Streamflow and Nutrient Delivery to the Gulf of Mexico for October 2007 to June 2008 (Preliminary)


Preliminary estimates of monthly nutrient fluxes from the Mississippi and Atchafalaya Rivers to the Gulf of Mexico are provided in July each year for the previous nine months (October through June). These data are used by scientists to estimate the size of the hypoxic zone in the northern Gulf of Mexico, which is measured each summer in July. It is believed that the size of the hypoxic zone that develops in the northern Gulf of Mexico each summer is affected by, among other things, delivery of streamflow and nutrients by the Mississippi-Atchafalaya River Basin.
• Streamflow and Nutrient Flux to the Gulf of Mexico October 2007 to June 2008 (Excel© Spreadsheet)
• Graphics of Spring (April, May, June) Nutrient Fluxes Through 2008
Although streamflow and nutrient flux information is usually calculated on a water year (October to September) basis, this information is provided in preliminary form in July so that the spring nutrient fluxes can be utilized in a timely manner for modeling of the areal extent of the hypoxic zone in the Gulf of Mexico. Note that the provisional data have been checked for errors, but some minor changes can be expected for stream-discharge data as rating curves for converting streamwater stage to stream discharge are finalized only after the completion of that water year. Final estimates, using the full 5-year calibration dataset, are provided after the water year is completed and streamflow and water-quality data are finalized.
The monitoring network, dataset preparation steps, and nutrient flux estimation methods used are the same as used by Aulenbach and others (2007). Links to specific information on data and methodology in the report are available here:
• Monitoring Network Used to Estimate Total Delivery of Flow and Nutrients to the Gulf
• Sources and Preparation of Data Used for Nutrient Flux Estimation
• Methods Used to Estimate Nutrient Fluxes
Note that flux estimates on a monthly time-step can be quite inaccurate and should be used with caution. They are provided with the intent to allow the user to sum up nutrient fluxes on either a seasonal basis or an annual basis other than water year.
Reference
Aulenbach, B.T., Buxton, H.T., Battaglin, W.T., and Coupe R.H., 2006, Streamflow and nutrient fluxes of the Mississippi-Atchafalaya River Basin and subbasins for the period of record through 2005: U.S. Geological Survey Open-File Report 2007-1080
http://toxics.usgs.gov/hypoxia/mississippi/oct_jun/index.html