Integrating information from across multiple sources is an important science literacy skill that involves the following: identifying intra- and intertextual ties, modeling relationships between sources and claims and making an evaluation of the claims made. Tasks that involve reading, interpreting and synthesizing multiple sources have been well explored particularly in the epistemic cognition literature. Interdisciplinarity is a growing area of interest in science education, in terms of the ways we induct students into interdisciplinary ways of thinking and working, including the synthesis of knowledge from across scientific disciplines. While interdisciplinary contexts frequently involve connecting multiple sources from different disciplines, how students complete these text-integration tasks has not been well investigated. This paper develops a model of interdisciplinary text integration for science literacy, drawing on dimensions of epistemic cognition. We exemplify the application of this approach in a specific case of environmental science graduate students, drawing on student syntheses to illustrate how our approach can be used to differentiate between students' written syntheses.