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5.1.1 Lecture - Forest Water Budgets
- 1. Monitoring the hydrologic cycle in the Sierra Nevada mountains Photo © Roger J. Wyan Photography
- 2. What is the hydrological cycle? Why do scientists measure the hydrological cycle? Who we are and where are we located? How do we calculate the water balance for a tree? We measure Collecting and retrieving data. Effect of increased density of the forest and forest treatments on water cycle.
- 3. What is the hydrologic cycle? The hydrologic or water cycle is the movement of water on, above, below, and through the earth’s surface.
- 4. Biological Property Transpiration Photosynthesis Chemical Property Precipitation Dissolution Physical Property Condensation Evaporation Energy Energy transfers through the water cycle Processor Properties of Water (Adapted from Ripl and Hilmann, 2000) “Water: the Bloodstream of the Biosphere”
- 5. Why do scientists measure the hydrologic cycle? Weather forecasting Water use forecasting Understand climate trends Flood preparation Hydrologic modeling Why is it important for scientists to measure the hydrologic cycle?
- 6. Who We Are: The Southern Sierra Critical Zone Observatory Professors, students and staff from over 9 different universities and institutions Main site is located 10 mi E of Shaver Lake Second site in Sequoia National Park 3 additional flux tower sites at different elevations Image courtesy SSCZO
- 7. The Southern Sierra Critical Zone Observatory The Critical Zone lies between rock and sky... where water, atmosphere, ecosystems, and soils interact. It is essential to life on Earth, including food production and water quality. (NSF 2005) The SSCZO is one of 10 observatories throughout the US We focus on how the CZ interacts with water Key goal: to predict how water budgets and vegetation will respond to climate change, land management and disturbance.
- 8. 4 measurement stations located west to east transect at approx. 800 m elevation intervals beginning at 405 m. All the sites were on soil developed from granitic parent material, and had vegetation that had not been disturbed recently. Four Critical Zone measurement stations in and around the Upper Kings River basin . .. . Illustrated map courtesy Lynn Sullivan From Goulden et al., 2012
- 9. Water Budget Precipitation (P) = Evapotranspiration (ET) + Runoff (Q) + Recharge (R) + Change in Storage (ΔS) (can be soil moisture or groundwater) P = ET + Q + R + S P ET + Q + S Note: in granitic mountains, such as the Sierra Nevada, R & ΔSgroundwater are often very small
- 10. Precipitation (P)Tree transpiration (T) Evaporation from soil (E) Runoff (Q) Deep percolation (R) Which are the stores & which are the fluxes? Rainfall Partitioning Tree image courtesy SSCZO Groundwater Atmosphere Soil Moisture Infiltration/Recharge (R)
- 11. Precipitation Evapotranspiration Sublimation Infiltration Reservoirs Runoff Can one scale up from a single tree to estimate the water balance of a forest?
- 12. Measuring Streamflow Flumes make the stream fit into a known shape. Runoff is the movement of water over the land surface. Stream flow is the flow of surface water runoff contained in a stream channel. Water depth sensors measure the height of water. Photos courtesy SSCZO and USFS
- 13. Tipping Bucket rain gauge measures liquid and solid precipitation Precipitation measurements Precipitation is the general name given for any form of condensed water that falls to Earth’s surface. Snow depth sensors use sound to record snow depth Snow pillow records weight of snow Photos courtesy SSCZO and USFS
- 14. Measuring evapotranspiration The movement of water from the liquid phase to the gas phase occurs by evaporation and/or transpiration. Evaporation is the change of water from a liquid to a gas by heating. Transpiration is water released from plants. Combined, this process is called evapotranspiration. Sap flow Flux tower instruments Photo © Roger J. Wyan Photography Photo courtesy SSCZO
- 15. Measuring evapotranspiration The eddy-covariance flux tower measures water vapor from the surrounding forest. The tower measures: - wind speed and direction - CO2 and H2O gas concentrations - air temperature - relative humidity - solar radiation The flux tower extends high above the surrounding forest. Photo © Roger J. Wyan Photography
- 16. Visualizing tree's heartbeat: A sap-flux meter monitors a Critical Zone Tree. Photo courtesy SSCZO
- 17. Measuring soil moisture Water that does not flow to the stream channel moves through the soil and/or rock through a process called infiltration. This water is known as groundwater. Soil moisture sensors buried at different depths underground. A series of soil moisture sensors buried underground to understand water uptake by tree roots. Photo courtesy SSCZO Image courtesy SSCZO
- 18. Weather stations This weather station is used to measure: - air temperature - wind speed - relative humidity - solar radiation - precipitation - snow depth Peak snow depth many years ago Photo courtesy SSCZO
- 19. Collecting and retrieving data An immense amount of data are collected each year. Instruments are located in remote areas, making it hard to collect data on foot during the winter Data stored on a datalogger and can be downloaded with a laptop From Kerkez et al., 2012 Photo © Roger J. Wyan Photography
- 20. Collecting and retrieving data The wireless embedded sensor network (WSN) was developed to make it easier to collect data remotely. Cell phone on the flux tower can be called to retrieve data. Small radios send data from one node to the next, and end at the base station at the flux tower. Photo © Roger J. Wyan Photography From Kerkez et al., 2012
- 21. Powering instruments A series of solar panels and batteries power all the instruments within the basin. Photo courtesy SSCZO Photo courtesy SSCZO Photo © Roger J. Wyan Photography
- 22. Explore a tree root model by P. Hartsough: https://youtu.be/L9F-QgQb2YY Fun with Trees: One large healthy tree can lift up to 4,000 liters of water from the ground and release it into the air. A tree can absorb up to 48 pounds of carbon dioxide per year and sequester 1 ton of carbon dioxide by the time it is 40 years old. One large tree can provide a day's supply of oxygen for up to four people. By late summer, trees transpire more water than we can measure in the soil. Perhaps there is a deeper rooting depth. Excavate the tree to discover the root system. Image courtesy SSCZO
- 24. TRANSPIRATION Stoma open, transpiration draws water outside the leaf Roothairs Water uptake in roots Cohesion (H-bonds) and adhesion (to cell walls) in the xylem draw the water to the leaves WaterPotentialGradient Outside air Ψ= -10 to -100 MPa Root xylem ψ=-0.6MPa Soil ψ = -0.3MPa Trunk xylem ψ=- 0.8MPa Leaf (cell wall) Ψ= -1Mpa Leaf (air spaces) Ψ= -7MPa Negative ψ (high) More negative ψ (low) Ψ = water potential (units = Pressure) Image courtesy SSCZO
- 25. Sierra National forests have had a tradition of fire suppression for the last 100 years. What might be some of the consequences of fire suppression? FOREST HISTORY
- 26. Photo by Eric Knapp, USFS THINNED UNIT WITH CONTROL IN BACKGROUND STANISLAUS-TUOLUMNE EXPERIMENTAL FOREST
- 27. How much water is being lost due to excess tree canopies? How much moisture is getting caught in the canopy and evaporating into the air? Photos by Matthew Meadows
- 29. Summary Water balance is accounting for the partitioning of precipitation into various fluxes and stores. Water accounting can be done on any time step; we often do it on an annual time step. Soil moisture is a store important for tree growth. We can do a water balance on a tree (sapflux) or a forest (flux tower). Scaling up from a point measurement involves making assumptions about spatial patterns. Sierra Nevada forests are overgrown.
