Using conceptual model diagrams as rapid evidence screening and evaluation tools
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A key part of the problem formulation phase of environmental assessment is the development of conceptual model diagrams. These diagrams, which explicitly illustrate hypothesized pathways between sources, stressors, and responses relevant to the focal issue, are used in scoping and structuring the assessment. These diagrams also can provide a useful framework for initial evaluation of the literature-based evidence relevant to each pathway, to identify available bodies of evidence across the complex web of relationships that often must be considered in the assessment. As part of a larger project examining potential drivers of increasing phosphorus concentrations in lakes, we developed a conceptual model diagram focused on potential stressors from agricultural sources that could result in lake phosphorus responses. We used a subset of the pathways included in this diagram as a test case for developing a rapid literature screening process to evaluate the available literature in a standardized, transparent manner. Standardized literature database searches were conducted for each of seven test pathways; for each pathway, a set number of returns was screened at the title/abstract level to identify papers that explicitly evaluated or quantified relationships between the variables in that pathway. We compared results across different literature databases and different numbers of screened returns to evaluate how methodology affected results and inform future efforts. Ultimately, this process allowed us to generate evidence maps across the pathways, highlighting knowledge gaps and hotspots and helping to more effectively focus next steps (and potentially future research) in the assessment of agricultural contributions to increased aquatic phosphorus concentrations.