Georgia Water Science Center

USGS Scientific Investigations Report 2008-5046

Algal and Invertebrate Community Composition along Agricultural Gradients: A Comparative Study from Two Regions of the Eastern United States

This report is available online in pdf format (2 Mb): USGS SIR 2008-5046

Daniel L. Calhoun, M. Brian Gregory, and Holly S. Weyers

U.S. Geological Survey Scientific Investigations Report 2008-5046, 33 pages (Published May 2008)

ABSTRACT

Benthic algal and invertebrate communities in two Coastal Plain regions of the Eastern United States—the Delmarva Peninsula (27 sites) and Georgia Upper Coastal Plain (29 sites)—were assessed to determine if aspects of agricultural land use and nutrient conditions (dissolved and whole-water nitrogen and phosphorus) could be linked to biological community compositions. Extensive effort was made to compile land-use data describing the basin and riparian conditions at multiple scales to determine if scale played a role in these relations. Large differences in nutrient condition were found between the two study areas, wherein on average, the Delmarva sites had three times the total phosphorus and total nitrogen as did the sites in the Georgia Upper Coastal Plain. A statistical approach was undertaken that included multivariate correlations between Bray-Curtis similarity matrices of the biological communities and Euclidean similarity matrices of instream nutrients and land-use categories. Invertebrate assemblage composition was most associated with land use near the sampled reach, and algal diatom assemblage composition was most associated with land use farther from the streams and into the watersheds. Link tree analyses were conducted to isolate portions of nonmetric multidimensional scaling ordinations of community compositions that could be explained by break points in abiotic datasets. Invertebrate communities were better defined by factors such as agricultural land use near streams and geographic position. Algal communities were better defined by agricultural land use at the basin scale and instream nutrient chemistry. Algal autecological indices were more correlated with gradients of nutrient condition than were typically employed invertebrate metrics and may hold more promise in indicating nutrient impairment in these regions. Nutrient conditions in the respective study areas are compared to draft nutrient criteria established by the U.S. Environmental Protection Agency. Substantial reductions in some nutrients would be required to meet proposed reference conditions on the Delmarva Peninsula.


CONTENTS

Abstract

Introduction

Purpose and Scope

Study Areas

Acknowledgments

Site Selections

Data Collection and Processing

Habitat

Water Chemistry

Benthic Algae

Invertebrates

Basin and Riparian Land-Use Analysis

Statistical Analyses

Stream Habitat, Nutrients, and Community Composition in Agricultural Streams

Habitat

Nutrients

Nutrient Loadings

Invertebrate and Algal Communities

Linking Environmental Variables to Biological Communities

Summary and Conclusions

References

Appendix A. Variables determined by LINKTREE Procedures, Algal and Invertebrate Indices, and Abiotic Variables for the Delmarva Peninsula Study as Illustrated in Figures 3 and 5

Appendix B. Variables determined by LINKTREE Procedures, Algal and Invertebrate Indices, and Abiotic Variables for the Georgia Upper Coastal Plain Study as Illustrated in Figures 4 and 6

 


REPORT AVAILABILITY

This report is available online in pdf format (2 Mb): USGS SIR 2008-5046
To view the PDF document, you need the Adobe Acrobat® Reader installed on your computer. (A free copy of the Acrobat® Reader may be downloaded from Adobe Systems Incorporated.)

Suggested citation:

Calhoun, D.L., Gregory, M.B., and Wyers, H.S., 2008, Algal and invertebrate community composition along agricultural gradients—A comparative study from two regions of the Eastern United States: U.S. Geological Survey Scientific Investigations Report 2008–5046, 33 p., also available online at http://pubs.usgs.gov/sir/2008/5046


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