Combining Hydrologic Simulations and Stream‐network Models to Reveal Flow‐ecology Relationships in a Large Alpine Catchment

“10.1029/2020WR028496 4 of 17 Water Resources Research according to the Nash-Sutcliffe efficiency index (NSE; Nash & Sutcliffe, 1970), by using the Particle Swarming Optimization algorithm (Kennedy & Eberhart, 1995).”

“10.1029/2020WR028496 4 of 17 Water Resources Research according to the Nash-Sutcliffe efficiency index (NSE; Nash & Sutcliffe, 1970), by using the Particle Swarming Optimization algorithm (Kennedy & Eberhart, 1995).”

“The data set was developed by interpolating the measurements available at the meteorological stations within and nearby the river basin by means of kriging with external drift (Goovaerts, 1997; Mallucci et al., 2019).”

“We included metrics related to the diversity of the community, such as taxonomic richness, Shannon diversity (as effective number of species of order q = 1; Jost, 2006), Functional Dispersion (FDis, which is minimally influenced by taxonomic richness), as these have been shown to reflect flow alterations elsewhere (e.”

“Introduction The flow regime of streams and rivers has been modified by human activities at a global scale (Grill et al., 2019; Tonkin et al., 2019).”

“Biotic metrics expressed as proportions (i.e., feeding and size traits) were logit-transformed as recommended (Warton & Hui, 2011), and maximum-likelihood was used for parameter estimation in all SSN models.”

“As the human population continues to grow, the increasing demand for water supply, flood protection, and energy production has prompted the widespread adoption of engineering solutions such as the construction of dams, levees, and other hydraulic infrastructures (Couto & Olden, 2018; Shumilova et al., 2018; Zarfl et a…”

“To further validate the degree of separation among the classified regimes, we ran a Permutational Multivariate Analysis of Variance (PERMANOVA; Anderson, 2017) based on the Euclidean distance matrix of the weighted PCA scores.”

“This is of particular concern since freshwater ecosystems support about 10% of all known species (Strayer & Dudgeon, 2010) and are essential for human well-being, providing a wealth of ecosystem services (Green et al., 2015).”

“…streamflow time series at specific network locations by integrating the hydrological processes acting within the drainage area: i.e., precipitation, snowmelt, interception, evapotranspiration, infiltration, surface, and sub-surface flow, as well as their interactions (see e.g., Beven, 2012).”

“Hydrologic Metrics We used the 23 years MAD-normalised daily streamflow values to calculate 34 hydrologic metrics following the indicator of hydrologic alteration (IHA; Richter et al., 1997) approach (Table 1), implemented in R software with the “IHA” package (R Core Team, 2019).”

“However, this highlights how defining a baseline flow-ecology relationship under natural conditions might become increasingly difficult as river catchments are modified globally (Tickner et al., 2020).”

“Summer discharge is high in nivo-glacial streams, where increasing flows could cause higher drift rates and thus lower the observed benthic richness (e.g., Brittain & Eikeland, 1988).”

“Information for functional traits of the taxa was gathered from the online database of freshwater ecology (www.freshwaterecology.info; Schmidt-Kloiber & Hering, 2015).”

“, spatial statistics applied to river networks) have provided the tools to model these spatial dependencies over the Euclidean and watercourse dimension, while also accounting for flow directionality (Carrara et al., 2012; Ver Hoef & Peterson, 2010; Zimmerman & Ver Hoef, 2017).”

“Future developments should address the challenge of incorporating hydrologic variability when setting environmental flows, and of assessing the ecological effects of specific flow events or sequence of events without relying on stationary long-term flow records as baseline reference (Horne et al., 2019; Poff, 2018).”

“…to grow, the increasing demand for water supply, flood protection, and energy production has prompted the widespread adoption of engineering solutions such as the construction of dams, levees, and other hydraulic infrastructures (Couto & Olden, 2018; Shumilova et al., 2018; Zarfl et al., 2015).”

“The few studies that have compared flow-ecology relations across classified flow regimes (e.g., Bruckerhoff et al., 2019; Mims & Olden, 2012), also showed that ecological responses can often diverge.”

“…variography (i.e., spatial statistics applied to river networks) have provided the tools to model these spatial dependencies over the Euclidean and watercourse dimension, while also accounting for flow directionality (Carrara et al., 2012; Ver Hoef & Peterson, 2010; Zimmerman & Ver Hoef, 2017).”

“, 2015; Patrick & Yuan, 2017), or by means of geostatistical interpolation (Skøien et al., 2006).”

