REFINING CHLOROPHYLL-NUTRIENT RELATIONSHIPS ACROSS THE US CONSIDERING THE EFFECTS OF DEPTH, TROPHIC STATUS, LIGHT AVAILABILITY, AND TEMPERATURE.

Lake eutrophication is a significant challenge for water-quality management across the world. Many management strategies focus on reducing nutrient inputs, but other environmental factors can substantially influence nutrient-algal relationships. While there have been various large-scale studies assessing how different lake characteristics impact eutrophication, there remains a need to integrate these factors into a comprehensive model.  In this study, we aim to refine chlorophyll-nutrient relationships across the United States (US) by considering auxiliary variables (e.g., depth, light, non-algal turbidity, temperature) within a Bayesian hierarchical framework. We leverage over 4000 sampling events from the National Lakes Assessments (US EPA, 2007-2022) to inform model development. We first consider auxiliary variables independently, exploring how they influence the critical nutrient ratio (nitrogen:phosphorus) and the chlorophyll-to-limiting-nutrient ratio. Results indicate substantial variability in these ratios, particularly related to trophic status and depth. Next, we integrate significant variables into a comprehensive model for chlorophyll prediction. We apply the model to map nitrogen versus phosphorus limitation, as well as sensitivities to other factors (like temperature), across the US. Our model can serve as an effective tool to aid water resources management, particularly at large spatial scales.

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Primary Presenter: Brian Baird, North Carolina State University (bwbaird@ncsu.edu)

Authors:

Brian Baird, North Carolina State University  (bwbaird@ncsu.edu)

Smitom Borah, North Carolina State University  (sborah@ncsu.edu)

James Elser, University of Montana  (jim.elser@umontana.edu)

Daniel Obenour, North Carolina State University  (drobenour@ncsu.edu)