Estuaries and Coasts

, Volume 32, Issue 4, pp 621–641

Narragansett Bay Hypoxic Event Characteristics Based on Fixed-Site Monitoring Network Time Series: Intermittency, Geographic Distribution, Spatial Synchronicity, and Interannual Variability

  • Daniel L. Codiga
  • Heather E. Stoffel
  • Christopher F. Deacutis
  • Susan Kiernan
  • Candace A. Oviatt
Article

DOI: 10.1007/s12237-009-9165-9

Cite this article as:
Codiga, D.L., Stoffel, H.E., Deacutis, C.F. et al. Estuaries and Coasts (2009) 32: 621. doi:10.1007/s12237-009-9165-9

Abstract

Low dissolved oxygen events were characterized in Narragansett Bay (NB), a moderate-size (370 km2) temperate estuary with a complex passage/embayment geometry, using time series from 2001 to 2006 at nine fixed-site monitoring stations. Metrics for event intensity and severity were the event-mean deficit relative to a threshold (mg O2 l−1) and the deficit-duration (mg O2 l−1 day; product of deficit and duration [day]). Hypoxia (threshold 2.9 mg O2 l−1) typically occurred intermittently from late June through August at most stations, as multiple (two to five per season) events each 2 to 7 days long with deficit-duration 2 to 5 mg O2 l−1 day. Conditions were more severe to the north and west, a pattern attributed to a north–south nutrient/productivity gradient and east–west structure of residual circulation. Spatial patterns for suboxic and severely hypoxic events (thresholds 4.8 and 1.4 mg O2 l−1) were similar. The view that different processes govern event variability in different regions, each influenced by local hydrodynamics, is supported by both weak spatial synchronicity (quantified using overlap of event times at different sites) and multiple linear regressions of biological and physical parameters against event severity. Interannual changes were prominent and season-cumulative hypoxia severity correlated with June-mean river runoff and June-mean stratification. Benthic ecological implications for areas experiencing events include: NB hypoxia classifies as periodic/episodic on a near-annual basis; highest direct mortality risk is to sensitive and moderately sensitive sessile species in the northern West Passage and western Greenwich Bay, with some risk to Upper Bay; direct risk to mobile species may be ameliorated by weak spatial synchronicity; and indirect impacts, including reduced growth rates and shifts in predator–prey balances, are very likely throughout the sampled area due to observed suboxic and hypoxic conditions.

Keywords

HypoxiaSuboxicOxygen deficiencyTime seriesNarragansett BayWater quality

Supplementary material

12237_2009_9165_MOESM1_ESM.pdf (2.1 mb)
Electronic supplementary material(PDF 2128 kb)

Copyright information

© Coastal and Estuarine Research Federation 2009

Authors and Affiliations

  • Daniel L. Codiga
    • 1
  • Heather E. Stoffel
    • 1
  • Christopher F. Deacutis
    • 2
  • Susan Kiernan
    • 3
  • Candace A. Oviatt
    • 1
  1. 1.Graduate School of OceanographyUniversity of Rhode IslandNarragansettUSA
  2. 2.Narragansett Bay National Estuary ProgramUniversity of Rhode IslandNarragansettUSA
  3. 3.Department of Environmental ManagementOffice of Water ResourcesProvidenceUSA