How does agriculture affect the hydrologic and nitrogen cycles?

While on a recent drive through the southeastern part of Georgia I passed by several cotton fields.  I was reminded of the class discussion about how human activities influence the biogeochemical cycles.  An earlier blog posting shared the importance of our biogeochemical cycles.  It is not about finding balance between the needs of humans and the needs of the environment.  Without the environment, there is no us.  Imbalance between the biogeochemical cycles can lead to environmental refugees, war, and famine.

What is the connection between cotton fields of Georgia and the biogeochemical cycles?  As my students have learned, cotton plants require a lot of nitrogen (so does tobacco and corn).  This need for nitrogen means farmers will need to fertilize with nitrates more often than they do for other crops such as soybeans.  The addition of more nitrate fertilizer to agricultural fields adds more nutrients to the watershed.  Excess nutrients can be picked-up by surface runoff during irrigation or rainfall and find its way to lakes, streams, rivers, and the ocean.  These excess nutrients cause eutrophication and promote the creation of hypoxic zones in our freshwater and marine ecosystems.

Besides the need of fertilizer for growth, plants also need water.  Water for agricultural fields worldwide can come from aquifers, reservoirs, or rivers.    Worldwide, agriculture is the biggest user of freshwater.  Rivers do not know boundaries such as County lines, State lines, or International lines.  The Chattahoochee River shares its boundaries with Georgia, Alabama and Florida and it has led to some disputes as to how its water can be used.  Can you imagine the arguments between neighboring countries which share a river?

The Tigris and Euphrates Rivers headwaters are in Turkey and flow through Syria and Iraq on their way to the Persian Gulf.   This past Spring Turkey completed the construction of a dam on the Tigris River (they have already constructed a dam on the Euphrates River).  The completion of this dam project and the filling of the reservoir behind it has resulted in much less water going downstream to Iraq.  Iraq needs the water not only as a supply of drinking water, but also to help irrigate its agricultural fields.  Furthermore, the water flowing from the Tigris and Euphrates Rivers feed the Mesopotomian Marshes, a valuable ecosystem.   Between the 1950s and 1990s the Mesopotomian Marshes were being drained and degraded for agriculture, decrease mosquito reproduction, and political reasons.  Saddam Hussein ordered the draining of parts of the marshes to punish those depending on the marshes for their participation in the uprising against him and his government.  Citizens of Iraq are trying to restore this ecosystem and less water coming downstream from the Tigris and Euphrates Rivers could diminish this restoration project.  What will happen between Turkey and Iraq if they are unable to agree upon how much water is released downstream?  How will climate change influence the amount of water released downstream from Turkey to Iraq?  Time will tell.

A major water diversion project has caused what might be considered one of the world’s worst environmental disasters.  The Aral Sea, once the world’s fourth largest lake in the world, provided a vast array of resources which supported a healthy economy.  In the 1950s  Russia began using canals to divert water from the Amu Dayra River and the Syr Dayra River to irrigate the desert as Russia was attempting to become the world’s largest exporter of cotton.  These two rivers were the major source of water for the Aral Sea.  The diversion of water from these rivers eventually led to the Aral Sea now holding onto about 10% of its original volume.  Most of the Aral Sea is now a desert and the people living around the Aral Sea suffer from loss of jobs, clean drinking water, and arable land.

We will always be planting crops to feed people and provide resources to make products.  Massive agricultural operations come with an environmental cost.  Water diversion projects to provide people with drinking water and irrigation water means less water going downstream.  Growing massive amounts of crops require massive amounts of fertilizer which can lead to eutrophication and unwanted algal blooms.  Are we capable of providing food and water for everyone without governmental disputes and environmental disasters?

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