Department Surface Waters - Research and Management

Waterborne pathogens pose a serious threat to public health, emphasizing the need for reliable and efficient water treatment technologies. Wastewater treatment plants employ a range of processes to reduce microbial contamination, with membrane filtration emerging as a promising solution due to its ability to physically remove pathogens without the production of harmful chemical by-products. This study investigates the effectiveness of a gravity-driven membrane (GDM) filtration system for pathogen removal from wastewater and evaluates the associated public health risks with and without treatment. A quantitative microbial risk assessment model was employed to estimate infection probabilities for various waterborne pathogens. The results demonstrated a significant decrease in pathogen concentrations following treatment, with up to a 10⁴-fold reduction in norovirus infection risk. Three critical factors influencing membrane performance were identified: membrane integrity, pore size characteristics, and membrane fouling. Maintaining membrane integrity was found to be essential for ensuring consistent pathogen removal. While nominal pore size is commonly used to predict rejection efficiency, the overall pore size distribution was found to have a greater influence on virus retention. Additionally, although membrane fouling is often considered detrimental, it was shown to enhance virus removal by up to two orders of magnitude. These findings underscore the potential of GDM systems for effective virus removal and highlight the importance of proper membrane design, maintenance, and monitoring in ensuring long-term operational efficiency and maximizing public health protection in wastewater treatment applications.

Harmful algal blooms (HABs) caused by the dinoflagellate Alexandrium minutum can pose risks to human and ecosystem health. HABs of different species can coexist in coastal waters and accumulate near the shoreline, challenging their detection through Earth observation (EO). In this study, we use in situ geo-bio-optical and taxonomical data from the Rías Baixas (NW Spain) to develop a new method for identifying high-concentration blooms of A. minutum and its application to Sentinel-2 Multispectral Instrument (S2 MSI). Our approach named A. minutum index (AMI) was developed to capture the low absorption and high backscattering properties of A. minutum cells between 560 and 570 nm. We tested and validated the performance of three atmospheric correction algorithms (AC) (C2RCC, POLYMER and ACOLITE) using matchups between in situ and satellite-derived R_rs. Results show that C2RCC had the lowest error across most wavelengths. Applying AMI to S2 MSI indicates that our approach can accurately identify high-concentration blooms of A. minutum (F1 score: 70 %, Kappa: 68.3 %, balanced accuracy: 87.7 %, MCC: 68.3 %) and discriminate blooms of A. minutum from other phytoplankton species. We compared AMI with three existing indices for detecting HABs in coastal waters and found that our approach achieved a better performance, with the NDTI, RGCI and NDCI yielding F1 scores of 21.28, 21.74, and 0.0 % and MCC values of 15.0, 15.0 and 0.0 %, respectively. We also investigated the spatial resolution of S2 MSI to Sentinel-3 Ocean and Land Colour Instrument (S3 OLCI) for mapping fine-scale variations in A. minutum blooms. We found that the higher spatial resolution data from S2 MSI were highly useful for detecting small-scale variations in A. minutum in nearshore waters, enabling their detection in the mid-inner part of the Rías, where aquaculture activities are more prominent. This study also showcases the significance of accurate AC in near-shore waters, where high-concentration blooms can be more prevalent. Our findings show that greater errors in AC are observed in near-shore pixels, where the socio-economic and environmental impact of HABs are typically more severe.

Carbon dioxide (CO₂) fluxes in regulated Alpine rivers are driven by multiple biogeochemical and anthropogenic processes, acting on different spatiotemporal scales. We quantified the relative importance of these drivers and their effects on the dynamics of CO₂ concentration and atmospheric exchange fluxes in a representative Alpine river segment regulated by a cascading hydropower system with diversion, which includes two residual flow reaches and a reach subject to hydropeaking. We combined instantaneous and time-resolved water chemistry and hydraulic measurements at different times of the year, and quantified the main fluxes by calibrating a one-dimensional transport-reaction model with measured data. As a novelty compared to previous inverse modeling applications, the model also included carbonate buffering, which contributed significantly to the CO₂ budget of the case study. The spatiotemporal distribution and drivers of CO₂ fluxes depended on hydropower operations. Along the residual flow reaches, fluxes were directly affected by the upstream dams only in the first 2.5 km, where the supply of supersaturated water from the reservoirs was predominant. Downstream ofthe hydropower diversion outlets, the fluxes were dominated by systematic sub-daily fluctuations in CO₂ transport and evasion fluxes (“carbopeaking”) driven by hydropeaking. Hydropower operational patterns and regulation approaches in Alpine rivers affect fluxes and their response to biogeochemical drivers significantly across different temporal scales. Our findings highlight the importance of considering all scales of CO₂ variations for accurate quantification and understanding of these impacts, to clarify the role of natural and anthropogenic drivers in global carbon cycling.