This is quite a common phenomenon, as with inflows of rain water, the salinity reduces, and with no inflows in winter, the salinity goes up.

I agree on this answer. It is not only temperature that affects the salinity of an estuary, but also the addition of low-salinity water, such as meteoric (rain) water during the wet (warm) season.

Well,

means, wet warm season, the impact of mixing mechanism of low concentration rain water (high quantities)with the estuarine water is higher than the impact of evaporation, where this phenomenon not occur during dry cold winter.

Sincerely

Increase in salinity with increase in temperature is a general phenomenon. However in your case there is occurrence of rainfall, and this will definitely reduce / dilute the level of salinity, even though there is rise in temperature. This means one has to consider both temperature and freshwater input, due to rainfall / release of reservoir water for agricultural purposes, while analysing the salinity in the coastal areas.

Thanks to all of you, yes you are right... there are several factors influencing the salinity changes along an estuary like a coastal lagoon. Since my study area is a negative estuary, it receives very low fluvial inputs and the evaporation exceeds the precipitation, so I think given this and your answers that evaporation is playing an important role in my salinity measurements.

Thanks for your guidance.

Best wishes

This is actually a fantastic question that shows how the environments we call Estuaries differ one from the other.

The first phenomenon shown here is increased evaporation with increased temperature which will cause positive correlation of temperature and salinity

The second phenomenon is correlation with precipitation. During monsoon for instance you will get warm temperature and a lot of precipitation which will cause negative correlation of temperature and salinity.

We (http://reco.ruppin.ac.il/eng/) work in the mediterranean where we have precipitation during winter (cold and rainy). This is expected to cause positive correlation of temperature and salinity (less salinity is expected during winter) but when we took the measurement we found out the estuary was fresher during summer.

The reson is that the estuary we study is partially connected (A natural sandy sill is formed at the estuary outfall). During the low precipitation summer, the sill is high and solid which causes the water level at the estuary to be higher than the sea level and prevents seawater entry to the estuary. On the other hand, during winter, the sill is destroyed by winter floods, the estuarine water level is lower, seawater enter the estuary, which elevates the salinity.

in short, Estuaries tend to be complex.....

I just recollected another impact of meteoric water into an esturay, namely that of pH-influence. Whereas the seawater in the estuary is expected to have a normal pH-value somewhere between 7.9 and 8.2, the addition of rainwater will impede this value. The pH of distilled water, e.g., rainwater (meteoric water) has a considerably less pH-value, perhaps even as low as 5.6 (at least here in Norway, where I live).

This means that during torrential rain, from a cyclone (low pressure) system, or even from a very large cumulunimbus cloud (thunder-cloud/super-cell/ anvil cloud), which is located and precipiting over your relatively small esturay (less than 10 sq km?), you can expect large (extreme) temporal deviations in pH-values in the upper meters of the estuary water column. The animals you observe, will most probably dive to deeper layers to prevent exposure to this temporal parameter deviation.

Soil salinity is a dynamic soil chemical property. It fluctuates depending on factors affecting sources of salinity and loss mechanisms. Seasonal climate is one factor.