Catchment-scale response functions, such as transit time distribution (TTD) and evapotranspiration time distribution (ETTD), are considered fundamental descriptors of a catchment’s hydrologic and ecohydrologic responses to spatially and temporally varying precipitation inputs. Yet, estimating these functions is challenging, especially in headwater catchments where data collection is complicated by rugged terrain, or in semi-arid or sub-humid areas where precipitation is infrequent. Hence, we developed practical approaches for estimating both TTD and ETTD from commonly available tracer flux data in hydrologic inflows and outflows without requiring continuous observations. Using the weighted wavelet spectral analysis method of Kirchner and Neal  for δ18O in precipitation and stream water, we specifically calculated TTDs that contribute to streamflow via spatially and temporally variable flow paths in a sub-humid mountain headwater catchment in Arizona, USA. Our results indicate that composite TTDs most accurately represented this system for periods up to approximately one month and that a Gamma TTD was most appropriate thereafter. The TTD results also suggested that some contribution of subsurface water was beyond the applicable tracer range. For ETTD and using δ18O as a tracer in precipitation and xylem waters, a Gamma ETTD type best matched the observations, and stable water isotopes were capable tracers for the majority of vegetation source waters. This study contributes to a better understanding of a fundamental question in mountain catchment hydrology; namely, how tracer input fluxes are modulated by spatially and temporally varying subsurface flow paths that support evapotranspiration and streamflow at multiple time scales.
Accurately quantifying the evaporation loss of surface water is essential for regional water resources management, especially in arid and semi-arid areas where water resources are already scarce. The long-term monitoring of stable isotopes (δ18O and δ2H) in water can provide a sensitive indicator of water loss by evaporation. In this study, we obtained surface water samples of Shiyang River Basin from April to October between 2017 and 2019. The spatial and temporal characteristics of stable isotopes in surface water show the trend of enrichment in summer, depletion in spring, enrichment in deserts and depletion in mountains. The Surface Water Line (SWL) has been defined by the lines: δ2H=7.61δ18O+14.58 for mountainous area, δ2H=4.19δ18O-17.85 for oasis area, δ2H=4.08δ18O-18.92 for desert area. The slope of SWL shows a gradual decrease from mountain to desert, indicating that the evaporation of surface water is gradually increasing. The evaporation loss of stable isotopes in surface water is 24.82% for mountainous area, 32.19% for oasis area, and 70.98% for desert area, respectively. Temperature and air humidity are the main meteorological factors affecting the evaporation loss, and the construction of reservoirs and farmland irrigation are the main man-made factors affecting the evaporation loss.
Soil and nutrient loss play a vital role in eutrophication of water bodies. Several simulated rainfall experiments have been conducted to investigate the effects of a single controlling factor on soil and nutrient loss. However, the role of precipitation and vegetation coverage in quantifying soil and nutrient loss is still unclear. We monitored runoff, soil loss, and soil nutrient loss under natural rainfall conditions from 2004 to 2015 for 50-100 m2 runoff plots around Beijing. Soil erosion was significantly reduced when vegetation coverage reached 20 and 60%. At levels below 30%, nutrient loss did not differ among different vegetation cover levels. Minimum soil N and P losses were observed at cover levels above 60%. Irrespective of the management measure, soil nutrient losses were higher at high-intensity rainfall (Imax30>15 mm/h) events compared to low-intensity events (p < 0.05). We applied structural equation modelling (SEM) to systematically analyze the relative effects of rainfall characteristics and environmental factors on runoff, soil loss, and soil nutrient loss. At high-intensity rainfall events, neither vegetation cover nor antecedent soil moisture content (ASMC) affected runoff and soil loss. After log-transformation, soil nutrient loss was significantly linearly correlated with runoff and soil loss (p < 0.01). In addition, we identified the direct and indirect relationships among the influencing factors of soil nutrient loss on runoff plots and constructed a structural diagram of these relationships. The factors positively impacting soil nutrient loss were runoff (44-48%), maximum rainfall intensity over a 30-min period (18-29%), rainfall depth (20-27%), and soil loss (10-14%). Studying the effects of rainfall and vegetation coverage factors on runoff, soil loss, and nutrient loss can improve our understanding of the underlying mechanism of slope non-point source pollution.
Aggregate disintegration is a critical process in soil splash erosion. However, the effect of soil organic carbon (SOC) and its fractions on soil aggregates disintegration is still not clear. In this study, five soils with similar physical and chemical properties and different contents of SOC have been used. The effects of slaking and mechanical striking on splash erosion were distinguished by using deionized water and 95% ethanol as raindrops. The simulated rainfall experiments were carried out in four heights (0.5, 1.0, 1.5, and 2.0 m). The result indicated that the soil aggregate stability increased with the increases of SOC and light fraction organic carbon (LFOC). The relative slaking and the mechanical striking index increased with the decreases of SOC and LFOC. The reduction of macroaggregates in eroded soil gradually decreased with the increase of SOC and LFOC, especially in alcohol test. The amount of macroaggregates (>0.25mm) in deionized water tests were significantly less than that in alcohol tests under the same rainfall heights. The contribution of slaking to splash erosion increased with the decrease of heavy fractions organic carbon (HFOC). The contribution of mechanical striking was dominant when the rainfall kinetic energy increased to a range of threshold between 9 J m-2 mm-1 and 12 m-2 mm-1. This study could provide the scientific basis for deeply understanding the mechanism of soil aggregates disintegration and splash erosion.
