The Hammond Hill Research Catchment (HH) is a small (120 ha), temperate, second order tributary to Six Mile Creek, Cayuga Lake, and the Great Lakes (42.42°, -76.32°). The HH has been monitored since January 2017 for the purpose of understanding how recent infiltration mixes with antecedent soil water on hillslope forest floors and the spatial and temporal patterns of Root Water Uptake (RWU) by temperate northeastern US tree species (eastern hemlock [Tsuga canadensis], American beech [Fagus grandifolia], and sugar maple [Acer saccharum]). These data are informing us about the hydrologic consequences of anticipated tree species composition change and supporting the development of more refined ecohydrological models. The glaciated catchment is underlain by a shallow confining siltstone layer (1 – 1.5 m depth) and dense with a regrowth (approximately 60 years old) mixed species forest of hemlock, beech, and other deciduous tree species common to the northeastern US. Current datasets from the HH include fixed-internal precipitation snow water equivalent, and discharge, and associated isotopic water compositions (2H & 18O). Frequent (<1 month) measurements of shallow (top 10 cm) soil water content and bulk soil water and hemlock and beech xylem isotopic compositions are made at six locations across a topographic wetness gradient. The near-term role of the HH is to support an understanding of the environmental and ecological drivers of plant RWU competition and ecohydrologic education.

Modelling results in the small (1.78 km2) experimental catchment Uhlířská located in the northern part of the Czech Republic at the average elevation of 822 m a.s.l. are presented. While the basic hydrological and meteorological monitoring has started already in 1982, investigation of the subsurface flow adjoined in 1995. A detailed survey of water and isotope (18O, 2H, 3H, 3H/3He) fluxes across the catchment storage compartments has been in operation since 2006. The combined vadose/saturated zones modeling with support of partial extrapolation of 18O content in precipitation yielded the following mean balance for the period 1961-2014: 456 out of 1220 mm annual precipitation depth are percolating through the soil matrix domain and 534 mm through the preferential domain in the hillslope soil profile. The saturated zone is recharged annually by 416 mm, consisting of the entire matrix flow and 12,5 % of the preferential flow from the permeable hillslopes covered by Cambisols and Podzols, as well as by the contribution of 22 mm from the less permeable riparian wetland Histosols. The aquifer geometry was determined by means of electrical resistivity tomography (ERT) including inverse modelling (RES2DINV). Water and isotope fluxes were computed using a sequence of models. They include S1D software for the vadose zone modeling including 18O transport and Modflow, Modpath and MT3DS determining residence time and flow trajectories in the saturated zone. Isotopes 3H and 3H/3He improved the model confidence. The water residence time on the hillslopes does not exceed 1 year, while the saturated zone indicates about 10 years, with a 20% portion of water older than 100 years in the deepest part of the aquifer. The combination of numerical modelling approaches with computation of water balance and isotope-supported calibration is considered innovative, particularly the 3H/3He method to determine water residence times of young groundwater in the saturated zone.

Soil water repellency (SWR) increases surface runoff and preferential flows. Thus, quantitative evaluation of SWR distribution is necessary to understand water movements. Because the variability of SWR distribution makes it difficult to measure directly, we developed a method for estimating an SWR distribution index, defined as the areal fraction of surface soil showing SWR (SWRarea). The theoretical basis of the method is as follows: (1) SWRarea is equivalent to the probability that a position on the soil surface is drier than the critical water content (CWC); SWR is present (droplets absorbed in >10 s) when the soil surface is drier than the CWC and absent when it is wetter. (2) CWC and soil moisture content (θ) are normally distributed independent variables. (3) Thus, based on probability theory, the cumulative normal distribution of θ – CWC (f(x)) can be obtained from the distributions of CWC and θ, and f(0), the cumulative probability that θ – CWC < 0, gives the SWRarea. To investigate whether the method gives reasonable results, we repeatedly measured θ at 0–5 cm depth and determined the water repellency of the soil surface at multiple points in fixed plots with different soils and topography in a humid-temperate forest. We then calculated the CWC from the observed θ–SWR relationship at each point. We tested the normality of the CWC and θ distributions and the correlation between CWC and θ. Then, we determined f(x) from the CWC and θ distributions and estimated the SWRarea on each measurement day. Although CWC and θ were both normally distributed, in many cases they were correlated. Nevertheless, the CWC–θ dependency had little effect on the estimation error, and f(x) explained 69% of the SWRarea variability. Our findings show that a stochastic approach is useful for estimating SWRarea.

