engleski

Effects of flow velocity, temperature, photoperiodism and hydroperiodism on periphytic assemblages dynamics

Three laboratory experiments were conducted to monitor development of periphytic assemblages under the concurrent influence of three temperature ranges, photoperiods and flow velocities. In each experiment there were nine aquaria each with a flume containing ten glass slides as sites for development of periphytic organisms scraped from cobbles of the Sava River. Initial colonization was very rapid regardless of the three factors and followed asymptotic model. Lower temperatures lead to drop in number, abundance and diversity of periphytic taxa, which becomes more pronounced with short photoperiod. High temperatures and slow flow lead to increase in Chl a and AFDM. While at short photoperiod AFDM decreases, Chl a increases. Availability of nutrients plays crucial role in forming of periphytic assemblages developing on river stones. In order to test the effects of inundation duration and water temperature on the release of nutrients and organic matter, sediment samples from seven floodplain habitats and leaf litter (Populus nigra L.) were collected on the island-braided Tagliamento floodplain, and inundated at 4, 12 and 25°C for 12, 36 and 96 hours. The relative content and leaching of C, N, and P was similar in all floodplain sediments (size fraction < 2mm), and significantly higher in leaves. Most leaching occurred during the first 12 hours. There was no consistent pattern on the effect of temperature on leaching. Leaf litter is a key source for C and P in floodplains, while sediments contribute almost equally to the N release, as inorganic substrates leach N more readily than C and P.

periphytic assemblages; water temperature; photoperiodism; flow velocity; artificial substrates; Tagliamento River floodplain; nutrient leaching; inundation duration

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