- 30. Complex-forested terrain surrounding P301, with patchy snow. Photo by Matthew Meadows
Editor's Notes
- Photo Credit: Roger J Wyan Photography http://www.rogerwyan.com
- BACKGROUND FOR INSTRUCTOR Why are forests so important when studying the hydrologic cycle? 1. SCALE. Forest occupy about 1/3 of the earth's land area. 2. LEAVES. Tree leaves account for > 2/3 of the leaf area of land plants; therefore, they play a very important role in terrestrial hydrology. Leaves also can impact local humidity levels. 3. ROOTS. Extensive root systems stabilize soil. They affect water movement in soil through the capillary process. 4. VASCULAR SYSTEM. This system creates a soil-plant-atmosphere continuum moving large amounts of water from the soil though the plant and into the atmosphere. 5. CANOPY. Intercepts precipitation
- To understand the hydrologic cycle, one must think about “pools” and “fluxes”. A movement of water through the different spheres of the earths systems: atmosphere, biosphere, hydrosphere, and lithosphere. A pool within the water cycle refers to any storage area for water in any form. Pools include: oceans, lakes, rivers, streams, marshes, bays, ice sheets, glaciers, clouds, and ground water. Fluxes are the transfer processes that are involved in the cycle. Evaporation and precipitation are the major transfer processes that move water from the surface to the atmosphere (evaporation) and from the atmosphere to the surface (precipitation). Whereas evaporation converts liquid water into water vapor, condensation is the opposite process. Water vapor in the atmosphere condenses to form liquid water within clouds and eventually becomes precipitation. Surface runoff moves water across land, while infiltration and percolation moves water down into the soil. Transpiration is evaporation of water from plant surfaces; it moves soil water back into the atmosphere. The volume of the reservoirs remain constant. Residence time = volume of reservoir/total flux Solar energy drives the hydrologic cycle, and physical processes are the most important ones in this cycle. However, water does cycle through the biological community. Organisms gain the water they need from the food they eat and/or from water available in their environment. Water leaves living things either in biomass, in wastes, or as water vapor as evaporation occurs. Check out this reference and animated water cycle http://online.wvu.edu/Faculty/demo/Module_2/hydrologic.html A fun water cycle site http://www.discoverwater.org/water-cycle/ and more games here http://www.discoverwater.org/meet-bridger/
- Physical, chemical, biology properties transfer Solar Energy through the water cycle like cogs in a wheel. Sun from openclipart.org ‘Water is the basis of our nature: the most important liquor of life is the most precious agent also to mankind. No wonder that this mysterious agent is compared to blood. Ubiquitous and appearing in the form of vapour, of a liquid and as frozen ice, forming the most wonderful crystals.” ‘Water, the bloodstream of the biosphere, determines the sustainability of living systems. The essential role of water is expanded in a conceptual model of energy dissipation, based on the water balance of whole landscapes. In this model, the underlying role of water phase changes—and their energy-dissipative properties—in the function and the self-organized development of natural systems is explicitly recognized. The energy-dissipating processes regulate the ecological dynamics within the Earth’s biosphere, in such a way that the development of natural systems is never allowed to proceed in an undirected or random way. A fundamental characteristic of self-organized development in natural systems is the increasing role of cyclic processes while loss processes are correspondingly reduced. This gives a coincidental increase in system efficiency, which is the basis of growing stability and sustainability. Growing sustainability can be seen as an increase of ecological efficiency, which is applicable at all levels up to whole landscapes. Criteria for necessary changes in society and for the design of the measures that are necessary to restore sustainable landscapes and waters are derived.” “Water is the basis of our nature: the most important liquor of life is the most precious agent also to mankind. No wonder that this mysterious agent is compared to blood. Ubiquitous and appearing in the form of vapour, of a liquid and as frozen ice, forming the most wonderful crystals.” Resonate
- Forest thinning for fire and water management
- Goulden, M. L., R. G. Anderson, R. C. Bales, A. E. Kelly, M. Meadows, and G. C. Winston (2012), Evapotranspiration along an elevation gradient in California's Sierra Nevada, J. Geophys. Res., 117, G03028, doi:10.1029/2012JG002027. Color Map on Right: False color Landsat 5 Thematic Mapper image for September 4, 2011 (red is band 5, green is band 4, blue is band 3). The scale bar is km, and the blue polygon is the Upper Kings River watershed. Pine Flat Reservoir is near the southwestern edge of the watershed and the city of Fresno is in the southwestern corner of the image. The straight white lines connect the locations of the eddy covariance sites. The inset graph shows the elevation profiles along the segments of the eddy covariance transect.
