FoodprintUnderstanding Connections Between Food Choices and the Environment

Prof. Jennifer Jay

Chapter 5Freshwater as a Resource

Section 1. Learning Outcomes

By the end of this chapter, you will be able to: Discuss the importance of water as a resource Describe the hydrologic cycle Discuss whether water is a renewable resource Discuss water equity issues Understand the concept of hidden water Calculate the water footprint of a 2000 cal/day diet Estimate the energy use associated with bottle water use based on Gleick and Cooley’s

paper assessing life cycle impacts of bottle use in Los Angeles

Section 2. Chapter Overview

Section 3. Is freshwater a renewable resource?

To answer this question, let’s look first at the hydrologic cycle:

Freshwater cycles around the globe by the hydrologic cycle. There are several important processes:

Evapotranspiration: The combination of:o Evaporation—heat from sun causes water molecules to vaporizeo Transpiration--plants take in water through roots and release it through leaves

Condensation: water changes from vapor to a liquid. In cool air, water vapor condenses and forms clouds.

Precipitation: water releases from clouds as rain, sleet, snow, hail Infiltration: a portion of precipitation seeps into ground. The water hits the water table,

where the spaces between rocks and particles are saturated. Groundwater moves slowly toward the ocean.

Runoff--precipitation that doesn’t infiltrate runs off into creeks and rivers.

So, is freshwater a renewable resource?

Yes and no. It’s complicated. Let’s look at surface and groundwater separately:

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Surface water:

In some places, reduced rainfall and/or upstream diversions cause depletions in flows that have ecological consequences. The Delta Smelt is a good example.

In some places, rainfall is plentiful, and surface water amount isn’t so much of an issue. However:

With climate change, we are having shifts in the hydrologic cycle that could alter patterns. Many farmers around the world are having to abandon their livelihoods due to unreliable rainfall.

If it is polluted, it can’t be used in the same ways. Polluted water does get purified by the hydrologic

cycle, but not on the time scale that’s needed.

Groundwater:

Groundwater can be used unsustainably, and the timescale that it takes for infiltration to replenish the aquifer may be too long for it to be considered renewable.

Case study:For example, water is plentiful in Bangladesh, but the major rivers bringing water into

Bangladesh are contaminated before the water even crosses the border into Bangladesh. Bangladesh gets a lot of rain, which is pure water, but it comes during a monsoon cycle. Water is difficult to store and keep sterile. What about the groundwater? Much of the groundwater has arsenic at elevated levels. So even though there is so much water, clean water is precious.

The arsenic in the groundwater is actually connected to the aquaculture ponds. Organic matter is present at high levels in the water that seeps into the ground under the aquaculture ponds, which are fertilized with manure. This organic matter gets degraded in the subsurface, which results in anoxic conditions. When oxygen is not present, some bacteria will use iron hydroxide minerals as an electron acceptor (the same way we use oxygen!), which causes the mineral to dissolve. When the mineral dissolves, the arsenic that was attached to its surface is then liberated and can accumulate to high levels in the water.

Section 4. Global freshwater planetary boundary

Water use is one of the planetary boundaries. Too much manipulation of the freshwater cycle can result in negative impacts on biodiversity, food security, health security, the resilience of ecosystems, and ecosystem services including habitat, carbon sequestration, and climate regulation. Humanity is the dominant force altering river flows globally.

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Green water is water in unsaturated soil (soil moisture) and plants.Blue water is used to describe surface and ground water resourcesGray water is the amount of water needed to dilute contamination to background

levels.

Figure . Green water versus blue water. Source: Falkenmark and Rockstrom, 2006.

Global freshwater disruption can affect ecosystems through:

Loss of blue water (surface and groundwater). Blue water is necessary for humans (hygiene, agriculture, industry) and healthy ecosystems. An example would be the diversion of water from northern CA reducing flows to the point of endangering fish populations.

Land degradation, alteration, and deforestation can lead to losses of green water, and the lower soil moisture can affect ecosystems.

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There can even ben impacts on climate regulation due to decline of moisture feedback of green water flows, affecting local and regional precipitation

Section 5. Water equity

People may have unequal to access to water based on their income or gender.

Income:

Those who have less money are often paying more for water. When water is provided by utilities, it is typically at a relatively low cost. However, many people in developing countries do not live in areas that are served by utilities. Rather, informal providers are relied on for water. These providers may charge higher rates.

Gender

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Girls have typically borne the burden of obtaining water for the family more than boys. This is often very time consuming and can interfere with schooling.

Section 6. Hidden Water

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Exercise:

• Working with a a total of 2,000 calories, estimate how many calories you eat from each category.

• Find the multiplier for each item and multiply through.• Add it all up!

Section 7. Bottled water

Major findings from Gleick and Cooley:

Exercise: Calculate how far we could drive with the energy equivalent to providing 160 students a class that meets twice a week for 10 weeks, for two quarters.

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