Local community and research interest to better understand regional climate change impacts has led to the establishment of a long-term soil moisture and weather observation network in the Roaring Fork catchment of the Colorado River Headwaters. This catchment-wide suite of 10 stations collects frequent and continuous data on soil moisture, soil temperature, rain, air temperature, relative humidity, and (at some stations) snow across an elevational gradient from 1,800m to 3,680m in elevation. We demonstrate how this effort can support research on mountain hydrology with applications for resource management and climate change adaptation decision making. We also share perspectives on the value and opportunities a community science approach can bring to catchment studies moving forward. All data from this project are publicly available.
IntroductionThe Turkey Lakes Watershed (TLW) study (https://www.canada.ca/en/environment-climate-change/services/turkey-lakes-watershed-study.html) was established in 1979 and is one of the longest running watershed-based ecosystem studies in Canada (Foster, Beall & Kreutzweiser, 2005; Jeffries, Kelso & Morrison, 1988; Morrison, Cameron, Foster & Groot, 1999). The watershed drains 10.5 km2 of Eastern Temperate Mixed Forest (Baldwin et al., 2018) or Great Lakes – St. Lawrence forest region (Rowe, 1972) within the Boreal Shield Ecozone (Wiken, 1986), and is located approximately 60 km north of Sault Ste. Marie, Ontario (47°03’N, 84°25’W) (Figure 1). Researchers from several federal government departments (Natural Resources Canada (NRCAN), Environment and Climate Change Canada (ECCC) and Fisheries and Oceans Canada (DFO) established this research watershed to evaluate the impacts of acid rain on terrestrial and aquatic ecosystems (e.g., Foster, Hazlett, Nicolson & Morrison, 1989; Hazlett, Curry & Weldon, 2011; Jeffries, Semkin, Beall & Franklyn, 2002; Kelso 1988). Since its inception, many studies have taken a multi-disciplinary, whole-ecosystem approach to investigate the processes governing terrestrial and aquatic responses to natural and anthropogenic disturbances. This holistic approach has allowed research to expand from its original acidification focus to address a range of other ongoing and emerging environmental issues (e.g. habitat alteration, organic contaminants, forest management, climate change) and to involve numerous academic, government and industrial collaborators.
A. R. MacKenzie1,2,*, S. Krause1,2, K. M. Hart1, R. M. Thomas1,3, P. J. Blaen1,4, R.L. Hamilton1,2, G. Curioni1,2, S. E. Quick1,2, A. Kourmouli1,2, D. M. Hannah1,2, S. A. Comer-Warner1,2, N. Brekenfeld1,2, S. Ullah1,2 and M. C. Press1,51. Birmingham Institute of Forest Research, University of Birmingham, Birmingham B15 2TT, UK2. School of Geography, Earth and Environmental Science, University of Birmingham, Birmingham B15 2TT, UK3. Now at Big Sky Science Ltd, Sutton Coldfield, West Midlands, B72 1SY, UK4. Now at Yorkshire Water, Chadwick Street, Leeds, LS10 1LJ, UK5. Now at Manchester Metropolitan University, Manchester, M15 6BH, UK* Corresponding author:email@example.comKeywordsSoil moisture; stream metabolism; climate change; long-term monitoringSummary Paragraph The ecosystem services provided by forests modulate runoff generation processes, nutrient cycling and water and energy exchange between soils, vegetation and atmosphere. Increasing atmospheric CO2affects many linked aspects of forest and catchment function in ways we do not adequately understand. Most significantly, global levels of atmospheric CO2 will be around 40% higher in 2050 than current levels, yet estimates of how water and solute fluxes in forested catchments will respond to increased CO2 are highly uncertain. The Free Air Carbon Enrichment (FACE) facility of the University of Birmingham’s Institute of Forest Research (BIFoR) is an intensively monitored forest site specialising in fundamental studies of the response of whole ecosystem patches of mature, deciduous, temperate woodland to elevated CO2. Here, we introduce the facility, situated in a mixed land-use headwater catchment, with a particular focus on its environmental setting and the experimental infrastructure. The facility offers a significant opportunity to advance multi- and interdisciplinary understanding at the interfaces of soil, vegetation, hydrosphere and atmosphere under changed atmospheric composition.Site Description and MethodsThis summary complements online introductory videos (https://tinyurl.com/y3a2hkkx) and draws on the facility ‘White Book’, which is a live web-document containing extensive details of all the projects undertaken at the facility and details of instrument placement (heights, depths, spatial separation).The Wood Brook catchment and FACE facilityThe BIFoR FACE facility is situated in a mainly agricultural headwater catchment in the UK drained by the Wood Brook, and consists of the main elevated CO2 (eCO2) facility and a number of spatially nested satellite study sites including various forest plantations of different age and management (Figure 1). The facility is in lowland, rural, central England (52o48’ 3.6” N, 2o 18’ 0” W, 106 m above mean sea level (amsl)), within a patchy landscape typical of most temperate forest settings (Haddad et al., 2015). Wood Brook is a second-order stream with a 3.1 km² catchment ranging in elevation from 90 to 150 m amsl (Blaen et al., 2017) and subsequently draining into the River Severn catchment (the most voluminous river in England and Wales). The entire catchment is experiencing drastic land-use changes, having been converted to organic farming since 2019 and herbal lays in replacement of what was previously grass monoculture or arable, in addition to the new forest plantations.