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Eleven-year trend in acetanilide pesticide degradates in the Iowa River, Iowa

Journal of Environmental Quality

By:
, , ,
DOI: 10.2134/jeq2011.0426

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Abstract

Trends in concentration and loads of acetochlor, alachlor, and metolachlor and their ethanasulfonic (ESA) and oxanilic (OXA) acid degradates were studied from 1996 through 2006 in the main stem of the Iowa River, Iowa and in the South Fork Iowa River, a small tributary near the headwaters of the Iowa River. Concentration trends were determined using the parametric regression model SEAWAVE-Q, which accounts for seasonal and flow-related variability. Daily estimated concentrations generated from the model were used with daily streamflow to calculate daily and yearly loads. Acetochlor, alachlor, metolachlor, and their ESA and OXA degradates were generally present in >50% of the samples collected from both sites throughout the study. Their concentrations generally decreased from 1996 through 2006, although the rate of decrease was slower after 2001. Concentrations of the ESA and OXA degradates decreased from 3 to about 23% yr-1. The concentration trend was related to the decreasing use of these compounds during the study period. Decreasing concentrations and constant runoff resulted in an average reduction of 10 to >3000 kg per year of alachlor and metolachlor ESA and OXA degradates being transported out of the Iowa River watershed. Transport of acetochlor and metolachlor parent compounds and their degradates from the Iowa River watershed ranged from <1% to about 6% of the annual application. These trends were related to the decreasing use of these compounds during the study period, but the year-to-year variability cannot explain changes in loads based on herbicide use alone. The trends were also affected by the timing and amount of precipitation. As expected, increased amounts of water moving through the watershed moved a greater percentage of the applied herbicides, especially the relatively soluble degradates, from the soils into the rivers through surface runoff, shallow groundwater inflow, and subsurface drainage.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Eleven-year trend in acetanilide pesticide degradates in the Iowa River, Iowa
Series title:
Journal of Environmental Quality
DOI:
10.2134/jeq2011.0426
Volume
41
Issue:
5
Year Published:
2012
Language:
English
Publisher:
ASA, CSSA, SSSA
Publisher location:
Madison, WI
Contributing office(s):
Iowa Water Science Center
Description:
14 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
1566
Last page:
1579
Number of Pages:
14
Country:
United States
State:
Iowa;Minnesota
Other Geospatial:
Cedar River