Challenges of synthesizing literature-based evidence of diatom responses to nutrients in lotic ecosystems
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Monitoring programs often collect diatoms because the usefulness of diatoms as early indicators of water quality change is a common discussion point in the literature. Our literature review was motivated by the need for comprehensive information on stressor-response relationships for environmental managers in the United States to assess eutrophication of lotic ecosystems and support evidence-based environmental management. With this motivation in the forefront, how can we most effectively synthesize decades of research to obtain a comprehensive understanding of how diatom assemblages change with increasing nutrient concentrations? We compiled literature on diatom responses to total nitrogen and total phosphorus concentrations in the water column in streams and rivers to provide a state-of-the-science evidence base for summarizing nutrient impacts on diatoms. Searches for peer-reviewed and non-peer-reviewed articles were conducted using bibliographic databases, specialist websites, and search engines. Information on study design and contextual variables were extracted, along with quantitative response measure values if available, from over 90 references. Not surprisingly for complex ecological studies, there was high variability in analytical methods and types of diatom response measures reported in the literature. Without consistent methods and reporting, it can be difficult to conduct meta-analyses that inform evidence-based management decisions. The challenges of synthesizing secondary data from literature on diatoms will be discussed.