Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…2016), swine wastewater (Reddy et al., 2001; Lee et al., 2004; Kantawanichkul & Somprasert, 2005; Tunçsiper et al., 2015), plant nursery runoff (Huett et al., 2005), barnyardmanure (Hill et al., 2000), winery wastewater (De la Varga et al., 2013; Serrano et al., 2011; Rozema et al., 2016),…
Category: