La respiración de suelos urbanos versus naturales y las huellas de la contaminación de las ciudades Industriales

jardines-urbanos-emiten-co2-y-suelos-contaminados

Fuente: colaje de google imágenes

Si como algunos investigadores comentan, la respiración del suelo es un indicador de su resiliencia, ahora resultaría que los suelos urbanos lo son, mucho más que los naturales. No me parece obvio, por tanto, utilizar respiración como síntoma de resiliencia, al menos por si sola. Hoy analizaremos dos notas de prensa derivadas de otros tantos artículos de investigación. La primera nos advierte que la respiración de los suelos urbanos puede alcanzar en algunas ciudades, como es el caso de Boston, el 72% del CO2 emitido por los propios combustibles fósiles, hecho que no deja de ser tan sorprendente como interesante. Y tales fuentes de CO2 parecen doblar la de los suelos rurales, por lo que de hecho comienzan a ser motivo de preocupación a la hora de mitigar el calentamiento climático. Según el estudio, los altos contenidos en materia orgánica, el espesor del mantillo, y la razón carbono/nitrógeno se encontraban en estos ambientes urbanos/periurbanos positivamente correlacionados con la respiración del suelo, es decir el CO2 que emiten a la atmósfera. Refiriéndose a los jardines domésticos o a las zonas ajardinadas, los investigadores que llevaron a cabo este estudio advierten de que, cuando los propietarios y jardineros añaden enmiendas orgánicas, a los suelos mentados con vistas a que sus céspedes crezcan con vigor ofrecen sabroso alimento, rico en nutrientes, a los microrganismos del suelo y, como resultado, estimulan su crecimiento, pero también las emisiones de anhídrido carbónico a la atmósfera.  Más concretamente, en la ciudad de Boston, detallan que, alrededor del 64 por ciento de los propietarios de viviendas fertilizan el césped, el 37 por ciento el uso de compost o abono orgánico, y el 90 por ciento utiliza “enmiendas” orgánicas del tipo de los mulching (acolchado). Todas estas “opciones, principalmente llevadas a cabo en los espacios verdes, públicos o privados,  se traducen en adiciones de carbono al suelo, promoviendo, como ya hemos comentado, las emisiones de CO2. No obstante, los doseles de los arboles contrarrestan “en parte” este proceso al absorberlo.

De ser cierto, resultaría paradójico, crear zonas verdes en las ciudades con vistas a que sean más sostenibles ambientalmente, cuando en realidad tal iniciativa podría generar efectos de retroalimentación positiva sobre el calentamiento climático. Resumiendo, ¡no hay forma de aclararse! ¿Qué debemos fomentar: asfalto, tierra yerma o zonas verdes?. Para aquellos que defienden que la respiración es un indicador de la resiliencia del suelo, lo lógico sería que sustituyéramos muchos espacios geográficos baldíos por vertederos, ya que estos si emiten CO2, metano y otros gases de invernadero en enormes cantidades. ¡Sin comentarios!. Eso si, los suelos urbanos suelen estar muy contaminados, como ya os hemos reiterado en varias ocasiones. Empero, tengamos también en cuenta que las urbes siguen creciendo en detrimento de los paisajes agrarios y naturales.  ¿Más Co2?

La segunda noticia nos informa de los esfuerzos de las autoridades y vecinos de ciudad de Detroit, cuya economía se derrumbó (de hecho se encuentra en bancarrota) como consecuencia de la decadencia de la industria automovilística antaño, santo y seña de esta ciudad. Por tanto, esta ciudad se encuentra sufriendo una enorme crisis acompañada de un proceso de des-urbanización y éxodo al medio rural. Pues bien, de acuerdo a los investigadores que llevaron a cabo el segundo estudio, entre las herencias de su anhelada edad de oro industrial, se encuentran suelos fuertemente contaminados, lo cual dificulta e incluso impide en ocasiones la regeneración de las infraestructuras verdes de la urbe.  En sus propias palabras: “historia de la industrialización y la urbanización de Chicago dejó su marca en el suelo. El medio edáfico actúa como una esponja, llegando a albergar contaminantes durante muchos años. En Chicago, los residuos procedentes de la fabricación industrial han inducido la acumulación de los productos químico-orgánicos indeseablemente tóxicos, metales pesados y otras sustancias persistentes. Tal hecho plantea serios problemas para la salud humana, animal y vegetal. ¡En fin!: “lo que no mata engorda”.

