Fatigue Tests of Nodular Cast Iron at High and Low Frequency Loading
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As regards their faunas, the tarns in the Dobiegniewskie Lakeland are still in need of further research into. Likewise, not much data is available on the fauna of leeches in reservoirs of that type in Poland. The area concerned is to a large extent arable, while its soil is of good quality. The objective behind the research was to determine the leech species composition in the tarns and to find out whether the occurrence of the species was dependent on various environmental factors, and – ultimately – to show that such reservoirs play an important role in agrarian biocoenosis. All told, there were 16 tarns studied. They were located in arable fields in the lakeland. The material was collected from the vegetation and from objects immersed in the water, and by means of a mesh scoop to collect samples from deeper sites. The collected samples were put into glass containers and preserved with a 4% formaldehyde solution. A total of 1121 leech individuals were collected, and 14 species were determined, including Piscicola geometra and Dina Lineata. On our penetration of the area we noticed that some of the tarns had been drained agriculturally, which we considered ill-advised as they normally are breeding sites for many species of insects and amphibians, and wildfowl sanctuaries. Tarns are a habitat for many species of invertebrate fauna and should be included in the research programmes of other specialists. The reservoirs we studied were differentiated as regards their size and occurrence of aquatic flora; they need to be classified. A call to protect tarns and abandon their liquidation through drainage is well justified.
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