High-tide transects from Mount Hope Bay, the Kickemuit, Lee, Cole, and Taunton Rivers were conducted to assess dissolved metals, organic carbon, and phosphate ions in the water column. Replicate water samples were collected at the surface, mid-depth, and near-bottom with Niskin bottles, then either filtered or unfiltered, evaporated to dryness, and analyzed. Metals were directly measured by XRF and resuspension in DI (pH 2) for ICP-OES, while organic carbon and bicarbonate were quantified by loss-on-ignition (500°C, 1000°C). Cluster analysis identified the Lee River as the greatest source of suspended organic matter into the bay. Phosphate distributions reflected salinity and depth profiles. Surface waters (19.5–26.5 psu) showed low phosphate concentrations (0.01–0.28 mg/L) from runoff. Mid-depth waters in Mount Hope Bay and the Taunton River ranged from 0.6–1.0 mg/L, suggesting sediment resuspension or trapping. Bottom waters had consistently low phosphate concentrations and the highest salinity, consistent with Ca₃(PO₄)₂ precipitation in alkaline, calcium-rich conditions. Similarly, the Cole River showed phosphate concentrations declining with salinity, the Lee River remained low throughout (20.40 psu), and Kickemuit peaked at mid-depths (23.09 psu), from salt wedge mixing. Phosphate concentration and salinity were found to have a ratio of 0.008 mg/L:1 psu, demonstrating that increased psu values lead to decreased phosphate concentrations. Phosphate-to-iron (3:1) and phosphate-to-manganese (37,000:1) ratios indicated iron was well mixed and conserved, while manganese was negligible in the water column. XRF analyses showed constant surface concentrations of Cu, Zn, and PO^3-₄ in dried solids. Phosphate was determined to have higher concentrations (2000-3000 ppm) than other metals, notably at mid-to bottom concentrations (330-400, 15-20 ppm). Comparisons between ICP and XRF data suggested that some phosphate wasn’t detected by XRF due to being matrix-bound in the residue.

Donovan Reilly

Roger Williams University

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