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   John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Sunday, 03-May-2026 05:16:43 JST John Carlos Baez

   ECOLOGICAL ENGINEERING

   The term “ecological engineering” was coined by Howard Odum, the founder of systems ecology. The field was pioneered by his student William J. Mitsch in collaboration with Sven Jørgensen [MiJ], but it is the work of many.

   Its goal is to design systems that work *with* ecosystems rather than replacing them. Its central insight is that ecosystems have a self-designing capability: given the right conditions, nature assembles and maintains its own populations of species, food chains, and biogeochemical cycles, running on solar energy rather than fossil fuels. The ecological engineer’s job is thus not to build and control a system from scratch, as a conventional engineer would, but to act as a facilitator between human needs and natural processes, letting the ecosystem do most of the work. Doing this requires deep ecological knowledge.

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   [MiJ] Mitsch, W.J. & Jørgensen, S.E. (2004). Ecological Engineering and Ecosystem Restoration. New York: Wiley.

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Sunday, 03-May-2026 07:12:42 JST John Carlos Baez

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     The restoration of the Skjern did not attempt to bring this river back to an imagined “state of nature” separate from the Danish economy. Reeds are harvested across 250 hectares for commercial sale. The restored river valley is also popular among tourists.

     The Royal Danish Agricultural University concluded that the project was a good public investment at a 3% discount rate and a time horizon of 20 years, or even a 7% discount rate if we allow an indefinite time horizon [DKPL]. Their calculation did not attempt to put a value on the 15,000 tonne annual reduction in CO2 emissions—not because the reduction was uncertain, but because Denmark’s international obligations at the time did not allow reductions of this kind to be counted in the national CO₂ account. They did, however, put a value on the reduced amounts of nitrates and phosphates flowing out of the Skjern, and the increased biodiversity.

     This leads naturally to our next topic, another field pioneered by Odum and his students: ecological economics! I'll talk about that next time.

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     [DKPL] Dubgaard A., Kallesøe, M., Petersen, M. L. & Ladenburg, J. (2002). Cost-benefit analysis of the Skjern River restoration project, Social Science Series 10, Department of Economics and Natural Resources, Royal Veterinary and Agricultural University, Copenhagen.

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Sunday, 03-May-2026 07:12:43 JST John Carlos Baez

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     The restoration of the river Skjern was carried out from 1999 to 2002. It transformed 19 kilometers of channelized river into 26 kilometers of meandering river. The river valley changed rapidly from agricultural fields into meadows, with weeds typical of arable land displaced by natural wetland plants. Birds returned, along with otter, and the number of salmon coming to the Skjern River to spawn grew tenfold [PANL].

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     [PANL] Pedersen, M. L., Andersen, J. M., Nielsen, K., & Linnemann, M. (2007). Restoration of Skjern River and its valley: project description and general ecological changes in the project area. Ecological Engineering 30(2), 131-144.

     Blaise Pabón - controlpl4n3 repeated this.
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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Sunday, 03-May-2026 07:12:44 JST John Carlos Baez

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     Another good example of ecological engineering is river and wetlands restoration. The Skjern, Denmark’s largest river by water flow, once had a huge expanse of marshland at its mouth, full of meandering watercourses, reed beds, and meadows. It was a habitat for thousands of migratory birds, along with stable breeding populations of local birds, plus otters and Atlantic salmon.

     All this was virtually destroyed following a campaign of land reclamation and river channelization in the 1960s. Part of the river was straightened into a canal - see the picture below. The wetlands were drained for agricultural purposes.

     In only 25 years the area lost its agricultural value. The drained peat soils subsided and degraded, and the farmland was not productive enough to justify its maintenance costs. The channelization also caused sedimentation and eutrophication at the river’s outflow. The rationale for restoration was therefore clear. The goals were to reinstate the natural flow conditions, allow species to return, and develop the area’s recreational and tourist potential.

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     John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Sunday, 03-May-2026 07:12:45 JST John Carlos Baez

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     However, Käthe Seidel of the Max Planck Institute did not need Odum’s theoretical framework to practice what would later be considered one of the prime examples of ecological engineering [Se]. In the 1950s she began using wetland plants like bulrushes to treat wastewater, trying to improve the poor performance of rural septic tanks and pond systems.

     By the early 1980s the technology had been introduced to Denmark, and by 1987 nearly 100 systems were in operation there. The UK, France, Netherlands, and Austria followed. By now, constructed wetlands are recognized as a reliable treatment technology suitable for many types of wastewater [EG,Vy].

     In Europe, Seidel’s system has become the norm: waste water percolates through basins filled with coarse sand and planted with bulrushes or reeds. In North America and Australia, open ponds with marsh plants are more popular, thanks in part to Odum’s work on recycling partially treated sewage in cypress swamps. To run any of these systems successfully requires detailed ecological expertise—not just “wetland plants treat water” but *which* wetland plants, in *which* climate, supporting *which* groups of microbes to carry out *which* activities.

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     [Se] Seidel, K. (1976). Macrophytes and water purification. Biological Control of Water Pollution. J. Tourbier & R.W. Pierson Jr. (eds.), Philadelphia: University of Pennsylvania Press, pp. 109–121.

     [EG] Entnier C. & Guterstam B. (1996). Ecological Engineering for Wastewater Treatment. Boca Raton: CRC Press.

     [Vy] Vymazal, J. (2011). Constructed wetlands for wastewater treatment: five decades of experience, Environmental Science & Technology 45(1), 61–69. https://doi.org/10.1021/es101403q

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     Blaise Pabón - controlpl4n3 (blaise@hachyderm.io)'s status on Sunday, 03-May-2026 08:02:42 JST Blaise Pabón - controlpl4n3

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     @johncarlosbaez
     Fwiw, I am super interested to learn about ecological economics.
     If for no other reason than my family owns an abandoned coffee farm in #PuertoRico and they tried to make it an outdoor museum in the 70s.

     In a colonial culture based on Profit=(Revenue-Expense) we don't have any other way to reason about land.
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     Fun fact: The museum project stopped when the Smithsonian consultants concluded that we needed to put in a parking lot.