engleski

Wind stress and distribution of chemical parameters in the Krka River Estuary

Krka river estuary is a carstic, mainly stable stratified estuary, characterised by close interactions of hydrometeorological phenomena, underground carstic waters and nearshore saline water of the Adriatic sea. Some enquieries were made during windy weather (autumn 1987), and some (autum 1984, partially 1986)during stable hydrometeorological conditions. Selected surveys showed no great diferences in river flow and similar stratification. So, we supposed windy weather was the main factor influenced on dynamic and distribution of chemical parameters. Thermocline and halocline sinked during windy weather. In the same situations current field was formed under influence of drift currents. Even in these conditions, prevailing effects on current direction were by periodic tide currents. Tide oscilations were taken from tide gauge registration in Zlarin, near the mouth of estuary. Validity of this data were checked by visual hours registrations on a few places along the estuary. It was established Zlarin's tide gauge registrations has been representative for the whole estuary under the waterfall. General picture of the current field indicated that in the upper part of the estuary and Prokljan lake dominated influence of the river flow, while near mouth of the estuary and Šibenik, harbour, dominate periodical tide currents.Distribution of the chemical parameters offered important efects of wind stress upon surface fresh layer and the upper part of deep saline layer. For example, oxygen content shows undersaturation, even during wind blowing. Aeration played important role only in the upper part of the water column, while near bottom undersaturation remained. During windy days sinking of thermocline and halocline enables oxygen supersaturation. This was a short time disaster and after few hours former state returned. Distribution of nutrients were also examined. While, for phosphate, there was no way to get a straight line of mixing, because of small concentration and antropogenic influences, nitrate and silicate gave straight line near theoretic for situations without wind, for the whole estuary. During a windy conditions, we registred dropping concentration of nutrients in surface fresh water layer, and growing in saline layer. It's possible that processes of remineralization also play a role in last phenomena. Higher values of total alkalinity indicate that convection also intensifie mixing of layers. Results confirmed influence of wind stress on dynamic of the estuary and distribution of some chemical parameters. More conservative parameters were representative for a windy situation. Some parameters like phosphorus and amonia made a problem because of a small concentration and urban influences. In next investigations it had been proposed better quantification of the registered phenomena.

wind stress; distribution of chemical parameters; Krka River Estuary

Rapports et procè s verbaux des réunions - Commission internationale pour l'exploration scientifique de la mer Méditerranée (ISSN 0373-434X) 31 (1988) 38-38