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Water Quality in Walnut Creek Watershed: Herbicides and Nitrate in Surface Waters
Author(s) -
Jaynes D. B.,
Hatfield J. L.,
Meek D. W.
Publication year - 1999
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1999.00472425002800010005x
Subject(s) - alachlor , metolachlor , metribuzin , atrazine , watershed , surface runoff , water quality , hydrology (agriculture) , acetamide , nitrate , environmental science , surface water , chemistry , environmental chemistry , pesticide , agronomy , zoology , environmental engineering , ecology , biology , weed control , geotechnical engineering , organic chemistry , computer science , engineering , machine learning
There is a lack of quantitative information describing the impact of farming on water quality at the watershed scale. This study documents the surface water quality of Walnut Creek—a 5130‐ha watershed with about 86% of the land used for crop production. Starting in 1990, flow and concentrations of NO 3 ‐N and four herbicides—atrazine [6‐chloro‐ N ‐ethyl‐ N ′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine], alachlor [2‐chloro‐ N ‐(2,6‐diethylphenyl)‐ N ‐(methoxymethyl)acetamide], metribuzin [4‐amino‐6‐(1,1‐dimethylethyl)‐3‐(methylthio)‐1,2,4‐triazin‐5(4 N )‐one], and metolachlor [2‐chloro‐ N ‐(2‐ethyl‐6‐methylphenyl) ‐ N ‐ (2 ‐methoxy ‐1‐methylethyl)acetamide]—were measured at eight locations. Nitrate‐N concentrations often exceeded 10 mg L −1 during May, June, and July. Total losses from the watershed ranged from 4 to 66 kg ha −1 yr −1 and represented 6 to 115% of the N applied as fertilizer in any year. Atrazine and metolachlor were detected at concentrations >0.2 µg L −1 in about half of all water samples, while alachlor and metribuzin were seldom detected. Median concentrations for atrazine and metolachlor were below 1 µg L −1 for all locations within the watershed. During runoff events, herbicide concentrations in the stream increased while NO 3 ‐N concentrations decreased. Yearly losses from the watershed ranged from 0.2 to 7.5 g ha −1 for atrazine and from 03 to 6.7 g ha −1 for metolachlor. These losses represent 0.18 to 5.6% of the atrazine and 0.047 to 1.6% of the metolachlor applied in any year.