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Mixing between water column and sediment is a crucial physical process for the fate of nutrients and for the biogeochemical reactions in the stream ecosystem. There are two factors that characterize this mixing process: the mixing magnitude at the sediment water interface, which controls the amount of solutes exchange between water column and its underlying sediment layer; and the mixing extent that defines how quickly the mixing rate decays with depth of the sediment laye. The vertical mixing process has been shown to be well represented by a 1-D equivalent diffusivity model with exponentially decaying profile in the vertical direction. This exponential profile is controlled by two parameters: the effective diffusion at the sediment water interface, that is equivalent to the mixing magnitude, and the decay coefficient of the exponential, that represents the reciprocal of the mixing extent.The 1-D diffusivity model was applied to a large dataset of experiments from literature that were conducted with conservative solutes on three different morphology types: flat beds, dunes and ripples, and alternate bars. The mixing magnitude and extent appears to be the largest in alternate bars, the smallest in flatbed and intermediate in dunes and ripples. Afterwards, the dependence of the mixing magnitude and mixing extent on stream and sediment characteristics was studied to derive a regression model to infer the values of the mixing controlling parameters from stream and sediment characteristics. This regression model was developed in dimensionless form using the Multiple Linear Regression (MLR) technique. The regression formulae demonstrate no dependence of the mixing magnitude on morphology type, while it is significantly correlated to the permeability Reynolds number (Re_k) that depends on sediment permeability, shear velocity and water viscosity. On the other hand, the mixing extent of solutes within the benthic biolayer can be categorized based on the morphology type. Specifically, for flat beds the mixing extent exhibits different trends of dependance on the permeability Reynolds number due to the dominance of different physical process for each interval of Re_k. Instead, for dunes and ripples the mixing extent is monotonically correlated to the bedform (ripple or dune) wave number, as expected from literature. Finally, due to the limited number of experiments on alternate bars we were not able to derive a robust and reliable regression formula for this morphology type. Therefore, more experiments under different conditions should be performed with alternate bars. These results help to unravel the influence on mixing processes of different characteristics of streams and their sediments.

Water scarcity and sanitation are two challenges deeply related to urbanization and climate change. Thus, the future development of urban areas requires innovative design solutions to increase cities’ resilience (SDG11), looking for new resources. One answer is the use of nature-based solutions (NBS) for wastewater treatment, to provide multiple benefits while transforming a waste into a new resource. Green walls for greywater (GW) treatment are the NBS that converts the unused vertical facades into important ecosystem services, treating the amount of domestic wastewater that excludes the toilet flush. To better understand the removal processes and improve green walls design, pilot studies have been performed in recent years, usually in controlled conditions. However, it is important to evaluate also the influence of more real operating conditions that can stress the biological component or damage the whole system, affecting the effectiveness of the GW treatment.This study aims to test stressing conditions due to chemical loads caused by variations in GW composition. Fifteen identical vegetated pots have been filled with a mix of coconut fibre and perlite (1:1 in volume) and one Hedera helix per pot. Every pot received 24 L day-1 of standard GW (Diaper et al., 2008), provided in 15-minute batches every hour (HLR=740 L m-2 day-1). The pots were organised in 5 configurations (3 pots each as replicates) and four of them received periodic spikes of modified GW: (i) – always standard GW as control (ii) bleach, (iii) floor cleaner, (iv) drain opener, (v) sodium hydroxide added to the standard recipe at increasing concentrations. The concentration was selected simulating the common use of these cleaning products in buildings, provided with wastewater collecting tanks of different sizes, resulting in (a) 500 ppm for (ii-iv) and 100 ppm for (v); (b) 1000 ppm for (ii-iv) and 200 ppm for (v); (c) 2500 ppm for (ii-iv) and 500 ppm for (v). The input and output water were weekly sampled from May 2022 and different parameters (pH, Temperature, Electric Conductivity, Dissolved Oxygen, Biochemical Oxygen Demand - BOD5, Chemical Oxygen Demand - COD, Sulphate, anionic surfactants - MBAS) have been measured to evaluate the effects on biological systems (plants and biofilm) through their removal performance.Results showed that all configurations were not damaged by load events (a) and (b). Experiments on high chemical load (c) are still ongoing. The plants’ health was generally similar for all configurations and removal performances for BOD5, COD and MBAS were good for all configurations.

Streams can carry and spread numerous pathogen species, either free floating or attached to the surface of fine particles. These pathogens can pose serious threats to human health in places where untreated water is directly consumed or by contact with the water when using for recreation, washing or irrigation purposes. The most important sources of pathogens to streams in urbanized catchments are wastewater treatment plants that continuously release wastewater effluent, which is still infectious. Moreover, untreated wastewater is also discharged to streams through combined sewer overflows during heavy rain events, resulting in the release of high loads of pathogens. Once pathogens are introduced to a stream from these sources, their fate is controlled not only by transport in surface water but also by exchange with streambed sediments. Within streambeds, pathogens are subject to a complex array of processes that include seepage transport, sorption to sediment surface, and decay, with some pathogens being eventually released back to surface water. Recently, a model for stream transport of pathogens has been developed that is based on the Continuous Time Random Walk (CTRW) framework. This model describes the stream corridor as the interaction of a mobile and immobile zones, and a few applications to pathogen transport have been discussed in the literature. This contribution will present an application of this model approach to predict the fate of pathogens in an urban stream in Vienna. The model application will be tailored to work with the uncertainty that typically affects the information that is available in these situations. Thus, stochastic boundary conditions will be applied to consider the variability of pathogen loads to the stream, and model parameters will be calibrated on available concentrations of C. perfringens spores (used as conservative microbial tracer for municipal sewage) and the human genetic fecal marker HF183/BacR287, and eventually validated based on concentrations of the reference pathogens Cryptosporidium and Giardia, observed at the catchment outlet.

In this study, we describe a sustainable system for treatment and reuse of grey wastewater in urban areas through vertical green walls constructed on unused surfaces of buildings. The system integrates the benefits linked to the introduction of green spaces in urban areas with the advantages connected with the reuse of purified greywater (non-potable reuse) and the reduction of potable water use, allowing a sustainable use of water resources. We constructed a vertical green wall composed of modular panels with 12 vegetated pots per panel. The green wall was irrigated with synthetic greywater, and the removal efficiency was monitored weekly with regards to different parameters (e.g., BOD5, COD, nitrogen, phosphorus). The results showed good results in terms of treatment performances, indicating the suitability of the green wall for treatment of greywater.

The hyporheic exchange below dune-shaped bedforms has a great impact on the stream environment. One of the most important properties of the hyporheic zone is the residence time distribution (RTD) of flow paths in the sediment domain. Here, we evaluate the influence of dimensionless sediment depths d b * = 2 π d b / λ where λ is the dune wavelength and different values of dimensionless groundwater underflow values u b * (similar to dune migration celerity), on the shape of the hyporheic exchange RTD. Empirical RTDs were generated, over a range of combinations between d b * and u b * values, from numerical particle tracking experiments in which 10000 particles were released over a flat domain. These empirical RTDs are represented by different distributions over the range of d b * and u b * . A Fréchet RTD is the best fit for deep beds ( d b * >3.2) and negligible underglow ( u b *

Green and blue infrastructures are an innovative solution to contrast climate changes (SDG 13 of UN 2030 Agenda) and increase cities resilience (SDG 11), using a smarter water management that transform wastewater into a new resource for non-potable reuses. Due to the lack of horizontal surfaces in urban areas, green walls are one of the most suitable nature-based solution to treat greywater (i.e. the portion of household wastewater that exclude toilet flush and kitchen sink). Green walls allow for a multidisciplinary approach, providing multiple benefits such as thermal and acoustic regulation, biodiversity preservation, decreasing heat islands effects and removing CO2, improving life quality and buildings value.Green walls have also been proposed for treating the large amount of greywater that is daily produced (e.g. around 100 L/PE/die in Italy), an approach that also provides urban green while reducing the need of irrigation water. Following previous work on a pilot system, this study aims to improve the green walls design and test its resilience to variations in the flow rate of greywater fed to the green wall. Two panels have been built in which synthetic greywater flows by gravity along three levels of pots with different plant species. The 18 pots (arranged in a 3x3 matrix in each panel) have been filled with a mix of coconut fibre and perlite (1:1 in volume) and fed with greywater, and output water samples have been collected almost weekly from June to December 2021. The control panel has been regularly fed with 24 L/die/col (standard flow rate), the other has been fed with different flow rates (standard, underflow, overflow and maintenance) that usually changed after three weeks. Different parameters (e.g. TSS, BOD5, COD, DO, TN, TP, MBAS), have been monitored in the outflow of each pot and average performances of each level has been evaluated. Results indicate a good efficiency of the green wall in removing contaminants even when the provided flow rate is not constant.The treatment performances increase along the columns in both panels and the first two levels guarantee a good compounds removal during standard flow and underflow rates. On the other hand, the overflow rate caused a performances decrease in the variable flow panel for many parameters, followed by a visible plant stress. However, one week of standard flow rate was sufficient to reduce the negative effects of the three- weeks-overflow. This demonstrated the resilience of the green wall facing flow variability, that can be caused by seasonal variation or system failure.

Stream dunes have been widely recognized among the major morphological features driving water exchange between a stream and its sediments, and many modeling studies have been performed to characterize hyporheic exchange induced by this type of bedforms. Despite of these efforts, the high number of factors that affect hyporheic exchange has not been completely addressed yet, mainly because of the simplifying assumptions that are unavoidably required to reduce the complexity of the problem. For instance, the effect of the limited extent of the thickness of the sediment layer on the Residence Time Distribution (RTDs) of hyporheic exchange has not been fully explored. This incomplete knowledge is particularly relevant due to the paramount role of RTDs in controlling biogeochemical reactions in microbiologically active sediments.In this context, this study presents a modeling analysis of RTDs in dune-shaped streambeds of finite depth in the presence of groundwater flow. Numerical simulations of particle tracking have been performed to determine the combined influence of sediment depth and horizontal underflow on the shape of RTDs. Moreover, different analytical distributions (Exponential, Gamma, LogNormal, Fréchet) have been fitted to the numerical RTDs, and the best distribution for each range of dimensionless sediment depth and underflow velocity have been identified on the basis of Anderson-Darling tests.

The hyporheic exchange below dune-shaped bedforms has a great impact on the stream environment. One of the most important properties of the hyporheic zone is the residence time distribution (RTD) of flow paths in the sediment domain. Here we evaluate the influence of an impervious layer, at a dimensionless sediment depth of db*=2πdbλ where λ is the dune wavelength, on the form of the hyporheic exchange RTD. Empirical RTDs were generated, over a range of db*values, from numerical particle tracking experiments in which 10000 particles sinusoidally distributed over a flatbed domain were released. These empirical RTDs are best represented by the Gamma, Log-Normal and Fréchet distributions over normalized bed depth of 0<=db*≤1.2,1.23.1, respectively. The depth dependence of the analytical distribution parameters is also presented, together with a set of regression formulae to predict these parameters based on db*with a high degree of accuracy (R2>99.8%). These results contribute to our understanding of the physical and mixing processes underpinning hyporheic exchange in streams and allow for a quick evaluation of its likely impact on nutrient and contaminant processing (e.g., based on the magnitude of the Damköhler number). Keywords: Dunes, bedforms, residence times distribution, sediment depth effect, Hyporheic residence times, analytical representation, two parametric distributions, Damköhler Number.

In this session speakers will present their research covering a range of topics within the Nature-based solutions theme including, agriculture, biodiversity, REDD+, off-setting and water management.

The simultaneous identification of location and source release history in complex river networks is a very complicated ill-posed problem, particularly in a case of multiple unknown pollutant sources with time-varying release pattern. This study presents an innovative method for simultaneous identification of the number, locations and release histories of multiple pollutant point sources in a river network using minimum observation data. Considering two different type of monitoring stations with an adaptive arrangement as well as real-time data collection at those stations and using a reliable numerical flow and transport model, at first the number and suspected reach of presence of pollutant sources are determined. Then the source location and its intensity function is calculated by solving inverse source problem using a geostatistical approach. A case study with three different scenarios in terms of the number, release time and location of pollutant sources are discussed, concerning a river network with unsteady and non-uniform flow. Results showed the capability of the proposed method in identifying of sought source characteristics even in complicated cases with simultaneous activity of multiple pollutant sources.

In karst catchments, aquifer recharge occurs through a composite mosaic of subsurface flow paths. Precipitation infiltrates in the subsurface and flows along a complex network of fractures – that are characterized by different sizes and degrees of saturation – before eventually reaching the catchment outlet. The discharge of a karst spring is the result of the contributions of these flow paths, that may differ widely in terms of lengths, velocities, and travel times. Monitoring the spring discharge can thus provide information about flow within the aquifer. In particular, the spring discharge signal can be interpreted as the lagged response of the aquifer to precipitation inputs over the catchment, with the aquifer being characterized by a distribution of response times that relates input (precipitation) to output (discharge). Identifying these response times is not a trivial task as the input-output problem is often mathematically ill-posed, which leads to amplification of the errors and may prevent finding a physically meaningful solution.In this work we propose a method to evaluate the distribution of response times of a karst aquifer. The method, that was originally developed to deal with ill-posed problems in geostatistical applications, relies on a probabilistic description of precipitation inputs and discharge outputs, and it provides an estimate of the response time distribution and of its uncertainty. The method is here tested through the application to two datasets collected in two cave systems in Northern Italy (the Bossea system and the Vene/Fuse system) with different hydrogeological properties. The results demonstrate that the method successfully identifies different response time distributions that reflect the differences in aquifer characteristics of the two systems. Furthermore, differences among response time distributions relative to different precipitation events in each system provide valuable insights on seasonal variations in aquifer recharge and fracture saturation. The method can hence be applied as a tool for the indirect investigation of karst systems.

According to the European Research and Innovation Policy Agenda, nature-based solutions (NBSs) are key technologies to improve the sustainability of urban areas. Among NBSs, green walls have been recently studied for several applications, among the others the treatment of lowly polluted wastewater flows as greywater (GW, e.g. domestic wastewater excluding toilet flushes). This work is aimed at the evaluation of the influence of four additives (compost, biochar, granular activated carbon, polyacrylate) mixed with a base filter medium made of coconut fibre and perlite, on the performances of a green wall fed in batch mode with synthetic GW. The green wall was operated with a high hydraulic loading rate of GW (740.8 L/m2/day) in open-air winter conditions (3.5–15 °C measured for GW) between January and April. The performances of the green wall have been assessed though the monitoring every 1–2 weeks of physicochemical and biological parameters (pH, electric conductivity, total suspended solids, dissolved oxygen, BOD5 and COD, nitrogen and phosporus compounds, chlorides and sulphates, anionic surfactants and E. coli). Removal performances were excellent for BOD5 (>95%) and E.coli (>98%) for all additives; compared to the base medium, biochar was the best performing additive over the highest number of parameters, achieving removals equal to 51% for COD, 47% for TKN and nitric nitrogen and 71% for anionic surfactants. Compost also achieved high removal performances, but the frequent clogging events occurred during the monitoring period do not make its use recommendable. Granular activated carbon and the combination of biochar and polyacrylate performed better than the base medium, but only about the removal of nitric nitrogen. These results demonstrated that, in the considered experimental boundaries, biochar could improve the overall treatment performances of a green wall fed by GW and operated in challenging conditions.

In-stream environments, many biogeochemical processes occur in the benthic biolayer, i.e., within sediments at a very shallow depth close to the sediment-water interface (SWI). These processes are important for stream ecology and the overall environment.Here, a 1D diffusive model is used to analyze the vertical exchange of solutes through the SWI and in the benthic biolayer. The model is applied to an extensive set of previously published laboratory experiments of solute exchange with different bed morphologies: flatbeds, dunes, and alternate bars. Although these different bed features induce mixing that is controlled by different physical processes at the SWI, overall mixing within the sediment is well represented by a parsimonious diffusive model, provided that the diffusivity profile declines exponentially with sediment depth.For all morphology types, mixing is better simulated by an exponential diffusivity model than a constant diffusivity approach. Two parameters define the exponential diffusivity model; the effective diffusivity at the SWI, and a depth scale over which the exponential profile decays. Using a combination of classification and regression trees (CART) and multiple linear regression approaches, we demonstrate that a single predictive model captures measured variability in the effective diffusivity coefficient at the SWI across all morphological types. The best predictive model for the decay depth scale, on the other hand, is tailored to each morphological type separately.The predictive framework developed here contributes to our understanding of the physical processes responsible for mixing across the SWI, and therefore the in-bed processes that contribute to the biogeochemical processing of nutrients and other contaminants in streams.

Graywater (GW), i.e., the portion of household wastewater that excludes toilet flushes, is an interesting wastewater type because it requires only mild treatment. Green walls have been proposed as ...

Many water quality and ecosystem functions performed by streams occur in the benthic biolayer, the biologically active upper (similar to 5 cm) layer of the streambed. Solute transport through the benthic biolayer is facilitated by bedform pumping, a physical process in which dynamic and static pressure variations over the surface of stationary bedforms (e.g., ripples and dunes) drive flow across the sediment-water interface. In this paper we derive two predictive modeling frameworks, one advective and the other diffusive, for solute transport through the benthic biolayer by bedform pumping. Both frameworks closely reproduce patterns and rates of bedform pumping previously measured in the laboratory, provided that the diffusion model's dispersion coefficient declines exponentially with depth. They are also functionally equivalent, such that parameter sets inferred from the 2D advective model can be applied to the 1D diffusive model, and vice versa. The functional equivalence and complementary strengths of these two models expand the range of questions that can be answered, for example, by adopting the 2D advective model to study the effects of geomorphic processes (such as bedform adjustments to land use change) on flow-dependent processes and the 1D diffusive model to study problems where multiple transport mechanisms combine (such as bedform pumping and turbulent diffusion). By unifying 2D advective and 1D diffusive descriptions of bedform pumping, our analytical results provide a straightforward and computationally efficient approach for predicting, and better understanding, solute transport in the benthic biolayer of streams and coastal sediments. U.S. NSFNational Science Foundation (NSF) [1840504, 1830172]; Virginia Tech's ICTAS EFO Opportunity Seed Investment Grant; UC Office of the President [MRP17-455083]; Compagnia di San Paolo awardCompagnia di San Paolo; U.S. DOE Biological and Environmental Research (Subsurface Biogeochemistry Research Program)United States Department of Energy (DOE); U.K. EPSRC Established Career FellowshipEngineering & Physical Sciences Research Council (EPSRC) [EP/P012027/1]; Australian Research Council (ARC) Discovery Projects funding schemeAustralian Research Council [DP120102500]; Geological Survey Water Availability and Use Science Program Funding included U.S. NSF (1840504), Virginia Tech's ICTAS EFO Opportunity Seed Investment Grant, and UC Office of the President (MRP17-455083) awards to S. B. G.; a Compagnia di San Paolo award to A. M. and F. B.; a U.S. NSF (1830172) and U.S. DOE Biological and Environmental Research (as part of the Subsurface Biogeochemistry Research Program) award to J. G.; a U.K. EPSRC Established Career Fellowship (EP/P012027/1) to I. G.; an Australian Research Council (ARC) Discovery Projects funding scheme (DP120102500) to M. G.; and support from the Geological Survey Water Availability and Use Science Program to J. H. The authors thank Andrea Bottacin-Busolin, two anonymous reviewers, and the Associate Editor for their helpful review of the manuscript, E. Gee and L. Grant for assistant with Figures 1 and 7, respectively, and M. Rippy and S. Bhide for edits. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

In this paper we develop and test a rigorous modeling framework, based on Duhamel’s Theorem, for the unsteady one-dimensional transport and mixing of a solute across a flat sediment-water interface...

Many of the most important ecosystem services performed by streams occur in the benthic biolayer, the biologically active upper layer of the streambed. Here we develop and test a rigorous modeling framework for the unsteady one-dimensional transport and mixing of a solute in the benthic biolayer of a turbulent stream. Our framework allows for depth-varying diffusivity profiles, accounts for the change in porosity across the sediment-water interface and captures the two-way feedback between evolving solute concentrations in both the overlying water column and interstitial fluids of the sediment bed. We apply this new modeling framework to an extensive set of previously published laboratory data, with the goal of evaluating four diffusivity profiles (constant, exponentially declining, and two hybrid models that account for molecular diffusion and enhanced turbulent mixing in the surficial portion of the bed). The exponentially declining and enhanced mixing profiles are superior and their reference diffusivities scale with a dimensionless measure of stream turbulence and streambed permeability called the Permeability Reynolds Number, ReK. The dependence on ReK changes abruptly at ReK = 1, reflecting different modes of mixing below (dispersion) and above (turbulent diffusion) this threshold value. Because our modeling framework can be applied to open systems, it should inform the prediction and management of pollutant migration through a diverse array of aquatic ecosystems.

Exchange of water and nutrients between a river and the surrounding hyporheic zone is controlled by multiple factors, including river morphology, streamflow variability, connection with groundwater, and sediment properties. Among these factors, the heterogeneity of river sediments is known to strongly affect the fate of nutrients exchanged with the hyporheic zone, but this influence has received relatively little attention compared to other factors. Moreover, sediments are heterogeneous in terms of both physical properties (i.e., hydraulic conductivity) and chemical composition (e.g., organic carbon content), but studies about heterogeneity have mostly focused on variations of hydraulic conductivity compared to the variations of chemical properties of sediments.This contribution presents a modeling analysis of the influence of physical and chemical heterogeneity of alluvial sediments on lateral hyporheic exchange in meandering rivers. Sediments are treated as a binary mixture of mineral sand and organic silt, and a coupled hydraulic and biogeochemical model is employed to simulate the effect of different silt/sand ratios on exchange and reaction of organic carbon, oxygen, nitrate, and ammonium. Model results show that sediments with higher content of silt are characterized by lower exchange fluxes, but their higher carbon availability fosters higher rates of biochemical reactions and hence leads to higher nitrogen removal by net denitrification. These results indicate the importance of improving the description of sediment heterogeneity in modeling studies of hyporheic exchange.

We investigated the impact of intermittence in previously-perennial Alpine stream reaches, targeting the role of the hyporheic zone in increasing the resilience of these aquatic systems. We selected a perennial and an intermittent site in a reach of the Po River (North-Western Italy). We installed piezometers reaching &minus, 1 m (permanent and intermittent site), and &minus, 3 m (intermittent site) and monitored three supraseasonal droughts over a period of three years. We classified the hyporheic fauna into three categories of increasing affinity to life in the hyporheic (stygoxene, stygophile, stygobite), and used communities composition, abundance, beta-diversity and functional groups: (1) to compare assemblages at the same depth but with different hydrological characteristics, as well as assemblages from two depths at the intermittent site, and (2) to assess how the connection with surface water and the direction of the vertical aquifer flow determined the faunistic assemblages. Different taxonomic groups responded differently to intermittence, the hyporheic zone acted as a refuge increasing the resilience of the system, but resilience decreased with increasing degree of affinity to hyporheic life. Disentangling the effects of intermittence on the different faunistic component in the hyporheic zone can help guiding effective protection and restoration measures of river systems with temporary reaches.

The Impacts of Water Quality Changes on Aquatic Ecosystems: A Case Study of Clariano River, Spain Hamed Vagheei1, Paolo Vezza2, Guillermo Palau-Salvador3, Fulvio Boano4PhD Student, the Polytechnic University of Turin, hamed.vagheei@polito.it Assistant professor, the Polytechnic University of Turin, paolo.vezza@polito.it Associate Professor, the Polytechnic University of Valencia, guipasal@agf.upv.es Associate Professor, the Polytechnic University of Turin, fulvio.boano@polito.it AbstractWater quality degradation resulting from different anthropogenic activities such as agriculture, deforestation and urbanization is a serious worldwide challenge which have negative impacts on aquatic ecology. Unfortunately, it is still difficult to quantitatively determine the impacts of water quality changes on aquatic communities. The objective of the present research activity is to investigate aquatic ecosystem responses to water quality deterioration using a case study of Clariano River, Spain. The Clariano River faces low water quality and the loss of biodiversity in some parts as a result of agricultural, industrial and livestock activities as well as wastewater treatment plants (WWTP) effluents entering the river. The Soil and Water Assessment Tool (SWAT), an eco-hydrological model, is used in the present study for the modelling of discharge, sediment and nutrients. SWAT-CUP is also used to calibrate and validate the SWAT model. We are currently employing the results from the calibrated model to obtain a better understanding of possible relations between water quality and biodiversity. In fact, the present study will focus on macroinvertebrates as biological indicators of stream health, and the model predictions will be coupled with empirical correlations between stream water quality and macroinvertebrates presence in order to assess the impacts of water quality changes on aquatic ecosystem. In addition, different model scenarios will be compared to explore the potential impacts of changes in land use, climate and WWTPs operation on the aquatic ecosystem.Keywords: aquatic ecosystem, Clariano River, eco-hydrological modelling, water quality, water resources management

In this paper, we develop and validate a rigorous modeling framework, based on Duhamel's Theorem, for the unsteady one-dimensional vertical transport of a solute across a flat sediment-water interface (SWI) and through the benthic biolayer of a turbulent stream. The modeling framework is novel in capturing the two-way coupling between evolving solute concentrations above and below the SWI and in allowing for a depth-varying diffusivity. Three diffusivity profiles within the sediment (constant, exponentially decaying, and a hybrid model) are evaluated against an extensive set of previously published laboratory measurements of turbulent mass transfer across the SWI. The exponential diffusivity profile best represents experimental observations and its reference diffusivity scales with the permeability Reynolds number, a dimensionless measure of turbulence at the SWI. The depth over which turbulence-enhanced diffusivity decays is of the order of centimeters and comparable to the thickness of the benthic biolayer. Thus, turbulent mixing across the SWI may serve as a universal transport mechanism, supplying the nutrient and energy fluxes needed to sustain microbial growth, and nutrient processing, in the benthic biolayer of stream and coastal sediments. U.S. National Science FoundationNational Science Foundation (NSF) [1840504, 2021015, EAR 1830172]; Virginia Tech's ICTAS EFO Opportunity Seed Investment Grant; UC Office of the President Multicampus Research Program Initiative award [MRP-17-455083]; U.S. Department of Energy, Office of Biological and Environmental Research (BER), as part of BER's Subsurface Biogeochemistry Research Program (SBR)United States Department of Energy (DOE); UK EPSRC Established Career FellowshipEngineering & Physical Sciences Research Council (EPSRC) [EP/P012027/1]; Australian Research CouncilAustralian Research Council [DP120102500]; Fulbright program; U.S. Geological Survey Water Availability and Use Science Program S. B. G. was supported by the U.S. National Science Foundation (Awards 1840504 and 2021015), Virginia Tech's ICTAS EFO Opportunity Seed Investment Grant, and the UC Office of the President Multicampus Research Program Initiative award (MRP-17-455083). J. G. V. was funded by the U.S. National Science Foundation (Award EAR 1830172) and the U.S. Department of Energy, Office of Biological and Environmental Research (BER), as part of BER's Subsurface Biogeochemistry Research Program (SBR). This contribution originates from the SBR Scientific Focus Area (SFA) at the Pacific Northwest National Laboratory (PNNL). I. G. was supported by UK EPSRC Established Career Fellowship (Award EP/P012027/1). M. G. was funded by an Australian Research Council Discovery Project (DP120102500). K. R. R. was supported by the Fulbright program. J. H. was supported by the U.S. Geological Survey Water Availability and Use Science Program. Supporting Information includes tables and text. The authors thank M. Chappell, A. Monofy, three anonymous reviewers, and the Associate Editor for their insightful comments and manuscript edits. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Many of the most important ecosystem services performed by streams occur in the benthic biolayer, the biologically active upper ( 10 cm) layer of the streambed. Here we develop and test a rigorous ...

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.

Riverbed sediments host important biogeochemical processes that play a key role in nutrient dynamics. Sedimentary nutrient transformations are mediated by bacteria in the form of attached biofilms. The influence of microbial metabolic activity on the hydrochemical conditions within the hyporheic zone is poorly understood. We present a hydrobiogeochemical model to assess how the growth of heterotrophic and autotrophic biomass affects the transport and transformation of dissolved nitrogen compounds in bedform-induced hyporheic zones. Coupling between hyporheic exchange, nitrogen metabolism, and biomass growth leads to an equilibrium between permeability reduction and microbial metabolism that yields shallow hyporheic flows in a region with low permeability and high rates of microbial metabolism near the stream-sediment interface. The results show that the bioclogging caused by microbial growth can constrain rates and patterns of hyporheic fluxes and microbial transformation rate in many streams.

Benthic (streambed) biofilms metabolize a substantial fraction of particulate organic matter and nutrient inputs to streams. These microbial communities comprise a significant proportion of overall biomass in headwater streams, and they present a primary control on the transformation and export of labile organic carbon. Biofilm growth has been linked to enhanced fine particle deposition and retention, a feedback that confers a distinct advantage for the acquisition and utilization of energy sources. We quantified the influence of biofilm structure on fine particle deposition and resuspension in experimental stream mesocosms. Biofilms were grown in identical 3-m recirculating flumes over periods of 18-47 days to obtain a range of biofilm characteristics. Fluorescent, 8-μm particles were introduced to each flume, and their concentrations in the water column were monitored over a 30-minute period. We measured particle concentrations using a flow cytometer and mesoscale (10 μm to 1 cm) biofilm structure using optical coherence tomography. Particle deposition-resuspension dynamics were determined by fitting results to a stochastic mobile-immobile model, which showed that retention timescales for particles within the biofilm-covered streambeds followed a power-law residence time distribution. Particle retention times increased with biofilm areal coverage, biofilm roughness, and mean biofilm height. Our findings suggest that biofilm structural parameters are key predictors of particle retention in streams and rivers. This article is protected by copyright. All rights reserved.

