The Need for Sustainable, Integrative Long-Term Monitoring of the Gulf of Mexico Hypoxic Zone Summit on Long-Term Monitoring of the Gulf of Mexico Hypoxic Zone January 30-31, 2007 Alan Lewitus

Boesch & Rabalais begin monitoring (1985) NOAA’s Coastal Ocean Program study documented issue (NECOP ; supplemental research ) – evidence for increasing hypoxic zone over time History of Monitoring

Areal Extent of Gulf of Mexico Hypoxic Zone: Area (km ) 2 Rabalais et al.

Hypoxia has increased since the 1950’s River N load is main driver of hypoxia NO 3 load is > 3X that of 1950’s: 90% of nitrate inputs from non-point sources; 74% of nitrate load is from agricultural non-point sources. CENR Conclusions

Record = 22,000 km 2 in 2002 Since mid 1990s, the 5-yr running average size of hypoxic zone has hovered around 15,000 km 2 Rabalais et al. Extension of Monitoring

Justić et al. (2002) Areal Extent of Hypoxic Zone – Coastal Goal Metric Areal extent of the hypoxic zone at the peak time of hypoxia (July) has been well characterized and is a good indicator of the intensity of hypoxia in any given year

Model: Hypoxia area (km 2 ) = x May NOx flux x Year x 105 (R 2 = 0.82) Turner et al 2006 Statistical models suggest that spring/early Summer nutrient fluxes (primarily nitrate) are good predictors of mid summer size of hypoxia Areal Extent of Hypoxic Zone – Coastal Goal Metric

Justić et al. (2002) Hypoxic Zone Monitoring

Need for Extension of Monitoring Action Plan (2001): “greatly expand the long-term monitoring program for the hypoxic zone, including greater temporal and spatial data collection, measurements of macro-nutrient and micronutrient concentrations, and hypoxia…” Monitoring, Modeling, and Research Workgroup Report (MMR, 2004): “(monitoring) efforts need to be increased in frequency, at a minimum monthly from May through September. To develop a more complete understanding of ecosystem dynamics, selected sites should be monitored year-round. The spatial boundaries of some of these existing monitoring efforts should be expanded to collect data for defining boundary conditions in modeling efforts."

Causes of Hypoxia: Expansion of spatial boundaries Greater temporal resolution Science Needs DiMarco et al. (2006); image from N. Walker

Causes of Hypoxia: Benthic processes Hypoxic volume Science Needs

Need to trace effects of habitat loss through the food web to understand ecosystem-level effects Hypoxia effects in the Gulf are: Indirect Spatially-mediated responses to the environment Occur across multiple trophic levels Impacts of Hypoxia:

Moderate Hypoxia Severe Hypoxia ( 1983, 1987, 1988, 2000) ( 1993, 1995, 1996, 1997) Hypoxia Effects on Atlantic Croaker Distribution ~33-50% habitat loss from K. Craig

Science Needs Support models used to: quantify the relationship between nutrient loading and hypoxia understand the causes of hypoxia understand the impacts of hypoxia Hetland – ROMS model Justic et al. (1996) N Load Reduction Area (km) 2 Scavia et al 2003, % Nitrogen Load Reduction % Increase in Oxygen Bierman et al 1994, 1999

Science Needs