[Figure 1 here]The BIFoR FACE forest at the bottom of the Wood Brook catchment is a mature deciduous woodland, with dominant (25-m tall) English oak (Quercus robur ) planted around 1850. Sub-dominant (ca. 10 m tall) species consist of common hazel (Corylus avellana ), common hawthorn (Crataegus monogyna ), sycamore maple (Acer pseudoplatanus ) and other native species (Hart et al., 2019). Each stem with diameter-at-breast-height greater than 10 cm has been geolocated and tagged. Centimetre-scale forest structure was measured by a lidar overflight in August 2014 and by terrestrial laser scanning (private communication, Eric Casella, Forest Research, Surrey, UK); this structure establishes the basis for penetration of air, light, and water into the forest canopy.The central, eCO2 component of BIFoR FACE consists of nine experimental patches of 15 m radius (Hart et al., 2019). Three ‘undisturbed’ (or ‘ghost’) patches have no CO2-dosing infrastructure; three ‘control’ patches are exposed to ambient CO2 concentrations delivered via the same infrastructure used in the three ‘treatment’ patches to maintain +150 ppmv above ambient CO2 at all levels of the canopy. Elevated CO2 is maintained during daylight hours from oak bud burst (ca. 1st April) to last leaf fall (ca. 31st October). The CO2-dosing system works well; one-minute running means are within 15% of target in the treatment plots, with less than 1% of the time showing deviation above 10% of the baseline value in the control plots (Hart et al., 2019). The first season with eCO2 was 2017 and the treatment will continue until at least 2026. A parallel study of the effect of nitrogen and phosphorus addition began in 2020 in the forest away from the FACE patches.Surrounding the BIFoR FACE, the Wood Brook catchment hosts several long-term forest hydrological observatories. In partnership with the estate owners, young mixed-deciduous plantations are subjected to different manipulation treatment including irrigation and fertilisation experiments.The environmental contextThe climate at the Wood Brook catchment is that of the temperate maritime zone of north-west Europe (Barry and Chorley, 2010). The site-mean annual temperature (MAT) measured between 2016 and 2019 was 10.6 ± 0.8 oC and its mean annual precipitation (MAP) was 676 ± 66 mm. This situates BIFoR FACE well inside the MAT-MAP climate space for temperate forests (Sommerfeld et al., 2018). The catchment is within the area covered by the Central England Temperature record, which provides a time series back to 1772 (Parker et al., 1992).The Wood Brook catchment is situated in a Nitrate Vulnerable Zone (European Union Directive 91/676/EEC) with mean nitrate concentrations in the Wood Brook ranging from 5 to 7 mg N l-1 (Blaen et al., 2017). The contemporary reactive nitrogen deposition from the atmosphere in the catchment is ~22 kg N ha-1 y-1 with an ammonium to nitrate deposition ratio of 7:3 (private communication, S. Tomlinson, UK Centre for Ecology & Hydrology). Deposition of this scale represents less than about 15% of the total nitrogen nutrition of temperate deciduous forest trees (Rennenberg and Dannenmann, 2015).Site infrastructureThe Wood Brook is equipped with two continuous water quality monitoring stations comprising in-stream sensors measuring stage, water temperature, and electrical conductivity continuously (up to every 10 seconds). Sensors to measure further parameters (UV-VIS absorbance, DO, pH, and turbidity) are housed in an insulated kiosk located on the streambank (Blaen et al., 2017a). An ISCO peristaltic pump (Lincoln, NE, USA) passes 1 L of stream water through these sensors every hour. Continuous stream monitoring is supplemented with campaign-based sampling facilitated by networks of surface water ISCO autosamplers, for instance during tracer tests (Blaen et al., 2017a,b), as well as spatially nested multi-level mini-piezometers installed in the streambed to investigate streambed biogeochemical processes and groundwater-surface water interactions (Comer-Warner et al., 2019, Comer-Warner et al., 2020).Soil moisture in the main BIFoR FACE facility is monitored by 12 cm long frequency domain sensors (CS655 by Campbell Scientific, claimed accuracy ± 3 % v/v for ‘typical’ soils) installed diagonally from the surface in groups of three spaced 1 m apart, with two groups in the ’control’ and ’treatment’ patches and one group in the ’ghost’ patches, and monitoring at 15 to 30 min resolution.In addition, one of the juvenile plantations close to the catchment outlet has been instrumented since 2016 with active fibre-optic distributed temperature sensing (FO-DTS) for measuring soil temperature and soil moisture at a submeter spatial resolution, resulting in 1850 soil temperature and soil moisture sampling locations across the site, ranging from 10-40 cm depths (Ciocca et al., 2020). The retrieval from the FO-DTS has a maximum at 38%v/v, a value empirically determined from a soil-specific field calibration against point soil moisture sensors installed adjacent to the fibre-optic cable. The variability shown for the FO-DTS is that for 4 quasi-independent measurements per day at 25 cm intervals along the fibre-optic cable. Uncertainties of ca. 3-5% v/v have been reported for soil moisture measurements with the DTS technique (Gamage et al. 2018).Each treatment (eCO2) and control experimental patch is ringed by 16 free‐standing, climbable, lattice towers that reach 2-3 m above the local oak canopy; a 17th tower is sited in the centre of each patch. The lattice towers are secured by screw piles; the experimental site contains no concrete foundations or guy wires. Access to the experimental patches is via low-level walkways raised