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Herbicide Persistence and Mobility in Recharge Lake Watershed in York, Nebraska

Water Sciences Laboratory, 103 Natural Resources Hall, Univ. of Nebraska-Lincoln, Lincoln, NE 68583-0844

^* Corresponding author (rspaldin{at}unlinfo.unl.edu).

ABSTRACT

Elevated levels of herbicides in surface and groundwater are a concern in the Cornbelt in the USA. This study was conducted to interpret the herbicide behavior in a watershed system using data collected from runoff, Recharge Lake, and groundwater influenced by agriculture and lake seepage. The York Ground Water Recharge Project was constructed on a tributary of Beaver Creek, which drains a 3327-ha watershed of primarily row-cropped heavily irrigated farmland. The estimated average runoff is 1.48 x 10⁶ m³ yr^–1 under a precipitation norm of 635 mm yr^–1. Maximum atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) inputs to Recharge Lake occurred in May and June runoff events and resulted in average lake concentrations of 36 and 17 µg L^–1 in 1993 and 1994, respectively. Only about 0.28 and 0.19% of total applied atrazine was lost to runoff in 1993 and 1994, respectively. The deethylatrazine (DEA) to atrazine molar ratio (DAR) decreased rapidly over a period of several hours in runoff samples, which is consistent with inputs from recently atrazine-treated soil. After the spring runoff, herbicide levels in Recharge Lake rose rapidly in response to the runoff event, then diminished gradually over a period of months. Atrazine concentrations in Recharge Lake decreased exponentially with time. Degradation half-lives were 237 d (r = 0.93) in 1993 and 209 d (r = 0.91) in 1994. Adjusted DEA concentrations in Recharge Lake remained relatively constant, indicating little evidence for biotic degradation and suggesting that abiotic degradation of atrazine to hydroxyatrazine (2-hydroxy-4-ethylamino-6-isopropylamino-s-triazine) was the most likely major degradative pathway in Recharge Lake.

The ARD no. of this publication is 11168.

Received for publication June 15, 1995.

This article has been cited by other articles:

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