River renaturisation (restoration) as a chance to protect the sand martin Riparia riparia population in Poland

Abstract

The regulation and reconstruction of rivers and their valleys, apart from drastic hydrological changes, often lead to the change or disappearance of the habitats of valuable plant and animal species. Particularly vulnerable to the loss of breeding sites are species directly associated with precipitous banks and river slopes, which are formed as a result of erosive and landslide processes. Intensive hydrotechnical treatments, such as straightening of the channels or elimination of irregularities of the river banks, resulted in the inhibition of the desirable natural river processes. Bird species native to Poland that require the above nesting conditions, include: sand martin Riparia riparia, kingfisher Alcedo atthis and bee-eater Merops apiaster. More and more actions are taken to restore rivers to a near-natural state. The aim of restoration is not only to increase retention capacity, protect against floods, social and economic benefits, but also to improve the overall functioning of river ecosystems and preserve biodiversity within their valleys. Renaturation includes activities such as the creation of exposed slopes that mimic erosive undercuts, the removal of bank reinforcements or the maintenance of bank gaps, which promote their occupation by the aforementioned bird species. In addition to predation, the loss of suitable breeding sites is the greatest threat to the sand martin population, such as the American mink Neovison vison, the fox Vulpes vulpes and the locally raccoon dog Nyctereutes procyonoides. A regulated river, where the implemented hydrotechnical measures disrupt the functioning of natural river processes, also causes losses in bird broods due to flash floods that destroy many nests together with eggs or nestlings. Sand martins in many places have stopped using riverbeds as breeding places, occupying anthropogenic habitats which, however, have certain limitations and threats. Renaturation is therefore an important measure to be taken in places where past regulations have caused the greatest damage to the environment. The development of anthropogenic areas should be supported in accordance with the principles of sustainable use of natural resources.