The measurement of methane emissions from landfills is important to the understanding of landfills' contribution to greenhouse gas emissions. The Tracer Dispersion Method (TDM) is becoming widely accepted as a technique, which allows landfill emissions to be quantified accurately provided that measurements are taken where the plumes of a released tracer-gas and landfill-gas are well-mixed. However, the distance at which full mixing of the gases occurs is generally unknown prior to any experimental campaign.To overcome this problem the present paper demonstrates that, for any specific TDM application, a simple Gaussian dispersion model (AERMOD) can be run beforehand to help determine the distance from the source at which full mixing conditions occur, and the likely associated measurement errors. An AERMOD model was created to simulate a series of TDM trials carried out at a UK landfill, and was benchmarked against the experimental data obtained. The model was used to investigate the impact of different factors (e.g. tracer cylinder placements, wind directions, atmospheric stability parameters) on TDM results to identify appropriate experimental set ups for different conditions.The contribution of incomplete vertical mixing of tracer and landfill gas on TDM measurement error was explored using the model. It was observed that full mixing conditions at ground level do not imply full mixing over the entire plume height. However, when full mixing conditions were satisfied at ground level, then the error introduced by variations in mixing higher up were always less than 10%.

This work presents an algorithm for real-time fault detection in the SCADA system of a modern water supply system (WSS) in an Italian alpine valley. By means of both hardware and analytical redundancy, the proposed algorithm compares data and isolates faults on sensors through analysis of residuals. Moreover, the algorithm performs a real-time selection of the most reliable measurements for the automated control of the WSS operations. A coupled model of the hydraulic and remote-control system is developed to test the performance of the WSS when the proposed algorithm is applied or not. Simulations show that the occurrence of errors in the sensors causes significant worsening in the economic, energy and mechanical performance of the infrastructure. In many cases, the operations of the WSS are seriously compromised. The error detection and measurement assessment performed by the proposed algorithm proves to be crucial for the safe control of the WSS.

Carbon in surface waters is widely recognized as a key element that influences nutrient cycling, metal availability and water quality. Its degradation in streams occurs primarily by benthic microbial communities that colonize the underlying sediment, which is commonly termed the hyporheic zone (HZ). The biodegradation of a labile dissolved organic carbon (DOCL), exemplified by sodium benzoate, was studied in a novel laboratory flume system under a combination of different overlying water velocities, losing or gaining fluxes, and biofilm distribution ("surficial" or "homogeneous distribution"). The overall objective of this study was to evaluate the effect of different flow conditions on DOCL biodegradation in the HZ. The results showed that overlying velocity was the dominant factor affecting DOCL biodegradation, regardless of biofilm distribution. Gaining flow conditions also induced a slight increase in the biodegradation rates as compared to losing or neutral flow conditions, due to additional oxygen input from the upwelling water. The aerobic reactive zone under all flow conditions was limited to the upper section of the benthic biofilm (several millimeters), where the surficial biofilm showed the highest activity. Our results and interpretation of DOCLbiodegradation processes in the hyporheic zone are expected to improve the understanding and modeling of DOC transport in streams

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.

Este artículo contiene 8 páginas, 3 figuras, 1 tabla., Rivers are a means of rapid and long-distance transmission of pathogenic microorganisms from upstream terrestrial sources. Pathogens enter streams and rivers via overland flow, shallow groundwater discharge, and direct inputs. Of concern is the protozoal parasite, Cryptosporidium, which can remain infective for weeks to months under cool and moist conditions, with the infectious stage (oocysts) largely resistant to chlorination. We applied a mobile-immobile model framework to assess Cryptosporidium transport and retention in streams, that also accounts for inactivation. The model is applied to California’s Central Valley where Cryptosporidium exposure can be at higher risk due to agricultural and wildlife nonpoint sources. The results demonstrate that hyporheic exchange is an important process to include in models characterizing pathogen dynamics in streams, delaying downstream transmission and allowing for immobilization processes, such as reversible filtration in the sediments, to occur. Although in-stream concentrations decrease relatively quickly (within hours), pathogen accumulation of up to 66% of the inputs due to immobilization processes in the sediments and slower moving surface water could result in long retention times (months to years). The model appropriately estimates baseflow pathogen accumulation and can help predict the potential loads of resuspended pathogens in response to a storm event., This project was supported by an NSF EAR-PF awarded to J. Drummond.

This work presents the technical characteristics and the regulation system of a complex water supply system (WSS) in an Italian Alpine valley. The WSS faced multiple challenges: water suppl...

