Determining in situ periphyton community responses to nutrient and atrazine gradients via pigment analysis

Abstract

Agrochemicals, including fertilizers and herbicides, are significant contributors of non-point source pollution to surface waters and have the potential to negatively affect periphyton. We characterized periphyton communities using pigment markers to assess the effects of nutrient enrichment and the herbicide atrazine with in situ experimental manipulations and by examining changes in community structure along existing agrochemical gradients. In 2008, the addition of nutrients (20 mg/L nitrate and 1.25 mg/L reactive phosphate), atrazine (20 μg/L) and a combination of both nutrients and atrazine had no significant effect on periphyton biomass or community structure in a stream periphytometer experiment. In 2009, similar experiments with higher concentrations of atrazine (200 μg/L) at two stream sites led to some minor effects. In contrast, at the watershed scale (2010) periphyton biomass (mg/m(2) chlorophyll a) increased significantly along correlated gradients of nitrate and atrazine but no direct effects of reactive phosphate were observed. Across the watershed, the average periphyton community was composed of Bacillariophyceae (60.9%), Chlorophyceae (28.1%), Cryptophyceae (6.9%) and Euglenophyceae (4.1%), with the Bacillariophyceae associated with high turbidity and the Chlorophyceae with nitrate enrichment. Overall, effects of nitrate on periphyton biomass and community structure superseded effects of reactive phosphate and atrazine.

Toxicity of atrazine to Scenedesmus quadricauda under different nitrogen concentrations

“…Means with asterisks are significantly (p \ 0.05) different from the control per time reduced the growth and cell density of S. quadricauda, regardless of the N condition. Nitrogen and ATR have contrasting effects on S. quadricauda, with replete nitrogen stimulating growth and ATR inhibiting it (Dalton et al 2015). While there is evidence that low concentrations of ATR can stimulate algal growth (Murdock and Wetzel 2012), all concentrations used in the present study inhibited the growth of S. quadricauda, which is in accordance with the results obtained with several algal species (Guasch et al 2007;Jeannette et al 2007;Vallotton et al 2008;Richard et al 2012;Bai et al 2015;Chia et al 2015a).…”

“…Selection of these concentrations was based on 96 h EC 50 of atrazine that was obtained in preliminary experiments. This concentration range of atrazine is within environmentally realistic levels (Dalton et al 2015). The final concentration of acetone in the treatments and each control was\0.1 % (v/v) (Tang et al 1997;Qian et al 2008), and preliminary analysis indicated that this concentration had no effect on the growth of the microalga.…”

“…This is because under limited nitrogen, increasing concentrations of the herbicide did not significantly (p [ 0.05) decrease the pigment content and dry weight of S. quadricauda between the ATR treatments. Interestingly, under field conditions, Dalton et al (2015) reported that nitrate and ATR levels were highly correlated because of their widespread use on corn crops, a major annual crop in South Nation River Watershed, eastern Ontario, Canada. However, the authors could not clearly separate the effect of ATR from those of nitrate because nitrate effect superseded observable effects of ATR.…”

“…This can result in a decline of aquatic primary production and, subsequently, the disruption of aquatic ecological balance (Gustavson et al 2003). The solubility and partitioning behavior of herbicides determine their impact on nontarget aquatic organisms in the water column or sediments; they also determine herbicide persistence, which in turn influences the potential exposure period (Cedergreen and Streibig 2005;Deblois et al 2013;Dalton et al 2015). Atrazine, 2-chloro-4-ethylamino-6-isopropylamino-s-triazine, is a member of the triazine family of herbicides.…”

“…For example, nitrogen content which determines the trophic status of aquatic ecosystems is known to vary spatially and temporally in aquatic ecosystems (Chia et al 2011;Sugimoto et al 2014). Most studies of nutrient influence on atrazine toxicity have been biased toward periphyton communities (Guasch et al 2007;Murdock et al 2013;Dalton et al 2015). In addition, the results from these studies have been more or less contradictory.…”