approximately 30 cm above ground level to prevent compaction. Canopy access above 5 m is contracted to climbing arborists or achieved using a bespoke canopy access system (CAS) installed from the 17th central tower of each infrastructure array. The CAS is operated by trained staff so that rope access training is not required for researchers. Welfare and simple laboratory facilities are provided. Elevated CO2 dosing, canopy access, and routine monitoring is operated by a team of six technical staff permanently stationed at BIFoR FACE.Four meteorological masts are located at the periphery of the woodland and a 40 m ‘flux tower’ stands towards the downwind end of the wooded area so that its flux ‘footprint’ is within the forest for the prevailing south-westerly winds. During dosing, true biogeochemical CO2 fluxes are, of course, obscured by the gas released to provide the eCO2 treatment effect but sensible and latent heat fluxes are recorded.Figure 2 illustrates the flow of data and tissue samples into their permanent repositories. Other equipment (not shown) is deployed ad hoc within specific projects.[Figure 2 here.]To complement the experimental infrastructure in the Wood Brook catchment and BIFoR FACE facility, an integrated groundwater-surface water model has been developed and validated by a combination of flow signatures and applied to investigate stream and subsurface water and energy balance in response to forest shading (Qiu et al., 2019).Example ResultsSoil moisture dynamics, stream discharge, and water quality in mature forest and young plantationExample core data (precipitation and FACE soil water content, discharge and DO) and project-specific data (field-scale soil moisture measured by FO-DTS at 10 cm) demonstrate the value of long-term integrated monitoring in ecohydrological observatories such as the Wood Brook catchment (Figure 3).The variability of the temperate maritime climate is evident: prolonged wetting and drying events with occasional, shorter, high-intensity rainfall events. Signals can take a long time to emerge within such variability, which is a key argument for a long-term experimental platform such as BIFoR FACE. The time series at this relatively early stage suggests that: (i) the plantation is systematically wetter than the neighbouring FACE forest even though the plantation slopes downwards towards FACE; (ii) there is significant spatial variability in the plantation and FACE forest; and (iii) the eCO2 patches are drier than the aCO2 and undisturbed patches. Point (iii) is a result of spatial variability in the forest; the strength of soil moistening due to eCO2, if any is present (cf. Ellsworth, 1999; Drake et al., 2016), remains to be quantified.Corresponding water levels at the Wood Brook catchment outlet highlight the general “flashiness” of the flow regime with relatively fast responses to precipitation events for a permeable catchment as well as fast recession of flow (Figure 3 bottom). This example time series of one of our monitoring stations also indicates some of the challenges in maintaining consistent quality control throughout long-term observation networks. In addition to data losses induced by power supply failures in Spring 2019, observed values up to early 2019 were an order of magnitude lower than from summer 2019 onwards due to repeated sedimentation of the water level sensor and recurring changes to the channel cross sectional profile that finally led to a relocation of the sensor as indicated in Figure 3. The additional value of continuously monitored water level and water quality data (as highlighted by the example of dissolved oxygen in Fig 3 bottom) extends beyond the ability to observe long-term trends in catchment behaviour in response to land-use changes but also provides opportunity to enhance mechanistic process understanding of in stream metabolism and biogeochemical processing as well as event-based activation of pollution sources (Blaen et al., 2017a).[Figure 3 here.]Data protocol and availabilityAll projects form part of the overall collaborative effort to understand catchment behaviour and forest form and function, and all facility users sign a data protocol to that effect. The BIFoR FACE science community believe and advocate transparency in science, assured through open data after an agreed period of privileged use.The facility is supported by a full-time data manager (author GC), responsible for tracking all data and tissue samples. The data is available upon request; an open data repository for a subset of core data is under construction.The continuous streams of data are handled by a suite of dataloggers and a local LAN network which allows data to be saved on the BIFoR FACE facility server (Figure 2). A back-up server located on site in a separate building stores a daily image of the primary server. Data is transferred daily to the University of Birmingham servers and the raw and processed data (i.e. organised in a consistent format and cleared of evident issues) are stored separately to improve resilience. Non-continuous data collected by researchers is stored in the University of Birmingham servers and handled directly between researchers and the data manager.All tissue is recorded when sampled and a chain-of-custody initiated using Pro-curo. Quenching of biological samples to -70oC is accomplished on-site using a dry shipper (BioTrex-10, Statebourne Cryogenics, Tyne & Wear, UK), avoiding the need for transporting liquid nitrogen. Short-term tissue storage at 5oC and -20 oC can be accommodated on-site, but the permanent tissue bank resides at the University of Birmingham Edgbaston campus.In summary, BIFoR FACE is an ambitious field facility designed primarily to measure the whole-system response