A knowledge of the exchanges of energy and water over the terrestrial surface is the first step to understand the ecohydrological mechanisms, particularly in water-limited ecosystems in the dryland environments. However, patterns of energy exchange and evapotranspiration (ET) are not well understood in the oasis-desert ecotone, which plays an important role in protecting oasis against the threat of desertification in northwestern China’s arid regions. Here the continuous measurements of surface energy fluxes were made using eddy covariance in conjunction with auxiliary measurements for two years (2014-2015) at a shrubland within an oasis-desert ecotone in the arid regions, northwestern China. Statistical analysis on 30-min time scale indicates that about 50% of daytime net radiation (Rn) over the shrubland is dissipated as H on average, which peaks in spring; one third Rn is consumed by soil heat flux (G). Only 9% of Rn was consumed for latent heat flux (λE), which peaks in summer (21% in 2014 and 16% in 2015), corresponding to the season with highest rainfall among all seasons. Daily mean ET is about 1 mm·d−1 during growing season of the shrub species. The rapid and transient increase in ET occurs following a rainfall event. A switch in surface soil moisture from 0.04 to 0.11 m3·m−3 causes an increase in Rn by about 11% and λE by 151% at the shrubland, respectively. Accumulated annual ET were 195 and 181 mm in 2014 and 2015, respectively, exceeding the corresponding P by about 87 and 77 mm, indicating that groundwater may be another important source of water for ET over the shrubland aside from P. These results provide valuable insight into the mechanisms of sustaining energy and water balance at the ecotone, and then produce some management guidelines for allocating water resources and protecting vegetation.

Particle selectivity plays an important role in clarifying sediment transport processes in vegetative filter strips (VFS). 10-m long grass strips at slopes of 5○ and 15○were subjected to a series of silt-laden inflows experiments with different particle sizes to investigate the sediment transport and its response to overland flow hydraulics. The inflow sediments came from local soil, river-bed sand, and mixed, with median particle size d50 of 39.9, 207.9, and 77.4 μm, respectively. Three independent repeated experiments were carried for each treatment. The results show that when the sediment trapping lasted for a certain length of time, the re-entrainment of some small-sized particles was greater than the deposition; that is, negative deposition occurred, which was not erosion of the original soil. Negative deposition of particles is mainly determined by the particle diameter. The coarser the inflow sediment particles and/or the steeper the slope, the coarser the particles can be negatively deposited. Deposited sediment causes the VFS bed surface to become smooth and hydraulic resistance decrease exponentially. Stream power P is more suitable than shear stress τ of overland flow to be used to describe the process of sediment particle transport in VFS. The relationship between P and d50 of outflow sediment is very consistent with the form of power function with a constant term. These results are helpful to understand the physical process of sediment transport on vegetation hillslopes.

The water agreements between Mexico and the United States have been crucial to restore and preserve the wetlands of the Colorado River Delta. Nowadays, the increase of water demand and climate change in the northwest of Mexico could threaten the conservation of the Cienega de Santa Clara, a coastal wetland composed of 4,709 ha of marsh area in the limits of the Sonoran Desert. This ecosystem was recognized internationally by the international Ramsar convention for playing vital ecological roles, including the habitat service for endemic, endangered and migratory species. Since the inflow reductions by the trial run of the Yuma Desalting Plant during 2010-2011, and earlier events, the hydrology of the wetland has not been completely understanding due to accessibility. Therefore this study was conducted to obtaining the hydrological elements to conserve the wetland, analyzing three scenarios: 1] normal inflow conditions of the Wellton-Mohawk canal; 2] inflow reductions, and; 3] an increase of temperature in consequence of global warming. Water and mass balances were conducted every month during one year; in-situ measurements of inflows were carried out on Wellton-Mohawk, Riíto Drain, groundwater, and precipitation; also were including evapotranspiration outputs estimated using local weather registers and Penman-Monteith formulations. The implications of the increase in temperature considered include the Intergovernmental Panel on Climate Change projections for the one hundred years. Finally, the results showed superficial water disconnections between the hydrological system of the wetland and the Gulf of California. This behavior was observed in the three scenarios, mainly in the summer months. A continuous disconnection reduced the wetland area and the water storage. Therefore, the hydrological functionality of the wetland depends on the water supply thru Wellton-Mohawk canal, which was determinate that at least a continuous discharge of 5.10 m3 s-1 during summer months is needed to maintain its functionality.

