Multiple stressors in periphyton – comparison of observed and predicted tolerance responses to high ionic loads and herbicide exposure

Abstract

Summary1. As a result of the increasing human impact on aquatic ecosystems, freshwater organisms are often exposed to multiple stressors simultaneously. The joint actions between stressors can result in combined effects and unexpected ecological effects. Therefore, a better understanding of the interactive effects on ecosystems is required. 2. This study aimed to identify potential interactions between high ionic loads and herbicides. A microcosm study, using periphyton as model community, was conducted with a factorial design. Two levels of ionic loads were used as single stressor and in combination with prometryn. Structural (biomass, algal class and diatom composition) and functional parameters (tolerance development) were determined over a growth period of 6 weeks. The concept of pollution-induced community tolerance (PICT) was applied to quantify integrated community responses. Long-term community responses to the combined exposure were predicted using the model of independent action. 3. No co-tolerance of high ionic loads and prometryn or vice versa was found. Stress-induced succession resulted in a distinct community structure for each stressor and combination of stressors. Multiple stressors led to the selection of opportunistic species and higher tolerances to prometryn than predicted by the model of independent action. However, joint effects for high ionic loads and prometryn were concentration and time-dependent. The PICT concept enabled the quantification of community-level effects in systems receiving multiple stresses. 4. Synthesis and applications. Multiple stressors might explain the failure to achieve good ecological status for many European water bodies within the context of the EU-Water Framework Directive (WFD). We propose PICT as a diagnostic tool for investigative monitoring to clarify stressor conditions by testing the tolerances of local communities to preselected site-specific compounds.

Effects of flow intermittency and pharmaceutical exposure on the structure and metabolism of stream biofilms

“…In a river segment impacted by wastewater treatment plant (WWTP) effluents, the biofilms receiving chronic inputs were those with higher tolerance to diclofenac and ibuprofen (Corcoll et al, 2014). This was not fully observed in our study, probably because of insufficient time for the development of community tolerance (Tlili et al, 2011;Rotter et al, 2013), but higher sensitivity (23% lower photosynthetic efficiency EC 50 value) was in biofilms exposed to pharmaceuticals. This greater sensitivity of algal communities to pharmaceutical exposure may be somehow associated to promoted changes of species composition.…”

Pollution‐induced community tolerance (PICT): towards an ecologically relevant risk assessment of chemicals in aquatic systems

“…Since tolerance increase is related to a shift in community composition that results from the replacement of sensitive species by tolerant species, structural analyses are performed complementary to PICT measurements to support the species selection hypothesis (Blanck, ; Tlili & Montuelle, ). They also allow PICT results to be linked to traditional assessment parameters such as biotic indices (Rotter et al ., ). Thus, taxonomic analysis of algal communities (Bérard & Benninghoff, ) or more specifically of diatoms (Tiam et al ., ) has been used.…”

Accounting for regional variation in both natural environment and human disturbance to improve performance of multimetric indices of lotic benthic diatoms

“…Past surveys of the US show human disturbance and the stressors they produce differed among ecoregions (Paulsen et al, 2006). In addition, algal metric responses vary with stressors : Rotter et al, 2013. Algal metrics may also respond differently to the same stressor in different ecoregions if the ranges of those stressors vary among ecoregions (Potapova and Charles, 2007).…”

“…Variation in human disturbance among study regions should also be considered in developing MMIs because responses of metrics vary with different kinds of human disturbance (Danielson et al, 2011;Rotter et al, 2013). Human disturbance differs among regions.…”