“As the human population continues to grow, the increasing demand for water supply, flood protection, and energy production has prompted the widespread adoption of engineering solutions such as the construction of dams, levees, and other hydraulic infrastructures (Couto & Olden, 2018; Shumilova et al., 2018; Zarfl et a…”

“Recent analyses of historical hydro-climatic trends revealed that the basin is sensitive to climate change with the ongoing reduction of winter snowfall and anticipation of the snow-melting season (Diamantini et al., 2018; Lutz et al., 2016; Mallucci et al., 2019), which are likely to alter its flow regime by the seco…”

“This is of particular concern since freshwater ecosystems support about 10% of all known species (Strayer & Dudgeon, 2010) and are essential for human well-being, providing a wealth of ecosystem services (Green et al., 2015).”

“Introduction The flow regime of streams and rivers has been modified by human activities at a global scale (Grill et al., 2019; Tonkin et al., 2019).”

“…they convey information about the functional role of organisms in the ecosystems and on size traits that are a proxy of multiple life-history characteristics like e.g. life cycle duration, longevity (Poff et al., 2006) and may respond to variation in shear stress (e.g., Merigoux & Doledec, 2004).”

“, 2019), which are likely to alter its flow regime by the second half of 21st century (Majone et al., 2016).”

“Such stream-network models have been used to derive spatially explicit estimates of water quality and population abundance across river basins (Isaak et al., 2017; McGuire et al., 2014), but applications to flow-ecology research are surprisingly scarce (Bruckerhoff et al.”

“…we focused on benthic macroinvertebrates as model organisms because of their essential role in the functioning of lotic systems, their widespread use as biological indicators, and the availability of monitoring data in the region (De Pauw et al., 2006; Friberg, 2014; Larsen et al., 2019).”

“ArcMap 10.5 and the STARS toolset (Peterson & Hoef, 2014) were used to generate the spatial data necessary to analyze stream-network models.”

“Therefore, it is necessary to classify flow regimes into distinct and easily interpretable classes in order to define reference flow conditions and implement targeted e-flows schemes, while also minimizing the effects of other co-varying environmental factors (Belmar et al., 2011; Booker et al., 2015).”

“Conversely, in temperate streams characterized by pluvial regimes, minimum densities often occur in winter (Brittain & Eikeland, 1988; Naman et al., 2016), when higher-than-average flows could further decrease benthic richness.”

“To this end, species life-history traits can provide the mechanistic link between river biota and flow conditions that could be valid across large spatial scales (Heino et al., 2013; Mims & Olden, 2012).”

“On a more fundamental level, it indicates that the often-observed nonlinear flow-ecology relationships (Rosenfeld, 2017) can reflect the distinct response of multiple flow regimes in the basin.”

“The Adige River is the second-longest Italian river, with the typical natural streamflow regime of the Alpine region showing two seasonal maxima, one occurring in spring-summer due to snow and glacial melt, and the other in autumn triggered by cyclonic storms (Chiogna et al., 2016; Mallucci et al., 2019).”

“Recent analyses of historical hydro-climatic trends revealed that the basin is sensitive to climate change with the ongoing reduction of winter snowfall and anticipation of the snow-melting season (Diamantini et al., 2018; Lutz et al., 2016; Mallucci et al., 2019), which are likely to alter its flow regime by the seco…”

“Hydrologic Simulations Hydrological simulations were performed at the daily time scale with the HYPERstreamHS model (Avesani et al., 2021; Laiti et al., 2018), which couples the HYPERstream routing scheme (recently proposed by Piccolroaz et al.”

“In this paper, we develop and discuss a framework that addresses these challenges using the Adige River basin (northeastern Italy) as a case study.”

“…and Anterselva gauging stations is in line with the general understanding that accurate reproduction of observed streamflows in small catchments would require accurate and spatially well-resolved precipitation and temperature fields at small spatial scales (e.g., Heisterman & Kneis, 2011).”

“Such stream-network models have been used to derive spatially explicit estimates of water quality and population abundance across river basins (Isaak et al., 2017; McGuire et al., 2014), but applications to flow-ecology research are surprisingly scarce (Bruckerhoff et al.”

“Therefore, it is necessary to classify flow regimes into distinct and easily interpretable classes in order to define reference flow conditions and implement targeted e-flows schemes, while also minimizing the effects of other co-varying environmental factors (Belmar et al., 2011; Booker et al., 2015).”

“Specifically, we focused on benthic macroinvertebrates as model organisms because of their essential role in the functioning of lotic systems, their widespread use as biological indicators, and the availability of monitoring data in the region (De Pauw et al., 2006; Friberg, 2014; Larsen et al., 2019).”