of mature temperate forest to elevated CO2, but suitable for a wide range of complementary catchment studies. The facility is highly collaborative in nature and welcomes partners11https://www.birmingham.ac.uk/research/bifor/get-involved/index.aspx who wish to contribute as part of a multidisciplinary Community of Practice.AcknowledgmentsWe very gratefully acknowledge support from the JABBS Trust, Norbury Park Estate, The John Horseman Trust, Ecological Continuity Trust, NERC (grants NE/S015833/1, NE/P003486/1, NE/N020502/1; NE/T000449/1; NE/T012323/1), and the University of Birmingham. The soil moisture FO-DTS system installation was led by Francesco Ciocca while holding joint positions at the University of Birmingham and at Silixa Ltd. (London, UK).The BIFoR FACE facility cannot run without the dedicated support of its operations team (currently; Nicholas Harper, Peter Miles, Thomas Downes, Gael Denny and Robert Grzesik, formerly; Gary McClean and Anna Gardner). Foundational contributions to the design and implementation of the facility were made by Michael Tausz and Sabine Tausz-Posch. The FACE facility eCO2 treatment uses the system designed by John Nagy and installed by Keith Lewin, both of Brookhaven National Lab, USA. We acknowledge the considerable scientific input of visiting fellows (David Ellsworth, Kristine Crous, Debbie Hemming, Rich Norby, Theresa Blume and Mantha Phanikumar) and former researchers (Will Allwood, Alex Poynter, Elizabeth Hamilton). We gratefully acknowledge strategic guidance from BIFoR Directors (Rob Jackson, Jerry Pritchard, and Nicola Spence) and the Science Committee (Christine Foyer, Vincent Gauci, Francis Pope, and Estrella Luna Diez).ReferencesBarry, R. G., and Chorley, R. J. (2010) Atmosphere, Weather and Climate, 9th ed., Routledge, London.Blaen, P., K. Khamis, C. Lloyd, S. Comer-Warner, F. Ciocca, R. M. Thomas, A. R. MacKenzie, Stefan Krause (2017a), High-frequency monitoring of catchment nutrient exports reveals highly variable storm-event responses and dynamic source zone activation, J. Geophys. Res-Biogeosciences, 10.1002/2017JG003904Blaen P., Brekenfeld N., Comer-Warner S., Krause S. (2017b). Multitracer Field Fluorometry: Accounting for Temperature and Turbidity Variability during Stream Tracer Tests. Water Resources Research, 53,https://doi.org/10.1002/2017WR020815.Ciocca F., Abesser C., Findlay J., Chalari A., Mondanos M., Hannah D.M., Blaen P., Krause S. 2020. A Distributed Heat Pulse Sensor Network for Thermo-Hydraulic Monitoring of the Soil Subsurface. Quarterly Journal of Engineering Geology and Hydrogeology. 53. 352-365,https://doi.org/10.1144/qjegh2018-147Comer-Warner S., Ullah S., Kettridge N., Gooddy D., Krause S. (2019). Seasonal variability of sediment controls on carbon cycling in an agricultural stream. Science of the Total Environment. 688, 732-741,https://doi.org/10.1016/j.scitotenv.2019.06.317Comer-Warner, S.A., Gooddy, D.C., Ullah, S., Glover L., Kettridge N., Wrexler S.K., Kaiser J., Krause S. 2020. Seasonal variability of sediment controls of nitrogen cycling in an agricultural stream. Biogeochemistry. 148, 31–48 (2020). https://doi.org/10.1007/s10533-020-00644-zDrake, J.E., Macdonald, C.A., Tjoelker, M.G., Crous, K.Y., Gimeno, T.E., Singh, B.K., Reich, P.B., Anderson, I.C. and Ellsworth, D.S. (2016), Short‐term carbon cycling responses of a mature eucalypt woodland to gradual stepwise enrichment of atmospheric CO2concentration. Glob Change Biol, 22: 380-390. doi:10.1111/gcb.13109Ellsworth, D.S. (1999), CO2 enrichment in a maturing pine forest: are CO2 exchange and water status in the canopy affected?. Plant, Cell & Environment, 22: 461-472. doi:10.1046/j.1365-3040.1999.00433.xGalloway, J.N., Dentener, F.J., Capone, D.G. et al. (2004) Nitrogen Cycles: Past, Present, and Future. Biogeochemistry 70, 153–226. https://doi.org/10.1007/s10533-004-0370-0Gamage, D.N.V., Biswas, A., Strachan, I.B., Adamchuk, V.I. 2018. Soil Water Measurement Using Actively Heated Fiber Optics at Field Scale. Sensors 18 (4): 1116 DOI: 10.3390/s18041116Haddad, N.M., Brudvig, L.A., Clobert, J., Davies, K.F., Gonzalez, A., Holt, R.D., Lovejoy, T.E., Sexton, J.O., Austin, M.P., Collins, C.D., Cook, W.M., Damschen, E.I., Ewers, R.M., Foster, B.L., Jenkins, C.N., King, A.J., Laurance, W.F., Levey, D.J., Margules, C.R., Melbourne, B.A., Nicholls, A.O., Orrock, J.L., Song, D.X., Townshend, J.R., 2015. Habitat fragmentation and its lasting impact on Earth’s ecosystems. Sci. Adv. 1.https://doi.org/10.1126/sciadv.1500052Hart, Kris; Curioni, Giulio; Blaen, Philip; Thomas, Rick; Harper, Nicholas; Miles, Peter; Lewin, Keith; Nagy, John; Bannister, Edward; Cai, Xiaoming ; Krause, Stefan; Tausz, Michael; MacKenzie, A. Robert (2019) Characteristics of Free Air Carbon Dioxide Enrichment of a Northern Temperate Mature Forest. Glob Change Biol. doi:10.1111/gcb.14786Norby, R. J., M. G. De Kauwe, T. F. Domingues, R. A. Duursma, D. S. Ellsworth, D. S. Goll, D. M. Lapola, K. A. Luus, A. R. MacKenzie, B. E. Medlyn, R. Pavlick, A Rammig, B Smith, R Thomas, K Thonicke, A. P. Walker, Xiaojuan Yang, and Sönke Zaehle, Model-data synthesis for the next generation of forest FACE experiments, New Phytologist, 2015, DOI: 10.1111/nph.13593.Parker, D.E., T.P. Legg, and C.K. Folland. 