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USGS Open-File Report 2007-1080 - Streamflow and Nutrient Fluxes of the Mississippi-Atchafalaya River Basin and Subbasins for the Period of Record Through 2005

Background and Introduction

The U.S. Geological Suevey (USGS) has monitored streamflow and water quality systematically in the Mississippi-Atchafalaya River Basin (MARB) for more than five decades. Recently, management concerns have focused on delivery of nutrients and streamflow to the Gulf of Mexico because of their influence on the formation and extent of a zone of hypoxic waters in the northern Gulf (Rabalais and others, 1999, and CENR, 2000). Nutrient flux and yield estimates (see text box for explanation of flux and yield) for subbasins also are of great interest because of the effects of downstream accumulation and delivery to receiving waters and because they provide a means to identify the primary source areas and the relative contributions of both streamflow and nutrients from different parts of the Basin. Many studies have previously estimated nutrient fluxes for larger subbasins within the MARB. For example, Goolsby and others (1999) presented nutrient fluxes for six water-quality constituents for the period of record through 1996 for 9 major and 42 smaller subbasins of the MARB. Kelly and others (2001) published fluxes for the National Stream Quality Accounting Network (NASQAN) program stations for the period 1996 through 2000 for a wide variety of water-quality constituents including nutrients at 20 subbasins within the MARB.

This report provides streamflow and estimates of nutrient delivery (flux) to the Gulf of Mexico from both the Atchafalaya River and the main stem of the Mississippi River. This report provides streamflow and flux estimates for nine major subbasins of the Mississippi River. This report also provides streamflow and flux estimates for 21 selected subbasins of various sizes, hydrology, land use, and geographic location within the Basin. The information is provided at each station for the period for which sufficient water-quality data are available to make statistically based flux estimates. Flux estimates are reported on a water year and monthly basis. The USGS defines a water year as October 1st of the previous year to September 30th of the designated year; for example, water year 2005 is from October 1st, 2004 to September 30th, 2005. 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 fluxes on either a seasonal basis or an annual basis other than water year. Streamflow and nutrient fluxes for five major subbasins comprising the Mississippi-Atchafalaya River Basin were then calculated from estimates at monitored stations.

Flux and yield estimates are provided for six water-quality constituents: dissolved nitrite plus nitrate (NO₂ + NO₃), total organic nitrogen plus ammonia nitrogen (total Kjeldahl nitrogen, TKN), dissolved ammonia (NH₃), total phosphorous (TP), dissolved orthophosphate (OP), and dissolved silica (SiO₂).

References

Committee on Environment and Natural Resources (CENR), 2000, Integrated Assessment of Hypoxia in the Northern Gulf of Mexico: National Science and Technology Council Committee on Environment and Natural Resources, Washington, D.C., 58 p.

Goolsby, D.A., Battaglin, W.A., Lawrence, G.B., Artz, R.S., Aulenbach, B.T., Hooper, R.P., Keeney, D.R., and Stensland, G.J., 1999, Flux and sources of nutrients in the Mississippi-Atchafalaya River Basin—Topic 3, Report for the integrated assessment on hypoxia in the Gulf of Mexico: National Oceanic and Atmospheric Administration NOAA Coastal Ocean Program Decision Analysis Series No. 17, 129 p.

Kelly, V.J., Hooper, R.P., Aulenbach, B.T., and Janet, Mary, 2001, Concentrations and annual fluxes for selected water-quality constituents from the USGS National Stream Quality Accounting Network (NASQAN), 1996-2000: U.S. Geological Survey Water-Resources Investigations Report 01-4255 (On-Line Only).

Rabalais, N.N., Turner, R.E., Justić, Dubravko, Dortch, Quay, and Wiseman, W.J., Jr., 1999, Characterization of Hypoxia—Topic 1, Report for the Integrated Assessment on Hypoxia in the Gulf of Mexico: Silver Spring, MD NOAA Coastal Ocean Program, NOAA Coastal Ocean Program Decision Analysis Series No. 15. 167 pp.

Report Site Map > Background and Introduction