Rivers play an important role in the coastal biogeochemical cycling of mercury (Hg), however, the fate of Hg in these environments remains poorly understood. In this study, we determine how processes such as mixing, flocculation, and settling of particles in the river mouths of the Vistula and the Reda rivers in the southern Baltic Sea, affect the transformation and migration of mercury. The most important process was the mixing of river water with seawater. This process led to a decrease in the concentration of total mercury and particulate mercury with increasing distance from the river mouth. The second most important process affecting the distribution of Hg was flocculation and particle settling. This process most effectively occurred in the middle part of the mouth, where the highest salinity gradient was observed. It was responsible for approximately 32% loss of Hg from the water column with a simultaneous increase in Hg concentration in sediments. In consequence, it significantly limited the transport of Hg to the open Baltic Sea. The assimilation of Hg by marine plankton was also observed. As riverine organic matter stimulated the growth of marine plankton, they actively accumulated Hg and then transferred this metal to the higher trophic level. In both of the river mouths the processes affected the fate of Hg in a similar way. We therefore concluded that the size of the river did not affect the Hg transformation in the river mouth. However, the area of the river catchment, depth of the mouth and hydrological conditions had a significant impact on Hg cycling in the coastal zone in the vicinity of the river mouth.

河流在汞 (Hg) 的沿海生物地球化学循环中发挥着重要作用，然而，人们对汞在这些环境中的归宿仍知之甚少。在这项研究中，我们确定了混合、絮凝等过程如何, 以及波罗的海南部维斯杜拉河和瑞达河河口的颗粒沉降影响汞的转化和迁移。最重要的过程是河水与海水的混合。这一过程导致总汞和颗粒汞的浓度随着距河口距离的增加而降低。影响汞分布的第二个最重要的过程是絮凝和颗粒沉降。这个过程最有效地发生在嘴巴的中部，在那里观察到最高的盐度梯度。它导致水柱中约 32% 的汞损失，同时沉积物中的汞浓度增加。因此，它极大地限制了汞向开阔的波罗的海的运输。海洋对汞的同化还观察到了浮游生物。由于河流有机质刺激了海洋浮游生物的生长，它们积极积累汞，然后将这种金属转移到更高的营养级。在两个河口，这些过程都以类似的方式影响了汞的归宿。因此我们得出结论，河流的大小不影响河口中汞的转化。但流域面积、河口深度和水文条件对河口附近海岸带汞循环有显着影响。