Podcast Summary: New Books Network

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

Host: Dr. Miranda Melcher

Guest: Dr. Seth Denizen

Release Date: December 10, 2025

Episode Overview

In this episode, Dr. Miranda Melcher interviews Dr. Seth Denizen, co-author (with Montserrat Bonvehi Rosich) of Thinking Through Soil: Wastewater Agriculture in the Mezquital Valley. The discussion explores one of the world’s largest and oldest wastewater agricultural systems in Mexico—the Mezquital Valley—and dives into the complex entanglements of environment, technology, social politics, and history made visible in its soils. Dr. Denizen shares how their research weaves technical, historical, and cultural dimensions into a portrait of planetary urbanization. The conversation emphasizes the intricate interplay between scientific understanding, local and global politics, and the lived experiences of the region’s diverse farming communities.

Key Discussion Points & Insights

1. Origins and Methodologies of the Book

• Interdisciplinary Approach
  • Denizen (landscape architect) and Bonvehi Rosich (architect) merged visual and scholarly methods out of necessity during the COVID-19 pandemic, conducting much of their research remotely.
  • “There's really a bunch of different ways of representing the knowledge that we're kind of encountering in our process… visual methods as well as scholarly methods.” – Dr. Seth Denizen (02:49)

2. Why the Mezquital Valley?

• Global and Local Significance
  • Largest and oldest (since 1901) functioning wastewater agriculture system in the world; serves as a microcosm for planetary urbanization.
  • The valley is “a kind of portrait of Mexico City—the good, the bad, and the ugly in the wastewater of Mexico City.” (05:57)
• Uniqueness and Generalizability
  • The valley’s uniqueness makes it a focal point for studying the broader implications of wastewater reuse in agriculture. (06:36)

3. Scientific and Technical Research Focus

• Environmental “Laboratory Animal”
  • The valley is used for research into contaminant flows, pharmaceutical residues, and issues like antibiotic resistance.
  • Gap Identified: Most research is technical/scientific—lacking focus on social dynamics. The book contributes by addressing the system as a socio-environmental process. (07:39)

4. Opening the Book: The 2018 Farmers’ Protest

• Farmers' Opposition to Wastewater Treatment Plant
  • Protest targeted the region’s new, state-of-the-art wastewater treatment plant, demanding its closure.
  • Reason: The plant removes organic matter (key for fertilizing fields), lowering yields. Farmers accused the government of “stealing the shit out of the water” while the country focused on oil theft. (09:59)
  • “We actually find ourselves deeply sympathetic to what they were trying to tell us in those protests. And in order to kind of explain how that particular logic works, we really had to write something book length.” (13:39)
• Paradox Unveiled:
  • The very plant meant as a public good transforms the local resource in ways detrimental to community livelihoods.

5. Analyzing the Wastewater System’s Sustainability

• Nutrient Flows vs. Contaminants
  • Wastewater brings essential nutrients—N, P, K—but also surfactants, antibiotics, heavy metals, and drugs.
  • “Some of the wastewater canals wouldn’t pass a federal drug test for cocaine.” (16:02)
• Complex Soil Chemistry
  • Paradox: The same organic matter that fertilizes crops also binds heavy metals. Reduced organic content could dangerously remobilize contaminants stored in soils for decades.
  • “You have to keep running in order to stay in the same place.” (Red Queen scenario) (19:53)

6. Layered Histories of the Valley: Racial and Political Narratives

• Historical Framing as “Empty”/Impoverished
  • The valley was framed, especially by outsiders, as backward, “empty,” or in need of remediation—often ignoring indigenous Otomí farming and lifeways.
  • Irrigation was introduced as a civilizing tool for assimilation, shaped by eugenic and racialized thinking. (26:01)
  • “Building a giant irrigation dam and a kind of enormous network of irrigation canals were considered the solution to this, because not only would it provide the valley with economy, but it would also teach the indigenous Otomi people how to farm in the right way.” (28:22)

7. Early Infrastructure: From Flood Control to Agriculture

• Origins in Drainage and City Planning
  • The system started as a massive engineering project to drain Mexico City’s lakes and prevent flooding, later adapted for agriculture. (31:17–32:56)

8. Racial/Identity Politics and Land Ownership

• Land Redistribution and Lasting Inequalities
  • Two main groups: indigenous Otomí and mestizo (descendants of land redistribution post-Mexican Revolution). Distribution of water and land remains unequal and shapes social and political dynamics. (34:31–37:41)
• Fragmented Farmer Interests
  • Diversity within “the farmers” complicates collective organizing and political futures.

