The spring runoff in nebraska's (USA) Elkhorn River watershed and its impact on two sentinel organisms

Abstract

The objectives of the present study were to determine 1) if temporal variability influenced the toxicity of Elkhorn River water and 2) if the toxic effect was consistent between two sentinel organisms, the fathead minnow (Pimephales promelas) and the northern leopard frog (Rana pipiens). During spring 2012, atrazine indicator strips were used to document the occurrence of agrichemical pulses in the Elkhorn River. Polar organic chemical integrative samplers (POCIS) were deployed for 14 d during both a pulse and post-pulse period as indicated by the atrazine strips. Pesticide concentrations detected in the POCIS extracts ranged from 1.6 to 281 fold higher during the pulse period compared to the post-pulse period. Fish and frog bioassays were conducted for 7 d, and hepatic mRNA expression of vitellogenin (Vtg) and estrogen receptor-α (ERα) was determined by quantitative real-time PCR (RT-qPCR). Compared to lab water controls, fish exposed to water collected during an agrichemical pulse experienced significant reductions in Vtg and ERα, whereas exposed female frogs did not. Male leopard frogs, in contrast experienced significant increases in the expression of ERα, whereas pulse exposed male minnows did not. The significant effects observed following agrichemical pulse exposure demonstrate 1) that episodic agrichemical runoff adversely impacts sentinel organisms, and 2) that the adverse impacts observed depends upon the sex and species of the sentinel organism.

Compensatory response of fathead minnow larvae following a pulsed in-situ exposure to a seasonal agricultural runoff event

“…Briefly, beginning April 15, 2015 atrazine test strips were used to test whether concentrations of atrazine in surface water in the Elkhorn River were above or below 3 μg·L . These test strips have been demonstrated to accurately detect the presence of atrazine and other triazine herbicides at 3 μg·L −1 in surface water (US EPA 2004), with further confirmation of there accuracy by previously collected field data (Knight et al 2013;Ali and Kolok 2015). Tests were conducted every three to four days where the detection of three consecutive positive atrazine strips determined the start of the spring agrichemical pulse on May 8, 2015 (Fig.…”

“…Exposure of all fathead minnow larvae was conducted at the Elkhorn River Research Station (ERRS) where previous field studies have identified biological impacts and changes in endocrine responsive gene expression following in situ exposure to agricultural runoff (Knight et al 2013;Ali and Kolok 2015;Zhang et al 2015;Ali et al 2016). The ERRS is an open-air facility located approximately 10 km upstream from the confluence of the Elkhorn and Platte Rivers, Nebraska, USA.…”

“…The start of the agrichemical pulse was determined using atrazine test strips (Abraxis, Warminster, PA) as described in previous studies within the Elkhorn River watershed (Knight et al 2013;Ali and Kolok 2015;Zhang et al 2015). Briefly, beginning April 15, 2015 atrazine test strips were used to test whether concentrations of atrazine in surface water in the Elkhorn River were above or below 3 μg·L .…”

“…A suite of pesticides was selected for measurement due to regional application practices and their regular detection during the spring pulse in previous studies within the Elkhorn River watershed Zhang et al 2015). Included in this suite of pesticides were atrazine, acetochlor, metolachlor all of which are consistently detected within spring to early summer runoff (Lerch et al 2011a;Lerch et al 2011b;Knight et al 2013;Ali and Kolok 2015;Fairbairn et al 2016). …”

“…Indeed, field studies exposing fish to seasonally occurring agricultural runoff have documented endocrine disruption in the reproductive axis of otherwise intact adult females (Sellin et al 2009;Sellin Jeffries et al 2011a;Sellin Jeffries et al 2011b;Knight et al 2013;Ali and Kolok 2015;Zhang et al 2015). Periods of elevated discharge and pesticide loads were associated with decreased expression of the steroid responsive genes vitellogenin (VTG), estrogen receptor subtype α (ERα) and androgen receptor (AR) (Knight et al 2013;Ali and Kolok 2015;Zhang et al 2015).…”