Abstract
Water quality degradation, exacerbated by population growth and urban development, is a pressing
issue in the United States. In Florida, harmful algal blooms (HABs) present a significant challenge,
impacting both human health and the economy. This study focuses on the Peace River Basin,
region influenced by nutrient enrichment, which ultimately drains in the Charlotte Harbor, an
estuary vulnerable to HABs. Traditional water quality monitoring methods, such as grab sampling,
are labor-intensive and offer limited temporal resolution. This study evaluated the effectiveness of
automated In-Situ® branded sensors for continuous water quality monitoring in the Peace River
Basin to determine whether they can be reliably used alongside coarser, periodic grab sampling
data for early detection and monitoring of algal bloom development. By comparing sensor data
with laboratory analyses, this work assessed the accuracy and reliability of nutrient and algal
related indicators. In addition, the sensors were evaluated under flowing river conditions in the
Peace River, where waters are less stagnant than in Charlotte Harbor, the downstream outlet of the
basin and an area at greatest risk for algal blooms. Results demonstrated that while In-Situ®
sensors provide valuable insights into temporal patterns and correlations between chlorophyll-α
and phycocyanin with nutrient levels and temperature, their measurements should be interpreted
as relative indicators rather than absolute concentrations. Moderate correlations between sensor
derived Relative Fluorescence Units (RFUs) and extracted chlorophyll-α and phycocyanin
highlight the influence of environmental complexity, biofouling, and sensor drift on field
performance. Total nitrogen (TN; µg/L) emerged as the most consistent driver of both pigment
concentrations and fluorescence responses, whereas total phosphorus (TP; µg/L) and temperature
exhibited weaker and site-dependent influences. These findings underscore the importance of
rigorous maintenance, calibration procedures, and complementary laboratory validation when
using sensors for freshwater monitoring and HABs early-warning applications.