Como puede observarse, generar ciudades verdes sostenibles, resulta ser una terea bastante más compleja de lo que usualmente pensamos. Vivimos en una sociedad enferma y como todos sabéis: “a perro flaco todo son pulgas”.

Os dejo con las noticias mentadas…….

Juan José Ibáñez

Urban soil emits a surprising amount of CO2

By Suzanne Jacobs on 23 Feb 2016 39 comments

Watch out, fossil fuels. There’s another CO2 emitter in town, and she’s been letting you take all the heat for greenhouse gases.

A new study published in the journal Environmental Pollution shows that urban soil can emit up to 72 percent as much CO2 as fossil fuels burned within a city and at a rate of up to twice that of rural soils. And this is important, the researchers note, because most climate action plans only account for anthropogenic sources of CO2 like cars and buildings, not the seemingly innocent biological sources like dirt.

The study focused on Boston (cue someone from New York talking shit about Boston’s dirt), where researchers picked 15 sites stretching from the city’s downtown area to its outer suburbs. At each site, they took measurements from forest, lawn, and landscaped soil every two weeks between May and November of 2014 — not only of CO2 emissions, but also of things like soil moisture, soil acidity, and air temperature.

 By the end of the study, they found that forested areas emitted the least amount of CO2, and landscaped areas — those defined by the shrubs, flowers, and trees that we humans like to arrange in unnaturally organized patternsemitted the most. Lawns fell somewhere in between like the boring swaths of wasted space that they are.

Fortunately, the city’s 26 percent tree canopy cover probably compensates for a lot of these emissions through photosynthesis, the researchers note. But out in the residential areas of greater Boston, where canopy cover is more scarce, that might not be the case.

Crucially, the researchers found that high organic matter concentration, leaf litter depth, and carbon-to-nitrogen ratios were all positively correlated with high emissions, indicating that the more we “manage” the land, the more CO2 it emits.

When people mulch their landscaped areas or fertilize their lawns, they’re putting out yummy fresh highly decomposable carbon that soil microbes can use. … And that’s stimulating microbial growth and loss of CO2 out of these urban soils,” Pamela Templer, a biology professor at Boston University and one of the study’s coauthors, said in a press release.

According to a survey of Massachusetts residents, about 64 percent of residential landowners fertilize their lawns, 37 percent use compost or organic fertilizer, and 90 percent use organic “amendments” like mulch. All of these “residential management choices” add carbon to the soil and thus promote the microbial activity responsible for emissions, Templer and her colleagues report.

So basically, even this supposedly non-anthropogenic source of CO2 is actually kind of an anthropogenic source of CO2. The more we prune and beautify the landscape, the more it emits. And the more we cut down on canopy cover in favor of wastelands like this, the more those emissions matter.

Still, the researchers aren’t saying that we should stop landscaping and let nature run wild, just that we should be sure to account for these emissions when we make our climate action plans. That said, it wouldn’t hurt to reassess our obsession with lawns and gardens and clear-cut suburban streets. Most of it looks terrible, and forests are objectively awesome.

 Healing the soil

Repurposing abandoned urban lots starts with soil test

Date: February 10, 2016; Source: American Society of Agronomy

Summary: Chicago’s history of industrialization and urbanization left its mark on the soil. Soil acts as a sponge, and can host contaminants for years. In Chicago, the waste from industrial manufacturing causes undesirable toxic organic chemicals, heavy metals, and other chemicals to linger in the soil. A non-profit youth development center hopes to repurpose the lots into useful spaces for the community. However, the poor quality soils in the lots create challenges. However, the most incriminating evidence of the past lies beneath the surface, in the soil.

