Sammendrag
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 flood-ing of adjacent areas provided that it is performed regularly.2.In this study, we examined linkages between weed cutting practice and water level reductions in 126 small- and medium-sized Danish streams (catchment size6 annual cuttings. Further-more, we found that the ecological status was either moderate or poor/bad in streams with more than one annual cutting.4.Our findings highlight that it is by no means certain that the current weed cut-ting 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.
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