- Yet the exercise also wishes us to discuss soil characteristics https://water.usgs.gov/edu/watercycleinfiltration.html Anywhere in the world, a portion of the water that falls as rain and snow infiltrates into the subsurface soil and rock. How much infiltrates depends greatly on a number of factors. Infiltration of precipitation falling on the ice cap of Greenland might be very small, whereas, as this picture of a stream disappearing into a cave in southern Georgia, USA shows, a stream can act as a direct funnel right into groundwater! Some water that infiltrates will remain in the shallow soil layer, where it will gradually move vertically and horizontally through the soil and subsurface material. Eventually, it might enter a stream by seepage into the stream bank. Some of the water may infiltrate deeper, recharging groundwater aquifers. If the aquifers are porous enough to allow water to move freely through it, people can drill wells into the aquifer and use the water for their purposes. Water may travel long distances or remain in groundwater storage for long periods before returning to the surface or seeping into other water bodies, such as streams and the oceans. Factors affecting infiltration Precipitation: The greatest factor controlling infiltration is the amount and characteristics (intensity, duration, etc.) of precipitation that falls as rain or snow. Precipitation that infiltrates into the ground often seeps into streambeds over an extended period of time, thus a stream will often continue to flow when it hasn't rained for a long time and where there is no direct runoff from recent precipitation. Soil characteristics: Some soils, such as clays, absorb less water at a slower rate than sandy soils. Soils absorbing less water result in more runoff overland into streams. Soil saturation: Like a wet sponge, soil already saturated from previous rainfall can't absorb much more ... thus more rainfall will become surface runoff. Land cover: Some land covers have a great impact on infiltration and rainfall runoff. Vegetation can slow the movement of runoff, allowing more time for it to seep into the ground. Impervious surfaces, such as parking lots, roads, and developments, act as a "fast lane" for rainfall - right into storm drains that drain directly into streams. Agriculture and the tillage of land also changes the infiltration patterns of a landscape. Water that, in natural conditions, infiltrated directly into soil now runs off into streams. Slope of the land: Water falling on steeply-sloped land runs off more quickly and infiltrates less than water falling on flat land. Evapotranspiration: Some infiltration stays near the land surface, which is where plants put down their roots. Plants need this shallow groundwater to grow, and, by the process of evapotranspiration, water is moved back into the atmosphere.
- Sun and tree images from openclipart.org. Think of a forest instead of a single tree. Can we scale up? Trees radiate heat. They are warmer that the snow. There is increased sublimation in denser forests. Furthermore snow melts out early around a tree trunk, but can last weeks or months longer away from the canopy or ion a shady spot nearby. Think about the annual cycle, most of the precipitation coming as snow, it melting, infiltrating and creating runoff which fill our reservoirs, providing water for agriculture (irrigation), domestic & industrial use & environmental flows (water in rivers for ecosystems)
- Embedded sensor networks of snow-pingers instruments which measure the distance from a solid surface - the top of the surface of the snow to the ground. These sensors are located at various locations in the catchment. They measure how much snow are being melted from (or added to) surfaces of the ground during the course of the water/snow season. The ultrasonic depth sensor measures distance by “pinging” the surface with an ultrasonic pulse. The time required for that pulse to return is used to calculate distance traveled to the target surface and back. An air temperature sensor connects the measurement to account for changes in air density. Distance to target (m) = 0.5 [ time(s) * Sound (m*s-1) ] where Sound is the speed of sound, corrected for air temperature Knowing the distance to the bare ground surface, the snow depth is determined as follows: distance to ground-distance to snow=snow depth
