River Macrophyte Index for ecological status assessment of the non-karst and Dinaric karst waters

Abstract

Assessing the ecological status of surface waters is essential for evaluating the ecosystem health and for defining of river basin management strategy. River Macrophyte Index (RMI) is uniformly used for assessing the trophic status of rivers and was intercalibrated for Mediterranean and Eastern-Continental lowland rivers in European Union but not for Dinaric karst rivers. Karst rivers are specific due to extreme water level fluctuations that might reflect in macrophyte communities' response. We built a composite stressor gradient as a proxy for trophic status, classified 85 plant species in the ecological indicator groups using large, representative data set, separately examined sites from karst and non-karst rivers and validated updated River Macrophyte Index (RMIup) with the independent data set. We found the differences in the response of macrophyte communities of karst and non-karst waters to the composite stressor gradient what resulted in type-specific boundary values. RMI reference values were significantly higher for karst waters in comparison to non-karst waters, but the normalised boundary values were similar for both water types indicating that key shifts in macrophyte communities occur at similar deviations along the stressor gradient. Boundary values of the updated RMI differed from those from the original RMI version as lower normalised RMI values were observed using the updated RMI version, but only at high to moderate ecological status sites. The updated RMI is showing a good relationship with the composite stressor gradient using the development and validation dataset and provides us with an effective assessment system and river management tool.