Vertical Transfer of Cd Content Between Two Parallel Currents in Opposite Motion

Abstract

Based on the investigation data about Cd in Jiaozhou Bay in August, 1992, we calculated the horizontal increase amount and vertical diluted amount of Cd content in surface and bottom layers from the southwest waters of the bay to the west waters of the bay mouth, and set up the model block diagram of horizontal and vertical changes of Cd content. The results present that in August, the absolutely increase amount of Cd content in surface and bottom layers was 0.16-0.34μg/L, and the relatively increase amount of Cd content in surface and bottom layers was 51.51-66.66%. In the waters of southwest bay and west bay mouth, Cd content in surface and bottom layers had absolutely vertical diluted amount of 0.24-0.42μg/L, and its relatively vertical diluted amount was 63.63-75.00%. In the horizontal migration process of Cd content in the surface and bottom layers, the horizontal increase amount of Cd content in the surface and bottom layers reached a relatively high level from the southwest of bay to the west of bay mouth. It reveals that in the bay waters, in the parallel and opposite movement of the two currents, the current entering into the bay carried a high value of Cd content, and the Cd content migrated from the water with high content to the water with low content through the diffusion and migration of Cd content. Moreover, the migration direction of Cd content was perpendicular to the parallel movement direction of the two currents. In this way, the low-value Cd content in the outward current was increased, and at the same time, the vertical diffusion, migration and settlement of the high-value Cd content led to the increase of the Cd content in bottom layer in the outward current. In the process of vertical sediment of Cd content in the surface and bottom layers, the current had a low value of Cd content in the bay waters, and the vertical diluted amount of Cd content in the surface and bottom layers reached a high level; in the bay mouth waters, the current had high Cd content, but the vertical diluted amount of Cd content in the surface and bottom layers was also very high. In conclusion, the vertical diluted amount of Cd content in the surface and bottom layers kept a high value regardless of whether the current left the bay or whether the current carried high or low Cd content.