“The data set was developed by interpolating the measurements available at the meteorological stations within and nearby the river basin by means of kriging with external drift (Goovaerts, 1997; Mallucci et al., 2019).”

“Subsurface return flow was modeled by a nonlinear reservoir (Majone et al., 2010).”

“The sensitivity of grazers to flow conditions, for example, can derive from their reliance on attached algae, which can be scoured during high flows or buried by fines during low flows (Buchanan et al., 2013; Doretto et al., 2020; Kennen et al., 2010).”

“In agreement with recent investigations (Larsen et al., 2019; Quadroni et al., 2017), these results provide additional evidence of the limited sensitivity of WFD biological quality indicators, such as the Star_ICMi index, to stream hydrologic conditions.”

“These findings are in line with a recent study from the US where SSN models were used to examine variation in fish community traits (Bruckerhoff et al., 2019).”

“…variography (i.e., spatial statistics applied to river networks) have provided the tools to model these spatial dependencies over the Euclidean and watercourse dimension, while also accounting for flow directionality (Carrara et al., 2012; Ver Hoef & Peterson, 2010; Zimmerman & Ver Hoef, 2017).”

“The importance of using spatially explicit approaches to model empirical data in river networks is increasingly recognized (Frieden et al., 2014; Isaak et al., 2017; Larsen et al., 2019), and our results further support their application in flow-ecology research (Bruckerhoff et al.”

“To achieve the above-mentioned goals, first, we used the process-based HYPERstreamHS hydrological model (Avesani et al., 2021) to simulate the natural streamflow series of one-hundred stream reaches throughout the Adige River basin where biological information was available.”

“25 (Belmar et al., 2011; Legendre & Legendre, 2012; Mazor et al., 2018), which provides an intermediate solution between chaining obtained via single linkage, and space dilation deriving from complete linkage.”

“In this paper, we develop and discuss a framework that addresses these challenges using the Adige River basin (northeastern Italy) as a case study.”

“Statistical hydrological models aim to predict flow metrics at ungauged locations from the observed relation between available streamflow series and catchment characteristics (Booker et al., 2015; Patrick & Yuan, 2017), or by means of geostatistical interpolation (Skøien et al., 2006).”

“In agreement with recent investigations (Larsen et al., 2019; Quadroni et al., 2017), these results provide additional evidence of the limited sensitivity of WFD biological quality indicators, such as the Star_ICMi index, to stream hydrologic conditions.”

“Besides the range of anthropogenic influence, the three streamflow types analyzed here are characterized by different levels of environmental severity, which declines with decreasing glacial influence (Brighenti et al., 2021).”

“Hydrological simulations were performed at a daily timescale with the HYPERstreamHS model (Avesani et al., 2021; Laiti et al., 2018; Larsen et al., 2021); HYPERstreamHS couples the HYPERstream routing scheme, recently proposed by Piccolroaz et al. (2016), with a continuous module for surface and…”

“This feature not only allows for obtaining enhanced insights into the impacts of local landscape factors on water quality, but also takes care of any spatial inconsistencies brought about by the location of the sites along with the stream network (e.g., Larsen et al. 2021).”

“Precipitation and contributions from underground water, along with evapotranspiration, play a significant role in determining flows in the val - leys, especially in the southern portion of the basin (Chiogna et al. 2016; Larsen et al. 2021 ).”

“, 2021) and spatial autocorrelation effects (e.g. Bruckerhoff et al., 2019; Larsen et al., 2021).”

“…to simulation of relatively few sites and HMs, (Caldwell et al., 2015; Eddy, Moreda, et al., 2017; Shrestha et al., 2014; Teutschbein et al., 2018; Worthington et al., 2019) and have provided insight into several flow–ecology analyses (Drew et al., 2018; Larsen et al., 2021; Phelan et al., 2017).”

“Furthermore, the drying up of the river caused a series of ecological impacts, including a reduction in aquatic habitats, a drop in the groundwater table and increased surface water infiltration (Larsen et al. 2021).”

“These environmental shifts, along with alterations in hydrologic regimes and glacial recession, exert substantial impacts on alpine ecosystems and the kind of habitats available for aquatic organisms over time (Fornaroli et al. 2019; Meißner et al. 2019; Larsen et al. 2021).”

“Such as in most research producing simulations of habitats due to hydrological variations [64, 65], changes in substrate grain size due to observed variations in flow over time were not accounted for in this study.”