The growing demand for water resources associated with the increase in the world’s population has led to a global transformation of the landscape that has altered the structure and functioning of fluvial ecosystems. Intermittent streams located in the Mediterranean region are particularly vulnerable to human pressure because to a high variability on the hydrologic regime. This phenomenon is especially relevant in streams that receive effluents from sewage treatment plants (WWTP), since they have a low dilution capacity of the solutes from the effluent, mainly nutrients, and some emerging pollutants (pharmaceutical, pesticides and industrial chemicals). Most stream management strategies used to ameliorate stream water quality target reductions in inputs from terrestrial point sources (e.g., by Waste Water Treatments Plants, WWTP). However the efficiency of most WWTPs is limited and WWTP effluents may cause important imbalances on the C:N:P stoichiometric relationships in the receiving streams, which may have implications on their self-depuration capacity. In the case of dissolved organic carbon, not only the quantity but also the quality may importantly affect major biogeochemical processes. It is thus important to explore less-costly and more sustainable alternative management strategies . Additionally, despite the large amount of information related to nutrient dynamics in non-disturbed river basins, there is a lack in the understanding of these processes in urbanized river basins that makes difficult to develop adequate management strategies to control eutrophication problems, and emergent pollutants dispersion, which is a big challenge to face in such urbanized river basins. On the other hand, those effects of WWTPs effluents on stream or riparian biogeochemical processes could exhibit contrasted responses if different alluvial substrates are considered (i.e. calcareous as compared to siliceous ones) because chemical processes occurring under this two lithologies are different and may affect stoichiometric ratios of C:N:P. Given this context, this project aims to assess the biogeochemical reactivity of the riparian-stream ecosystems and how sensitive and resilient are to mitigate the impacts of WWTP effluents in intermittent fluvial networks. We propose different experimental actions to evaluate how efficient are the riparian zone, the riparian-stream interface and the stream in retaining and transforming dissolved organic carbon, nutrients (nitrogen and phosphorus) and emerging pollutants from WWTP effluent inputs. We will approach these questions in stream-riparian ecosystems draining catchments with contrasted lithology (siliceous and calcareous) since this can influence the biogeochemical response of the different ecosystems. We expect that the results derived from ECO-Reactors project will contribute to improve the management of the receiving stream ecosystems by considering the interaction between WWTP operation, effluent release, and the characteristics of the receiving ecosystems. Relevance of this Project is supported by the fact that results target at key issues considered in both national and international strategic plans for improvement of environmental standards as well as for more efficient use of good quality of freshwater under water scarcity.