Variable time scale changes in the river Neretva salinity regime

Our study stems from in situ observations of temperature, EC and salinity performed during 2021-2023 along the river Neretva bed within the Republic of Croatia territory. Apart from the local water column profiling performed several times per year, mostly during dry period, continuous observations of EC, and temperature have been performed at fixed locations and for variable depths. As a main driving forces controlling the termohaline stratification of the Neretva water column caused by seawater intrusion, river Neretva discharge and Adriatic Sea level have been observed continuously. 
The data sets offer insight to changes in seawater-freshwater interface (SFI) and its shape ranging from typical salt wedge to complete stratification diminishing conditions. Hereby, within the data sets we identify three main scenarios of mechanisms controlling the seawater intrusions and thus the SFI: i) dominant influence of the mean sea level during the dry period with natural discharge kept below 250 m3/s, ii) dominant influence of intermittent discharge events caused by upstream hydropower plant operation and iii) rain period with on average annual duration of app. 25 % when river Neretva natural discharge controls the salinity vanishing from the river bed downstream. 
In this way, specific changes in the salinity corresponding to different time scales have been determined. Natural hydrologically induced changes in the salinity are identified to correspond to largest time scales of several days and even weeks, unless intermittent discharge caused changes occur very fast decrease in the salinity, typically less than three hours, with recovery time corresponding to app. three to six hours.
Although the data sets offer the definition of different time scale changes in the river salinity as mentioned above, an improvement in continuous stratification observation has been suggested and implemented as a result of conducted study.