Unit 5.1: Water Balance of a Tree

Introduction

The assignment is to calculate an annual water balance for a tree using data gathered at the Southern Sierra Critical Zone Observatory. In the framework of experimental design, you will organize around a research question "Is there enough water in the soil to account for transpiration?" After gathering and organizing data, you will calculate the annual water fluxes and reservoirs using a mass balance approach - later these lessons can be expanded to catchment scale calculations. In this unit, you will:

• integrate CZO data from multiple sensors to calculate a water balance centered on a tree
• apply concepts of fluxes and reservoirs to complete a mass balance equation on an annual time scale

Unit 5.1: Water Balance of a Tree

Part 1 - Water Cycle Measurement

Pre-class

• Read the following articles:
• Dingman, S. Lawrence. Chapters 1 and 2. "Introduction to Hydrologic Science" and "Basic Hydrologic Concepts". Physical Hydrology. Second Ed. Prentice Hall: New Jersey, 2002.
• The USGS Water Science School
• Answer the following guided questions as you read the chapters and browse the website:
• How do water properties and cycling processes vary spatially? Temporally?
• How do scientists measure water properties and processes?
• How does water cycling impact Critical Zone function and properties?
• How do processes in the Critical Zone affect water balance?

Lecture Discussion

• Introduction to Measuring the Water Cycle in the Sierra Nevada which covers water balance equations, fluxes and reservoirs, and how to think about the water balance in the context of a forested catchment. You will also be introduced to the Southern Sierra Critical Zone Observatory. This will give you background for the water balance worksheet activity we'll do later in class.

Water Balance Worksheet Activity

• In this activity you will identify the components in the water balance of a tree and the measurements needed to obtain the needed data. You will start this activity in class and then finish it outside of class prior to the next class period.
• 5.1.1 Worksheet - Water Balance (Microsoft Word 200kB Apr17 17)

Homework Assignment

• Complete water balance worksheet you started in class.

Part 2 - Water Cycles in the Critical Zone

Lecture Discussion

• Continue to explore the water cycles at Critical Zone Observatories (CZOs). We will talk about making measurements and using CZO water balance data at the Southern Sierra CZO. This will give you the background for the tree scale water balance activity we'll do later in class.
• Water Budgets for Sierra Nevada Catchments (PowerPoint 2007 (.pptx) 14.7MB May30 17)

Tree Scale Water Budget Activity

• This activity uses streamlined data from the Southern Sierra CZO flux towers, soil sensors, and Critical Zone Tree in a framework for estimating contributions to stream discharge and calculating the water balance for a tree. You will assess the role of trees in moving water from subsurface to atmosphere, the fraction that flows to the stream, and investigate differences in the water balance between seasons as changing soil water, precipitation, and ET shift in response to seasonal shifts in precipitation and temperature. You will end up using a selection of the data files. However, a larger set of data files is presented. You need to evaluate and choose which files to work with, as researchers do. More data can be explored at the SSCZO digital library (see additional resources).
• Tree Water Budget 5.1.2 Worksheet - Tree Water Budget (Microsoft Word 37kB Apr17 17)
• Modified Data sets: transpiration (radiation, tree parameters), infiltration (soil moisture and soil characteristics), time period for infiltration (time of snow cover), discharge from stream (Providence (P300) and smaller subcatchments). These data sets contain more than enough data to do the calculation.
• 5.1.2 Data - Soil moisture (Excel 145kB May1 17)
• 5.1.2 Data - Discharge from Providence P301 (Excel 21kB May1 17)
• 5.1.2 Data - Discharge from all Providence streams (Excel 2007 (.xlsx) 28kB May1 17)
• 5.1.2 Data - Flux Tower Precip and ET (Excel 45kB May1 17)

Homework

• Finish up the Tree Scale Water Budget activity that you began in class.

Additional Resources

You may also look through the official data files at the following locations. Please note that evapotranspiration is not currently available (2016) :

• https://eng.ucmerced.edu/snsjho/files/MHWG/Field/Southern_Sierra_CZO_KREW/Critical_Zone_Tree/CZTree1/Level_1b
• https://eng.ucmerced.edu/snsjho/files/MHWG/Field/Southern_Sierra_CZO_KREW/P301_Flux_Tower/Data/Level_1
• https://eng.ucmerced.edu/snsjho/files/MHWG/Field/Southern_Sierra_CZO_KREW/Providence_Creek/Discharge/Level_1b

Additional references:

• Bales, R.C., J.W. Hopmans, A.T. O'Geen, M. Meadows, P.C. Hartsough, P. Kirchner, C.T. Hunsaker, and D. Beaudette. 2011. Soil Moisture Response to Snowmelt and Rainfall in a Sierra Nevada Mixed-Conifer Forest. Vadose Zone J. 10:786–799. doi:10.2136/vzj2011.0001.
• Baldocchi, Dennis D., Xu, Liukang, and Kiang, Nancy, 2004. How plant functional-Type, Weather, Seasonal Drought, and Soil Physical Properties Alter Water and Energy Fluxes of an Oak-Grass Savanna and an Annual Grassland. Agricultural and Forest Meteorology, 123, 13-39.
• Fernandez-Illescas, C. P., A. Porporato, F. Laio, and I. Rodriguez-Iturbe. 2001. The ecohydrological role of soil texture in a water-limited ecosystem. Water Resources Research 37:2863-2872.
• Le Maitre, David C., Scott, David F., and Colvin, C., 1999. A Review of Information on Interactions between Vegetation and Groundwater. Water SA, 25 (2), 137-152.
• Lutz, James, A., van Wagtendonk, Jan W., and Franklin, Jerry F., 2010. Climatic Water Deficit, Tree Species Ranges, and Climate Change in Yosemite National Park. Journal of Biogeography, 37, 936-950.
• Neilson, Ronald P., 1995. A Model for Predicting Continental-scale Vegetation Distribution and Water Balance. Ecological Applications, 5(2), 362-385.
• Royce, E.B. and Barbour, M.G., 2001. Mediterranean Climate Effects. I. Conifer Water Use Across a Sierra Nevada Ecotone. American Journal of Botany, 88(5), 911-918.
• Stephenson, Nathan L., 1998. Actual Evapotranspiration and Deficit: Biologically Meaningful Correlates of Vegetation Distribution Across Spatial Scales. Journal of Biogeography, 25, 855-870.
• Stephenson, Nathan L., 1990. Climatic Control of Vegetation Distribution – The role of the Water Balance. The American Naturalist, 135, 649-670.
• Seyfried, M. S. and B. P. Wilcox. 2006. Soil water storage and rooting depth: key factors controlling recharge on rangelands. Hydrological Processes 20:3261-3275.