1. Toxic stress in multiply stressed ecosystems
Helmut Segner, Daniel Bontje, Pavel Jurajda, Bob Kooi, Isabel Munoz, Peter von der Ohe, Marketa Ondrakova, Stefanie Rotter, Sergi Sabater, Mechthild Schmitt-Jansen, Michael Wenger, Dick de Zwart

2. Motivation: understanding the relation between chemical and ecological status of aquatic resources
Chemical status relates to ecological status
Chemical status does not relatesto ecological status
Cf. presentationm Jos van Gils

3. Why are there mismatches between chemical and ecological status ?
Effects of unknown chemicals (cf. presentation Werner Brack)
Flaws in predicting of ecological responses to complex chemical mixtures on the basis of single compound, single chemical laboratory tests
Impacts of multiple stressors, chemical and non-chemical ones (hydromorphology, pathogens, climate change,...)

4. Case study of MODELKEY: disaggregating multiple stressors in the Bilina river, Czech Republic
Toxic chemical impact expressed as „toxic units“
Linear downstream increase of toxic impact
Nachdem wir nun mehrfach Korrelationen geshene haben, nun ein konkretes Beispiel
Wenger et al., in press

5. Fish ecological status does not relate to chemical status
Case study of MODELKEY: disaggregating multiple stressors in the Bilina river, Czech Republic
Fish ecological status does not relate to chemical status
U shape
Only fish species left; chub  hypoxia trolerant
Wenger et al., in press

6. Fish ecological status relates to water oxygen levels
Case study of MODELKEY: multiple stressors in the Bilina river, Czech Republic
Fish ecological status relates to water oxygen levels
U-shape
Wenger et al., in press

7.  But how to tackle this practically ?
The WFD expresses the need to consider non-chemical together with chemical stressors
The WFD requires „the identification of significant anthropogenic pressures and the assessment of their impacts on water bodies„ (Annex II, WFD).
In European river basins we are frequently confronted with multiple stressor situations, with the role of non-chemical stressors increasing at decreasing toxic stress.
In order to decide on priority actions for improving the ecological status, water managers must be able to define a hierarchy amongst the various stressors and to understand combined impacts of multiple stressors.
 But how to tackle this practically ?

8. (MODELKEY case study; redundancy analysis)
Correlational approaches to diagnose the importance of toxic chemicals in relation to other stressors
A3A
1.0
Ibuprofen
Temperature
Pharmaceuticals and temperature explain 71 % of the species variance in the Llobregat river
(MODELKEY case study; redundancy analysis)
LL4C
LL3A
LL4A
LL1A
LL2C
LL3C
LL1C
LL2A
LL2B
A2C
A3B
Propranolol
A1A
LL3B
A3C
A1C
A1B
Indomethacine
LL1B
A2A
LL4B
Die limitierung ist natürlich, dass wir abhängen von den Daten die wir haben !
The use of the multivariate analysis allow us to link different groups of variables and select those statistical significant in the characterization of the sampling point or the community. In this case with the invertebrates and the environmental variables jointly with pharmaceuticals, we observe that in sites with higher concentration of some pharmaceuticals there is higher biomass of some insect larvae or worms. RDA: Variance explained 71%
-0.6
A2B
-0.4
1.2
Muñoz et al.; Env.Tox.Chem., 28 (12): (2009) 8

9. Effect-and-possible-cause pies (EPCs)
Correlational approaches to diagnose the importance of toxic chemicals in comparison to other stressors
Effect-and-possible-cause pies (EPCs)
Size of pie informs how different or similar species composition at a study site is to a reference ecologcial conditison or site: a small pie indicates no or small difference, a big pie indicates a large difference. Thus, teh size informs on ecologcioal status of the site. The composition of the pie informs on the magnitude of the various stressors that were quantified fo this site. Of course, as before, it all depends on what stressors are quantified and how well tehy can be quantified (nor all stressors are nicely to quantify). However, the approach rpovides a diagnostic information to – depending on data quality – either formulate effective remediation measurs, or to trigger more in-depth investigations
Dick de Zwart et al. 2009

10. A major challenge is to assess stressor interactions: for instance, combination effects
Dose metrics to measure the interaction between water ion concentrations and prometryn toxicvity on biofilm communities
Synergism ?
Rotter et al. 2009

11. A major challenge is to assess stressor interactions: for instance, non-linear effects
Organism
altered repro-duction
Estrogen-active compounds
Molecular and physiological effects
Molecular and physiological effects
reduced survival
Also in the retrospective/diagnostic approach, where we start with an observed ecological impairment and try to identify the causative stressor or stressor combinations, mechanistic understanding is important since it enables us to formulate conceptual models which offer a likely explanation how a suspect stressor could impair biological elements. Mechanistic understanding and models can also show where different stressors may interact and thus can direct additional data collection
pathogen

12. Synergistic effect on survival
A major challenge is to assess stressor interactions: for instance, non-linear effects
altered repro-duction
Estrogen-active compounds
Molecular and physiological effects
Molecular and physiological effects
Synergistic effect on survival
Also in the retrospective/diagnostic approach, where we start with an observed ecological impairment and try to identify the causative stressor or stressor combinations, mechanistic understanding is important since it enables us to formulate conceptual models which offer a likely explanation how a suspect stressor could impair biological elements. Mechanistic understanding and models can also show where different stressors may interact and thus can direct additional data collection
pathogen

13. Worldwide decline of amphibians: consequence of interactions between toxicants and pathogens ?
PNAS, 2002
Importantly: when thinking on the impact of multiple stressors, it is not only
to recognize which stressors are relevant at a given site and to add them up
But also it may be that one particluar stressor which itself is not „relevant“ in terms of biological impact, may render the organisms more susceptible to the impact of another stressor (these hidden stressor interactions are a particular conceptual challenge
Ein stressor per se (hier pathogen) löst keinen negativen oder moderatent negativen effetc aus (here:sirvival), aber in kombination mit chemischen stressor kommt es zu einer duetlich verstärkten reaktion

14. Additional complication in assessing combined stressor impact: biological scaling
e.g., prediction to population level:
Example: Critical prometryn concentrations for flagellate population in combination with varying nitrogen levels
More: :
Presentation Leo Posthuma
e.g., species traits and sensitivities
pesticides
Pharmaceuticals
Biofilm
Effect on com-munity structure
No effect
invertebratess
Effect on com-munity structure

15. Conclusions
To identify causes of ecological impairment in a multiple stressor situation, water managers need tools, approaches and models
for setting hierarchies on the relative importance of stressors: e.g., tools to quantify various stressors and stressor-related responses;
for evidencing cause-effect relationships: e.g., toxico-genomics to identify unexpected interactions, bioenergetic models, dose metrics to determine thresholds of combined effects, species vulnerability models,
for extrapolating multiple stressor effects across biological, spatial and temporal scales: e.g. epidemiological tools, ecology-based models
Aufgabe: msPAF Ableitung einlesen
Figure 3, de Zwart et al. 2009: at low toxic pressure (< 25 %) (importantly: the toxic pressure was calcualted on the basis of the known/analysed chemicals) seems not directly associated to local losses of taxa
Recent years have seen much progress in approaches to assess ecological impact of toxic chemicals and chemical mixtures, we are now ready to close the existing gaps in multiple stressor assessment.