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Diel-Cycling Hypoxia in Northern Gulf of Mexico Estuaries: Impacts and Protection of Aquatic Life
Citation:
Jarvis, B., Jim Hagy, J. Lehrter, M. Murrell, AND M. Beck. Diel-Cycling Hypoxia in Northern Gulf of Mexico Estuaries: Impacts and Protection of Aquatic Life. Presented at Mattie Kelly Environmental Symposium, Niceville, FL, October 10, 2014.
Impact/Purpose:
This presentation will be given to regional water quality managers, and will serve to inform them about GED research on a prevalent water quality issue.
Description:
Eutrophication of coastal ecosystems is a longstanding environmental concern, exacerbated by population growth and associated nutrient pollution, and ultimately resulting in increased incidence of hypoxia. Shallow and highly productive estuaries and embayments are particularly susceptible to diel-cycling hypoxia, associated with day-night cycles of production and respiration, which can cause extreme excursions in dissolved oxygen (DO) concentrations from anoxia to super-saturation within a single day. Diel oxygen dynamics in these systems are complex, and may be influenced by wind forcing, vertical and horizontal mixing, variation in freshwater inflow, cloud cover and temperature. This study examined DO conditions in four northern Gulf of Mexico Estuaries (Weeks Bay, AL; Wolf Bay, AL; Fowl River, AL; and St. Louis Bay, MS). Dissolved oxygen varied strongly on a diel basis in all four systems, with periods of sustained low oxygen (>24 h) observed in both Weeks Bay and Wolf Bay. The duration and persistence of diel-hypoxia further varied in response to changing salinity regimes and regional weather. Using a 10-year continuous DO record from the Weeks Bay National Estuarine Research Reserve, we applied empirical relationships and logical scaling arguments to predict how reducing nutrient loads may lessen the frequency, severity and duration of hypoxic events. We also utilized species sensitivity test data to evaluate the impacts and potential benefits to aquatic life under existing and reduced nutrient scenarios. Complex DO dynamics and multifaceted trophic interactions in these systems underscore the need to directly monitor hypoxia induced impacts to aquatic life.