engleski

Hydrological variability of the river Krka estuary (1984-86)

The river Krka estuary, due to its beauty, represents an unique green oasis in the midst of greysh middle adriatic coastal karstic area. As such and for reasons of its protection, was proclamined a natural parc. 23 km in lenght, all of canyon configuration, it originated during postpleistocenic period by inundation of an eroded karstic valley. Predominancies of estuarine processes in karstic areas, make the river Krka estuary object of interdisciplinary investigations and an ideal scientific polygon. Montly flows of river Krka are characterised by a great variability of their fluvio-nival regimes with maximum in autum/winter (humid period with 400 m3/s) and minima during the summer(dry period with 10-30 m3/s). So, hydrograms of the river Krka obtained in such a way, show a great variability. The river Krka estuary can be classified as a type of partialy mixed estuary with a stable stratification during the summer period and instability during spring and autum. The most characteristic feature of the mentioned stratification are clearly expressed picnocline on the depth from 0, 5-4, 0 m. The increased salinity value gradients are present only in the layer that spreads from the picnocline tovard the bottom. Vertical oscilations in the estuary reach up to 0, 5 m and essentialy have no influence to the estuary stratification. Except for the surface fresh water layer and the saline near bottom layer, intrusions were occasionaly registred, and their appearence mechanisms are yet under research. The estuary dynamics was investigated by currents mesaurements on a few main stations. The currents are essentialy influenced by the river flow, tidal cycle, regional morphology and specially the main local winds (NE and SE). The surface fresh water layer shows the maximum current velocity (1.2 Knots). Transparency as a function of bioproduction, suspended matter and turbidity clouds, vary from about 1-10 m. The thermohaline estuar relations are closely connected by the seasonal changes of air temperature as well as with water column stability. The summer relations are characterised by high discontinuity layer (thermo-halo-picnocline) T°C = 14.0-24.0, Sal % = 0.0-38.0 whyle the winter relations by isothermy and temperature inversion T°C = 12, Sal % = 0.0-38.0. Changes of thermohaline relations much influence on variation of density, pH and alkalinity parameters. The whole Krka estuary represents a well aerated area. Oversaturations expressed in spring and summer period are caused by a high fotosintetic activity. The concentrations of all nutrient salts (P, N and Si) as measured in the estuary indicate high bioproductive potentials (with exception of reactive dissolved phosphorus). From the biological analisis of the phytoplancton catchies is evident, that in all seasons of the year the biomass is temporarly increasing (especially micro and nanoplancton).

hidrological variability; the river Krka estuary; fluvio-nival regimes; bioproduction

Rapports et procè s verbaux des réunions - Commission internationale pour l'exploration scientifique de la mer Méditerranée (ISSN 0373-434X) 30 (1986) 36-36