Intermittent Rivers as a Challenge for Freshwater Ecosystems Quality Evaluation: A Study Case in the Ribeira de Silveirinhos, Portugal

Intermittent rivers and streams are aquatic ecosystems that lose hydrological connectivity during drought periods. Anthropogenic pressures combined with climate change accelerate the spatial and temporal intermittency of these ecosystems, promoting alterations in ecology and ecosystem functions. This study aimed to assess the ecological status of Ribeira de Silveirinhos, located in the municipalities of Valongo and Gondomar (north of Portugal), using the metrics described in the Water Framework Directive. Thus, five sampling sites were selected along Ribeira de Silveirinhos. Sampling was done in three different periods, spring of 2019 and 2020, and autumn of 2019. At each site, physical and chemical water parameters were measured, and the benthic macroinvertebrates community was characterized. Physical and chemical parameters showed low pH values at upstream sites (where the dry phase occurs and is surrounded by Eucalyptus monoculture) and high concentrations of phosphorus at the downstream sites (subjected to several anthropogenic activities, iron waters, and agriculture). The macroinvertebrate community revealed low values of specific abundance and richness, especially during the dry period. Sensitive taxa (Ephemeroptera, Plecoptera, and Trichoptera) were negatively correlated with flow intermittency. Results showed that Ribeira de Silveirinhos is classified between poor and moderate in terms of ecological status. Intermittent streams are undervalued, so their protection is at risk. Thus, it is important to consider the specific ecological functioning of these ecosystems and to adjust the planning and management models in order to guarantee ecological quality and conservation processes.

Automated summary

This study assessed the ecological status of Ribeira de Silveirinhos in northern Portugal and found that anthropogenic pressures and climate change have led to changes in the hydrological connectivity and ecosystem functions of the river. The upstream areas, surrounded by Eucalyptus monoculture during drought periods, showed low pH values, while the downstream areas subjected to anthropogenic activities, iron waters, and agriculture had high concentrations of phosphorus. The macroinvertebrate community was also affected by the intermittency of flow. The results indicated that Ribeira de Silveirinhos had a poor to moderate ecological status. However, the protection of intermittent rivers and streams is often overlooked, highlighting the need to consider their specific ecological functioning and adapt planning and management models to ensure ecological quality and conservation processes.