Florida’s Indian River Lagoon is undergoing a silent yet profound transformation—one that imperils the foundation of its complex marine ecosystem. This estuary, renowned for its biological richness and productivity, has been suffering from an array of environmental stresses that remain largely invisible to casual observation. Over recent years, factors such as nutrient pollution, episodic harmful algal blooms, and excessive freshwater influxes have compromised water quality and contributed to widespread seagrass die-offs. Now, a groundbreaking study conducted by Florida Atlantic University’s Harbor Branch Oceanographic Institute reveals a darker chemical shift within the Lagoon waters, one which threatens a keystone group of marine life: shell-building organisms.
At the crux of this investigation lies aragonite saturation, a pivotal metric that signifies the water’s capacity to sustain calcifying organisms like oysters, clams, and other shellfish. Aragonite is a crystalline form of calcium carbonate essential for shell and skeleton formation. When saturation levels decline below certain thresholds, these animals face physiological stress, resulting in inhibited growth, weakened shells, and increased vulnerability to environmental pressures and predation. The research team embarked on a comprehensive measurement campaign between 2016 and 2017, systematically sampling throughout the Indian River Lagoon to map the spatial and temporal variations in aragonite saturation relative to nutrient loading, salinity, and other water chemistry parameters.
The interdisciplinary methodology combined two complementary approaches. First, a broad geographic survey spanned from the northern reaches of the Lagoon, where nutrient concentrations and algal bloom occurrences are elevated, down through southern sections influenced by freshwater inflows from rivers and canals. This gradient provided a natural laboratory to observe how distinct environmental pressures modulate aragonite saturation. Second, the team implemented high-frequency weekly sampling at three strategically chosen sites that represented contrasting salinity regimes and differing anthropogenic impacts—urban canals, agriculturally influenced river mouths, and a relatively pristine reference station with robust ocean exchange.
The results, recently published in Marine Pollution Bulletin, elucidated critical correlations. Northern sections with pronounced nutrient enrichment exhibited suppressed aragonite saturation, partly driven by recurrent harmful algal blooms and associated microbial respiration that elevate dissolved carbon dioxide, acidifying the water column. Conversely, freshwater incursions in the southern reaches diluted the mineral content and lowered salinity, independently reducing saturation states despite lower nutrient inputs. These findings underscore a dual mechanism: nutrient pollution intensifies carbon-driven acidification, while freshwater inflows act through physical dilution, both converging to threaten calcifiers.
Coastal acidification arises when ambient and biologically produced carbon dioxide dissolves in estuarine waters, forming carbonic acid. This process reduces pH and depletes carbonate ion availability crucial for shell synthesis. Unlike open-ocean acidification driven predominantly by atmospheric CO₂, estuarine systems like the Indian River Lagoon experience enhanced variability due to land-based inputs of nutrients and freshwater, sluggish water exchange, and localized biological activity. The study’s nuanced understanding of these intertwined drivers signifies a notable advancement in coastal biogeochemistry, filling critical knowledge gaps about acidification within shallow, dynamic estuarine environments.
Dr. Rachel Brewton, a lead co-author, emphasizes the ecological stakes: “Declines in aragonite saturation slow organisms’ shell formation, rendering them more fragile and jeopardizing survival. This cascade reverberates across trophic levels, influencing fish populations, marine mammals, and ultimately the livelihoods of human communities reliant on these fisheries.” Such biological ramifications resonate broadly, as shellfish serve not only as ecosystem engineers and food resources but also as indicators of estuarine health.
These findings carry profound implications for estuary management worldwide. As human activities intensify coastal nutrient inputs through urban runoff, agriculture, and wastewater discharge, the synergistic effect on carbonate chemistry accelerates ecosystem degradation. The study’s authors advocate for integrated water quality management strategies targeting nutrient load reductions and controlled freshwater inflows. By addressing these dual challenges, restoration efforts may halt or even reverse acidification trends, bolstering resilience among vulnerable shell-building populations.
Technological innovation plays a pivotal role in ongoing environmental stewardship. Florida Atlantic University’s Indian River Lagoon Observatory Network of Environmental Sensors (IRLON) now incorporates cutting-edge pH and CO₂ monitoring capacities, enabling near real-time computation of aragonite saturation. This continuous data stream empowers scientists and resource managers to detect early-warning signals of acidification hotspots, forecast ecosystem responses, and tailor mitigation measures with unprecedented precision.
Moreover, by elucidating the chemical fingerprints underpinning estuarine acidification, this research opens pathways for comparative studies in similar ecosystems grappling with coastal eutrophication and freshwater perturbations globally. It also highlights the necessity of multidisciplinary approaches that marry chemical oceanography, ecology, and hydrology to unravel complex environmental puzzles.
Dr. Brian Lapointe, senior author, notes, “Our work reveals that acidification in estuaries is not a uniform phenomenon but varies intricately with nutrient loading, salinity, and local biological processes. Understanding these mechanisms allows targeted intervention, which is critical given the accelerating pace of coastal environmental change.” The study thus marks a crucial turning point, spotlighting the hidden chemistry compromising one of Florida’s premier natural treasures.
In conclusion, the Indian River Lagoon exemplifies how intricate chemical and ecological interactions govern estuarine health. The emergence of coastal acidification as a silent threat underscores the urgent need for comprehensive monitoring, informed management, and public awareness. As shellfish continue to shrink and seagrass beds retreat, the urgency for actionable solutions intensifies. This pioneering research not only advances scientific understanding but also serves as a clarion call to safeguard estuaries worldwide before these fragile ecosystems reach tipping points beyond recovery.
Subject of Research: Not applicable
Article Title: Coastal eutrophication and freshwater inputs drive acidification in the Indian River Lagoon, Florida
News Publication Date: 12-Jan-2026
Web References:
- Florida Atlantic University Harbor Branch Oceanographic Institute: www.fau.edu/hboi
- Indian River Lagoon Observatory Network of Environmental Sensors (IRLON): https://www.fau.edu/hboi/research/marine-ecosystem-conservation/irlo/irlon/
- Marine Pollution Bulletin article DOI: http://dx.doi.org/10.1016/j.marpolbul.2025.119175
References:
Brewton, R., Lapointe, B., Conkling, M., Kaiser, B.R., Davis, K.S., Jiang, M. (2026). Coastal eutrophication and freshwater inputs drive acidification in the Indian River Lagoon, Florida. Marine Pollution Bulletin. DOI: 10.1016/j.marpolbul.2025.119175
Image Credits: Credit: FAU Harbor Branch
Keywords
Estuaries, Acidity, Chemical properties, Salinity, Environmental chemistry, Carbon emissions, Pollution, Water pollution, Pollutants, Anthropogenic carbon dioxide, Ecology, Ecosystems, Aquatic ecosystems, Coastal ecosystems, Wastewater, Water quality, Shellfish, Aquatic animals