1992. A new daily Central England Temperature Series, 1772-1991. Int. J. Clim., Vol 12, pp. 317-342.Payne, Richard John, Dise, Nancy B., Field, Christopher D et al. (3 more authors) (2017) Nitrogen deposition and plant biodiversity : past, present and future. Frontiers in Ecology and the Environment.https://doi.org/10.1002/fee.1528Qiu, H., Blaen, P., Comer‐Warner, S., Hannah, D. M., Krause, S., & Phanikumar, M. S. 2019. Evaluating a coupled phenology – surface energy balance model to understand stream – subsurface temperature dynamics in a mixed‐use farmland catchment. Water Resources Research, 55.https://doi.org/10.1029/2018WR023644Rennenberg, H., Dannenmann, M. (2015) Nitrogen nutrition of trees and temperate forests – the significance of nitrogen availability in pedosphere and atmosphere. Forests 6, 2820-2835.Sommerfeld, A., Senf, C., Buma, B. et al. (2018) Patterns and drivers of recent disturbances across the temperate forest biome. Nat Commun 9, 4355. https://doi.org/10.1038/s41467-018-06788-9Figure CaptionsFigure 1. (a) BIFoR FACE is located in Mill Haft (white dashed line; lighter patches show locations of the FACE arrays and control patches) in a patchwork of old-growth forest, new forest plantation on arable land, and arable fields. (b) Wood Brook catchment (white dashed line) with the stream running along the northern edge of Mill Haft. (c) Central England location of Mill Haft.Figure 2. A schematic view of the sensor deployment and tissue and data flow through BIFoR FACE and Wood Brook. The main experimental infrastructure elements are shown (left); replicates are indicated by “n = “. Data from electronic sensors are recorded in networked field dataloggers and relayed to the facility server. Back-up is carried out on-site and by daily data download to the main University of Birmingham servers with Retrospect software (Retrospect Inc. USA). Initial quality assurance is under the control of the BIFoR Data Manager (author GC) before data is released to the BIFoR FACE community. A parallel system operates for physical samples, the metadata from which enters the BIFoR FACE database via chain-of-custody software (Pro-curo Software Ltd, West Sussex, UK).Figure 3. a) time series of daily top-of-forest precipitation and soil moisture from distributed temperature sensing (DTS) by fibre-optic cable embedded at 10 cm depth between rows on new broadleaf forest plantation immediately south of the FACE forest (see Figure 1). b) Time series of shallow soil water content from an array of sensors in the FACE forest. The numbers of sensors at each part of the time series are reported in the top of the panel. c) Water level (in blue) and dissolved oxygen (in green) measured on the Wood Brook stream (see Figure 1).
In this study, we introduce datasets that include both hydrological and meteorological records at the Nučice experimental catchment (0.53 km2) which is representative for an intensively farmed landscape in the Czech Republic. The Nučice experimental catchment was established in 2011 for the observation of rainfall-runoff processes, soil erosion processes, and water balance of a cultivated landscape. The average altitude is 401 m a.s.l., the mean land slope is 3.9%, and the climate is humid continental (mean annual temperature 7.9 °C, annual precipitation 630 mm). The catchment is drained by an artificially straightened stream and consists of three fields covering over 95 % of the area which are managed by two different farmers. The typical crops are winter wheat, rapeseed, and alfalfa. The installed equipment includes a standard meteorological station, several rain gauges distributed across the basin, and an H-flume that monitors stream discharge, water turbidity, and basic water quality indicators. Additionally, the groundwater level and soil water content at various depths near the stream are recorded. Recently, large-scale soil moisture monitoring efforts have been introduced with the installation of two cosmic-ray soil moisture sensors. The datasets consist of measured precipitation, air temperature, stream discharge, and soil moisture and are available online for public use. The cross seasonal, open access runoff generation datasets at this small-scale agricultural catchment will benefit not only hydrologists but also local farmers.
The present dataset is related to the Arc-Isère long-term environmental research part of the Rhône Basin Long Term Environmental Research Observatory. This alpine watershed located in the French Alps is characterized by high Suspended Particulate Matter (SPM) in very anthropogenized valleys. Suspended Sediment Concentrations (SSC) naturally observed in the river are very high, ranging from a few tens of milligrams per litre at low flow to tens of grams per litre during major natural hydrological events (floods, debris flows) or river dam hydraulic flushes. One research objective related to this site aims at better understanding the SSC dynamics along the river using a system of nested watersheds (Arvan, Arc, and Isère) in order to access to both temporal and spatial dynamics. Studies using this dataset are on the quantification of fine sediment fluxes but also on the related morphological changes due to fine sediment deposition or resuspension. Additionally, the observatory database can support studies on contaminants (either dissolved or particulate contaminant). Six hydro sedimentary stations monitor SSC with high frequency via turbidity sensors associated to automatic samplers. Discharge is measured via classical water level measurements and a rating curve. The oldest station (Grenoble-campus) started recording data from 2006 while others hydro-sedimentary stations were built from 2009 to 2011. Data are available in an online data website called “Base de Données des Observatoires en Hydrologie” (Hydrological observatory database, https://bdoh.irstea.fr/ARC-ISERE/) with DOI references for each site. The hydrological and sediment transport time series are stored, managed and made available to a wide community in order to be used at their full extent. This database is used as a data exchange tool for both scientists and operational end-users and as an online tool to compute integrated fluxes.
