engleski

Periphytic diatoms in a karstic river and its highly stratified estuary (Zrmanja river, eastern Aadriatic Sea)

The harstic Zrmanja River (69 km long) discharges into the eastern-central Adriatic Sea. Due to weak tides and sufficient outflow most of the year (average 38 m3/sec) it forms a highly stratified estuary. Taxonomic composition and abundance of periphytic diatoms were analysed on samples taken from artificial substrates (plexiglas) in the river and its estuary, during June-July 2000. The extremly low concentrations of nutrients in the river indicate its oligotrophic character. Relatively low river water inflow in July (average 1.43 m3/sec) formed a sharp halocline in the upper, narrow reach of the estuary (in the 1-1.5 m layer). Salinity and temperature varied between 8 and 14 PSU and 19 to 24°C above the halocline, and 30 to 34 PSU and 21 to 23°C below the halocline, respectively. Concentration of orthophosphates increased from 0.05 mikromol/L in the brackish layer, to 0.08 mikromol/L in the marine layer. Concentration of total inorganic nitrogen and silicate were higher above (6.92 mikromol/L TIN, 10.6 mikromol/L silicate), than below the halocline (1.95 mikromol/L, 3.1 mikromol/L silicate). The oxygen saturation was high (80-90%) throughout the water column. The periphytic diatom community was composed of 40 taxa in the river and 59 taxa in the estuary. The most frequent (f>80%) and most abundant (>10 000 000 cells/cm) estuarine diatoms were Navicula veneta, Amphora coffeaeformis var. coffeaeformis and Cocconeis sp. The most frequent (f>80%) and most abundant (>1 000 000 cells/cm) diatoms in the river were Achnanthes sp. and Fragilaria sp. Sixteen freshwater diatoms successfully inhabited the upper reach of the estuary.

periphytic diatoms; karstic river; stratified estuary; Zrmanj; Adriatic Sea

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