- http://www.rogerwyan.com
- Heat-pulse methods date back to the work of Huber (1932) who first conceived the idea of using heat as a tracer of sap flow. Later, Marshall (1958) developed a theoretical framework for heat-pulse, based on a set of analytical solutions to the following heat flow equation, to read more check out this website http://www.tranzflo.co.nz/index_files/Page416.htm. PLEASE NOTE SAP FLOW DATA is provided to the students in terms of water depth/unit area. This website located in our CZO network is much more informative and offers an improved understanding of how tree transpiration varies across the critical zone (CZ). It will help to explain the formulas and how the vertical water flux modulates the soil moisture balance which in turn influences the subsurface biogeochemical and landscape evolution process across the CZ. http://cals.arizona.edu/research/papuga/docs/CZO_SapFlowFactSheet.pdf http://sapflowtool.com/SapFlowToolManual.html#GettingStarted http://www.sciencedirect.com/science/article/pii/S0168192313003134 Agricultural and Forest Meteorology Volume 187, 15 April 2014, Pages 72–82 Forest transpiration from sap flux density measurements in a Southeastern Coastal Plain riparian buffer system (Bosch et al, 2014) Sap flux density, groundwater, and climatic data are collected to determine transpiration rates for different tree species and their relationship to potential ET rates and hydrologic and environmental conditions. The data indicate that transpiration within regional buffers uses a disproportionate amount of water on a per area basis compared to upland land covers, an important consideration when examining overall water consumption in regional watersheds. While the data indicate decreasing transpiration as a function of decreasing vadose zone soil water, no clear relationship to proximity to groundwater was observed. While landscape position did not consistently impact tree transpiration, vadose zone soil water does appear to influence transpiration rates. The lack of a consistent groundwater effect may have been due to an accessible water table even under declining groundwater conditions.
- Snow melts out early around a tree trunk, but can last for weeks or months away from the tree canopy or in a shady spot nearby. At our study sites, sensors are arrayed around different tree species: under the canopy, at the edge of the canopy, and outside the canopy.
- Kerkez, B., S. D. Glaser, R. C. Bales, and M. W. Meadows (2012), Design and performance of a wireless sensor network for catchment-scale snow and soil moisture measurements, Water Resour. Res., 48, W09515, doi:10.1029/2011WR011214.
- Kerkez, B., S. D. Glaser, R. C. Bales, and M. W. Meadows (2012), Design and performance of a wireless sensor network for catchment-scale snow and soil moisture measurements, Water Resour. Res., 48, W09515, doi:10.1029/2011WR011214.
- One large, healthy tree can lift up to 4,000 litres of water from the ground and release it into the air A tree can absorb as much as 48 pounds of carbon dioxide per year and can sequester 1 ton of carbon dioxide by the time it reaches 40 years old. One large tree can provide a day's supply of oxygen for up to four people.
- Image Citation: OpenStax, Transport of Water and Solutes in Plants. OpenStax CNX. May 10, 2013 http://cnx.org/contents/e5aabc6f-71d9-40d5-99f0-0fb2d8d47317@5.
- The foreground is a thinned forest – back to the early 1900’s tree density. The background is a current forest with about 5-6 times the number of stems, but only twice the biomass (i.e. many smaller trees) – basically a forest where fire suppression has been practiced for the last 100 years.
- Photos by Matt Meadows, c. 2012. Upper left: Gridded snow survey at Providence for peak snow. Dr Pete Hartsough taking snow water equivalent measurements. Grad student Estelle Eumont holding the scale. Lower Right: Pete Hartsough collects snow for isotopic analysis
- The size of the gaps between trees affect the energy balance and the amount of snow that is collected and stored.
- This is a photo of part of the SSCZO. It has patches of dense vegetation and open areas. It was thinned in 2012 as part of the Kings River Experimental Watershed management plan.; post thinning treatments (prescribed fire treatments have not happened as of fall 2016. http://www.fs.fed.us/psw/topics/water/kingsriver/