Beasley Lake Watershed is an agriculturally influenced drainage basin in western Mississippi that has been intensively studied for 25 years. As part of the USDA Conservation Effects Assessment Project (CEAP), the watershed has archived hydrology, precipitation, and water quality data in order to measure the effects of multiple USDA Natural Resources Conservation Service conservation practices on lake water quality. The long-term database is available to researchers using a web-based application, Sustaining the Earth’s Watersheds, Agricultural Research Data System (STEWARDS). STEWARDS is a GIS-based data retrieval application that encompasses spatial and temporal data collected from multiple sites within the watershed. This data note describes information located in the STEWARDS Beasley Lake Watershed database, including hydrology, precipitation, and water quality data. This information is valuable to researchers and agencies beyond the USDA as an available and useful database to improve the understanding of how land-use practices affect the water quality of shallow lake systems.
The 20 km² Galabre catchment belongs to the French network of critical zone observatories. It is representative of the sedimentary geology and meteorological forcing found in Mediterranean and mountainous areas. Due to the presence of highly erodible and sloping badlands of various lithologies, the site was instrumented in 2007 to understand the dynamics of suspended sediments (SS) in such areas. Two meteorological stations including measurements of air temperature, wind speed and direction, air moisture, rainfall intensity, raindrop size and velocity distribution are installed both in the upper and lower part of the catchment. At the catchment outlet, a gauging station records the water level, temperature and the turbidity (10 min. time-step). Water and sediment samples are collected automatically to estimate SS concentration-turbidity relationships, providing SS fluxes quantifications with known uncertainties. The sediment samples are further characterized by measuring their particle size distributions (PSD) and by applying a low-cost sediment fingerprinting approach using spectrocolorimetric tracers. Thus, the contributions of badlands on different lithologies to total SS flux are quantified at a high temporal resolution providing the opportunity to better analyze the links between meteorological forcing variability and watershed hydrosedimentary response. The set of measurements was extended to the dissolved phase in 2017. Both the river electrical conductivity and its major ion concentrations are measured each week and every three hours during storm events. This allows progress in understanding both the origin of the water during the events and the partitioning between particulate and dissolved fluxes in the critical zone.
Internal erosion is one of the most common causes of failure in hydraulic engineering structures, such as embankments and levees. It also plays a vital role in the geohazards (such as landslides and sinkhole developments) and more importantly, the earth landscape evolution, which has a broad environmental and ecosystem impacts. The groundwater seepage is multi-directional, and its multi-dimensional nature could affect the initiation and the progression of internal erosion. With a newly developed apparatus, we carry out nine internal erosion experiments under five different seepage directions. The results reveal that the critical hydraulic gradient increases as the seepage direction varies from the horizontal to the vertical. After a global erosion is triggered, preferential erosion paths distribute randomly from the bottom to the top of the specimen. If the seepage direction is not vertical, small preferential erosion paths merge into a large erosion corridor, in which the loss of fine particles is significant but negligible outside. Results of experiments manifest that the erosion is heterogeneous and three-dimensional, even in the unidirectional seepage flow. The particles are rapidly eroded at the early stage of the erosion, indicating a high erosion rate. With the erosion time increasing, the particle loss slows down and even ceases if the time is long enough. The erosion rate increases if the seepage direction approaches a vertical direction. Overall, the erosion rate approximately decreases with erosion time exponentially. We proposed exponential equations to illustrate the variation of the erosion rate in the erosion process.
Evapotranspiration (ET) plays an important role in integrated water resource planning, development and management. This process is particularly relevant in semiarid regions. The aim of the present study is to compare the actual spatial and temporal evapotranspiration (ETa) patterns and temporal trends in two semiarid forests, one in Brazil (Aiuaba) and the other in Spain (Valladolid). We used the Surface Energy Balance Algorithm for Land (SEBAL) to assess the effect of climatic variation in both areas. In the Brazilian semiarid forest, Caatinga is the main vegetation, while it is stone pine in Spain. For this purpose, 69 Landsat-5 and 42 Landsat-8 images (1995 – 2019) were used. The Mann-Kendall test was applied to assess the occurrence of trends in precipitation, temperature and potential evapotranspiration data; and the Temporal Stability Index (TSI) to know which areas have greater seasonal ETa. The annual amplitude of the potential evapotranspiration (ET0) is the same in both areas, however, the Caatinga values are higher. In the Caatinga forest, when ET0 presents its highest values throughout the year, ETa presents the lowest, and vice versa. In the Pinares forest, ETa follows the ET0 dynamics during the year, and the difference between ET0 and ETa is maximum during the summer. The Caatinga forest showed a greater spatial variation of ETa than the Pinares forest as well as a greater extension with lower temporal stability of ETa than the Pinares forest. Both the Caatinga forest and the Pinares forest showed significant annual trends of increase for ET0 and ETa: 3.5 mm and 2.2 mm, and 7.0 mm and 3.9 mm, respectively.
