Physicochemical water quality in coastal marine ecosystems: spatiotemporal variation between protected and disturbed areas

The monitoring of the continuous fluctuation of seawater environmental conditions plays a critical role in the management and conservation of marine and coastal ecosystems. Although previous studies in the Santa Marta region (Colombian Caribbean) have examined aspects of seawater quality, the spatiotemporal dynamics of key water quality parameters, impact gradients, and contaminant dispersion remain poorly characterized. This study presents the results of a 14-month monitoring program conducted from 2021 to 2024 at seven sampling stations: four in Santa Marta Bay and three within Tayrona National Natural Park (TNNP). These stations cover areas experiencing varying degrees of anthropogenic impact. The assessment of spatiotemporal dynamics of physicochemical seawater parameters revealed seasonal and anthropogenic influences on water quality. During the rainy periods, increased levels of turbidity, nutrients, pollutants, and oxygen demand were observed, particularly at stations impacted by wastewater discharges. Overall, these parameters exceeded the permissible limit frequency during the rainy periods, where 60% of the samples showed elevated levels of organic load. This revealed an eutrophication gradient extending from the most impacted stations to the sites located within the TNNP. Water quality index (Integrated Coastal Area Management; ICAM) assessments confirmed degraded conditions near sewage, river, and port discharge points, while TNNP stations exhibited acceptable environmental quality. These findings emphasize the protective role of marine protected areas as buffers against pollution, and highlight the need for periodic, long-term monitoring to elucidate links between water quality and ecosystem health, critical for informing conservation and management efforts in regions facing substantial anthropogenic pressures such as Santa Marta Bay and the TNNP.