USGS Open-File Report 2008-1163

National Water-Quality Assessment Program

Data to Support Statistical Modeling of Instream Nutrient Load Based on Watershed Attributes, Southeastern United States, 2002

By Anne B. Hoos, Silvia Terziotti, Gerard McMahon, Katerina Savvas, Kirsten C. Tighe, and Ruth Alkons-Wolinsky

U.S. Geological Survey Open-File Report 2008-1163, 50 pages (Published online, July 2008; data revised August 2009)

This report is available online in PDF format: OFR 2008-1163 (Opens the PDF file in a new window. ) (72 MB)
Because of the large PDF file size, you will need to download the PDF file (PC: right-click the link; Macintosh: option-click).

The report also is available in parts:
Part 1 (1.3 MB) | Part 2 (13.7 MB) | Part 3 (17.6 MB) | Part 4 (8.9 MB) | Part 5 (11.9 MB) | Part 6 | (9 MB) Part 7 (10.7 MB)

The PDF file contains links to data files. These files can be downloaded from the Data directory. (An 18-KB PDF readme file gives a description of each data file.) Alternately, the Data directory is compressed for downloading as Data.zip (29.2 MB). The Data directory needs to reside at the same level on disk as the PDF file for the links within the PDF file to work.

Cover thumbnailThis report presents and describes the digital datasets that characterize nutrient source inputs, environmental characteristics, and instream nutrient loads for the purpose of calibrating and applying a nutrient water-quality model for the southeastern United States for 2002. The model area includes all of the river basins draining to the south Atlantic and the eastern Gulf of Mexico, as well as the Tennessee River basin (referred to collectively as the SAGT area). The water-quality model SPARROW (SPAtially-Referenced Regression On Watershed attributes), developed by the U.S. Geological Survey, uses a regression equation to describe the relation between watershed attributes (predictors) and measured instream loads (response). Watershed attributes that are considered to describe nutrient input conditions and are tested in the SPARROW model for the SAGT area as source variables include atmospheric deposition, fertilizer application to farmland, manure from livestock production, permitted wastewater discharge, and land cover. Watershed and channel attributes that are considered to affect rates of nutrient transport from land to water and are tested in the SAGT SPARROW model as nutrient-transport variables include characteristics of soil, landform, climate, reach time of travel, and reservoir hydraulic loading. Datasets with estimates of each of these attributes for each individual reach or catchment in the reach-catchment network are presented in this report, along with descriptions of methods used to produce them.

Measurements of nutrient water quality at stream monitoring sites from a combination of monitoring programs were used to develop observations of the response variable—mean annual nitrogen or phosphorus load—in the SPARROW regression equation. Instream load of nitrogen and phosphorus was estimated using bias-corrected log-linear regression models using the program Fluxmaster, which provides temporally detrended estimates of long-term mean load well-suited for spatial comparisons. The detrended, or normalized, estimates of load are useful for regional-scale assessments but should be used with caution for local-scale interpretations, for which use of loads estimated for actual time periods and employing more detailed regression analysis is suggested. The mean value of the nitrogen yield estimates, normalized to 2002, for 637 stations in the SAGT area is 4.7 kilograms per hectare; the mean value of nitrogen flow-weighted mean concentration is 1.2 milligrams per liter. The mean value of the phosphorus yield estimates, normalized to 2002, for the 747 stations in the SAGT area is 0.66 kilogram per hectare; the mean value of phosphorus flow-weighted mean concentration is 0.17 milligram per liter.

Nutrient conditions measured in streams affected by substantial influx or outflux of water and nutrient mass across surface-water basin divides do not reflect nutrient source and transport conditions in the topographic watershed; therefore, inclusion of such streams in the SPARROW modeling approach is considered inappropriate. River basins identified with this concern include south Florida (where surface-water flow paths have been extensively altered) and the Oklawaha, Crystal, Lower Sante Fe, Lower Suwanee, St. Marks, and Chipola River basins in central and northern Florida (where flow exchange with the underlying regional aquifer may represent substantial nitrogen influx to and outflux from the surface-water basins).

CONTENTS

Foreword (Part 1)

Abstract

Introduction

Purpose and Scope

Acknowledgments

Hydrologic Network of Reaches and Associated Catchments (Part 2)

Watershed Attributes

Nutrient-Source Attributes (Part 3 and Part 4)

Nutrient-Transport Attributes (Part 5)

Accumulation of Catchment-Level Estimates of Watershed Attributes to Estimates for the Total Upstream Watershed (Part 6)

Reach Attributes (Part 7)

Mean Annual Nitrogen and Phosphorus Load at Stream Monitoring Sites

Selection of Monitoring Sites

Review and Revision of Nutrient Concentration Results

Estimation of Nutrient Load Representing Long-Term Mean for 1975–2004, Normalized to 2002

Error Associated with Estimating Mean Nitrogen and Phosphorus Load from Monitoring Data

Characteristics of Monitored Mean Annual Nitrogen and Phosphorus Load and Streamflow

Summary

References Cited

Data Files

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Suggested citation: Hoos, A.B., Terziotti, Silvia, McMahon, Gerard, Savvas, Katerina, Tighe, K.C., and Alkons-Wolinsky, Ruth, 2008, Data to support statistical modeling of instream nutrient load based on watershed attributes, southeastern United States, 2002: U.S. Geological Survey Open-File Report 2008–1163, 50 p.

For more information, please contact Anne B. Hoos.

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