Distribution of biochemical components in sedimentary organic matter of a Coastal Wetland: Anthropogenic and detrital influences

Coastal wetlands, particularly tidal flats, play a crucial role in carbon sequestration and nutrient cycling in temperate environments. This study investigates the biochemical composition of sedimentary organic matter (SOM) in the tidal flats of Puerto Rosales (Bahía Blanca Estuary, Argentina), emphasizing the dual influences of natural processes and anthropogenic activities. Sampling was conducted seasonally (2014–2015) at two sites: ST1, an intertidal zone affected by untreated sewage discharge, and ST2, a supratidal zone dominated by microbial mats. Surface (0–5 mm) and subsurface (5–10 mm) sediment layers were analyzed to assess early diagenetic processes, SOM component and trophic status. Results indicated that the organic carbon (OC) in sediments was predominantly non-biogenic, with proteins as the major component of the labile fraction, influenced by seasonal phytoplankton blooms and urban discharges. While the tidal flat exhibited meso-oligotrophic to eutrophic conditions, refractory material dominated over labile fractions (proteins and carbohydrates). Additionally, distinct spatial and seasonal variations in SOM quality and composition, linked to redox conditions and organic detrital quality were observed.These findings underscore the ecological importance of Puerto Rosales tidal flats as dynamic systems for carbon storage and nutrient recycling. They highlight the need for sustainable management strategies to mitigate anthropogenic pressures and preserve the critical ecosystem functions of these coastal wetlands.