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[Study region]: Albaida Valley, Spain. [Study focus]: Rivers are experiencing a rapid biodiversity loss largely due to water quality degradation imposed by anthropogenic activities. To show the capability of modeling to inform water management at watershed scales, this research develops an eco-hydrological model of the Albaida Valley (Spain). SWAT (Soil and Water Assessment Tool) is used for modeling of discharge and nutrients after calibration with SWAT-CUP (SWAT Calibration and Uncertainty Program). Results from SWAT are coupled to regressions between nutrients concentrations and macroinvertebrate-based metrics obtained from field monitoring. The spatio-temporal assessment of ecological status of streams is then carried out using simulated chemical and biological quality indicators (nitrate, ammonium, phosphorus, and macroinvertebrates). [New hydrological insights for the region]: Management measures (e.g., improving treatment of wastewater and/or adopting policies for reducing fertilizer use) are needed as the ecological status of Albaida Valley rivers is mostly classified as poor because of nutrients pollution. The reasonably low uncertainty in the model prediction (expressed by R-factor: discharge (0.2–0.61), nitrate (0.79–1.27) and total phosphorus (0.8–1.68)) demonstrates the potential of the presented model for future applications (i.e., for investigating possible responses of the Albaida Valley ecosystem to changes in climate, land-use, and local management policies). The modeling approach provided in this study could be generally used as a complementary technique to field monitoring in assessing and managing ecological conditions of rivers.

Urban runoff negatively impacts the receiving streams and different solutions have been proposed in literature to limit the effect of urbanization on the water balance. These solutions suggest to manage urban runoff in order to switch from a post-development river hydrograph (high peak and short duration) back again to a pre-development hydrograph (low peak and high duration). Combined sewer overflows (CSOs) represent severe pollutant sources for receiving streams due to the combination of first flush of roads and sewers and black water conveyed by combined sewer systems. Constructed wetlands for CSO treatment (CSO-CWs) are adopted with increasing frequency for reducing pollutant inputs to streams. Moreover, these systems exhibit the characteristic to behave similarly to ponds, wetlands, and bioretention systems that provide flood mitigation by decreasing the intensity of peak flows. This work aims to show the additional ecosystem service provided by CSO-CWs in term of limitation of the hydraulic impact of CSO on stream hydrograph. A mathematical model is developed to simulate the hydraulic behavior of a real case study situated in Gorla Maggiore (Italy), which includes vertical flow subsurface beds (VF) as first stage and a free water surface bed (FWS) as second stage. The model simulates the unsaturated flow within VF and the accumulation of water on the top of VF and within FWS. Results show a satisfactory lamination performance of the system for both single and up to 5 consecutive flood events, with a peak flow reduction ranging from 52.7% to 95.4%. Withdrawn of flow rate from the river in order to cope with long dry period does not significantly affect the lamination performances. The considered CSO-CW exhibits an excellent lamination efficiency also during more intense floods events, with a peak flow reduction of 86.2% for a CSO event with return period of 10 years. The flow rate frequency density function determined by the CSO-CW is more shifted towards lower values compared to untreated CSOs. These results indicate that CSO-CWs work properly in terms of reduction of CSO urbanization impact on stream hydrology.

Interfaces between sediments and water bodies often represent biochemical hotspots for nutrient reactions and are characterized by steep concentration gradients of different reactive solutes. Vertical profiles of these concentrations are routinely collected to obtain information on nutrient dynamics, and simple codes have been developed to analyze these profiles and determine the magnitude and distribution of reaction rates within sediments. However, existing publicly available codes do not consider the potential contribution of water flow in the sediments to nutrient transport, and their applications to field sites with significant water-borne nutrient fluxes may lead to large errors in the estimated reaction rates. To fill this gap, the present work presents GRADIENT, a novel algorithm to evaluate distributions of reaction rates from observed concentration profiles. GRADIENT is a Matlab code that extends a previously published framework to include the role of nutrient advection, and provides robust estimates of reaction rates in sediments with significant water flow. This work discusses the theoretical basis of the method and shows its performance by comparing the results to a series of synthetic data and to laboratory experiments. The results clearly show that in systems with losing or gaining fluxes, the inclusion of such fluxes is critical for estimating local and overall reaction rates in sediments.