Midwestern cities require forecasts of surface nitrate loads to bring additional treatment processes online or activate alternative water supplies. Concurrently, networks of nitrate monitoring stations are being deployed in river basins, co-locating water quality observations with established stream gauges. Here, we construct a synthetic data set of stream discharge and nitrate for the Wabash River Basin - one of the U.S.’s most nutrient polluted basins - using the established Agro-IBIS model. While real-world observations are limited in space and time, particularly for nitrate, the synthetic data set allows for sufficiently long periods to train machine learning models and assess their performance. Using the synthetic data, we established baseline 1-day forecasts for surface water nitrate at 12 cities in the basin using support vector machine regression (SVMR; RMSE 0.48-3.3 mg/L). Next, we used the SVMRs to evaluate the improvement in forecast performance associated with deployment of additional sensors. Synthetic data enable us to quantitatively assess the expected value of an additional nitrate sensor being deployed, which is, of course, not possible if we are limited to the present observational network. We identified the optimal sensor placement to improve forecasts at each city, and the relative value of sensors at all possible locations. Finally, we assessed the co-benefit realized by other cities when a sensor is deployed to optimize a forecast at one city, finding significant positive externalities in all cases. Ultimately, our study explores the potential for AI to make short-term predictions and provide an unbiased assessment of the marginal benefit and co-benefits to an expanded sensor network. While we use water quantity in the Wabash River Basin as a case study, this approach could be readily applied to any problem where the future value of sensors and network design are being evaluated.

Bioretention is widely used in urban sustainable stormwater management. However, limited numerical research has been conducted on its performance in cold regions, particularly for winter snowmelt, spring runoff and summer large storms (> 50 mm) for urban flood mitigation. In this study, HYDRUS 1D was used to explore these knowledge gaps. The model was comprehensively calibrated and validated against 2-year hydrologic and water quality data of four bioretention columns with different designs under lab-simulated cold region conditions. The Morris method was used to measure the sensitivity and interaction of the calibrated hydraulic parameters. The model revealed that the effective hydraulic conductivity ( KS) values of the soil media were similar for winter snowmelt and spring runoff when the soil temperature was around -0.5 °C. Preferential flow is likely to occur in soil media during winter or spring of cold regions. The summer modeling showed that the bioretention could substantially reduce peak flow, ponding depth and duration for large storm events (even for 1:100 local storm with 83.4 mm in 4 hours). The water quality modeling confirmed experimental results that the bioretention effectively removed phosphate and ammonium but had leaching issues for chloride and nitrate. Finally, optimization and recommendations of bioretention columns were provided.

Soil moisture plays a significant role in land-atmosphere interactions. Changing fractions of latent and sensible heat fluxes caused by soil moisture variations can affect near-surface air temperature, thus influencing the cooling effect of the oasis in arid regions. In this study, the framework for the evaporative fraction (EF) dependence on soil moisture is used to analyze the impacts of soil moisture variation on near-surface air temperature and the oasis effect. The results showed that the contribution rate of soil moisture to EF was significantly higher than that of EF to temperature. Under the interaction of temperature sensitivity to EF and EF to soil moisture, the ∂T/∂ϴ presented a similar tempo-spatial variation with both of the above. It was most significant in oasis areas during summer (−1.676), while it was weaker in plain desert areas during the autumn (−0.071). In the study region, the effect of soil moisture variation on air temperature can reach 0.018–0.242 K for different land-cover types in summer. The maximum variation of soil moisture in summer can alter air temperature by up to 0.386 K. The difference in temperature variability between the oasis and desert areas promoted the formation of the oasis effect. For different oasis, the multi-year average oasis cold effect index (OCI) ranged from −1.36 K to −0.26 K, while average summer OCI ranged from −1.38 K to −0.29 K. The lower bound of the cooling effect of oasis ranged from −4.97 to −1.69 K. The analysis framework and results of this study will provide a new perspective for further research on the evolution process of the oasis effect and water-heat balance in arid areas.

