Abrupt chlorophyll shift driven by phosphorus threshold in a small subtropical estuary

Chlorophyll trends in subtropical and tropical estuaries are under characterized may reveal patterns not shared by their temperate analogues. Detection of requires long-term monitoring programs, but these uncommon. In this study, we utilized an 18-year chlorophyll- a time series from 2002 to 2020 Weeks Bay, AL, detect quantify chlorophyll variability over multiple scales. Our analysis included up 30 years contemporaneous data for variables such as river discharge, nitrogen, phosphorus relate the environmental drivers. We detected abrupt shift that was linked changes hydrology. The followed increase total concentration upstream primary system discharges into Bay. Total continued rise after shift, there no detectable change . propose exceedance threshold at 0.1 mg l -1 , combined with period very low discharge variability, induced This opposed pattern proportional usually observed result nutrient enrichment. Not all stations underwent which demonstrated complexity phytoplankton response drivers significance spatial differences even small estuaries.