Seasonal and Spatial Variability of Absorption Properties in Cartagena Bay’s Complex Waters

Abstract

Characterizing inherent optical properties (IOPs) of water constituents is crucial for remote sensing applications. Remote sensing in Cartagena Bay is particularly challenging due to significant variations in constituent concentrations caused by the seasonal and annual variability of discharges from the Canal del Dique. This article presents the variability in absorption coefficients of phytoplankton, chromophoric dissolved organic matter (aCDOM), and non-algal particles (aNAP) in Cartagena Bay. Absorption coefficients were measured in the laboratory across multiple monitoring campaigns, with seasonal analyses conducted to establish relationships between absorption properties and biogeochemical parameters such as chlorophyll-a, salinity, and turbidity. Results indicate that at 440 nm, aCDOM and aNAP primarily dominate absorption during the rainy season, while aNAP dominates during the dry season. This variation is influenced by inflows from the Canal del Dique. Lower CDOM absorption in 440 nm (aCDOM440), and higher CDOM absorption slope (SCDOM275–295) and higher salinity values were observed during the dry season, which is consistent with the reduced fluvial influx. Spatial variability shows that higher CDOM values prevail in the river plume area during both seasons, with particularly higher values in the rainy season. Median values of aNAP were similar in both seasons, with a strong relationship found between all aNAP data and turbidity (rp = 0.785). Compared to other estuaries, Cartagena Bay exhibits optical characteristics typical of a coastal water body subjected to river discharges, including the elevated turbidity and the high dissolved organic matter influenced by significant inflow from the Canal del Dique. These features highlight the bay’s dynamic interactions with terrestrial inputs. This study provides invaluable information on the optical characteristics of Cartagena Bay, which is crucial for improving the accuracy and effectiveness of remote sensing models for optically active parameters such as turbidity, suspended solids, CDOM, and chlorophyll-a.