Stream and river restoration measures may be showcase projects for conservationists, but – in the absence of systematic monitoring – it is often unclear what benefits they provide for ecosystems. Eawag scientists extended and synthesized methods for river assessment and demonstrated their usefulness to better quantify ecological effects of river rehabilitation. By Andres Jordi
Before: a linear, monotonous concrete channel – and after: a river meandering through idyllic floodplains. The quality of a restored watercourse may appear to be obvious, but is what is pleasing to humans also, in fact, valuable for nature? According to Amael Paillex, an environmental scientist at Eawag, “Although the number of restoration projects is increasing, we know very little about their ecological effects.” And if the effects are studied, he adds, assessments are often limited to a single group of organisms, while factors such as water quality or hydrological conditions are neglected. “Because outcomes are not adequately evaluated,” Paillex says, “experience from earlier restoration efforts cannot be fed into future projects.” Over the next 80 years, under the revised Waters Protection Act (2011), the cantons are required to rehabilitate a quarter of those rivers and streams which are heavily engineered and in a poor ecological condition. This amounts to around 4000 kilometres of watercourses across Switzerland.
Working with colleagues from the Department of Systems Analysis, Integrated Assessment and Modelling, and the University of Duisburg-Essen, Paillex therefore developed a method that allows the ecological effects of restoration measures to be assessed systematically. The method, which involves a mathematical approach used in decision analysis, is based on the modular stepwise procedure developed for the assessment of Swiss lakes and rivers. It addresses all the relevant states of a watercourse – physical (morphology and hydrology), chemical (water quality) and biological (animals and plants). Existing assessment methods for fish and macroinvertebrates were combined with new methods for the evaluation of ground beetles, riparian vegetation and aquatic plants.
In each case, a number of variables are measured – e.g. the width variability of the river bed, concentrations of nutrients and pesticides, or the number of species. These values are then compared with reference values for near-natural waters so as to determine how the actual state differs from the ideal. Paillex explains: “Using a mathematical method, we can then calculate quality values and assign the various parameters to quality classes.” The scale of values ranges from 0 (bad quality) to 1 (high quality). Comparison of the quality of unrestored and restored river reaches indicates how restoration measures have affected the various sub-states and the overall ecological state. In addition, to determine whether the effects observed are statistically significant – rather than merely being due to methodological imprecision – uncertainty ranges are calculated for all values derived from the measurements.