# Continental seawater residence time can't exceed 57 years?

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Continental seawater residence time can't exceed 57 years?

Hi,

I'm using USEtox to calculate fate of metals in the continental seawater compartment. I want to adjust the residence time of continental seawater, to see how will the residence time affect Fate Factor of emissions received in seawater.

I looked into the model. The flow of global seawater to continental seawater is calculated from (Contiental seawater volumne) / (continental seawater residence time) - (waterflow from continental freshwater to seawater). When the continental seawater residence time exceed 57 years, this equation will give a negative value, which means there's only waterflow from continental seawater to global seawater, not vise verse. As a consequence, the fate factor of emissions received in global ocean becomes negative. In case of very low Kpss value (e.g. kpss=5), the fate factor of metals in continental seawater compartment also becomes negative.

Does this observation means that there's an upper limitation on the continental seawater residence time in USEtox??  How can I emplmente a seawater residence time longer than 57 years?

USEtox Team
Residence time of continental seawater

In USEtox, it is assumed that the seawater flow from continental to global scale is 1000 m3/s, assuming the volume of continental coastal seawater (Volume.w2R) to be 1E+11 m3 (i.e. the water volume of the southern North Sea), assuming a residence time of continental coastal waters of 365 days (1 yr, for the residence time of seawater in the southern North Sea), and a freshwater inflow (WATERflow.w1R.w2R) of 2200 m3/s (the discharge of the river Rhine into the southern North Sea).

The residence time of continental coastal seawater and the freshwater inflow can be adjusted and obtain adjusted values of the water outflow from the continental seawater compartment (into the global scale). In the official USEtox version, the water outflow becomes negative (leaving other parameters invariant), when the residence time is adjusted to a value greater than approximately 520 days (1.5 yr).

In general, we do not recommend to change the residence time of continental coastal seawater without simultaneously adjusting other model settings, particularly the corresponding volume and the freshwater inflow.