Water quality woes in SW Florida linked to seeping septic systems

Results showed the nutrient and microbial connections between septic systems, ground and surface water, and harmful algal blooms in the Caloosahatchee River Estuary

From fecal bacteria to blue-green algae to red tides, Southwest Florida’s water quality has declined as its population has increased. Researchers from Florida Atlantic University’s Harbor Branch Oceanographic Institute took a deep dive into this region’s degrading water quality. Multiple lines of evidence from their multi-year microbial source tracking study point to septic systems as a contributing source for this decline.

Florida’s coastal regions are particularly vulnerable to pollution from septic systems because of shallow water tables and porous soils. Yet, there are about 39,768 “known” and about 57,054 “likely” septic systems in Southwest Florida’s Lee County (about 100,000 total). To identify sources of pollution contributing to the water quality woes, researchers examined septic system- groundwater- surface water couplings through the analysis of various parameters.

In collaboration with the Lee County Department of Natural Resources, researchers measured nutrient and bacteria levels, and employed a suite of microbial source tracking tools related to fecal indicator bacteria to discern the presence of human versus animal feces. They used molecular markers for humans, birds and ruminants (cows, deer, goats, etc.) coupled with chemical tracers that included the artificial sweetener sucralose, pharmaceuticals, herbicides and pesticides. Sucralose, the over-the-counter pain reliever acetaminophen, and the prescription anticonvulsants carbamazepine and primidone were used as indicators of human waste contamination. Groundwater and phytoplankton stable isotopes serve as a reliable tracer of nutrient sources and were measured throughout the study and during red tide and Microcystis spp. harmful algal bloom events.