9. Present-Day Controversies and Divergent Interests

• Treatment Plant’s Mixed Economic Promises
  • Market crops such as lettuce are attractive (higher value) but pose health/ecological risks (hyperaccumulators of heavy metals).
  • Indigenous farmers aren’t necessarily interested in market crops requiring more water and Western diets.
• Agricultural Epistemologies
  • Comparison of extractive (industrial) vs. regenerative (Otomí) agricultural practices (xerophytic triad vs. “Three Sisters”).
  • “A completely different way of thinking about the world... It’s really to become a different person.” (47:05–48:30)

10. Imagining the Future

• Unsustainable Water Flow
  • As Mexico City faces its own water crises, sending as much wastewater as before is increasingly untenable. This challenges the valley’s resource base. (49:47)
• Recovery of Indigenous Practices
  • Calls for a renaissance of Otomí dryland farming techniques, linking culinary heritage and resilience to future adaptation. (51:00)
• Ecosystem Services as Policy Innovation
  • Proposing to “pay the farmers” for the nutrient cycling service they provide, capturing nutrients that would otherwise create downstream ecological harm (dead zones). (52:45–55:18)
• Targeting Contaminants at the Source
  • Only reducing upstream (city-source) heavy metals and pollutants can make the system sustainable—reframes the valley as part of city infrastructure. (56:13)

11. Concluding Reflections: Eco-Social Thinking

• Integrating Scientific and Social Perspectives
  • “We can't just think about environmental problems as separate from politics, as separate from culture, as separate from kind of human thriving and non-human thriving.” (58:10)
  • The book positions itself as a model for “thinking rigorously in a sort of eco-social way or a kind of geosocial way.” (59:43)

Notable Quotes & Memorable Moments

• On Soil as Portrait of Urbanization
  “The properties of this soil offer a kind of portrait of 20th century urbanization, a kind of portrait of everything that... We might call it the good, the bad and the ugly in the wastewater of Mexico City.”
  — Dr. Seth Denizen (05:57)

• Farmers and Protest Logic
  "The government is stealing the organic matter out of the wastewater that we need to fertilize our fields… effectively what they're accusing the government of is stealing the shit out of the water at the same time that the whole country is worried about the theft of oil out of the kind of national pipelines."
  — Dr. Seth Denizen (10:39)

• On Agricultural Transformation and Identity
  “…It’s a completely different way of thinking about the world…really to become a different person. And in that way, I think the eugenicists were probably onto something, right? Like, you really can change people by changing the way that they live and the food that they eat and the way in which they think about themselves as subjects.”
  — Dr. Seth Denizen (48:10)

• Paying for Ecosystem Services
  “What if, instead of trying to build this incredibly expensive machine [treatment plant] ...we started to really pay the farmers for this ecological service… They're able to cycle nitrogen at an efficiency of 70%...far higher than farms that use industrial fertilizer.”
  — Dr. Seth Denizen (54:41–55:18)

• Final Takeaway
  “In order to think through soil, we need to start thinking about human, environmental, or sort of eco social processes together. ...Opportunities for thinking about better environmental futures will actually require us to do precisely this kind of thinking.”
  — Dr. Seth Denizen (57:50–59:43)

Timestamps for Key Segments

• Intro and Author Background – 01:31–04:07
• Why Mezquital Valley? Local-global context – 04:13–07:13
• Technical focus vs. Social Dimensions – 07:13–08:58
• Opening Protest: Farmers vs. Wastewater Plant – 08:58–13:39
• Contaminants, Soil Chemistry, and Paradox – 14:22–20:57
• Historic Narratives & Racial Politics – 23:52–29:44
• Engineering History: Floods to Farms – 30:27–33:54
• Land, Identity, and Social Division – 34:27–39:25
• Protest Nuance and Economic Promises/Failures – 40:39–47:05
• Future Possibilities: Water Scarcity and Otomí Knowledge – 49:47–52:45
• Policy Innovation: Paying for Ecosystem Services – 52:45–56:13
• Source Control and Urban Responsibility – 56:13–57:35
• Eco-social Thinking & Book’s Implications – 57:35–59:43
• Upcoming Projects (Destino Mezquital symposium) – 59:57–61:51

Further Reading & Forthcoming Work

• Look out for the collective volume from the “Destino Mezquital” symposium, involving multidisciplinary proposals for future sustainable interaction between Mexico City and the Mezquital Valley. (59:57–61:51)

Tone of the Episode:
Academic yet accessible; reflective, open to complexity; thoughtful about social/environmental justice and scientific nuance; respectful towards overlooked histories and indigenous knowledge.

For Listeners:
This episode is essential for those interested in urban infrastructure, environmental justice, the politics of agriculture, and the integration of scientific and social approaches to global environmental problems—using Mexico’s Mezquital Valley as a uniquely compelling case study.