Bebrų patvenktos sausinimo sistemos veikimas ir žvėrelių elgesys reguliuojant patvankos dydį

Abstract

Kai populiacijos tankumas didelis, bebrai nevengia melioracijos griovių, kuriuose statydami užtvankas patvenkia ir griovius, ir drenažo sistemas. Buvo atliktas bandymas, įtaisius vamzdines pralaidas bebrų užtvankose, esančiose melioracijos griovyje Žiedupis (Nevėžio baseinas, Lietuva), nustatyti jų veikimą ir bebrų reakciją į vandens lygio pažeminimą tvenkiniuose bei patvankos poveikį drenažui ir sausinamų dirvožemių hidrologinėms sąlygoms. Tinkamai įrengtos vamzdinės pralaidos pažemino ir norimame aukštyje palaikė vandens lygius patvenktuose griovio ruožuose. Tai padėjo atkurti nusausinimo normą patvenktu vamzdynu sausinamoje sistemos dalyje ir ją palaikyti vegetacijos metu. Kokio nors patvankos apčiuopiamo neigiamo poveikio drenažo vamzdynui nenustatyta. Tačiau vamzdinių pralaidų įtaisymas bebrų užtvankose vandens lygiui patvenktame griovio ruože pažeminti neapsaugojo nuo naujų užtvankų statymo, neprivertė žvėrelių palikti bebravietę

When there is high density of the population, beavers readily occupy open drains. Inhabiting and impounding the drains, beavers at once dam up subsurface drainage systems that fall into them. The paper provides results of the trial that took place in the beaver obstructed stretch of the open drain Žiedupis (the Nevėžis river basin, Lithuania) and its environs. The trial comprised the following subjects: workings of pond drains installed in beaver dams for lowering of water level; behavior of beavers reacting botch to pond drains and water level lowering; the conditions of tile drain tubes operating under damming as well as hydrological conditions of soils drained by those tiles. It was found out that: (1) properly installed pond drains were able to maintain water surface at the desirable level; beavers or swimming litter and ice did not stop these drains. (2) If the water column above the mouth of main drain was not over, the subsurface system was operating right enough and ensured satisfactory soil water table depth in the headed-in section of the system during a vegetation period. (3) Beavers caused heading-in of subsurface drains did not harm technical condition of the drain tubes more than it usually occurred in normally (by gravity) operating subsurface drains. (4) Although the pond drains, lowering water level in the ponds, benefited workings of drainage system, those drains did not prevent the beavers from building of new dams, and did not get the animals to abandon the beaver-site. It will be observed, that the trial was conducted under the following natural circumstances. (1) The catchment area at the beaver obstructed stretch of the open drain approximated to two sq kilometers. (2) The soil of the adjacent field was of light (sand, sandy loam) texture. (3) The years comprised by trial period were rather dry and worm as compared to the normal ones