Research papersThe spatial organization of CAFOs and its relationship to water quality in the United States
Graphical abstract
Introduction
Starting in the 1950′s, animal agriculture in the United States (US) began shifting from smaller, distributed farms to larger facilities to increase the efficiency of production (Mallin and Cahoon, 2003, Key et al., 2017, Walljasper, 2018). These large and often confined facilities, called animal feeding operations (AFOs) in the Code of Federal Regulations, currently represent a majority of the livestock production in the US. An animal operation is defined as an AFO if it confines and feeds animals for 45 days or more and does not sustain crop growth on a regular basis; an AFO is regulated as a CAFO (Concentrated AFO) if it also meets a threshold number of animals that varies by animal type, actively discharges to waters of the US (WOTUS), or is deemed so by the regulating body (USEPA, 2004). These operations yield over 130 million tons of manure annually (Burkholder et al., 2007) and tend to periodically apply this manure to surrounding fields as a means of waste disposal (Long et al., 2018). Although manure is composed of important nutrients such as phosphorus (P) and nitrogen (N) (USEPA, 2004), it may also contain heavy metals, pathogens, antibiotics, and other harmful substances that, in excess, may pose a risk to soil, air, and water quality (Mallin and Cahoon, 2003, Barrett, 2005, Burkholder et al., 2007, Harun and Ogneva-Himmelberger, 2013, Ebner, 2017). A study recently found that significant land-use change and environmental degradation occur within the typical radius of manure application near these facilities (Miralha et al., 2021b). In addition to standard operational activities, accidental discharges such as CAFO lagoon breaks (Mallin and Cahoon, 2003), as well as leaching and runoff of contaminants from manure-applied fields into nearby water bodies (Sousan et al., 2021), can lead to severe ecological degradation. As CAFOs tend to cluster in space for production and logistical purposes, their associated environmental impacts may also intensify.
Clustering has become the cornerstone of efficiency and economic success in industrialized production and development (Porter, 1998, Ayres and Ayres, 2002, Deutz and Gibbs, 2008). Although it is argued that industrial clusters may provide environmental benefits (Lifset and Graedel, 2002), few studies in industrial ecology have investigated the relationship between the clustering of point sources and the impact on the surrounding environment (Kennedy, 1999, Lall and Mengistae, 2005, Anh et al., 2011, Yoon and Nadvi, 2018). Spatially concentrated production can potentially generate negative environmental outcomes regardless of the specific industry. Like many other industries, CAFOs tend to cluster in space for economic reasons, which may lead to similar drawbacks. The clustering of animal agriculture may lead to cumulative adverse environmental effects because individual production facilities add animals over time, whether or not they own sufficient cropland to handle the additional manure produced (Thurow and Thompson, 1998). However, studies have not explored the spatial clustering of CAFOs and its relationship with the conditions of the surrounding environment. Daniels (1997) determined that for cluster zoning to be an effective method of land protection, planners must delineate reasonable densities for development such that the carrying capacity of the local environment is not exceeded, especially in a watershed. Excessive density, inappropriate locations, a combination of these two, or unreasonable expectations about what cluster development can do, are the major potential clustering misuses of a given operation (Daniels, 1997, Porter, 1998). These issues may exacerbate with the expansion of CAFOs both in the US and worldwide, principally when it comes to socio-environmental impacts. While watersheds with high concentrations of CAFOs are potentially at higher risk of degradation than others (Martin et al., 2018, Brown et al., 2020), studies have yet to investigate if the spatial organization of CAFOs is a characteristic of higher negative environmental outcomes. Specifically, this spatial clustering pattern has yet to be investigated in water quality studies that account for agricultural sources of pollution.
Eutrophication, driven by excess nutrients, is a common result of water quality deterioration, so monitoring and controlling nutrient inputs is fundamental to water resource conservation (USEPA, 1996). CAFOs are major sources of nutrient pollution; however, their manure is typically considered a non-point source of pollution when applied to nearby fields (Copeland, 2010, Rosov et al., 2020). Studies have previously explored the impact of CAFOs on water quality. For instance, concentrations of nitrate, ammonium, total nitrogen (TN), and other ions were higher in CAFO-impacted streams than in control streams where CAFOs were not present (Harden, 2015). Additionally, overaccumulation of total phosphorus (TP) by manure application has increased export into surface and subsurface water bodies impacting the aquatic ecosystem (Withers and Jarvie, 2008). For instance, the Neuse River watershed in North Carolina received approximately 41,000 metric tons of N and 16,000 metric tons of P from CAFO waste alone in the 2000s (Glasgow and Burkholder, 2000). These additions of large amounts of nutrients often introduce the potential for eutrophic/hypoxic conditions to surface water bodies (Muenich et al., 2016, Tullo et al., 2019, Miralha et al., 2021a, Raff and Meyer, 2021), an impact that must be prevented and monitored to avoid severe ecological damages. Assessing the spatial organization of CAFOs and its links to water quality conditions could improve our understanding of managing and regulating these and other facilities to prevent future environmental impacts.
