Summary:
We propose to measure water chemistry and phytoplankton productivity along transects in the Breton Sound estuary, which receives Mississippi River water from the Caernarvon freshwater diversion, and potentially has been impacted by the Gulf oil spill. This study aims to answer the following question: Did the Macondo 252 Oil Spill result in large scale perturbation of aquatic primary production in the Gulf of Mexico, especially in the Breton Sound estuary?
The objectives of this study are to:
1. Continue an ongoing monthly water quality sampling in the Breton Sound estuary that has been carried out almost continuously since 1999
2. Analyze new and historical data to determine spatial and temporal patterns of nutrients, sediments, salinity and chlorophyll a in the Breton Sound estuary
3. Correlate factors influencing aquatic primary production, especially light and nutrient concentrations, with special reference to the stoichiometric ratios of inorganic nitrogen, phosphorus and silicate
4. Determine the impact of different oil concentrations on aquatic primary productivity in the Breton Sound estuary.
This work builds on an extensive series of studies summarized in Day et al. (2009), and is a continuation of a very similar study carried out previously in 2007 (www.lasegrant.org, J. Day, PI), and builds on an initial NGI project funded from August to December, 2010. Water quality transects will be carried out monthly from January-December 2011 to measure water chemistry and related hydrographic parameters. A flow-through system will be used to map suspended sediment, chlorophyll a, salinity, and temperature in the major bayous and water bodies of the estuary. Discrete water samples for nutrient and hydrocarbon analysis will be collected at 16 locations in the estuary, along with measurements of the underwater light attenuation coefficient (kd). We will measure phytoplankton production seasonally for several locations using the light, semi-shaded and dark bottle oxygen technique in a field incubator (Harding et al. 1982; Madden and Day 1992).
We will extrapolate the results using data from the flow-through system and the bottle experiment to map basin wide aquatic primary productivity. The impacts of petroleum hydrocarbons will be measured by adding environmentally relevant concentrations (10, 100, and 1000 ppm) to a subset of the light-dark bottles. The results of the study will be shared with managers of the Caernarvon diversion structure so that operation can be done in a way that minimizes water quality problems while still achieving coastal restoration objectives. The results will also be shared with scientists and managers dealing with impacts of the oil spill.