The circulation in estuaries promotes the transport of organisms, nutrients, oxygen and sediments. Simultaneously, the mixture of fresh and salt water leads to variations of the physicochemical and biological components of the region. Therefore, it is important to further understand the hydrodynamic patterns of an estuary as one of the bases to understand the whole dynamic of these systems, ecologically important regions that must be preserved. However, little is known about the hydrodynamics of some estuarine systems. In order to bridge the knowledge gap about the Sado estuary, sampling was conducted with the purpose of evaluating some circulation patterns of the estuary and classifying it according to the stratification of the water column. The campaigns were conducted to collect monthly data on the intensity and direction of the currents, and on the temperature and salinity of the water column, between September 2018 and September 2019. The data indicated that water circulation in the Sado estuary, occurred through the two main navigation channels (North and South), according to the tidal regime. Both the temperature and the salinity were homogeneous along the water column, revealing little stratification. The analysis suggests possible hydrodynamic changes of the estuary in the past years.

中文翻译：

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温带河口系统中水流和水柱结构的变化（葡萄牙佐渡河口）

河口的循环促进了生物，营养，氧气和沉积物的运输。同时，淡水和盐水的混合物导致该区域的物理化学和生物成分的变化。因此，重要的是进一步了解河口的水动力模式，作为了解这些系统的整体动力的基础之一，这些系统是必须保留的重要生态区域。但是，对某些河口系统的流体动力学知之甚少。为了弥补关于佐渡河口的知识鸿沟，进行了抽样调查，目的是评估河口的某些环流模式，并根据水柱的分层对其进行分类。开展这些运动是为了收集有关潮流强度和方向的每月数据，以及在2018年9月至2019年9月之间的水柱温度和盐度方面。数据显示，根据潮汐政权，佐渡河口的水循环是通过两个主要的航道（南北）发生的。沿水柱温度和盐度均一，几乎没有分层。分析表明，过去几年河口可能发生水动力变化。