This work presents an algorithm for real-time fault detection in the SCADA system of a modern water supply system (WSS) in an Italian Alpine Valley. By means of both hardware and analytical redundancy, the proposed algorithm compares data and isolates faults on sensors through the residual analysis. Moreover, the algorithm performs a real- time selection of the most reliable measurements for the automated control of the WSS operations. A coupled model of the hydraulic and remote-control system was developed to test the effectiveness of the proposed algorithm. Simulations showed that error detection and measurement assessment are crucial for the safe operation of the WSS.

International audience; The average organic and hydraulic loads that Constructed Wetlands (CWs) receive are key parameters for their adequate long-term functioning. However, over their lifespan they will inevitably be subject to either episodic or sustained overloadings. Despite that the consequences of sustained overloading are well known (e.g., clogging), the threshold of overloads that these systems can tolerate is difficult to determine. Moreover, the mechanisms that might sustain the buffering capacity (i.e., the reduction of peaks in nutrient load) during overloads are not well understood. The aim of this work is to evaluate the effect of sudden but sustained organic and hydraulic overloads on the general functioning of CWs. To that end, the mathematical model BIO_PORE was used to simulate five different scenarios, based on the features and operation conditions of a pilot CW system: a control simulation representing the average loads; 2 simulations representing +10% and +30% sustained organic overloads; one simulation representing a sustained +30% hydraulic overload; and one simulation with sustained organic and hydraulic overloads of +15% each. Different model outputs (e.g., total bacterial biomass and its spatial distribution, effluent concentrations) were compared among different simulations to evaluate the effects of such operation changes. Results reveal that overloads determine a temporary decrease in removal efficiency before microbial biomass adapts to the new conditions and COD removal efficiency is recovered. Increasing organic overloads cause stronger temporary decreases in COD removal efficiency compared to increasing hydraulic loads. The pace at which clogging develops increases by 10% for each 10% increase on the organic load.

Stream physics set the limits A combination of physical transport processes and biologically mediated reactions in streams and their sediments removes dissolved inorganic nitrogen (DIN) from the water. Although stream chemistry and biology have been considered the dominant controls on how quickly DIN is removed, Grant et al. show that physics is what sets the limits on removal rates of nitrate (a component of DIN). Residence time in the hyporheic zone (the region below the sediment surface where groundwater and surface water mix) determines the maximum rate at which nitrate can be removed from stream water. Nevertheless, at local scales, chemistry and biology modify how closely to that maximum rate removal occurs. Science , this issue p. 1266

Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed.

© 2014 American Chemical Society. A simple analytical model is presented for the removal of stream-borne contaminants by hyporheic exchange across duned or rippled streambeds. The model assumes a steady-state balance between contaminant supply from the stream and first-order reaction in the sediment. Hyporheic exchange occurs by bed form pumping, in which water and contaminants flow into bed forms in high-pressure regions (downwelling zones) and out of bed forms in low-pressure regions (upwelling zones). Model-predicted contaminant concentrations are higher in downwelling zones than upwelling zones, reflecting the strong coupling that exists between transport and reaction in these systems. When flow-averaged, the concentration difference across upwelling and downwelling zones drives a net contaminant flux into the sediment bed proportional to the average downwelling velocity. The downwelling velocity is functionally equivalent to a mass transfer coefficient, and can be estimated from stream state variables including stream velocity, bed form geometry, and the hydraulic conductivity and porosity of the sediment. Increasing the mass transfer coefficient increases the fraction of streamwater cycling through the hyporheic zone (per unit length of stream) but also decreases the time contaminants undergo first-order reaction in the sediment. As a consequence, small changes in stream state variables can significantly alter the performance of hyporheic zone treatment systems.

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.

[1] Water exchange between streams and hyporheic zones is highly dynamic, and its temporal variation is related to the hydrologic fluctuations of stream discharge and groundwater levels. Unfortunately, predictions of temporal patterns of exchange are difficult due to the many hydrodynamic and morphodynamic processes that are involved and also to their complex nonlinear interactions. Examples of these processes include the evolution of streambed morphology in response to changing streamflow as well as the feedback on surface flow induced by drag resistance due to evolving bed forms. In this work, we have employed a stochastic method to analyze the temporal dynamics of bed form-driven hyporheic exchange in a stream characterized by subcritical flow and daily discharge variations. The method is an extension of previous studies that includes current-induced alterations of bedform size and celerity and their effect on water exchange. The modeling results show that during high flows, stream water penetrates deeper and for longer times in the sediments. At the same time, the predicted rate of water exchange per unit streambed area decreases because the streambed area occupied by each bed form increases faster than the volumetric rate of stream water exchange induced by the same bed form. This reduction can be compensated by the increase in wetted area with discharge, which may provide additional streambed area for water exchange. One the main finding of the study is that the time-averaged values of exchange flux and depths are quite similar to those modeled for a steady mean discharge, while residence times are somewhat lower. Predicted temporal variations of exchange depths and times around their time-averaged values are moderate compared to steady state values.