Questions How can conservation status of rich fen and alkaline spring areas be assessed most cost‐effectively based on existing monitoring data? What is the precision and accuracy of available indicators? Location Rich fen and alkaline spring areas in Denmark. Methods Potential indicators of conservation status were evaluated based on: accuracy, measured as the ability to predict the number of typical species in monitoring plots; precision, measured as variation over years of indicators in repeated plots; and cost of obtaining data for the indicator. Indicators were derived using data from the Danish National Monitoring and Assessment Programme for the Aquatic and Terrestrial Environment from 2000 to 2009. Indicators included biotic indices derived from species lists, abiotic measurements of pH and nutrients and structural measurements of vegetation height and tree cover. Results The majority of indicators showed a significant correlation with the number of typical species. Floristic indicators, especially based on Ellenberg nutrient values, showed superior correlation and were furthermore very stable over years. Structural indicators were generally accurate, but were highly imprecise with high between‐year variation. Among the abiotic indicators, pH and soil P were inaccurate, whereas tissue N content and nitrate in water were accurate but with low precision. When balancing efficiency of indicators with monitoring costs, laboratory analyses stand out as expensive compared to recording of a species list, the latter providing up to five valuable indicators. Conclusions Floristic indicators derived from Ellenberg values, and especially those related to nutrient availability, are cost‐effective indicators of conservation status. The method is applicable to all regions where Ellenberg indicator values have been calibrated to fit local conditions.

Summary 1. Effects of the frequency and duration of flooding on the structural and functional characteristics of riparian vegetation were studied at four sites (n = 80, 50 × 50 cm, plots) along medium‐sized naturally meandering lowland streams. Special focus was on rich fens, which – due to their high species richness – are of high priority in nature conservation. 2. Reed beds, rich fens and meadows were all regularly flooded during the 20‐year study period, with a higher frequency in reed bed areas than in rich fen and meadow areas. In rich fens, species richness was higher in low frequency flooded areas (≤3 year−1) than in areas with a high frequency of flooding (>3 year−1) or no flooding, whereas species richness in reed beds and meadows was unaffected by flood frequency. 3. The percentage of stress‐tolerant species was higher in low intensity flooded rich fen areas than in high intensity and non‐flooded areas, indicating that the higher species richness in low frequency flooded rich fens was caused by competitive release. We found no indication that increased productivity was associated with high flooding frequencies. 4. We conclude that the restoration of morphological features in stream channels to increase the flooding regime can be beneficial for protected vegetation within riparian areas, but also that groundwater discharge thresholds and critical levels for protected vegetation should be identified and considered when introducing stream ecosystem restoration plans.

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At present, scientific evidence documenting effects of weed cutting in streams as a measure to improve flood protection and run‐off from agricultural land is scarce, which is surprising considering the huge effect that it has on stream ecology. Instead, weed cutting is performed under the assumption that removal of aquatic plant biomass improves runoff from agricultural land and prevents flooding of adjacent areas provided that it is performed regularly. In this study, we examined linkages between weed cutting practice and water level reductions in 126 small‐ and medium‐sized Danish streams (catchment size <100 km2) with continuously monitored discharge and water level data (from 1990 to 2012). Specifically, we hypothesised that (1) weed cutting reduces stream water levels more in late summer when the biomass of aquatic plants is higher than in early summer; (2) the efficiency of cutting declines with increasing cutting frequency as the aquatic plant community changes with increasing abundance of species able to regrow fast following a cutting event; (3) the high‐frequency cutting in Danish streams lowers the ecological status of the streams as evaluated from aquatic plant assemblages. The average effect of weed cutting on the water level was largest in July, August and September with an average reduction of 16 cm and lowest in early spring and late autumn with an average reduction of 11 cm. Regrowth was largest in June, with an increase in water level of 0.41 cm/day, whereas regrowth was absent in autumn. Regrowth also varied with the frequency of weed cutting, from an average of 0.04 cm/day in streams subjected to one annual cutting to an average of 0.6 cm/day in streams subjected to >6 annual cuttings. Furthermore, we found that the ecological status was either moderate or poor/bad in streams with more than one annual cutting. Our findings highlight that it is by no means certain that the current weed cutting practice is efficient for flood control since (1) regrowth is stimulated by frequent cuttings and a positive feedback loop may develop, necessitating even more frequent cuttings to maintain the discharge capacity of the streams, and (2) many species stimulated by weed cutting, like for instance Sparganium emersum, form dense canopy beds across the entire stream profile and therefore reduce the discharge capacity of the stream more than species growing in confined patches. We encourage more studies with the aim to identify how stream maintenance should be performed to optimise flood control without compromising the ability to reach good ecological stream quality.