MurKy waters: Modeling the succession from r to K strategists (diatoms to dinoflagellates) following a nutrient release from a mining facility in Florida

Abstract

AbstractThe impacts of pulsed nutrient injections or extreme runoff events on marine ecosystems are far less studied than those associated with long‐term eutrophication, particularly in regard to mechanisms regulating the response of plankton community structure. Over 800 million liters of nutrient‐rich water from a fertilizer mine were discharged over a 2‐week period into Tampa Bay, Florida, in 2021, providing a unique opportunity to document the plankton response. A 3D‐coupled hydrodynamic biogeochemical model was developed to investigate this response and to understand the observed succession of a large, short diatom bloom followed by a secondary Karenia brevis bloom that lasted through the summer. The model reproduced the observed changes in nutrient concentration, total chlorophyll a, and diatom and K. brevis biomass in Tampa Bay. With a faster growth rate and spring temperature close to the optimal window of growth, diatoms had an initial competitive advantage, with 2/3 of the nutrient uptake due to ammonium and 1/3 due to nitrate. However, exhaustion of external nutrients led to the rapid decline of the diatom bloom, and the associated particular organic nitrogen sank onto the bay sediment. Enhanced sediment release of ammonium during the weeks following, and summer remineralization of dissolved organic nitrogen provided sufficient regenerated nitrogen to support slow‐growing K. brevis that could capitalize on low nutrient conditions. Modeling analysis largely confirmed Margalef's conceptual model of r to K‐selected species succession and provided additional insights into nutrient cycling supporting the initial diatom bloom and the subsequent bloom of a slow‐growing harmful algal species.