Posted by: Chip Small | July 10, 2013

Closing the Loop in Urban Ecosystems

In the Bible Jesus turned water into wine, but can students at the University of St. Thomas turn coffee grounds into tilapia and basil?  Turning food waste into new food is a question being explored by the students in my Urban Ecosystem Ecology course.

Because cities have a lot of people living in a relatively small area, large inputs of food, energy, water, and other materials are required in order to support these urban ecosystems.  Our waste products leave the system in the form of garbage going to the landfill, nutrients in wastewater and runoff entering the river, and carbon dioxide emitted to the atmosphere.  Cities exemplify open systems, with lots of inputs, lots of outputs, and lots of waste.

     The concept of waste is unique to humans.  In natural ecosystems, the waste products of one species are resources that will be used by another species.  Nutrients and energy are too valuable to waste.

As humans have modified ecosystems, we have increased their productivity (by using fertilizer or irrigation in growing crops, for example) while decreasing the efficiency.  In a world of unlimited resources, this might be a good strategy.  But as human population has shot past 7 billion, resources such as fresh water, fossil fuels, and phosphorus are becoming more scarce, and our waste products are causing global scale problems such as eutrophication and climate change.  Moving towards sustainability demands that we increase efficiency.  In the parlance of ecosystem ecology, this means increasing cycling to compensate for decreased inputs and outputs.  Closing the loop, so to speak.

Which brings us to coffee grounds, tilapia, and basil.  Student videographer Austin Riordan has produced the first in a series of video blogs documenting our students’ experiment to evaluate whether we can turn the detritus of a college campus–that is, coffee grounds–into worms, turn the worms into fish, and the fish waste into basil.  It’s a small step, but it illustrates the kind of outside-the-box thinking that might be required in order to produce more food, and less waste.



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