Stream Chemistry

The main objective of the stream-chemistry component of the study was to assess the relation between agricultural land use and basin size and chemical constituents of surface water. Stream and river sampling locations were distributed among subbasins and on the Illinois River. Sampling locations included Basic and Intensive Fixed Sites—sampled at regular intervals for a period of 2 to 3 years—and Synoptic Sites that were sampled during a 2-week period in August 1997.

Stream Ecology

The main objective of the ecology component of the study was to assess surface-water quality by integrating the physical, chemical, and biological factors. Ecology Sites were distributed at the basic fixed sites and at smaller subbasins that are all predominantly agricultural land. Sites were classified as either intensive or synoptic on the basis of the level and schedule of sampling effort.

Ground-Water Chemistry

One objective of the ground-water chemistry component of the study was to determine whether chemical constituents of ground water were related to agricultural land uses (land-use surveys). Another objective in two surveys of domestic (household) and public-supply (municipal) wells (Study-Unit surveys) was to assess the overall water quality in selected drinking-water-source aquifers (Mahomet aquifer and the western and southern shallow aquifers) and to determine whether they are affected by land-use practices. The full extent of the Mahomet aquifer (in the Mahomet bedrock valley) is not shown. Results for the Mahomet aquifer are representative only for that part shown.

Stream Chemistry

Basic Sites--general water quality

Concentrations, seasonal variation, and annual loads. Data included streamflow, nutrients, major ions, organic carbon, suspended sediment, water temperature, specific conductance, alkalinity, pH, and dissolved oxygen.

Basic Fixed Sites: representative of common land uses, as well as major tributary and basin outflow sites.

8

Monthly plus storms;
2 years

Intensive Sites--pesticides

Concentrations and seasonal variations in pesticides and breakdown products. Data included 75 pesticides and 13 breakdown products of the most heavily applied herbicides.

Subset of Basic Sites: Two watersheds with greater than 90 percent row-crop agriculture and the basin inflow and outflow sites.

4

Weekly to monthly Jan. 1996-June 1998

Synoptic Sites--water chemistry and pesticides

Spatial distribution of nutrients, pesticides, and pesticide breakdown products. Data included nutrients and 24 pesticides and pesticide breakdown products.

Basic Sites

Additional sites

4

17

Once in August 1997 during minimum flow

Contaminants in bed sediments

Occurrence and distribution of contaminants in bed sediment. Data included total PCBs, 32 organochlorine pesticides, 63 semivolatile organic compounds, and 44 trace elements.

Depositional zones of Basic Fixed Sites and some additional sites.

21

Once; June-October in 1996-97

Contaminants in fish

Occurrence and distribution of contaminants in biota. Data included total PCBs, 30 organochlorine pesticides in whole fish, and trace elements in fish livers.

Most stream sites also sampled for bed sediments.

20

Once; June-October in 1996-97

Stream Ecology

Intensive assessments

Relations among biological communities and water chemistry, physical habitat, and land use. Includes spatial relations, along with spatial variation. Data included algae, invertebrates, fish communities, and physical habitat.

Basic Fixed Sites

8

1 reach, 1 year (1996)
1 reach, 3 years (1996-98)
3 reaches, 1 year (1996 or 1997)

Synoptic studies

Better spatial assessment. Data collected were same as above.

Synoptic Sites

21

Once in August 1997

Ground-Water Chemistry

Aquifer survey--domestic and public-supply wells

Occurrence and distribution of chemicals in domestic and public-supply wells. Data included major ions, nutrients, 75 pesticides,13 pesticide breakdown products, 73 volatile organic compounds, dissolved organic carbon, trace elements, and radon.

Domestic and public supply wells across the subunit aquifers

2 public-
supply wells and 58 domestic or private wells

Once; May-November in 1996-97

Resample selected aquifer survey wells

Confirmation of low-level or questionable detections of pesticides, breakdown products, and age-dating chemicals.

A subset of the wells above

19

Once in 1998

Resample selected aquifer survey wells

Confirmation of high-level detections of arsenic and to determine the chemical nature of the dissolved arsenic. Data included major ions and selected dissolved metals in addition to two chemical forms of arsenic.

A subset of wells from the deep aquifer survey with arsenic that exceeded the drinking-water standard.

10

Once in 1997

Land-use effects--corn and soybean row crops

Describe the effects of agricultural land use on shallow ground water in the area underlain by most recent glacial geologic material. Data included major ions, nutrients, 75 pesticides, 13 pesticide breakdown products, dissolved organic carbon, trace elements, and radon.

Very shallow monitoring wells installed for this study.

57

Once in 1997

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U.S. Geological Survey Circular 1209

Suggested citation:

Groschen, G.E., Harris, M.A., King, R.B., Terrio, P.J., and Warner, K.L., 2000, Water Quality in the Lower Illinois River Basin, Illinois, 1995–98: U.S. Geological Survey Circular 1209, 36 p., on-line at https://pubs.water.usgs.gov/circ1209/