---

Aims: This research aimed to evaluate the spatial patterns of water quality and its controlling factors in the Mazandaran coastal ecosystem during winter using the multivariate analysis methods.
Materials and methods: Water quality parameters such as nutrients, temperature, conductivity, salinity, DO, pH, chlorophyll-a and turbidity were measured monthly in 16 stations (44 layers) along 4 transects (Amirabad, Babolsar, Noushahr and Ramsar). To evaluate the data, several multivariate statistical methods were used including discriminant function analysis, cluster and factor analysis as well as correlation test.
Findings: Results of cluster analysis showed that the sampling sites (44 layers) were classified into 4 groups. Based on discriminant analysis, 93.20% of the sampling sites correctly classified. Factor analysis extracted 4 principal components that explained 74.05% of the total variance. Based on these analyses, organic phosphorus, organic nitrogen, turbidity, chlorophyll-a and temperature were the most effective parameters on the spatial variation of water quality.
Conclusion: This study suggested that the number of sampling locations could be reduced to 3 transects including Amirabad, Babolsar and west coasts (Noushahr and Ramsar) and 2 stations (one surface layer and one deep layer). Transport of nutrients from land, sea floor and fish cage culture were the most effective factors on spatial patterns of water quality in Mazandaran coasts. Based on the results, multivariate statistical methods are also introduced as one of the useful methods for identifying the spatial pattern of water quality.

---

Aims: In the present study, a three-dimensional numerical hydrodynamic model with the capability to simulate the diffusion of chemical pollutants released in marine basins was developed and used as a case study to simulate the diffusion of phosphate released by fish culture cages located in the Sisangan marine basin.
Materials & Methods: The equations of the model including momentum equations, continuity of mass equation, temperature, salinity, representative of vertical velocity, the tendency of bottom pressure equations and an extra three-dimensional advection-diffusion equation for simulation of pollutant’s diffusion rewritten in the earth’s spherical coordinates with a vertical Sigma coordinate were solved using finite difference method. To provide the open boundary conditions, the model was used for simulation of wind driven currents in the Caspian Sea from 20 October 2018 to 20 May 2019. For the application of wind field and real geometric condition, it was used the time series of wind fields supplied by ECMWF reanalysis dataset and GEBCO bathymetry with 0.125 degrees resolution and 15 seconds of geographical resolution, respectively.
Findings: Considering the concentration of 17ppb for the phosphate as a concentration of pollutant in the source of the pollution in the location of the fish culture cages, wind induced currents and the diffusion of the phosphate were simulated for 8 months in both horizontal and vertical directions. The results of the simulations were demonstrated and analyzed within the framework of the horizontal surface current, distribution of the phosphate’s concentration in both horizontal and a vertical latitude-depth cross section.
Conclusion: The phosphate’s diffusion is affected by the wind induced currents and after 8 months, it could be extended to the distance of 11, 8.5, 9.5, and 5.7 kilometers far from the cages in eastern, western, southern, and northern directions, respectively. With the generation of vertical velocity and the turbulence effects in the upper layers, phosphate might be diffused in the vertical direction up to 400m depth, as well.