Using long-term satellite image records to map swine concentrated animal feeding operations and estimate their historical impact on nutrient inputs in the NC Coastal Plain

Abstract:

North Carolina (NC) experienced a dramatic increase in swine production throughout the 1980s and early 1990s through the development of intensive animal agriculture facilities known as concentrated animal feeding operations (CAFOs). In NC production systems, swine manure is usually stored in one or several open-air lagoons and later applied to spray fields, potentially contributing nutrient and emerging chemical contaminants that can accumulate over time in soils and groundwater. In order to better characterize the effects of swine CAFOs on surrounding landscapes, more information is needed on the locations of CAFOs, as well as the ages of existing operations. Prior to 1997, swine CAFO construction dates in NC were unknown. In order to evaluate the potential long-term accumulation of nutrients due to this management strategy, the historical expansion of swine CAFOs across the NC landscape was reconstructed through the analysis of satellite imagery. Locations of existing lagoons (n = 2000) were analyzed over the Landsat 5 library of images through Google Earth Engine to identify the years in which individual lagoons were constructed. Years of construction were determined by identifying breakpoints in band 4 reflectance. Band 4 was found to be effective at capturing the presence or absence of lagoons across the landscape; abrupt changes in the band 4 time series indicated the land use of a pixel converted from forest, grassland, or cropland to a waste lagoon. The year of waste lagoon construction was correctly detected 85% of the time. Results showed that over 60% of the waste lagoons were constructed in the first half of the 90s. In particular, the Cape Fear River watershed experienced a dramatic increase in the number of waste lagoons in the years 1991 when over 300 lagoons were constructed. Nutrient loading rates from CAFOs across the NC Coastal Plain were estimated using the newly-identified construction years from the satellite remote sensing analysis and information embedded in historical regulatory documentation, nutrient management plans, and the literature. This study demonstrates how knowledge on CAFO ages increases understanding of CAFOs’ long-term impacts on water resources and provides useful information that can be used as inputs for environmental simulation models.