Montserrat Bonvehi Rosich and Seth Denizen, "Thinking Through Soil: Wastewater Agriculture in the Mezquital Valley" (Harvard UP, 2025)

Dec 10, 2025

Seth Denizen, a landscape architect and environmental design scholar, discusses the significance of the Mezquital Valley, the world's largest wastewater agriculture system. He explores the valley's complex history, including the impact of urbanization on soil formation and the implications of farmer protests against wastewater treatment. Denizen also delves into soil chemistry, the challenges posed by heavy metals, and the importance of integrating ecological, social, and historical perspectives for a sustainable future. His insights highlight the urgent need for equitable environmental solutions.

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INSIGHT

Valley as Living Portrait Of Urbanization

The Mezquital Valley is the world's largest and longest-running wastewater agriculture system, formed alongside Mexico City's growth since 1901.
Its soils physically record urbanization's materials, making the valley both unique and globally representative.

ANECDOTE

Farmers Protested A New Treatment Plant

In November 2018 farmers protested the new wastewater treatment plant and demanded it be shut down immediately.
They accused authorities of "stealing the organic matter" from sewage that fertilizes their fields and reported yield drops.

INSIGHT

Fertility Comes With Diverse Contaminants

Wastewater both supplies fertility (organic matter) and carries diverse contaminants like pharmaceuticals and heavy metals.
Different contaminants follow different environmental paths; some break down quickly while others persist for decades.

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To think through soil is to engage with some of the most critical issues of our time. In addition to its agricultural role in feeding eight billion people, soil has become the primary agent of carbon storage in global climate models, and it is crucial for biodiversity, flood control, and freshwater resources. Perhaps no other material is asked to do so much for the human environment, and yet our basic conceptual model of what soil is and how it works remains surprisingly vague.

In cities, soil occupies a blurry category whose boundaries are both empirically uncertain and politically contested. Soil functions as a nexus for environmental processes through which the planet’s most fundamental material transformations occur, but conjuring what it actually is serves as a useful exercise in reframing environmental thought, design thinking, and city and regional planning toward a healthier, more ethical, and more sustainable future.

Through a sustained analysis of the world’s largest wastewater agricultural system, located in the Mexico City–Mezquital hydrological region, Thinking Through Soil: Wastewater Agriculture in the Mezquital Valley (Harvard UP, 2025) by Montserrat Bonvehi Rosich & Dr. Seth Denizen imagines what a better environmental future might look like in central Mexico. More broadly, this case study offers a new image of soil that captures its shifting identity, explains its profound importance to rural and urban life, and argues for its capacity to save our planet.

This interview was conducted by Dr. Miranda Melcher whose book focuses on post-conflict military integration, understanding treaty negotiation and implementation in civil war contexts, with qualitative analysis of the Angolan and Mozambican civil wars. You can find Miranda’s interviews on New Books with Miranda Melcher, wherever you get your podcasts.

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