Ecological approach to management of open drains

Most natural streams were made into drains when they were converted into recipients of subsurface tile systems. During the process the variety of biotic and abiotic conditions within and around the streams was totally destroyed, and the new watercourses (open drain recipients) were deprived of the greater part of the ecological importance that the former streams had possessed in the landscape. The data collected over the last decade in Lithuania about drain bed deformations, sediment accumulation, vegetation cover successions, intentional afforestation of slopes, beaver expansion and succeeding water quality changes, revealed some self‐perpetuating natural alterations which raise the ecological significance of open drains as refuges and corridors in the landscape for vegetation (the succession of herbage and appearance of woody vegetation on slopes), and the barriers protecting surface runoff from diffuse agricultural pollution (beaver impoundments). On the other hand, these alterations are useful in terms of maintenance of the functioning of those drains as recipients because they result in steadier (roughly parabola‐shaped) cross‐section profiles, less threat of bed silting up and no need for the mowing of slopes (because of the growth of woody vegetation). This paper presents and discusses the study results highlighting the above‐mentioned bidirectional effect of self‐renaturalization, and considers the preconditions and possible methods of introduction for the ecologically acceptable management of open drains. Copyright © 2006 John Wiley & Sons, Ltd. La plupart des écoulements naturels ont été canalisés dans des drains lors de leur conversion en collecteurs des flux de drainage souterrain. A cette occasion, la variété des conditions biotiques et abiotiques internes et externes aux écoulements a été totalement détruite, et les nouvelles voies d'eau (collecteurs à ciel ouvert) ont été privées de l'essentiel du contenu écologique des ruissellements naturels. Les données rassemblées depuis dix ans en Lithuanie sur les déformations des collecteurs, l'accumulation des sédiments, les successions du couvert végétal, le reboisement intentionnel des pentes, la prolifération des castors et les changements de qualité de l'eau, ont révélé quelques unes des altérations autoentretenues qui posent la question du poids écologique des drains à ciel ouvert comme refuge et couloirs de végétaux dans le paysage (succession des herbes et apparence de végétation boisée sur le