Watershed-scale effects of a novel agricultural conservation practice on atrazine in channelized agricultural headwater streams.

Elevated springtime atrazine concentrations in agricultural streams of the US Midwest highlight the need for conservation practices that reduce atrazine transport to surface waters. Blind inlets are a novel water control structure that is an alternative to conventional tile risers. Information is lacking on the effect of replacing tile risers with blind inlets on atrazine in channelized agricultural headwater streams at the watershed scale. Our research questions were as follows: (1) Does replacing tile risers with blind inlets reduce atrazine concentrations and loads during storm events within channelized agricultural headwater streams? (2) Do these effects differ seasonally? To answer these questions, we conducted an 8-year before-after-control-impact experiment in two channelized agricultural headwater streams in Northeastern Indiana. During the before period (2004-2009), when both watersheds had tile risers, eight atrazine response variables during spring storm events did not differ (p-value > 0.400) between streams. After replacing tile risers with blind inlets in the impact stream (2010-2011), mean and maximum atrazine concentrations, total atrazine loads, mean drinking water toxicity index scores, and mean fish chronic toxicity index scores during spring storm events were lower (p-value < 0.001) in the impact stream compared to the control stream. Additionally, replacing tile risers with blind inlets did not affect any of the atrazine response variables during summer and fall storm events. These results indicate that replacing conventional tile risers with blind inlets is an effective conservation practice for reducing elevated springtime atrazine concentrations and loads in channelized agricultural headwater streams in the US Midwest.