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No. 400: Technical basis for determining ecological potential in artificial and heavily modified streams

Baattrup-Pedersen, A., Fejerskov, M.L., Johnsen, T.J. & Larsen, S.E., J. 2020. Teknisk grundlag for fastlæggelse af økologisk potentiale i kunstige og stærkt modificerede vandløb. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 24 s. - Videnskabelig rapport nr. 400. http://dce2.au.dk/pub/SR400.pdf

Summary

In Denmark, a number of highly modified and artificial streams have been designated for which the objective is to obtain good ecological potential, corresponding to a slight deviation from the maximum ecological potential for individual biological quality elements (aquatic plants, invertebrates and fish in the form of EQR values). This project provides the technical basis for establishing the thresholds between maximum, good, moderate, poor and bad ecological potential and thus quantifies the importance of a slight and minor deviation from the maximum ecological potential. The thresholds must be determined from the values of the biological quality elements that are obtainable for the most comparable type of surface water, which is natural streams given the physical conditions resulting from the characteristics of the heavily modified stream.

The designated highly modified and artificial streams can be grouped into two main types of physical modification, where one main type is streams with low coverage of mud on the stream bed (< 10%) and the other main type is streams with significant coverage of mud on the stream bed (> 10%). Thus, it is possible to set identical environmental objectives for streams exhibiting the same type of modification, and for which you can therefore expect the same degree of impact on the biological quality elements.

For the two main types of physical modification, it was only possible to analyse the correlation between DVFI and the physical parameters as the amount of data on plants and fish was too poor to allow further analyses. On the basis of significant empirical correlations between DFI and DVFI EQR values for the two main types of physical modification, probability models were developed, in which the probability of fulfilment of objectives as a function of DFI could be identified and subsequently compared with the value that is critical for fulfilling objectives in natural streams  (Baattrup-Pedersen et al. 2016).

Based on the analyses conducted, the technical basis for determining the thresholds between maximum, good and moderate ecological potential in heavily modified and artificial aquatic areas was obtained, allowing setting of type-specific threshold values for artificial and highly modified streams. Thus, from the analyses, a threshold between good and moderate ecological potential for DVFI EQR is set to 0.52 in streams with coverage of mud below 10%, while the threshold between good and moderate ecological potential for DVFI EQR is 0.43 for streams with mud coverage above 10%. Using these threshold values, the level of protection will be comparable with that applied in natural streams, but taking into account the physical modifications occurring in artificial and highly modified streams.