Aaron Smith1, Doerthe Tetzlaff1,2,3, Marco Maneta4,Chris Soulsby3,21IGB Leibniz Institute of Freshwater Ecology and Inland Fisheries Berlin, Berlin, Germany2Humboldt University Berlin, Berlin, Germany3Northern Rivers Institute, School of Geosciences, University of Aberdeen, UK4Department of Geosciences, University of Montana, Missoula, Montana, USACorrespondence to: Aaron Smith ([email protected])

The catchment approach has been traditionally limited to small, experimental catchments where water fluxes can be determined with high accuracy. However, larger catchments where landscape management occurs have emergent drivers of streamflow at scale, and thus may exhibit novel responses to land cover disturbance. We used statistical models of water yield and annual maximum peak streamflow for multiple forested catchments in the low-relief glaciated region of central North America to investigate how forest disturbance may affect water yield and peak flows in similar landscapes. We utilized linear models, linear mixed effects models, and probabilistic flood-frequency analysis, with Bayesian parameter estimation in two case studies in Minnesota, USA: 1) a wildfire comprising ~30% of a 650km 2 wilderness Upper Kawishiwi catchment, and 2) 11 catchments within the St. Louis River Basin ranging from 56 to 8,880 km 2 with a patchwork disturbance regime wherein ~0.25% to 1% of the catchment is harvested or converted to non-forest land use each year. We also assessed for the most likely hydrological recovery year after forest disturbance, and the relative importance of stationary and nonstationary drivers of streamflow. We found forest disturbance correlated with declines in water yield for low-level disturbance regimes, but that water yield increased in response to the large-scale wildfire. Positive and negative associations of forest disturbance with peak flows were observed, generally with low confidence. Hydrologic recovery time ranged from 5 to 12 years for water yield and peak flows following disturbance. Despite these effects of forest disturbance on streamflow, effects of climate variability and stationary catchment size factors were more prominent drivers of streamflow. Basins larger than ~50 km 2 in low-relief glaciated regions were resilient to forest cover change when it comprised <30% of basin area, but climate change may have a larger effect than could be mitigated by land management.

Channel banks can contribute a significant proportion of fine-grained (<63 µm) sediment to rivers, thereby also contributing to riverine total particulate phosphorus loads. Improving water quality through better agricultural practices alone can be difficult since the contributions from non-agricultural sources, including channel banks, can generate a ‘spatial mismatch’ between the efficacy of best management applied on farms and the likelihood of meeting environmental objectives. Our study undertook a reconnaissance survey (n=76 sites each with 3 profiles sampled) to determine the total phosphorus (TP) concentrations of channel banks across England and to determine if TP content can be predicted using readily accessible secondary data. TP concentrations adjacent field topsoils and local soil soil type/texture and geological parent material were examined as potential predictors of bank TP. Carbon and nitrogen content were also analysed to explore the impacts of organic matter content on measured TP concentrations. The results suggest that channel bank TP concentrations are primarily controlled by parent material rather than adjacent topsoils, but significant local variability in concentrations prevents the prediction of bank TP content using mapped soil type or geology. A median TP concentration of 873 mg kg -1 was calculated for the middle section of the sampled channel bank profiles, with a 25 th percentile of 675 mg kg -1, and 75 th percentile of 1159 mg kg -1. Using these concentrations and, in comparison with previously published estimates, the estimated number of inland WFD waterbodies in England for which channel bank erosion contributes >20% of the riverine total PP load increased from 15 to 25 (corresponding range of 17 to 35 using the 25 th and 75 th percentiles of measured TP concentrations). Collectively, these 25 waterbodies account for 0.2% of the total inland WFD waterbody area comprising England.