The amount of manure produced and applied in the vicinity of clustered CAFOs may exceed the assimilative capacity of the land to a greater extent than in systems with spatially dispersed CAFOs. Additionally, the number of animals these aggregated operations hold may influence the degree of pollution in nearby waterbodies, due to the amounts of manure produced and hauled. Hence, we hypothesize that CAFO-clustered watersheds are likely to present higher concentrations of TP and TN than CAFO-dispersed basins. We tested this hypothesis by examining the relationship between the spatial pattern (i.e., clustering or dispersion) of CAFOs in 16 states across the US and the TP and TN flow-weighted mean concentrations per watershed in these states. To distinguish the impact of clustering from the number of CAFOs present in a watershed, we also investigated the linear relationship between TN and TP concentrations, the number of CAFOs per watershed, and each watershed’s CAFO spatial pattern. We gathered the states that provided animal number information per CAFO and evaluated the relationship between the spatial cluster of the number of animals per CAFO and TP and TN concentrations. This study brings a comprehensive evaluation of the relationship between the spatial organization of CAFOs and water quality, provides the basis for further management of livestock production, and calls for spatially-explicit strategies to prevent environmental impacts associated with intensified animal agriculture and other pollution sources in the US.
Section snippets
CAFO locations database
Any AFO that discharges manure or wastewater into a natural or man-made ditch, stream or jurisdictional waterway is defined as a CAFO, regardless of size (Copeland, 2010). These operations are regulated by the Environmental Protection Agency (EPA) under the National Pollutant Discharge Elimination System (NPDES) and thus subjected to specific regulations defined in the Clean Water Act (USEPA, 2003, USEPA, 2018). The 2003 CAFO rule stated that CAFOs had the duty to apply for NPDES permits,
CAFO facility spatial organization and water quality
Of the 443 8-digit HUC watersheds, CAFO-dispersion was detected in only 88 watersheds, while 355 presented CAFO-clustering patterns (Fig. 2). By excluding watersheds without significant patterns (p < 0.1), we had a total of 249 CAFO-clustering watersheds and 31 CAFO-dispersion watersheds subsequently available to compare to TP and TN concentrations. States such as IA, NC, MO, IN, and FL presented overall clustered patterns, while CAFO-dispersion watersheds were detected in states in the western
Discussion
While studies have mentioned that the spatial aggregation of CAFOs is likely to exacerbate environmental impacts (Thurow and Thompson, 1998, Yang et al., 2016, Martin et al., 2018, Miralha et al., 2021b), we investigated this spatial component and revealed that the clustering of these operations by itself leads to stronger negative environmental outcomes. Specifically, we found that CAFO-clustered watersheds were negatively impacted in terms of water quality. Watersheds with clustered CAFOs
Conclusion
Our study revealed spatial patterns of CAFOs are important drivers of water quality, which has been previously unaccounted for in the literature. With the nearest neighbor index, we revealed that the spatial organization of CAFOs influences surrounding water quality conditions. We also found that the spatial autocorrelation of these farms with respect to their animal units (Local Moran’s I analysis) drove water quality outcomes. Our results demonstrated that although larger CAFOs tend to
CRediT authorship contribution statement
Lorrayne Miralha: Conceptualization, Methodology, Formal analysis, Data curation, Writing – original draft, Visualization. Suraya Sidique: Data curation, Writing – review & editing. Rebecca Logsdon Muenich: Conceptualization, Methodology, Writing – review & editing, Supervision, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We thank the Ira A. Fulton Schools of Engineering and the School of Sustainable Engineering and the Built Environment for supporting this project. Author Miralha was also funded by an American Association of University Women International Fellowship which helped to support this work. Author Sidique was supported on a USDA National Institute of Food and Agriculture, Capacity Building Projects for Non-Land Grant Colleges of Agriculture project 1017146, grant number 2018-70001-28751 to contribute
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