Decomposing estuarine salt transport mechanisms following the salt front

As areas between open seas and landward located ports and cities, estuaries have a high ecological and social importance. In such areas, changes in salinity can have severe consequences. Hence, salt intrusion is an important parameter to understand and monitor. The unique ecosystem as well as the freshwater abstraction for e.g. agricultural irrigation or drinking water can suffer under increasing salt intrusion. 

A decomposition of the along-channel salt transport is a useful tool to understand the driving salt transport mechanisms as 
well as the impact of environmental changes. Cross-sectionally integrated as well as spatially resolved analyses have been performed and revealed insightful results.

However, to date these mechanisms are mainly analyzed at fixed geographic locations in the estuaries. Especially in tidal estuaries, however, the salt intrusion has a very high natural variability with tides and discharge shifting the salinity front on a kilometer scale. Therefore, fixed locations can experience a high salinity range, resulting in different salinity regimes. 
This makes it impossible to extract processes going on in the low salinity regimes that are critical for freshwater abstraction.

In this study, we address this issue by analyzing salt transport mechanisms following the salt intrusion front. 
We use a numerical model setup of the Weser River Estuary as an application for the decomposition method. This mesotidal estuary, located in
North-West Germany, connects the North Sea with major ports via a navigational channel. The channel is strongly influenced by anthropogenic measures like dredging.  Dredging can lead to a further landward salt intrusion. 
Here, we analyze the mechanisms driving the salt transport dynamics in critical low salinity areas and how a possible dredging scenario impacts those dynamics.