Analyses of BMP and land use change effects in a Northwest Arkansas agricultural watershed

Abstract

Nonpoint source transport of nutrients, sediment, and pathogens from agricultural activities is a major concern in the Ozark Highlands of Northwest Arkansas; rolling hills in this region are home to thousands of poultry farms and pastures that produce forage for numerous beef and dairy cattle, resulting in an abundance of animal manure. The predominant use of manure in the area has been as a fertilizer for perennial forage crops. There is growing concern that excess land applications of the manure can lead to surface and ground water pollution due to increased runoff losses of sediment, nutrients, and pathogens. Additionally, this region is experiencing a rapid urbanization resulting in the loss of forest and pasture lands and adding to existing concerns regarding nonpoint pollution. There has, however, been some best management practice (BMP) implementation in the area over the years, these mainly pertaining to nutrient and grazing management. This study seeks to quantify the effects of implementation, timing, and spatial distribution of the BMPs on sediment and nutrient loss reduction and watershed ecological integrity, with a focus on Lincoln Lake watershed, a primarily agricultural watershed in NW Arkansas. An analysis of historical land use and BMP implementation for this watershed showed a 9% increase in urban areas and an 11% decrease in pastured areas during the years 1992-2004. About 10% of the watershed was in a transitional land use, comprising newly cleared forests and abandoned pastures. Over the same time period, BMP implementation increased from <1% to 34% of the watershed area, extending across most of the pasture lands in the watershed. During this time, sediment and total phosphorus losses declined by 22% and 4% respectively, while total nitrogen losses increased by 11%, based on analyses of historical in-stream water quality data. Because of the overlap between BMP implementation and occurrence of land use changes, detailed modeling analyses were found necessary to help distinguish between the effects of BMPs and those due to land use changes. This paper discusses the assessment of BMP impacts based on historical data, as well as on preliminary modeling analyses using the Soil and Water Assessment Tool (SWAT).