## 3 Results
### Factors Controlling Pollution  
_Harbor-Bottom Cleaning_  
In general, the observed pollution level and spatial differences are influenced and/or controlled by the emission level, possible harbor-bottom cleanings, resuspension and reallocation of particles to other areas by wave action and bottom currents, and, last but not least, our data-collection methods. A survey and interviews with harbor managers were carried out to get an insight into harbor waste-management and the potential role of harbor-bottom cleanings. Only four surveys, including additional interviews, were obtained. In Strande, Germany, and Marina Cap Monastir, Tunisia, floating litter is removed with nets; in Yasmine Hammamet, Tunisia, floating litter is removed manually; and Schilksee, Germany, uses a Seabin. All four harbors have appropriate waste-collection systems in place, and floating litter appears to be removed as needed. Two interviewees mentioned direct rainwater-outlets discharging into the harbor. Kiel and Rostock have combined sewer systems [44]. Wastewater and stormwater are treated jointly in wastewater-treatment plants and discharged into different parts of the city harbors. Heavy rains can temporarily cause sewer overflows and the discharge of untreated water. For other harbors, such as Bizette, it is known that wastewater can enter the harbor temporarily. This means that wastewater-and-stormwater discharge can potentially play a role in harbor-bottom pollution. Hygienic items, such as cotton bud sticks, can be indicators of untreated sewage water. However, a detailed analysis of all items for each harbor does not indicate an important role of untreated sewage on sea-bottom pollution. None of the interviewees were aware of any harbor-bottom cleaning. It seems that harbor-bottom cleaning is rare and most likely does not influence our data collection and the observed sea-bottom pollution. ### Factors Controlling Pollution  
_Litter Resuspension and Reallocation_  
The observed pollution levels potentially might be affected by resuspension and reallocation of pieces by wave-induced turbulence and currents. This question can be addressed exemplary with 3D hydrodyamic model simulations. Further, the simulations provide an insight into the spatio-temporal behavior of sinking litter, especially plastic. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & \multicolumn{6}{c}{**Plastic**} & & & & \\
**Location** & **Cigarette But** & **Undefined Iter** & **Rope** & **Reetiles** & **Bag** & **Bottle** & **Metal Can** & **Glass Bottle** & **Wood, Paper etc.** & **Total** \\ \hline
**Germany** & & & & & & & & & & \\ City harbors & 36 & 18 & 24 & 5 & 0 & 3 & 5 & 22 & 113 \\ Sport & 2 & 5 & 9 & 0 & 0 & 0 & 1 & 4 & 21 \\
**Egypt** & & & & & & & & & \\ City harbors/marina & 0 & 11 & 3 & 4 & 1 & 0 & 0 & 7 & 26 \\ Tunisia & & & & & & & & & \\ City har- & 48 & 23 & 69 & 17 & 20 & 21 & 8 & 35 & 241 \\bors/marina & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Item distribution in the marina-bottom marine-litter screening. Figure 4 shows the transport of hypothetical litter emitted to the sea during the Hanse Sails in August. As said before, it can be assumed that the Hanse Sail is a major pollution event. The Hanse Sail years 2009 and 2010 show contrasting wind directions and wind speeds temporally exceeding 7 m/s (4 Beaufort; moderate breeze). The wind velocities in 2009 and 2010 were above the average that is usually observed during Hanse Sails. Therefore, it can be expected that the transport was more intensive compared to common Hanse Sail years. The model simulations for Hanse Sails 2009 and 2010, do not indicate any significant transport of particles deposited on the sediment. Some of the emitted particles are transported along the shoreline and remain in the city-harbor area. Under normal summerly wind conditions, resuspension and reallocation of particles at the bottom does not play a  
Figure 4: **(a) Wind speed and direction during Hanse Sail 2009 which lasted from 6 th to 9 th August.