Citation:

Mudahy, A., J. Hagy, C. Sullivan, AND J. Ammerman. Quantifying and forecasting the seasonal and spatial extent of hypoxia in Long Island Sound. Long Island Sound Research Conference 2024, Port Jefferson, NY, May 15, 2024.

Impact/Purpose:

This presentation will share progress with the Long Island Sound science and management community on analysis of existing Long Island Sound data to characterize and predict the extent and severity of hypoxia in Long Island Sound, ultimately leading to development of a hypoxia forecast tool for Long Island Sound.  By sharing progress, we expect to build interest and support among the stakeholder community, which at this point is principally people who are well involved and the science and management community in the region.  The presentation will be made to the 2024 Long Island Sound Research Conference.

Description:

Nitrogen management in Long Island Sound (LIS) has reduced N loading and the extent of hypoxia over the last 2 decades. To support communication around successful remediation of hypoxia and the remaining challenges of N management, we are analyzing 30 years of water quality data to better quantify temporal and spatial variability and long-term trends in DO, evaluate trends in the extent of low DO, and develop models to forecast hypoxia for upcoming summers. We developed an effective time-space model of DO in LIS using Generalized Additive Models (GAMs), however, the model likely underestimates the spatial extent of low DO. Conversely, spatial interpolation bottom water DO (e.g., using kriging) can overestimate hypoxia extent by underpredicting bottom water DO in shallow water. We evaluated DO profiles to estimate the depth at which DO attains a threshold level, modeled the estimates in time and space using GAMs, and estimated the hypoxic area and volume by intersecting the response surface with the basin bathymetry. The estimated area with DO<3 mg/L decreased rapidly from 286 km2 in 1995 to a local minimum in 1999, increased again, then decreased strongly after 2010. The average extent of hypoxia in 2014-2020 (40 km2) represents an 83% decrease from the average during 1995-2009 (233 km2), while the average duration of hypoxia decreased from 56 days to 47 days. Long-term responses of hypoxia extent to freshwater inputs, N loading, water temperature, and stratification are evaluated, and the prospects for forecasting hypoxia are evaluated.

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