Dissolved organic nutrients at the interface of fresh and marine waters: flow regime changes, biogeochemical cascades and picocyanobacterial blooms—the example of Florida Bay, USA

Abstract The availability of dissolved inorganic and organic nutrients their transformations along the fresh to marine continuum are being modified by various natural anthropogenic activities climate-related changes. Subtropical central eastern Florida Bay, located at southern end peninsula, is classically considered have nutrient conditions that in higher-than-Redfield ratio proportions, high levels chemically-reduced forms nitrogen. However, salinity, pH nutrients, both inorganic, change with changes freshwater flows bay. Here, using a time series water quality physico-chemical from 2009 2019, impacts distinct managed flow, drought, El Niño-related increases precipitation, intensive storms hurricanes explored respect resulting ecosystem effects, focus on understanding why picocyanobacterial blooms formed when they did. Drought produced hyper-salinity were associated seagrass die-off. Years later, precipitation hurricane loads declines pH, likely due acid input decaying matter, collectively leading physiologically favorable for growth picocyanobacterium, Synechococcus spp. These conditions, including very concentrations NH 4 + , inhibiting recovery competing phytoplankton or grazers. Given projected future climate anticipated cycles drought storms, likelihood die-offs high.