Delays in forest recovery from terrestrial acidification combined with climate change is leading Acadian Forest ecosystems into new territory. Kejimkujik Calibrated Catchments (KCC) Study Program was established in an around Kejimkujik National Park and Historic Site (KNPHS) in Southwest Nova Scotia (SWNS) in the late 1970s to increase our understanding of the impacts of acid precipitation on relatively pristine ecosystems. KCC now have one of the longest continuously monitored water chemistry records in North America, with data collection beginning in 1980. Its infrastructure includes three gauged streams, twelve forest inventory plots, an atmospheric deposition monitoring station, and three streams with continuous water quality monitoring and regular lab analysis of stream chemistry, and recent LiDAR coverage. The KCC fits into a wider network of monitored lakes. Data collected at the KCC form a key datapoint in comparisons of catchment response to terrestrial acidification in the context of a warming climate, due to their high and increasing DOC levels, highly dilute waters, lowland topography and extensive wetlands. KCC are also emerging as an important source of information for species at risk protection as SWNS was declared one of the 11 national priority places for biodiversity protection.

Our understanding of the mechanisms routing precipitation inputs to evapotranspiration and streamflow in catchments is still very fragmented, particularly in the case of saturated flows. Here we explore five mechanisms by which plants and streams compete with each other for water, based on multiple scales of observations in a flat semiarid sedimentary catchment of central Argentina subject to abrupt hydrological transformations. Since the 80s, the “El Morro” catchment (1334 km2, -33.64°, -65.36°) experienced a fast expansion of crops over native forests and grasslands, rapid water table level rises (~0.3 m y-1), spontaneous expansion of wetlands and permanent streams by groundwater sapping. Based on episodic and continuous groundwater level, stream flow, and remote sensing data we show that plants not only take away water from streams by drying the unsaturated zone (mechanism 1), but by tapping the saturated zone in the expanding waterlogged environments (mechanism 2) and in the upland environments that remain uncultivated and display increasing tree cover (mechanism 3). Conversely, streams take away water from plants through pulsed bed-deepening and water table depression (mechanism 4), and riparian and wetland zones burying with fresh sediments (mechanism 5). While earlier work established widespread support for mechanisms 1 preventing stream formation, diurnal and seasonal fluctuations of water table levels and base streamflow records in this study proved the importance of mechanisms 2 and 3 under the current high-water table conditions. These data together with remotely-sensed greenness showed a growing but localized relevance of mechanism 4 and 5 as the stream network developed. The distinction of recharge- vs. topography-controlled groundwater systems is useful to organize the interplay of these concurrent mechanisms. Findings point to the unsaturated-saturated contact zone as a crucial and dynamic hub for water partition and for ecological, geomorphological, and hydrological knowledge integration.

Short-term surges in stream temperature in response to storm events have frequently been observed in urban areas , highlighting the need for improved understanding of the factors influencing urban stream temperature. Urban land cover complexity and infrastructure designed for rapid water routing to the sewer system create a direct link between storm events and water release processes, influencing urban stream temperature responses. This study aims to identify predictors of diverse stream temperature response patterns to summer storms. We analyzed 403 storm events from six urban and semi-urban catchments along the US East Coast using dynamic time warping to identify archetype patterns of stream temperature responses. We further disentangled observed stream temperature increase patterns to reveal the drivers associated with “heat pulses”, which are characterized by a rapid but high-magnitude temperature increase followed by a sharp temperature drop at the start of the hydrograph. Our results show that stream temperature patterns were event-specific and linked to pre-event conditions and rainfall-runoff characteristics, with the shape of the hydrograph and rainfall-runoff response identified as the most important determinators of the observed temperature response patterns. Ponded surface waters and storm drains, as well as cooler water from the shallow subsurface, were identified as likely sources contributing to temperature patterns. These findings have important implications for understanding urban hydrology and the contributions of different source zones in urban catchments. Specifically, our results suggest that streamwater temperature can serve as a cost-effective tracer of information about urban water sources and pathways, aiding in the understanding of complex urban hydrology.

