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Water-Resources Investigations Report 2003-4203

Occurrence and distribution of nutrients, suspended sediment, and pesticides in the Mobile River Basin, Alabama, Georgia, Mississippi, and Tennessee, 1999-2001

U.S. Geological Survey Water-Resources Investigations Report 2003-4203, 109 pages (Published 2003)


By Ann K. McPherson, Richard S. Moreland, and J. Brian Atkins

This report is available online in pdf format: USGS WRIR 2003–4203 (8 MB)

Errata Sheet 8/19/2004 (30KB)
Replacement pages:
     P. 17 pdf (34KB)
     P. 33-38 pdf (64KB)
     P. 42 pdf (81KB)


Cover of SIR 2003-4203.

The Mobile River Basin is one of more than 50 river basins and aquifer systems being investigated as part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program. This basin is the sixth largest river basin in the United States and the fourth largest in terms of streamflow. The Mobile River Basin encompasses parts of Alabama, Georgia, Mississippi, and Tennessee, and almost two-thirds of the 44,0000-square-mile basin is located in Alabama. The extensive water resources of the Mobile River Basin are influenced by an array of natural and cultural factors, which impart unique and variable qualities to the streams, rivers, and aquifers and provide abundant habitat to sustain the diverse aquatic life in the basin.

From January 1999 to December 2001, a study was conducted of the occurrence and distribution of nutrients, suspended sediment, and pesticides in surface water of the Mobile River Basin. Nine sampling sites were selected on the basis of land use. The nine sites included two streams draining agricultural areas, two urban streams, and five large rivers with mixed land use. Surface-water samples were collected from one to four times each month to characterize the spatial and temporal variation in nutrient and pesticide concentrations.

Nutrient and suspended-sediment concentrations were highest in watersheds dominated by urban or agricultural land uses. Forty-two percent of the total phosphorus concentrations at all nine sites exceeded the U.S. Environmental Protection Agency’s recommended maximum concentration of 0.1 milligram per liter. Flow-weighted mean concentrations at the Mobile River Basin sites generally were in the lower to middle percentile ranges compared with data from other NAWQA studies across the Nation. However, flow-weighted mean concentrations of ammonia, total nitrogen, orthophosphate, and total phosphorus at Bogue Chitto Creek, an agricultural watershed, ranked in the upper 20th percentile of agricultural sites sampled across the Nation as part of the NAWQA Program. Nutrient loads in the Tombigbee River were nearly twice as high compared with nutrient loads in the Alabama River. Nutrient yields were highest in Bogue Chitto Creek, Cahaba Valley Creek, and Threemile Branch because of agricultural and urban land uses in these watersheds.

Of the 104 pesticides and degradation products analyzed in the stream samples, 69 were detected in one or more samples. Of the 69 detected pesticides, 51 were herbicides, 15 were insecticides, and 3 were fungicides. A relatively small number of heavily used herbicides accounted for most of the detections, including atrazine and its metabolites (deethylatrazine, 2-hydroxyatrazine, deisopropylatrazine, and deethyldeisopropylatrazine), simazine, metolachlor, tebuthiuron, prometon, diuron, and 2,4-D. Diazinon, chlorpyrifos, and carbaryl were the most frequently detected insecticides; metalaxyl was the most frequently detected fungicide in the Mobile River Basin.

Concentrations of pesticides detected in surface water of the Mobile River Basin were among the highest concentrations recorded nationally by the NAWQA Program during 1991 to 2001. The three highest concentrations of atrazine detected at sites across the country were recorded at Bogue Chitto Creek; the highest concentrations of 2,4-D, imazaquin, and malathion recorded nationally were detected at Threemile Branch. Aquatic-life criteria were exceeded by concentrations of five herbicides (2,4-D, atrazine, cyanazine, diuron, and metolachlor), six insecticides (carbaryl, chlorpyrifos, diazinon, dieldrin, malathion, and p,p '-DDE), and one fungicide (chlorothalonil). Drinking-water standards were exceeded by concentrations of four herbicides (2,4-D, atrazine, cyanazine, and simazine), three insecticides (alpha-HCH, diazinon, and dieldrin), and one fungicide (chlorothalonil).

The types and concentrations of pesticides found in surface water are linked to land use and to the types of pesticides used in each setting. Herbicides were detected more frequently and usually at higher concentrations in the agricultural stream, Bogue Chitto Creek. Insecticides, however, were detected more frequently and usually at higher concentrations in urban streams (Cahaba Valley Creek, Threemile Branch). Concentrations of pesticides varied seasonally in streams in response to the timing and amount of pesticides used and the frequency and magnitude of runoff from precipitation and irrigation. At Bogue Chitto Creek, the highest concentrations of atrazine were observed in April, May, and June, which coincide with its use as a preemergent herbicide on corn; the highest concentrations of cyanazine were observed in July and August, which coincide with its use as a postemergent herbicide on cotton. Seasonal patterns were less evident in urban streams, where concentrations of herbicides and insecticides remained relatively constant throughout the year.

Concentrations of pesticides in the large rivers generally were much lower than in their corresponding tributaries because of dilution and runoff from other land-use areas within the larger, more integrated basins. However, marked similarities were noted between the small streams with one primary land use and the large rivers draining basins encompassing these small streams. For example, the agricultural pesticides found in the Tombigbee River reflected those compounds present in its tributary, Bogue Chitto Creek, and the urban pesticides found in the Cahaba River reflected those compounds found in its tributary, Cahaba Valley Creek.




Purpose and Scope


Description of the study unit

Description of the sampling sites

Estimated pesticide use in the study area


Sampling frequency

Sample collection

Selection of pesticide analytes

Data analysis and review

Quality-control methods and results




Organic carbon

Loads and yields of nutrients


Suspended sediment

Loads and yields of suspended sediment


Occurrence of pesticides by sampling site

Bogue Chitto Creek near Memphis, Alabama

Cahaba River at Centreville, Alabama

Cahaba Valley Creek at Cross Creek Road at Pelham, Alabama

Threemile Branch at North Boulevard at Montgomery, Alabama

Alabama River at Claiborne, Alabama

Black Warrior River below Bankhead Lock and Dam near Bessemer, Alabama

Tombigbee River below Coffeeville Lock and Dam near Coffeeville, Alabama

Occurrence of pesticides in the Mobile River Basin

Occurrence of pesticides in the Mobile River Basin compared to other NAWQA Study Units


Selected references



This report is available online in pdf format: USGS WRIR 2003–54203 (8 MB)
To view the PDF document, you need the free Adobe Acrobat® Reader installed on your computer.

Suggested citation:

McPherson, Ann K.; Moreland, Richard S.; Atkins, J. Brian, 2003, Occurrence and Distribution of Nutrients, Suspended Sediment, and Pesticides in the Mobile River Basin, Alabama, Georgia, Mississippi, and Tennessee, 1999-2001: U.S. Geological Survey Water-Resources Investigations Report 2004 – 5135, 109 p.

For more information, contact the Alabama Water Science Center.

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