129-54 Temporal Migration of a Salinity Transition Zone Along a Coastal Salt-Marsh Channel, Carpinteria, California

Abstract:

Our research examines temporal changes in water quality across six fixed sampling sites in Santa Monica Creek within Carpinteria Salt Marsh, California. Water quality parameters, including temperature, dissolved oxygen, specific conductance, salinity, pH, oxidation-reduction potential, and turbidity, were measured in March 2025, January 2026, and May 2026 using a YSI ProDSS water meter. GIS and LiDAR-derived measurements of channel distance, width,  and confinement are used to evaluate whether channel morphology influences the location of  the salinity transition zone. Results show that salinity generally increased downstream during all three sampling events, but the location of the strongest transition shifted. Mean salinity across all sampling locations was 8.83 ppt in January, 21.64 ppt in March, and 26.94 ppt in May. The largest adjacent-site increase occurred between Sites 2 and 3 in March (13.50 ppt), Sites 4 and 4.5 in January (7.88 ppt), and Sites 1 and 2 in May (26.41 ppt). The May transition, between Sites 1 and 2, accounted for 90.9% of the total salinity change across the channel. Dissolved oxygen saturation generally decreased downstream and averaged 107.0% in January, 101.8% in March, and 150.4% in May. Mean turbidity ranged from 6.05 NTU in March to 28.53 NTU in May. These results suggest that the salinity transition zone migrates along the channel between sampling events. Combining water quality data with GIS and LiDAR measurements provides a hydrogeomorphic framework for understanding environmental variability in Carpinteria Salt Marsh and establishes a baseline for future micropaleontological analyses (e.g. foraminiferal test size, ostracod carapace size).

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