Module 5: Water transfer through the critical zone
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This page first made public: May 15, 2017
Summary and Overview
This module will teach students about Critical Zone water transfers at multiple scales. First, students calculate a mass balance for an individual tree before scaling up to the catchment level. Multiple approaches are used, including an equation-based problem set, and a graphical simulation exercise. This Water Transfers module encourages systems thinking, with the ultimate focus on two points: first, that in a mass balance, inputs must equal outputs plus the change in storage, and second that a tree can be an important part of the water balance. This module then teaches the students how to scale up from point measurements to catchment measurements and perform water balances on a catchment scale. The students are given an activity on water resource allocation.Jump down to: Strengths of the Module | Module Goals | Assessment | Module Outline
This module teaches students to evaluate the water balance of an ecosystem---a growing challenge as we face increasingly unpredictable water supplies coupled with rising demand for water across all sectors. Predicting water supplies impacts not only scientists, but all professions and all residents in their everyday lives. Understanding these water transfers and decisions will aid students in their civil and academic endeavors, even if they are outside the field of hydrology.
In this module, students learn about the links between the water cycle and the different components of the Critical Zone. By using mathematical and symbolic models, students will use a systems-based approach to analyze water balance components. Features of this module include the application of an experimental design for water-balance assessment, the use of data gathered by researchers at Critical Zone Observatories, and practice developing a water resource management plan under a given context. The final activity is to develop a water resource allocation plan while acknowledging the trade-offs between the environmental needs and human population needs.
- Students will apply a large variety of scientific principles to explain water interactions with regolith, air, and life that occur in the Critical Zone.
- Students are introduced to the importance of water movement in linking the key components of the critical zone: atmosphere, biology, and landforms. Students analyze data and use simple models to interpret spatial and temporal trends in water fluxes and reservoirs in a catchment and subcatchment context to answer questions about Critical Zone services.
- By the end of this module, students should be able to describe the features of a mass balance and how to solve for the different components. They should also be able to describe the role of a single tree (or collectively, vegetation) in the water cycle. Students are expected to identify and discuss variations in water balance research from plot to regional scales as well as water resource allocation decisions.
Students will be able to:
- Explain the reservoirs and fluxes of water cycling among the different parts of the Critical Zone.
- Analyze the water budget of a catchment that includes both biotic and abiotic processes.
- Calculate water budget components at multiple scales.
- Assess anthropogenic changes to the water cycling in a catchment.
Linking Unit Content to Overall Course Objectives
Below is a brief outline of examples within each Learning Unit where instructors can find resources that meet the overarching and four primary learning objectives for the whole Critical Zone curriculum.Overarching Learning Objective: Describe and characterize how interaction among the atmosphere, lithosphere, hydrosphere, biosphere, and soil (The Critical Zone) support and influence life.
- Unit 5.1: Vegetation acts as an intermediary in water transfers between the lithosphere and the atmosphere and regulates discharge of water from subsurface to surface water bodies. In Activities 5.1 and 5.2, students describe components of the water balance and quantify the role of vegetation in the water balance on a tree scale.
- Unit 5.2: Water flows in the Critical Zone link atmosphere, lithosphere, biosphere, and soil. Students will describe methods of studying water transfers in the Critical Zone at different scales. Students will learn to interpolate point data to areal averages in Activity 5.3. Students will make and justify water management decisions where water supply (amount, location and timing) limits uses in Activity 5.4.
Four primary objectives:
Objective 1) Identify grand challenges that face humanity and societies, ways which humans depend upon and alter the Critical Zone, and the potential role for Critical Zone science to offer solutions for these challenges.
- Unit 5.1: N/A
- Unit 5.2: Managing water integrates the ways humans depend upon and alter land use, surface waters, and vegetation. The water system faces growing demand and increased unpredictability for water quality and quantity. Students consider how to scale scientific measurements across scales to yield effective data (Activity 5.3), and weigh competing demands for water resources at a regional scale (Activity 5.4).
Objective 2) Use and interpret multiple lines of data to explain Critical Zone processes.
- Unit 5.1: To calculate a water balance, scientists integrate data from measurements of the atmosphere, subsurface soils and lithosphere, vegetation, and surface waters. In this unit students will use modified data from the Southern Sierra CZO to calculate a water balance in Activity 5.2.
- Unit 5.2: Discussions of appropriate time and space scales are common in environmental and ecological research. Students will discuss a study using Southern Sierra CZO data to scale up to a large river basin and then they will learn interpolation approaches (Activity 5.3). Students will also weigh competing demands in the water system to supply human and environmental needs (Activity 5.4).
Objective 3) Evaluate how the structure of the Critical Zone influences Critical Zone processes/services.
- Unit 5.1: Water transfers through the Critical Zone are mediated by soil depth, soil texture, vegetation type and density, climatic variables, and other factors. This unit, and Activity 5.2 in particular, explore how soil water storage, vegetation use, and climatic variables determine water discharge to surface streams. Using these data in the Sierra, it could be expanded to explore vegetation type and density in the historical context of logging and fire suppression.
- Unit 5.2: Critical Zone structure influences the surface and subsurface flows of water, including delivery of water to human users. This unit emphasizes the time and location of precipitation in the system, its influence on the water balance, and managing surface water for human needs (both Activities 5.3 and 5.4).
Objective 4) Analyze how water, carbon, nutrients, and energy flow through the Critical Zone and drive Critical Zone processes.Back to top
- Unit 5.1: Scientists study water transfers through the Critical Zone to analyze how water availability and timing influences forest productivity, soil development, and the carbon balance. This unit provides the building blocks to set up experimental measurements and calculate a water balance with data (conclusion of Activity 5.1, and all of Activity 5.2).
- Unit 5.2: Managing water supplies requires policy makers, resource managers, and scientists to communicate. The water simulation in Activity 5.4 emphasizes the balance between water that falls in uplands and is needed for various uses in the lower watersheds and valleys.
- Students use data from one of the CZOs to calculate a mass balance for an individual tree and later for a catchment. They will need to explain the different aspects of the water balance in that ecosystem, including reservoirs and fluxes, as well as diurnal and seasonal variations. For graduate students, the challenge of this activity can be increased by retrieving and using appropriate data from another CZO, or from other water years at the Southern Sierra CZO.
- Active participation in the water balance and scaling discussions as well as worksheet completion using the water balance simulation will assess the student's understanding and application of lessons in this module.
- Unit 5.1: Water balance of a tree (roots to leaves) (Two 75 min class sessions)
- Students complete a monthly mass balance for water use in a single tree, asking the question: Is there enough water in the soil to account for transpiration?
- Learning outcome: Assess the role of trees in moving water from subsurface to atmosphere
- Key concept: Trees have a sphere of influence where they impact the water balance. In a seasonally snow-covered environment, snow accumulation and retention is dependent on energy balance (snow subliming due to tree as a heat source and trees as shade) -- which is tied to tree density on the landscape.
- Unit 5.2: Assess water supplies and determine distribution at a regional scale (Two 75 min class sessions)
- In-class discussion focuses on concepts of scaling and conducting hydrologic research across multiple scales. Students complete two activities focused on measurement scaling and water resource management.
- Learning outcome: Understanding of assumptions and procedures to scale calculations across different scales and a decision basis for making water allocations.
- Key concept: Assumptions are required to apply small-scale datasets to catchment and regional scales. When used appropriately, these scaled data can help us further our understanding of regional water cycling and make quantitative, data-driven decisions for water resource management.