Urban infrastructure and seasonal hydrology alter dissolved organic matter along coastal ecosystem gradients

Dissolved organic carbon (DOC) concentrations and dissolved organic matter (DOM) composition are shaped by multiple factors in urban waters. In coastal cities, interactions among tidal flooding, stormwater infrastructure, and freshwater inputs can create variable DOM pools, but the timing and seasonal dynamics of these hydrological and biogeochemical interactions remain unclear. We investigated how subtropical wet and dry seasonal variability and marine tidal flooding (high tide events) affect DOC concentrations and DOM composition across n = 100 canal sites in Miami (Florida, USA), and assessed how DOM varied with impervious ground, stormwater infrastructure, and septic density. Sites were sampled in wet and dry seasons during five synoptic events in 2021 and 2022 and analyzed for DOC concentrations and DOM characteristics using absorbance and fluorescence spectroscopy. DOC concentrations and DOM composition remained stable between the wet and dry seasons, which may be related to consistent hydrological conditions maintained through management strategies that reduce flooding. In contrast, marine tidal flooding events led to distinct shifts in DOM composition, characterized by increases in protein-like, tryptophan-like, and fresh lignin-like DOM and decreases in microbial- and terrestrial humic-like DOM. Marine intrusions can promote the transformation toward more labile DOM, overriding typical seasonal dynamics. Higher stormwater influence was associated with elevated dissolved oxygen and a shift in DOM composition toward fresher, microbial-like material. Results highlight the importance of considering hydrological water management and episodic marine intrusions when evaluating DOM dynamics in urban coastal ecosystems.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Liz Ortiz Munoz, Florida International University (lortizmu@fiu.edu)

Authors:

John Kominoski, Florida International University  (jkominos@fiu.edu)

Rebecca Hale, Smithsonian Institution  (haler@si.edu)

Shuo Chen, University of Florida  (schen83@crimson.ua.edu)

Daniel Gann, Florida International University  (gannd@fiu.edu)

Valentina Caccia, Miami Dade County DERM  (valentina.caccia@miamidade.gov)

Omar Abdelrahman, Miami Dade County DERM  (omar.abdelrahman@miamidade.gov)