Chicago’s history of industrialization and urbanization left its mark on the soil. Soil acts as a sponge, and can host contaminants for years. In Chicago, the waste from industrial manufacturing causes undesirable toxic organic chemicals, heavy metals, and other chemicals to linger in the soil. This can pose problems for the health of the humans and plants that inhabit the land years later.

The four empty lots are owned by the Gary Comer Center, a non-profit youth development center in the Greater Grand Crossing neighborhood. The Comer Center’s long-term hope is to repurpose the lots into useful spaces for the community. However, the poor quality soils in the lots create challenges.

“They are going to need some serious TLC to bring them back,” says urban soil scientist James Montgomery.

Montgomery is an associate professor in the Department of Environmental Science and Studies at DePaul University. He and his team trained a group of undergraduate students from DePaul to test the soil on the lots in collaboration with the Comer Center. The soils are all in poor shape. They have a high alkaline level, and contain chemical and lead levels above the amount recommended by the EPA.

To Montgomery, this isn’t a hopeless case: “We want to work with the Comer Center and help them realize their vision for using these lots, whatever that might be,” he says.

The Comer Center’s eventual goal, whether it’s the installation of urban gardens, parks, or buildings, will dictate how much cleanup is needed to improve the soil. Remediation can be as intensive as physically removing and replacing the soil, or as simple as tilling it up and adding amendments.

The presence of lead, heavy metals, and excess chemicals may call for containment using green infrastructure. One purpose of green infrastructure is to interrupt the journey of contaminants into water sources, where they can spread or infiltrate drinking water sources. It can include bioswales, rain gardens, or vegetative buffers. Plans can include plant species capable of ingesting heavy metals or excess chemicals in the soil.

Montgomery says that soil testing should come first when deciding what to do with a piece of property. “You go to a doctor for a preventative check-up and we should do the same with soil.”

Testing the soil is usually inexpensive and can indicate what’s needed–and what isn’t needed–to improve it. “It’s part of understanding your home,” says Montgomery. “If you have a soil test done and it’s showing you’ve got excess chemicals, then maybe you don’t need to spend as much money on amendments to the soil.”

For Montgomery, soil health is an environmental justice issue. Low-income and underserved neighborhoods are rife with poor soils. There has been little reconstruction in the Greater Grand Crossing neighborhood since the 1930′s. Approximately 78 percent of the residents are below the poverty line. “We definitely need to be at the table advocating for environmental justice in these communities that are wracked by poor soil quality,” says Montgomery.

Montgomery notes that community participation in this project is particularly important. “The point is not to have the university come in and dictate,” he says. “The Comer Center is driving this bus and that’s how it should be.”

Montgomery says they plan to hold planning sessions with the community to discover what they envision for the lots. They will use the results of the soil test to better inform their next move.

Story Source: The above post is reprinted from materials provided by American Society of Agronomy. Note: Materials may be edited for content and length.

Journal Reference: James A. Montgomery, Christie A. Klimas, Joseph Arcus, Christian DeKnock, Kathryn Rico, Yarency Rodriguez, Katherine Vollrath, Ellen Webb, Allison Williams. Soil Quality Assessment Is a Necessary First Step for Designing Urban Green Infrastructure. Journal of Environment Quality, 2016; 45 (1): 18 DOI: 10.2134/jeq2015.04.0192

Cite This Page:MLA, APA, ChicagoAmerican Society of Agronomy. “Healing the soil: Repurposing abandoned urban lots starts with soil test.” ScienceDaily. ScienceDaily, 10 February 2016. <www.sciencedaily.com/releases/2016/02/160210135336.htm>.

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