Evaporation is the key to the basin’s water cycle. Agricultural irrigation has resulted in a significant variation of regional potential evaporation (Epen). The spatiotemporal variation of Epen and the influencing factors in the natural, agricultural, and desert areas in different developmental stages of irrigation in the Heihe River Basin (HRB) from 1970 to 2017 are comparatively analyzed in this study. This work focused on the correction effect of irrigation on the variation of Epen. The agricultural water consumption in HRB significantly varied around 1998 due to the agricultural development and water policy. Under the influence of irrigation, the annual variation of Epen in the agricultural, natural, and desert areas was significantly different. From 1970 to 1998, the annual trend slope of Epen in the natural area only reduced by 1 mm decade-1, while that in the agricultural area significantly decreased by 39 mm decade-1. After the implementation of water-saving irrigation, the Epen in the natural and agricultural areas increased by 11 and 54 mm decade-1, respectively, from 1998 to 2017. In contrast with the natural and agricultural areas, Epen in the desert area decreased by 80 mm decade-1 from 1970 to 1998 and continuously decreased by 41 mm decade-1 from 1998 to 2017. However, the regulatory effect of irrigation on Epen in the desert area started to manifest due to the expansion of the cultivated land area in the desert area from 2010 to 2017. Irrigation has a significant regulatory effect on the variation of Epen in HRB. The regulatory effect is mainly reflected on the aerodynamic term (Eaero). The analytical results of the main meteorological factors affecting Epen in different regions indicated that the main meteorological factors influencing the variation of Epen in each region are the wind speed 2 m above the surface (U2) and the water vapor pressure difference (VPD).
Subalpine forests are hydrologically important to the function and health of mountain basins. Identifying the specific water sources and the proportions used by subalpine forests is necessary to understand potential impacts to these forests under a changing climate. The recent ‘Two Water Worlds’ hypothesis suggests that trees can favour tightly bound soil water instead of readily available free-flowing soil water. Little is known about the specific sources of water used by subalpine trees Abies lasiocarpa (Subalpine fir) and Picea engelmannii (Engelmann spruce) in the Canadian Rocky Mountains. In this study, stable water isotope (δ18O and δ2H) samples were obtained from Subalpine fir and Engelmann spruce trees at three points of the growing season in combination with water sources available at time of sampling (snow, bound soil water, saturated soil water, precipitation). Using the Bayesian Mixing Model, MixSIAR, relative source water proportions were calculated. In the drought summer examined, there was a net loss of water via evapotranspiration from the system. Results highlighted the importance of tightly bound soil water to subalpine forests, providing insights of future health under sustained years of drought and net loss in summer growing seasons. This work builds upon concepts from the ‘Two Water Worlds’ hypothesis, showing that subalpine trees can draw from different water sources depending on season and availability. In our case, water use was largely driven by a tension gradient within the soil allowing trees to utilize tightly bound soil water and saturated soil water at differing points of the growing season.
Long-term experimental watershed studies have significantly influenced our global understanding of hydrological processes. The discovery and characterization of how stream water quantity and quality respond to a changing environment (e.g., land use change and acidic deposition) has only been possible due to the establishment of catchments devoted to long-term study. One such catchment is the Fernow Experimental Forest (FEF) located in the headwaters of the Appalachian Mountains in West Virginia, a region that provides essential freshwater ecosystem services to eastern and mid-western USA communities. Established in 1934, the FEF is among the earliest experimental watershed studies in the Eastern USA that continues to address emergent challenges to forest ecosystems, including climate change and other threats to forest health. This data note summarizes some of the seminal findings from more than 50 years of hydrologic research in the FEF. During the first few decades, research at the FEF focused on the relationship between forest management and hydrological processes – especially those related to the overall water balance. Later, research efforts included the examination of interactions between hydrology and soil erosion, biogeochemistry, N-saturation, and acid deposition. Hydro-climatologic and water quality datasets from long-term measurements and data from short-duration studies are publicly available to provide new insights and foster collaborations that will continue to advance our understanding of hydrology in forested headwater catchments. As a result of its rich history of research and abundance of long-term data, the FEF is uniquely positioned to continue to advance understanding of forest ecosystems in a time of unprecedented change.
Wildfires are a cause of soil water repellency (hydrophobicity), which reduces infiltration while increasing erosion and flooding from post-fire rainfall. Post-fire soil water repellency degrades over time, often in response to repeated wetting and drying of the soil. However, in mountainous fire-prone forests such as those in the Western USA, the fire season often terminates in a cold and wet winter, during which soils not only wet and dry, but also freeze and thaw. Little is know about the effect of repeated freezing and thawing of soil on the breakdown of post-fire hydrophobicity. This study characterized the changes in hydrophobicity of Sierra Nevada mountain soils exposed to different combinations of wet-dry and freeze-thaw cycling. Following each cycle, hydrophobicity was measured using the Molarity of Ethanol test. Hydrophobicity declined similarly across all experiments that included a wetting cycle. Repeated freezing and thawing of dry soil did not degrade soil water repellency. Total soil organic matter content was not different between soils of contrasting hydrophobicity. Macroscopic changes such as fissures and cracks were observed to form as soil hydrophobicity decayed. Microscopic changes revealed by scanning electron microscope imagery suggest different levels of soil aggregation occurred in samples with distinct hydrophobicities, although the size of aggregates was not clearly correlated to the change in water repellency due to wet-dry and freeze-thaw cycling. A nine year climate and soil moisture record from Providence Critical Zone Observatory was combined with the laboratory results to estimate that hydrophobicity would persist an average of 144 days post-fire at this well-characterized, typical mid-elevation Sierra Nevada site. Most of the breakdown in soil water repellency (79%) under these climate conditions would be attributable to freeze-thaw cycling, underscoring the importance of this process in soil recovery from fire in the Sierra Nevada.