Recognizing greywater as a relevant secondary source of water and nutrients represents an important chance for the sustainable management of water resource. In the last two decades, many studies analysed the environmental, economic, and energetic benefits of the reuse of greywater treated by nature-based solutions (NBS). This work reviews existing case studies of traditional constructed wetlands and new integrated technologies (e.g., green roofs and green walls) for greywater treatment and reuse, with a specific focus on their treatment performance as a function of hydraulic operating parameters. The aim of this work is to understand if the application of NBS can represent a valid alternative to conventional treatment technologies, providing quantitative indications for their design. Specifically, indications concerning threshold values of hydraulic design parameters to guarantee high removal performance are suggested. Finally, the existing literature on life cycle analysis of NBS for greywater treatment has been examined, confirming the provided environmental benefits.

Although horizontal flow constructed wetlands (HF CWs) are usually subjected to unsteady loads in real application, the modelling of HF CW response to time-variable loads has been scarcely studied in literature yet. The aim of this study is to test the capability of HYDRUS-CWM1 to simulate the behavior of HF CWs subjected to unsteady loads. Hence, we applied HYDRUS-CWM1 to simulate laboratory results of HF CWs subjected to variable COD inflows. The modelling results adequately fit the experimental data, with an almost perfect agreement in global COD removal efficiencies (67 and 68% from laboratory experiments and simulations, respectively), and mean percent error equal to 20 and 31% for effluent COD and NH 4 + concentrations, respectively. The obtained results suggest that HYDRUS-CWM1 can be a powerful tool to simulate the response of HF CWs under time-variable loads. Additionally, more detailed data are shown to be crucial in order to better exploit process-based model tools.

Water losses, the portion of water introduced in a pipe network but not consumed by users, represent a significant problem in water distribution system (WDS) management. Modern guidelines suggest to divide the pipe network in clusters, in order to compute a water balance and measure water consumption by each group. These clusters are called district metered areas (DMAs). The division of a pipe network in DMAs is usually realized with a visual exam supported by technical experience. This approach, which is convenient for small WDSs, becomes difficult to apply to large WDSs characterized by thousands of user nodes and pipes. Therefore, it is necessary to have an automatic tool to recognize the affinity degree of neighbouring nodes and to decide how to assign a node to a particular DMA. We propose an automated approach to subdivide pipes, that only requires flow rates through the network. The method has been tested to a large WDS often used as benchmark. The approach successfully divides the pipe network in an acceptable number of DMAs. Each resulting DMA is characterized by a low number of external links and by a proper number of users.

Chlorine-based disinfection agents are known to favor the production of Disinfection By-Products (DBPs), whose concentrations are restricted by international guidelinesto ensure a safe consumption of drinking water. Hence, it is important to understand the behavior of DBPs within Water Distribution Networks (WDNs) to avoid exposure of WDN users to concentrations higher than guideline values. The buildup in chlorate concentration resulting from disinfectant reaction is here simulated with EPANET for two hypothetical WDNs. Results indicate that increases in chlorate concentrations within the WDN are very limited (

