Understanding the natural dynamics of estuaries and their response to changes in the human-related or climatic drivers is fundamental to guarantee their environmental quality. This study aims to contribute to a better understanding of the water quality dynamics in an urban estuary, the Tagus estuary (Portugal), across different temporal scales. This estuary supports diverse uses and activities and its ecological value is well recognized. Three field campaigns were performed covering distinct seasons (Spring, Summer and Autumn – 2018). Physical, chemical and biological data were measured along the estuary. The acquired data was then integrated into a set of indicators and compared with historical data, to assess the long-term evolution of the water quality in the estuary. Results showed marked spatial gradients, typically with larger concentrations of chlorophyll a, nitrate and silicate upstream. Silicate and nitrate presented a conservative behavior. Ammonium and phosphate were not conservative, which suggests an anthropogenic pressure along the estuary. Seasonally, the highest nutrients and suspended solids concentrations were found in Autumn, after a period of rainfall, pointing out to the relevance of land runoff for material supply into the estuary. These conditions were favorable for phytoplankton development upstream, once chlorophyll a was maximum during this campaign (24 μg/L in the upper estuary). Regarding the nutrients classification, results suggest that the upper estuary is at risk with a “Medium” status. The middle and downstream areas presented a “High” status, with the exception of the middle-right margin that is also at risk (“Medium” status). The assessment of the historical data suggests that high loads of nutrients have been reaching the Tagus estuary over time, with a decreasing trend in recent years. The trophic index (TRIX) suggests a “Moderate” trophic status in the middle and upstream areas of the estuary. As for nutrients, a “Poor” classification was obtained in the middle-right margin of the estuary, mainly due to ammonium concentrations, confirming an intensification of anthropogenic pressure at this site. Similarly to the nutrients status, TRIX suggests some improvement of the water quality in the Tagus estuary in recent years compared to the 1980s. These results provide further insight regarding the water quality dynamics in the Tagus estuary and are useful to support management.

了解河口的自然动态及其对与人类有关或气候驱动因素变化的响应，对于保证其环境质量至关重要。这项研究旨在帮助人们更好地理解城市河口塔霍河口（葡萄牙）在不同时间尺度上的水质动态。该河口支持多种用途和活动，其生态价值得到公认。在不同的季节（春季，夏季和秋季– 2018年）进行了三个野外活动。沿河口测量了物理，化学和生物学数据。然后将获取的数据整合到一组指标中，并与历史数据进行比较，以评估河口水质的长期演变。结果显示明显的空间梯度，a，硝酸盐和硅酸盐的上游。硅酸盐和硝酸盐表现出保守的行为。铵和磷酸盐并不保守，这表明沿河口的人为压力。在季节性降雨之后，经过一段时间的降雨，秋季的养分和悬浮固体含量最高，这表明土地径流与向河口的物质供应有关。这些条件有利于上游的浮游植物发育，一旦叶绿素a在此运动期间最大（最高河口为24μg/ L）。关于营养成分的分类，结果表明河口处于“中等”状态的危险。中部和下游区域显示为“高”状态，右中边距也处于危险状态（“中”状态）。对历史数据的评估表明，随着时间的推移，高含量的养分已进入塔霍河口，近年来呈下降趋势。营养指数（TRIX）表明在河口中上游地区的营养状态为“中等”。至于养分，主要由于铵盐浓度的影响，在河口右中边缘获得了“差”分类，这证实了该地点的人为压力增强。与营养状况类似，TRIX建议，与1980年代相比，近年来塔霍河口的水质有所改善。这些结果提供了关于塔霍河口水质动态的进一步见解，可用于支持管理。