Hydrological models require a complete and accurate time series of weather inputs to adequately represent watershed-scale responses. The Global Historical Climatology Network (GHCN) is the most comprehensive ground-based global weather database and is often used in hydrological modeling studies. Since higher density, lower reliability precipitation measurements from private citizens collected by the Community Collaborative Rain, Hail, and Snow (CoCoRaHS) network data were integrated into the GHCN, hydrological modelers in the U.S. have access to a much greater amount of weather data. However, the benefit of using CoCoRaHS data has not been assessed. The objectives of this work were to develop a method for generating a complete weather data time series based on the combination of data from multiple GHCN monitors and to assess several methods for estimation of missing weather data. Weather data from GHCN monitors located within a specific radius of a watershed were obtained and interpolated using three estimation methods (Inverse Distance Weighting (IDW), Inverse Distance and Elevation Weighting (IDEW), and Closest Station), creating a seamless time-series of weather observations. To evaluate the performance of the methodologies, weather data obtained from each estimation method was used to force the Soil and Water Assessment Tool (SWAT) models of 21 U.S. Department of Agriculture-Conservation Effects Assessment Project watersheds in different climate regions to simulate daily streamflow for 2010-2021. Except for three watersheds, all SWAT models had Nash-Sutcliffe Efficiency above 0.5, the ratio of the root mean square error to the standard deviation of observations below 0.7, and percent bias from -25% to 25% with a satisfactory performance rating. Overall, IDEW and IDW performed similarly, and the Closest Station method resulted in the poorest streamflow simulation. A comparison with published SWAT model results further corroborated improved model performance using newly combined GHCN data with all Closest Station, IDW, and IDEW methods.

The snowpack regime influences the timing of soil water available for transpiration and synchrony with the evapotranspiration (ET) energy demand (air temperature, VPD, and shortwave radiation). Variability of snowmelt timing, soil water availability, and the energy demand results in heterogeneous ET rates throughout a watershed. In this study, we assess how ET and growing season length vary across five sites on an elevational gradient in the Dry Creek Watershed, ID, USA. We compared trends of daily and annual ET between 2012 and 2017 to environmental parameters of soil moisture, air temperature, vapor pressure deficit, snow cover, and precipitation and evaluate how ET varies between sites and what influences annual ET at each site. We observed three trends in ET across the watershed. The first trend is at the low elevation site where the snow cover is not continuous throughout the winter and rain is the dominant precipitation form. The first day of the growing season and ET occurs early in the season when the energy demand is low and soil water is available. Annual ET at the low elevation site is a balance between spring precipitation providing soil water into the summer season and limiting the ET energy demand. The second trend occurs at the middle elevation site located in the rain-snow transition. At this site, ET increases with snow depth and spring precipitation extending the soil water availability into the summer season. At the higher elevation sites, ET is aligned with the energy demand and limited by growing season length. At the high elevation sites, decreasing snow depth and spring precipitation and increasing spring air temperatures result in greater annual ET rates. The observations from this study highlight the influence of environmental parameters and the potential sensitivity of ET to climate change.

Dew is closely related to the micro-use of water and to large-scale hydrological processes. Dew formation on grasslands plays a particularly vital role in maintaining the ecohydrological cycle, however, its characteristics and sources were rarely reported. Here, stable isotope for dew, ambient water vapor, soil water, plant water, creek water, and precipitation were tracked to determine the characteristics of dew from ecohydrological processes in the meadow. The structural equation model was used to investigate how environmental factors affect dew formation. The Mix SIAR model in R was used to determine the sources of dew, and explore the dew transport route of six species of the graminoid-Kobresia meadow in an alpine graminoid-Kobresia meadow in northern Qinghai-Tibet Plateau. Our results showed that the annual amount was about 37.92 ± 1.03 mm, acounting for 7.13% of precipitation. Both atmospheric pressure and temperature showed significant positive effects on dew formation, while wind speed had a negative effect. Evapotranspiration indirectly affected dew formation. The contribution rates of soil water, plant water, and ambient water vapor to dew formation were 48.20±5.46%, 38.30±5.07%, and 13.50±1.82%, respectively. The proportion of dew utilization by graminoid and Kobresia species showed no significant species differences, the mean value was 10.5±3.8%. Our statistical analysis determines the role of dew in an alpine graminoid-Kobresia meadow in the northern Qinghai-Tibet Plateau, which provides an improved understanding of dew formation based on a stable isotope technology.