Microbial fuel cells (MFCs) are bioelectrochemical systems able to generate electricity from wetland soils, including paddies, exploiting the microbial decomposition of organic matter. Additionally, MFCs can also be applied as a novel mitigation strategy for emissions of methane (CH4) from paddy fields. The MFC efficiency in reducing CH4 fluxes is still poorly understood, and it is here investigated via a one-dimensional process-based model that simulates the vertical and temporal dynamics of the chemical compounds affecting CH4 fate within paddy soil. The DOC oxidation rate of MFC is modeled assuming a zero-order kinetics proportional to the generated electricity and different anode depths and current densities are tested. By assuming current densities presently achieved in paddies, MFCs are able to reduce up to −27.9%, −16.7%, and −22.0% of daily minimum, daily maximum, and total CH4 emissions, respectively. Moreover, CH4 reductions are even higher (up to −28.1%, −24.1%, and −26.5%) if we assume 5% of the current density developed on laboratory acetate-fed MFC. The system shows a limiting effect of transport processes on the mitigation of CH4 emissions at high current density. In order to maximize the reduction of CH4 emissions, simulation results suggest to place the anode in the middle portion of the superficial layer of paddy soil. The findings demonstrate the need to further investigate and develop this new technology for field-scale applications.

Summary The mixing of stream water and subsurface water in the hyporheic zone is an important function of fluvial ecosystems. Among the factors that drive water exchange between a stream and its sediments, turbulence is the most ubiquitous as rivers are always in turbulent flow regime. However, there is still much uncertainty about the role of turbulent processes in hyporheic exchange, probably because of the complex nonlinearities that characterize the dynamics of turbulent velocity and pressure fluctuations. In this paper, we adopt a numerical modeling approach to investigate the relationship between turbulent pressure properties and the resulting features of surface–subsurface exchange. In particular, we discuss the importance of large coherent structures of turbulence in driving exchange at depths that are much larger than the penetration depth of small turbulent eddies. The results of the numerical simulations elucidate the response of turbulent hyporheic exchange to changes in stream depth.

The interactions between the stream and the geomorphologic units that compose the stream channel result in an exchange of water, heat, and chemicals that is an important component of the flows of energy and nutrients in the river ecosystem. This exchange is characterized by complex spatial and temporal dynamics that depend on the characteristics of the stream flow and morphology. At present, many studies have addressed the development of spatial patterns of hyporheic exchange that are induced by many geomorphological factors at different scales. However, much less is known about the temporal evolution of the surface–subsurface exchange in response to the dynamics of the stream discharge. In order to investigate this problem, the present work analyzes the influence of streamflow variability on the hyporheic exchange induced by fluvial bedforms. A stochastic approach is employed to generate streamflow series whose statistical properties are representative of streams with different hydrological regimes. The resulting exchange fluxes and travel times are then computed, and the relationships between the streamflow regime and the dynamics of the exchange flux and travel times are investigated. The results show that the mean stream discharge can be used to estimate the average features of the temporal dynamics of hyporheic exchange. Moreover, exchange fluxes and residence times distributions exhibit significant fluctuations, which are tightly related to the coefficient of variation of the streamflow hydrograph.

The interaction between surface and subsurface water has a crucial influence on the biochemistry of stream environments. Even though the river discharge and the flow conditions can seldom be considered to be steady, the influence of this unsteadiness on the hyporheic exchange has often been neglected. In this work, a model for the study of hyporheic exchange during unsteady conditions has been developed. The model provides a sound analytical framework for the analysis of the effects of a varying stream discharge on the exchange between a stream and the hyporheic zone. The effects of the unsteadiness on the water exchange flux, the residence time of the solutes in the bed, and the stored mass are quantified. A synthetic example shows the substantial influence of a flood on the hyporheic exchange, and that the application of a steady model can lead to an underestimation of the exchanged mass, even after the flood has ended.

A stochastic model for the evolution of DO and BOD components along a river with independent BOD point inputs has been developed. The model examines the case in which the initial conditions and the concentrations of the inputs are affected by uncertainty. The uncertain quantities are modelled as random variables, for which any kind of probability distribution can be adopted. The possibility of separately analysing the different components of BOD (e.g., CBOD and NBOD) is included. A semi-analytical expression for the joint probability density function (pdf) of the concentrations is derived. The application of this relationship greatly reduces the computation efforts compared to Monte-Carlo methods. A procedure for the analytical determination of the concentration moments is also described.