Abstract
Rivers in tropical and subtropical regions often exhibit dark brown appearance due to a high concentration of chromophoric dissolved organic matter (CDOM). The composition and concentration of CDOM significantly impact riverine processes, including light penetration and primary production, which are crucial for the ecological health of the river and its estuary. This study aimed to characterize the seasonal DOM and hydrogen peroxide in the Caloosahatchee River, Florida, using a multivariate approach to assess environmental and biological influences. Our results suggest that from August to November, the river exhibits high levels of humic content, increased water color, and larger molecular sizes (humic-rich phase). Conversely, samples collected from February 2021 to July 2021 and December 2021 to January 2022 suggest recently produced DOM with more protein-like components and reduced water color (non humic-rich phase). These DOM patterns did not align with seasonal precipitation patterns but correlated closely with water discharge patterns from manmade structures. Hydrogen peroxide (H2O2) is a long-lived very oxidative compound which is strongly link the DOM. Remarkably, a significant strong correlation between H2O2 and chlorophyll a (r = 0.54), suggests that biological activity influences H2O2 dynamics. Furthermore, we found that three humic-like components (peaks A, C, and M) were mainly derived from external inputs rather than internal production. These results highlight the importance of integrating environmental and biological factors to comprehensively understand DOM and H2O2 dynamics in subtropical rivers, providing a foundation for improved water quality management and ecosystem health.
