5-11 IMPACTS TO SEDIMENT QUALITY OF RECEIVING ESTUARY SYSTEMS FROM SMALL DAM REMOVAL

Session: Nearshore and Estuarine Research: Dynamics and Future Resiliency in the Coastal Zone (Posters)

Presenting Author:

Authors:

Abstract:

Small legacy dams in coastal New England are increasingly targeted for removal to restore sediment continuity and aquatic connectivity; however, impounded sediments may serve as long-term reservoirs for contaminants that could be remobilized during or following removal. Characterizing the physical and chemical properties of these sediments is critical for evaluating potential downstream impacts in river–estuary systems.

This study focuses on sediment quality within the Patchogue River (Westbrook, CT), representing recently (2025) collected field and laboratory data, and evaluates these results in relation to sediments associated with the Spring Lot Brook Dam (Patchogue River) to assess potential implications of dam removal. Additional sediment datasets from the Branford River estuary and Wards Millpond Dam (Branford, CT) are used to provide comparative regional context. Sediment samples from the Patchogue River impoundment were analyzed for grain-size, organic content (loss-on-ignition), and trace metal concentrations, and results were integrated with geospatial analysis to assess spatial variability in sediment properties.

Preliminary results show pronounced heterogeneity in sediment texture and geochemistry within the Patchogue River estuary system. Zinc concentrations in Patchogue River sediments range from 18 to 158 mg/kg and show a positive association with finer grain sizes and higher organic content. Sediments from the Spring Lot Brook Dam exhibit overlapping zinc concentration ranges, approximately 11 to 175 mg/kg, providing a comparative framework for evaluating contaminant enrichment and potential impacts to the receiving estuary should the dam be removed.

The spatial co-occurrence of fine sediments, elevated organic matter, and trace metal concentrations suggests that sediment disturbance during dam removal may result in selective transport of contaminant-enriched material but that this sediment will transport into an estuary that already demonstrates similar contaminant compositions. Ongoing components of this research include suspended sediment concentration and advective sediment transport modeling to quantify sediment and contaminant fluxes under varying hydrologic conditions. This poster presents sediment quality data and spatial analyses that establish a geochemical baseline for assessing contaminant risks associated with small dam removal in coastal river systems.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.