278-9 Non-tidal Exchange in Tidal Creeks Controls Longitudinal Variability in Water and Dissolved Inorganic Carbon in Tropical Mangrove Estuaries

Session: Understanding Temporal Dynamics in Hydrogeochemistry and Sedimentary Processes in Estuarine Environments

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Abstract:

We investigated the physical, chemical, and isotopic properties of an 11-kilometer-long tidal creek in a tropical mangrove estuary. Our goal was to assess how variability in sampling relative to the tide reflects or does not reflect similar hydrobiogeochemical processes, which is important for understanding how semidiurnal tide cycles and anthropogenic inputs influence the production and distribution of solutes and carbon cycling. Spatial sampling was conducted during the summer of 2022 and 2023 at both low and high tides. Water samples were analyzed for silica, nitrate, dissolved inorganic carbon (DIC) components (alkalinity, total DIC, and partial pressure of CO₂ (pCO₂)), along with stable isotopes of water (δ¹⁸O and δD) and carbon isotopes of DIC (δ¹³C_DIC). We found that (1) spatial trends in the data show consistency from the open estuary to about 3 km into the tidal creek, with either a steady increase or decrease in water properties during high and low tides, remaining nearly constant in the middle segment of the tidal creek up to 8 km. Data from 8-11 km showed significant variability, including anomalously high nitrate and DIC parameters. (2) A two-end-member seawater-freshwater mixing model reveals multiple sources of water input into the creek during all three surveys. (3) Miller-Tans and Keeling plot analyses identified three major DIC sources in the tidal creek, each showing similar hydrobiogeochemical processes. We suggest that the significant variability in water properties along the tidal creek is driven by a combination of waste discharge, river water input, submarine groundwater discharge, evaporative enrichment, and the extent of tidal transport and mixing of residual water within the creek. Our results demonstrate that tidal creeks in tropical mangrove estuaries experience longitudinal variations in water and DIC exchange driven by non-tidal exchange of water with the open estuary. The findings provide important insights for understanding estuarine carbon and solute budgets and for managing tidal creeks and estuarine ecosystems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9682

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