The hierarchy of multiple stressors’ effects on benthic invertebrates: a case study from the rivers Erft and Niers, Germany

Environmental Sciences Europe

Table 3 Statistical key parameters of the redundancy analysis

	Inertia	Proportion	p-value	Adjusted R²
Total model	21	1	0.001	0.38
Conditional (i.e. explained by the co-variable stream type)	5.92	0.28
Constrained (i.e. explained by stressors)	10.7	0.51
Unconstrained (i.e. unexplained)	4.38	0.21
Marginal effects (permutation)
Longitudinal profile (HP2)			0.003
Sulphate (SO4)			0.009
Iron (Fe)			0.023
Chloride (Cl)			0.025
High flow frequency (fh5)			0.037
Number of day rises (ra5)			0.071
Cross profile (HP4)			0.074
Total constrained variation of stressor groups (pRDA)
Physico-chemistry				0.33
Mixture toxicity				0.01
Hydrology				0.21
Morphology				0.17

A selection of 21 benthic macroinvertebrate metrics and 19 stressor variables of four stressor groups (physico-chemistry, micropollutants, morphological degradation, hydrological alteration) were analysed. Significance of the RDA model and of marginal effects of stressor variables were tested using an ANOVA on the results of 999 permutations. Only stressors with significant marginal effects (p < 0.1) are shown. Total explained variance of each stressor group was calculated using variance partitioning. Individual fractions are shown in Fig. 3