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189-20 Effect of Improved Water Quality on Molluscan Communities in Long Island Sound

Session: Paleontology, Paleoecology/Taphonomy (Posters)

Poster Booth No.: 105

Presenting Author:

Gregory Dietl

Authors:

Dietl, Gregory P.¹, Pruden, Matthew J.², Handley, John C.³

(1) Paleontological Research Institution, Ithaca, NY, USA; Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA, (2) Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA, (3) Paleontological Research Institution, Ithaca, NY, USA; Simon Business School, University of Rochester, Rochester, NY, USA,

Abstract:

Excess nitrogen input has contributed to recurring summer hypoxia in Long Island Sound (LIS), with long-term impacts on the structure and condition of benthic macroinvertebrate communities over time. In 2001, the Connecticut Department of Energy and Environmental Protection and New York State Department of Environmental Conservation adopted a Total Maximum Daily Load (TMDL) management strategy to reduce nitrogen pollution and hypoxia in the Sound. Reduced hypoxia was predicted to result in ecological benefits, including overall improvement of benthic habitat conditions. Although TMDL targets were met by 2016, no consistent benthic monitoring data exist to assess management success. Time-averaged molluscan death assemblages (DAs) that readily preserve and accumulate within the sediment provide a unique opportunity to reconstruct past habitat condition. Here we use the remains of dead mollusc shells retained in 10 benthic grab samples collected from the Sound as part of the Environmental Protection Agency-led 2020 National Coastal Conditions Assessment (NCCA) to evaluate the response of benthic communities to the TMDL intervention. We hypothesized that habitat condition—measured using the AZTI Marine Biotic Index (AMBI)—improved over time as water quality (indexed as the frequency of summer hypoxic events at each sampling location) improved. Bomb-pulse radiocarbon dating results confirm that the molluscan DAs reflect pre-TMDL conditions (with an average median age of 1985 CE). Post-TMDL reductions in hypoxia improved benthic conditions in eastern LIS (indexed by lower AMBI scores), but some western Narrows sites showed no improvement, likely due to poor sediment quality conditions. Our results show that molluscan DAs collected with standard benthic sampling protocols can offer a cost-effective means of retroactively acquiring data to assess restoration success when long-term monitoring data are lacking.

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

doi: 10.1130/abs/2025AM-9181

Effect of Improved Water Quality on Molluscan Communities in Long Island Sound

Description

Session Format: Poster

Presentation Date: 10/21/2025

Presentation Room: HBGCC, Hall 1

Poster Booth No.: 105

Author Availability: 9:00–11:00 a.m.

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