STUDY UNIT DESIGN
The objective of the Eastern Iowa Basins NAWQA study was to assess the water-quality conditions in streams and ground water in the Study Unit. The study design is based on a nationally consistent structure that incorporates an interdisciplinary approach (Gilliom and others, 1995). Stream-water quality was assessed using three interrelated components: stream chemistry, streambed-sediment chemistry, and stream ecology. Ground-water quality of the alluvial aquifers was selected for assessment because these aquifers are the major source of water for municipal and domestic supplies and they provide flow to streams. Water quality in the Silurian-Devonian and Upper Carbonate aquifers also was investigated.
 |
Stream Chemistry
The Basic Fixed Site sampling network was designed to characterize the effects of physiographic differences on water quality in the primarily agricultural Study Unit. Water-chemistry, bed-sediment, and reservoir-core data were collected. Sites were selected on large rivers and smaller streams. Fixed sites on large rivers were located near the mouth of the four major rivers to characterize the integrated effects of differing land use and environmental setting on stream quality. Two additional large river sites were chosen to assess the upper part of the Cedar River and the Iowa River, before it flows into Coralville Reservoir. Fixed sites on streams were selected to characterize each of the physiographic areas. A reference site was selected on a watershed that retains a large amount of bottomland wetlands. Another site was selected to assess the effects of concentrated animal feeding operations on stream quality. A subset of the Basic Fixed Site network was intensively sampled (weekly to biweekly) through the spring and summer of 1997. Two synoptic studies were conducted during base-flow conditions (high and low base flow) to improve the spatial resolution and to better evaluate the effects of soil type and riparian buffers on stream-water quality and biological communities.
 |
Stream Ecology
Ecological data including fish-tissue chemistry and fish, macroinvertebrate, and algal community structure were collected to provide better understanding of the relations among physical, chemical, and biological characteristics of a stream. Data were collected at the Basic Fixed Site sampling network plus four additional sites to provide better spatial coverage.
Ground-Water Chemistry
The ground-water network was designed to characterize water quality in the most heavily used aquifers in the Study Unit. A Study Unit survey characterized the water quality in the Silurian-Devonian and Upper Carbonate bedrock aquifers, the second greatest source of municipal and domestic supplies in the Study Unit. Another Study Unit survey characterized the water quality of the alluvial aquifers using domestic wells. Land-use studies assessed the occurrence and distribution of water-quality constituents in recently recharged water in the alluvial aquifers. Agricultural and urban land-use effects on quality of shallow ground water was characterized by sampling two networks of monitoring wells constructed at randomly selected sites.
|
Study |
What data were collected and why |
Types of sites sampled |
Number of sites |
Sampling |
|---|---|---|---|---|
| Stream chemistry |
||||
| Basic Fixed Sites--large rivers |
Major ions, organic carbon, suspended sediment, nutrients, pesticides, and streamflow were determined to describe concentrations and the amount of selected constituents transported from the study area |
Streams draining basins from about 2,300 to more than 12,000 square miles that integrate the effects of urban and agricultural land use and physiographic regions |
6 in 1996, 5 in 1997-98 |
Monthly beginning in March 1996 and during selected flood events |
| Basic Fixed Sites-- |
Major ions, organic carbon, suspended sediment, nutrients, pesticides, and streamflow were determined to evaluate physiographic effects on stream-water quality |
Streams draining basins from 120 to 418 square miles of homogeneous land use and physiography |
6 |
Monthly beginning in March 1996 and during selected flood events |
| Intensive Fixed Sites |
Major ions, organic carbon, suspended sediment, nutrients, pesticides, and streamflow were determined to define short-term temporal variability |
One large river and two stream Basic Fixed Sites |
3 |
Weekly during 1997 growing season; biweekly for remainder of the year |
| Base-flow synoptic study |
Nutrients, pesticides, organic carbon, and streamflow were determined to refine spatial variability during both low and high base-flow conditions |
Streams draining basins ranging from 120 to 530 square miles representing greater than 90 percent agricultural land use |
25 |
August 1997 and May 1998 |
| Bed-sediment chemistry |
||||
| Bed sediment and tissue |
Trace elements, organochlorine, and semivolatile organic compounds in streambed sediment to determine presence of these potentially toxic, hydrophobic compounds |
Ecological sites--Large river and tributary/headwater fixed sites plus four additional sites for better spatial coverage |
16 |
September 1995 |
| Reservoir core study |
Trace elements and organochlorine compounds in sediment to determine the historical occurrence (from filling in 1958 to 1993) |
Site in a deep depositional zone of the Coralville Reservoir about 1.5 miles upstream from the dam |
1 |
November 1993 |
| Stream ecology |
||||
| Bed sediment and tissue |
Trace elements and organochlorine compounds in fish tissue to determine occurrence |
Ecological sites |
16 |
September 1995 |
| Intensive assessments |
Fish, benthic invertebrates, algae, and aquatic and riparian habitat were sampled and described to assess community structure and to document within stream and annual variation |
Ecological sites |
12 |
All fixed sites in 1996 and intensive sites in 1997-98 |
| Ecological |
Benthic invertebrates, algae, and aquatic and riparian habitat were sampled to assess biological responses in relation to water quality and hydrologic variability |
Streams draining basins ranging from 120 to 530 square miles representing greater than 90 percent agricultural land use |
25 |
August 1997 |
| Ground-water chemistry |
||||
| Bedrock aquifer survey |
Major ions, nutrients, pesticides, pesticide degradates, VOCs, and tritium were determined to assess quality in second most-used aquifer in Study Unit |
Existing domestic
wells completed in the |
33 |
June-July 1996 |
| Alluvial aquifer survey |
The same constituents as in bedrock aquifer survey were determined to assess quality in most-used aquifer in the Study Unit |
Existing domestic wells completed in unconsolidated alluvial deposits |
32 |
June-July 1998 |
| Land-use effects
study-- |
The same constituents as in bedrock aquifer survey were determined to assess water-quality differences due to agricultural and urban land use |
Newly constructed monitoring wells at sites randomly selected on alluvial deposits and completed at the water table (31 agricultural and 30 urban wells) |
61 |
June-August 1997 |
| Ground-water chemistry special study |
||||
| Changing land-use study |
The same constituents as in bedrock aquifer survey were determined to assess changes in water-quality due to conversion of row crops to wetlands and prairie |
Existing monitoring wells plus three new monitoring wells completed at various depths in the Iowa River alluvial aquifer |
28 |
August 1996 and 1998 |
| Table of Contents || Previous Section || Next Section || Glossary U.S. Geological Survey Circular 1210 Suggested citation:
|
