Benthic invertebrate assemblages and their relation to physical and chemical characteristics of streams in the Eastern Iowa Basins, 1996-98

Water-Resources Investigations Report 2000-4256




Over 250 benthic invertebrate taxa were identified from snags and woody debris in streams and rivers of the Wapsipinicon, Cedar, Iowa, and Skunk River Basins in the Eastern Iowa Basins (EIWA) study unit of the U.S. Geological Survey National Water-Quality Assessment Program. The composition, distribution, and abundance of 74 predominant taxa were related to environmental conditions in the study unit, using habitat, hydrologic, and water-quality data. Four groups of sites were defined, based on the distribution and relative abundance of taxa. Detrended correspondence analysis was used to identify relations in the structure of the invertebrate assemblages, and the correspondence of taxa and sites in the groups was related to habitat, hydrologic, and water-quality information. Responses of invertebrate assemblages were explained by natural factors, such as surficial geology or physical habitat conditions, as well as human influences, such as agriculture or high-density hog-feeding operations.

Mayflies, caddisflies, and true flies were well represented in streams and rivers of the EIWA study unit. The mayflies Tricorythodes and Baetis intercalaris, the net-spinning caddisflies Hydropsyche bidens and H. simulans, and the Chironomidae Glyptotendipes, Polypedilum, and Rheotanytarsus predominated. Spatial variation in benthic invertebrate assemblages within a site was less than that observed among sites. Assemblages from 3 years of sampling generally were grouped by site, with exceptions related to differences in discharge among years.

The benthic invertebrate assemblages associated with the four groups of sites reflected the cumulative effects of agricultural and urban land use, sources of nutrient and organic enrichment, and longitudinal stream succession—the natural sequence of communities in streams from headwaters to large rivers. These factors, especially the natural changes from upstream to downstream, were influential in characterizing the benthic invertebrate assemblages of the site groups.

Stream size, a reflection of basin area, was a principal influence in categorizing the benthic invertebrate assemblages, with sites that have the largest basin areas forming a separate group. Although it is difficult to distinguish among the contributions of large basin area, increased concentrations of nutrients and pesticides, and decreasing instream habitat diversity, the resulting invertebrate assemblage described was distinct. The remaining sites were headwater or tributary streams that reflected conditions more common to smaller streams, such as higher gradients and the potential for more diverse or extensive riparian habitat, but were distinguished by landform. Following basin area in importance, landform contributed to the differences observed among the benthic invertebrate communities at the remaining sites.

Study Area

Table of Contents

     Purpose and Scope
     Description of the Eastern Iowa Basins
     Site Selection and Description
     Water-Quality Variables
     Benthic Invertebrate Collection and Data Preparation
          Field Sampling
          Laboratory Processing
          Data Preparation
     Statistical Analysis and Other Calculations
Distribution of Benthic Invertebrates
     Spatial and Temporal Variability
          Spatial Variability
          Temporal Variability
     Differences in Benthic Invertebrates Among Site Groups
Influence of Physical and Chemical Characteristics of Streams on Benthic Invertebrate Assemblages
     Identification of Important Environmental Variables
     Distinctions Among Site Groups
     Responses of Benthic Invertebrates to Nutrients and Organic Enrichment
References cited
Supplemental Data

Additional publication details

Publication type:
Publication Subtype:
USGS Numbered Series
Benthic invertebrate assemblages and their relation to physical and chemical characteristics of streams in the Eastern Iowa Basins, 1996-98
Series title:
Water-Resources Investigations Report
Series number:
Year Published:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Iowa Water Science Center
vii, 44 p.; ill., col. map; 28 cm.
United States
Iowa, Minnesota
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