. 1) which includes parts of Blaine, Canadian and Dewey Counties, located in northwest Oklahoma, USA, occupies a drainage area of approximately 1,970 km. The Canton-Overholser corridor of the North Canadian watershed (Fig. 1) which includes parts of Blaine, Canadian and Dewey Counties, located in northwest Oklahoma, USA, occupies a drainage area of approximately 1,970 km2 Streams throughout this wheat and cattle producing area are impaired due to excess nutrients, suspended solids and siltation.

Objectives

Methods

Results

Discussion

Conclusion