Modeling Concepts - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 253

Salting factor for Darss-Zingst Bodden Chain and Vistula Lagoons

1.1

1

0.9

0.8

0.7

0.6

0.5

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Year

Vistula Lagoon Darss-Zingst Bodden Chain Lagoon

FIGURE 6.11 Seasonal variations of monthly average salting factor for two Baltic lagoons:
the Vistula Lagoon and Darss-Zingst Bodden Chain Lagoon.

The Grande-Entrée Lagoon can barely be distinguished from the open sea because it
has no river inflow and only receives a small freshwater volume through precipitation.
Both the Ria Formosa and the Mar Menor lagoons are examples of weak hypersaline
lagoons where evaporation exceeds both precipitation and river inflow. The Kara Bogaz
Gol Lagoon is a strong hypersaline lagoon where evaporation is extremely high.
The analysis of the temporal variation of the salting factor can be useful for
lagoons where freshwater inflow plays a significant role. For example, monthly
salting factors in the Vistula Lagoon over a year are presented in Figure 6.11. The
average annual salinity (2

÷ 5 psu) of this lagoon is less than that of the Baltic Sea

waters (6 8 psu). Even then, the salting factor indicates that the Vistula Lagoon

remains more influenced by the marine water than the land influx during the whole
year (0.5 < F s < 1). The salting factor for the Vistula Lagoon is characterized by one
spring minimum (maximum of river run-off, F s

÷

= 0.68) and one summer maximum

(before the rainy season, F s = 0.92). The salting proceeds very actively from May

to July. Smooth desalinisation then starts until an equilibrium is achieved between
the salting and refreshing processes in winter.
The next desalinization of the lagoon coincides with the beginning of the fresh
river run-off in spring. The temporal variation of the salting factor provides indica-
tions when two main processes, salting and desalinisation, are taking place.
Lagoons located in the same geographical conditions may express different behav-
ior in terms of these two processes. This is seen, for example, in Figure 6.11 showing
the salting factor for two Baltic region lagoons: the period of salting in the Darss-
Zingst Bodden Chain is longer than that in the Vistula Lagoon and there is no period
of equilibrium between the salting and desalination factors. The annual course for the
salting factor is also characterized by a minimum and a maximum in the Darss-Zingst
Bodden Chain Lagoon, but they are not as sharp as the corresponding extremes in the
Vistula Lagoon and they do not coincide with the peak in the river run-off.
The lagoon hydrological annual cycle can also be characterized by using a
temperature-salinity (T-S) diagram evolving with time ( Figure 6.12A) . This is useful